JPH09331597A - Aerial ultrasonic wave sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aerial ultrasonic wave sensor by reducing mechanical restriction to an acoustic matching layer, not causing interference between ultrasonic waves from each part of the acoustic matching layer without the need for a large exciting force and enhancing heat dissipation so as to prevent fluctuation in a resonance point thereby obtaining a large sound pressure. SOLUTION: In the aerial ultrasonic wave sensor in which an ultrasonic wave is emitted in air from an ultrasonic wave vibrator 3 via an acoustic matching layer 1, the acoustic matching layer 1 is supported at ends of a plurality of cunti-levers 2 from the side with respect to an ultrasonic wave radiation axis A in axis symmetry and the canti-levers 2 includes the ultrasonic wave vibrator 3 in the 1st view point. The acoustic matching layer 1 is integrally formed from an ultrasonic wave radiation section 1A and a vibration delivery section 1B extended nearly at a right angle from the circumferential ridge of the ultrasonic wave radiation section 1A and whose tip is fixed and the ultrasonic wave vibrator 3 is fixed to the vibration delivery section 1B in the 2nd view point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aerial ultrasonic sensor that emits ultrasonic waves into the air from an ultrasonic transducer via an acoustic matching layer. An ultrasonic sensor in the air typically uses a piezoelectric element as an ultrasonic transducer, and emits the ultrasonic wave generated by the piezoelectric element into the atmosphere, or an ultrasonic wave reflected from or transmitted through the detection target. It is a detection device that receives a sound wave from the atmosphere into the piezoelectric element, and is used as, for example, a vehicle speed sensor that detects the vehicle speed, a back sonar that detects an obstacle behind the vehicle, or the like.

[0002]

2. Description of the Related Art When ultrasonic waves pass through an interface between different transmission media, the transmittance decreases as the difference in acoustic impedance between the media increases. The piezoelectric element is typically made of ceramics such as PZT and has a significantly higher acoustic impedance than the atmosphere. Even if the piezoelectric element tries to radiate directly into the atmosphere, the transmittance will be extremely small or total reflection will occur. The required sound pressure cannot be obtained.

Therefore, in an aerial ultrasonic sensor, an acoustic matching layer having an acoustic impedance intermediate between the piezoelectric element and the atmosphere is interposed to secure the transmittance so that a sound pressure necessary for practical use can be obtained. There is. An epoxy resin or the like is generally used as the matching layer. Also, Japanese Patent Application Laid-Open
In Japanese Patent Laid-Open No. -65795, in order to improve the output sound pressure, glass balloons (glass hollow particles) are mixed in the resin that constitutes the matching layer, and the acoustic matching layer is heated so that its elastic modulus is optimized. Or, the mixing amount of the glass balloon is increased toward the radiation surface side (atmosphere side) of the matching layer, and the acoustic impedance of the matching layer becomes a large value close to that of the piezoelectric element on the piezoelectric element side and close to the atmosphere on the atmosphere side. It is disclosed that the acoustic impedance is graded in the matching layer to a low value.

In these conventional aerial ultrasonic sensors, as shown in FIG. 1, an acoustic matching layer 11 made of resin containing glass balloon is fixed to a vibrator 13 and is also joined to a metal body 12. . Note that, in FIG. 1, other members such as a lead wire for operating the vibrator are omitted. The conventional airborne ultrasonic sensor having such a structure has a limit in improving the sound pressure in the following points.

(1) Since the acoustic matching layer is joined to the metal body with a relatively high rigidity and the mechanical restraint against displacement is large, vibration with a large amplitude is hindered. (2) If the outer diameter of the acoustic matching layer is increased in order to obtain a large amplitude, the ultrasonic waves emitted from each part of the acoustic matching layer interfere with each other and cancel each other out, so that a large sound pressure cannot be obtained.

(3) When the vibration force of the vibrator is increased to obtain a large amplitude, the amount of heat generated from the vibrator inevitably increases, and the resin that constitutes the material of the acoustic matching layer has a thermal conductivity. Since the temperature is low and the heat radiation from the vibrator is poor, the temperature tends to rise during operation, and as a result, the resonance point of the sensor as a whole tends to fluctuate.

[0007]

DISCLOSURE OF THE INVENTION The present invention reduces mechanical constraints on displacement of the acoustic matching layer, does not cause interference between ultrasonic waves from various portions of the acoustic matching layer, and requires a large excitation force. And improve heat dissipation to prevent resonance point fluctuations,
It is an object of the present invention to provide an aerial ultrasonic sensor capable of obtaining a large sound pressure.

[0008]

In order to achieve the above object, the aerial ultrasonic sensor of the present invention is an aerial ultrasonic sensor which emits ultrasonic waves into the air from an ultrasonic transducer through an acoustic matching layer. In the first aspect, the acoustic matching layer is supported at the ends of a plurality of cantilevers in axisymmetric manner from the side with respect to the ultrasonic radiation axis, and the cantilever includes an ultrasonic transducer. In the second aspect, the acoustic matching layer is integrally formed of an ultrasonic wave radiating portion and a vibration transmitting portion extending at a substantially right angle from the periphery of the ultrasonic wave radiating portion and having a fixed tip. An ultrasonic transducer is fixed to the portion.

According to the first aspect, since the acoustic matching layer is supported at the end of the cantilever including the ultrasonic vibrator, the vibration of the vibrator is enlarged and amplified by the cantilever according to the leverage principle. A large amplitude is obtained by being transmitted to the acoustic matching layer. Since it is supported at the end of the cantilever, there is no mechanical constraint on the displacement of the acoustic matching layer. Since a large amplitude can be obtained without increasing the outer diameter of the acoustic matching layer, the ultrasonic waves emitted from each part of the acoustic matching layer do not interfere with each other. Since a large amplitude can be obtained without increasing the deformation of the vibrator, the amount of heat generated from the vibrator does not increase and the resonance point does not change due to the temperature rise. Since the engaging portion between the cantilever including the oscillator and the acoustic matching layer is only the end portion of the cantilever, heat radiation from the oscillator is not hindered by the acoustic matching layer,
The heat dissipation is enhanced and the resonance point does not change due to the temperature rise.

According to the second aspect, since the tip of the vibration transmitting portion extending from the ultrasonic wave emitting portion of the acoustic matching layer is fixed and the vibrator is fixed to this vibration transmitting portion, the vibrator is fixed. The vibration of is also amplified by the principle of leverage and transmitted to ultrasonic radiation, and a large amplitude is obtained. Since the ultrasonic wave emitting portion itself of the acoustic matching layer is supported only in the peripheral portion connected to the vibration transmitting portion, there is no mechanical restraint on the displacement of the acoustic matching layer. Since a large amplitude can be obtained without increasing the outer diameter of the acoustic matching layer, the ultrasonic waves emitted from each part of the acoustic matching layer do not interfere with each other. Since the vibration transmitting portion of the acoustic matching layer is oriented almost at right angles to the ultrasonic wave emitting portion, the paths of the ultrasonic waves emitted from both do not intersect and no interference occurs. Since a large amplitude can be obtained without increasing the vibration force of the vibrator, the amount of heat generated from the vibrator does not increase,
The resonance point does not change due to the temperature rise. Since the oscillator is fixed only to the vibration transmitting part of the acoustic matching layer, it is possible to connect small oscillators in multiple stages and to fix only one end of the connected oscillator row to the vibration transmitting part. A large heat radiation surface with respect to the volume can be secured for the entire row, heat radiation performance is improved, and the resonance point does not change due to temperature rise.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the invention according to the first aspect, a cantilever is a vibrating plate made of a material having a smaller damping capacity than an acoustic matching layer, and an ultrasonic vibration fixed to at least one surface of the vibrating plate. It is also possible to adopt a mode in which it is configured with a child, or a mode in which the entire cantilever is configured with an ultrasonic transducer. A bimorph type piezoelectric element can be used as the ultrasonic transducer. In the case of the former mode, it is possible to increase the vibration amplifying / amplifying action by using a metal plate having a large elastic deformation as the vibration plate. In the case of the latter mode, the convex portion of the cantilever end can be fitted into the concave portion of the acoustic matching layer to support, and the convex portion of the cantilever end portion can be provided at the bottom of the concave portion of the acoustic matching layer. It is also possible to engage and support the tip of the line contact by line contact. In either support form, the sound pressure can be efficiently improved with an extremely simple structure. In particular, in the supporting mode by the engagement by line contact, since the engagement area between the acoustic matching layer and the vibrator is extremely small, the influence of vibration damping by the acoustic matching layer can be minimized.

In the invention according to the second aspect, the amplitude can be further increased by connecting the small vibrators in multiple stages.

[0013]

【Example】

[Embodiment 1] FIG. 2 shows a first example of the structure of an aerial ultrasonic sensor according to the first aspect of the present invention. In this structure, the acoustic matching layer 1 is arranged in the direction perpendicular to the ultrasonic radiation axis A from the direction perpendicular to the axis A.
1. The ultrasonic transducer 3 is fixed and supported symmetrically with respect to one end of the left and right two vibrating plates 2, and the ultrasonic transducer 3 is fixed to at least one surface of the vibrating plate 2. The other end of the diaphragm 2 on both sides is the body 4 respectively.
The vibration plate 2 constitutes a cantilever together with the ultrasonic vibrator 3. In the figure, other members including the lead wire for applying the operating voltage of the vibrator 3 are omitted.

The acoustic matching layer 1 is made of an epoxy resin, an epoxy resin containing glass balloons, or the like.
Is made of a lightweight metal plate such as aluminum or magnesium. The ultrasonic vibrator 3 is composed of, for example, a PZT ceramic piezoelectric element. The vibrator 3 expands and contracts in the left-right direction of the drawing (longitudinal direction of the diaphragm 2) to give the diaphragm 2 a bending displacement in the vertical direction of the drawing. The vibrators 3 provided on both sides of the vibration plate 2 can have the expansion and contraction displacements in opposite phases so as to form a bimorph type.

When an operating voltage is applied to the piezoelectric element 3 to vibrate it, the left and right diaphragms 2 vibrate vertically with the fixed end to the body 4 as a fulcrum. By setting the diaphragm 2 to have the maximum amplitude at the end supporting the acoustic matching layer 1,
At the supporting end, the vibration of the vibrator 3 is enlarged and amplified by the leverage principle, and the matching layer 1 vibrates with a large amplitude. At this time, the matching layer 1
Since the vibration impedance of the diaphragm 2 and the vibrator 3 that are other than the above is significantly different from the atmosphere, ultrasonic waves are substantially radiated into the atmosphere only from the matching layer 1. Do not interfere with each other.

Further, since the vibrator 3 is fixed to the metal vibrating plate 2 having good heat conduction, the heat dissipation is good and the resonance point does not fluctuate due to temperature rise. [Embodiment 2] FIG. 3 shows a second example of the structure of the aerial ultrasonic sensor according to the first aspect of the present invention. In this structure, the acoustic matching layer 1 is arranged in the direction perpendicular to the ultrasonic radiation axis A from the direction perpendicular to the axis A.
On the other hand, the object is supported by one end of two cantilever beams 2 on the left and right. Each of the left and right cantilevers 2 is composed of a bimorph type oscillator in which upper and lower ultrasonic oscillators 3 are bonded together.
Electrodes 3p are formed on the upper surface and the lower surface of the two ultrasonic transducers 3. However, the electrode 3p on the two bonding surfaces is shared by both. The phase of the expansion and contraction displacement of the vibrator 3 is set to the opposite phase as a bimorph type on the upper side and the lower side, but the upper side and the lower side of the left and right cantilever beams (bimorph type vibrator) 2 are in the order phase. It is set. Note that FIG.
Although not shown, the left and right ends of the left and right cantilevers 2 are fixed to fixing members similar to the body 4 shown in FIG. Also in FIG. 3, other members including the lead wire for applying the operating voltage of the vibrator 3 are omitted.

The matching layer 1 is formed with wedge-shaped recesses on the left and right, and the left and right cantilever beams 2 formed by the bimorph type vibrator 2 are formed.
The wedge-shaped convex portion formed at the end portion of is fitted into this concave portion and fixed by adhesion. The structure of this embodiment is simpler than that of the first embodiment because the matching layer 1 is directly supported by the vibrator 3 without using a diaphragm made of metal or the like.

When an actuating voltage is applied to the piezoelectric element 3 through the electrode 3p to vibrate, the left and right cantilever beams (bimorph type vibrators) 2 vertically vibrate with a fixed end (not shown) as a fulcrum. Since the cantilever 2 has the maximum amplitude at the end supporting the acoustic matching layer 1, the vibration of the bimorph oscillator 2 (a pair of antiphase oscillators 3) is expanded and amplified at the supporting end by the leverage principle. The matching layer 1 vibrates with a large amplitude.

At this time, since the cantilever beam (bimorph type oscillator) 2 which is the vibrating portion other than the matching layer 1 has a large acoustic impedance different from that of the atmosphere, ultrasonic waves are substantially transmitted only from the matching layer 1 to the atmosphere. Since they are radiated, the ultrasonic waves from the vibrating parts do not interfere with each other. Further, since the vibrator 3 radiates heat through the electrode 3p made of metal or the like having good heat conductivity, the resonance point does not change due to the temperature rise. [Third Embodiment] FIG. 4 shows a third example of the structure of the aerial ultrasonic sensor according to the first aspect of the present invention. This structure is almost the same as the structure of the second embodiment shown in FIG. 3, except that the tip of the wedge-shaped convex portion formed at the end of the cantilever 2 composed of the ultrasonic transducer 3 is attached to the acoustic matching layer 1. The difference is that the bottoms of the wedge-shaped recesses formed on the left and right are brought into line contact with each other to be engaged and supported. That is, the engagement between the two is performed only at the line T, and a gap G is provided between the wedge slopes other than the line T. This further reduces the mechanical restraint of the acoustic matching layer 1 with respect to the vibration displacement of the cantilever 2 composed of the oscillator 3, which is advantageous in obtaining a larger amplitude.
However, in order to make the support engagement more stable, the gap G can be filled with an adhesive or the like.

Also in the case of this embodiment, the operation mode itself is the same as the structure of the second embodiment. [Example 4] The acoustic matching layer 1 in Examples 2 and 3
The shape is shown as a quadrangle as shown in FIGS. 3 and 4 for simplicity of illustration, but as shown in FIG.
By making the circle circular, a more uniform radial sound field can be obtained. [Embodiment 5] In Embodiments 1 to 4, the case where the cantilever 2 supports the acoustic matching layer 1 from the left and right directions has been described.
It is also possible to support the ultrasonic radiation axis A from multiple directions that are axially symmetrical.

For example, in the embodiment of the second or third embodiment, the acoustic matching layer 1 can be supported by the cantilever 2 from three axially symmetrical directions as shown in FIG. 6 (a). In that case, the acoustic matching layer 1 may be formed into the shape shown in FIG. By supporting from three or more directions in this way, the engagement between the acoustic matching layer 1 and the cantilever 2 becomes more difficult to disengage than the structure, and particularly in the case of the embodiment 3 by line contact, it is more stable. This is advantageous for causing large-amplitude vibration. [Embodiment 6] FIG. 7 shows a structural example of an aerial ultrasonic sensor according to the second aspect of the present invention. In this structure, the acoustic matching layer 1 is integrally composed of the ultrasonic wave radiating portion 1A and the vibration transmitting portion 1B which extends substantially at a right angle from the peripheral edge of the ultrasonic wave radiating portion 1A and whose tip is fixed to the body 4, thereby transmitting the vibration. The ultrasonic transducer 3 is fixed to the portion 1B. The radiation area of the radiation unit 1A may be the same as in the above-described first to fifth embodiments. Since the vibrator 3 is fixed to the vibration transmitting portion 1B, which is smaller than the radiating portion 1A, the fixing area is small, so that small ones are connected in multiple stages, and only the leftmost one of the connected vibrator rows is connected to the vibration transmitting portion 1B. It is fixed at position 5. Body 4 is at the right end of the transducer row
It is fixed at position 6 to secure mechanical strength.

The tip 1E of the vibration transmitting portion 1B extending from the ultrasonic wave emitting portion 1A of the acoustic matching layer 1 is fixed to the body 4, and the vibrator 3 is fixed to the vibration transmitting portion 1B. The vibration of No. 3 is also expanded and amplified by the principle of leverage and transmitted to the ultrasonic wave radiating section 1A, and a large amplitude is obtained.
Since the ultrasonic wave emitting portion 1A of the acoustic matching layer 1 itself is supported only in the peripheral portion connected to the vibration transmitting portion 1B, there is no mechanical constraint on the displacement of the acoustic matching layer 1. Since a large amplitude can be obtained without increasing the outer diameter of the acoustic matching layer 1, ultrasonic waves emitted from each part of the acoustic matching layer 1 do not interfere with each other. Since the vibration transmitting portion 1B of the acoustic matching layer 1 is oriented almost at right angles to the ultrasonic wave radiating portion 1A,
The paths of the ultrasonic waves emitted from B do not intersect and no interference occurs. Since a large amplitude can be obtained without increasing the vibration force of the vibrator 3, the amount of heat generated from the vibrator 3 does not increase, and the resonance point does not change due to temperature rise.

The amplitude can be further increased by connecting the small vibrators 3 in multiple stages, and since only the left end of the connected vibrator row is fixed to the vibration transmitting portion 1B, the entire vibrator row is provided. A large heat dissipation surface for the volume can be secured, heat dissipation is improved, and the resonance point does not change due to temperature rise.

[0024]

As described above, according to the present invention,
Mechanical restraint against displacement of acoustic matching layer is reduced, interference between ultrasonic waves from each part of acoustic matching layer does not occur, large excitation force is not required, and heat dissipation is improved to prevent resonance point fluctuation However, an aerial ultrasonic sensor that can obtain a large sound pressure is provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a conventional airborne ultrasonic sensor.

FIG. 2 is a cross-sectional view showing a structural example of an aerial ultrasonic sensor according to the first aspect of the present invention.

FIG. 3 is a sectional view showing another structural example of the aerial ultrasonic sensor according to the first aspect of the present invention.

FIG. 4 is a sectional view showing still another structural example of the aerial ultrasonic sensor according to the first aspect of the present invention.

FIG. 5 is a view of the first embodiment of the present invention shown in FIG. 3 or FIG.
FIG. 3 is a perspective view showing a desirable shape of an acoustic matching layer used in the aerial ultrasonic sensor from the viewpoint of FIG.

6 is a perspective view showing (a) another embodiment of the aerial ultrasonic sensor according to the first aspect of the present invention shown in FIG. 3 or 4, and (b) an acoustic matching layer used in this embodiment. FIG.

7 (a) is a plan view and FIG. 7 (b) is a sectional view showing a structural example of an aerial ultrasonic sensor according to a second aspect of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Acoustic matching layer 1A ... Radiating part 1B ... Vibration transmitting part 1S ... Radiating surface 2 ... Vibrating plate or bimorph type ultrasonic transducer 3 ... Ultrasonic transducer 3p ... Electrode 4 ... Body A ... Ultrasonic radiation axis G ... Gap Engagement line by T ... line contact

Claims (7)

[Claims] 1. An aerial ultrasonic sensor that emits ultrasonic waves from an ultrasonic transducer into the air through an acoustic matching layer, wherein the acoustic matching layer has a plurality of cantilevers that are axially symmetrical with respect to the ultrasonic radiation axis. An aerial ultrasonic sensor supported by an end of a beam, the cantilever including an ultrasonic transducer. 2. The cantilever comprises a diaphragm made of a material having a smaller damping capacity than the acoustic matching layer, and an ultrasonic transducer fixed to at least one surface of the diaphragm. 1. The airborne ultrasonic sensor according to 1. 3. The airborne ultrasonic sensor according to claim 1, wherein the cantilever comprises an ultrasonic transducer. 4. The aerial ultrasonic sensor according to claim 3, wherein the ultrasonic vibrator comprises a bimorph type piezoelectric element. 5. The aerial ultrasonic sensor according to claim 3, wherein the convex portion at the end of the cantilever is fitted into the concave portion of the acoustic matching layer to perform the support. 6. The airborne superstructure according to claim 3, wherein the bottom of the concave portion of the acoustic matching layer is engaged with the tip of the convex portion of the end portion of the cantilever in line contact to perform the support. Sound wave sensor. 7. An aerial ultrasonic sensor that emits ultrasonic waves into the air from an ultrasonic transducer through an acoustic matching layer, wherein the acoustic matching layer is substantially perpendicular to the ultrasonic radiator and the periphery of the ultrasonic radiator. An aerial ultrasonic sensor, characterized by being integrally formed with a vibration transmitting part having an extended and fixed tip, wherein an ultrasonic transducer is fixed to the vibration transmitting part.