JP2000346685A - Ultrasonic sensor, ultrasonic sensing device and ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an integrated and high-sensitivity ultrasonic sensor used for both transmission and reception, to provide an ultrasonic sensing device and to provide an ultrasonic flowmeter. SOLUTION: This device is provided with a first ultrasonic vibrator 2 in which an electrode 22a and an electrode 22b are constituted at an inorganic piezoelectric material 21 and which is in a longitudinal vibration mode or a perpendicular vibration mode. The device is provided with a second ultrasonic vibrator 3 in which a flexible electrode 24a and a flexible electrode 24b are constituted on both faces of a polymer piezoelectric membrane 31, one face of which is bonded to the side of the ultrasonic emission face of the first ultrasonic vibrator 2 and the other face of which is used as an ultrasonic radiation face 25. Thereby, the first ultrasonic vibrator 2 is used as an ultrasonic sensor for transmission so as to be excited, and an ultrasonic signal is transmitted to an object from the the ultrasonic radiation face 25 via the second ultrasonic vibrator 3. In addition, the second ultrasonic vibrator 3 is used as an ultrasonic sensor for reception, and it receives an ultrasonic signal which is transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor using an ultrasonic technique for sensing by radiating an ultrasonic wave to an object to be measured and a sensing device using the sensor, and more particularly to an ultrasonic flowmeter. .

[0002]

2. Description of the Related Art A sensing device that performs sensing using ultrasonic technology includes a device for measuring position, distance, or velocity by emitting ultrasonic waves to an object or a medium and detecting reflected waves thereof, or an image processing device. Also, there is an ultrasonic flowmeter that radiates ultrasonic waves to a medium to be measured, detects the propagation time of the transmitted wave, and measures the flow velocity of the medium, for example.

[0005] FIG. 5 shows an ultrasonic flowmeter in which a pair of ultrasonic sensors are arranged opposite to each other along the flow of a fluid to transmit ultrasonic waves alternately upstream and downstream, and to measure the flow velocity from the time difference until reception. FIG. In FIG. 5, an ultrasonic flowmeter according to the prior art is, for example, lead zirconate titanate (PZ).
Ultrasonic transducers 6A and 6B each comprising an ultrasonic vibrator 2 having an electrode formed of an inorganic piezoelectric material (T) and an acoustic matching layer 4 joined to the ultrasonic vibrator 2 and emitting a sound wave from the other surface.
Is arranged in the medium of the measurement fluid 5 or inclined with respect to a not-shown measurement pipeline through which the measurement fluid 5 is conveyed, and the transmission side and the reception side are arranged to face each other.

In such a configuration, the ultrasonic flowmeter excites the ultrasonic vibrator 2 (2A) of one ultrasonic sensor (for example, 6A) from the transmission / reception circuit 61A to match the acoustic impedance with the fluid 5. An ultrasonic signal 5a is transmitted to the medium 5 via the matching layer 4A. The other ultrasonic sensor (6B) receives the transmitted ultrasonic signal 5a by the ultrasonic transducer 2 (2B) via the acoustic matching layer 4B, and transmits and receives the ultrasonic signal by the transmission / reception circuit 61B.
5a is detected. The transmission / reception functions of the transmission / reception circuits 61A and 61B are alternately switched to measure the propagation time difference ΔT between the ultrasonic wave propagation time to the upstream side and the ultrasonic wave propagation time to the downstream side. 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.

FIG. 6 shows ultrasonic sensors 6A and 6B according to the prior art.
The characteristics of In FIG. 6, the horizontal axis represents the frequency, and the vertical axis represents the transmission sensitivity 2S of the ultrasonic output with respect to the electric excitation power from the transmission / reception circuits 61A and 61B, and the reception sensitivity 2R indicating the conversion power of the received ultrasonic output into an electric 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 by the material characteristics and the shape of the ultrasonic vibrator 2, and their peak values differ in transmission sensitivity and reception sensitivity. . For example, the vibration characteristics of the electromechanical system of the ultrasonic sensors 6A and 6B made of an inorganic piezoelectric material such as lead zirconate titanate (PZT) show that when the ultrasonic sensors 6A and 6B are used for transmission, Curve 2S having a peak characteristic at a resonance frequency fr determined from the material characteristics and the shape of the ultrasonic transducer 2
The characteristics of On the other hand, when the ultrasonic sensors 6A and 6B are used for reception, the vibration characteristic of the electromechanical system of the ultrasonic vibrator 2 is represented by a curve 2R having a peak characteristic at an anti-resonance frequency fa composed of the material characteristic and its shape. The characteristics of As a result, when the same ultrasonic sensor 6A, 6B is used for both transmission and reception, the ultrasonic sensors 6A, 6B are driven in a frequency band fo near the center between the resonance frequency fr and the anti-resonance frequency fa, That is, the frequency fo, which is a common part of the transmission characteristics and the reception characteristics,
The optimum sensitivity characteristic of the ultrasonic sensors 6A and 6B is to be used with the characteristic shown in the characteristic 2SR having the center frequency as the center frequency, and the ultrasonic sensors 6A and 6B for both transmission and reception have been manufactured from such a viewpoint. In this way, the transmission / reception integrated ultrasonic sensors 6A and 6B
Since the sensitivity characteristic of the sensor has a different peak frequency between the resonance frequency fr and the anti-resonance frequency fa, when used for both transmission and reception, the result is that the device is used outside of these peak characteristics. Not.

[0006]

As described above, when the same ultrasonic transducer is used for both transmission and reception in the conventional ultrasonic sensor, ultrasonic sensing device and ultrasonic flow meter, (1) inorganic The acoustic impedance of an ultrasonic vibrator made of a piezoelectric material has a very large value with respect to the acoustic impedance of a medium (a liquid or a gas) for transmitting sound waves, and acoustic impedance cannot be matched. In order to improve the coupling with a medium such as a liquid or a gas, an ultrasonic sensor generally includes an ultrasonic transducer and an acoustic matching layer. In addition, (2) resonance frequency for transmission and reception
A deviation occurred in the anti-resonance frequency, and a high-sensitivity ultrasonic sensor for both transmission and reception could not be manufactured.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to solve the above-mentioned problems and to make the resonance frequency and anti-resonance frequency of an ultrasonic sensor integrated for both transmission and reception substantially coincide. By producing an integrated ultrasonic sensor whose acoustic impedance can be made relatively low, it is possible to provide a high-sensitivity ultrasonic sensor, an ultrasonic sensing device and an ultrasonic flow meter for both transmission and reception. is there.

[0008]

According to the present invention, there is provided an ultrasonic sensor comprising: a first ultrasonic vibrator in a longitudinal vibration mode or a thickness vibration mode in which an electrode is formed on an inorganic piezoelectric material; Flexible electrodes are formed on both sides of the molecular piezoelectric film, and one side is joined to the ultrasonic emission side of the first ultrasonic vibrator, and the other side is an ultrasonic emission plane. And a second ultrasonic vibrator.

With this configuration, the first ultrasonic vibrator and the second ultrasonic vibrator are integrally formed, the first ultrasonic vibrator is excited as an ultrasonic sensor for transmission, and the second ultrasonic vibrator is excited. An ultrasonic signal can be transmitted from the ultrasonic radiation surface to the object via the ultrasonic radiation surface, and an ultrasonic signal transmitted using the second ultrasonic transducer as a receiving ultrasonic sensor can be received.

The first ultrasonic vibrator can be made of an inorganic piezoelectric material, for example, lead zirconate titanate (PZT) or lead zirconate. In addition, the polymer piezoelectric film of the second ultrasonic vibrator is made of polyfukka vinylidene (PVD).
F).

A sensing device using the ultrasonic sensor excites a first ultrasonic vibrator of the ultrasonic sensor and transmits an ultrasonic signal from the ultrasonic radiation surface via a second ultrasonic vibrator. It is assumed that the second ultrasonic transducer receives an ultrasonic signal emitted to the measurement object or medium and reflected back from the object.

An ultrasonic flowmeter using an ultrasonic sensor uses a medium as a measurement object as a fluid, detects a transmitted wave transmitted through the fluid, and detects an ultrasonic wave propagation time to an upstream side and an ultrasonic wave to a downstream side. The flow velocity of the fluid is calculated from the difference from the sound wave propagation time.

With this configuration, the transmission and reception of the ultrasonic signal can be stably performed by using the high-sensitivity ultrasonic sensor for both transmission and reception. As a result, depending on the balance with the surrounding noise environment, for example, the transmission level of the ultrasonic signal can be used lower than the conventional technology level, and the electric signal level for exciting the ultrasonic sensor can be reduced for practical use. Can be.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a main part of an ultrasonic sensor according to an embodiment of the present invention, FIG. 2 is a diagram showing a main part of an ultrasonic sensing device according to an embodiment, and FIG. FIG. 4 is a frequency characteristic diagram of the ultrasonic sensor according to the present invention, and the same members corresponding to FIGS. 5 and 6 are denoted by the same reference numerals.

In FIG. 1, an ultrasonic sensor 1 according to the present invention comprises a first ultrasonic vibrator 2 in a longitudinal vibration mode or a thickness vibration mode in which electrodes 22a and 22b are formed on an inorganic piezoelectric material 21; Electrodes 24a having flexibility on both surfaces of the membrane 31,
A thickness vibration mode in which one surface (24a) is joined to the ultrasonic emission surface side (22b) of the first ultrasonic vibrator 2 and the other surface (24b) is an ultrasonic radiation surface 25. Second ultrasonic transducer 3
And is provided.

With this configuration, the first ultrasonic vibrator 2 and the second ultrasonic vibrator 3 are integrally formed, and in the transmission mode, the first ultrasonic vibrator 2 is excited as a transmitting ultrasonic sensor. This ultrasonic radiation surface via the second ultrasonic vibrator 3
An ultrasonic signal (5a) is transmitted from 25 to the object (5). In the reception mode, the ultrasonic signal (5b) transmitted from the second ultrasonic transducer 3 as an ultrasonic sensor for reception can be received.

[0017]

(Embodiment 1) In FIG. 1A, an ultrasonic sensor 1 shown in the drawing is an example in which an electrode provided with flexibility at both ends of an inorganic piezoelectric material 21, for example, lead zirconate titanate (PZT). 22a, 22
The first ultrasonic vibrator 2 of the longitudinal vibration mode or the thickness vibration mode that vibrates in the direction of the electrodes 22a and 22b can be formed by configuring the electrode b and applying a voltage to the electrodes 22a and 22b. Similarly, the second ultrasonic vibrator 3 in the thickness vibration mode is formed by forming the electrodes 24a and 24b having flexibility on both surfaces of the polymer piezoelectric film 31, for example, by depositing a metal film. Can be. The electrode 22b of the first ultrasonic vibrator 2 and the electrode 24a of the second ultrasonic vibrator 3 are joined by a flexible electric insulating layer (for example, an insulating resin film) 23 by means such as adhesion. By doing
The first ultrasonic transducer 2 for transmission and the second ultrasonic transducer 3 for reception can be integrated.

In the ultrasonic sensor 1 having such a configuration, the transmission circuit 11 to which a high excitation voltage is applied and the reception circuit 12 having a relatively low reception voltage can be insulated between the electrodes 22b and 24a. It is easy to prevent noise from entering the transmission circuit 11 into the reception circuit 12. Although the ultrasonic signal is slightly attenuated at the joint portion with the insulating layer 23, sufficient excitation energy is obtained, so that there is no practical problem, and the advantage of high sensitivity reception by the second ultrasonic transducer 3 is enjoyed. be able to.

In FIG. 1B, the insulating layer 23 is omitted and the electrodes 22b and 24a are directly joined, or one electrode 22b (or the electrode 24a) is omitted and the other electrode 24a (or It can be joined to the electrode 22b) by means such as adhesion.
In this case, a technique is required to prevent noise from entering the transmission circuit 11 into the reception circuit 12, but the attenuation of the ultrasonic signal at the joint can be reduced.

Next, FIG. 4 shows the frequency characteristics of the ultrasonic sensor 1 according to the present invention. In FIG. 4, the horizontal axis represents frequency,
The vertical axis shows the transmission sensitivity and the reception sensitivity. The frequency characteristic of the first ultrasonic transducer 2 is such that the transmission sensitivity characteristic 2S of the ultrasonic signal 5a with respect to the electric excitation power from the transmission circuit 11 has a characteristic that the peak transmission sensitivity is at the frequency fr1, and The reception sensitivity characteristic 2R to the electric signal with respect to the signal 5b has a peak reception sensitivity at the frequency fa1. The frequency of the peak value is determined by the material characteristics and the shape of the first ultrasonic transducer 2. In particular, by controlling the thickness dimension of the first ultrasonic transducer 2, the frequency fr1, fa1 can be moved.

Similarly, the frequency characteristic of the second ultrasonic transducer 3 is such that the transmission sensitivity characteristic 3S of the ultrasonic signal 5a with respect to the electric excitation power from the transmission circuit 11 indicates the peak transmission sensitivity at the frequency fr.
2 and the reception sensitivity characteristic 3R of the received ultrasonic signal 5b to the electric signal with respect to the received ultrasonic signal 5b has the 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 vibrator 3, and the frequency fr2, fa2 is moved by controlling the thickness of the second ultrasonic vibrator 3. be able to.

In the example shown in FIG. 4, the first ultrasonic transducer 2 for transmission is made of an inorganic piezoelectric material such as lead zirconate titanate (PZT) or lead zirconate, and the second ultrasonic transducer for reception is used. The element 3 is made of a polymer piezoelectric film of polyfukka vinylidene (PVDF).
The dimension in the thickness direction is selected under the condition that the resonance frequency fr1 for transmission of the first ultrasonic transducer 2 and the anti-resonance frequency fa2 for reception of the second ultrasonic transducer 3 are matched. I do.

With this configuration, it is possible to use lead zirconate titanate (PZT) or lead zirconate having a higher electromechanical coupling coefficient with respect to vibration than a polymer piezoelectric material, and to set the resonance frequency fr1 to a polymer piezoelectric material for reception. By making the ultrasonic sensor 1 operate at the frequency fo = fr1 (= fa2) by matching the anti-resonance frequency fa2 of the second ultrasonic vibrator 3 of the material, the transmission sensitivity and the reception sensitivity can be further enhanced. Thus, a high-sensitivity ultrasonic sensor for both transmission and reception can be manufactured.

Further, the polymer piezoelectric film of polyfukkavinylidene (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 plastic. It can be used as an ultrasonic sensor for transmitting ultrasonic waves in a liquid or a gas without adding an additional acoustic matching layer. In addition, the polymer piezo film
Since the (PVDF) film has the property of high ultrasonic reception sensitivity, the signal-to-noise ratio (S
/ N ratio) can be improved. (Embodiment 2) In FIG. 2, a sensing device using an ultrasonic sensor according to the present invention has a structure in which one ultrasonic sensor 1A is disposed at a predetermined position, and the first ultrasonic vibration of the ultrasonic sensor 1A is performed. Transmitter for child 2
An ultrasonic signal 5a is excited from the ultrasonic wave emitting surface 25 through the second ultrasonic transducer 3 and transmitted from the ultrasonic radiation surface 25 to the object 5 or the medium 5 to be measured.
And the second ultrasonic transducer 3 can receive an ultrasonic signal 5b reflected from the object 5 and returned.

In this configuration, the transmission circuit 11 excites the second ultrasonic transducer 3 in a pulsed manner, emits a burst-shaped ultrasonic signal 5a to the measurement object 5, and reflects the ultrasonic signal 5a from the object 5 to return. The distance to the object 5 can be measured by receiving the sound wave signal 5b by the second ultrasonic transducer 3 and measuring the time from the transmission pulse to the detection of the ultrasonic signal 5b. Also, by measuring this temporal change,
For example, when the ultrasonic sensor 1A is fixed on the ground, the speed of the object 5 can be measured relative to the object 5.

Further, a continuous sine wave is transmitted from the transmission circuit 11, and the transmitted ultrasonic signal 5a and the ultrasonic signal 5b of the reflected wave from the object 5 are received by the second ultrasonic transducer 3, By performing a homodyne detection of a transmission wave and a reception wave with a non-linear element in the reception circuit 12, the moving speed of the object 5, that is,
The amount of Doppler shift can be detected. 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 vibrator 3, and compared with the superheterodyne detection method. Signal detection with a high signal-to-noise ratio (S / N ratio) can be performed.

In FIG. 3, a sensing device using the ultrasonic sensor of the present invention includes a pair of ultrasonic sensors 1A and 1A.
B is arranged at a predetermined position, and for example, the first ultrasonic vibrator 2 of the ultrasonic sensor 1A is excited from the transmission circuit 11A, and the ultrasonic wave is radiated through the second ultrasonic vibrator 3 surface
An ultrasonic signal 5a is radiated from 25 to the object 5 or the medium 5 and an ultrasonic signal 5b reflected from the object 5 and returned is received by the second ultrasonic transducer 3 of the ultrasonic sensor 1B separately provided. , Can be detected by the receiving circuit 12B.

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 measuring object 5 and reflected from the object 5 and returned. The second ultrasonic sensor 1B separately provided with the sound wave signal 5b
The distance from the transmission pulse to the detection of the ultrasonic signal 5b by the receiving circuit 12B is measured by the receiving by the ultrasonic transducer 3, and the distance to the object 5 is determined by the position of the ultrasonic sensors 1A and 1B. By performing triangulation including this, a more accurate distance can be measured.

Further, in the configuration of FIG. 2 or FIG.
By measuring the detection time of the reflected wave or the transmitted wave, it is possible to perform a non-destructive inspection on the detection of a scratch or a foreign substance existing in the object 5. (Embodiment 3) In FIG. 3, an ultrasonic flowmeter using the ultrasonic sensor of the present invention is a set of ultrasonic sensors 1A and 1B.
Is arranged in the medium of the measurement fluid 5 or inclined with respect to a measurement pipe (not shown) through which the measurement fluid 5 is conveyed so that the transmission side and the reception side are opposed to each other at a predetermined position. be able to.

With this configuration, the medium 5 to be measured is used as a fluid, a transmitted wave transmitted through the fluid is detected, and the difference between the ultrasonic wave propagation time to the upstream side and the ultrasonic wave propagation time to the downstream side is used to detect the transmitted wave. The flow velocity can be calculated. For example, the first ultrasonic transducer 2 of the ultrasonic sensor 1A disposed 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 to the ultrasonic signal. 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 disposed on the downstream side.
At B, the ultrasonic propagation time to the downstream side is measured. Next, the first ultrasonic vibrator 2 of the ultrasonic sensor 1B disposed on the downstream side is excited from the transmitting circuit 11B, and the ultrasonic wave is transmitted from the ultrasonic radiation surface 25 through the second ultrasonic vibrator 3 to the ultrasonic wave. 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 is propagated to the upstream side by the receiving circuit 12A. By measuring the time and calculating the difference between the two ultrasonic propagation times, the flow velocity or flow rate of the fluid 5 can be measured.

According to the present invention, the resonance frequency and the resonance frequency of an ultrasonic sensor integrated for both transmission and reception using a first ultrasonic oscillator made of an inorganic piezoelectric material and a second ultrasonic oscillator made of a polymer piezoelectric film. By manufacturing an integrated ultrasonic sensor that has almost the same anti-resonance frequency and can match acoustic impedance with liquid or gas, it is possible to provide a high-sensitivity ultrasonic sensor for both transmission and reception. Further, by using the high-sensitivity ultrasonic sensor for both transmission and reception, it is possible to provide various ultrasonic sensing devices and ultrasonic flow meters having a high signal-to-noise ratio.

[0032]

As described above, the ultrasonic sensor according to the present invention is integrated for both transmission and reception, the resonance frequency and the anti-resonance frequency are almost the same, and the acoustic impedance of the liquid or gas can be matched. To provide various types of ultrasonic sensing devices and ultrasonic flowmeters having a high signal-to-noise ratio by using the high-sensitivity ultrasonic sensor. Can be.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an ultrasonic sensor as one embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of an ultrasonic sensing device according to an embodiment.

FIG. 3 is a main part configuration diagram of an ultrasonic sensing device according to another embodiment.

FIG. 4 is a frequency characteristic diagram of the ultrasonic sensor according to the present invention.

FIG. 5 is a configuration diagram of a main part of an ultrasonic sensing device according to a conventional technique.

FIG. 6 is a frequency characteristic diagram of an ultrasonic sensor according to the related art.

[Explanation of symbols]

 1,1A, 1B, 6A, 6B Ultrasonic sensor 11,11A, 11B Transmitting circuit 12,12A, 12B Receiving circuit 2 First ultrasonic transducer 21 Inorganic piezoelectric material 22,22a, 22b, 24a, 24b Electrode 23 Insulating layer 25 Ultrasonic radiation surface 2S, 3S Transmission sensitivity characteristics 2R, 3R Reception sensitivity characteristics 3 Second ultrasonic transducer 31 Polymer piezoelectric film 5 Object 5a, 5b Ultrasonic signal 61A, 61B Transmission / reception circuit fr, fr1, fr2 Resonance frequency fa, fa1, fa2 Anti-resonant frequency fo Operating frequency

Claims (5)

[Claims] A first ultrasonic vibrator in a longitudinal vibration mode or a thickness vibration mode in which electrodes are formed on an inorganic piezoelectric material;
A flexible electrode is formed on both surfaces of the polymer piezoelectric film, and one surface is joined to the ultrasonic emission surface side of the first ultrasonic transducer,
A second ultrasonic vibrator in a thickness vibration mode having the other surface as an ultrasonic wave emitting surface, wherein the first ultrasonic vibrator is excited as a transmitting ultrasonic sensor,
An ultrasonic signal is transmitted from the ultrasonic radiating surface to the object via the second ultrasonic transducer, and an ultrasonic signal transmitted from the second ultrasonic transducer as a receiving ultrasonic sensor is received. An ultrasonic sensor, comprising: 2. The ultrasonic sensor according to claim 1, wherein the first ultrasonic vibrator is made of an inorganic piezoelectric material, for example, lead zirconate titanate (PZT) or lead zirconate. Ultrasonic sensor featuring. 3. The ultrasonic sensor according to claim 1, wherein the high-molecular piezoelectric film of the second ultrasonic vibrator is made of a polyfukka vinylidene (PVDF) film. 4. A sensing device using the ultrasonic sensor according to claim 1, wherein the first ultrasonic transducer of the ultrasonic sensor is excited to produce a second ultrasonic transducer. An ultrasonic signal is radiated from the ultrasonic radiation surface to the measurement object or medium via the ultrasonic radiation surface, and an ultrasonic signal reflected from the object and returned is received by the second ultrasonic vibrator. Sound wave sensing device. 5. An ultrasonic flowmeter using the ultrasonic sensor according to claim 1, wherein a medium to be measured is a fluid, and a transmitted wave transmitted through the fluid is detected. And calculating the flow velocity of the fluid from the difference between the ultrasonic wave propagation time to the upstream side and the ultrasonic wave propagation time to the downstream side.