JP2002159085A - Acoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic transducer that can withstand water pressure at a deep sea and can obtain a specific front-to-back ratio in reception sensitivity or transmission sensitivity even in the case of an array configuration of a compact piezoelectric element. SOLUTION: The acoustic transducer comprises a plurality of piezoelectric elements 1 for mainly receiving arrival sound waves from the front, a signal take-out substrate 2 for interconnecting each electrode of the plurality of piezoelectric elements and each conductor of a cable 3 via internal pattern wiring, and a rubber material layer 4 that is installed at the rear side of the signal take-out substrate, and material quality and thickness are set so that the amount of compression distortion when pressure is applied becomes small and the amount of attenuation when the sound wave is propagated becomes a specific value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic receiver or an acoustic transmitter.

[0002]

2. Description of the Related Art Known examples of underwater acoustic receivers having a frequency of several hundred KHz and having unidirectionality include the following known documents 1 and 2, for example. Known Document 1: Japanese Patent Publication No. 58-51477 "Ultrasonic Receiver Array" Known Document 2: Proceedings of the Acoustical Society of Japan, October 1979
Tsuki, Kamada, “Before and after ratio of transducer backed by acoustic mismatch layer”, p.13-14

FIG. 4 is an explanatory view of the structure of the acoustic wave receiver disclosed in the above-mentioned known document 1 and when a water pressure is applied. FIG. 4A is a side sectional view of the acoustic receiver, and 21 in FIG. 4 is an individual piezoelectric element (vibrator). In this example, 16 piezoelectric elements have four rows on the same surface. , Arranged in a two-dimensional array of four rows. Reference numeral 22 denotes kilk rubber, which contains air bubbles therein. This kilk rubber 22 is used as a baffle material of sound waves (a material for preventing propagation of sound waves), and is provided so as to wrap all the rear and side surfaces of each piezoelectric element 21. However, the kilk rubber 22 is not provided since the front direction of each piezoelectric element 21 is the sound wave receiving direction. The electrodes of each piezoelectric element 21 are connected to a cable 23 via a signal lead 24, and an output signal at the time of receiving a signal is extracted. Since the acoustic receiver is used in water, the entire structure from the front surface of the piezoelectric element 21 to one end of the cable 23 is watertight molded with a watertight molding material 25.

In FIG. 4, the sound field medium in this case is water because it is used as a receiver for underwater sound waves. When the acoustic impedance of each element is compared, the piezoelectric element 21 which is a receiving element of the incoming sound wave has an acoustic impedance of about 20 times that of water, and the kilk rubber 22 has an acoustic impedance of about 1/3 of water. is there. When the acoustic receiver configured as shown in FIG. 4A receives a sound wave propagating in water, incident sound waves from a direction parallel to the array plane of the array are canceled by the baffle material of the kilk rubber 22, The sound wave incident from the rear side in the drawing is substantially sound-insulated by the baffle material of the kilk rubber 22 and receives only the sound wave incident from the front side in the drawing, so that the receiver has a unidirectional characteristic.

FIG. 5 is an explanatory view of the structure of the acoustic receiver disclosed in the above-mentioned known document 2 and its problems. FIG. 5A is a side cross-sectional view of the acoustic receiver, and 21 in FIG. 5 represents individual piezoelectric elements. The piezoelectric element 21 of FIG. 5 is also similar to the case of FIG.
A plurality of piezoelectric elements are two-dimensionally arranged to form an array. The electrodes of each piezoelectric element 21 are connected to a cable 23 via a signal lead 24. Reference numeral 25 denotes a watertight molding material, which has a structure in which the whole from the front surface of the piezoelectric element 21 to one end of the cable 23 is watertight molded, as in the case of FIG. 5A are different from those of FIG. 4A in that they are 26 rubber material layers and 27 metal layers, and are provided on the back side of each piezoelectric element 21 arranged two-dimensionally. Is
An acoustic mismatch layer having a two-layer structure including a rubber material layer 26 and a metal layer 27 is provided. In the acoustic receiver using the acoustic mismatch layer, a rubber material layer is used instead of making a through hole for the signal lead wire 24 in both the rubber material layer 26 and the metal layer 27 as shown in FIG. There is also a structure in which the signal lead wire 24 is connected to the cable 23 avoiding the metal layer 27 by making a hole only in the metal layer 27 and not making a hole in the metal layer 27.

In the case of FIG. 5 as well, the sound field medium is water, and when the acoustic impedance of each element is compared, the acoustic impedance of the piezoelectric element 21 is about 20 times that of water. The material layer 26 has an acoustic impedance approximately similar to that of water, and the metal layer 27 is made of, for example, steel.
The acoustic impedance is about 30 times that of water. Thus, the rubber material layer 26 and the metal plate 27 have an acoustic impedance of 3
The difference is about 0 times, and the backing by the two-layered acoustic mismatch layer can provide a ratio of the front and rear of the receiving sensitivity of the acoustic transducer of about 30 dB at the center frequency of the sound wave. Therefore, even in the acoustic receiver having the structure shown in FIG. 5A, the sound incident from the rear side in the drawing is substantially blocked by the two-layer acoustic mismatch layer, and only the sound wave incident from the front side in the drawing is received. Therefore, unidirectionality can be obtained.

[0007]

However, in the acoustic wave receiver disclosed in the above-mentioned known document 1, a material of kilk rubber is used as a baffle material. Bubbles are crushed and easily compressed. Therefore, when this acoustic receiver is used, for example, in the deep sea, the water pressure from the surroundings compresses the kilk rubber and changes its acoustic impedance, thereby losing sound insulation against incident sound from the rear side. As a result, it is not possible to determine whether the received signal is due to the sound wave arriving from either the front surface or the back surface of the piezoelectric element. In addition, when the kilk rubber or the like is compressed, a crack may be generated in a watertight mold material covering the entire receiver, thereby impairing watertightness or disconnecting a signal lead wire (see FIG. 4B).

In the acoustic receiver disclosed in the above-mentioned known document 2, when the rubber material layer is made of a material having a small amount of compressive strain due to water pressure and a low acoustic impedance, the rear surface of the rubber material layer does not suffer from compressive failure even at a considerable water depth. Sound insulation to incoming sound from a direction can be maintained. However, FIG.
As shown in (b), when the piezoelectric element is small, most of the area of the rear surface is occupied by the electrode mounting portion, and the sound insulating effect by the acoustic mismatching layer is not obtained very much. Further, when an array is formed by arranging a plurality of piezo-electrons, and signal extraction lines are extracted from each of the piezoelectric electrons, holes for passing individual signal extraction lines through the rubber material layer and the metal layer are required.
Processing of the through hole of this signal lead wire becomes difficult as the piezoelectric electrons become smaller, and by providing a large number of through holes,
The area of the acoustic mismatch layer is reduced, and the sound insulation effect is also reduced. Further, in a method in which a signal lead line is provided without making a hole in a metal layer to avoid this, when the number of piezoelectric electrons increases as in a two-dimensional array, it is difficult to route the wiring.

[0009]

An acoustic receiver according to the present invention mainly receives an incoming sound wave from the front of a piezoelectric element.
In an acoustic wave receiver having a piezoelectric material and a rubber material layer provided on the rear side of the piezoelectric material, the material of the rubber material layer has a small amount of compressive strain when pressure is applied and an attenuation coefficient of sound wave propagation. By using a large material and setting the thickness of the rubber material layer so that the amount of attenuation when a sound wave propagates through the rubber material layer of the used material becomes a predetermined value, the sound reception sensitivity can be increased or decreased. The ratio is configured to be a predetermined value.

Further, the acoustic wave receiver according to the present invention comprises a plurality of piezo-electrons, respective electrodes of the plurality of piezo-electrons, and respective conductors of a signal output cable, each of which mainly receives an incoming sound wave from the front of each of the piezo-electrons. In an acoustic wave receiver having a signal extraction board interconnecting between them via an internal pattern wiring, and a rubber material layer provided on the rear side of the signal extraction board, the material of the rubber material layer is applied with pressure. A material having a small amount of compressive strain at the time and a large attenuation coefficient at the time of sound wave propagation is used, and a rubber material is used so that the amount of attenuation when the sound wave propagates through the rubber material layer of the used material becomes a predetermined value. By setting the thickness of the layer, the front-to-back ratio of the acoustic wave receiving sensitivity becomes a predetermined value.

An acoustic wave transmitter according to the present invention is directed to an acoustic wave receiver for transmitting a sound wave mainly in front of a piezoelectric element, comprising a piezoelectric element and a rubber material layer provided on the rear side of the piezoelectric element. As the material of the rubber material layer, a material having a small amount of compressive strain at the time of applying pressure and a large attenuation coefficient at the time of sound wave propagation is used, and attenuation when sound wave propagates through the rubber material layer of the used material. By setting the thickness of the rubber material layer such that the amount becomes a predetermined value, the front-to-back ratio of the acoustic transmission power becomes a predetermined value.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Embodiment 1 is an example in which the present invention is applied to a two-dimensional acoustic receiver array. FIG. 1 is a structural diagram of an acoustic receiver according to Embodiment 1 of the present invention, and the figure is a side sectional view of the acoustic receiver. In FIG. 1, reference numeral 1 denotes individual piezo-electrons. In this example, a plurality of piezo-electrons 1 are two-dimensionally arranged and mounted on a planar signal extraction board 2 to form an array configuration.

Reference numeral 2 denotes a signal extraction board, which is a flat board in this example. On one surface of the board, a terminal (herein referred to as an input terminal) for connecting electrodes of each piezoelectric element is provided. Terminals (herein, output terminals) for connecting the respective conductors of the cable 3 are provided on the other surface, and pattern wiring for electrically connecting the input terminals and the output terminals are provided inside the substrate. Have been. Therefore, each electrode (both positive electrode and negative electrode) of each of the plurality of piezoelectric elements 1 is connected to the input side terminal of the signal extraction board 2 by, for example, soldering, and the signal passing through the internal pattern wiring from this input side terminal. A lead wire for each channel of the cable 3 is connected to the output side terminal of the extraction board 2. The plurality of piezoelectric elements 1 are fixed to the signal extracting board 2 in a state where several piezoelectric elements 1 are grouped together by, for example, an epoxy resin 6 or the like.

In FIG. 1, reference numeral 4 denotes a rubber material layer. This material has a small amount of compressive strain when subjected to pressure, does not cause compression breakage when a predetermined pressure is applied, and has a sound wave passing through this material layer. Attenuation coefficient when passing as a propagation medium (dB
/ m) is selected. In this example, a urethane rubber material is used. The rubber material layer 4 is formed on the rear surface of the signal extraction board 2, and the thickness of the rubber material layer is adjusted so that the attenuation when a sound wave propagates in the urethane rubber material layer becomes a predetermined value. To determine. As a result, the front-to-back ratio of the acoustic reception sensitivity is a predetermined value (for example, 30 dB shown in FIG. 2).
Degree).

The urethane-based rubber material layer 4 has a small amount of strain compressed by water pressure from the surroundings even when an acoustic wave receiver made of this material is used in the deep sea. When a pressure (for example, about 39 MPa described in FIG. 2) is applied, no compression breakage occurs. Although the cable 3 penetrates through the rubber material layer 4, only one hole is required for this purpose, so that the function as a sound wave attenuating material is hardly impaired by the through hole. . The entire structure from the front surface of the piezoelectric element 1 to one end of the cable 3 is watertight molded with a watertight molding material 5.

The operation of the acoustic receiver shown in FIG. 1 will be described. FIG.
The incident sound wave from the front side shown in FIG. 1 is received by each of the piezoelectric elements 1 arranged two-dimensionally, converted into an electric signal, and passed through the pattern wiring of the signal extraction board 2 for each output signal of each piezoelectric element. Then, it is extracted from the cable 3 to the outside of the receiver for each channel. The surface of the piezoelectric device and the entire receiver are watertight, and have electrical insulation. Here, when the signal extraction board 2 is, for example, a glass epoxy-based board, its acoustic impedance is about twice that of water, and the acoustic impedance of the rubber material layer 4 is a value close to that of water. A part of the incident sound wave passes through the signal extraction board 2 and the rubber material 4, but is attenuated by the rubber material layer 4 during this passage.

If a sound wave reflecting object is present behind the acoustic receiver, the sound wave incident from the front and attenuated in the passage (outward path) of the rubber material layer 4 inside the receiver is reflected by the reflecting object. When the light is again incident on the acoustic receiver, it is reflected from behind and the rubber material layer 4 inside the receiver.
In the passing path (return path), the signal is attenuated again, so that the piezoelectric element 1 is not affected much. Similarly, a sound wave directly incident from the rear side of the drawing passes through the rubber material layer 4 and the signal extraction board 2 and reaches the piezoelectric element 1. However, a predetermined attenuation amount when passing through the rubber material layer 4 is secured. Therefore, the level converted into an electric signal by the piezoelectric element 1 is extremely small (a predetermined front-to-back ratio) as compared with the case of an incident sound wave from the front. That is, the acoustic receiver can be configured such that the ratio of the reception sensitivity between the front surface and the rear surface thereof becomes a predetermined value.

FIG. 2 is a diagram showing a measurement example of the directional characteristics of the acoustic receiver of FIG. In the measurement example of FIG. 2, urethane rubber was used for the rubber material layer 4 and the watertight molding material 5. The thickness of the rubber material layer 4 (the thickness of the cable 3 in the penetrating direction)
Was about 60 mm. The measurement frequency of the underwater sound wave is 500
KHz and measured using an anechoic water tank. As a result of the measurement, as shown in FIG. 2, unidirectionality was obtained, and the front-to-back ratio of the acoustic wave receiving sensitivity was about 30 dB. In addition, as a result of testing the acoustic receiver of FIG. 1 with hydrostatic pressure, it was confirmed that the acoustic receiver could withstand a pressure up to about 39.2 MPa (MPa is megapascal, equivalent to the former unit of 400 kgf / cm ² ).

The acoustic receiver having the configuration shown in FIG. 1 can be applied to, for example, a two-dimensional receiver array (acoustic camera) of an underwater acoustic imaging apparatus. Can be used. The receiver of the configuration shown in FIG. 1 having the water pressure resistance of receiving an acoustic wave having a frequency of several hundred KHz in a single directivity is used for underwater acoustic imaging, acoustic sounding, sea floor exploration, etc. Can also be applied.

Embodiment 2 Embodiment 2 is an example in which the present invention is applied to an acoustic transmitter. FIG. 3 is a structural diagram of an acoustic transmitter showing Embodiment 2 of the present invention, and the figure is a side sectional view of the acoustic transmitter. FIG.
In the figure, reference numeral 16 denotes a housing, which is formed of a metal such as brass in the following shape. That is, the front end of the housing 16 is formed in a hemispherical shape, the rear end of the hemispherical shape is formed in a cylindrical shape, and is a shell-shaped container as a whole, and the rear is formed in an opening.

Reference numeral 11 denotes a single piezoelectric element for transmitting a sound wave.
The shape of the piezoelectric element 11 is formed in a spherical shape having the same shape as a cutout portion obtained by cutting out a part of the hemisphere at the tip end of the housing 16. Therefore, the piezo-electron 11 is fitted into the opening when a part of the hemisphere at the tip of the housing 16 is cut off (however, the piezo-electron 11
And the housing 16 are fitted in an electrically insulated state), so that the outer shape of the transmitter can be formed into a shell shape.

The reason why the shape of the piezo-electrons 11 is made spherical is to make the transmission beam a desired directivity with a single piezo-electron. This is because the rear housing is used as a ball baffle. Both electrodes (positive electrode and negative electrode) of the piezoelectric element 11 are connected to respective conductors of the cable 13 via signal connection lines 14.

Reference numeral 12 denotes a rubber material layer.
As in the case of the first embodiment, a material having a small amount of compressive strain when pressure is applied and having a large attenuation coefficient during sound wave propagation (for example, the urethane rubber material) is used. The thickness of the rubber material layer is determined so that the attenuation when the sound wave propagates in the rubber material layer has a predetermined value.
This means that the length of the cylindrical portion of the housing 16 is designed so that the thickness of the rubber material layer 12 is sufficient to attenuate the sound waves. It was.

In FIG. 3, the urethane rubber material is used as the rubber material layer 12, and the electrodes of the piezoelectric element 11 and the cable 1 are used.
After the connection with each of the signal connection lines 14 of No. 3, this material was filled into the inside of the housing 16 from the rear surface of the piezoelectric element 11 to one end of the cable 13. As a result, the ratio of the front and rear transmission sensitivities can be set to a predetermined value. The front and end faces of the piezoelectric element 11 are covered with a watertight molding material 15 so that the piezoelectric element 11 is electrically insulated, and the watertight molding material 15 is bonded to the front end of the housing 16.

The operation of the acoustic transmitter shown in FIG. 3 will be described. When an excitation voltage is applied to the piezoelectric element 11 from outside via the cable 13 and the signal connection line 14, the piezoelectric element 11 vibrates to generate a sound wave. A sound wave emitted from the piezoelectric element 11 toward the front side of the illustrated transmitter is a watertight molding material 15 (for example, rubber material).
However, since the thickness of the water-tight molding material 15 is small, the attenuation is small, and most of the water-tight molding material 15 propagates in the front direction. On the other hand, a sound wave radiated from the piezoelectric element 11 toward the rear surface of the illustrated transmitter is attenuated by passing through a rubber material layer 12 provided with a sufficient thickness so as to obtain a sufficient attenuation. Is extremely small. Therefore, the ratio of the front and rear transmission sensitivities can be set to a predetermined value.

The features of the structure of the acoustic transmitter of FIG. 3 will be described in comparison with those of the prior art. Conventionally, in this type of unidirectional acoustic transmitter, a backing layer made of a metal layer is provided on the back surface of the piezoelectric element to prevent sound waves from being emitted to the back surface, and to transmit a wave with a larger amplitude to the front surface by that amount. Is used. However, if the back surface of the piezoelectric element 11 is not flat as shown in FIG. 3, it is difficult to make the metal layer adhere to the piezoelectric element with an appropriate thickness, and the backing effect is obtained in the part that is not adhered. For example, the unidirectional performance of the transmitter is deteriorated. Furthermore, since the part that is not brought into close contact becomes an air chamber and is inherent in the transmitter, in an environment where pressure is applied, such as in the deep sea, the air chamber is compressed and the transmitter causes pressure destruction. There was a problem.

In contrast, in the configuration shown in FIG. 3, the sound wave is attenuated, and the rubber material layer 12 such as urethane rubber having a small amount of compressive strain due to the application of pressure is brought into close contact with the back surface of the piezoelectric element 11 to provide a sufficient pressure. Since it is provided at the rear only by the thickness, FIG.
Even if the transmitter is used in the deep sea or the like, pressure rupture due to water pressure does not occur, and the radiated sound wave backward from the piezoelectric element 11 is sufficiently attenuated, whereas the radiated sound wave forward is not attenuated. A transmitter having a sufficiently large front-to-back ratio of the acoustic transmission sensitivity can be configured. Furthermore, since a metal plate is not used on the back surface of the piezoelectric element as in the conventional case, the shape of the piezoelectric element 11 is not limited to a flat surface, and any shape including a curved surface or the like can be used to optimize the transmission sensitivity and directivity. Has the flexibility to design the piezo-electrons.

The acoustic transmitter having the configuration shown in FIG. 3 can be applied to, for example, an acoustic source (corresponding to an optical light source) of an underwater video apparatus, and can be used without trouble even in the deep sea where water pressure is required. Can be used. In particular, the configuration of FIG. 3 is effective when a transmitter is configured using piezo-electrons such as a curved surface that is not flat to optimize the transmission sensitivity and directivity. In addition to the above-mentioned underwater acoustic image, the transmitter of the configuration shown in Fig. 3 which has the water pressure resistance of transmitting acoustic waves with a frequency of several hundred KHz with unidirectionality is applicable not only to the underwater acoustic image but also to the sea floor exploration etc. can do.

[0029]

As described above, according to the present invention, in an acoustic wave receiver having a piezoelectric element and a rubber material layer provided on the rear side of the piezoelectric element, the rubber material layer has a pressure A material having a small amount of compressive strain at the time of application and a large attenuation coefficient at the time of sound wave propagation is used, and the rubber is used so that the amount of attenuation when the sound wave propagates through the rubber material layer of the material used becomes a predetermined value. Since the thickness of the material layer is set, it is possible to configure so that the front-to-back ratio of the acoustic wave receiving sensitivity becomes a predetermined value.

According to the present invention, a plurality of piezo-electrons, a signal extraction board for interconnecting each electrode of the plurality of piezo-electrons and each conductor of a signal output cable via an internal pattern wiring, In the acoustic receiver having a rubber material layer provided on the back side of the take-out substrate, the material of the rubber material layer is:
A material having a small amount of compressive strain at the time of applying pressure and having a large attenuation coefficient at the time of sound wave propagation is used so that the amount of attenuation at the time of sound wave propagation in the rubber material layer of the used material becomes a predetermined value. Since the thickness of the rubber material layer is set, the front-to-back ratio of the acoustic reception sensitivity can be configured to have a predetermined value, and the directivity pattern can have a desired shape.

According to the present invention, in an acoustic transmitter having a piezoelectric element and a rubber material layer provided on the rear side of the piezoelectric element, the material of the rubber material layer has a compression strain when a pressure is applied. A material having a small amount and a large attenuation coefficient at the time of sound wave propagation is used, and the thickness of the rubber material layer is set so that the amount of attenuation when the sound wave propagates through the rubber material layer of the used material becomes a predetermined value. Is set, so that the front-to-back ratio of the acoustic transmission sensitivity can be set to a predetermined value, and the piezo-electrons that transmit the sound waves in an arbitrary shape to optimize the transmission sensitivity and directivity can be formed. can do.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an acoustic receiver according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a measurement example of the directional characteristics of the acoustic receiver in FIG. 1;

FIG. 3 is a configuration diagram of an acoustic transmitter according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating the structure of the acoustic receiver disclosed in the known document 1 and when a water pressure is applied.

FIG. 5 is an explanatory diagram of the structure of the acoustic receiver disclosed in the known document 2 and its problems.

[Explanation of symbols]

 1,11,21 Piezoelectric 2 Signal extraction board 3,13,23 Cable 4,12,26 Rubber material layer 5,15,25 Watertight molding material 6 Epoxy resin 14 Signal connection line 16 Housing 22 Kirk rubber 24 Signal extraction line 27 Metal layer

Claims (8)

[Claims] 1. An acoustic receiver mainly receiving a sound wave arriving from the front of a piezoelectric element and comprising a piezoelectric element and a rubber material layer provided on the rear side of the piezoelectric element, wherein the material of the rubber material layer is Uses a material having a small amount of compressive strain at the time of applying pressure and a large attenuation coefficient at the time of sound wave propagation, and a predetermined amount of attenuation at the time of sound wave propagation in the rubber material layer of the used material. The acoustic receiver according to claim 1, wherein the front-to-back ratio of the acoustic reception sensitivity is set to a predetermined value by setting the thickness of the rubber material layer as described above. 2. A plurality of piezo-electrons, which mainly receive a sound wave arriving from the front of each piezo-electron, and respective electrodes of the plurality of piezo-electrons and respective conductors of a signal output cable are interconnected via internal pattern wiring. In the acoustic receiver having a signal extraction board connected to the signal extraction board and a rubber material layer provided on the rear side of the signal extraction board, the material of the rubber material layer has a small amount of compressive strain when pressure is applied and a sound wave. By using a material having a large attenuation coefficient at the time of propagation, and by setting the thickness of the rubber material layer so that the amount of attenuation when a sound wave propagates in the rubber material layer of the used material becomes a predetermined value. An acoustic wave receiver characterized in that the front-to-back ratio of the acoustic wave reception sensitivity has a predetermined value. 3. The acoustic receiver according to claim 1, wherein a material of the rubber material layer is a urethane rubber material. 4. The method according to claim 1, wherein the piezo-electrons or the incoming sound waves received by each of the piezo-electrons is a sound wave having a frequency of several hundred KHz. Acoustic receiver. 5. An acoustic transmitter that mainly transmits a sound wave in front of a piezoelectric element and includes a piezoelectric element and a rubber material layer provided on the rear side of the piezoelectric element, wherein the material of the rubber material layer is: A material having a small amount of compressive strain at the time of applying pressure and having a large attenuation coefficient at the time of sound wave propagation is used so that the amount of attenuation at the time of sound wave propagation in the rubber material layer of the used material becomes a predetermined value. An acoustic wave transmitter characterized in that the thickness of the rubber material layer is set so that the front-to-back ratio of the wave transmission sensitivity becomes a predetermined value. 6. The acoustic transmitter according to claim 5, wherein a material of the rubber material layer is a urethane rubber material. 7. The acoustic wave transmitter according to claim 5, wherein the piezoelectric element for transmitting the sound wave has a sound wave transmission surface formed by a surface other than a plane. 8. The acoustic wave transmitter according to claim 5, wherein the sound wave transmitted by the piezoelectric element is a sound wave having a frequency of several hundred KHz.