JPH06269090A - Piezoelectric ultrasonic wave transmitter-receiver - Google Patents

Abstract

(57) [Summary] A horn 18 provided with a vibration case 15 having a ring-shaped piezoelectric ceramic element 11 adhered thereto and having an airtightness, and a horn 18 arranged in front of the vibration case 15.
Thereby forming a vibration space 19 having a shape substantially equal to the outer contour of the piezoelectric ceramic element 11 and positioned in front of the piezoelectric ceramic element 11.
Of the piezoelectric supersonic wave having a shape substantially equal to the inner contour of the horn 18 and having an opening 19a located in front of the vibration space 19 and a convex sound wave reflection surface 19b located in front of the opening 19a. Sound wave transceiver. [Effect] It is possible to easily apply an acoustic load to the diaphragm of the vibration case 15, facilitate acoustic matching with air, and increase the transmitted sound pressure in air. Further, the S / N ratio can be increased, and a long-distance object can be accurately detected. Further, it is possible to prevent heat generation and damage of the piezoelectric ceramics element 11, and it is possible to improve energy conversion efficiency. Furthermore, the environment resistance can be maintained, and the reliability can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ultrasonic wave transmitter / receiver using a piezoelectric ceramic element, and more particularly to a piezoelectric ultrasonic wave transmitter / receiver used for obstacle detection and distance measurement.

In the following description, acoustic impedance means a ratio of sound pressure to volume velocity.

[0003]

2. Description of the Related Art Piezoelectric ultrasonic transducers are also called ultrasonic sensors or ultrasonic microphones and have been used in many fields. FIG. 6 is a cross-sectional view schematically showing the simplest construction of this type of transceiver. A conductive thin plate is used for the case main body 32, the peripheral edge portion is bent and formed, and a lid 33 is bonded and fixed to the opening side of the case main body 32.
A case 34 having a closed structure is constituted by 3 and 3. A piezoelectric ceramic element 31 formed in a substantially disk shape is adhered to the inner central flat portion of the case body 32, and the piezoelectric ceramic element 31 and the case body 32 are connected to the lead wire 3 respectively.
The piezoelectric ultrasonic transducer 30 is connected to the lead terminals 35a and 35b via 6a and 36b, and the case 34 and the piezoelectric ceramics element 31 and the like constitute the piezoelectric ultrasonic transducer 30. When an AC voltage is applied to the piezoelectric ceramics element 31 through the lead terminals 35a and 35b, the piezoelectric ceramics element 31 expands and contracts, and the expansion and contraction causes a bending motion in the case body 32 to generate a sound wave. The light is emitted in the direction of arrow A in the figure.

FIG. 7 is a sectional view schematically showing another piezoelectric ultrasonic wave transmitter / receiver 40 which has been conventionally used. In the figure, reference numeral 42 denotes a case body. The case main body 42 is made of a material having a large acoustic impedance and is formed into a substantially cylindrical shape having a ceiling 42a. A lid 43 is adhered and fixed to the opening 42b side of the case main body 42. The lid 43 and the lid 43 form a case 44 having a closed structure. Further, a disc member 47 formed of a material having a low acoustic impedance is bonded to the ceiling portion 42a of the case body 42. A piezoelectric ceramic element 41 formed in a substantially disc shape is adhered to a central flat portion in the case main body 42, and electrodes 41a and 41b formed on both surfaces of the piezoelectric ceramic element 41 are connected via lead wires 46a and 46b, respectively. Connected to the lead terminals 45a and 45b, and the case 44 and the piezoelectric ceramic element 4 are connected.
A piezoelectric ultrasonic wave transmitter / receiver 40 is configured by 1 and the like. When an AC voltage is applied to the piezoelectric ceramics element 41 through the lead terminals 45a and 45b, the piezoelectric ceramics element 41 expands and contracts, and the expansion and contraction causes the case body 42 to bend and vibrate. The sound waves are propagated to the air through the member 47, and sound waves are emitted in the direction of arrow B in the figure (Actual exploitation 62-17).
No. 7198).

FIG. 8 is a cross-sectional view schematically showing a piezoelectric type ultrasonic wave transmitter / receiver 50 with a horn which has been conventionally used. In the drawing, 55 is formed in a substantially hollow cylindrical body shape using a conductive thin plate. It shows the case that was done. A piezoelectric ceramic element 51 formed in a substantially disc shape is formed at a substantially central portion of the case 55.
Are adhered to each other, and the piezoelectric ceramics element 51 is held in the case 55 by using a support tool 54. Further, a conical horn 53 having a linear shape in cross section is disposed on the upper surface of the piezoelectric ceramic element 51, and one opening 57a and a plurality of sound emission holes 57b are formed on the upper surface of the case 55 above the conical horn 53. A parabolic horn 58 having a curved surface convex downward from the side surface of the case 55 is formed. The lead terminals 56a and 56b are fixed to the lower portion of the case 55, and
6a and 56b are connected to the piezoelectric ceramics element 51 via lead wires, and the case 55, the piezoelectric ceramics element 51, the parabolic horn 58, and the like constitute a piezoelectric ultrasonic transducer 50. And lead terminal 5
When an AC voltage is applied to the piezoelectric ceramics element 51 through 6a and 56b, the piezoelectric ceramics element 51 expands and contracts to generate vibrations, which are generated by the conical horn 53.
Sound waves are emitted from the parabolic horn 58 in the direction of arrow C in the figure after propagating to the air via the opening 57a and the sound output hole 57b (Japanese Patent Laid-Open No. 58-85699). Issue).

[0006]

In recent years, for obstacle detection,
There is an increasing demand for accurate detection of longer distances using sensors for distance measurement, etc. Therefore, the sound pressure of ultrasonic waves transmitted is high, the S / N ratio is high, and the structure is hermetic. There is a need for piezoelectric ultrasonic transducers that have environmental resistance.

In the piezoelectric ultrasonic wave transmitter / receiver 30 shown in FIG. 6, the case 34 has a hermetically sealed structure and is environmentally resistant. However, since the density of air as a medium is smaller than that of the piezoelectric ceramics element 31, it is difficult to apply an acoustic load to the air, and the vibration energy of the case 34 cannot be sufficiently propagated to the air. There was a problem that could not be increased. Further, if the input energy is increased to increase the sound pressure, there is a problem that the piezoelectric ceramic element 31 may generate heat or be damaged.

Further, the piezoelectric ultrasonic transducer 4 shown in FIG.
In No. 0, the case 44 has a sealed structure and has environmental resistance. Further, the disk member 47 having a low acoustic impedance is adhered onto the case 44 to improve the acoustic matching to the air to some extent, but there is still a problem that the sound pressure level of ultrasonic waves is insufficient. It was

The piezoelectric ultrasonic wave transmitter / receiver 5 shown in FIG.
0, the conical horn 53 and the parabolic horn 58 are provided, or the opening 57a and the sound emitting hole 5 are provided.
7b is formed and some improvement in acoustic matching to air is achieved. However, the sound pressure level of the ultrasonic waves is still insufficient, and the opening 57a and the sound emitting hole 57b are not included.
Due to this, there is a problem that the sealed structure is not formed and the environment resistance is impaired.

The present invention has been made in view of the above problems, and can increase the sound pressure of ultrasonic waves to be transmitted, increase the S / N ratio, and accurately detect long distances. It is an object of the present invention to provide a piezoelectric ultrasonic transducer that can be manufactured and can maintain environment resistance with a closed structure.

[0011]

In order to achieve the above object, a piezoelectric ultrasonic transducer according to the present invention comprises a vibration case having a ring-shaped piezoelectric ceramic element bonded thereto and having a hermeticity, and the vibration case. A horn disposed in front of the piezoelectric ceramics element, the horn having a shape substantially equal to the outer contour of the piezoelectric ceramics element, and forming a vibration space located in front of the piezoelectric ceramics element. It is characterized in that an opening having a shape substantially equal to the contour and located in front of the vibrating space and a convex sound wave reflecting surface located in front of the opening are formed on the horn.

[0012]

[Function] The piezoelectric ceramic element as the vibration source is
The density is extremely high with respect to air as a sound wave propagation medium. Therefore, when the piezoelectric ceramic element emits a sound wave, the acoustic load received from the air is extremely small, and therefore the energy used as the sound wave is small.

In order to solve this problem, the present inventors conducted a vibration measurement test using the apparatus shown in FIG. 5 (a). In the figure, reference numeral 12 indicates a disk-shaped diaphragm, and the diaphragm 12 is an internal diaphragm 12a as shown in FIG. 5B.
And the external diaphragm 12b. A ring-shaped piezoelectric ceramic element 11 is bonded to the lower surface of the external diaphragm 12b to form a bimorph structure 24, and the outer peripheral portion of the bimorph structure 24 is constrained and held by a clamp 25 or the like. When the piezoelectric ceramic element 11 is vibrated by energizing the device 20 configured as described above, the vibration has a small amplitude in the outer diaphragm 12b portion and a large amplitude in the inner diaphragm 12a portion as shown by the dotted line in the figure. Was obtained. In the device in which the ring-shaped piezoelectric ceramics element 11 is bonded to the vibration plate 12 as described above, acoustic load is easily applied because the internal vibration plate 12a portion is light, and the transmitted sound pressure in the air is increased because the amplitude is large. It becomes easy to increase. On the other hand, since the piezoelectric ceramic element 22 provided on the outer peripheral portion has a small amplitude, heat generation and damage of the piezoelectric ceramic element 22 are reduced,
The reliability can be improved and the energy conversion efficiency can be improved.

According to the piezoelectric ultrasonic transducer of the present invention, it is provided with a vibration case having a ring-shaped piezoelectric ceramic element adhered thereto and having a hermeticity, and a horn arranged in front of the vibration case. With the horn, a vibration space having a shape substantially equal to the outer contour of the piezoelectric ceramic element and located in front of the piezoelectric ceramic element is formed,
Since an opening having a shape substantially equal to the inner contour of the piezoelectric ceramic element and located in front of the vibrating space and a convex sound wave reflecting surface located in front of the opening are formed on the horn. The acoustic load is likely to be applied to the diaphragm of the vibrating case inside the ring-shaped piezoelectric ceramic element, the amplitude is increased, and acoustic matching with air is facilitated. Further, since the opening of the horn is formed in front of the vibration case inside the piezoelectric ceramic element and the sound wave reflection surface is gradually widened, acoustic matching with air can be more easily achieved. The sound pressure of can be further increased. As a result, the S / N ratio is increased, and it is possible to accurately detect a long distance object. Further, since the outer peripheral portion of the piezoelectric ceramic element is constrained by the inner peripheral surface of the horn,
A vibration mode in which the vibration of the piezoelectric ceramic element is suppressed is achieved, heat generation and damage are prevented, and acoustic efficiency can be increased. Further, since the vibrating case is formed in a hermetically sealed structure, environmental resistance is maintained and the reliability of the piezoelectric ultrasonic wave transmitter / receiver can be improved.

[0015]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of piezoelectric ultrasonic transducers according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view schematically showing a piezoelectric ultrasonic transducer having a resonance frequency of about 30 kHz according to the embodiment, and 11 in the drawing denotes a piezoelectric ceramic element. The piezoelectric ceramic element 11 is made of a material SPEM-6F, and is formed into a ring shape having an outer diameter of about 14 mm, an inner diameter of about 8 mm, and a thickness of about 1.0 mm. The diaphragm 12 is made of stainless steel and has a diameter of 30.
The piezoelectric ceramics element 11 is bonded to the lower surface of the vibration plate 12 using an epoxy adhesive agent. Further, a case body 13 having a substantially cylindrical shape is adhered and fixed to the outer peripheral portion of the diaphragm 12, and a substantially disc-shaped lid 14 is adhered and fixed to the lower portion of the case body 13. The case 12, the case body 13 and the lid 14 constitute a vibration case 15 having a hermetically sealed structure. Lead terminals 16a and 16b are fixed to the lid body 14, the lead terminal 16a is connected to the piezoelectric ceramic element 11 via a lead wire 17a, and the lead terminal 16b is connected to the diaphragm 12 via a lead wire 17b. . On the other hand, a horn 18 is arranged on the vibrating case 15, and the horn 18 is made of aluminum and is formed into a substantially cylindrical shape having an outer diameter of about 30 mm and a height of about 21 mm. A vibration space 19 having a height of approximately 1.0 mm and a height H of approximately 14 mm is formed. The vibration space 19 is ± 0 mm above the outer diameter portion of the piezoelectric ceramic element 11.
It is arranged with the tolerance of. An opening 19a having a diameter of about 8 mm is formed in the center of the upper portion of the vibration space 19, and the opening 19a is arranged above the inner diameter of the piezoelectric ceramic element 11 (or the vibration plate 12a) with a tolerance of ± 0 mm. .
Further, a sound wave reflecting surface 19b is formed above the opening portion 19a, and the sound wave reflecting surface 19b is formed above the opening portion 19a in a curved shape having a convex shape in cross section. The horn 18 and the vibrating case 15 are bonded and fixed to the horn lower end surface 18a with an epoxy-based adhesive to form the piezoelectric ultrasonic transducer 10.

The results of measuring the transmitted sound pressure using the piezoelectric ultrasonic wave transmitter / receiver 10 thus constructed under the conditions of input of 30 cm × 10 Vrsm will be described below. As a comparative example, the conventional piezoelectric ultrasonic transducer 30 shown in FIG. 6 is used.
Was used.

FIG. 2 is a curve diagram showing the measurement result of the transmitted sound pressure. The curve (a) is the curve (b) in the case of the embodiment.
Indicates the case of the comparative example. As is clear from this figure, the transmitted sound pressure is about 120 dB in the case of the embodiment.
It is possible to raise the effective sound pressure level by about 2 dB compared to 112 dB (compared to our company) in the case of the comparative example.
I was able to increase it more than twice.

Piezoelectric ultrasonic transducer 10 according to this embodiment.
Makes it possible to easily apply an acoustic load to the vibration case 15 inside the ring-shaped piezoelectric ceramics element 11, increase the amplitude, and easily achieve acoustic matching with air. Further, since the opening 19a of the horn 18 is formed in front of the vibration case 15 inside the piezoelectric ceramic element 11, and the sound wave reflection surface 19b is gradually widened, acoustic matching with air can be further facilitated. Therefore, the sound pressure in the air can be further increased. As a result, the S / N ratio can be increased, and an object at a long distance can be accurately detected. Further, since the outer peripheral portion of the piezoelectric ceramics element 11 is constrained by the inner peripheral surface 18a of the horn, and the vibration mode that suppresses the vibration of the piezoelectric ceramics element 11 is set, heat generation and damage can be prevented, and acoustic efficiency is increased. You can Further, since the vibration case 15 is formed in a hermetically sealed structure, it is possible to maintain environment resistance and improve the reliability of the piezoelectric ultrasonic wave transmitter / receiver 10.

In the embodiment, the case where the resonance frequency is 30 kHz and the thickness H (FIG. 1) of the vibration space 19 is about 1 mm has been described. However, as shown in FIG. When the thickness t is 2 mm and 0.5 mm, it is possible to obtain substantially the same effect as that of the embodiment.

Further, in the embodiment, the tolerance of the vibration space 19 and the opening 19a is set to ± 0 mm. However, as shown in FIG. 4, the tolerance of the vibration space 19 and the opening 19a is ± 10% of each dimension. Within the range, it is possible to obtain substantially the same effect as in the case of the embodiment.

In the embodiment, stainless steel was used as the material of the diaphragm 12, but as another embodiment, aluminum alloy such as duralumin, which has a lower specific gravity, titanium,
When a titanium alloy or the like is used, higher acoustic pressure can be obtained because the acoustic impedance becomes smaller than that of the examples.

In the embodiment, the piezoelectric ceramic element 1 is also used.
As the first example, a hard material compatible with continuous input is used, but as another embodiment, when used in a pulse or when continuous input is not used, the voltage sensitivity can be increased by using a soft material, and the bimorph type is used. It is possible to obtain higher-performance transmission / reception characteristics by using the element.

[0023]

As described in detail above, in the piezoelectric ultrasonic transducer according to the present invention, a vibrating case having a ring-shaped piezoelectric ceramic element adhered thereto and having a hermeticity is provided in front of the vibrating case. A horn that is disposed, and that has a shape that is substantially the same as the outer contour of the piezoelectric ceramic element and that forms a vibrating space located in front of the piezoelectric ceramic element; The ring-shaped piezoelectric ceramics element has substantially the same shape, and an opening located in front of the vibration space and a convex sound wave reflection surface located in front of the opening are formed in the horn. The acoustic load can be easily applied to the diaphragm of the vibrating case on the inside of the chamber, and the amplitude can be increased to facilitate acoustic matching with the air. Can. Further, since the opening of the horn is formed in front of the vibration case inside the piezoelectric ceramic element and the sound wave reflection surface is gradually widened, acoustic matching with air can be more easily achieved. The sound pressure in the air can be further increased. As a result, the S / N ratio can be increased, and an object at a long distance can be accurately detected. Further, since the outer peripheral portion of the piezoelectric ceramic element is constrained by the inner peripheral surface of the horn, a vibration mode in which the vibration of the piezoelectric ceramic element is suppressed can be prevented, and heat generation and damage can be prevented.
The acoustic efficiency can be increased. Further, since the vibrating case is formed in a hermetically sealed structure, it is possible to maintain the environment resistance and improve the reliability of the piezoelectric ultrasonic transducer.

[Brief description of drawings]

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

FIG. 2 is a curve diagram showing the measurement result of transmitted sound pressure, wherein curve (a) shows the case of the example and curve (b) shows the case of the comparative example.

FIG. 3 is a curve diagram showing the relationship between the thickness H of the vibration space and the radiated sound pressure.

FIG. 4 is a curve diagram showing the relationship between the vibration space and the tolerance of the opening and the transmitted sound pressure.

5A is a cross-sectional view schematically showing a vibration plate to which a ring-shaped piezoelectric ceramic element is bonded and a curve diagram showing a result of amplitude distribution measurement by a dotted line, and FIG. The division model at the time of designing a ring-shaped piezoelectric ceramics element is shown.

FIG. 6 is a cross-sectional view schematically showing the simplest of the conventional piezoelectric ultrasonic wave transmitters / receivers.

FIG. 7 is a cross-sectional view schematically showing another conventionally used piezoelectric ultrasonic transducer.

FIG. 8 is a cross-sectional view schematically showing a conventional piezoelectric ultrasonic wave transmitter / receiver with a horn.

[Explanation of symbols]

 10 Piezoelectric Ultrasonic Transducer 11 Piezoelectric Ceramics Element 15 Vibration Case 18 Horn 19 Vibration Space 19a Opening 19b Sound Reflecting Surface

Claims (1)

[Claims] 1. A vibrating case having a ring-shaped piezoelectric ceramic element adhered thereto and having a hermeticity, and a horn arranged in front of the vibrating case, and the horn substantially equals the outer contour of the piezoelectric ceramic element. Have a shape,
An oscillating space located in front of the piezoelectric ceramic element is formed and has a shape substantially equal to the inner contour of the piezoelectric ceramic element, and an opening located in front of the oscillating space and a convex shape located in front of the opening. And a sound wave reflecting surface thereof are formed on the horn.