WO2013118185A1

WO2013118185A1 - Airborne ultrasonic sensor

Info

Publication number: WO2013118185A1
Application number: PCT/JP2012/000878
Authority: WO
Inventors: 井幡　光詞; 友則木村; 井上　悟
Original assignee: 三菱電機株式会社
Priority date: 2012-02-09
Filing date: 2012-02-09
Publication date: 2013-08-15

Abstract

This airborne ultrasonic sensor is equipped with: a tubular case (1) with a bottom that has an opening on one end in the axial direction thereof and the bottom on the other end; a piezoelectric vibrator (2) that is fixed to the inner bottom surface of the tubular case (1) with the bottom; and a piezoelectric vibrator (3) that is fixed to the outer bottom surface of the tubular case (1) with the bottom and has a direction of polarization opposite to that of the piezoelectric vibrator (2).

Description

Aerial ultrasonic sensor

The present invention relates to an aerial ultrasonic sensor that transmits ultrasonic waves in the air and receives ultrasonic waves propagated in the air.

Conventionally, airborne ultrasonic sensors using piezoelectric vibrators have been used in obstacle detection systems that detect obstacles. In this aerial ultrasonic sensor, an obstacle is detected by transmitting an ultrasonic wave in the air and receiving the ultrasonic wave reflected in the air and propagated in the air.

Conventionally, this type of aerial ultrasonic sensor has a configuration in which plate-like piezoelectric vibrators having electrodes formed on both surfaces are fixed to the bottom surface of a bottomed cylindrical case (see, for example, Non-Patent Document 1).
On the other hand, generally, when an ultrasonic wave passes through a boundary between different types of propagation media, the transmittance decreases as the difference in acoustic impedance between the media increases. In contrast, in conventional aerial ultrasonic sensors, the bottomed cylindrical case is usually made of metal such as aluminum, and the acoustic impedance of the aerial ultrasonic sensor consisting of a bottomed cylindrical case and a piezoelectric vibrator is significantly higher than that of the atmosphere. large. For this reason, the conventional aerial ultrasonic sensor has a problem of poor transmission and reception efficiency.

Therefore, as a method for improving the transmission / reception efficiency, there is a method using an acoustic matching layer (see, for example, Patent Document 1). In the aerial ultrasonic sensor disclosed in Patent Document 1, a piezoelectric vibrator is fixed to an inner bottom surface of a bottomed cylindrical case, and an acoustic matching layer is fixed to an outer bottom surface. Thereby, the acoustic impedance matching between the piezoelectric vibrator and the outside air through which the ultrasonic wave is propagated can be performed, and transmission / reception efficiency can be improved.

JP 2005-184687 A

However, the air ultrasonic sensor using the acoustic matching layer disclosed in Patent Document 1 requires an adhesive for fixing the acoustic matching layer to the bottomed cylindrical case. Therefore, there is a problem that transmission / reception sensitivity changes depending on the material and thickness of the adhesive. In addition, a foamable material is used for the acoustic matching layer, and there is a problem in environmental resistance such as heat.

The present invention has been made to solve the above-described problems, and is capable of transmitting and receiving by increasing vibration displacement on the radiation surface without using an acoustic matching layer and without increasing power consumption. An object is to provide an aerial ultrasonic sensor capable of improving sensitivity.

The aerial ultrasonic sensor according to the present invention has a bottomed cylindrical case having an opening at one end in the axial direction and a bottom surface at the other end, and a first piezoelectric vibration fixed to the inner bottom surface of the bottomed cylindrical case. And a second piezoelectric vibrator fixed to the outer bottom surface of the bottomed cylindrical case and having a polarization direction opposite to that of the first piezoelectric vibrator.

According to the present invention, since it is configured as described above, it is possible to improve transmission / reception sensitivity by increasing vibration displacement on the radiation surface without using an acoustic matching layer and without increasing power consumption. it can.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the structure of the airborne ultrasonic sensor which concerns on Embodiment 1 of this invention, (a) is a side view, (b) is a top view, (c) is an A-A 'sectional view. It is a figure explaining the generation principle of the ultrasonic wave in the air ultrasonic sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the example of a dimension of the air ultrasonic sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the example of a dimension of the conventional airborne ultrasonic sensor. It is a graph which shows the vibration displacement calculation result in the radiation | emission surface of the air ultrasonic sensor shown in FIG. It is a graph which shows the radiation sound pressure distribution calculation result of the air ultrasonic sensor shown to FIG. It is the schematic which shows the structure of the airborne ultrasonic sensor which concerns on Embodiment 2 of this invention, (a) is a side view, (b) is a top view, (c) is a B-B 'sectional view. It is a figure which shows the example of a dimension of the air ultrasonic sensor which concerns on Embodiment 2 of this invention. It is a graph which shows the vibration displacement calculation result in the radiation | emission surface of the air ultrasonic sensor shown to FIG. It is a graph which shows the vibration displacement calculation result in the outer side surface of the bottomed cylindrical case of the aerial ultrasonic sensor shown to FIG. It is a graph which shows the radiation sound pressure distribution calculation result of the air ultrasonic sensor shown to FIG. It is the schematic which shows the structure of the airborne ultrasonic sensor which concerns on Embodiment 3 of this invention, (a) is a side view, (b) is a top view, (c) is a C-C 'sectional view. It is a figure which shows the example of a dimension of the air ultrasonic sensor which concerns on Embodiment 3 of this invention. It is a graph which shows the relationship between the magnitude | size of the level | step-difference part of the ultrasonic sensor shown in FIG. 13, and a resonant frequency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a schematic view showing the configuration of an aerial ultrasonic sensor according to Embodiment 1 of the present invention, where (a) is a side view, (b) is a top view, and (c) is a cross-sectional view taken along line AA ′. It is.
As shown in FIG. 1, the airborne ultrasonic sensor has a bottomed cylindrical case 1 having an opening at one end in the axial direction and a bottom surface at the other end. A piezoelectric vibrator (first piezoelectric vibrator) 2 is fixed substantially at the center of the inner bottom surface of the bottomed cylindrical case 1. In addition, a piezoelectric vibrator (second piezoelectric vibrator) 3 having the same shape as the piezoelectric vibrator 2 is fixed to substantially the center of the outer bottom surface of the bottomed cylindrical case 1. Although not shown, electrodes are formed on both surfaces of the

piezoelectric vibrators

2 and 3. The

piezoelectric vibrators

2 and 3 are fixed to the bottomed cylindrical case 1 so that the polarization directions are the same, but the bottomed cylindrical case 1 is so effective that the polarization directions are effectively reversed. The input /

output terminals

4a and 4b are connected to the inner side surface and the

piezoelectric vibrators

2 and 3, respectively.

In the aerial ultrasonic sensor configured as described above, a signal (voltage) having a predetermined frequency is supplied from a signal source (not shown) to the input /

output terminals

4a and 4b. The

piezoelectric vibrators

2 and 3 perform stretching vibration mainly in the radial direction by application of signals from the input /

output terminals

4a and 4b. At this time, since the polarization directions of both

piezoelectric vibrators

2 and 3 are effectively opposite to each other, when one of the

piezoelectric vibrators

2 and 3 is extended with respect to the electric field in the same direction, the other is contracted to generate a flexural vibration.

FIG. 2 is a view for explaining the principle of generation of ultrasonic waves in the aerial ultrasonic sensor according to Embodiment 1 of the present invention. In FIG. 2, only the bottom surface portion of the aerial ultrasonic sensor shown in FIG. 1 is shown for simplification.
First, when no voltage is applied, no displacement occurs in the bottomed cylindrical case 1 and the

piezoelectric vibrators

2 and 3 as shown in FIG. On the other hand, when a voltage in a predetermined direction is applied, the piezoelectric vibrator 2 expands and the piezoelectric vibrator 3 contracts as shown in FIG. , 3 protrudes downward. On the other hand, when a voltage in the opposite direction to the above is applied, the piezoelectric vibrator 2 contracts and the piezoelectric vibrator 3 expands as shown in FIG. The

piezoelectric vibrators

2 and 3 protrude upward.
Therefore, when an AC voltage is applied to the

piezoelectric vibrators

2 and 3, vibration corresponding to the power supply frequency is generated, and ultrasonic waves are generated by the vibration.

Here, in the aerial ultrasonic sensor according to the first embodiment, the

piezoelectric vibrators

2 and 3 that are effectively opposite in polarization direction are fixed to both sides of the bottom surface of the bottomed cylindrical case 1. As compared with the structure in which the piezoelectric vibrator is fixed only inside the bottom surface of the bottomed cylindrical case as in the example, the vibration displacement at the bottom surface of the bottomed cylindrical case 1 can be increased. And since the vibration displacement in the structure itself increases, there is no need to increase the power consumption. In general, when the vibration displacement at the bottom increases, the transmission / reception sensitivity of the aerial ultrasonic sensor is improved. Therefore, the aerial ultrasonic sensor according to Embodiment 1 has improved transmission / reception sensitivity compared to the conventional aerial ultrasonic sensor. To do.

Next, in order to show the effect of the aerial ultrasonic sensor according to the first embodiment, the vibration displacement calculation result on the outer bottom surface (radiation surface) of the bottomed cylindrical case 1 will be described. In addition, it shows together about the vibration displacement calculation result in the conventional aerial ultrasonic sensor.
FIG. 3 is a diagram illustrating a dimension example of the aerial ultrasonic sensor according to the first embodiment in which the vibration displacement calculation is performed, and FIG. 4 is a diagram illustrating a dimension example of the conventional aerial ultrasonic sensor. The conventional aerial ultrasonic sensor shown in FIG. 4 has the same configuration as the aerial ultrasonic sensor shown in FIG. 3 except that the piezoelectric vibrator 200 is fixed only to the inner bottom surface of the bottomed cylindrical case 100. ing. In the vibration displacement calculation, the bottomed

cylindrical case

1, 100 is made of aluminum, and the

piezoelectric vibrators

2, 3, 200 are made of PZT. In consideration of symmetry, the calculation is performed on a three-dimensional model having a central angle of 90 °.

FIG. 5 is a graph showing calculation results of vibration displacement at the outer bottom surface of the bottomed cylindrical case 1,100 of the aerial ultrasonic sensor shown in FIGS. For the aerial ultrasonic sensor according to Embodiment 1 shown in FIG. 3, the vibration displacement calculation result on the outer bottom surface of the bottomed cylindrical case 1 including the piezoelectric vibrator 3 is shown. In FIG. 5, the horizontal axis indicates the radial position with the center of the bottom surface as the origin, and the vertical axis indicates the vibration displacement in the vertical direction on the bottom surface. Further, symbol a indicates the vibration displacement in the aerial ultrasonic sensor according to the first embodiment of FIG. 3, and symbol b indicates the vibration displacement in the conventional aerial ultrasonic sensor in FIG.
From FIG. 5, it can be seen that in the aerial ultrasonic sensor according to the first embodiment, the vibration displacement at the center of the bottom surface is larger than that in the conventional example.

Next, in order to show the effect of the aerial ultrasonic sensor according to the first embodiment, the calculation result of the radiation sound pressure distribution will be shown. In addition, the radiation sound pressure distribution calculation result in the conventional aerial ultrasonic sensor is also shown. Further, the calculation of the radiated sound pressure is performed on the structure shown in FIGS. 3 and 4 and is performed on the axially symmetric model in consideration of symmetry.
FIG. 6 is a graph showing the calculation result of the radiation sound pressure distribution of the aerial ultrasonic sensor shown in FIGS. In FIG. 6, the horizontal axis indicates an angle when the front direction (perpendicular direction of the radiation surface) of the aerial ultrasonic sensor is 0 °, and the vertical axis indicates sound pressure. Further, symbol a indicates the sound pressure distribution in the aerial ultrasonic sensor according to Embodiment 1 in FIG. 3, and symbol b indicates the sound pressure distribution in the conventional aerial ultrasonic sensor in FIG.
From FIG. 6, it can be seen that, in the aerial ultrasonic sensor according to the first embodiment, the radiation sound pressure is generally increased as compared with the conventional example.

As described above, according to the first embodiment, the

piezoelectric vibrators

2 and 3 having effectively opposite polarization directions are fixed to both sides of the bottom surface of the bottomed cylindrical case 1. Without using an acoustic matching layer and without increasing power consumption, the vibration displacement on the radiation surface of the aerial ultrasonic sensor can be increased, and the transmission / reception sensitivity of the aerial ultrasonic sensor can be improved. Also, the radiation sound pressure can be increased.

In the aerial ultrasonic sensor according to the first embodiment, as shown in FIG. 1B, the bottom surface of the bottomed cylindrical case 1 and the

piezoelectric vibrators

2 and 3 are shown as being circular. However, the present invention is not limited thereto. For example, it may be oval or rectangular.

Embodiment 2. FIG.
7A and 7B are schematic views showing the configuration of an aerial ultrasonic sensor according to Embodiment 2 of the present invention, in which FIG. 7A is a side view, FIG. 7B is a top view, and FIG. 7C is a cross-sectional view along line BB ′. It is. The aerial ultrasonic sensor according to the second embodiment shown in FIG. 7 is obtained by adding a thick portion 1a to the bottomed cylindrical case 1 of the aerial ultrasonic sensor according to the first embodiment shown in FIG. Other configurations are the same, and the same reference numerals are given and description thereof is omitted.

The thick portion 1a is integrally provided on the side surface of the bottomed cylindrical case 1 so as to increase its thickness around the axis. FIG. 7 shows a case where the thick portion 1 a is provided on the entire circumference of the predetermined portion in the axial direction of the outer side surface of the bottomed cylindrical case 1.

Here, also in the aerial ultrasonic sensor according to the second embodiment, similarly to the aerial ultrasonic sensor according to the first embodiment, the

piezoelectric vibrators

2 and 3 that are effectively opposite in polarization direction are provided with bottomed cylinders. Since it is fixed to both sides of the bottom surface of the case 1, the vibration displacement in the structure itself can be increased. Therefore, the vibration displacement at the outer bottom surface of the bottomed cylindrical case 1 including the piezoelectric vibrator 3 can be increased as compared with the conventional example without increasing the power consumption.

On the other hand, in the aerial ultrasonic sensor according to the first embodiment shown in FIG. 1, the vibration displacement at the side surface of the bottomed cylindrical case 1 increases as the vibration displacement at the bottom surface of the bottomed cylindrical case 1 increases. To do. However, an increase in vibration displacement at the side surface causes unnecessary radiation.
In contrast, in the aerial ultrasonic sensor according to the second embodiment, the thick portion 1 a is provided on the side surface of the bottomed cylindrical case 1. And since this wall thickness part 1a suppresses the vibration in the side surface of the bottomed cylindrical case 1, unnecessary radiation can be reduced.

Next, in order to show the effect of the aerial ultrasonic sensor according to the second embodiment, the vibration displacement calculation results on the outer bottom surface and the outer side surface of the bottomed cylindrical case 1 will be described. In addition, the vibration displacement calculation result in the conventional aerial ultrasonic sensor and the aerial ultrasonic sensor according to Embodiment 1 is also shown.
FIG. 8 is a diagram showing a dimension example of the aerial ultrasonic sensor according to the second embodiment in which the vibration displacement calculation is performed. Note that examples of dimensions of the aerial ultrasonic sensor according to the first embodiment and the conventional aerial ultrasonic sensor are as shown in FIGS. The aerial ultrasonic sensor according to the second embodiment shown in FIG. 8 is the aerial ultrasonic sensor according to the first embodiment of FIG. 3 except that the thick portion 1a is provided on the side surface of the bottomed cylindrical case 1. It is configured identically. In the vibration displacement calculation, the symmetry is taken into consideration, and the calculation is performed on a three-dimensional model having a central angle of 90 °.

FIG. 9 is a graph showing calculation results of vibration displacement at the outer bottom surface of the bottomed cylindrical case 1,100 of the aerial ultrasonic sensor shown in FIGS. For the aerial ultrasonic sensors according to the first and second embodiments shown in FIGS. 3 and 8, the vibration displacement calculation results on the outer bottom surface of the bottomed cylindrical case 1 including the piezoelectric vibrator 3 are shown. . In FIG. 9, the horizontal axis indicates the radial position with the center of the bottom surface as the origin, and the vertical axis indicates the vibration displacement in the vertical direction on the bottom surface. Further, symbol a represents the vibration displacement of the aerial ultrasonic sensor according to the first embodiment of FIG. 3, symbol b represents the vibration displacement of the conventional aerial ultrasonic sensor of FIG. 4, and symbol c represents the embodiment of FIG. The vibration displacement of the aerial ultrasonic sensor which concerns on form 2 is shown.
From FIG. 9, it can be seen that in the aerial ultrasonic sensor according to the second embodiment, the vibration displacement at the center of the bottom surface is larger than in the conventional example and the first embodiment.

FIG. 10 is a graph showing the calculation results of the vibration displacement on the outer side surface of the bottomed

cylindrical case

1, 100 of the aerial ultrasonic sensor shown in FIGS. In FIG. 10, the horizontal axis indicates the position in the axial direction with the opening end of the outer side surface as the origin, and the vertical axis indicates the vertical vibration displacement on the side surface. Further, symbol a represents the vibration displacement of the aerial ultrasonic sensor according to the first embodiment of FIG. 3, symbol b represents the vibration displacement of the conventional aerial ultrasonic sensor of FIG. 4, and symbol c represents the embodiment of FIG. The vibration displacement of the aerial ultrasonic sensor which concerns on form 2 is shown.
As can be seen from FIG. 10, in the aerial ultrasonic sensor according to the second embodiment, the vibration displacement in the vicinity of 3 mm to 5 mm on the outer side of the side surface is smaller than in the conventional example and the first embodiment.

Next, in order to show the effect of the aerial ultrasonic sensor according to the second embodiment, the calculation result of the radiation sound pressure distribution will be shown. In addition, the radiation sound pressure distribution calculation result in the conventional aerial ultrasonic sensor and the aerial ultrasonic sensor according to Embodiment 1 is also shown. Further, the calculation of the radiated sound pressure is performed on the structure shown in FIGS. 3, 4 and 8, and is performed on the axially symmetric model in consideration of symmetry.
FIG. 11 is a graph showing the calculation results of the radiation sound pressure distribution of the aerial ultrasonic sensor shown in FIGS. In FIG. 11, the horizontal axis represents an angle with the front direction (perpendicular to the radiation surface) of the aerial ultrasonic sensor being 0 °, and the vertical axis represents sound pressure. Further, symbol a represents the sound pressure distribution of the aerial ultrasonic sensor according to the first embodiment of FIG. 3, symbol b represents the sound pressure distribution of the conventional aerial ultrasonic sensor of FIG. 4, and symbol c represents FIG. The sound pressure distribution of the airborne ultrasonic sensor according to the second embodiment is shown.
From FIG. 11, it can be seen that, in the aerial ultrasonic sensor according to the second embodiment, the radiated sound pressure in the 90 ° direction is reduced as compared with the aerial ultrasonic sensor according to the first embodiment. Further, it can be seen that the sound pressure distribution in the front direction is increased as compared with the conventional example and the aerial ultrasonic sensor according to the first embodiment.

As described above, according to the second embodiment, since the thick portion 1a is provided on the side surface of the bottomed cylindrical case 1, in addition to the effects of the first embodiment, the vibration displacement at the side surface , The radiated sound pressure in the front direction can be increased, and the radiated sound pressure in the 90 ° direction, which is unwanted radiation, can be decreased.

In the aerial ultrasonic sensor according to the second embodiment, the case where the bottom surface of the bottomed cylindrical case 1 and the

piezoelectric vibrators

2 and 3 are circular as shown in FIG. 7B is shown, but the present invention is not limited thereto. For example, it may be oval or rectangular.
In addition, in the aerial ultrasonic sensor according to the second embodiment, as shown in FIG. 7B, a case where the thick portion 1a is provided on the entire circumference around the axis of the outer side surface of the bottomed cylindrical case 1 is shown. However, the present invention is not limited to this, and a thick portion may be provided on the inner side surface, and the meat may be provided at predetermined intervals around the axis (for example, four locations on the top, bottom, left, and right in FIG. 7B). You may make it provide a thick part.

Embodiment 3 FIG.
12A and 12B are schematic views showing the configuration of an aerial ultrasonic sensor according to Embodiment 3 of the present invention. FIG. 12A is a side view, FIG. 12B is a top view, and FIG. 12C is a cross-sectional view taken along the line CC ′. It is. The aerial ultrasonic sensor according to the third embodiment shown in FIG. 12 is obtained by adding a step portion 1b to the bottomed cylindrical case 1 of the aerial ultrasonic sensor according to the second embodiment shown in FIG. Other configurations are the same, and the same reference numerals are given and description thereof is omitted.

The step portion 1b is configured by providing the thick portion 1a on the outer side surface so as to form a step with respect to the outer bottom surface of the bottomed cylindrical case 1.

Here, also in the aerial ultrasonic sensor according to the third embodiment, the thick portion 1a is provided on the side surface of the bottomed cylindrical case 1 as in the aerial ultrasonic sensor according to the second embodiment. By increasing the vibration displacement at the bottom surface of the bottom cylindrical case 1 and decreasing the vibration displacement at the side surface, it is possible to increase the radiation sound pressure in the front direction and decrease the radiation sound pressure in the 90 ° direction, which is unnecessary radiation.
Furthermore, in the aerial ultrasonic sensor according to the third embodiment, a step is formed with respect to the outer bottom surface of the bottomed cylindrical case 1, so that the resonance frequency of the aerial ultrasonic sensor can be adjusted.

Next, in order to show the relationship between the stepped portion 1b and the resonance frequency, the resonance frequency calculation result when the size of the stepped portion 1b is changed is shown. For comparison, the resonance frequency calculation result in the aerial ultrasonic sensor according to the first embodiment shown in FIG. 3 (when there is no stepped portion 1b) is also shown.
FIG. 13 is a diagram showing an example of dimensions of the aerial ultrasonic sensor according to the third embodiment in which the resonance frequency is calculated. Then, the resonance frequency was obtained when the size of the stepped portion 1b shown in FIG. 13 was changed (when the position of the thick portion 1a provided on the outer side surface of the bottomed cylindrical case 1 was changed). In the resonance frequency calculation, the symmetry is taken into consideration, and the calculation is performed on a three-dimensional model having a central angle of 90 °.

FIG. 14 is a graph showing the relationship between the size of the stepped portion 1b and the resonance frequency. In FIG. 14, the horizontal axis indicates the size of the stepped portion 1b, and the vertical axis indicates the resonance frequency. The resonance frequency of the aerial ultrasonic sensor according to the first embodiment shown in FIG. 3 is indicated by a broken line, and the resonance frequency of the ultrasonic sensor according to the third embodiment shown in FIG. 13 is indicated by a solid line.
FIG. 14 shows that the resonance frequency changes depending on the size of the step portion 1b, and the resonance frequency can be adjusted by the size of the step portion 1b. Further, when compared with the resonance frequency (broken line) of the aerial ultrasonic sensor according to the first embodiment, the size of the stepped portion 1b is made the same as the thickness of the bottom surface of the bottomed cylindrical case 1, thereby reducing the resonance frequency. The fluctuation can be reduced, and the influence of the thick portion 1a provided on the side surface of the bottomed cylindrical case 1 can be reduced.

As described above, according to the third embodiment, since the step is formed with respect to the outer bottom surface of the bottomed cylindrical case 1, in addition to the effects in the second embodiment, the radiation in the front direction is performed. It is possible to adjust the resonance frequency while increasing the sound pressure and reducing unnecessary radiation. Moreover, the influence of the thick part 1a provided in the side surface of the bottomed cylindrical case 1 can be reduced by making the level | step-difference part 1b the same magnitude | size as the thickness of the bottom face of the bottomed cylindrical case 1. FIG.

In the aerial ultrasonic sensor according to Embodiment 3, the case where the bottom surface of the bottomed cylindrical case 1 and the

piezoelectric vibrators

2 and 3 are circular as shown in FIG. 12B is shown. For example, it may be oval or rectangular.
In the aerial ultrasonic sensor according to the third embodiment, as shown in FIG. 12 (b), the case where the stepped portion 1b is provided around the axis of the bottomed cylindrical case 1 is shown. However, the step portions may be provided at predetermined intervals around the axis (for example, four locations on the top, bottom, left, and right in FIG. 12B).

Further, within the scope of the present invention, the invention of the present application can be freely combined with each embodiment, modified with any component in each embodiment, or omitted with any component in each embodiment. .

The aerial ultrasonic sensor according to the present invention can improve transmission and reception sensitivity by increasing vibration displacement on the radiation surface without using an acoustic matching layer and without increasing power consumption. It is suitable for use in an aerial ultrasonic sensor or the like that transmits ultrasonic waves and receives ultrasonic waves that have propagated in the air.

1 Bottomed cylindrical case, 1a thick part, 1b stepped part, 2, 3 piezoelectric vibrator, 4a, 4b input / output terminal.

Claims

A bottomed cylindrical case having an opening at one end in the axial direction and a bottom surface at the other end;
A first piezoelectric vibrator fixed to an inner bottom surface of the bottomed cylindrical case;
An aerial ultrasonic sensor comprising: a second piezoelectric vibrator fixed to an outer bottom surface of the bottomed cylindrical case and having a polarization direction opposite to that of the first piezoelectric vibrator.
The aerial ultrasonic sensor according to claim 1, wherein a thick portion is provided around an axis on a side surface of the bottomed cylindrical case.
The aerial ultrasonic sensor according to claim 2, wherein the thick portion is provided so as to form a step with respect to an outer bottom surface of the bottomed cylindrical case.
The aerial ultrasonic sensor according to claim 3, wherein the step is substantially the same as a thickness of a bottom surface of the bottomed cylindrical case.