JP2021186238A - Piezoelectric sensor - Google Patents

Abstract

To provide a piezoelectric sensor which improves reliability by improving waterproof performance and can be used for a long period outdoors.SOLUTION: Aerial vibrations of pulse wave and respiratory vibration being biological information about a subject is transmitted from an air pad installed on a bed, a chair or the like into a space 202 as atmospheric pressure variation through an introduction tube 134. Then, a pressure-receiving part 200 warps and deforms by atmospheric pressure variation, and the atmospheric pressure variation is transmitted into the space 102. A piezoelectric element 110 warps, and the atmospheric pressure variation is converted into an electric signal. When it is supposed that moisture and humidity enter through the introduction tube 134, they enter into the space 202, but the pressure-receiving part 200 functions as a waterproof wall and an adhesive layer 204 also has a waterproof function, so that the moisture stays in the space 202 and does not enter into the space 102.SELECTED DRAWING: Figure 1

Description

The present invention relates to a piezoelectric sensor that detects pressure or the like using a piezoelectric element, and relates to an improvement of a piezoelectric sensor suitable for measuring biological information such as pulse (pulse or pulse wave) and respiration, for example.

In recent years, various sensors have been used to monitor human activity in indoor or outdoor environments, detect vital signals of the human body, and monitor mental and physical conditions to detect abnormalities in the human body. Solutions that detect and avoid unforeseen circumstances are becoming widespread.

As a piezoelectric sensor for measuring such biological information, for example, there is a "pressure detecting device and a biological information measuring system" described in Patent Document 1 below. This is for the purpose of measuring minute pressure fluctuations generated in the object to be measured with high accuracy, and the pressure detection device is provided with an input chamber in which the piezoelectric element is a part of the wall surface, and this input is provided. Air is introduced into the room from the introduction portion in a direction inclined with respect to the piezoelectric element. The following Patent Document 2 discloses a "biological information measuring device", which is outside an air mat in which air is enclosed in an internal void which is arranged so as to be in direct or indirect contact with a subject and is substantially sealed by an encapsulation bag. A pressure sensor is provided on the surface or inside, whereby a signal corresponding to the pressure fluctuation of the air enclosed in the void is obtained, and biometric information is obtained from the signal.

Japanese Unexamined Patent Publication No. 2017-219341 Japanese Unexamined Patent Publication No. 2005-110969

By the way, the piezoelectric sensor used in industrial applications has a metal-sealed head part, and although it has sufficient waterproof measures, it has poor sensitivity and is good at detecting high-frequency mechanical vibrations such as motors that rotate at high speeds. It is not suitable for detecting weak low-frequency vibrations such as biological information (vital information). On the other hand, in the above-mentioned background technology, since the air mat has high water permeability, it cannot be said that the waterproof measures are sufficient, and there is a possibility that moisture may enter the piezoelectric element side from the air mat side. When moisture invades, the piezoelectric element and the circuit of the substrate deteriorate and corrode, causing a failure, and it is difficult to use it outdoors or in an environment where there is a possibility of flooding for a long period of time even indoors.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a piezoelectric sensor that can be used for a long period of time even outdoors by improving reliability by improving waterproofness.

The piezoelectric sensor of the present invention has a pressure receiving portion, a first room having the front surface of the pressure receiving portion as an inner wall, an introduction port attached to the first chamber, and at least one surface of the piezoelectric body. It has a piezoelectric element provided in the above, a back surface of the pressure receiving portion, and a second room having the piezoelectric element as an inner wall, respectively. According to one of the main forms, the piezoelectric element has a front surface and a back surface to be an inner wall of the second room, and the back surface of the piezoelectric element is a third configuration as an inner wall. Have more rooms. Alternatively, the second room is sealed with respect to the first room.

According to another form, the pressure receiving portion contains a rubber material. Further, the elongation rate of the rubber material is 800% to 100%. Alternatively, the elongation rate of the rubber material is 1000% to 100%. The above and other objects, features and advantages of the present invention will be clarified from the following detailed description and accompanying drawings.

According to the present invention, since the fluctuation of the fluid pressure generated from the measurement target is waterproofed by the pressure receiving portion and transmitted to the piezoelectric element, the waterproofness can be improved and the reliability can be improved.

It is a figure which shows the structure of the piezoelectric sensor of the Example of this invention.

Hereinafter, the present invention will be described in detail.

FIG. 1A shows a cross-sectional configuration of the piezoelectric sensor 100 according to this embodiment. In the figure, the piezoelectric sensor 100 has a configuration in which a piezoelectric element 110 is provided inside. The piezoelectric element 110 is a stack of a top cover 130 and a bottom cover 140, and has a cylindrical outer shape and an internal space. In the piezoelectric element 110, for example, the piezoelectric PE is formed on a metal plate MP made of brass or the like.

In this embodiment, the structure is the same as that of a known piezoelectric speaker (piezoelectric microphone), and one electrode of the piezoelectric PE is a metal plate MP. That is, one electrode of the piezoelectric PE is connected to the solder EA, and the other electrode is a metal plate MP, which is connected to the solder EB. The lead wire for drawing is electrically connected to the solder EA and EB so that the electric signal of the piezoelectric PE is output. When solder is used, a copper film or the like having good wettability of the solder may be formed depending on the type of the metal plate MP.

Further, the bottom cover 140 is provided with a circuit board CB, and circuit components such as an amplifier are provided. Lead wires (not shown) are connected to the solders EA and EB, and are electrically connected to an amplifier provided on the circuit board CB.

The upper part of the bottom cover 140 has an enlarged diameter, and a step 143 is provided in the enlarged diameter portion. The piezoelectric element 110 is arranged on the step 143. In the piezoelectric element 110, the metal plate MP described above is fixed to the step 143 by, for example, an adhesive 145. On the other hand, the lower part of the upper cover 130 has an enlarged diameter, and a step 132 is provided in the enlarged diameter portion. Then, the pressure receiving portion 200 is fixed by an adhesive between the step 132 and the upper end of the bottom cover 140. As a result, the adhesive layer 204 is formed between the pressure receiving portion 200 and the top cover 130 and the bottom cover 140. Further, in the upper center of the upper cover 130, an introduction tube 134 to which an air pressure that changes according to the pressure fluctuation generated in the object to be measured is supplied is provided. From each of the above parts, spaces 202, 102, and 103 are sequentially formed in the piezoelectric sensor 100 from the introduction tube 134 side. In this way, the piezoelectric element 110 is sealed by the bottom cover 140, the pressure receiving portion 200, and the adhesive layer 204. The pressure receiving unit 200 and the space 202 form the first room, and the piezoelectric element 110 and the space 102 form the second room.

Next, as the pressure receiving portion 200 described above, since it functions as a waterproof wall, a material having low water permeability and such that the vibration of the air pressure from the introduction tube 134 is satisfactorily transmitted to the piezoelectric element 110 is preferable. A resin or metal having low water permeability may be used to realize the waterproof function, but a rubber material is preferable in order to achieve both a pressure receiving function for transmitting pressure fluctuation and a waterproof function.

Table 1 shows a rubber material suitable for the pressure receiving portion 200. When the pressure receiving part 200 was prototyped for the rubber material shown in the figure and the detection sensitivity and the water immersion test for 100 hours were carried out, the results were obtained that there was no problem in practical use.

In Table 1, "elongation" corresponds to the elongation at the time of cutting in "JIS K 6251: 2010". As a measurement method for obtaining elongation at the time of cutting, for example,
a, As specified in "JIS K6251: 2010", measure the maximum tensile force until the test piece is cut and the tensile force at the time of cutting with a tensile tester.
b. In the case of a dumbbell-shaped test piece, measure the distance between the marked lines at the time of cutting by an appropriate method in order to obtain the elongation at the time of cutting.
c. In the case of a ring-shaped test piece, the distance between the gripping tools, which is the moving distance of the center of the pulley during cutting, is measured in order to obtain the elongation during cutting.
From the results in Table 1, the elongation rate is preferably 800% to 100%, and if the material is at least 1000% to 100%, sufficient pressure receiving property can be ensured.

Next, as the adhesive layer 204, any one may be used as long as it functions as a waterproof layer. For example, using the epoxy resin adhesive "Rubber Ace" manufactured by Asahi Bond Industries, the pressure receiving portion 200 formed of the rubber material in Table 1 was joined, and the detection sensitivity test of the piezoelectric element 110 and the water immersion test for 100 hours were performed. The results showed that there was no practical problem with any of the materials shown in Table 1.

Next, the overall operation of this embodiment will be described. For example, as in Patent Document 1, air vibrations of pulse waves and breathing vibrations, which are biological information of the subject, are transmitted as air pressure fluctuations in the space 202 through the introduction tube 134 from an air pad installed on a bed, a chair, or the like. It is transmitted. Then, the pressure receiving portion 200 bends and deforms due to the air pressure fluctuation, and the air pressure fluctuation is transmitted to the space 102. Then, the piezoelectric PE of the piezoelectric element 110 bends, and the air pressure fluctuation is converted into an electric signal.

In this case, if moisture or moisture enters from the introduction tube 134, they invade the space 202, but since the pressure receiving portion 200 functions as a waterproof wall and the adhesive layer 204 also has a waterproof function, the moisture is contained. It stays in space 202 and does not invade space 102. Therefore, it is possible to satisfactorily prevent moisture or moisture from invading the piezoelectric element 110 and circuit components around it and corroding. In addition, the improved waterproofness makes it more reliable and can be used outdoors for a long period of time. Further, since the pressure receiving unit 200 has elasticity, the air pressure fluctuation introduced from the outside is satisfactorily transmitted to the piezoelectric element 110, and the detection sensitivity of the air pressure fluctuation is also ensured.

Next, Example 2 of the present invention will be described with reference to FIG. 1 (B). This embodiment is an example in which two piezoelectric elements 110 and 120 are provided in the piezoelectric sensor 101. In the figure, the piezoelectric sensor 101 has a configuration in which piezoelectric elements 110 and 120 are provided in the upper and lower stages, respectively. These piezoelectric elements 110 and 120 are arranged in a tubular space in which an upper cover 130, an intermediate cover 141, a lower cover 150, and a bottom cover 160 are stacked. An engaging protrusion 162 is provided inside the upper surface of the bottom cover 160, and the lower end opening side of the lower cover 150 is engaged with the engaging protrusion 162. The upper part of the lower cover 150 has an enlarged diameter and is provided with a diameter-expanded portion 152, and the piezoelectric element 120 is arranged on a step 154 of the expanded-diameter portion 152 with a sealing 156 for enhancing airtightness interposed therebetween.

An intermediate cover 141 is arranged on the piezoelectric element 120. The lower side of the intermediate cover 141 is provided with an inner peripheral flange 142 having a reduced diameter, and a sealing 144 for enhancing airtightness is provided between the inner peripheral flange 142 and the periphery of the piezoelectric element 120. There is. On the other hand, the piezoelectric element 110 is arranged on the step 146 on the upper side of the inner peripheral flange 142 with the sealing 148 interposed therebetween. The upper side of the intermediate cover 141 has the same configuration as that of the first embodiment described above. From each of the above parts, spaces 202, 102, 104, and 106 are sequentially formed in the piezoelectric sensor 101 from the introduction tube 134 side.

According to this embodiment, the bending of the piezoelectric material PE1 of the piezoelectric element 110 causes the air pressure fluctuation of the space 104, whereby the piezoelectric body PE2 of the piezoelectric element 120 bends, and the air pressure fluctuation is converted into an electric signal. The electric signals output from the piezoelectric elements 110 and 120 are amplified by the amplifier of the circuit board CB, the gain is adjusted, and then appropriate frequency band filtering processing, peak detection, peak counting, etc. are performed to perform pulse waves and respiration. Get the necessary data such as.

According to this embodiment, signals are obtained from the two piezoelectric elements 110 and 120. Therefore, for example, even if the output signal of one piezoelectric element is saturated, necessary information can be obtained from the output signal of the other piezoelectric element. There is an advantage that it can be done.

<Other Examples> The present invention is not limited to the above-mentioned examples, and various modifications can be made without departing from the gist of the present invention. For example, the following are also included.
(1) The structure of the piezoelectric sensor shown in FIG. 1 is an example, and the shape and dimensions may be appropriately set so as to perform the same function.
(2) In the above embodiment, it is decided to measure the pulse and respiration which are biological information, but it may be applied to the measurement of various air pressure fluctuations.
(3) In the above embodiment, the fluctuation of the air pressure is measured, but a fluid such as a gas other than air or various liquids may be used.

According to the present invention, the fluctuation of the fluid pressure generated from the measurement target is waterproofed by the pressure receiving portion and transmitted to the piezoelectric element, so that the waterproofness is improved and the reliability is high, and it can be used for a long time even outdoors. Therefore, it is suitable as a piezoelectric sensor for biological information and the like.

100, 101: Piezoelectric sensor 102, 103, 104, 106: Space 110, 120: Piezoelectric element 130: Top cover 132: Step 134: Introduction tube 140: Bottom cover 141: Intermediate cover 142: Inner peripheral flange 143: Step 144: Sealing 145: Adhesive 146: Step 148: Sealing 150: Bottom cover 152: Expanded diameter part 154: Step 156: Sealing 160: Bottom cover 162: Engagement protrusion 200: Pressure receiving part 202: Space 204: Adhesive layer EA, EB: Electrode CB: Circuit board MP: Metal plate PE: Piezoelectric material

Claims (6)

With the pressure receiving part
The first room, which has the front surface of the pressure receiving portion as an inner wall,
The inlet installed in the first room and
Piezoelectric elements with piezoelectrics on at least one side,
A second room having the back surface of the pressure receiving portion and the piezoelectric element as inner walls, respectively.
Piezoelectric sensor with. The piezoelectric element has a front surface and a back surface that serve as an inner wall of the second room.
Further having a third chamber having the back surface of the piezoelectric element as an inner wall.
The piezoelectric sensor according to claim 1. The piezoelectric sensor according to claim 1 or 2, wherein the second room is sealed with respect to the first room. The piezoelectric sensor according to any one of claims 1 to 3, wherein the pressure receiving portion includes a rubber material. The piezoelectric sensor according to claim 4, wherein the elongation rate of the rubber material is 800% to 100%. The piezoelectric sensor according to claim 4, wherein the elongation of the rubber material is 1000% to 100%.

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