JP3680635B2 - Ultrasonic sensor, ultrasonic sensing device and ultrasonic flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic sensor using an ultrasonic technique for sensing by radiating ultrasonic waves to a measurement object and a sensing device using the sensor, and more particularly to an ultrasonic flowmeter.
[0002]
[Prior art]
A sensing device that performs sensing using ultrasonic technology radiates an ultrasonic wave to a measurement object or medium and detects the reflected wave to detect a position, distance, or speed measurement device or image processing device, For example, there is an ultrasonic flowmeter that radiates ultrasonic waves to a medium and detects the propagation time of the transmitted wave to measure the flow velocity of the medium.
[0003]
FIG. 5 is a conceptual diagram of an ultrasonic flowmeter in which a pair of ultrasonic sensors are arranged opposite to each other along the fluid flow, ultrasonic waves are alternately transmitted to the upstream side and the downstream side, and the flow velocity is measured from the time difference until reception. Indicates. In FIG. 5, an ultrasonic flowmeter according to the prior art is joined to an ultrasonic vibrator 2 in which an electrode is formed on an inorganic piezoelectric material of lead zirconate titanate (PZT), for example, and the ultrasonic vibrator 2. The ultrasonic sensors 6A and 6B including the acoustic matching layer 4 that radiates sound waves from the other surface are placed in the medium of the measurement fluid 5 or a measurement pipe (not shown) through which the measurement fluid 5 is conveyed. Inclined and configured so that the transmitting side and the receiving side are opposed to each other.
[0004]
In this configuration, the ultrasonic flowmeter excites the ultrasonic transducer 2 (2A) of one ultrasonic sensor (for example, 6A) from the transmission / reception circuit 61A, and matches the acoustic impedance with the fluid 5 by the acoustic matching layer 4A. The ultrasonic signal 5a is transmitted to the medium 5 via The other ultrasonic sensor (6B) receives the ultrasonic signal 5a transmitted by the ultrasonic transducer 2 (2B) via the acoustic matching layer 4B, and detects the ultrasonic signal 5a by the transmission / reception circuit 61B. . Then, by alternately switching the transmission / reception functions of the transmission / reception circuits 61A and 61B and measuring the propagation time difference ΔT between the ultrasonic propagation time to the upstream side and the ultrasonic propagation time to the downstream side, the fluid in the measurement pipe line A flow rate or flow rate of 5 can be measured. That is, the ultrasonic sensors 6A and 6B according to the prior art use the ultrasonic transducer 2 of the same sensor by switching between transmission and reception.
[0005]
FIG. 6 shows the characteristics of the ultrasonic sensors 6A and 6B according to the prior art. In FIG. 6, the horizontal axis indicates the frequency, and the vertical axis indicates the transmission sensitivity 2S of the ultrasonic output with respect to the electrical excitation power from the transmission / reception circuits 61A and 61B and the reception sensitivity 2R indicating the conversion power to the electrical signal with respect to the received ultrasonic output. Take. The transmission / reception integrated ultrasonic sensors 6A and 6B according to the prior art have electromechanical vibration characteristics determined from the material characteristics and shape of the ultrasonic vibrator 2, and the peak values differ depending on transmission sensitivity and reception sensitivity. . For example, the vibration characteristics of the electromechanical system of ultrasonic sensors 6A and 6B composed of inorganic piezoelectric materials such as lead zirconate titanate (PZT) are supersonic when the ultrasonic sensors 6A and 6B are used for transmission. The characteristic of the curve 2S having the peak characteristic at the resonance frequency fr determined from the material characteristic and the shape of the acoustic wave vibrator 2 is shown. On the other hand, when the ultrasonic sensors 6A and 6B are used for reception, the vibration characteristic of the mechanical electric system of the ultrasonic vibrator 2 is a curve 2R having a peak characteristic at an anti-resonance frequency fa composed of material characteristics and shapes thereof. The characteristics of As a result, when the same ultrasonic sensor 6A, 6B is used for both transmission and reception, the ultrasonic sensor 6A, 6B is driven in the frequency band fo near the center of the resonance frequency fr and the anti-resonance frequency fa. That is, the sensitivity characteristics of the ultrasonic sensors 6A and 6B that are optimally used with the characteristics shown in the characteristic 2SR with the frequency fo, which is the common part of the transmission characteristics and the reception characteristics, as the center frequency. Combined ultrasonic sensors 6A and 6B were manufactured. In this way, the sensitivity characteristics of the transmission / reception integrated ultrasonic sensors 6A and 6B have different peak frequencies between the resonance frequency fr and the anti-resonance frequency fa, so they deviated from these peak characteristics when used for both transmission and reception. By the way, it results in use, and it has not become a highly sensitive ultrasonic sensor.
[0006]
[Problems to be solved by the invention]
In this way, when the same ultrasonic transducer is used for both transmission and reception in conventional ultrasonic sensors, ultrasonic sensing devices, and ultrasonic flowmeters, (1) ultrasonic vibration composed of inorganic piezoelectric materials The acoustic impedance of the child is very large with respect to the acoustic impedance of the medium (liquid or gas) that propagates the sound wave, and the acoustic impedance cannot be matched. In order to improve the coupling with a medium such as liquid or gas, an ultrasonic sensor is generally configured by including an acoustic matching layer in an ultrasonic transducer. In addition, (2) the transmission / reception resonance frequency / anti-resonance frequency was shifted, and a high-sensitivity ultrasonic sensor for both transmission and reception could not be manufactured.
[0007]
The present invention has been made in view of the above points, and its purpose is to solve the above-described problems, and the resonance frequency and anti-resonance frequency of an ultrasonic sensor integrated for transmission and reception are substantially the same, and An object of the present invention is to provide a highly sensitive ultrasonic sensor, an ultrasonic sensing device, and an ultrasonic flowmeter that are used for both transmission and reception by manufacturing an integrated ultrasonic sensor that can have a relatively low acoustic impedance.
[0008]
[Means for Solving the Problems]
According to the present invention, the ultrasonic sensor is flexible on both sides of the first ultrasonic vibrator in the longitudinal vibration mode or the thickness vibration mode in which an electrode is formed on an inorganic piezoelectric material and the polymer piezoelectric film. A second ultrasonic transducer in a thickness vibration mode in which one surface is joined to the ultrasonic emission surface side of the first ultrasonic transducer and the other surface is an ultrasonic radiation surface; It shall be prepared.
Further, the first to match the first ultrasonic resonance frequency for transmission oscillator (fr1) and the second anti-resonance frequency for reception of the ultrasonic transducer (fa2) ultrasonic vibrator and the second It is assumed that the dimension in the thickness direction of the ultrasonic transducer is selected and the ultrasonic sensor is operated at a frequency ( fo = fr1 = fa2) that matches the resonance frequency and the antiresonance frequency .
[0009]
With this configuration, the first ultrasonic transducer and the second ultrasonic transducer are integrally configured, the first ultrasonic transducer is excited as a transmission ultrasonic sensor, and is transmitted via the second ultrasonic transducer. An ultrasonic signal can be transmitted from the ultrasonic radiation surface to the object, and an ultrasonic signal transmitted using the second ultrasonic transducer as a reception ultrasonic sensor can be received.
[0010]
The first ultrasonic transducer can be made of an inorganic piezoelectric material such as lead zirconate titanate (PZT) or lead zirconate.
Further, the polymer piezoelectric film of the second ultrasonic transducer can be composed of a polyfucavinylidene (PVDF) film.
[0011]
In addition, the sensing device using the ultrasonic sensor excites the first ultrasonic transducer of the ultrasonic sensor, and transmits the ultrasonic signal from the ultrasonic radiation surface via the second ultrasonic transducer. Alternatively, it is assumed that an ultrasonic signal radiated to the medium and reflected and returned from the object is received by the second ultrasonic transducer.
[0012]
In addition, an ultrasonic flowmeter using an ultrasonic sensor uses a fluid as a medium to be measured, detects a transmitted wave that passes through the fluid, detects the ultrasonic wave propagation time to the upstream side, and the ultrasonic wave propagation time to the downstream side. The flow rate of the fluid is calculated from the difference.
[0013]
With this configuration, an ultrasonic signal can be stably transmitted and received by using a highly sensitive ultrasonic sensor that is also used for transmission and reception. As a result, depending on the balance with the surrounding noise environment, for example, the ultrasonic signal transmission level can be used lower than the prior art level, and the electric signal level for exciting the ultrasonic sensor can be lowered for practical use. Can do.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of an essential part of an ultrasonic sensor according to an embodiment of the present invention, FIG. 2 is a block diagram of an essential part of an ultrasonic sensing device according to an embodiment, and FIG. FIG. 4 is a diagram showing the frequency characteristics of the ultrasonic sensor according to the present invention. The same members corresponding to those in FIGS. 5 and 6 are given the same reference numerals.
[0015]
In FIG. 1, an ultrasonic sensor 1 according to the present invention includes a first ultrasonic vibrator 2 in a longitudinal vibration mode or a thickness vibration mode in which electrodes 22 a and 22 b are formed on an inorganic piezoelectric material 21, and a polymer piezoelectric film 31. The electrodes 24a and 24b having flexibility are formed on both surfaces, and one surface (24a) is joined to the ultrasonic emission surface side (22b) of the first ultrasonic transducer 2 and the other surface (24b) is And a second ultrasonic transducer 3 in a thickness vibration mode serving as a sound wave radiating surface 25.
[0016]
With this configuration, the first ultrasonic transducer 2 and the second ultrasonic transducer 3 are integrated, and in the transmission mode, the first ultrasonic transducer 2 is excited as a transmission ultrasonic sensor, and the second supersonic transducer 2 is excited. An ultrasonic signal (5a) is transmitted from the ultrasonic radiation surface 25 to the object (5) via the ultrasonic transducer 3. In the reception mode, an ultrasonic signal (5b) transmitted using the second ultrasonic transducer 3 as a reception ultrasonic sensor can be received.
[0017]
【Example】
(Example 1)
In FIG. 1A, an ultrasonic sensor 1 in the illustrated example includes electrodes 22a and 22b having flexibility at both ends of an inorganic piezoelectric material 21, for example, lead zirconate titanate (PZT). By applying a voltage to the electrodes 22a and 22b, the first ultrasonic transducer 2 in the longitudinal vibration mode or the thickness vibration mode that vibrates in the direction of the electrodes 22a and 22b can be configured. Similarly, the second ultrasonic transducer 3 in the thickness vibration mode is configured by forming the electrodes 24a and 24b having flexibility on both surfaces of the polymer piezoelectric film 31 by, for example, depositing a metal film. Can do. Then, the electrode 22b of the first ultrasonic transducer 2 and the electrode 24a of the second ultrasonic transducer 3 are joined by a flexible electrical insulating layer (for example, an insulating resin film) 23 by means such as adhesion. Thus, the first ultrasonic transducer 2 for transmission and the second ultrasonic transducer 3 for reception can be integrated.
[0018]
The ultrasonic sensor 1 having such a configuration can insulate the transmission circuit 11 to which a high excitation voltage is applied from the reception circuit 12 having a relatively low reception voltage between the electrodes 22b and 24a. It is easy to prevent noise from entering from the side to the receiving circuit 12 side. Although the ultrasonic signal is slightly attenuated at the junction with the insulating layer 23, there is no practical problem because sufficient excitation energy is obtained, and the advantage of high sensitivity reception by the second ultrasonic transducer 3 is enjoyed. be able to.
[0019]
Further, in FIG. 1B, the insulating layer 23 is omitted and the electrodes 22b and 24a are directly joined, or one electrode 22b (or electrode 24a) is omitted and the other electrode 24a (or electrode 22b) is omitted. It is also possible to join them to each other by means such as adhesion. In this case, a technique is required to prevent noise from being mixed from the transmission circuit 11 side to the reception circuit 12 side, but attenuation of the ultrasonic signal at the joint portion can be reduced.
[0020]
Next, FIG. 4 shows frequency characteristics of the ultrasonic sensor 1 according to the present invention. In FIG. 4, the horizontal axis represents frequency, and the vertical axis represents transmission sensitivity and reception sensitivity. The frequency characteristic of the first ultrasonic transducer 2 is that the transmission sensitivity characteristic 2S of the ultrasonic signal 5a with respect to the electric excitation power from the transmission circuit 11 has the characteristic that the peak transmission sensitivity is at the frequency fr1, and the received ultrasonic wave. The reception sensitivity characteristic 2R for the electric signal with respect to the signal 5b has a peak reception sensitivity at the frequency fa1. The frequency of this peak value is determined by the material characteristics of the first ultrasonic transducer 2 and its shape. In particular, by controlling the thickness dimension of the first ultrasonic transducer 2, the frequencies fr1 and fa1 can be moved.
[0021]
Similarly, the frequency characteristic of the second ultrasonic transducer 3 has the characteristic that the transmission sensitivity characteristic 3S of the ultrasonic signal 5a with respect to the electric excitation power from the transmission circuit 11 has the peak transmission sensitivity at the frequency fr2, and The reception sensitivity characteristic 3R to the electrical signal with respect to the received ultrasonic signal 5b has a peak reception sensitivity at the frequency fa2. The frequency of the peak value is determined by the material characteristics and the shape of the second ultrasonic transducer 3, and in particular, by controlling the thickness dimension of the second ultrasonic transducer 3, the frequencies fr2 and fa2 are moved. be able to.
[0022]
In the illustrated example of FIG. 4, the first ultrasonic transducer 2 for transmission is composed of inorganic piezoelectric material, lead zirconate titanate (PZT) or lead zirconate, and the second ultrasonic transducer 3 for reception is formed. It is composed of a polymer piezoelectric film of polyfucavinylidene (PVDF), and the first ultrasonic transducer 2 has a resonance frequency fr1 for transmission and the antiresonance frequency fa2 for reception of the second ultrasonic transducer 3. Select the dimension in the thickness direction under the condition to match.
[0023]
With this configuration, it is possible to use a lead zirconate titanate (PZT) or lead zirconate system having a higher electromechanical coupling coefficient related to vibration than that of the polymer piezoelectric material, and the resonance frequency fr1 of the polymer piezoelectric material for receiving is the first. 2 By matching the antiresonance frequency fa2 of the ultrasonic transducer 3 and operating the ultrasonic sensor 1 at the frequency fo = fr1 (= fa2), the transmission sensitivity and the reception sensitivity can be further enhanced. A highly sensitive ultrasonic sensor for both transmission and reception can be manufactured.
[0024]
In addition, the polymer piezoelectric film of polyfucavinylidene (PVDF) has a lower acoustic impedance than that of the inorganic piezoelectric material lead zirconate titanate (PZT), and is close to the acoustic impedance of water and plastics. As an ultrasonic sensor for propagating ultrasonic waves in gas, it can be used without adding an additional acoustic matching layer. Furthermore, the polymer piezoelectric film polyfucavinylidene (PVDF) film has high ultrasonic reception sensitivity, so the signal-to-noise ratio (S / N ratio) can be reduced by using it for ultrasonic reception. Can be improved.
(Example 2)
In FIG. 2, in the sensing device using the ultrasonic sensor of the present invention, one ultrasonic sensor 1A is arranged at a predetermined position, and the first ultrasonic transducer 2 of the ultrasonic sensor 1A is transmitted. An ultrasonic signal 5b which is excited from 11 and radiates an ultrasonic signal 5a from the ultrasonic radiation surface 25 to the measurement object 5 or the medium 5 via the second ultrasonic transducer 3 and is reflected from the object 5 and returned. Can be received by the second ultrasonic transducer 3.
[0025]
In such a configuration, the second ultrasonic transducer 3 is excited in a pulse form from the transmission circuit 11, and a burst-like ultrasonic signal 5 a is radiated to the measurement object 5 and reflected from the object 5 and returned. Is measured by the second ultrasonic transducer 3, and the distance from the transmission pulse to the detection of the ultrasonic signal 5b is measured, whereby the distance to the object 5 can be measured. Further, by measuring this temporal change, the relative speed with respect to the object 5 can be measured, and when the ultrasonic sensor 1A is fixed on the ground, for example, the speed of the object 5 can be measured.
[0026]
Further, a continuous sinusoidal wave is transmitted from the transmission circuit 11, the transmission ultrasonic signal 5 a and the ultrasonic signal 5 b of the reflected wave from the object 5 are received by the second ultrasonic transducer 3, and the reception circuit 12. The moving speed of the object 5, that is, the Doppler shift amount can be detected by performing a homodyne detection of the transmission wave and the reception wave with a nonlinear element. By using the integrated ultrasonic sensor 1 of the present invention, a mixing signal of a transmission wave and a reception wave can be detected by one second ultrasonic transducer 3, and compared with a superheterodyne detection method. Signal detection with a high signal-to-noise ratio (S / N ratio) can be performed.
[0027]
In FIG. 3, the sensing device using the ultrasonic sensor of the present invention has a pair of ultrasonic sensors 1A and 1B arranged at predetermined positions, for example, the first ultrasonic wave of the ultrasonic sensor 1A. The vibrator 2 is excited from the transmission circuit 11A, and the ultrasonic signal 5a is radiated from the ultrasonic radiation surface 25 to the measuring object 5 or the medium 5 via the second ultrasonic vibrator 3, and from the object 5. The ultrasonic signal 5b reflected and returned can be received by the second ultrasonic transducer 3 of the ultrasonic sensor 1B provided separately and detected by the receiving circuit 12B.
[0028]
With this configuration, the second ultrasonic transducer 3 is excited in a pulse form from the transmission circuit 11A, and a burst-like ultrasonic signal 5a is radiated to the measurement object 5 and reflected from the object 5 and returned. Is received by the second ultrasonic transducer 3 of the ultrasonic sensor 1B separately provided, and the distance from the transmission pulse to the detection of the ultrasonic signal 5b by the receiving circuit 12B is measured, whereby the distance to the object 5 is measured. Can be triangulated including the position where the ultrasonic sensors 1A and 1B are arranged, and a more accurate distance can be measured.
[0029]
Furthermore, in the configuration of FIG. 2 or FIG. 3, the detection time of the reflected wave or the transmitted wave is measured, so that the detection of the scratch or the foreign substance existing in the object 5 can be performed nondestructively.
(Example 3)
In FIG. 3, the ultrasonic flowmeter using the ultrasonic sensor of the present invention is not shown in the figure, in which a set of ultrasonic sensors 1A and 1B is conveyed in the medium of the measurement fluid 5 or the measurement fluid 5 is conveyed. The transmission side and the reception side can be arranged opposite to each other at a predetermined position while being inclined with respect to the measured measurement pipeline.
[0030]
With this configuration, the medium 5 to be measured is a fluid, a transmitted wave passing through the fluid is detected, and the flow velocity of the fluid is calculated from the difference between the ultrasonic propagation time upstream and the ultrasonic propagation time downstream. can do. For example, the first ultrasonic transducer 2 of the ultrasonic sensor 1A arranged on the upstream side is excited from the transmission circuit 11A, and the ultrasonic signal is transmitted from the ultrasonic radiation surface 25 via the second ultrasonic transducer 3. 5a is radiated to the medium 5, and the transmitted wave transmitted through the medium 5 is received by the second ultrasonic transducer 3 of the ultrasonic sensor 1B arranged on the downstream side, and the ultrasonic wave propagation time to the downstream side is received by the receiving circuit 12B. Measure. Next, the first ultrasonic transducer 2 of the ultrasonic sensor 1B arranged on the downstream side is excited from the transmission circuit 11B, and the ultrasonic wave is emitted from the ultrasonic radiation surface 25 via the second ultrasonic transducer 3. The signal 5b is radiated to the medium 5, and the transmitted wave transmitted through the medium 5 is received by the second ultrasonic transducer 3 of the ultrasonic sensor 1A arranged on the upstream side, and the ultrasonic wave propagation to the upstream side is received by the receiving circuit 12A. By measuring the time and calculating the difference in propagation time between the two ultrasonic waves, the flow velocity or flow rate of the fluid 5 can be measured.
[0031]
According to the present invention, the resonance frequency and anti-resonance frequency of an ultrasonic sensor integrated for transmission and reception using a first ultrasonic transducer of an inorganic piezoelectric material and a second ultrasonic transducer of a polymer piezoelectric film. By manufacturing an integrated ultrasonic sensor that substantially matches the acoustic impedance of the liquid and gas and can be used for transmission and reception, a highly sensitive ultrasonic sensor that can be used for both transmission and reception can be provided. By using a highly sensitive ultrasonic sensor for both transmission and reception, it is possible to provide various ultrasonic sensing devices and ultrasonic flowmeters having a high signal-to-noise ratio.
[0032]
【The invention's effect】
As described above, the ultrasonic sensor according to the present invention is integrated for transmission / reception, the resonance frequency and the anti-resonance frequency are substantially the same, and the integrated high sensitivity that can match the acoustic impedance with the liquid or gas. In addition, by using this highly sensitive ultrasonic sensor, various ultrasonic sensing devices and ultrasonic flowmeters having a high signal-to-noise ratio can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram of an essential part of an ultrasonic sensor as an embodiment of the present invention. FIG. 2 is a block diagram of an essential part of an ultrasonic sensing device according to an embodiment. Fig. 4 is a frequency characteristic diagram of an ultrasonic sensor according to the present invention. Fig. 5 is a main component configuration diagram of an ultrasonic sensing device according to the prior art. Fig. 6 is a frequency characteristic diagram of an ultrasonic sensor according to the prior art. Explanation of symbols]
1,1A, 1B, 6A, 6B Ultrasonic sensor
11,11A, 11B Transmitter circuit
12,12A, 12B Reception circuit 2 1st ultrasonic transducer
21 Inorganic piezoelectric materials
22,22a, 22b, 24a, 24b electrode
23 Insulation layer
25 Ultrasonic radiation surface
2S, 3S transmission sensitivity characteristics
2R, 3R reception sensitivity characteristics 3 2nd ultrasonic transducer
31 Polymer piezoelectric film 5 Object
5a, 5b Ultrasonic signal
61A, 61B transceiver circuit
fr, fr1, fr2 resonance frequency
fa, fa1, fa2 Anti-resonance frequency
fo operating frequency

Claims (5)

A longitudinal vibration mode or thickness vibration mode first ultrasonic transducer comprising an electrode made of an inorganic piezoelectric material and a flexible electrode are formed on both sides of the polymer piezoelectric film, and one surface of the first ultrasonic transducer is A second ultrasonic transducer in a thickness vibration mode, which is bonded to the ultrasonic emission surface side of the ultrasonic transducer and has the other surface as an ultrasonic radiation surface,
The first ultrasonic transducer is excited as an ultrasonic sensor for transmission, and an ultrasonic signal is transmitted from the ultrasonic radiation surface to the object via the second ultrasonic transducer, and the second ultrasonic transducer in the ultrasonic sensor that will receive an ultrasonic signal transmitted as ultrasonic sensor receives the,
The first ultrasonic transducer and the second ultrasonic transducer are arranged in the thickness direction so that the resonance frequency for transmission of the first ultrasonic transducer and the anti-resonance frequency for reception of the second ultrasonic transducer coincide with each other. Selecting the dimensions and operating the ultrasonic sensor at a frequency matching the resonant and anti-resonant frequencies,
An ultrasonic sensor.   2. The ultrasonic sensor according to claim 1, wherein the first ultrasonic transducer is composed of an inorganic piezoelectric material such as lead zirconate titanate (PZT) or lead zirconate. Sensor.   2. The ultrasonic sensor according to claim 1, wherein the polymer piezoelectric film of the second ultrasonic transducer is formed of a polyfucavinylidene (PVDF) film. In the sensing apparatus using the ultrasonic sensor according to any one of claims 1 to 3,
The first ultrasonic transducer of the ultrasonic sensor is excited, an ultrasonic signal is radiated from the ultrasonic radiation surface to the measurement object or medium via the second ultrasonic transducer, and reflected back from the object. Receiving an ultrasonic signal by the second ultrasonic transducer;
An ultrasonic sensing device characterized by that. The ultrasonic flowmeter using the ultrasonic sensor according to any one of claims 1 to 3, wherein a medium to be measured is a fluid, a transmitted wave transmitted through the fluid is detected, and an upstream flow is detected. Calculate the fluid flow velocity from the difference between the ultrasonic propagation time and the ultrasonic propagation time downstream.
An ultrasonic flowmeter characterized by that.

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