JP2002112390A - Ultrasonic wave element and gas concentration measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic wave element that can enhance radiation efficiency of an ultrasonic wave. SOLUTION: In the ultrasonic wave element where a matching layer 31 is adhered to one end face 101 of a piezoelectric body 1 generating a sound wave through a piezoelectric action in a sound wave traveling direction inside the piezoelectric body 1 in a press contact way with the entire end face 101 so as to emit the ultrasonic wave from the piezoelectric body 1 via the matching layer 31, the end face 101 of the piezoelectric body 1 is formed so that an adhered face 303 of the matching layer 31 can easily be processed, and the other end face 102 is formed into a projected plane having a smooth curved face so that the other end face 102 acting like a vibrating plane can emit ultrasonic waves that are focused thereby enhancing the convergence of the emitted ultrasonic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic element and a gas concentration measuring device.

[0002]

2. Description of the Related Art An ultrasonic element is a device capable of emitting ultrasonic waves by feeding power. In addition to detecting obstacles such as a vehicle back sonar,
In recent years, a sound wave radiated from an ultrasonic element is received by a receiver, and a physical property of a substance serving as a medium through which the ultrasonic wave propagates is measured, for example, a hydrogen concentration in a reformed gas in a fuel cell system including a reformer. Is used in a gas concentration measuring device that measures the temperature. It is well known that an ultrasonic element to which a piezoelectric action is applied is known. Among these, there is an integrated transmission / reception type in which sound waves can be received by converting mechanical vibration into electric vibration. The main part of the ultrasonic element to which the piezoelectric action is applied is a piezoelectric body that generates mechanical vibration when an AC voltage is applied. The ultrasonic wave travels inside the piezoelectric body in the vibration direction of the mechanical vibration, and the traveling direction is the main radiation direction of the ultrasonic wave.

[0003] Any end face of the piezoelectric body in the direction of ultrasonic wave propagation can be a radiation surface of ultrasonic waves. However, radiation to the back of the ultrasonic element is usually unnecessary, and a matching layer is provided on one of the two end faces. In some cases, the direction of ultrasonic wave radiation is substantially limited to the matching layer side by bonding to increase the acoustic impedance on the matching layer side relative to the piezoelectric body. Here, the bonding surface of the matching layer is given a shape so as to contact the entire surface of the one end face so that the ultrasonic wave can be transmitted well through the interface between the piezoelectric body and the matching layer.

[0004]

In the measurement of physical properties of a substance serving as a medium through which an ultrasonic wave propagates, the ultrasonic wave is radiated from the ultrasonic element to a narrow sound receiving surface of a fixed receiver. Ultrasonic waves radiated to other than the receiver do not contribute to the measurement. Further, when the ultrasonic medium is a reformed gas containing a large amount of hydrogen having a low specific gravity, such as a gas concentration measuring device attached to a fuel cell system, the acoustic impedance is lowered and the matching layer As the reflection at the interface increases and the radiation intensity decreases, the wavelength of the ultrasonic wave becomes shorter, the diffraction increases, and the intensity at the receiver decreases.

[0005] For this reason, the measurement accuracy of the gas concentration measuring apparatus using a gas containing a large amount of light gas having a low specific gravity as a test gas cannot be said to have sufficient measurement accuracy.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide an ultrasonic element having good convergence of emitted ultrasonic waves and high radiation efficiency. It is another object of the present invention to provide a gas concentration measurement device with high measurement accuracy.

[0007]

According to the first aspect of the present invention, a matching layer is provided on one end face of a piezoelectric body which generates a sound wave by a piezoelectric action in the direction of sound wave propagation inside the piezoelectric body and the entire surface of the one end face. In an ultrasonic element that adheres so as to abut and emits ultrasonic waves from the piezoelectric body to the outside through the matching layer, the one end face of the piezoelectric body is a plane, and the other end face of the piezoelectric body is It shall be a gentle curved protruding surface.

Since the other end face of the piezoelectric body, which is the vibration surface of the piezoelectric body, is formed as a gentle curved protruding face, the ultrasonic waves radiated from the other end face are brought to the center to improve convergence,
Ultrasonic radiation efficiency is good. On the other hand, since one end surface of the piezoelectric body is a flat surface, the bonding surface of the matching layer can be a flat surface that can be easily processed.

According to a second aspect of the present invention, in the configuration of the first aspect, the other end face of the piezoelectric body is spherical.

Since the focal point is located at a position away from the other end face by the radius of curvature, convergence can be further improved.

According to the third aspect of the present invention, the gas concentration measuring device is provided with transmitting / receiving means for transmitting / receiving ultrasonic waves using a test gas as a medium, and a transmission signal and a reception signal of the transmission / reception means as inputs. 3. A configuration comprising: a measuring unit configured to measure a concentration of a component gas based on a sound speed of the ultrasonic wave that changes according to a concentration of a specific component gas, and the transmission / reception unit includes: And a configuration including the ultrasonic element.

By using the ultrasonic element having high convergence and easy processing, it is possible to construct a gas concentration measuring device which has good gas concentration measuring accuracy and is easy to manufacture. It is suitable for measuring the concentration of light gas such as hydrogen in the reformed gas.

[0013]

(First Embodiment) FIG. 1 shows a cross section of an ultrasonic element according to the present invention. The ultrasonic element is placed inside a cylindrical aluminum casing 3 with a bottom.
A disc-shaped piezoelectric body 1 slightly smaller than the inner diameter of the casing 3 is disposed coaxially with the casing 3, and a rear end opening of the casing 3 is closed by a lid member 4. The ultrasonic element is arranged such that the bottom 31 of the casing 3 is directed toward a receiving ultrasonic element (not shown) for receiving ultrasonic waves radiated from the ultrasonic element. The same ultrasonic element as that of the present ultrasonic element can be used as the ultrasonic element for reception, and the casing bottoms are arranged so as to face each other.

The piezoelectric body 1 is formed by molding a piezoelectric ceramic such as PZT into the above-mentioned shape, and forming both end faces 101 and 102 of the circular shape.
Is formed with a thin film electrode of silver or the like on the entire surface of the substrate. The shape such as the thickness of the piezoelectric body 1 is set so that the resonance frequency of the piezoelectric body 1 is in the ultrasonic range. Also, the front end face 101 of the piezoelectric body 1
Are formed flat, and the rear end surface 102 is a gently spherical protruding surface and is raised. Rear end face 10 of piezoelectric body 1
2 is approximately equal to the receiving ultrasonic element and the piezoelectric body 1.
The distance between the rear end faces 102 is set. The piezoelectric body 1 is different from the piezoelectric body of the conventional ultrasonic element in the shape of the rear end face 102. Therefore, a general manufacturing method can be applied to the manufacture of the piezoelectric body. That is, after the piezoelectric ceramic material is put into a mold, solidified and dried, silver or the like is applied to both end surfaces to form the thin-film electrode, and then fired. Thereafter, polarization is performed to complete the process.

Lead wires 2a and 2b for applying a voltage to the thin film electrode are soldered to the piezoelectric body 1,
The tips of a and 2b pass through the lid member 4 and are drawn out of the casing 3. When an AC voltage in an ultrasonic range is applied between the thin film electrodes from the ends of the lead wires 2a and 2b, electrostriction is induced in the piezoelectric body 1 by a piezoelectric effect, and mechanical vibration is generated. It proceeds in the thickness direction of the body 1.

The piezoelectric body 1 is bonded to the bottom surface 301 of the casing 3 with a flat front end surface 101. Casing bottom surface 30
1, a concave portion 302 having substantially the same diameter as the piezoelectric body 1 is formed for positioning the piezoelectric body 1. The bonding surface 303 that is bonded to the front end surface 101 of the piezoelectric body 1 is an interface between the casing bottom 31 acting as a matching layer that defines the ultrasonic radiation direction and the piezoelectric body 1. It is necessary to abut on the whole surface. In the present ultrasonic element, the front end face 10 of the piezoelectric body 1
1 is a plane, the casing bonding surface 303 is a plane like the front end surface 101 of the piezoelectric body 1. Therefore,
The formation of the concave portion 302 by lathing or the like is easy.

The front end face 101 of the piezoelectric body 1 is in close contact with the adhesive surface 303 of the casing 3, while the rear end face 102 of the piezoelectric body 1 is in contact with air, but the acoustic impedance of the substance is (density × sonic velocity) ), The acoustic impedance is air <piezoelectric 1 <casing bottom 31. That is, the casing bottom 31 acts as a matching layer,
Ultrasonic waves generated by the piezoelectric body 1 are radiated through the casing bottom 31 into the air. The other end surface 102 of the piezoelectric body 1, which is an interface with the air in the casing 3, is
An ultrasonic wave having a vibration plane is also included.

Ultrasonic waves radiate in the normal direction of the vibrating surface,
In this ultrasonic element, since the rear end face 102 of the piezoelectric body 1 has a spherical surface, the ultrasonic wave is focused on the center of the piezoelectric body 1 in the radial direction and focuses on a predetermined position. Thus, if the receiving ultrasonic element is installed at approximately this focal position F, it is possible to efficiently receive radiated ultrasonic waves. FIG. 2 shows the normalized ultrasonic intensity in a plane perpendicular to the axial direction of the ultrasonic element, that is, the main radiation direction of the ultrasonic wave at the focal position F. In the figure, the rear end face of the piezoelectric body is flat. A conventional ultrasonic element is also shown. It is known that the present ultrasonic element has a more concentrated radiation range and better convergence than conventional ultrasonic elements, and that the emitted ultrasonic waves reach the ultrasonic element for reception efficiently.

Since the refraction at the interface between the piezoelectric body 1 and the casing bottom 31 and the interface between the casing bottom 31 and air can be almost ignored at the focal position, the focal point is located at a position substantially apart from the rear end face 102 of the piezoelectric body 1 by the radius of curvature. . Therefore, excellent convergence is exhibited by determining the radius of curvature of the rear end face 102 of the piezoelectric body 1 based on the arrangement of the transmitting ultrasonic element and the receiving ultrasonic element.

Moreover, the convergence is improved by making the rear end face 102 of the piezoelectric body 1 spherical, while the front end face 101 of the piezoelectric body 1 on the side from which the ultrasonic wave is radiated is made flat, so that the casing 3 Since the bonding surface 303 with the piezoelectric body 1 can be made a flat surface that can be easily processed, it can be manufactured at low cost.

The rear end face 102 of the piezoelectric body 1 is desirably a spherical surface as in this embodiment, but if it is a curved surface, sufficient convergence can be obtained depending on the specifications required for the ultrasonic element.

(Second Embodiment) FIGS. 3 and 4 show the configuration of a gas concentration measuring apparatus according to a second embodiment of the present invention. The gas concentration measuring device uses a reformed gas of a reformer as a test gas, and has a main body portion composed of a cell 5 and ultrasonic elements 61 and 62 constituting a transmitting / receiving means 6. The cell 5 is formed by molding stainless steel into a cylindrical shape. Holes 501 and 502 are formed in the peripheral wall at positions substantially 1/3 from both ends so as to penetrate the peripheral wall. 5 and an outlet 502 for discharging the reformed gas from the cell 5.

The ultrasonic elements 61 and 62 have substantially the same structure as that shown in the first embodiment. Threads are formed on the outer peripheral surface of the casing 3 of the ultrasonic elements 61 and 62 and the inner peripheral surface of the cell 5, and the ultrasonic elements 61 and 62 are arranged such that the casing bottom 31 side, which is a matching layer, extends from both ends of the cell 5. It is screwed so as to face. The screw-in position is set so that the opposing surfaces 61a and 62a of the ultrasonic elements 61 and 62 are slightly retreated from the inlet 501 and the outlet 502, which are close to each other, toward the end of the cell 5. Sound element 6
An inlet 501 is formed in a cell space (hereinafter referred to as a sound wave propagation chamber) 503 defined by the opposing surfaces 61a and 62a of the first and second surfaces.
A flow of the reformed gas is formed from the ultrasonic element 61 side near to the ultrasonic element 62 side near the discharge port 502.

A seal member 51 such as an O-ring is provided between the casing 3 of the ultrasonic elements 61 and 62 and the cell 5 at a position where the screw portion is not formed, to enhance airtightness.

The lead wires 2a and 2b of one ultrasonic element (ultrasonic element near the inlet in the illustrated example) 61 are connected to the signal generating circuit 7, and the other ultrasonic element (ultrasonic near the discharge port in the illustrated example). The lead wires 2 a and 2 b of the sonic element 62 are connected to the signal processing circuit 81.

As shown in FIG. 5, the signal generating circuit 7 generates a burst wave signal that generates a rectangular wave of several hundred kHz continuously for two to several tens of times and stops, and generates the burst wave signal on one side. The ultrasonic wave is output to the lead wires 2a and 2b of the acoustic wave element 61, whereby the ultrasonic wave element 61 emits an ultrasonic wave having a dull rectangular wave to the sound wave propagation chamber 503 ().

The other ultrasonic element 62 receives a radiated ultrasonic wave after a delay time corresponding to the speed of sound in the reformed gas, and outputs a reception signal from the lead wires 2a and 2b by a piezoelectric action (hereinafter, referred to as "hereinafter"). One ultrasonic element that emits ultrasonic waves is called a transmitting sensor, and the other ultrasonic element that receives ultrasonic waves is called a receiving sensor) (). This reception signal is received by the reception sensor 62.
Is a waveform that is substantially similar to the ultrasonic wave received.

The transmitting sensor 61 and the receiving sensor 62 have good convergence and radiation efficiency like the ultrasonic element of the first embodiment, and the receiving sensor 62 transmits ultrasonic waves from the transmitting sensor 61 at a high S / N. Although it is possible to receive the signal satisfactorily, the arrangement of the transmission sensor 61 and the reception sensor 62 is arranged such that the ultrasonic waves radiated from the transmission sensor 61 are collected on the front end face 101 and the rear end face 102 of the piezoelectric body 1 of the reception sensor 62. It is preferable that the piezoelectric element 1 be disposed such that it spreads over the rear end face 102 of the piezoelectric body 1. Here, the piezoelectric body 1 and the casing bottom 3
The path of the ultrasonic wave is determined by taking into account the refraction of the ultrasonic wave at the interface between the first and second casings and at the interface between the casing bottom 31 and the test gas. Just set it. FIG. 6 shows an example of this, and the rear end face 10 of the piezoelectric body 1 of the transmission sensor 61 is shown.
Ultrasonic waves radiated from the peripheral edge of the second sensor 2 are collected at the center of the rear end face 102 of the piezoelectric body 1 of the receiving sensor 62. Since the angle of refraction of the ultrasonic wave at the interface between the casing bottom 31 and the test gas depends on the acoustic impedance of the test gas, it is desirable to consider the approximate sound speed of the test gas. The numerical values in the figure are data in the case of a sound speed of 500 m / s.

A signal processing circuit 81 to which a reception signal is input from the reception sensor 62 is constituted by a zero cross circuit or the like, and shapes the reception signal into a rectangular wave and outputs it ().

An analysis circuit 82 is provided with a burst wave signal generated by the signal processing circuit 81 and an output signal of the signal processing circuit 81 as inputs. The analysis circuit 82 is provided with a timer circuit 83. The signal processing circuit 81, the analyzing circuit 82, and the timer circuit 83 constitute the measuring means 8. The signal generation circuit 7, the signal processing circuit 81, the analysis circuit 82, and the timer circuit 83 are stored in, for example, one casing.

The analysis circuit 82 is constituted by a microcomputer or the like. The propagation time T of the ultrasonic wave from the transmission sensor 61 to the reception sensor 62 is counted by a timer circuit 83 from both input signals, and based on the propagation time T Calculate gas concentration.

The analysis circuit 82 calculates the sound velocity V by dividing the facing distance L between the transmission sensor 61 and the reception sensor 62 by the propagation time T, and calculates the equation (1) which is a theoretical equation of the sound velocity.
Is inversely calculated to calculate the hydrogen concentration in the reformed gas. Where:
R is a gas constant (8.3145 J / molK). In the formula, Mi is the molecular weight of the component gas in the reformed gas, Cpi is the constant pressure molar specific heat of the component gas, Cvi is the constant volume molar specific heat of the component gas, and xi is the molar ratio of the component gas. Therefore, the hydrogen concentration can be obtained by giving parameters other than the hydrogen molar ratio xi in advance. Note that T is cell 5
If the temperature is a temperature of the test gas flowing therethrough and the temperature fluctuates greatly, a temperature sensor for detecting the temperature of the test gas may be provided, and the detected temperature may be used as the test gas temperature T.

[0033]

(Equation 1)

According to the present gas concentration measuring apparatus, the transmission sensor 61 and the reception sensor 62 exhibit good convergence and radiation efficiency even for a medium containing a large amount of a component gas having a low specific gravity, such as hydrogen. Therefore, the hydrogen concentration in the reformed gas can be measured with high accuracy.

The present gas concentration measuring apparatus can be suitably applied to measurement of not only the concentration of hydrogen in the reformed gas but also the concentration of light gases such as hydrogen and helium in other test gases.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ultrasonic element of the present invention.

FIG. 2 is a graph showing characteristics of the ultrasonic element.

FIG. 3 is a configuration diagram of a main part of the gas concentration measurement device of the present invention.

FIG. 4 is an overall configuration diagram including a circuit configuration of the gas concentration measurement device.

FIG. 5 is a timing chart showing an operation state of each part of the gas concentration measuring device.

FIG. 6 is a schematic view of a main part of the gas concentration measurement device, showing an ultrasonic wave propagation path of the gas concentration measurement device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric body 101 Front end surface (one end surface) 102 Rear end surface (the other end surface) 3 Casing 31 Bottom part (matching layer) 301 Bottom part 302 Depression 303 Adhesion surface 5 Cell 6 Transmitting / receiving means 61 Transmitting sensor (ultrasonic element) 62 Reception Sensor (ultrasonic element) 7 signal generation circuit 8 measuring means 81 signal processing circuit 82 analysis circuit 83 timer circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayoshi Sugino 14 Iwatani, Shimowasukamachi, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Takahiro Saito 14 Iwatani, Shimotsukamachi, Nishio City, Aichi Prefecture Stock (72) Inventor: Nao Watanabe 1st Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (Reference) 2G047 AA01 BA01 BC02 BC15 CA01 GA01 GF08 5D019 AA21 BB02 BB08 BB12 EE01 GG01

Claims (3)

[Claims] 1. A piezoelectric body for generating ultrasonic waves by a piezoelectric action, wherein a matching layer is adhered to one end face of the inside of the piezoelectric body in the ultrasonic wave traveling direction so as to be in contact with the entire surface of said one end face. An ultrasonic element that emits ultrasonic waves from the body through the matching layer to the outside, wherein the one end face of the piezoelectric body is a flat surface, and the other end face of the piezoelectric body is a gentle curved protruding surface. An ultrasonic element characterized by the above-mentioned. 2. The ultrasonic element according to claim 1, wherein the other end surface of the piezoelectric body has a spherical surface. 3. A transmission / reception means for transmitting / receiving ultrasonic waves using a test gas as a medium, and a transmission signal and a reception signal of the transmission / reception means as inputs, the transmission / reception means changing according to the concentration of a specific component gas in the test gas. It is a gas concentration measuring device provided with the measuring means which measures the concentration of the component gas based on the sound speed of the ultrasonic wave, The transmitting and receiving means, the structure provided with the ultrasonic element according to any one of claims 1 and 2. Gas concentration measuring device characterized by having done.