JP3379073B2 - Ultrasonic transducer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave having a function of radiating ultrasonic waves into the air and receiving ultrasonic waves radiated into the air. It relates to a transducer. 2. Description of the Related Art As disclosed in Japanese Patent Publication No. 6-17897, an ultrasonic transducer is used for a gas concentration detecting device or the like. The ultrasonic transducer generally has a structure in which a piezoelectric element plate is joined to a metal or plastic bottomed case, and the bottom surface of the case is used as a wave transmitting / receiving surface. [0003] Recently, a short-distance type ultrasonic wave which receives a reflected wave from a reflecting surface close to a transmitting / receiving surface of an ultrasonic transmitter / receiver and performs required measurement. Demand for transducers has increased. In such applications, the most problematic measurement error is the interference between the reverberation wave of the transmitted signal and the received signal. Therefore, at close distances, the reverberation characteristics determine its reliability. In such applications, the ratio between the received signal and the reverberation voltage is usually 1/10 to 1/100 (20 dB to 40 dB). Things are sought. For example, in the above-described gas concentration detecting apparatus for measuring the gas concentration using the propagation time of the ultrasonic wave, in order to avoid the reverberation wave of the transmitted signal and the interference of the received signal, a conventional transmission / reception system is used. It is necessary to increase the distance between the wavefront and the reflection surface, and the apparatus has been enlarged. However, improvement in reverberation characteristics is expected to reduce the size. On the other hand, in order to improve such reverberation characteristics, a bottomed cylindrical case is formed of an acoustic matching layer, and a piezoelectric element plate having electrode layers formed on the front and back surfaces is joined to the bottom of the case , and the inside of the case is formed. ultrasonic configuration in which embedded the damping layer
A transducer has been proposed. By the way, in such a configuration, when the characteristics were tested, the reverberation characteristics were not always sufficiently improved. This was found to be due to the effect of reverberation due to the peripheral wall of the acoustic matching layer. An object of the present invention is to provide an ultrasonic transducer capable of further improving reverberation characteristics and having a configuration optimal for application in an oily atmosphere, such as the above-described gas concentration detection device. Things. According to the present invention, an upper surface of a thin metal plate is coated with a resin thin film having excellent oil resistance and heat resistance.
Bonding the acoustic matching layer on the resin thin film, and further bonding the piezoelectric element plate which the electrode layer is formed on the front and back surfaces to the acoustic matching layer, sandwiching Tsubaen made of the metal sheet in the periphery is突成A piezoelectric joint, and a transmitting / receiving port is formed at the bottom center,
And a metal housing body having an upwardly open mounting cavity having an upper peripheral surface of the transmitting / receiving port as a locking surface, wherein the piezoelectric bonded body is formed in the mounting cavity, and a resin terminal terminal is formed from the upper end. The piezoelectric body is sequentially fitted inside, and the holding flange edge of the piezoelectric bonded body is held between the resin cylindrical body and the locking surface of the metal housing to expose the lower surface of the piezoelectric bonded body from the transmitting / receiving port. Further, while damping resin is injected into the resin cylinder to bury the upper portion of the piezoelectric joined body, and the terminal terminal,
An ultrasonic transducer, wherein the other end of a lead wire connected to an upper electrode layer of a piezoelectric element plate is connected. When an alternating voltage is applied to the piezoelectric element plate from an external circuit connected to the terminal terminal, an ultrasonic wave is radiated from the transmitting / receiving port, and a reflected wave is transmitted from the transmitting / receiving port to the piezoelectric joint. It is captured on the lower surface and detected by the piezoelectric element plate.
By detecting the reflection time, for example, the gas concentration in a gas atmosphere can be detected. In the above structure, the piezoelectric element plate is bonded to a thin metal plate via an acoustic matching layer, and the piezoelectric element plate and the acoustic matching layer are embedded in a damping resin, and the surrounding wall is formed. Division is separated. Therefore, the reflected wave received from the thin metal plate is suppressed as much as possible by the acoustic matching layer and detected by the piezoelectric element plate, and the reverberation wave from the peripheral portion is cut off by the damping resin. For this reason, the reverberation characteristics are significantly improved. Further, since the piezoelectric element plate is protected by a thin resin film having excellent oil resistance and heat resistance such as polyimide coated on a thin metal plate, the piezoelectric transducer is placed in an oily gas atmosphere. In this case, even if the oil component enters through the gap between the metal housing and the resin cylinder from the transmitting / receiving port, it is interrupted by the resin thin film, and problems such as deterioration of the piezoelectric transducer and insulation failure are caused. Does not occur. Further, the piezoelectric bonded body is held in a metal housing and a resin cylinder, and is sealed in a damping resin, thereby maintaining liquid tightness. FIG. 1 shows the configuration of an ultrasonic transducer 1 according to the present invention.
4 will be described with reference to FIG. Reference numeral 2 denotes a piezoelectric bonded body. As shown in an enlarged view in FIG. 4, a resin thin film of polyimide or the like having excellent oil resistance and heat resistance is formed on the upper surface side of a thin metal plate 3 made of copper, aluminum or the like. And a disk-shaped piezoelectric element plate on which a disc-shaped acoustic matching layer 5 is disposed on the resin thin film 4 and electrode layers 7a and 7b are formed on the acoustic matching layer 5 on the front and back surfaces. 6 are joined together, and a peripheral edge protruding from the disc-shaped acoustic matching layer 5 of the thin metal plate 3 is defined as a clamping flange edge 8. As described above, since the piezoelectric element plate 6 is supported by the metal thin plate 3, the mechanical strength is improved, and the holding of the holding flange edge 8 described below enables
The holding of the piezoelectric joined body 2 can be easily performed. The acoustic matching layer 5 is made of a foamable plastic material or a material obtained by mixing countless glass balloons with plastic. The thickness of the acoustic matching layer 5 is formed so as to correspond to １ ／ of the wavelength λ applied to the piezoelectric element plate 6. The outer diameter of the piezoelectric element plate 6 is smaller than the outer diameter of the acoustic matching layer 5. As shown in FIG. 4, the piezoelectric element plate 6
The electrode layer 7a located on the acoustic matching layer 5 side has its electrical lead-out end extended to the surface side, and the conductive wires 9a,
9b is connected to the electrode layers 7a and 7b on the upper surface side of the piezoelectric element plate 6. In the piezoelectric bonded body 2 having such a structure, a transmitting / receiving port 11 is formed in the center of the bottom portion, and the transmitting / receiving port 11 is provided inside.
Upwardly open mounting gap 14 with the peripheral upper surface as the locking surface 12
Is mounted in the metal housing 10 provided with The storage body 10 is made of aluminum, has an inner peripheral surface formed in a two-step shape, a mouth portion having a diameter larger than an inner diameter of a bottom portion, and a locking step surface 13 on an inner peripheral surface on the locking surface 12. Has formed. The diameter of the bottom is substantially equal to the diameter of the thin metal plate 3 of the piezoelectric joined body 2. Further, an annular groove is formed in the locking surface 12, and the O-ring 15 is fitted into the groove. The piezoelectric bonded body 2 is mounted in the mounting space 14 so that the holding flange 8 is positioned on the locking surface 12, and the center of the lower surface of the thin metal plate 3 of the piezoelectric bonded body 2 faces from the transmitting / receiving port 11. . After the piezoelectric joint 2 is mounted on the locking step 13, two terminal terminals 21a, 21b
Is embedded therein. The resin tubular body 20 has a mounting flange 22 on the lower edge, the inner diameter of the mounting flange 22 is substantially equal to the inner diameter of the wave transmitting / receiving port 11, and the outer diameter of the mounting flange 22 around the locking surface 12. A locking flange 23 which is set to be equal to the inner diameter of the bottom portion and which is mounted on the locking step 13
And the terminal terminals 21a, 2 are formed by molding.
The end of 1b protrudes from the upper end. The protruding ends of the terminal terminals 21a and 21b are bifurcated,
A connecting branch is bent outward from the crotch portion. By fitting the resin cylinder 20 inside, the clamping flange 8 of the piezoelectric joined body 2 is clamped between its lower end and the locking surface 12 of the metal housing 10. At this time, as described above, since the metal thin plate 3 is used, the mechanical strength or the degree of bending becomes appropriate, and the holding of the piezoelectric joined body 2 can be stably performed. The O-ring 15 further improves the liquid tightness. An aluminum fixed ring 30 is press-fitted onto the resin cylinder 20. That is, the fixed ring 30 is
A radial escape groove 31 is formed on the upper surface where the terminal terminals 21a and 21b are located, and the lower part thereof is formed in the housing 1
0, and the inner diameter is made equal to the outer diameter of the resin tubular body 20, and on the locking flange 23 of the resin tubular body 20, The lower small-diameter portion 32 is press-fitted between the cylindrical member 20 and the resin cylinder 20, whereby the holding members 8 are tightly held so as to tightly hold the holding flange edge 8 of the piezoelectric joined body 2. After the respective members are fixed in this manner, the ends of the lead wires 9 are drawn out, and the respective conductors 9a and 9b are connected by soldering between the crotches of the terminal terminals 21a and 21b. After the damping resin 3
5 is injected so that the upper surface of the metal sheet 3 of the piezoelectric joined body 2 is embedded in the damping resin 35. As the damping resin 35, a powder having a large specific gravity such as a ceramic powder such as lead titanate or lead zirconate titanate or a metal powder is mixed with a material having a large internal friction, such as a room temperature-curable silicone rubber or a urethane resin. And other materials. In the damping resin 35, the reverberation time becomes shorter as the acoustic impedance becomes larger (as the acoustic impedance of lead zirconate titanate becomes closer to about 30 × 10 ⁶ ). The terminal terminals 21a, 21b
May be configured such that the lower end protrudes inward from the inner peripheral surface of the resin-made cylindrical body 20, and the conductive wires 9 a and 9 b are connected to the lower end inside the resin-made cylindrical body 20. In the configuration, by injecting the damping resin 35, the connection portion is embedded in the damping resin 35. FIGS. 5 and 6 show an ultrasonic transducer 1 having such a configuration.
Is applied to a gas concentration detection device 40. The base portion 41 constituting the base of the gas concentration detecting device 40 has a reflecting surface 43 on the bottom surface, and a detecting gap 45 having an inlet 44a and an outlet 44b for detecting gas formed on the side surface. A mounting portion 46 for accommodating the ultrasonic transducer 1 on the detection gap 45;
A printed circuit board 47 is attached to one side surface.
The ultrasonic wave transmitter / receiver 1 housed in the mounting portion 46 has the wave transmitting / receiving port 11 downward, and the wave transmitting / receiving surface of the thin metal plate 3 is opposed to the reflecting surface 43 via the detection gap 45. . On the other hand, the terminal terminals 21a, 21b
2, the conductive pieces 48, 48 connected to the required electric circuit of the printed circuit board 47 are electrically connected by soldering (FIG. 2).
reference). Further, the input / output electric circuit of the printed circuit board 47 is connected to a connection pin 50 inserted into the connector section 49 to enable electrical connection with an external device connected to the connector section 49. In the above configuration, the gas concentration detecting device 40
Has a total length of 80.7 mm. In such a configuration, the gas vaporized at the fuel inlet of the automobile or the like is supplied from the inlet 44a to the detection gap 4
5 and discharged from the outlet 44b. Then, the terminal pieces 21a, 21
When voltage is applied to the piezoelectric element plate 6 via
The ultrasonic wave is radiated toward the reflection surface 43 from the light. The reflected wave from the reflecting surface 43 is captured by the lower surface of the piezoelectric joined body 2 in the transmission / reception port 11, detected by the piezoelectric element plate 6, and the reflection time is calculated. Then, the concentration of the gas introduced into the detection gap 45 can be detected by the reflection time. In such a configuration, the piezoelectric element plate 6 of the ultrasonic transducer 1 is joined to the thin metal plate 4 via the acoustic matching layer 5, and the acoustic matching layer 5 is
Buried inside. For this reason, the reflected wave received from the metal thin plate 4 is detected by the piezoelectric element plate 6 with reverberation suppressed as much as possible by the acoustic matching layer 5. Therefore, as described above, even if the interval between the transmitting / receiving wave surface on the lower surface of the thin metal plate 3 and the reflecting surface 43 is short, the reflected wave can be detected by improving the reverberation characteristics, and such a configuration is useful. I have. Since the piezoelectric element plate 6 is protected by an oil-resistant and heat-resistant resin thin film 4 made of polyimide or the like coated on the metal thin plate 4, the piezoelectric transducer 6 is made of gasoline gas. No problem such as deterioration or insulation failure occurs even when the electrodes are placed in an oily gas atmosphere. Further, the piezoelectric bonded body 2 is held in the metal housing 10 and the resin cylindrical body 20 and is sealed in a damping resin 35 to maintain high mechanical strength and liquid tightness. It is easy to mount on the device, and furthermore, the terminal terminal 2
The electrical connection is facilitated via the printed circuit boards 1a and 21b. According to the present invention, an oil-resistant and heat-resistant resin thin film is coated on the upper surface side of a thin metal plate, an acoustic matching layer is provided on the resin thin film, and the acoustic matching layer is further provided on the acoustic matching layer. The piezoelectric element plate having the electrode layer formed on the front and back surfaces is joined to form a piezoelectric joined body,
The piezoelectric element plate is joined to the metal sheet via the acoustic matching layer,
Moreover, the piezoelectric element plate and the acoustic matching layer are embedded in the damping resin. For this reason, the reflected wave received from the metal thin plate is suppressed as much as possible by the acoustic matching layer is detected by the piezoelectric element plate, the reverberation characteristics are improved, even when used for short distance measurement, The transmitted signal and the received signal do not interfere with each other, and the size can be reduced by applying the present invention to a sensor that measures the liquid concentration and the temperature using the propagation time of the ultrasonic wave. Further, since the piezoelectric element plate is protected by an oil-resistant and heat-resistant resin thin film such as polyimide coated on a thin metal plate, even if the piezoelectric transducer is placed in an oily gas atmosphere. It is suitable for use in an oily atmosphere without causing problems such as deterioration and insulation failure. In addition, since the piezoelectric element plate is supported by a thin metal plate, the mechanical strength is improved, and the holding of the piezoelectric bonded body can be easily performed by holding the holding flange edge. Further, the piezoelectric bonded body is held in the metal housing and the resin cylinder and is sealed in a damping resin, and has high mechanical strength and liquid tightness. Further, the ultrasonic transducer can be electrically connected via the terminal terminal. Therefore, the device can be easily connected to a printed circuit board or the like, the device design is simplified, and the device is easily integrated. Therefore, various apparatuses to which the ultrasonic transducer according to the present invention is applied can contribute to downsizing and integration, and are particularly suitable for application to a liquid concentration detecting apparatus. Has an effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional side view of an ultrasonic transducer 1 of the present invention. FIG. 2 is a plan view of the ultrasonic transducer 1; FIG. 3 is an exploded perspective view of the ultrasonic transducer 1; FIG. 4 is an enlarged sectional view of the piezoelectric joined body 2. FIG. 5 is a vertical side view of the gas concentration detection device 40. FIG. 6 is a plan view showing a half of the gas concentration detection device 40 cut away. DESCRIPTION OF SYMBOLS 1 Ultrasonic wave transmitter / receiver 2 Piezoelectric joint 3 Metal thin plate 4 Resin thin film 5 Acoustic matching layer 6 Piezoelectric element plate 8 Holding flange edge 10 Metal housing 11 Transmitting / receiving port 12 Locking surface 14 Mounting gap 20 Resin cylinders 21a, 21b Terminal terminal 30 Fixed ring 35 Damping resin 40 Gas concentration detector 41 Base cylinder 43 Reflection surface 45 Detection gap 47 Printed circuit board

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiharu Ito 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi Japan Special Ceramic Industry Co., Ltd. (72) Inventor Haruo Yamamori 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi Japan Special (56) References JP-A-6-184 (JP, A) JP-A-60-208199 (JP, A) JP-A-58-7994 (JP, A) Jpn. JP, U) JP-A-2-101695 (JP, U) JP-B 6-17897 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 29/00-29/28 H04R 17/00 330-332

Claims (1)

(57) [Claims 1] An upper surface side of a metal thin plate is coated with a resin thin film having excellent oil resistance and heat resistance, and an acoustic matching layer is bonded on the resin thin film. A piezoelectric element plate in which an electrode layer is formed on the front and back surfaces is joined on the matching layer to form a piezoelectric joined body in which a holding flange edge made of the metal thin plate is formed on the periphery, and a transmitting / receiving port is provided in the center of the bottom. Formed, and a metal housing body provided with an upwardly open mounting space having an upper peripheral edge upper surface of the transmitting / receiving port as a locking surface, the piezoelectric bonded body in the mounting space,
A resin cylinder body having terminal terminals protruding from the upper end is sequentially fitted thereinto, and the clamping flange edge of the piezoelectric joint body is sandwiched between the resin cylinder body and the locking surface of the metal housing body to form the piezoelectric joint body. The lower surface is exposed from the transmitting / receiving port, and furthermore, damping resin is injected into the resin cylinder to embed the upper portion of the piezoelectric joined body, and is connected to the terminal terminal and the upper electrode layer of the piezoelectric element plate. An ultrasonic transducer, wherein the other end of the connected lead wire is connected.