JP2012008122A - Elastic surface wave sensor, sensing system and pressure measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic surface wave sensor, a sensing system and a pressure measuring method that can accurately detect the state of a measuring object, even when a temperature changes.SOLUTION: A difference between output voltages of a first elastic surface wave element and a second elastic surface wave element is taken to obtain a first arithmetic value (including influence of pressure and temperature). A difference between output voltages of a third elastic surface wave element and the second elastic surface wave element is taken to obtain a second arithmetic value (including only influence of temperature). By using a map of the second arithmetic value and a substrate change amount by the temperature, the second arithmetic value is converted into the substrate change amount by (only) the temperature, a temperature correction amount (corresponding to a pressure reference value) is obtained from the substrate change amount by the temperature, an added value that the first arithmetic value is added to the temperature correction amount is obtained, and the substrate change amount by the pressure and temperature is obtained from the added value. By deducting the substrate change amount by only the temperature from the substrate change amount by the pressure and temperature, the substrate change amount by only the pressure is obtained.

Description

  The present invention relates to a surface acoustic wave sensor including at least three types of surface acoustic wave elements and a surface acoustic wave sensor to detect a change in a state (pressure or the like) of a measurement target using surface acoustic waves. The present invention relates to a sensing system that measures pressure based on a signal of the above and a pressure measurement method that measures pressure based on a signal from a surface acoustic wave sensor.

2. Description of the Related Art Conventionally, surface acoustic wave sensors (SAW devices) that detect the pressure, temperature, and the like of a measurement object have been developed using the characteristics of surface acoustic waves (SAW).
As a pressure / temperature monitor using this type of surface acoustic wave, as described in Patent Documents 1 and 2 below, a comb electrode (IDT: Inter Digital Transducer) or a reflector (element) is used as an element for detecting pressure fluctuation. A method (resonance frequency detection method) is disclosed that uses a resonant SAW element made of a reflector and detects pressure fluctuations from fluctuations in the resonance frequency of the SAW elements.

Apart from this, in recent years, a method (power detection method) for detecting pressure fluctuations from fluctuations in the intensity (for example, voltage level) of reflected signals of SAW elements has been studied.
Further, in a pressure / temperature monitor using a surface acoustic wave sensor, as means for compensating for the temperature effect, two SAW elements having the same characteristics are used as described in Patent Documents 3 to 5 below, and one of them is a pressure. A method is disclosed in which an element that is affected by both of the temperatures and an element that is affected only by the temperature are used, and the differential output of these two elements is subjected to a pressure detection signal to remove the temperature effect.

Japanese Patent No. 4099504 Japanese Patent No. 4320598 JP 2003-14572 A Japanese Patent No. 4088892 JP 2009-222589 A

  However, as in the above-described prior art, even when detecting the state (for example, pressure) of the target measurement object from the change in the difference between the output voltage values of both SAW elements, the state of the measurement object cannot be detected suitably. was there.

  That is, the characteristics of the surface acoustic wave sensor (particularly the relationship between the reflection coefficient and the frequency of the SAW element) are affected by the temperature, and the output voltage value varies depending on the temperature even at the same pressure. There are cases where the state of the measurement object cannot be detected with high accuracy simply by taking the difference.

  That is, in a situation where changes in temperature and pressure occur at the same time, the characteristics of both SAW elements themselves change. Therefore, simply taking the difference between the output voltage values of the SAW elements can accurately measure the object to be measured. There was a problem that the state could not be detected.

  The present invention has been made in view of such problems, and the purpose thereof is a surface acoustic wave sensor that can accurately detect the state of a target object to be measured, such as pressure, even when the temperature changes, It is an object to provide a sensing system and a pressure measurement method.

  (1) The surface acoustic wave sensor according to the present invention has, as a first aspect, a first surface acoustic wave element and a second elasticity in which the output of the element changes due to changes in the characteristics of the surface acoustic wave transmitted through the element due to external influences. A surface acoustic wave sensor including a surface acoustic wave element and a third surface acoustic wave element, wherein the first surface acoustic wave element and the second surface acoustic wave element have the same element output with respect to a temperature change. The third surface acoustic wave element is different from the first surface acoustic wave element and the second surface acoustic wave element in output of the element with respect to temperature change, and the first surface acoustic wave element has the temperature It is an element comprised so that the output of an element may change with the change of the state of measurement objects other than.

  In the present invention, the first surface acoustic wave element and the second surface acoustic wave element have the same element output (for example, voltage and power) with respect to temperature change, but the third surface acoustic wave element is the first surface acoustic wave element. The wave element and the second surface acoustic wave element differ in element output (for example, voltage and power) with respect to temperature change. The first surface acoustic wave element is an element configured such that the output (for example, voltage or power) of the element changes according to a change in the state of the measurement target other than temperature such as pressure.

Therefore, using these outputs, for example, as described in claims 7 to 16 described later, the influence of temperature can be eliminated and the state (for example, pressure) of the measurement target can be accurately detected.
Examples of the surface acoustic wave elements include elements provided with electrodes such as comb electrodes and reflectors on a piezoelectric substrate. In each element, for example, when the frequency characteristics of the reflector reflection coefficient are different. Even with the same temperature change, the output (for example, voltage or power) of each element varies depending on the temperature change.

(2) In the present invention, as a second aspect, a configuration is possible in which signals can be transmitted and received with an external device wirelessly.
(3) In this invention, a measurement object can be made into a pressure as a 3rd aspect.

(4) In the present invention, as a fourth aspect, a pressing force corresponding to the pressure can be applied to the first surface acoustic wave element by the pressing force application unit.
(5) In the present invention, as a fifth aspect, the delay times of signals in the first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element can be set to be all different.

Thereby, in the external device (transceiver) that has received the signal from each element transmitted from the surface acoustic wave sensor, the signal from each element can be separated by time.
(6) In the present invention, as a sixth aspect, the first surface acoustic wave element includes an electrode that generates a surface acoustic wave and a reflector that reflects the surface acoustic wave generated at the electrode. In addition to the configuration that elastically deforms when an external pressing force is applied, the configuration can include a pressing force application unit that applies the pressing force to the reflector.

  Thereby, when a stress is applied to the reflector by the pressing force application unit of the first surface acoustic wave element, the reflection coefficient of the reflector changes due to elastic deformation and deflection. Therefore, the applied stress can be detected based on a response (for example, the voltage level of the response signal) that varies greatly due to a change in the reflection coefficient. Further, the electrode can be fixed so as not to be deformed even when stress is applied. Thereby, even when stress is applied, the electrode itself is not deformed (therefore, the reflection coefficient of the electrode does not change), so that it is possible to accurately detect a change in response based on a change in the reflection coefficient of the reflector itself. . Furthermore, by configuring the pressing force application unit to receive the stress via an elastic member that deforms according to the stress, it is possible to suitably transmit the change in the stress to the surface acoustic wave element side.

  (7) As a seventh aspect, the sensing system of the present invention is a pressure sensing system including the surface acoustic wave sensor according to any one of claims 1 to 6, wherein the first surface acoustic wave is provided. When a pressing force corresponding to the pressure is applied to the element, a first calculated value indicating a voltage difference between the output voltage of the first surface acoustic wave element and the output voltage of the second surface acoustic wave element is obtained. 1 calculation means, 2nd calculation means for obtaining a second calculation value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element, and the second calculation Based on the value of the substrate change amount of the element due to the temperature, the third calculation means for obtaining the substrate change amount of the element due to the temperature, and the relationship between the first calculated value and the substrate change amount of the element due to the pressure. The amount of change in the substrate of the element due to pressure and temperature Based on the fourth calculation means for calculating a temperature correction amount serving as a reference for correction, a fifth calculation means for adding the first calculation value to the temperature correction amount to obtain an addition value, and the addition value A sixth calculating means for obtaining a change amount of the substrate of the element due to the pressure and temperature; and a difference between the change amount of the substrate of the element due to the pressure and temperature and the change amount of the substrate of the element due to the temperature. Seventh calculating means to be obtained, and eighth calculating means for calculating the pressure based on the substrate change amount of the element due to the pressure are provided.

Next, the principle by which the pressure can be obtained using the output of each element will be described with reference to FIG.
In each surface acoustic wave element, the member (substrate) that generates the surface acoustic wave has a shape (dimension) that varies depending on the temperature (hereinafter, the amount of change is referred to as a substrate change amount), and the substrate even when pressure is applied. The amount of change is different.

  In the seventh aspect, as described above, the element characteristics are based on the knowledge that both the change in the temperature and the change in the pressure (by application) can be expressed as the substrate change amount. The pressure (or temperature) applied to the surface acoustic wave element is detected.

  That is, as shown in the horizontal axis (X-axis) in FIG. 1, the change in temperature and pressure can be plotted on the same axis as the substrate change amount. Based on the above, even when there is a temperature change, a change in the applied pressure can be detected.

Here, the horizontal axis (X axis) in FIG. 1 represents the amount of change in the substrate due to temperature or pressure, and the vertical axis (Y axis) represents the difference (or power ratio) in output voltage between the elements.
Further, the solid line graph (pressure map) in the figure shows that the first surface acoustic wave element (SAW1) and the first surface acoustic wave element (SAW1) and the first surface acoustic wave element when the pressure applied to the first surface acoustic wave element (SAW1) is changed. It is a graph which shows the change of the difference (or power ratio: reflected power ratio) of the output voltage with 2 surface acoustic wave elements (SAW2).

  The graph (temperature map) indicated by the dotted line in the figure shows the output voltages of the third surface acoustic wave element (SAW3) and the second surface acoustic wave element (SAW2) when the temperature is changed (without applying pressure). It is a graph which shows the change of the difference (or power ratio: reflected power ratio).

In addition, although you may prescribe | regulate with an arithmetic expression instead of the said map, below, it demonstrates with a map.
In the seventh aspect, the first surface acoustic wave element is a pressure + temperature electrode that reacts to pressure and temperature, and the second surface acoustic wave element reacts only to temperature, and a reference of pressure in the calculation described later. The third surface acoustic wave element is a temperature electrode that reacts only to temperature.

Specifically, as illustrated in FIG. 1, first, a voltage difference between the output voltage of the first surface acoustic wave element and the output voltage of the second surface acoustic wave element (first calculated value) is calculated by the first calculation means. : V _SAW1 −V _SAW2 ).

  Here, the first surface acoustic wave element and the second surface acoustic wave element have the same characteristics with respect to temperature, and the characteristics (for example, the relationship between the reflection coefficient and the frequency) of both elements change with temperature. Therefore, the first calculation value includes the influence of pressure and temperature.

Further, the second calculating means, the voltage difference between the output voltage and the output voltage of the second surface acoustic wave device of the third surface acoustic wave element (second calculation value: V _SAW3 -V _SAW2) seek (Fig ( 1)).
Here, the second surface acoustic wave element and the third surface acoustic wave element have different characteristics with respect to temperature (no pressure is applied), and the second calculated value has a temperature (no influence by pressure). The effects of are included.

  In addition, by investigating the temperature characteristics of the third and second surface acoustic wave elements in advance, the influence of temperature can be extracted from the second calculated value. That is, since the outputs of the third and second surface acoustic wave elements change with temperature (thus, the difference between the output voltages of both elements also changes with temperature), the temperature can be obtained from the second calculated value.

Then, the voltage difference is the second calculation value (V _SAW3 -V _SAW2), since it corresponds to the substrate amount of change with temperature (alone), the third arithmetic means, the substrate changes due to the voltage difference between the temperature Using the map with the amount (temperature map), the substrate change amount due to temperature is obtained from the voltage difference (see (2) in the figure).

  Further, since the first calculated value and the substrate change amount of the element due to the pressure have a predetermined correspondence relationship, the fourth calculating means has a relationship between the first calculated value and the substrate change amount of the element due to the pressure ( For example, using a pressure map), a pressure reference value that serves as a reference for determining the substrate change amount due to the pressure and temperature from the substrate change amount due to the temperature (that is, the initial value when determining the substrate change amount due to the pressure alone). Is obtained (see (3) in the figure). The temperature correction amount (pressure reference value) is obtained from the pressure map.

  Here, regarding the concept of temperature correction amount, the first surface acoustic wave element and the second surface acoustic wave element have the same characteristics with respect to temperature. The reference point can be regarded as being shifted on the pressure map. Therefore, the shift amount of the reference point of the pressure map, that is, the temperature correction amount is obtained by obtaining the substrate change amount due to the temperature by the third calculating means.

  Then, in order to obtain a voltage difference including the influence of pressure and temperature, the fifth calculation means adds the first calculation value (including the influence of pressure and temperature) to the temperature correction amount that is the initial value, and adds Find the value.

  In addition, since there is a predetermined relationship between the added value and the amount of change in the substrate due to pressure and temperature, the sixth calculation means has a relationship between the voltage difference including the effect of pressure and temperature and the amount of change in the substrate due to pressure and temperature (eg, Using the pressure map, the amount of change in the substrate due to pressure and temperature is obtained from the added value (see (4) in the figure).

  Next, the seventh calculation means obtains the substrate change amount due to the pressure from the difference between the substrate change amount due to the pressure and temperature and the substrate change amount due to the temperature (see FIG. 5), and the eighth calculation means causes the pressure change. The pressure is calculated on the basis of the amount of change in the substrate.

  That is, in the seventh aspect, the substrate change amount due to the temperature corresponding to the voltage difference between the third surface acoustic wave element and the second surface acoustic wave element is obtained, and the substrate change amount due to this temperature (using a temperature map or the like). From this, the temperature correction amount is obtained. Since this temperature correction amount can be regarded as the starting point (pressure reference point) of the change in the substrate change amount due to pressure (such as a pressure map) under a certain temperature condition, the first calculated value is added to this temperature correction amount, Based on the added value, the substrate change amount corresponding to the pressure and temperature can be obtained. Therefore, by subtracting the substrate change amount due to temperature from the substrate change amount due to pressure and temperature, the substrate change amount corresponding only to the pressure can be obtained. Therefore, the pressure is obtained from the substrate change amount corresponding only to this pressure. Can do.

  As shown in FIG. 2, under a certain pressure, if the temperature conditions are different, the voltage difference and power ratio between the elements are different, that is, the amount of change in the substrate due to the temperature is different. , Only the pressure reference value (which varies depending on the temperature) is different, so that the substrate change amount due to pressure is the same. That is, the detected pressure is the same.

Here, it will be described that the characteristics of the element (particularly the reflection coefficient: accordingly, output (for example, voltage)) change depending on the temperature.
As shown in FIG. 3A, the reflection coefficient of a well-known electrode (for example, comb electrode: IDT) used for the surface acoustic wave element varies depending on the frequency of the input signal input to the comb electrode. For example, when the temperature is 25 ° C., the characteristic indicated by the solid line in the figure changes as indicated by the broken line in the figure when the temperature rises to 50 ° C.

  In addition, as shown in FIG. 3B, the reflection coefficient of a known reflector (reflector) used for the surface acoustic wave element also varies depending on the frequency of the input signal input to the reflector. For example, when the temperature is 25 ° C., the characteristics indicated by X1 to X3 in the figure change as Y1 to Y3 in the figure when the temperature rises to 50 ° C.

  X1 and Y1 indicate characteristics when no pressure is applied to the surface acoustic wave element, X2 and Y2 indicate characteristics when a pressure of 200 [kPa] is applied, and X3 and Y3 indicate 400 [ The characteristic when the pressure of kPa] is applied is shown.

  In the case of such a surface acoustic wave element, its output (here, voltage) is, for example, as shown in FIG. In the figure, P (X1 to X3) indicates the signal intensity (voltage) when 25 ° C., and P (Y1 to Y3) indicates the signal intensity when 50 ° C.

That is, when the surface acoustic wave element is used, as shown in FIG. 5, even if the pressure is the same, the signal intensity varies depending on the temperature.
Therefore, in the present invention, in order to eliminate the influence of the temperature of such a surface acoustic wave element, the configuration described above is adopted.

  That is, considering the case of taking the difference between the output of the element that detects temperature and pressure and the output of the element that detects only temperature as in the conventional case, specifically, for example, the pressure is 200 at 25 ° C. Considering the case where a predetermined output voltage difference ΔT is obtained when it changes to ˜400 [kPa], when a similar output voltage difference ΔT is obtained under other conditions where the pressure or temperature changes, the output is simply output. It is not easy to accurately detect the pressure from the voltage difference ΔT.

  Therefore, in the present invention, as described above, by providing three types of surface acoustic wave elements and using these element outputs, the influence of temperature is suitably eliminated even in a situation where both pressure and temperature change. Thus, the state (pressure) of the target measurement object can be detected with high accuracy.

  (8) The present invention provides, as an eighth aspect, a pressure sensing system including the surface acoustic wave sensor according to any one of the first to sixth aspects, wherein the first surface acoustic wave element includes the surface acoustic wave element. First calculating means for obtaining a first calculation value indicating a voltage difference between the output voltage of the first surface acoustic wave element and the output voltage of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied. And a second calculation means for obtaining a second calculation value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element, and based on the second calculation value Then, using the relationship between the second calculation value and the first calculation value based on the third calculation means for obtaining the substrate change amount of the element depending on the temperature, the pressure and temperature are determined based on the second calculation value. Act 4 for determining the temperature correction amount, which is the reference for determining the amount of change in the substrate of the element And a fifth calculation means for adding the first calculation value to the temperature correction amount to obtain the addition value, and a sixth calculation for obtaining the substrate change amount of the element due to pressure and temperature based on the addition value. Means, a seventh arithmetic means for obtaining a substrate change amount of the element due to the pressure from a difference between the substrate change amount of the element due to the pressure and temperature and a substrate change amount of the element due to the temperature; and a substrate change amount of the element due to the pressure. And an eighth calculating means for calculating the pressure based on the above.

  The eighth mode is different from the seventh mode in the fourth calculation means. In other words, in the fourth calculation means, the relationship between the second calculation value and the first calculation value is used, and from the second calculation value (the first calculation value corresponding to the second calculation value). A temperature correction amount serving as a reference (pressure reference value) for obtaining the substrate change amount due to pressure and temperature is obtained, and thereafter the same calculation as in the seventh aspect is performed.

  Therefore, if an offset map or the like indicating the relationship between the second calculation value and the first calculation value is prepared in advance, the temperature correction amount (without using the substrate change amount due to the temperature) from the second calculation value. Can be requested.

Also according to the eighth aspect, the same effect as in the seventh aspect can be obtained.
(9) The present invention provides, as a ninth aspect, a pressure sensing system including the surface acoustic wave sensor according to any one of the first to sixth aspects, wherein the first surface acoustic wave element includes the surface acoustic wave element. First calculation means for obtaining a first calculation value indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied. And second calculation means for obtaining a second calculation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element, and based on the second calculation value Then, the third calculation means for obtaining the substrate change amount of the element due to temperature, the relationship between the first calculation value and the substrate change amount of the element due to pressure, and the pressure based on the substrate change amount of the element due to the temperature. And a reference for determining the amount of change in the substrate of the element due to temperature Fourth calculation means for determining the degree of correction, fifth calculation means for adding the first calculation value to the temperature correction amount to obtain an addition value, and based on the addition value, pressure and Sixth calculating means for determining the substrate change amount of the element due to temperature, and seventh difference calculating the substrate change amount of the element due to pressure from the difference between the substrate change amount of the element due to pressure and temperature and the substrate change amount of the element due to temperature. It is characterized by comprising an arithmetic means and an eighth arithmetic means for calculating the pressure based on the change amount of the substrate of the element due to the pressure.

Below, the principle which can obtain | require a pressure using the power ratio of this 9th aspect is demonstrated based on the said FIG.
As illustrated in FIG. 1, first, the first calculation means obtains a power ratio (first calculation value) between the output voltage of the first surface acoustic wave element and the output power of the second surface acoustic wave element. Further, the second calculation means obtains the power ratio (second calculation value) between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element by the second calculation means (the same figure). (See (1)).

The second power ratio is an operation value (P _SAW3 / P _SAW2), since it corresponds to the substrate amount of change due to temperature, by the third calculation means, relationship between the substrate variation according to the power ratio and temperature ( For example, a temperature map) is used to determine the amount of substrate change due to temperature from the power ratio (see (2) in the figure).

As described above, since there is a predetermined relationship between the first calculation value and the substrate change amount of the element due to pressure, the fourth calculation means uses this relationship (for example, a pressure map) to change the substrate change amount due to temperature. From this, a temperature correction amount, which is a pressure reference value (initial value), which is a reference for determining the substrate change amount due to pressure and temperature is obtained (see (3) in the figure).
Here, regarding the concept of temperature correction amount, the first surface acoustic wave element and the second surface acoustic wave element have the same characteristics with respect to temperature. The reference point can be regarded as being shifted on the pressure map. Therefore, the shift amount of the reference point of the pressure map, that is, the temperature correction amount is obtained by obtaining the substrate change amount due to the temperature by the third calculating means.

  Then, in order to obtain a voltage difference including the influence of pressure and temperature, the fifth calculation means adds the first calculation value (including the influence of pressure and temperature) to the temperature correction amount that is the initial value, and adds Find the value.

  In addition, since there is a predetermined relationship between the added value and the amount of change in the substrate due to pressure and temperature, the sixth calculation means has a relationship between the voltage difference including the effect of pressure and temperature and the amount of change in the substrate due to pressure and temperature (eg, Using the pressure map, the amount of change in the substrate due to pressure and temperature is obtained from the added value (see (4) in the figure).

  Next, the seventh calculation means obtains the substrate change amount due to the pressure from the difference between the substrate change amount due to the pressure and temperature and the substrate change amount due to the temperature (see FIG. 5), and the eighth calculation means causes the pressure change. The pressure is calculated on the basis of the amount of change in the substrate.

  In other words, in the ninth aspect, the substrate change amount due to the temperature corresponding to the power ratio between the third surface acoustic wave element and the second surface acoustic wave element is obtained, and the substrate change amount due to this temperature (using a temperature map or the like). From this, the temperature correction amount is obtained. Since this temperature correction amount can be regarded as the starting point (pressure reference point) of the change in the substrate change amount due to pressure (such as a pressure map) under a certain temperature condition, the first calculated value is added to this temperature correction amount, Based on the added value, the substrate change amount corresponding to the pressure and temperature can be obtained. Therefore, by subtracting the substrate change amount due to temperature from the substrate change amount due to pressure and temperature, the substrate change amount corresponding only to the pressure can be obtained. Therefore, the pressure is obtained from the substrate change amount corresponding only to this pressure. Can do.

  (10) In the present invention, as a tenth aspect, the pressure sensing system includes the surface acoustic wave sensor according to any one of the first to sixth aspects, and the first surface acoustic wave element includes the surface acoustic wave element. First calculation means for obtaining a first calculation value indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied. And second calculation means for obtaining a second calculation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element, and based on the second calculation value Then, using the relationship between the second calculation value and the first calculation value based on the third calculation means for obtaining the substrate change amount of the element depending on the temperature, the pressure and temperature are determined based on the second calculation value. Determine the temperature correction amount that is the reference for determining the substrate change amount of the element 4 computing means, 5th computing means for adding the first computed value to the temperature correction amount to obtain an added value, and for obtaining a substrate change amount of the element due to pressure and temperature based on the added value. 6 arithmetic means, seventh arithmetic means for obtaining the substrate change amount of the element due to pressure from the difference between the substrate change amount of the element due to the pressure and temperature and the substrate change amount of the element due to the temperature, and the substrate of the element due to the pressure And an eighth calculating means for calculating the pressure based on the amount of change.

  The tenth aspect is different from the ninth aspect in the fourth calculation means. In other words, in the fourth calculation means, the relationship between the second calculation value and the first calculation value is used, and from the second calculation value (the first calculation value corresponding to the second calculation value). A temperature correction amount serving as a reference (pressure reference value) for obtaining the substrate change amount due to pressure and temperature is obtained, and thereafter the same calculation as in the ninth aspect is performed.

  Therefore, if an offset map or the like indicating the relationship between the second calculation value and the first calculation value is prepared in advance, the temperature correction amount (without using the substrate change amount due to the temperature) from the second calculation value. Can be requested.

According to the tenth aspect, the same effect as in the ninth aspect can be obtained.
(11) In the present invention, as an eleventh aspect, as an external device, a high-frequency applying unit that wirelessly applies a high-frequency signal to the surface acoustic wave sensor and a signal receiving unit that wirelessly receives a signal from the surface acoustic wave sensor And a signal detector that detects a signal (for example, voltage level) received by the signal receiver.

  When wirelessly transmitting / receiving a signal between a surface acoustic wave sensor and an external device and detecting the pressure using the relationship between outputs (for example, voltages) of each element, that is, a power detection method using wireless In the case where the pressure is detected by the method, the signal intensity (for example, the output voltage) changes with the variation of the wireless transmission distance, so that it is difficult to detect the pressure with high accuracy. As a countermeasure, when the timing at which the wireless transmission distance is constant is detected, sensing at that timing is required, and the system becomes complicated.

On the other hand, in the present invention, as described above, since the output voltage and power between the elements are calculated, the influence of the wireless transmission distance can be eliminated.
That is, by calculating the output voltage difference or power ratio between the elements, it is possible to cancel the change in signal strength due to the change in the wireless communication distance, that is, the influence of the wireless transmission distance can be eliminated. .

  (12) In the present invention, as the twelfth aspect, the delay times of the first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element are all different, and the first surface acoustic wave element and the first surface acoustic wave element The delay times of the second surface acoustic wave element and the third surface acoustic wave element are all longer than the output signal time output from the external device, and the first surface acoustic wave element, the second surface acoustic wave element, and the third elasticity The maximum delay time with the surface acoustic wave element can be set to be shorter than twice the minimum delay time.

  That is, in the response signal (reflected wave) to the input signal in each element, a shift due to the delay time in each element occurs as illustrated in FIG. A response signal (first reflected wave, second reflected wave,...) Obtained by repeating a plurality of reflections between the electrode and the reflector is set in each element by setting the conditions of each element as in the present invention. For example, a sufficient time shift can be given to the response signal so that the response signal can be time-separated on the external device side.

Here, “(1) The delay times of the first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element are all different” is a necessary condition for signal separation of the three elements. , “(2) The delay times of the first surface acoustic wave element, the second surface acoustic wave element and the third surface acoustic wave element are all longer than the output signal time output from the external device” Is a necessary condition for separating the input wave and the reflected wave of "3. The maximum delay time of the first surface acoustic wave element, the second surface acoustic wave element and the third surface acoustic wave element is the minimum delay time""Shorter than twice" is a necessary condition for separating the secondary reflected wave and the primary reflected wave.

  In the figure, τA, τB, and τC are the times (in the first, second, and third surface acoustic wave elements) until the signal transmitted from the electrode is reflected back to, for example, a reflector ( 2 times the delay time defined by the propagation path from the electrode to the reflector).

  (13) The present invention provides, as a thirteenth aspect, a pressure measuring method for measuring pressure using the surface acoustic wave sensor according to any one of the first to sixth aspects, wherein the first surface acoustic wave When a pressing force corresponding to the pressure is applied to the element, a first calculated value indicating a voltage difference between the output voltage of the first surface acoustic wave element and the output voltage of the second surface acoustic wave element is obtained. A first calculation step, a second calculation step for obtaining a second calculation value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element, and the second calculation Based on the third calculation step for obtaining the substrate change amount of the element based on the temperature and the relationship between the first calculation value and the substrate change amount of the element due to the pressure, and based on the substrate change amount of the element due to the temperature. The standard for determining the amount of change in the substrate of the element due to pressure and temperature A fourth calculation step for obtaining a temperature correction amount, a fifth calculation step for adding the first calculation value to the temperature correction amount to obtain an addition value, and an element based on pressure and temperature based on the addition value A sixth calculation step for obtaining the substrate change amount of the element, and a seventh calculation step for obtaining the substrate change amount of the element due to the pressure from a difference between the substrate change amount of the element due to the pressure and temperature and the substrate change amount of the element due to the temperature; And an eighth operation step of calculating the pressure based on the substrate change amount of the element due to the pressure.

The thirteenth aspect has the same operational effects as the seventh aspect.
(14) The present invention provides, as a fourteenth aspect, a pressure measuring method for measuring pressure using the surface acoustic wave sensor according to any one of the first to sixth aspects, wherein the first surface acoustic wave When a pressing force corresponding to the pressure is applied to the element, a first calculated value indicating a voltage difference between the output voltage of the first surface acoustic wave element and the output voltage of the second surface acoustic wave element is obtained. A first calculation step, a second calculation step for obtaining a second calculation value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element, and the second calculation Based on the value, the third calculation step for obtaining the amount of change in the substrate of the element due to temperature, and the relationship between the second calculation value and the first calculation value, and based on the second calculation value, And the temperature correction amount used as a reference when determining the amount of change in the substrate of the element due to temperature A fourth calculation step; a fifth calculation step of adding the first calculation value to the temperature correction amount to obtain an addition value; and a step of obtaining a substrate change amount of the element due to pressure and temperature based on the addition value. A seventh calculation step for obtaining a substrate change amount of the element due to the pressure from a difference between the element change amount due to the pressure and temperature and a substrate change amount of the element due to the temperature; and a substrate of the element due to the pressure. And an eighth calculation step of calculating the pressure based on the amount of change.

The fourteenth aspect has the same effects as the eighth aspect.
(15) The present invention provides, as a fifteenth aspect, a pressure measuring method for measuring pressure using the surface acoustic wave sensor according to any one of the first to sixth aspects, wherein the first surface acoustic wave When a pressing force corresponding to the pressure is applied to the element, a first calculated value indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element is obtained. A first calculation step, a second calculation step for obtaining a second calculation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element, and the second calculation Based on the third calculation step for obtaining the substrate change amount of the element based on the temperature and the relationship between the first calculation value and the substrate change amount of the element due to the pressure, and based on the substrate change amount of the element due to the temperature. The standard for determining the amount of change in the substrate of the element due to pressure and temperature A fourth calculation step for obtaining a temperature correction amount, a fifth calculation step for adding the first calculation value to the temperature correction amount to obtain an addition value, and a pressure from the addition value based on the addition value. And a sixth calculation step for obtaining a change amount of the substrate of the element due to temperature and a difference between the change amount of the substrate of the element due to pressure and temperature and the change amount of the substrate of the element due to temperature. And an eighth calculation step for calculating the pressure based on the substrate change amount of the element due to the pressure.

The fifteenth aspect has the same operational effects as the ninth aspect.
(16) The present invention provides, as a sixteenth aspect, a pressure measurement method for measuring pressure using the surface acoustic wave sensor according to any one of the first to sixth aspects, wherein the first surface acoustic wave When a pressing force corresponding to the pressure is applied to the element, a first calculated value indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element is obtained. A first calculation step, a second calculation step for obtaining a second calculation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element, and the second calculation Based on the value, the third calculation step for obtaining the amount of change in the substrate of the element due to temperature, and the relationship between the second calculation value and the first calculation value, and based on the second calculation value, And the temperature correction amount used as a reference when determining the amount of change in the substrate of the element due to temperature A fourth calculation step; a fifth calculation step of adding the first calculation value to the temperature correction amount to obtain an addition value; and a step of obtaining a substrate change amount of the element due to pressure and temperature based on the addition value. A seventh calculation step for obtaining a substrate change amount of the element due to the pressure from a difference between the element change amount due to the pressure and temperature and a substrate change amount of the element due to the temperature; and a substrate of the element due to the pressure. And an eighth calculation step of calculating the pressure based on the amount of change.

  The sixteenth aspect has the same effects as the tenth aspect.

It is explanatory drawing which shows the procedure for calculating | requiring a pressure by this invention. It explains that the pressure can be detected even if the temperature condition is different, (a) is an explanatory diagram showing a procedure for obtaining the pressure when the temperature change is small, and (b) is a procedure for obtaining the pressure when the temperature change is large. It is explanatory drawing which shows. (A) is a graph which shows the relationship between the reflection coefficient of a comb-tooth electrode, and a frequency, (b) is a graph which shows the relationship between the reflection coefficient of a reflector, and a frequency. It is a graph which shows the influence by temperature and pressure in the output voltage value of a surface acoustic wave sensor. It is a graph which shows the influence by the temperature in the output voltage value of a surface acoustic wave sensor. (A) is a graph showing the input wave and reflected wave of the first SAW element, (b) is a graph showing the input wave and reflected wave of the second SAW element, and (c) is a graph showing the input wave and reflected wave of the third SAW element. (D) is a graph which shows the input wave and reflected wave of each element. It is explanatory drawing which shows schematic structure of the sensing system in which the pressure sensor of Example 1 is used. It is explanatory drawing which shows schematic structure of the pressure sensor of Example 1. FIG. It is explanatory drawing which shows the structure of the pressure sensor of Example 1 in detail. It is explanatory drawing which shows the ZZ cross section of FIG. It is explanatory drawing which shows the electrical structure of the sensing system of Example 1. FIG. (A) is a graph showing the input wave and reflected wave of the first SAW element, (b) is a graph showing the input wave and reflected wave of the second SAW element, and (c) is a graph showing the input wave and reflected wave of the third SAW element. (D) is a graph which shows the input wave and reflected wave of each element. It is explanatory drawing which shows the procedure of the process of the signal in the sensing system of Example 1. FIG. It is explanatory drawing which shows the structure for the process in the transmission / reception side of Example 1 functionally. FIG. 6 is an explanatory diagram illustrating a processing procedure on the transmission / reception side according to the first exemplary embodiment. (A) is a graph showing the relationship between the voltage difference (V _SAW3 -V _SAW2) and substrate variation with temperature (temperature map), (b) the substrate varies according to the pressure and voltage difference (V _SAW1 -V _SAW2) It is a graph which shows the relationship (pressure map) with quantity. It is explanatory drawing which shows the structure for the process in the transmission / reception side of Example 2 functionally. FIG. 10 is an explanatory diagram illustrating a processing procedure on a transmission / reception side according to the second embodiment. (A) is explanatory drawing which shows the structure of the pressure sensor of Example 3, (b) is explanatory drawing which shows the structure of the pressure sensor of Example 4, (c) is explanatory drawing which shows the structure of the pressure sensor of Example 5. It is. (A) is a graph showing relationship between the (temperature map) of the substrate variation voltage difference between (V _SAW3 -V _SAW2) with temperature in Example 6, and (b) voltage difference (V _SAW1 -V _SAW2) It is a graph showing relationship between a substrate variation due to pressure (pressure map) shows a relationship between (c) a voltage difference between (V _SAW3 -V _SAW2) voltage difference between (V _SAW1 -V _SAW2) (offset map) It is a graph. FIG. 20 is an explanatory diagram illustrating a procedure of processing on the transmission / reception side according to the seventh embodiment. (A) is a graph showing relationship between the (temperature map) of the power ratio (P _SAW3 / P _SAW2) and substrate variation due to temperature in Example 7, and (b) the power ratio (P _SAW1 / P _SAW2) It is a graph which shows the relationship (pressure map) with the board | substrate variation | change_quantity by a pressure. Is a graph showing relationship (offset map) the power ratio (P _SAW3 / P _SAW2) and power ratio (P _SAW1 / P _SAW2) in Example 8. It is explanatory drawing which shows the procedure of the process in the transmission / reception side of Example 9. FIG. It is explanatory drawing which shows the procedure for calculating | requiring a pressure by Example 11, 12. FIG. FIG. 25 is an explanatory diagram illustrating a procedure of processing on the transmission / reception side according to the eleventh embodiment. (A) is a graph showing relationship between the (temperature map) of the substrate variation voltage difference between (V _SAW3 / V _SAW2) with temperature in Example 11, and (b) voltage difference (V _SAW1 / V _SAW2) is a graph showing relationship between a substrate variation due to pressure (pressure map), a (c) the relationship between the voltage difference (V _SAW3 / V _SAW2) and voltage difference _{(V SAW2 / V SAW2 *)} ( offset map) It is a graph to show. FIG. 20 is an explanatory diagram illustrating a processing procedure on the transmission / reception side according to the twelfth embodiment. (A) is a graph showing relationship between the (temperature map) of the power ratio (P _SAW3 / P _SAW2) and substrate variation due to temperature in Example 12, and (b) the power ratio (P _SAW1 / P _SAW2) is a graph showing relationship between a substrate variation due to pressure (pressure map), a (c) the relationship between the power ratio (P _SAW3 / P _SAW2) and power ratio _{(P SAW2 / P SAW2 *)} ( offset map) It is a graph to show.

  Embodiments to which the present invention is applied will be described below with reference to the drawings.

In the present embodiment, as a surface acoustic wave sensor, for example, a pressure sensor that is a tire pressure sensor that detects tire pressure of a vehicle will be described as an example.
As shown in FIG. 7, the pressure sensor 1 constitutes a sensing system that wirelessly transmits and receives signals to and from an external device (measuring device: transmitter / receiver) 3. Then, the pressure sensor 1 receives a signal (high frequency signal) from the external device 3 and transmits a response to the signal to the external device 3, and the external device 3 performs an operation based on the received signal, Find tire pressure.

  The pressure sensor 1 is attached to, for example, the inner surface of the tire 5, and the external device 3 is attached to, for example, a portion that does not rotate (for example, near the rim 7 or around the tire housing 9). Details will be described below.

a) First, the configuration of the pressure sensor 1 which is a surface acoustic wave sensor will be described.
As shown in FIGS. 8 and 9, the pressure sensor 1 of this embodiment includes three types of surface acoustic wave elements (first to third surface acoustic wave elements) 11, 13, and 15 having different characteristics. It is arranged and attached in parallel on the flat substrate 17 to be formed. Note that an antenna and a circuit connected to the antenna are omitted here.

Hereinafter, the surface acoustic wave elements 11 to 15 will be described.
The first surface acoustic wave element 11 has a pair of comb electrodes (IDT) that excite surface acoustic waves (SAW) on the same surface of the piezoelectric substrate 19 along the same direction (longitudinal direction of the piezoelectric substrate 19). 21 and 23 (see FIG. 8), a reflector 25 that reflects the surface acoustic waves excited by the comb-shaped electrodes 21 and 23 toward the comb-shaped electrodes 21 and 23, and a pair of left and right that absorb excess surface acoustic waves Sound absorbing materials 27 and 29 are provided. The pair of comb electrodes 21 and 23 is referred to as a comb electrode portion 24.

The first surface acoustic wave element 11 is an element that operates in the vicinity of 433 MHz, and the comb electrode 2
1 and 23, a high-frequency signal of one frequency (433 MHz) with a constant unit time is wirelessly (or wired) from an external device 3 (see FIGS. 9 and 11) as a signal source, as will be described later. Is applied (the same applies to the other elements 13 and 15). Here, the comb electrodes 21 and 23 are also used as electrodes for receiving the reflected wave from the reflector 25.

Below, each structure of the 1st surface acoustic wave element 11 is demonstrated still in detail.
As shown in FIG. 9, the piezoelectric substrate 19 is made of, for example, an ST-X quartz substrate (single crystal) having a length of 2 mm, a width of 16 mm, and a thickness of 0.5 mm.

  The comb electrodes 21 and 23 are electrodes to which a high frequency signal of 433 MHz is applied from a signal source (that is, electrodes to which positive and negative voltages are applied alternately), and a plurality of comb teeth (electrode fingers) 31 are respectively The electrode fingers 31 of the comb electrodes 21 and 23 facing each other are set so as to enter each other while being formed parallel to the longitudinal direction and the vertical direction.

  Here, the comb electrodes 21 and 23 are made of aluminum having a thickness of 0.1 μm, electrode width: 1 / 4λ (1.181 μm), electrode interval: 1 / 4λ (1.81 μm), logarithm: 100.5. Set to pair. Note that λ is the wavelength of the surface acoustic wave to be excited.

  The reflector (reflector: SMSA) 25 is made of aluminum having a thickness of 0.1 μm, electrode width: 1 / 4λ (1.181 μm), electrode interval: 1 / 4λ (1.81 μm), number: 200 Is set. The reflector 25 has a characteristic that the reflection coefficient changes according to the stress applied to itself and the ambient temperature.

The sound absorbing materials 27 and 29 are made of, for example, silicon, and are disposed outside the comb electrodes 21 and 23 and outside the reflector 25, respectively.
The propagation distance dR1 of the propagation path 33 (surface acoustic wave) between the comb electrodes 21 and 23 and the reflector 25 is set to 1500λ (4.735 mm), and the propagation time (and hence the delay time). ) Τ1 is equivalent to 1.5 μs.

  In particular, with respect to the first surface acoustic wave element 11, as shown in the ZZ cross section of FIG. 8 in FIG. 10, corresponding to the front end side (right side of the same figure) of the first surface acoustic wave element 11, A rectangular parallelepiped concave portion 35 is formed on the surface on the tip side (right side of the figure).

  That is, the first surface acoustic wave element 11 has the side (left side in the figure) on which the comb-tooth electrodes 21 and 23 are provided fixed to the surface of the substrate 17 and the side on which the reflector 25 is provided (same as above). The right side of the figure is arranged so as to protrude above the concave portion 35, whereby the tip side of the first surface acoustic wave element 11 is configured to be able to bend in the vertical direction of the figure.

  As shown in the figure, a cover 37 is disposed on the surface of the substrate 17 so as to cover the elements 11 to 13. An opening 39 is formed at the front end side (right side of the figure) of the cover 37, and an elastic member 41 made of, for example, rubber is attached so as to cover the opening 39. On the side of the substrate 17 at the center of the elastic member 41, a rod-shaped pressing member 43 is formed so as to protrude from the front end side of the first surface acoustic wave element 11. The elastic member 41 and the pressing member 43 constitute a pressing force application unit.

  Thus, when the elastic member 41 is pressed from the outside, the pressing member 43 presses the tip of the first surface acoustic wave element 11 (using the left end portion of the recess 35 as a fulcrum) of the first surface acoustic wave element 11. Since the tip portion is curved, the reflector 25 is also curved at the same time, and the reflection coefficient thereof changes.

  In the case of manufacturing the first surface acoustic wave element 11 described above, for example, a metal (aluminum) film is formed on the piezoelectric substrate 19 by a sputtering method, and the comb-tooth electrodes 21 and 23 or the like are formed by photolithography. A method of masking the shape corresponding to the reflector 25 and patterning the comb electrodes 21 and 23 and the reflector 25 by etching can be employed.

  As shown in FIG. 9, the second surface acoustic wave element 13, like the first surface acoustic wave element 11, has a pair of comb electrodes 53 and 55 and a reflector 57 on the surface of the piezoelectric substrate 51. Are formed apart by a predetermined propagation distance dR2 (> dR1), and the sound absorbing materials 59 and 61 are similarly arranged on the outside thereof. The pair of comb electrodes 53 and 55 constitutes a comb electrode unit 56.

  The second surface acoustic wave element 13 is the same as the first surface acoustic wave element 11 in the material and dimensions of the piezoelectric substrate 51, and the materials, dimensions, and shapes of the comb-tooth electrodes 53 and 55 and the reflector 57 are the same. It is.

  Accordingly, the characteristic of the reflection coefficient-frequency with respect to the temperature of the second surface acoustic wave element 13 is the same as that of the first surface acoustic wave element 11. However, the entire surface of the second surface acoustic wave element 13 is bonded onto the substrate 17 so that no pressure is applied (unlike the first surface acoustic wave element 11).

Since the configuration other than the above is basically the same as that of the first surface acoustic wave element 11, the description thereof is omitted.
As shown in FIG. 9, the third surface acoustic wave element 15 is formed on the surface of the piezoelectric substrate 71 (longer than the first surface acoustic wave element 11), like the first surface acoustic wave element 11. The pair of comb electrodes 73 and 75 and the reflector 77 are formed to be separated by a predetermined propagation distance dR3 (>dR2> dR1), and similarly, sound absorbing materials 79 and 81 are arranged on the outside thereof. Has been. The pair of comb electrodes 73 and 75 constitutes a comb electrode portion 76.

  The third surface acoustic wave element 15 is the same as the first surface acoustic wave element 11 in terms of the materials, dimensions, and shapes of the comb electrodes 73 and 75 and the reflector 77, and the material of the piezoelectric substrate. The dimensions of the piezoelectric substrate 71 are different. Specifically, the piezoelectric substrate 71 is made of, for example, an ST-X quartz substrate (single crystal) having a length of 2 mm, a width of 23 mm, and a thickness of 0.5 mm. Accordingly, the reflection coefficient-frequency characteristics with respect to the temperature of the third surface acoustic wave element 15 are different from those of the first and second surface acoustic wave elements 11 and 13. The entire surface of the third surface acoustic wave element 15 is bonded to the substrate 17 so that no pressure can be applied (similar to the second surface acoustic wave element 13).

Since the configuration other than the above is basically the same as that of the first surface acoustic wave element 11, the description thereof is omitted.
Since the first to third surface acoustic wave elements 11 to 15 are composed of the same type of piezoelectric substrate, when focusing on only this piezoelectric substrate, for example, under the same conditions (pressure and temperature) Changes by the same amount of substrate change.

b) Here, the relationship between the surface acoustic wave elements 11 to 15 as the main part of the present embodiment will be described together.
In this embodiment, as shown in Table 1 below, the first surface acoustic wave element 11 and the second surface acoustic wave element 13 are set so that the output voltages of the elements are the same with respect to temperature changes. That is, the piezoelectric substrates 19 and 51 and the comb electrodes 21, 23, 53, and the like constituting the first surface acoustic wave element 11 and the second surface acoustic wave element 13 so that the output voltages of the elements with respect to temperature changes are the same. 55 and reflectors 25 and 57 are set.

  The third surface acoustic wave element 15 is set so that the output voltage of the element differs from the first surface acoustic wave element 11 and the second surface acoustic wave element 13 with respect to temperature changes. That is, each of the piezoelectric substrates 19, 51, 71, etc. constituting the third surface acoustic wave element 15, the first surface acoustic wave element 11, and the second surface acoustic wave element 13 so that the output voltage of the element with respect to the temperature change is different. Is set.

  Specifically, the first surface acoustic wave element 11 and the second surface acoustic wave element 13 are the same in material, size, and shape of the comb electrodes 21, 23, 53, 55 and the reflectors 25, 57. The output voltage of the element is the same with respect to the temperature change, and the third surface acoustic wave element 15 has, for example, a frequency characteristic of the reflector reflection coefficient compared to the first surface acoustic wave element 11 and the second surface acoustic wave element 13. Since they are different, the output voltage of the element varies with temperature change.

  Further, the first surface acoustic wave element 11 is set so that the output voltage of the element changes according to a change in pressure. That is, only the first surface acoustic wave element 11 is configured such that the reflection coefficient is changed on the reflector 25 side so that the output voltage of the element changes due to a change in pressure, and its reflection coefficient changes.

  In addition, in the present embodiment, the propagation paths 33 of the first surface acoustic wave element 11, the second surface acoustic wave element 13, and the third surface acoustic wave element 15 are different so that the delay times τ1, τ2, and τ3 are all different. The length, and hence the propagation distances dR1, dR2, and dR3 (dR1 <dR2 <dR3) are set.

  That is, the propagation in the first to third surface acoustic wave elements 11 to 15 can be separated on the external device 3 side (transceiver side) so that the response signals in the first to third surface acoustic wave elements 11 to 15 can be separated. The distances dR1 to dR3 are set to be sufficiently different.

  The delay times τ1 to τ3 of the first surface acoustic wave element 11, the second surface acoustic wave element 13, and the third surface acoustic wave element 15 are all set longer than the output signal time output from the external device 3. Yes.

Further, the maximum delay time of the first surface acoustic wave element 11, the second surface acoustic wave element 13, and the third surface acoustic wave element 15 is set to be shorter than twice the minimum delay time.
c) Next, a sensing system using the pressure sensor 1 and the external device 3 will be described with reference to FIG.

  Although a wireless transmission / reception system will be described as an example here, stress may be detected by wire. Here, signals from the same signal source (that is, a transmitter / receiver which is an external device) 3 are transmitted from the comb-tooth electrodes 21, 23, 53, 55, 73 of the first to third surface acoustic wave elements 11-15. , 75. Similarly, each reflected signal (response signal) obtained from the first to third surface acoustic wave elements 11 to 15 is configured to be transmitted to the external device 3 side via one antenna.

  As shown in FIG. 11, the pressure sensor 1 including the first to third surface acoustic wave elements 11 to 15 and the antenna 91 is driven by a known external device 3 using radio. Therefore, here, the external device 3 corresponds to the signal source.

The external device 3 includes a control circuit (controller) 93 as its main part.
The external device 3 includes a high-frequency oscillation circuit (Osc) 95, a switch for switching on / off transmission (SW) 96, a band pass as a circuit for transmitting a signal (high-frequency signal) for driving the pressure sensor 1. A filter (BPF) 97, a power amplifier (PA) 99, a transmission / reception switch (SPDT) 101, and an antenna 103 are provided. Therefore, when the switch (SPDT) 101 is set to be able to transmit a signal, a signal is transmitted to the pressure sensor 1 via the antenna 103 by a control signal from the control circuit 93. The signal to be transmitted is, for example, a 10-mW 433 MHz single-pulse high-frequency signal.

  Further, the external device 3 is a circuit for receiving a signal from the pressure sensor 1, in addition to the antenna 103 and the switch (SPDT) 101, a low noise amplifier (LNA) 105, a band pass filter (BPF) 107, a log A detector (DET) 109 including an amplifier or a diode, an A / D converter 111, and the like are provided. Therefore, when the switch (SPDT) 101 is set to be able to receive a signal, the signal from the pressure sensor 1 is transmitted via the antenna 103 and input to the control circuit 93.

d) Next, a pressure measurement method using the sensing system will be described.
(1) First, basic transmission / reception operations in this sensing system will be described.

  First, when the pressure sensor 1 is driven, a high frequency signal is transmitted from the external device 3 to the pressure sensor 1 via the antenna 103 as described above. In the pressure sensor 1 that has received this high-frequency signal, by applying the received high-frequency signal to the comb-tooth electrodes 21, 23, 53, 55, 73, 75 of the first to third surface acoustic wave elements 11-15, Generate surface acoustic waves.

Here, for example, an input signal as shown in FIG. 12 (having a width of t _IN ) is input to each of the comb-tooth electrodes 21, 23, 53, 55, 73, of each of the first to third surface acoustic wave elements 11 to 15. Consider the case where the voltage is applied to 75.

  This input signal is converted into a surface acoustic wave by each comb-tooth electrode 21, 23, 53, 55, 73, 75. The surface acoustic wave is converted into each comb-tooth electrode 21, 23, 53, 55, 73, 75 and each Each reflector 25, 57, 77 is reached at a propagation time determined by the propagation distances dR1-dR3 between the reflectors 25, 57, 77 (that is, delay times τ1-τ3).

  Each reflector 25, 57, 77 reflects this surface acoustic wave, and this surface acoustic wave is similarly output to each comb electrode 21, 23, 53, after delay times τ1-τ3 determined by the propagation distances dR1-dR3. 55, 73, 75 are reached.

  A signal generated at each of the comb-tooth electrodes 21, 23, 53, 55, 73, and 75 due to the reflected surface acoustic wave (reflected wave) is a response signal (reflected signal), and this response signal is the transmitted signal. Contrary to (transmission signal), it is transmitted to the external device 3 via the antenna 91.

Therefore, the external device 3 can detect the pressure applied to the surface acoustic wave element 1 from the voltage (signal level) of the response signal as described below.
(2) Next, the processing procedure by the pressure measuring method will be described more specifically.

First, the flow of processing in the entire sensing system will be described along the time series based on FIG.
As shown in FIG. 13, on the external device 3 side, an inquiry signal is generated on the pressure sensor 1 side, and then the transmission / reception circuit is switched to reception.

On the other hand, the pressure sensor 1 side receives the inquiry signal transmitted from the external device 3 side.
Next, in the pressure sensor 1, the inquiry signal is distributed to the comb-tooth electrodes 21, 23, 53, 55, 73, 75 of the first to third elastic surface elements 11-15, and the comb-tooth electrodes 21, 23, 53 are distributed. , 55, 73, 75 generate surface acoustic waves (input waves). Then, the reflected waves reflected by the reflectors 25, 57, 77 (delayed by twice the delay time) are received by the comb electrodes 21, 23, 53, 55, 73, 75, and the response The signal is transmitted to the external device 3 side.

On the external device 3 side, the response signal transmitted from the pressure sensor 1 is received, amplified, noise-removed, etc., and then detected, and pressure and temperature are calculated from the signal as will be described later.
Next, the processing procedure on the external device 3 side will be described with reference to FIGS.

As functionally shown in both figures, processing by hardware is performed by the detection unit 121, and processing by software is performed by the arithmetic unit 123 (which performs arithmetic processing by a microcomputer or the like).
First, as shown in both figures, the detection voltage of the response signal of the pressure sensor 1 is converted into a digital signal by the A / D converter 111.

Specifically, first, second, each signal from the third surface acoustic wave element 11, 13, 15 (voltage signal _{V SAW1, V SAW2, V SAW3} ) each A / D converter 111 (FIG. 14 For convenience, the A / D converters for each signal are shown separately, and are input to the arithmetic unit 123.

-Next, the process in the calculating part 123 is demonstrated in detail based on FIG.15 and FIG.16.
Specifically, for example, a temperature map shown in FIG. 16A and a pressure map shown in FIG. 16B are used.

The temperature map and includes a substrate variation with temperature, the difference between the output voltage V _SAW2 the second surface acoustic wave element 13 is the output voltage V _SAW3 and temperature reference electrode of the third surface acoustic wave element 15 (V _SAW3 - V _SAW2 ) is a map showing the relationship.

Further, the pressure map, and substrates variation due to pressure difference (V between the output voltage V _SAW2 the second surface acoustic wave element 13 is the output voltage V _SAW1 and pressure reference electrode of the first surface acoustic wave element 11 _SAW1 -V _SAW2 ) is a map showing the relationship.

First, in Step 1, a voltage difference (V _SAW1 −V _SAW2 ) between the output voltage V _{SAW1 of} the first surface acoustic wave element 11 and the output voltage V _SAW2 of the second surface acoustic wave element 13 is _obtained .
In step 2, determined as the output voltage V _SAW3 the third surface acoustic wave element 15 the voltage difference between the output voltage V _SAW2 the second surface acoustic wave element 13 (V _SAW3 -V _SAW2), the temperature map, the The amount of substrate change due to temperature corresponding to the voltage difference is obtained. For example, when the voltage difference is 2 V, the substrate change amount due to temperature is 190 ppm from FIG.

Accordingly, a map or the like is prepared by examining the relationship between the temperature and the substrate change amount due to the temperature in advance, and the temperature can be obtained from the substrate change amount due to the temperature with reference to this map or the like.
Next, in step 3, the substrate change amount due to the temperature is applied as the substrate change amount due to the pressure of FIG. 16B, and a temperature correction amount (pressure reference value) is obtained from the pressure map of FIG. For example, when the substrate change amount due to temperature is 190 ppm, the temperature correction amount is 1.1 V from FIG.

Next, in step 4, a value (added value) obtained by adding the temperature correction amount to the voltage difference (V _SAW1 −V _SAW2 ) obtained in step 1 is obtained. For example, when the voltage difference is 1.2 V, 2.3 V obtained by adding 1.1 V of the temperature correction amount is the added value.

  Next, in step 5, the substrate change amount due to the pressure corresponding to the added value is obtained using the pressure map. Note that since the temperature correction amount is added to the added value, the substrate change amount due to the pressure includes not only the pressure but also the influence of the temperature. For example, from FIG. 16B, the substrate change amount due to the pressure corresponding to the added value 2.3 V is 500 ppm.

  Next, in step 6, the substrate change amount due to the pressure alone is obtained by subtracting the substrate change amount due to the temperature (caused only by the temperature) from the substrate change amount due to the pressure (including the influence of temperature). For example, when the substrate variation due to pressure is 500 ppm and the substrate variation due to temperature is 190 ppm, the difference of 310 ppm is the substrate variation due to pressure alone.

Accordingly, a map or the like is prepared by examining the relationship between the pressure and the substrate change amount due to the pressure in advance, and the pressure can be obtained from the substrate change amount based only on the pressure with reference to this map or the like.
e) As described above, in this embodiment, the pressure sensor 1 provided with the three types of surface acoustic wave elements 11 to 15 is used, and the output of these elements is used to change both the pressure and the temperature. However, it is possible to detect the target state (pressure) of the measurement object with high accuracy by suitably eliminating the influence of temperature.

  That is, first, a difference between output voltages of the first surface acoustic wave element 11 and the second surface acoustic wave element 13 is calculated to obtain a first calculated value (including the effects of pressure and temperature), and the third surface acoustic wave is obtained. A difference in output voltage between the wave element 15 and the second surface acoustic wave element 13 is taken to obtain a second calculated value (including the effect of temperature only).

  Then, using the temperature map, the second calculated value is converted into a substrate change amount due to temperature (only), and then from the substrate change amount due to this temperature using the pressure map (corresponding to the pressure reference value). Find the temperature correction amount. Next, an addition value obtained by adding the first calculation value to the temperature correction amount is obtained, and further, a substrate change amount due to pressure and temperature is obtained from the addition value using a pressure map. Then, by subtracting the substrate change amount due to only the temperature from the substrate change amount due to the pressure and temperature, the substrate change amount due to only the pressure can be obtained. Therefore, the pressure can be obtained accurately from the substrate change amount due to only this pressure. it can.

  Also, in this embodiment, when pressure is detected by a wireless power detection method, the signal strength (output voltage) changes as the wireless transmission distance varies by performing the pressure measurement method described above. However, the influence of the wireless transmission distance can be eliminated with a simple configuration.

Next, the second embodiment will be described, but the description of the same contents as the first embodiment will be simplified.
Here, since the method for calculating the pressure and the like in the external device is different from that in the first embodiment, different contents will be described.

As shown in FIGS. 17 and 18, in this embodiment, hardware processing is performed by the detection unit 201, and software processing is performed by the calculation unit 203.
As shown in both figures, the detection voltage of the response signal of the pressure sensor 1 is held in each hold circuit 205-209. Specifically, first, second, each signal from the third surface acoustic wave device (a voltage signal _{V SAW1, V SAW2, V SAW3} ) is respectively held in each holding circuit 205 to 209.

Then, for example, a difference (V _SAW1 −V _SAW2 ) _between the _held voltage signals V _SAW1 and V _SAW2 from the first and second surface acoustic wave elements is calculated by a differential calculation circuit (not shown). Similarly, the third is held, calculates a difference (V _SAW3 -V _SAW2) of the voltage signal V _SAW3, V _SAW2 from the second surface acoustic wave element.

The calculated values of these differences are input to the calculation unit 203 via the A / D converters 211 and 213, respectively.
After that, in the arithmetic unit 203, as in the first embodiment, as shown in FIG. 18, first, the voltage signal V _SAW1 from the first surface acoustic wave element 11 and the second electrode (which is a reference electrode for temperature and pressure). The difference (V _SAW1 −V _SAW2 ) of the voltage signal V _SAW2 from the surface acoustic wave element 13 is calculated. Similarly, it calculates a difference (V _SAW3 -V _SAW2) of the voltage signal V _SAW2 from the voltage signal V _SAW3 from the third surface acoustic wave element 15 and the second surface acoustic wave element 13.

Next, using a temperature map as FIG 16 (a), the voltage difference substrate displacement amount corresponding to (V _SAW3 -V _SAW2) (substrate variation due to temperature: first calculation value) is calculated .
Next, as described above, the temperature correction amount (corresponding to the pressure reference point) is calculated from the substrate change amount due to the temperature, using the pressure map as shown in FIG.

Next, the temperature correction amount is added to the voltage difference (V _SAW1 −V _SAW2 ), and the substrate displacement due to temperature and pressure is calculated from the addition value using the pressure map as shown in FIG. calculate.
Next, the substrate displacement amount due to temperature alone is calculated by subtracting the substrate displacement amount due to temperature from the substrate displacement amount due to temperature and pressure.

Accordingly, the pressure can be obtained from the amount of substrate displacement due to this pressure alone, using a map or the like showing the relationship between the pressure obtained beforehand and the amount of substrate displacement due to pressure alone.
Further, from the voltage difference (V _SAW3 -V _SAW2), as described above, by using a map or the like showing the relationship between a substrate displacement by only previously obtained temperature and the temperature, it is possible to calculate the temperature .

  Also according to this embodiment, the same effects as those of the first embodiment can be obtained.

Next, the third embodiment will be described, but the description of the same contents as the first embodiment will be simplified.
Here, since the configuration of the surface acoustic wave element is different from that of the first embodiment, different contents will be described.
As shown in FIG. 19A, in the pressure sensor 301 which is the surface acoustic wave sensor of the present embodiment, the lengths in the longitudinal direction of the first to third surface acoustic wave elements 303 to 307 are set to be different. Yes.

  Each element 303 to 307 is formed with comb electrode portions 315 to 319 (consisting of a pair of comb electrodes) and reflectors 321 to 325 on the piezoelectric substrates 309 to 313, respectively, as in the first embodiment. It has been done.

  Also in this embodiment, the first surface acoustic wave element 303 and the second surface acoustic wave element 305 have the same material, size, and shape of the comb electrode and the reflector, so that the output voltage of the element with respect to the temperature change. Are set to be the same.

  In addition, the third surface acoustic wave element 307 is different from the first surface acoustic wave element 303 and the second surface acoustic wave element 305 in that, for example, the frequency characteristics of the reflector reflection coefficient are different from each other in response to the temperature change. Are set to have different output voltages.

Further, only the first surface acoustic wave element 303 is set so that the output voltage of the element changes due to a change in pressure.
Also in the present embodiment, the same effects as in the first embodiment can be obtained.

Next, the fourth embodiment will be described, but the description of the same contents as the first embodiment will be simplified.
Here, since the configuration of the surface acoustic wave element is different from that of the first embodiment, different contents will be described.
As shown in FIG. 19B, in the pressure sensor 401 which is the surface acoustic wave sensor of this embodiment, the first and second surface acoustic wave elements 403 and 405 are arranged in a row in the longitudinal direction on the same piezoelectric substrate 407. Is formed.

  The first and second surface acoustic wave elements 403 and 405 have a comb electrode portion 409 (shared by both elements 403 and 405) formed at the center on the same piezoelectric substrate 407 and the piezoelectric substrate 407. Reflectors 411 and 413 are formed on both sides.

The third surface acoustic wave element 414 has a comb electrode part 417 and a reflector 419 formed on another piezoelectric substrate 415.
Also in this embodiment, the first surface acoustic wave element 403 and the second surface acoustic wave element 405 have the same material, size, and shape of the comb electrode and the reflector, so that the output voltage of the element with respect to the temperature change. Are set to be the same.

  The third surface acoustic wave element 414 is different from the first surface acoustic wave element 403 and the second surface acoustic wave element 405 in that, for example, the frequency characteristic of the reflector reflection coefficient is different from that of the first surface acoustic wave element 405. Are set to have different output voltages.

Further, only the first surface acoustic wave element 403 is set such that the output voltage of the element changes due to a change in pressure.
Also in the present embodiment, the same effects as in the first embodiment can be obtained.

Next, a description will be given of the fifth embodiment, but the description of the same contents as the first embodiment will be simplified.
Here, since the configuration of the surface acoustic wave element is different from that of the first embodiment, different contents will be described.
As shown in FIG. 18C, in the pressure sensor 501 which is the surface acoustic wave sensor of this embodiment, the lengths in the longitudinal direction of the first to third surface acoustic wave elements 503 to 507 are set to be different. Yes.

  Each element 503 to 507 is similar to the first embodiment, on each piezoelectric substrate 509 to 513, each element common (consisting of a pair of comb electrodes) 515 and each reflector 517 to 521 is formed.

  Also in the present embodiment, the first surface acoustic wave element 503 and the second surface acoustic wave element 505 have the same material, size, and shape of the comb electrode and the reflector, so that the output power of the element with respect to the temperature change. The values are set to be the same.

  Further, the third surface acoustic wave element 507 is different from the first surface acoustic wave element 503 and the second surface acoustic wave element 505 in that, for example, the frequency characteristics of the reflector reflection coefficient are made different from each other in response to a temperature change. Are set to have different output voltages.

Furthermore, only the first surface acoustic wave element 503 is set so that the output voltage of the element changes due to a change in pressure.
Also in the present embodiment, the same effects as in the first embodiment can be obtained.

Next, the sixth embodiment will be described, but the description of the same contents as the first embodiment will be simplified. In addition, since each member, such as an element, is the same as Example 1, the same number as Example 1 is used.
In this example, the temperature map of FIG. 20A and the pressure map of FIG. 20B are used, as in FIGS. 16A and 16B of Example 1, and FIG. Also use an offset map as shown in.

The offset map is a voltage difference on the vertical axis represents (V _SAW1 -V _SAW2), those taken voltage difference on the horizontal axis (V _SAW3 -V _SAW2). That is, the offset map, the voltage difference (V _SAW3 -V _SAW2), is set so that it is possible to obtain a voltage difference corresponding to the temperature correction amount (V _SAW1 -V _SAW2).

Therefore, when the offset map is obtained from the voltage difference (V _SAW3 -V _SAW2), the (without the use of temperature map) offset voltage corresponding to the temperature correction amount is offset voltage (V _SAW1 -V _SAW2) be able to.

Hereinafter, a procedure for measuring pressure using this offset map will be described.
First, in step 1, determined with the output voltage V _SAW3 the third surface acoustic wave element 15 the voltage difference between the output voltage V _SAW2 the second surface acoustic wave element 13 (V _SAW3 -V _SAW2), the temperature map, the The amount of substrate change due to the temperature corresponding to the voltage difference is obtained. For example, when the voltage difference is 2 V, the substrate change amount due to temperature is 190 ppm from FIG.

Next, in step 2, using the offset map of FIG. 20 (c), the voltage difference between the horizontal axis from (V _SAW3 -V _SAW2), temperature indicated directly by the voltage difference between the vertical axis (V _SAW1 -V _SAW2) Find the correction amount. For example, when the voltage difference is 2V, the temperature correction amount is 1.1V from FIG.

Next, in step 3, the voltage difference (V _SAW1 −V _SAW2 ) between the output voltage V _{SAW1 of} the first surface acoustic wave element 11 and the output voltage V _SAW2 of the second surface acoustic wave element 13 is set as the temperature correction amount. Add. Then, the substrate change amount due to the pressure corresponding to the added value is obtained from the pressure map. For example, when the voltage difference is 1.2 V, 2.3 V obtained by adding 1.1 V of the temperature correction amount is an added value, and from FIG. 20B, the substrate change amount due to pressure is 500 ppm.

  Next, in step 4, the substrate change amount due to the pressure alone is obtained by subtracting the substrate change amount due to the temperature (which is caused only by the temperature) from the substrate change amount due to the pressure (including the influence of temperature). For example, when the substrate change amount due to pressure is 500 ppm and the substrate change amount due to temperature is 190 ppm, the difference of 310 ppm is the substrate change amount due to pressure alone.

Accordingly, a map or the like is prepared by examining the relationship between the pressure and the substrate change amount due to the pressure in advance, and the pressure can be obtained from the substrate change amount based only on the pressure with reference to this map or the like.
As for the temperature, as in the first embodiment, the temperature is calculated from the substrate change amount due to the temperature using a map or the like showing the relationship between the temperature obtained in advance and the substrate displacement amount due only to the temperature. be able to.

  In the present embodiment, the same effects as in the first embodiment can be obtained, and by preparing an offset map in advance, there are advantages that the calculation can be simplified and the calculation time can be shortened.

Next, the seventh embodiment will be described, but the description of the same contents as the first embodiment will be simplified. In addition, since each member, such as an element, is the same as Example 1, the same number as Example 1 is used.
In the present embodiment, the pressure is detected in substantially the same procedure as in the first embodiment using the power ratio of the output of each element, and therefore, this will be briefly described with reference to FIGS.

  Note that the vertical axis of FIG. 22A shows the amount of change in the substrate due to the same temperature as in Example 1, while the horizontal axis shows the power ratio between the elements 15 and 13. Further, the vertical axis of FIG. 22B shows the amount of change in the substrate due to the same pressure as in Example 1, while the horizontal axis shows the power ratio between the elements 11 and 13.

As shown in FIGS. 21 and 22, first, the output voltages of the first to third surface acoustic wave elements 11 to 15 are determined according to the detection characteristics of the detector (DET) 109 including a log amplifier or a diode shown in FIG. by converting the input power, respectively converted to electric power _{P SAW1, P SAW2, P SAW3} .

Then, a power ratio (P _SAW1 / P _SAW2 ) between the power P _{SAW1 of} the first surface acoustic wave element 11 and the power P _{SAW2 of} the second surface acoustic wave element 13 (which is a reference electrode for temperature and pressure) is calculated. Similarly, to calculate the power P _SAW3 the third surface acoustic wave element 15 power ratio between the power P _SAW2 the second surface acoustic wave element 13 (P _SAW3 / P _SAW2).

As will be described later, the power ratio and the power difference are equivalent, and here, since the power is taken in dBm, the calculation of the power ratio is a differential operation.
Next, using a temperature map as FIG 22 (a), to calculate the substrate displacement amount corresponding to the value of the power ratio (P _SAW3 / P _SAW2) (substrate variation with temperature).

Next, using the pressure map as shown in FIG. 22B, a temperature correction amount (corresponding to the pressure reference point) is calculated from the substrate change amount due to the temperature.
Next, the temperature correction amount is added to the power ratio (P _SAW1 / P _SAW2 ), and the substrate displacement due to temperature and pressure is calculated from the added value using the pressure map as shown in FIG. calculate.

Next, the substrate displacement amount due to temperature alone is calculated by subtracting the substrate displacement amount due to temperature from the substrate displacement amount due to temperature and pressure.
Accordingly, the pressure can be obtained from the amount of substrate displacement due to this pressure alone, using a map or the like showing the relationship between the pressure obtained beforehand and the amount of substrate displacement due to pressure alone.

Further, the temperature can be calculated from the substrate change amount due to the temperature, using a map or the like showing the relationship between the previously obtained temperature and the substrate displacement amount due to only the temperature.
Also in the present embodiment, the same effects as in the first embodiment can be obtained.

  In addition, as shown in the following equation 1, when defined as in equation (1), as is clear from equation (2) or equation (3), calculating the difference with power in dBm is Since this is equivalent to taking the ratio of the true number (power W), each map is represented by a power difference.

Next, Example 8 will be described, but the description of the same contents as Example 7 will be simplified.
In this embodiment, the power ratio of the element as shown in the seventh embodiment is used, and the offset map as shown in the sixth embodiment is used.

In addition, since each member, such as an element, is the same as Example 1, the same number as Example 1 is used.
In this embodiment, the pressure is obtained by using both the maps shown in FIGS. 22A and 22B and the offset map shown in FIG.

The offset map is, as shown in FIG. 23, the power ratio on the vertical axis represents the (P _SAW1 / P _SAW2), in which took power ratio (P _SAW3 / P _SAW2) on the horizontal axis. That is, the offset map, from the power ratio (P _SAW3 / P _SAW2), is set so that it is possible to determine the power ratio corresponding to the temperature correction amount (P _SAW1 / P _SAW2).

Therefore, when the offset map is obtained from the power ratio (P _SAW3 / P _SAW2), the (temperature without the use of maps) power ratio corresponding to the temperature correction amount is offset voltage (P _SAW1 / P _SAW2) be able to.

The procedure for detecting the pressure using this offset map will be briefly described below.
First, in step 1, calculated power P _SAW3 the third surface acoustic wave element 15 power ratio between the power P _SAW2 the second surface acoustic wave element 13 (P _SAW3 / P _SAW2), the temperature shown in FIG. 22 (a) From the map, the amount of substrate change due to the temperature corresponding to this voltage ratio is obtained.

Next, in step 2, using the offset map of FIG. 23, the power ratio of the horizontal axis from (P _SAW3 / P _SAW2), a temperature correction amount indicated directly in the power ratio of the vertical axis (P _SAW1 / P _SAW2) Ask.
In step 3, the temperature correction amount is added to the power P _SAW1 the first surface acoustic wave element 11 power ratio between the power P _SAW2 the second surface acoustic wave element 13 (P _SAW1 / P _SAW2). Then, the amount of change in the substrate due to the pressure corresponding to the added value is obtained from the pressure map of FIG.

Next, in step 4, the substrate change amount due to the pressure alone is obtained by subtracting the substrate change amount due to the temperature (which is caused only by the temperature) from the substrate change amount due to the pressure (including the influence of temperature).
Accordingly, a map or the like is prepared by examining the relationship between the pressure and the substrate change amount due to the pressure in advance, and the pressure can be obtained from the substrate change amount based only on the pressure with reference to this map or the like.

Further, similarly to the seventh embodiment, the temperature can be obtained from the substrate change amount due to the temperature.
In the present embodiment, the same effects as in the seventh embodiment can be obtained, and there is an advantage that the calculation can be simplified and the calculation time can be shortened by preparing an offset map in advance.

Next, the ninth embodiment will be described, but the description of the same contents as the second embodiment will be simplified.
In addition, since each member, such as an element, is the same as Example 2, the same number as Example 2 is used.
In this embodiment, the pressure is detected using the same hold circuit as in the second embodiment and using the power ratio between elements similar to that in the seventh embodiment.

In this embodiment, as shown in FIG. 24, first, second, each signal from the third surface acoustic wave device (a voltage signal _{V SAW1, V SAW2, V SAW3} ) at each hold circuits 205 to 209 respectively Retained.

Then, for example, a difference (V _SAW1 −V _SAW2 ) _between the _held voltage signals V _SAW1 and V _SAW2 from the first and second surface acoustic wave elements is calculated by a differential calculation circuit (not shown). Similarly, the third is held, calculates a difference (V _SAW3 -V _SAW2) of the voltage signal V _SAW3, V _SAW2 from the second surface acoustic wave element.

The calculated values of these differences are input to the calculation unit 203 via the A / D converters 211 and 213, respectively.
Then, the arithmetic unit 203, first, a voltage signal V _SAW1 from the first surface acoustic wave element 11 of the voltage signal V _SAW2 from the second surface acoustic wave element 13 the difference (V _SAW1 -V _SAW2), in FIG. 11 A power ratio (P _SAW1 / P _SAW2 ) is _obtained by converting power according to the detection characteristics of a detector (DET) 109 formed of a log amplifier or a diode.

Similarly, with the third voltage signal V _SAW3 from the surface acoustic wave device 15 of the voltage signal V _SAW2 from the second surface acoustic wave element 13 the difference (V _SAW3 -V _SAW2) to power conversion, power ratio ( determine the P _SAW3 / P _SAW2).

Then, using these power ratios, the pressure is obtained in the same manner as in Example 7.
Specifically, using a temperature map as FIG 22 (a), to calculate the substrate displacement amount corresponding to the value of the power ratio (P _SAW3 / P _SAW2) (substrate variation with temperature).

Next, using the pressure map as shown in FIG. 22B, a temperature correction amount (corresponding to the pressure reference point) is calculated from the substrate change amount due to the temperature.
Next, the temperature correction amount is added to the power ratio (P _SAW1 / P _SAW2 ), and the amount of substrate displacement due to temperature and pressure is calculated from the added value using the map as shown in FIG. To do.

Next, the substrate displacement amount due to temperature alone is calculated by subtracting the substrate displacement amount due to temperature from the substrate displacement amount due to temperature and pressure.
Accordingly, the pressure can be obtained from the amount of substrate displacement due to this pressure alone, using a map or the like showing the relationship between the pressure obtained beforehand and the amount of substrate displacement due to pressure alone.

Further, similarly to the second embodiment, the temperature can be obtained from the substrate change amount due to the temperature.
According to the present embodiment, the same effects as those of the second embodiment can be obtained.

Next, Example 10 will be described, but the description of the same contents as Example 9 will be simplified.
In addition, since each member, such as an element, is the same as Example 9, the same number as Example 9 is used.

In the present embodiment, the pressure is detected using the hold circuit and the power ratio between elements similar to those in the ninth embodiment and using the offset map as in the eighth embodiment.
In the present embodiment, as shown in FIG. 24, in the same manner as in the ninth embodiment, the calculation unit 203 receives the voltage signal V _SAW1 from the first surface acoustic wave element 11 and the second surface acoustic wave element 13 from The power ratio (P _SAW1 / P _SAW2 ) is _obtained by converting the difference (V _SAW1 −V _SAW2 ) of the voltage signal V _SAW2 into power.

Similarly, with the third voltage signal V _SAW3 from the surface acoustic wave device 15 of the voltage signal V _SAW2 from the second surface acoustic wave element 13 the difference (V _SAW3 -V _SAW2) to power conversion, power ratio ( determine the P _SAW3 / P _SAW2).

Then, using these power ratios, the pressure is obtained in the same manner as in Example 8.
Specifically, in step 1, calculated power P _SAW3 the third surface acoustic wave element 15 power ratio between the power P _SAW2 the second surface acoustic wave element 13 (P _SAW3 / P _SAW2), FIG. 22 ( From the temperature map of a), the substrate change amount due to the temperature corresponding to this voltage ratio is obtained.

Next, in step 2, using the offset map of FIG 23, the power ratio of the horizontal axis from (P _SAW3 / P _SAW2), directly to the vertical axis (P _SAW1 / P _SAW2), i.e. obtaining the temperature correction amount.
In step 3, the temperature correction amount is added to the power P _SAW1 the first surface acoustic wave element 11 power ratio between the power P _SAW2 the second surface acoustic wave element 13 (P _SAW1 / P _SAW2). Then, from the pressure map of FIG. 22B, the substrate change amount due to the pressure corresponding to the added value is obtained.

Next, in step 4, the substrate change amount due to the pressure alone is obtained by subtracting the substrate change amount due to the temperature (which is caused only by the temperature) from the substrate change amount due to the pressure (including the influence of temperature).
Accordingly, a map or the like is prepared by examining the relationship between the pressure and the substrate change amount due to the pressure in advance, and the pressure can be obtained from the substrate change amount based only on the pressure with reference to this map or the like.

Further, similarly to the ninth embodiment, the temperature can be obtained from the substrate change amount due to the temperature.
Also in this embodiment, the same effects as those of the ninth embodiment are obtained.

Next, although Example 11 is demonstrated, description of the content similar to the said Example 1 is simplified.
a) First, in this embodiment, the principle by which the pressure can be obtained using the output of each element will be described with reference to FIG.

Note that the horizontal axis (X axis) in FIG. 25 indicates the amount of change in the substrate due to temperature or pressure, and the vertical axis (Y axis) indicates the difference in output voltage or power ratio between elements.
Further, the solid line graph (pressure map) in the figure shows the first surface acoustic wave element (SAW1) when the pressure applied to the first surface acoustic wave element (SAW1) is changed when the temperature is constant. It is a graph which shows the difference (or power ratio: reflected power ratio) of an output voltage with a 2nd surface acoustic wave element (SAW2). Further, a graph (temperature map) indicated by a dotted line in the figure shows a difference (or power) between output voltages of the third surface acoustic wave element (SAW3) and the second surface acoustic wave element (SAW2) when the temperature is changed. (Ratio: reflected power ratio).

  In addition, the graph (reference electrode temperature map) indicated by the alternate long and short dash line in FIG. 6 shows the change amount (or power change amount) of the output voltage of the second surface acoustic wave element (SAW2) which is the reference electrode when the temperature is changed. Reflected power variation), that is, the voltage difference between the output voltage (or power) of the second surface acoustic wave element (SAW2) and the output voltage (or power: reflected power) when the reference temperature (substrate variation is 0). (Or power ratio).

Note that the map is not provided and may be defined by an arithmetic expression, but the following description will be made using the map.
In the present embodiment, the change in applied pressure can be detected by the following procedure even when there is a temperature change.

As illustrated in FIG. 25, first, in step 1, a voltage difference (or power ratio) between SAW3 and SAW2 is obtained.
Since this voltage difference (or power ratio) corresponds to the substrate change amount due to temperature, in step 2, using the temperature map, the substrate change amount due to temperature corresponding to the power difference (or power ratio) is calculated. Ask.

  In step 3, using the reference electrode temperature map, the substrate change amount due to the temperature is converted into the substrate change amount due to the pressure to obtain a pressure reference value (initial value). That is, when the temperature characteristics of SAW1 and SAW2 match, the reference electrode temperature map and the pressure map completely match, and the pressure reference value shifts the reference electrode temperature map. The pressure reference value is obtained using the temperature map.

  Here, the reason why the reference electrode temperature map and the pressure map completely coincide is that the first surface acoustic wave element and the second surface acoustic wave element have an output (for example, voltage or power) of the element with respect to a temperature change. Because it is the same.

In step 4, the power difference (or power ratio) between SAW1 and SAW2 is obtained.
In step 5, a substrate change amount corresponding to the power difference (voltage ratio) obtained in step 4 from the pressure reference point (that is, a substrate change amount corresponding to only the pressure) is obtained using the pressure map.

Therefore, by obtaining the relationship between the pressure and the substrate change amount corresponding to only the pressure in advance, only the pressure can be obtained from the substrate change amount corresponding to only the pressure.
b) Next, based on the above-described principle, a specific procedure for pressure detection performed in the present embodiment will be described with reference to FIGS.

In addition, since each member, such as an element, is the same as Example 1, the same number as Example 1 is used.
Here, the temperature map shown in FIG. _27A is the difference between the substrate change amount due to temperature and the output voltage V _{SAW3 of} the third surface acoustic wave element 15 and the output voltage V _SAW2 of the second surface acoustic wave element 13. is a map showing the relationship between the (V _SAW3 -V _SAW2).

In addition, the pressure map shown in FIG. _27B is a difference between the substrate change amount due to pressure and the output voltage V _{SAW1 of} the first surface acoustic wave element 11 and the output voltage V _SAW2 of the second surface acoustic wave element 13 ( V _SAW1 −V _SAW2 ).

Further, the reference electrode temperature map shown in FIG. _27C is that the output voltage V _SAW2 of the second surface acoustic wave element 13 that is the reference electrode and the output voltage V _{SAW2 * of} the second surface acoustic wave element 13 at the reference temperature are voltage difference between (V _SAW2 -V _{SAW2 *),} the difference between the output voltage V _SAW3 the third surface acoustic wave element 11 and the output voltage V _SAW2 the second surface acoustic wave element 13 (V _SAW3 -V _SAW2), It is an offset map showing the relationship.

As shown in FIG. 26, the detection voltage of the response signal of the pressure sensor 1 is converted into a digital signal by the A / D converter 111.
Specifically, first, second, each signal from the third surface acoustic wave element 11, 13, 15 (voltage signal _{V SAW1, V SAW2, V SAW3} ) , respectively via the A / D converter 111 Input to the arithmetic unit 123.

Then, the arithmetic unit 123 calculates a voltage signal V _SAW1 from the first surface acoustic wave element 11 of the voltage signal V _SAW2 from the second surface acoustic wave element 13 the difference (V _SAW1 -V _SAW2). Similarly, it calculates a difference (V _SAW3 -V _SAW2) of the voltage signal V _SAW2 from the voltage signal V _SAW3 from the third surface acoustic wave element 15 and the second surface acoustic wave element 13.

Next, using a temperature map shown in FIG. 27 (a), to calculate the substrate displacement amount corresponding to the value of the voltage difference (V _SAW3 -V _SAW2) (substrate variation with temperature). Incidentally, for example, when the voltage difference (V _SAW3 -V _SAW2) is 2V, the substrate variation due to temperature becomes 190 ppm.

Then, the temperature correction amount using the offset map, the voltage difference between the horizontal axis from (V _SAW3 -V _SAW2), the vertical axis (V _SAW2 -V _{SAW2 *),} i.e. corresponding to the pressure reference value in FIG. 27 (c) Find the offset voltage. For example, when the voltage difference is 2V, the temperature correction amount is 1.1V.

Next, a voltage difference (V _SAW1 −V _SAW2 ) between the output voltage V _{SAW1 of} the first surface acoustic wave element 11 and the output voltage V _SAW2 of the second surface acoustic wave element 13 is added to the temperature correction amount.
Then, from the pressure map shown in FIG. 27B, the substrate change amount due to the pressure corresponding to the added value is obtained. For example, when the voltage difference is 1.2 V, 2.3 V obtained by adding 1.1 V of the temperature correction amount is an added value, and from FIG. 27B, the substrate change amount due to pressure is 500 ppm.

Next, the substrate change amount due to temperature (including only the temperature) is subtracted from the substrate change amount due to pressure (including the effect of temperature) to obtain the substrate change amount due to pressure alone.
For example, when the substrate change amount due to pressure is 500 ppm and the substrate change amount due to temperature is 190 ppm, the difference of 310 ppm is the substrate change amount due to pressure alone.

Accordingly, a map or the like is prepared by examining the relationship between the pressure and the substrate change amount due to the pressure in advance, and the pressure can be obtained from the substrate change amount based only on the pressure with reference to this map or the like.
As for the temperature, as in the first embodiment, the temperature is calculated from the substrate change amount due to the temperature using a map or the like showing the relationship between the temperature obtained in advance and the substrate displacement amount due only to the temperature. be able to.

  Also in the present embodiment, the same effects as in the first embodiment can be obtained.

Next, the twelfth embodiment will be described, but the description of the same contents as the tenth embodiment will be simplified.
In addition, since each member, such as an element, is the same as Example 10, the same number as Example 1 is used.

In the present embodiment, the hold circuit and the power ratio between elements similar to those in the tenth embodiment are used, and the pressure is detected using the offset map as in the eleventh embodiment.
Hereinafter, a specific procedure for pressure detection performed in this embodiment will be described with reference to FIGS.

Note that the temperature map shown in FIG. 29 (a), a substrate variation with temperature of the third surface acoustic wave element 15 power (P _SAW3) and the power (P _SAW2) of the second surface acoustic wave element 13 is a map showing a relationship between the power ratio (P _SAW3 / P _SAW2).

In addition, the pressure map shown in FIG. 29 (b) is the change in the substrate due to pressure, the power of the first surface acoustic wave element 11 (P _SAW1 ), and the power of the second surface acoustic wave element 13 (P _SAW2 ). It is a map which shows the relationship with a power ratio (P _SAW1 / P _SAW2 ).

Furthermore, the reference electrode temperature map shown in FIG. 29 (c), the power at the reference temperature of the second surface acoustic wave element 13 is a reference electrode (P _{SAW2 *)} and the second surface acoustic wave element 13 power (P _SAW3 ) and power ratio between _{(P SAW2 / V SAW2 *)} , the power of the third surface acoustic wave element 11 and the (P _SAW3) power ratio between the power (P _SAW2) of the second surface acoustic wave element 13 (P _SAW3 / P _SAW2 ) is an offset map showing the relationship.

In the present embodiment, as shown in FIG. 28, in the same manner as in the tenth embodiment, the calculation unit 203 uses the voltage signal V _SAW1 from the first surface acoustic wave element 11 and the second surface acoustic wave element 13 to The power ratio (P _SAW1 / P _SAW2 ) is _obtained by converting the difference (V _SAW1 −V _SAW2 ) of the voltage signal V _SAW2 into power.

Similarly, with the third voltage signal V _SAW3 from the surface acoustic wave device 15 of the voltage signal V _SAW2 from the second surface acoustic wave element 13 the difference (V _SAW3 -V _SAW2) to power conversion, power ratio ( determine the P _SAW3 / P _SAW2).

Then, using these power ratios, the pressure is obtained in the same manner as in Example 11.
Specifically, first, the power ratio between the power P _SAW2 the power P _SAW3 the third surface acoustic wave element 15 and the second surface acoustic wave element 13 (P _SAW3 / P _SAW2) look, FIG 29 (a) From this temperature map, the amount of change in the substrate due to the temperature corresponding to this voltage ratio is obtained.

Then, the temperature correction amount using an offset map, the power ratio of the horizontal axis from (P _SAW3 / P _SAW2), the vertical axis _{(P SAW2 / P SAW2 *)} , i.e. corresponding to the pressure reference value in FIG. 29 (c) Find the offset voltage.

Then, the temperature correction amount is added to the power P _SAW1 the first surface acoustic wave element 11 power ratio between the power P _SAW2 the second surface acoustic wave element 13 (P _SAW1 / P _SAW2).
Then, from the pressure map shown in FIG. 29B, the substrate change amount due to the pressure corresponding to the added value is obtained.

Next, the substrate change amount due to temperature (including only the temperature) is subtracted from the substrate change amount due to pressure (including the effect of temperature) to obtain the substrate change amount due to pressure alone.
Accordingly, a map or the like is prepared by examining the relationship between the pressure and the substrate change amount due to the pressure in advance, and the pressure can be obtained from the substrate change amount based only on the pressure with reference to this map or the like.

As for the temperature, the temperature can be calculated using a map or the like showing the relationship between the temperature obtained in advance and the substrate displacement amount based only on the temperature based on the substrate change amount based on the temperature.
Also in the present embodiment, the same effects as in the eleventh embodiment can be obtained.

(1) The present invention is not limited to a pressure sensor such as a tire air pressure sensor, but can be applied to various applications such as a stress sensor and a displacement sensor.
(2) In the present invention, the pressure or the like is obtained using the output voltage value. Alternatively, the pressure or the like may be obtained using the output current value obtained from the output voltage value.

1, 301, 401, 501 ... Pressure sensor (surface acoustic wave sensor)
3. External device (signal source)
11, 303, 403, 503... First surface acoustic wave element 13, 305, 405, 505... Second surface acoustic wave element 15, 307, 414, 507... Third surface acoustic wave element 19, 51, 71, 309, 311, 313, 407, 415, 509, 511, 513 ... Piezoelectric substrate 21, 23, 53, 55, 73, 75 ... Comb electrode 24, 56, 76, 315, 317, 319, 409, 417, 515 ... Comb Tooth electrode part 33 ... Transmission path 25, 57, 77, 321, 323, 325, 411, 413, 419, 517, 519, 521 ... Reflector 43 ... Pressing member

Claims (16)

A surface acoustic wave sensor including a first surface acoustic wave element, a second surface acoustic wave element, and a third surface acoustic wave element in which the output of the element changes due to a change in the characteristics of the surface acoustic wave transmitted through the element due to an external influence. Because
The first surface acoustic wave element and the second surface acoustic wave element have the same element output with respect to temperature change, and the third surface acoustic wave element includes the first surface acoustic wave element and the second surface acoustic wave element. The output of the element is different from the surface acoustic wave element with respect to temperature change,
The first surface acoustic wave element is an element configured such that an output of the element changes according to a change in a state of a measurement object other than the temperature.   The surface acoustic wave sensor according to claim 1, further comprising a configuration capable of wirelessly transmitting and receiving signals to and from an external device.   The surface acoustic wave sensor according to claim 1, wherein the measurement target is pressure.   The surface acoustic wave sensor according to claim 3, further comprising a pressing force application unit that applies a pressing force corresponding to the pressure to the first surface acoustic wave element.   The first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element are set so that delay times of signals in the respective elements are all different from each other. The surface acoustic wave sensor of any one of 1-4. The first surface acoustic wave element includes an electrode that generates a surface acoustic wave, and a reflector that reflects the surface acoustic wave generated by the electrode,
The reflector of the first surface acoustic wave element has a configuration that elastically deforms when an external pressing force is applied, and includes a pressing force application unit that applies the pressing force to the reflector. The surface acoustic wave sensor according to claim 1, wherein: A pressure sensing system comprising the surface acoustic wave sensor according to any one of claims 1 to 6,
A first difference indicating a voltage difference between an output voltage of the first surface acoustic wave element and an output voltage of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. First calculating means for calculating a calculated value of
Second computing means for obtaining a second computed value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element;
Based on the second calculated value, a third calculating means for obtaining a substrate change amount of the element due to temperature;
Using the relationship between the first calculated value and the substrate change amount of the element due to the pressure, based on the substrate change amount of the element due to the temperature, temperature correction serving as a reference when obtaining the substrate change amount of the element due to pressure and temperature A fourth calculation means for obtaining an amount;
A fifth calculation means for adding the first calculation value to the temperature correction amount to obtain an addition value;
Sixth arithmetic means for obtaining a change amount of the substrate of the element due to pressure and temperature based on the added value;
A seventh calculating means for obtaining a substrate change amount of the element due to pressure from a difference between the substrate change amount of the element due to the pressure and temperature and a substrate change amount of the element due to the temperature;
Eighth operation means for calculating the pressure based on the substrate change amount of the element due to the pressure;
Sensing system characterized by comprising A pressure sensing system comprising the surface acoustic wave sensor according to any one of claims 1 to 6,
A first difference indicating a voltage difference between an output voltage of the first surface acoustic wave element and an output voltage of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. First calculating means for calculating a calculated value of
Second computing means for obtaining a second computed value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element;
Based on the second calculated value, a third calculating means for obtaining a substrate change amount of the element due to temperature;
Using the relationship between the second calculated value and the first calculated value, a temperature correction amount serving as a reference for determining a substrate change amount of the element due to pressure and temperature is obtained based on the second calculated value. A fourth computing means;
A fifth calculation means for adding the first calculation value to the temperature correction amount to obtain an addition value;
Sixth arithmetic means for obtaining a change amount of the substrate of the element due to pressure and temperature based on the added value;
A seventh calculating means for obtaining a substrate change amount of the element due to pressure from a difference between the substrate change amount of the element due to the pressure and temperature and a substrate change amount of the element due to the temperature;
Eighth operation means for calculating the pressure based on the substrate change amount of the element due to the pressure;
Sensing system characterized by comprising A pressure sensing system comprising the surface acoustic wave sensor according to any one of claims 1 to 6,
A first ratio indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. First calculating means for calculating a calculated value of
Second computing means for obtaining a second computation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element;
Based on the second calculated value, a third calculating means for obtaining a substrate change amount of the element due to temperature;
Using the relationship between the first calculated value and the substrate change amount of the element due to the pressure, based on the substrate change amount of the element due to the temperature, temperature correction serving as a reference when obtaining the substrate change amount of the element due to pressure and temperature A fourth calculation means for obtaining an amount;
A fifth calculation means for adding the first calculation value to the temperature correction amount to obtain an addition value;
Based on the added value, sixth calculating means for obtaining a substrate change amount of the element due to pressure and temperature from the added value;
A seventh calculating means for obtaining a substrate change amount of the element due to pressure from a difference between the substrate change amount of the element due to the pressure and temperature and a substrate change amount of the element due to the temperature;
Eighth operation means for calculating the pressure based on the substrate change amount of the element due to the pressure;
Sensing system characterized by comprising A pressure sensing system comprising the surface acoustic wave sensor according to any one of claims 1 to 6,
A first ratio indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. First calculating means for calculating a calculated value of
Second computing means for obtaining a second computation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element;
Based on the second calculated value, a third calculating means for obtaining a substrate change amount of the element due to temperature;
Using the relationship between the second calculated value and the first calculated value, a temperature correction amount serving as a reference for determining a substrate change amount of the element due to pressure and temperature is obtained based on the second calculated value. A fourth computing means;
A fifth calculation means for adding the first calculation value to the temperature correction amount to obtain an addition value;
Sixth arithmetic means for obtaining a change amount of the substrate of the element due to pressure and temperature based on the added value;
A seventh calculating means for obtaining a substrate change amount of the element due to pressure from a difference between the substrate change amount of the element due to the pressure and temperature and a substrate change amount of the element due to the temperature;
Eighth operation means for calculating the pressure based on the substrate change amount of the element due to the pressure;
Sensing system characterized by comprising   The external device includes a high frequency applying unit that wirelessly applies a high frequency signal to the surface acoustic wave sensor, a signal receiving unit that wirelessly receives a signal from the surface acoustic wave sensor, and a signal receiving unit that receives the signal. The sensing system according to any one of claims 7 to 10, further comprising a signal detection unit that detects the detected signal. The delay times of the first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element are all different,
And, the delay times of the first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element are all longer than the output signal time output from the external device,
The maximum delay time of the first surface acoustic wave element, the second surface acoustic wave element, and the third surface acoustic wave element is shorter than twice the minimum delay time. The sensing system according to any one of the above. A pressure measurement method for measuring pressure using the surface acoustic wave sensor according to any one of claims 1 to 6,
A first difference indicating a voltage difference between an output voltage of the first surface acoustic wave element and an output voltage of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. A first calculation step for obtaining a calculated value of
A second calculation step of obtaining a second calculation value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element;
A third calculation step of obtaining a substrate change amount of the element due to temperature based on the second calculation value;
Using the relationship between the first calculated value and the substrate change amount of the element due to the pressure, based on the substrate change amount of the element due to the temperature, temperature correction serving as a reference when obtaining the substrate change amount of the element due to pressure and temperature A fourth calculation step for determining the quantity;
A fifth calculation step of adding the first calculation value to the temperature correction amount to obtain an addition value;
A sixth calculation step for obtaining a substrate change amount of the element due to pressure and temperature based on the added value;
A seventh calculation step of obtaining the substrate change amount of the element due to pressure from the difference between the substrate change amount of the element due to the pressure and temperature and the substrate change amount of the element due to the temperature;
An eighth calculation step of calculating the pressure based on the substrate change amount of the element due to the pressure;
A pressure measuring method comprising: A pressure measurement method for measuring pressure using the surface acoustic wave sensor according to any one of claims 1 to 6,
A first difference indicating a voltage difference between an output voltage of the first surface acoustic wave element and an output voltage of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. A first calculation step for obtaining a calculated value of
A second calculation step of obtaining a second calculation value indicating a voltage difference between the output voltage of the third surface acoustic wave element and the output voltage of the second surface acoustic wave element;
A third calculation step of obtaining a substrate change amount of the element due to temperature based on the second calculation value;
Using the relationship between the second calculated value and the first calculated value, a temperature correction amount serving as a reference for determining a substrate change amount of the element due to pressure and temperature is obtained based on the second calculated value. A fourth calculation step;
A fifth calculation step of adding the first calculation value to the temperature correction amount to obtain an addition value;
A sixth calculation step for obtaining a substrate change amount of the element due to pressure and temperature based on the added value;
A seventh calculation step of obtaining the substrate change amount of the element due to pressure from the difference between the substrate change amount of the element due to the pressure and temperature and the substrate change amount of the element due to the temperature;
An eighth calculation step of calculating the pressure based on the substrate change amount of the element due to the pressure;
A pressure measuring method comprising: A pressure measurement method for measuring pressure using the surface acoustic wave sensor according to any one of claims 1 to 6,
A first ratio indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. A first calculation step for obtaining a calculated value of
A second calculation step of obtaining a second calculation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element;
A third calculation step of obtaining a substrate change amount of the element due to temperature based on the second calculation value;
Using the relationship between the first calculated value and the substrate change amount of the element due to the pressure, based on the substrate change amount of the element due to the temperature, temperature correction serving as a reference when obtaining the substrate change amount of the element due to pressure and temperature A fourth calculation step for determining the quantity;
A fifth calculation step of adding the first calculation value to the temperature correction amount to obtain an addition value;
A sixth calculation step of obtaining a substrate change amount of the element due to pressure and temperature from the addition value based on the addition value;
A seventh calculation step of obtaining the substrate change amount of the element due to pressure from the difference between the substrate change amount of the element due to the pressure and temperature and the substrate change amount of the element due to the temperature;
An eighth calculation step of calculating the pressure based on the substrate change amount of the element due to the pressure;
A pressure measuring method comprising: A pressure measurement method for measuring pressure using the surface acoustic wave sensor according to any one of claims 1 to 6,
A first ratio indicating a power ratio between the output power of the first surface acoustic wave element and the output power of the second surface acoustic wave element when a pressing force corresponding to the pressure is applied to the first surface acoustic wave element. A first calculation step for obtaining a calculated value of
A second calculation step of obtaining a second calculation value indicating a power ratio between the output power of the third surface acoustic wave element and the output power of the second surface acoustic wave element;
A third calculation step of obtaining a substrate change amount of the element due to temperature based on the second calculation value;
Using the relationship between the second calculated value and the first calculated value, a temperature correction amount serving as a reference for determining a substrate change amount of the element due to pressure and temperature is obtained based on the second calculated value. A fourth calculation step;
A fifth calculation step of adding the first calculation value to the temperature correction amount to obtain an addition value;
A sixth calculation step for obtaining a substrate change amount of the element due to pressure and temperature based on the added value;
A seventh calculation step of obtaining the substrate change amount of the element due to pressure from the difference between the substrate change amount of the element due to the pressure and temperature and the substrate change amount of the element due to the temperature;
An eighth calculation step of calculating the pressure based on the substrate change amount of the element due to the pressure;
A pressure measuring method comprising: