JP3341092B2 - Ultrasonic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer in which an ultrasonic device comprising a piezoelectric thin plate and interdigital electrodes is provided on a non-piezoelectric substrate.

2. Description of the Related Art To excite ultrasonic waves in a liquid, an ultrasonic transducer comprising a piezoelectric thin plate provided with interdigital electrodes has been conventionally used. By using such an ultrasonic transducer, a leaky Rayleigh wave or a leaked Lamb wave can be excited in a liquid. Leaky Rayleigh waves have a constant frequency with respect to speed, so the structure is simple, but the degree of freedom in device design is small, and the plate surface including the interdigital electrodes is on the side that comes into contact with the liquid. have. When using the ultrasonic transducer for acoustic imaging or the like, it is necessary to drive at a higher frequency in order to improve the resolution, or to drive in multiple modes and multiple frequencies to finely control the position of the focal point of the device under test. And may be. This suggests that the use of leaky Lamb waves with multiple modes with velocity dispersion is likely to be effective, but it requires further thinning of the piezoelectric thin plate with the increase in frequency, and the thinner the thinner, the more brittle The problem of having sex is left. As described above, the conventional ultrasonic wave excitation means for liquid has a limitation in the structure of the ultrasonic transducer itself, and therefore, such an ultrasonic transducer is applied to generation and detection of ultrasonic waves in liquid. The area was limited.

SUMMARY OF THE INVENTION It is an object of the present invention not only to efficiently excite ultrasonic waves in a liquid with low power consumption, but also to efficiently convert ultrasonic waves existing in the liquid into electric signals. An object of the present invention is to provide an ultrasonic transducer which can be converted, has a short response time, has high sensitivity, and is excellent in workability and mass productivity.

According to a first aspect of the present invention, there is provided an ultrasonic transducer, comprising: an ultrasonic device comprising a piezoelectric thin plate and an interdigital transducer provided on one plate surface F1 of a non-piezoelectric substrate. Ultrasonic waves are radiated to the liquid L1 that has come into contact with the other plate surface F2 of the substrate, or the liquid L2 is brought into contact with the plate surface F2 of the non-piezoelectric substrate.
An ultrasonic transducer for receiving ultrasonic waves propagating through the inside of the piezoelectric thin plate, wherein
The thickness of the piezoelectric thin plate is less than or equal to the electrode period length of the interdigital transducer, and the velocity of the bulk wave propagating through the non-piezoelectric substrate alone is provided on the plate surface P1 of the two plate surfaces P1 and P2. Is characterized in that the velocity is smaller than the velocity of the surface acoustic wave propagating through the piezoelectric thin plate alone. 3. The ultrasonic transducer according to claim 2, wherein the means for radiating ultrasonic waves to the liquid L1 uses the interdigital transducer as an input, and inputs an electric signal to the interdigital transducer so that the non-piezoelectric substrate and the ultrasonic transducer are electrically connected to each other. A surface acoustic wave of a zero-order symmetric mode or a higher-order mode is excited at the interface B with the acoustic device, and the surface acoustic wave is mode-converted as a bulk wave in the non-piezoelectric substrate. It radiates as a longitudinal wave into the liquid L1, and the piezoelectric thin plate is fixed to the non-piezoelectric substrate via the plate surface P2. The ultrasonic transducer according to claim 3, wherein the non-piezoelectric substrate is made of an acrylic plate, and the piezoelectric thin plate is made of piezoelectric ceramic,
The direction of the polarization axis of the piezoelectric ceramic is perpendicular to the surface of the piezoelectric ceramic having the interdigital electrodes. According to a fourth aspect of the present invention, in the ultrasonic transducer, the non-piezoelectric substrate is made of an acrylic plate, and the piezoelectric thin plate is made of LiNbO ₃ or another single crystal.

The ultrasonic transducer of the present invention has a simple structure in which an ultrasonic device composed of a piezoelectric thin plate and interdigital electrodes is provided on a non-piezoelectric substrate. By employing a structure in which the IDT electrode is used as an input and an electric signal is input to the IDT, a surface acoustic wave having a speed of V _S can be excited in the piezoelectric thin plate. In addition, by employing a structure in which the ultrasonic device is fixed to the non-piezoelectric substrate, the mode conversion can be performed in such a manner that the surface acoustic wave leaks to the non-piezoelectric substrate as a bulk wave. At this time, the phase velocity of the surface acoustic wave leaked is the velocity V of the transverse wave in the non-piezoelectric substrate alone.
Greater than _AT . That is, the surface acoustic waves excited on the piezoelectric thin plate that satisfy the relationship that V _S is larger than V _AT leak to the non-piezoelectric substrate. The surface acoustic wave is leaked to the non-piezoelectric substrate as a bulk wave, and the leaked surface acoustic wave is mode-converted into a bulk wave and propagates in the non-piezoelectric substrate. In this way, of the surface acoustic waves excited on the piezoelectric thin plate, the phase velocity is the velocity V _AT of the transverse wave in the non-piezoelectric substrate alone.
Waves larger than the longitudinal wave speed V _{AL and} larger than the speed V _AT
Is efficiently converted into a wave having a speed substantially equal to the above and leaked to the non-piezoelectric substrate. Also, of the surface acoustic waves excited on the piezoelectric thin plate, a wave whose phase velocity is higher than the velocity V _AL of the longitudinal wave in the non-piezoelectric substrate alone is converted into a wave having a velocity almost equal to the velocity V _AT or the velocity V _AL. It is well converted and leaks to non-piezoelectric substrates. Further, when the liquid comes into contact with the surface of the non-piezoelectric substrate on which the ultrasonic device is not provided, a part of the bulk wave leaked in this manner can efficiently _generate a longitudinal wave having a velocity VW in the liquid. Radiated as In this way, the ultrasonic transducer of the present invention enables efficient emission of ultrasonic waves into a liquid. The ultrasonic transducer of the present invention, when the IDT electrode is used for output, when the liquid comes into contact with the surface of the non-piezoelectric substrate on which the ultrasonic device is not provided, the liquid is present in the liquid. Ultrasonic waves can be output as electrical signals from the interdigital transducer. By adopting a structure that effectively converted into a wave having a substantially equal rate longitudinal wave velocity V _W, which is excited in the liquid at the interface between V _AT or V _AL of the non-piezoelectric substrate and the liquid, can propagate longitudinal wave velocity V _W, which is excited in the liquid efficiently to the non-piezoelectric substrate. Waves with a rate approximately equal to the rate V _AT or V _AL propagated on non-piezoelectric substrate is converted into a surface acoustic wave velocity V _S at the interface between the piezoelectric thin propagates to the piezoelectric sheet, the electrical signal in the IDT It is converted and output. In this way, the ultrasonic transducer of the present invention can output, as an electric signal, an ultrasonic wave having a target wavelength among ultrasonic waves having various wavelengths existing in a liquid. For example, it is possible to detect abnormal sound in water at the ultrasonic level. By adopting a structure in which the thickness of the piezoelectric thin plate is set to be equal to or less than the electrode cycle length of the interdigital transducer, not only can the degree of conversion of electrical energy applied to the interdigital transducer to surface acoustic waves be increased, It is possible to suppress reflection and the like caused by acoustic impedance mismatch at the interface between the piezoelectric thin plate and the non-piezoelectric substrate. Therefore, effective leakage of the surface acoustic wave to the non-piezoelectric substrate can be promoted. The ultrasonic transducer of the present invention overcomes the brittleness associated with reducing the thickness d of the piezoelectric thin plate by fixing the piezoelectric thin plate to the non-piezoelectric substrate. That is, the non-piezoelectric substrate plays an important role in overcoming the fragility of the piezoelectric thin plate. By adopting an acrylic plate as the non-piezoelectric substrate, a piezoelectric ceramic as the piezoelectric thin plate, and a structure in which the direction of the polarization axis of the piezoelectric ceramic is perpendicular to the plate surface having the interdigital electrodes in the piezoelectric ceramic The surface acoustic wave can be efficiently excited on the piezoelectric thin plate, and the surface acoustic wave can be efficiently leaked to the non-piezoelectric substrate. By employing an acrylic plate as the non-piezoelectric substrate and employing LiNbO ₃ or other single crystal as the piezoelectric thin plate, a surface acoustic wave can be efficiently excited on the piezoelectric thin plate. It can leak efficiently. P as a piezoelectric thin plate
By using VDF and other piezoelectric polymer films, it is possible to efficiently excite a surface acoustic wave to a piezoelectric thin plate in a form that can handle higher frequencies, and to efficiently leak the surface acoustic wave to a non-piezoelectric substrate. be able to. By fixing the piezoelectric thin plate to the non-piezoelectric substrate via the plate surface having no IDT, the electric energy applied to the IDT can be efficiently converted into a surface acoustic wave.

1 is a sectional view showing an embodiment of the ultrasonic transducer according to the present invention. This embodiment comprises an interdigital electrode 1, a piezoelectric ceramic thin plate 2, and an acrylic plate 3. The surface of the acrylic plate 3 not having the piezoelectric ceramic thin plate 2 is in contact with the liquid. The interdigital electrode 1 is made of an aluminum thin film. The piezoelectric ceramic plate 2 is made of TDK 10 having a thickness of d.
It is made of 1A material (product name). The thickness of the acrylic plate 3 (T _A)
Is 2 mm. The interdigital transducer 1 is provided on a piezoelectric ceramic plate 2, and the piezoelectric ceramic plate 2 is provided on an acrylic plate 3. The piezoelectric ceramic thin plate 2 is fixed on the acrylic plate 3 with an epoxy resin. The interdigital transducer 1 is of a regular type having an electrode cycle length of 2P, and has ten pairs of electrode fingers. The interdigital transducer 1 of the ultrasonic transducer of FIG.
Is used for input, when an electric signal is input to the interdigital transducer 1, only the electric signal of the center frequency corresponding to the interdigital transducer 1 and the frequency near the electric signal among the electric signal frequencies are converted into surface acoustic waves. Speed of the piezoelectric ceramic thin plate 2
Propagate in _S. If the velocity V _{S of the} surface acoustic wave is greater than the velocity V _AT of the shear wave in the acrylic plate 3 alone, the velocity V of the longitudinal wave
When less than _AL, the surface acoustic wave is converted into a shear wave velocity V _AT is leaked to the acrylic plate 3. The leakage angle θ _AT when a bulk wave is leaked from the piezoelectric ceramic thin plate 2 is V
It correlates with the ratio of _AT to V _S (V _AT / V _S ). Acrylic board 3
Bulk waves propagating is emitted to be converted into longitudinal waves in the liquid velocity V _W in the interface between the acrylic plate 3 and the liquid.
At this time, the radiation angle θ _W is the ratio of the speed V _W to V _AT (V _W / V
_AT ). FIG. 1 shows a propagation mode until a surface acoustic wave propagating through the piezoelectric ceramic thin plate 2 propagates through the acrylic plate 3 as a longitudinal wave into the liquid. Since the speed V _S changes in accordance with the frequency of the electric signal input to the interdigital transducer 1, the leakage angle θ _AT and the radiation angle θ _W can be changed by changing the frequency of the electric signal. . Therefore, when radiating the ultrasonic wave into the liquid, the ultrasonic wave can be radiated at the most effective angle according to the purpose and application. FIG. 2 shows a case where the interdigital electrode 1 is used as an input, and the speed V _{S of the} surface acoustic wave propagating in the piezoelectric ceramic thin plate 2 is larger than the speed V _AL of the longitudinal wave in the acrylic plate 3 alone. It is a figure showing the propagation form of a sound wave. In this case, the surface acoustic wave is converted into a longitudinal wave of the shear wave and the velocity V _AL velocity V _AT is leaked to the acrylic plate 3. The leakage angle θ _AT when a transverse wave is leaked as a bulk wave from the piezoelectric ceramic thin plate 2 is V _AT
And correlated to the ratio (V _AT / V _S) and V _S, leak angle theta _AL in the case of longitudinal wave is correlated to the ratio (V _AL / V _S) of the V _AL and V _S. Bulk wave that excites the acrylic plate 3 is emitted are converted into longitudinal waves velocity V _W in the interface between the acrylic plate 3 and the liquid in the liquid. At this time, the radiation angle θ _W is determined by the ratio of the speed V _W to V _AT (V _W / V _AT ) or the ratio of the speed V _W to V _AL (V _W / V
_AL ). Since the velocity V _S is varied depending on the frequency of the electric signal which is input to the interdigital transducer 1, by changing the frequency of the electrical signal, the velocity V _S 1
(V _AT <V _S <V _AL ) or the condition (V _AL <V _S ) as shown in FIG. In addition, it becomes possible to vary the respective leakage angles θ _AT and θ _AL and the radiation angle θ _W. Therefore, when radiating the ultrasonic wave into the liquid, the ultrasonic wave can be radiated at the most effective angle according to the purpose and application. When using the interdigital electrodes 1 of the ultrasonic transducer 1 for output, it is possible to output a longitudinal wave velocity V _W in the liquid from the interdigital transducer 1 as an electric signal. The longitudinal wave of the velocity V _{W in} the liquid is converted into a bulk wave of the velocity V _AT or V _AL at the interface between the liquid and the acrylic plate 3 and propagates through the acrylic plate 3. is converted into a surface acoustic wave velocity V _S at the interface, only the center frequency surface acoustic wave having a frequency in the vicinity thereof showing the interdigital electrodes 1 of the surface acoustic wave velocity V _S is converted into an electric signal interdigital Output from the electrode 1. In this way, by changing the electrode cycle length of the interdigital electrode 1 according to the purpose or application, it becomes possible to output ultrasonic waves of a predetermined wavelength in the liquid as electric signals. FIG. 3 is a cross-sectional view showing the propagation form of ultrasonic waves near the interface between the acrylic plate 3 and water contacted with the acrylic plate 3. However, this is when the speed V _S satisfies the condition of FIG. 1 (V _AT <V _S <V _AL ). When the bulk shear wave propagating through the acrylic plate 3 reaches the interface, the three components of the shear wave reflectance R _T indicating the reflection angle θ _AT , the longitudinal wave reflectance _RL indicating the reflection angle θ _AL , and the longitudinal wave transmittance _TL are calculated. Occurs. In this way, the acrylic plate 3
Bulk shear wave propagating through a portion at the interface is reflected as a transverse wave reflectivity R _T and the longitudinal wave reflectivity R _L, the remainder is emitted to the water in the radiation angle theta _W as a longitudinal wave transmittance T _L. FIG.
FIG. 4 is a characteristic diagram showing a velocity dispersion curve of a surface acoustic wave propagating through a layered medium composed of the piezoelectric ceramic thin plate 2 and the acrylic plate 3 in the ultrasonic transducer of FIG. 1, and shows the frequency f of the surface acoustic wave and the thickness of the piezoelectric ceramic thin plate 2. FIG. 7 is a diagram illustrating a phase velocity of each mode with respect to a product of the height d. However, in the piezoelectric ceramic thin plate 2, both the plate surface of the piezoelectric ceramic thin plate 2 that contacts the acrylic plate 3 (the acrylic side plate surface) and the other plate surface that contacts the air (the air side plate surface) are electrically connected. Used in the open state. In this figure, "open" indicates that the device is in an open state. In addition, ○ indicates an actually measured value. A surface acoustic wave has a plurality of modes. fd value is approximately 0.4 MH
Wave A ₀ mode when the following z · mm speed is less than the shear wave velocity V _AT acrylic plate 3. Such a wave is a surface wave in which energy of the wave is localized and propagates near the surface, and is not leaked to the acrylic plate 3. Speed is V _AT
Waves of the A ₀ mode and other modes larger than the above have an imaginary component of the velocity, and a part of the energy of the wave leaks into the acrylic plate 3 as a bulk wave. Wave region speed is smaller than the larger V _AL than V _AT of the surface acoustic wave of each mode can be effectively leakage as a bulk shear wave into the acrylic plate 3. Wave area rate is greater than V _AL acrylic plate 3 as a bulk longitudinal waves and bulk shear wave
Leaked inside. FIG. 5 is a characteristic diagram showing a relationship between the mode conversion efficiency C and the fd value in the ultrasonic transducer of FIG. However, the piezoelectric ceramic thin plate 2 used had both the acrylic side plate surface and the other air side plate surface of the piezoelectric ceramic thin plate 2 electrically open. It can be seen that the surface acoustic wave is also propagated to the piezoelectric ceramic thin plate 2 in any mode except the A ₀ mode is leaky as a bulk wave efficiently acrylic plate 3. FIG. 6 is a characteristic diagram showing the relationship between the effective electromechanical coupling coefficient k ² calculated from the phase velocity difference of the piezoelectric ceramic thin plate 2 under two different electrical boundary conditions and the fd value. However, the piezoelectric ceramic thin plate 2 is one in which the interdigital electrode 1 (IDT) is provided on the air side plate surface of the piezoelectric ceramic thin plate 2 and the acrylic side plate surface is electrically opened. K ^{2 in the} A ₀ mode shows a substantially constant value (k ² = 4%) from around fd = 2.8 MHz · mm. S ₀ mode is fd =
One peak around 1.4 MHz · mm (k ² = 17.
5%). This peak is considered to correspond to the surface wave leaking from the piezoelectric ceramic thin plate 2 to the acrylic plate 3. The A ₁ and A ₂ modes also show good values efficiently. In this way, also it is possible to leak efficiently SAW from the piezoelectric ceramic thin plate 2 to the acrylic plate 3 in which mode except A ₀ mode, by adjusting the fd value of the most efficient of the acrylic plate 3 Good leakage can be realized. Further, the structure in which the interdigital electrode 1 is provided on the air-side plate surface of the piezoelectric ceramic thin plate 2 has an advantage that it is easy to manufacture. FIG. 7 is a characteristic diagram showing the relationship between the effective electromechanical coupling coefficient k ² calculated from the phase velocity difference under two different electrical boundary conditions of the piezoelectric ceramic thin plate 2 and the fd value. However, the piezoelectric ceramic thin plate 2 is one in which the interdigital electrode 1 is provided on the air side plate surface of the piezoelectric ceramic thin plate 2 and the acrylic side plate surface is electrically short-circuited.
In the present embodiment, the plate surface of the piezoelectric ceramic thin plate 2 is coated with a metal thin film to electrically short the plate surface. In this drawing, "short" indicates a short-circuit state. Figure also similar to FIG. 6 in 7, A ₀ piezoelectric ceramic thin plate 2 a surface acoustic wave in any mode except the mode
Can efficiently leak to the acrylic plate 3 from f
By adjusting the d value, the most efficient leakage to the acrylic plate 3 can be realized. Further, the structure in which the interdigital electrode 1 is provided on the air-side plate surface of the piezoelectric ceramic thin plate 2 has an advantage that it is easy to manufacture. FIG. 8 is a characteristic diagram showing the relationship between the energy distribution ratio and the angle with respect to the phase velocity of the shear wave reflectance _RT , the longitudinal wave reflectance _RL, and the longitudinal wave transmittance _TL shown in FIG. That is, it is a characteristic diagram relating to a bulk shear wave. However, the reflection angle theta _AT for angle transverse wave reflectivity R _T of this time, the radiation angle is the reflection angle theta _AL, the longitudinal wave transmission T _L for the longitudinal wave reflectivity R _L Indicates θ _W. The value of the longitudinal wave transmittance T _L is the largest in the region where the phase velocity is approximately from 1800 m / s to 2400 m / s, and the radiation angle θ _{W at} this time may be about 60 to 40 degrees. Understand. Figure 9 is a characteristic diagram showing the relationship between the energy distribution ratio and the angle with respect to the phase velocity of the bulk shear wave reflectivity about the longitudinal wave R _T, the longitudinal wave reflectivity R _L and the longitudinal wave transmittance T _L. It can be seen that the transmittance of the longitudinal wave transmittance _TL is the largest in the region where the phase velocity is greater than approximately around 2800 m / s, and the radiation angle θ _{W at} this time is about 40 degrees or less. FIG. 10 is a characteristic diagram showing an example of the relationship between the insertion loss and the frequency in the ultrasonic transducer of FIG. 1, where the thickness d of the piezoelectric ceramic thin plate 2 is 200 μm, and the electrode period length 2P of the interdigital transducer 1 is 460 μm. It is a result in the case of. In this figure, a solid line indicates a case where water is not in contact with the acrylic plate 3, and a dotted line indicates a case where water is in contact with the acrylic plate 3. Since the degree is large, which is emitted as longitudinal waves in water larger the difference between the solid line and the dotted line at each frequency, that is efficiently radiated as longitudinal wave in water in the surface wave which mode except A ₀ mode Understand. In particular, it can be seen that the degree of surface waves of the S ₀ mode having a center frequency of about 6 MHz and the S ₂ mode of a center frequency of about 13 MHz being radiated as longitudinal waves into water is large.

According to the ultrasonic transducer of the present invention, it is possible to excite a piezoelectric thin plate with a surface acoustic wave having a speed of V _S by using an interdigital transducer as an input and inputting an electric signal to the interdigital transducer. it can. In addition, by employing a structure in which the ultrasonic device is fixed to the non-piezoelectric substrate, the mode conversion can be performed in such a manner that the surface acoustic wave leaks to the non-piezoelectric substrate as a bulk wave. At this time, the phase velocity of the leaked surface acoustic wave is higher than the velocity V _AT of the shear wave in the non-piezoelectric substrate alone. That is, the surface acoustic waves excited on the piezoelectric thin plate that satisfy the relationship that V _S is larger than V _AT leak to the non-piezoelectric substrate. In this way, of the surface acoustic waves excited on the piezoelectric thin plate, the wave whose phase velocity is larger than the velocity V _AT of the transverse wave and smaller than the velocity V _{AL of the} longitudinal wave in the non-piezoelectric substrate alone is almost equal to the velocity V _AT. The waves are efficiently converted into waves having the same speed and leak to the non-piezoelectric substrate. Also, of the surface acoustic waves excited on the piezoelectric thin plate, a wave whose phase velocity is higher than the velocity V _AL of the longitudinal wave in the non-piezoelectric substrate alone is converted into a wave having a velocity almost equal to the velocity V _AT or the velocity V _AL. It is well converted and leaks to non-piezoelectric substrates.
Further, when the liquid comes into contact with the surface of the non-piezoelectric substrate on which the ultrasonic device is not provided, a part of the bulk wave leaked in this manner can efficiently _generate a longitudinal wave having a velocity VW in the liquid. Radiated as In this way, the ultrasonic transducer of the present invention enables efficient emission of ultrasonic waves into a liquid. When the interdigital transducer is used for output, when the liquid comes into contact with the surface of the non-piezoelectric substrate on which the ultrasonic device is not provided, the ultrasonic waves present in the liquid are transmitted to the interdigital transducer. Can be output as an electric signal. By adopting a structure that effectively converted into a wave having a substantially equal rate longitudinal wave velocity V _W, which is excited in the liquid at the interface between V _AT or V _AL of the non-piezoelectric substrate and the liquid, can propagate longitudinal wave velocity V _W, which is excited in the liquid efficiently to the non-piezoelectric substrate. The wave propagated to the non-piezoelectric substrate is converted into a surface acoustic wave having a speed of V _{S at} the interface with the piezoelectric thin plate, propagates to the piezoelectric thin plate, and is converted into an electric signal at the IDT and output. In this way, it is possible to output ultrasonic waves having a target wavelength among various ultrasonic waves present in the liquid as electric signals. For example, it is possible to detect abnormal sound in water at the ultrasonic level. By adopting a structure in which the thickness of the piezoelectric thin plate is set to be equal to or less than the electrode cycle length of the interdigital transducer, not only can the degree of conversion of electrical energy applied to the interdigital transducer to surface acoustic waves be increased, It is possible to suppress reflection and the like caused by acoustic impedance mismatch at the interface between the piezoelectric thin plate and the non-piezoelectric substrate. Therefore, effective leakage of the surface acoustic wave to the non-piezoelectric substrate can be promoted. Thus, the thickness d of the piezoelectric thin plate
The fragility associated with reducing the size is overcome by fixing the piezoelectric thin plate to the non-piezoelectric substrate. That is, the non-piezoelectric substrate plays an important role in overcoming the fragility of the piezoelectric thin plate. By adopting an acrylic plate as the non-piezoelectric substrate, a piezoelectric ceramic as the piezoelectric thin plate, and a structure in which the direction of the polarization axis of the piezoelectric ceramic is perpendicular to the plate surface having the interdigital electrodes in the piezoelectric ceramic The surface acoustic wave can be efficiently excited on the piezoelectric thin plate, and the surface acoustic wave can be efficiently leaked to the non-piezoelectric substrate. By employing an acrylic plate as the non-piezoelectric substrate and employing LiNbO ₃ or other single crystal as the piezoelectric thin plate, a surface acoustic wave can be efficiently excited on the piezoelectric thin plate. It can leak efficiently. By adopting PVDF or other piezoelectric polymer film as the piezoelectric thin plate, surface acoustic waves can be efficiently excited on the piezoelectric thin plate in a form that can handle higher frequencies, and the surface acoustic wave can be efficiently applied to the non-piezoelectric substrate. Can leak well. By fixing the piezoelectric thin plate to the non-piezoelectric substrate via the plate surface having no IDT, the electric energy applied to the IDT can be efficiently converted into a surface acoustic wave.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an ultrasonic transducer according to the present invention.

FIG. 2 shows a case where the interdigital transducer 1 is used for input;
Shows the propagation mode of the ultrasonic wave when the speed V _S is greater than the speed V _AL.

FIG. 3 is a cross-sectional view showing an ultrasonic wave propagation pattern near an interface between an acrylic plate 3 and water contacted with the acrylic plate 3;

FIG. 4 is a characteristic diagram showing a velocity dispersion curve of a surface acoustic wave propagating through a layered medium including the piezoelectric ceramic thin plate 2 and the acrylic plate 3 in the ultrasonic transducer of FIG.

FIG. 5 is a characteristic diagram showing a relationship between a mode conversion efficiency C and an fd value in the ultrasonic transducer of FIG.

FIG. 6 is a characteristic diagram showing a relationship between an effective electromechanical coupling coefficient k ² calculated from a phase velocity difference under two different electrical boundary conditions of the piezoelectric ceramic thin plate ² and an fd value.

FIG. 7 is a characteristic diagram showing a relationship between an effective electromechanical coupling coefficient k ² calculated from a phase velocity difference under two different electrical boundary conditions of the piezoelectric ceramic thin plate ² and an fd value.

FIG. 8 is a characteristic diagram showing the relationship between the energy distribution ratio and the angle with respect to the phase velocity of the shear wave reflectance R _T , longitudinal wave reflectance _RL, and longitudinal wave transmittance _TL shown in FIG.

[9] characteristic diagram showing the relationship between the energy distribution ratio and the angle with respect to the phase velocity of the shear wave reflectivity for Bulk longitudinal wave R _T, the longitudinal wave reflectivity R _L and the longitudinal wave transmittance T _L.

FIG. 10 is a characteristic diagram showing an example of the relationship between insertion loss and frequency in the ultrasonic transducer of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Interdigital electrode 2 Piezoelectric ceramic thin plate 3 Acrylic plate

Claims (4)

(57) [Claims] 1. An ultrasonic device comprising a piezoelectric thin plate and an interdigital electrode is provided on one plate surface F1 of a non-piezoelectric substrate, and an ultrasonic device is provided on a liquid L1 contacting the other plate surface F2 of the non-piezoelectric substrate. An ultrasonic transducer which emits ultrasonic waves or receives ultrasonic waves propagating in the liquid L2 by bringing the liquid L2 into contact with the plate surface F2 of the non-piezoelectric substrate, wherein the IDT electrodes are Two plate surfaces P in the piezoelectric thin plate
1 and P2, the thickness of the piezoelectric thin plate is less than or equal to the electrode cycle length of the interdigital transducer, and the speed of a bulk wave propagating through the non-piezoelectric substrate alone is An ultrasonic transducer, wherein the velocity is lower than the velocity of a surface acoustic wave propagating in a single thin plate. 2. The means for radiating ultrasonic waves to the liquid L1 uses the interdigital transducer as an input, and inputs an electric signal to the interdigital transducer to thereby provide an interface B between the non-piezoelectric substrate and the ultrasonic device. A surface acoustic wave of a zero-order symmetric mode or a higher-order mode is excited, and the surface acoustic wave is mode-converted as a bulk wave in the non-piezoelectric substrate. 2. The ultrasonic transducer according to claim 1, wherein the piezoelectric thin plate is radiated into the non-piezoelectric substrate via the plate surface P <b> 2. 3. 3. The non-piezoelectric substrate is made of an acrylic plate, the piezoelectric thin plate is made of piezoelectric ceramic, and the direction of the polarization axis of the piezoelectric ceramic is perpendicular to the surface of the piezoelectric ceramic having interdigital electrodes. Claim 1.
Or the ultrasonic transducer according to 2. 4. The ultrasonic transducer according to claim 1, wherein the non-piezoelectric substrate is made of an acrylic plate, and the thin piezoelectric plate is made of LiNbO ₃ or another single crystal.