JP2022166536A - ultrasonic sensor - Google Patents

Abstract

To realize an ultrasonic sensor that protects an ultrasonic element for transmission and reception from an external environment while improving the accuracy of direction detection of an external obstacle.SOLUTION: In an ultrasonic sensor 1, an ultrasonic element 2 is adhered to a mounting substrate 4 by an adhesive 3, and these are housed in a housing space 54 of a case material 5. A diaphragm 25 that functions as a vibrating portion of the ultrasonic element 2 communicates with an external space through a waveguide 511 of the case material 5. Between the ultrasonic element 2 and the mounting substrate 4 or in the waveguide 511 or both the ultrasonic element 2 and the mounting substrate 4, a resonance space 6 having a planar size larger than the diameter of the waveguide 511 is formed. In the ultrasonic sensor 1, the ultrasonic element 2 receives a sound wave in which a phase difference due to an acoustic resonance mode generated in the resonance space 6 is added to the phase difference with respect to the arrival angle of the reflected wave generated at the outer end of the waveguide 511.SELECTED DRAWING: Figure 1

Description

The present invention relates to an ultrasonic sensor having a plurality of receiving ultrasonic elements.

Conventionally, at least one ultrasonic element for transmission (hereinafter referred to as "transmitting element") and a plurality of ultrasonic elements for receiving (hereinafter referred to as "receiving element") are provided, and the distance and direction to the obstacle are measured. A detectable ultrasonic sensor is known (for example, Patent Document 1). The ultrasonic sensor described in Patent Document 1 includes a base material, a transmitting element, a plurality of receiving elements arranged at predetermined intervals in the base material, and provided on the base material, between the outside and the outer surface of the receiving element and a waveguide for guiding ultrasonic waves in. In this ultrasonic sensor, the ultrasonic element is protected by the base material, and the waveguide guides the ultrasonic waves reflected from the outside to the receiving element while maintaining both good appearance and impact resistance. This constitutes an object detection device capable of detecting the distance to an obstacle or the like and its orientation.

JP-A-2008-89569

This ultrasonic sensor transmits an ultrasonic wave of a predetermined frequency to the outside by a transmitting element, receives the reflected wave by a plurality of receiving elements arranged at predetermined intervals, and based on the phase difference of the reflected wave, Detects the orientation of external obstacles and the like with respect to the ultrasonic sensor.

Hereinafter, for convenience of explanation, the direction along the normal direction to the receiving surface of the receiving element will be referred to as the "reference direction (0°)", the incident direction of the reflected wave with respect to the receiving surface will be referred to as the "direction of arrival", and the reference direction and the arrival direction An angle formed with a direction is called an "arrival angle".

Specifically, this ultrasonic sensor calculates the arrival direction of the reflected waves by utilizing the fact that the phase difference between the reflected waves received by the plurality of receiving elements changes according to the arrival angle of the reflected waves.

In recent years, in object detection using this type of ultrasonic sensor, there is a need to further improve the accuracy of object direction detection. In order to improve the accuracy of azimuth detection by the above method, it is conceivable to increase the amount of change in the phase difference of the reflected wave with respect to the angle of arrival, thereby increasing the sensitivity to the angle of arrival.

Here, the phase difference of the reflected wave with respect to the angle of arrival is uniquely determined by the interval between the adjacent receiving elements and the wavelength of the ultrasonic wave to be transmitted to the outside (hereinafter referred to as "transmission wave"). Therefore, in order to increase the sensitivity to the arrival angle, it is necessary to change the spacing of the receiving elements or the wavelength of the transmission wave.

However, the ultrasonic sensor described in Patent Document 1 transmits and receives ultrasonic waves through a waveguide arranged or formed in the substrate while the transmitting element and the receiving element are arranged in the substrate. configuration, it is difficult to arbitrarily change the spacing between the receiving elements. In addition, while the method of changing the wavelength of the transmitted wave, that is, the driving frequency, improves the sensitivity to the arrival angle, it causes a decrease in the attenuation rate of the ultrasonic wave and a decrease in the resolution of the distance measurement to the object. There is a limit to improving sensitivity.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an ultrasonic sensor that protects the transmitting/receiving ultrasonic element from the external environment while improving the azimuth detection accuracy of external obstacles and the like.

To achieve the above object, the ultrasonic sensor according to claim 1 comprises an ultrasonic element (2) having a vibrating part (25) capable of vibrating at a predetermined driving frequency, and an adhesive (3) and a mounting board (4) having a through hole (41) formed at a position corresponding to the vibrating part, a storage space (54) in which the ultrasonic element and the mounting board are stored, the through hole and At least a case material (5) having a waveguide (511) communicating with an external space, and a resonance space (6, 7) formed between the ultrasonic element and the mounting substrate or in the waveguide and , wherein the resonance space has a minimum dimension of a plane perpendicular to the extending direction of the waveguide, which is larger than the diameter of the waveguide.

As a result, in an ultrasonic sensor in which a transmission wave from an ultrasonic element is transmitted to the outside through a waveguide and a reflected wave is received through the waveguide, at least one of the resonance spaces formed in the The resonance space has a minimum dimension larger than the diameter of the waveguide in a plane formed in a radial direction with the extension direction of the waveguide as an axis. By providing the above-mentioned resonance space in the propagation path of the ultrasonic wave, this ultrasonic sensor has a structure in which the phase difference of the reflected wave with respect to the arrival angle can be adjusted without changing the spacing of the receiving elements or the wavelength of the transmitted wave. be. Therefore, this ultrasonic sensor protects the transmitting/receiving ultrasonic element from the external environment, and can improve the accuracy of azimuth detection of external obstacles and the like.

It should be noted that the reference numerals in parentheses attached to each component etc. indicate an example of the correspondence relationship between the component etc. and specific components etc. described in the embodiments described later.

It is a sectional view showing the ultrasonic sensor of a 1st embodiment. FIG. 2 is a perspective exploded view showing an ultrasonic element, an adhesive, and a mounting substrate; 3 is a cross-sectional view showing a cross-sectional configuration between III-III in FIG. 2; FIG. FIG. 4 is a plan view showing the ultrasonic element and the adhesive as viewed from the waveguide side; FIG. 5 is an explanatory diagram for explaining the relationship between an arrival angle and a phase difference; FIG. 4 is a diagram showing an example of a cubic waveguide; FIG. 4 is a diagram showing an example of acoustic modes generated in a cubic space; FIG. 4 is a diagram showing an example of a model in acoustic simulation; FIG. 4 is a diagram showing characteristics obtained by acoustic simulation of a model with resonance space; It is a sectional view showing the ultrasonic sensor of a 2nd embodiment. FIG. 11 is a cross-sectional view showing an example of a modification of the ultrasonic sensor of the second embodiment; FIG. 11 is a cross-sectional view showing another example of a modification of the ultrasonic sensor of the second embodiment; FIG. 11 is a diagram showing an arrangement example in an opening of a waveguide according to the ultrasonic sensor of the third embodiment; FIG. 10 is a diagram showing another arrangement example of the openings of the waveguide according to the ultrasonic sensor of the third embodiment; It is an explanatory view for explaining a modification of the ultrasonic sensor of a 3rd embodiment. It is a sectional view showing the ultrasonic sensor of a 4th embodiment. FIG. 17 is a cross-sectional view showing a cross-sectional configuration between XVII-XVII of FIG. 16; It is a sectional view showing the ultrasonic sensor of a 5th embodiment. FIG. 11 is a cross-sectional view showing an ultrasonic sensor according to a sixth embodiment; FIG. 11 is a model in acoustic simulation, showing a model corresponding to the ultrasonic sensor of the sixth embodiment; FIG. 21 is a diagram showing characteristics obtained by acoustic simulation of the analysis model of FIG. 20, with the dimension of the resonance space in the thickness direction changed. FIG. 21 is a diagram showing characteristics obtained by acoustic simulation of the analytical model of FIG. 20, with the dimensions of the resonance space in the plane direction changed. FIG. 21 is a diagram showing characteristics obtained by acoustic simulation of the analysis model of FIG. 20 when the distance between the resonance space and the reception point is changed; FIG. 12 is a cross-sectional view showing a first modification of the ultrasonic sensor of the sixth embodiment; FIG. 21 is a cross-sectional view showing a second modification of the ultrasonic sensor of the sixth embodiment; FIG. 14 is a cross-sectional view showing a third modification of the ultrasonic sensor of the sixth embodiment; FIG. 11 is a perspective exploded view showing an ultrasonic element, an adhesive, and a mounting substrate in an ultrasonic sensor according to a seventh embodiment; FIG. 14 is a plan view showing the ultrasonic element and the adhesive of the ultrasonic sensor of the seventh embodiment as viewed from the waveguide side;

An embodiment of the present invention will be described below with reference to the drawings. In addition, in each of the following embodiments, portions that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
An ultrasonic sensor 1 of a first embodiment will be described with reference to FIGS. 1 to 4. FIG. For example, the ultrasonic sensor 1 is preferably mounted on a vehicle such as an automobile and used as an object detection device that detects external objects such as obstacles, but it can of course be applied to other uses.

In FIG. 1, part of the outline of the ultrasonic element 2, the adhesive 3, the mounting substrate 4, and the base material 51, which will be described later, in another cross section is indicated by broken lines. In FIG. 2, a region of the surface 4a of the mounting substrate 4 that contacts the adhesive 3 and an outline of a diaphragm 25, which will be described later, which is not visible at the angle shown in FIG. In addition, in FIG. 2, auxiliary lines indicating corresponding positions of the ultrasonic element 2, the adhesive 3, and the mounting board 4 are indicated by two-dot chain lines. In FIG. 3, the outline of the adhesive 3, which is not a component of the ultrasonic element 2, is indicated by a chain double-dashed line. In FIG. 4, the outline of the piezoelectric film 26 which is not visible at the angle shown in FIG. 4 is indicated by a broken line.

For example, as shown in FIG. 1, the ultrasonic sensor 1 of this embodiment includes an ultrasonic element 2 having a vibrating portion capable of vibrating at a predetermined drive frequency, an adhesive 3, and a through hole 41 corresponding to the vibrating portion. A mounting board 4 having a structure, a case material 5 and a waveguide 511 are provided. The ultrasonic sensor 1 is, for example, as shown in FIGS. 1 and 2, in which the ultrasonic element 2 is adhered to the mounting board 4 via the adhesive 3, and is housed in the housing space 54 of the case material 5. , through-hole 41 and waveguide 511 communicating with external space. The ultrasonic sensor 1 further has a resonance space 6 , and the resonance space 6 is formed between the ultrasonic element 2 and the mounting substrate 4 in this embodiment.

For example, as shown in FIG. 3, the ultrasonic element 2 is constructed using an SOI (abbreviation for Silicon on Insulator) substrate in which a supporting substrate 21, a buried insulating film 22, and a semiconductor layer 23 are laminated in this order. . The ultrasonic element 2 is provided with, for example, a recess 24 that penetrates the support substrate 21 and the embedded insulating film 22 and exposes the semiconductor layer 23 , and the portion of the semiconductor layer 23 corresponding to the recess 24 serves as a diaphragm 25 . there is The ultrasonic element 2 has, for example, a piezoelectric film 26 formed on the surface of the diaphragm 25 opposite to the embedded insulating film 22 . The piezoelectric film 26, for example, is configured such that a piezoelectric material is sandwiched between paired electrodes, and is contracted or expanded in a predetermined direction by application of an electric field. The diaphragm 25 is a vibrating portion that can vibrate at a predetermined drive frequency (for example, but not limited to, 30 kHz to 100 kHz for in-vehicle applications) by driving the piezoelectric film 26 . For example, as shown in FIG. 2, the ultrasonic element 2 has four diaphragms 25 (driving units), and as shown in FIG. It is an array element. The ultrasonic element 2 is, for example, of the MEMS (abbreviation of Micro Electro Mechanical Systems) type having a plurality of drive units. The ultrasonic element 2 has, for example, the diaphragm 25 serving as a vibrating portion, and functions as a transmitting element that transmits ultrasonic waves to the outside and a receiving element that receives the sound waves from the outside.

Hereinafter, for simplification of explanation, the diaphragm 25 functioning as a drive unit will be referred to as a "cell", the diameter of the cell will be referred to as a "cell diameter", and a plurality of cells will be provided, with α rows and β columns (α, β: natural numbers). are sometimes referred to as "α×β array elements". In the example above, the ultrasonic element 2 is a 2×2 array element with four cells. In addition, a transmission wave transmitted from the ultrasonic element 2 to the outside and a reception wave incident on the waveguide 511 from the outside may be collectively referred to as a "transmission/reception wave".

The adhesive 3 is a member that adheres and fixes the ultrasonic element 2 to the mounting board 4, and for example, an arbitrary adhesive resin material is used. For example, as shown in FIGS. 2 and 4, the adhesive 3 has the same outer shape as the ultrasonic element 2, and has a planar size larger than that of the diaphragm 25 in a region of the ultrasonic element 2 directly below the diaphragm 25. It has a grid-like frame shape having a plurality of openings 31 . The thickness of the adhesive 3 is, for example, about 10 μm to 200 μm, but is not limited to this.

The openings 31 are provided in the same number as the cells of the ultrasonic element 2, and are independent of each other in this embodiment. For example, as shown in FIG. 1, the plurality of openings 31 are arranged to accommodate the entire area of one corresponding diaphragm 25 among the plurality of diaphragms 25 . In the plurality of openings 31, the corresponding one waveguide 511 among the plurality of waveguides 511 provided in the base material 51 is entirely inside the opening 31 in the same manner as the diaphragm 25. It is arranged to fit in. That is, the plurality of openings 31 have a minimum dimension larger than the cell diameter of the ultrasonic element 2 and the diameter of the waveguide 511, and are arranged to include the corresponding cells and the waveguide 511 in plan view. there is The plurality of openings 31 become internal spaces when the adhesive 3 is adhered to the ultrasonic element 2 and the mounting substrate 4, and serve as propagation paths for transmission and reception waves. function as

The mounting board 4 is a circuit board on which wiring and circuits (not shown) are formed on a board made of any insulating material such as glass epoxy resin or ceramic, on which various electronic components and the like can be mounted. The mounting board 4 is, for example, electrically connected to the ultrasonic element 2 by wires or the like in a region located outside the contour of the ultrasonic element 2, and is also connected to a control section, a power supply, and the like (not shown). 2 drive control and electrical signal exchange. A plurality of through holes 41 are formed in the mounting substrate 4 at positions corresponding to the diaphragm 25, as shown in FIG. 2, for example. The plurality of through-holes 41 are propagation paths of transmission and reception waves independent of each other, and are, for example, circular, but not limited to this, and may be of any shape such as elliptical or polygonal. The through-holes 41 have, for example, the same shape and dimensions as the communicating waveguide 511 .

The case material 5 includes, for example, a base material 51 having a plurality of waveguides 511 formed thereon, a frame body part 52 surrounding the ultrasonic element 2, the adhesive material 3, and the mounting board 4 while being separated from them, and a frame body and a lid portion 53 arranged on the portion 52 . A space surrounded by the base member 51 , the frame portion 52 and the lid portion 53 of the case member 5 serves as a storage space 54 for storing the ultrasonic element 2 , the adhesive 3 and the mounting substrate 4 . The case material 5 is made of, for example, metal, resin, ceramic, or a composite material in which a part or all of these are combined.

The substrate 51 is, for example, as shown in FIG. 1, a base member on which the mounting substrate 4 is mounted with an adhesive or the like (not shown), and has a plurality of waveguides 511 formed thereon. One surface of the base material 51 on which the opening of the waveguide 511 on the side of the external space is formed is the outer surface 51a. , or arranged to be in contact with each other.

A plurality of waveguides 511 are formed in the base material 51 and are through holes that serve as propagation paths for transmission and reception waves. It can be of any shape, such as a polygonal tube. A plurality of waveguides 511 are independent of each other and communicate with one corresponding through-hole 41, opening 31 and cell. For example, the plurality of waveguides 511 have an outer end 511a at the end (opening) of the waveguide 511 on the side of the external space, and an inner end at the opposite end. are through holes that are connected in a straight line. The direction in which the waveguides 511 are extended is defined as the “extension direction”, and the extension directions of the plurality of waveguides 511 are aligned in this embodiment. In other words, the substrate 51 has a configuration in which a plurality of waveguides 511 extending linearly are arranged in parallel. The number of waveguides 511 is, for example, the same as the number of cells of the ultrasonic element 2, and when the cell arrangement of the ultrasonic element 2 is α×β, the outer ends 511a are arranged in an α×β array. It is said that

The frame portion 52 is a portion of the case member 5 surrounding the ultrasonic element 2 , the adhesive 3 , and the mounting substrate 4 , and has an inner shell shape that follows the outer shape of the mounting substrate 4 , for example.

The lid portion 53 is a member that is arranged at the end portion of the frame body portion 52 opposite to the base material 51 and closes the frame body portion 52 .

In the above description, an example in which the base material 51, the frame body part 52, and the lid part 53 constituting the case material 5 are separate bodies has been described. The frame body part 52 and the lid part 53 may be integrated, and the configuration thereof may be changed as appropriate.

The resonance space 6 is a space provided on the propagation path of the transmitted and received waves in order to adjust the phase difference of the reflected waves with respect to the angle of arrival of the ultrasonic sensor 1. In this embodiment, the ultrasonic element 2 and the mounting substrate 4. For example, the resonance spaces 6 are provided in the same number as the cells of the ultrasonic element 2 and are independent of each other. In the resonance space 6, one of the plurality of waveguides 511 that communicates is defined as a "communicating waveguide", and the minimum dimension of a plane orthogonal to the extending direction of the communicating waveguide is It has a size larger than the perpendicular of the waveguide. Specifically, the resonance space 6 has a planar size larger than the diameter of the communicating waveguide, and is in a state of including the outer shell of the communicating waveguide when viewed from the extending direction of the communicating waveguide. there is In addition, since the diameter of the waveguide 511 is approximately the same as the cell diameter, for example, the resonance space 6 is larger than the cell diameter of the ultrasonic element 2 and contains the corresponding cells. Note that the positional relationship of the through-hole 41 and the waveguide 511 with respect to the resonance space 6 can be appropriately determined according to the acoustic resonance mode described later.

The above is the basic configuration of the ultrasonic sensor 1 of the present embodiment. The ultrasonic sensor 1 is provided with a resonance space 6 having a predetermined size on the propagation path of the transmitted and received waves between the ultrasonic element 2 and the external space, thereby increasing the amount of change in the phase difference with respect to the arrival angle of the reflected wave. It has a structure that allows

In the ultrasonic sensor 1, the linear distance from the diaphragm 25 to the outer end 511a of the waveguide 511 is L, and the wavelength conversion value of the driving frequency is λ. It is preferably within ±10% of the value represented by (n: an odd number equal to or greater than 1).

[Resonance space]
Next, the effect of the resonance space 6 will be described with reference to FIGS. 5 to 7. FIG.

First, the arrival angle and phase difference of reflected waves will be described with reference to FIG.

For example, as shown in FIG. ₅ , two waveguides extending linearly are arranged at a pitch d0, and a reflected wave with a wavelength λ from the outside is incident at an arrival angle θ. Assume that the reflected wave incident on 511 has a phase difference of Δx. In this case, the arrival angle θ is represented by the following formula (1).

θ=sin ⁻¹ (Δx×λ/(2π×d ₀ )) (1)
When the ultrasonic element cells are arranged on the extension of two waveguides, the pitch _d0 of the waveguides is substantially the same as the pitch of the receiving elements. The wavelength λ [unit: mm] of the incident reflected wave depends on the wavelength of the transmission wave transmitted from the ultrasonic element 2, that is, the driving frequency of the cell. Also, as shown in FIG. ₅ , the pitch d0 is determined by the arrangement of the outer ends of the waveguide on the receiving surface, with the plane facing the outer ends of the waveguides as the receiving surface. Then, when the pitch _d0 and the wavelength λ of the reflected wave are fixed at one value, the phase difference Δx depends on the arrival angle θ according to the equation (1). That is, the relationship between the arrival angle θ and the phase difference Δx is basically uniquely determined by the pitch _d0 on the receiving surface and the drive frequency. Therefore, in order to improve the sensitivity of the ultrasonic sensor to the angle of arrival θ and improve the accuracy of azimuth detection, it is necessary to increase the amount of change in the phase difference Δx per 1° of the angle of arrival.

A conventional ultrasonic sensor that does not have a resonance space 6 (hereinafter simply referred to as "conventional ultrasonic sensor") has a small degree of freedom in design, and it is difficult to improve the sensitivity with respect to the arrival angle θ. Specifically, in conventional ultrasonic sensors, the spacing between the receiving elements of the ultrasonic elements or the spacing of the waveguides in the receiving plane (i.e., pitch _d0 ), or the driving frequency (i.e., wavelength λ), or both are adjusted. There is a need to.

However, when changing the interval between receiving elements or the interval between waveguides, it is necessary to change the structure, arrangement, etc. of the ultrasonic elements or waveguides. is difficult. In addition, it is necessary to satisfy the conditional expression d ₀ <λ/2 between the receiving elements. Specifically, when d ₀ >λ/2, the sign of the phase difference Δx is reversed when the arrival angle θ deviates from the predetermined range based on equation (1), and one phase difference Δx corresponds to In this case, two or more arrival angles θ exist (so-called binarization), which makes it difficult to estimate the arrival angles θ. Therefore, it is difficult to freely change the interval between the receiving elements also from the viewpoint of the constraint of d ₀ <λ/2.

In addition, when changing the drive frequency of the ultrasonic element, although there is no need to change the structure or arrangement, etc., the attenuation rate of the ultrasonic wave and the resolution of distance measurement with the object will be reduced, so the sensitivity to the arrival angle will be reduced. can be improved, other characteristics are degraded.

On the other hand, the ultrasonic sensor 1 of the present embodiment is provided with a resonance space 6 in which a resonance mode of reflected waves occurs in the propagation path of the transmitted and received waves.

Here, acoustic resonance modes in a cubic waveguide will be described with reference to FIG. For example, as shown in FIG. 6, in a cubic waveguide having a dimension of a _{0 [unit: m] in one direction of the waveguide and a dimension of b 0 [} unit: m] in a direction orthogonal to this, the waveguide Acoustic resonance modes that can exist in the wave path are represented by the following equations.

上記の式において、ｆ_ｍｎはモードｍ、ｎ（ｍ、ｎ：自然数）の共振周波数〔単位：ｋＨｚ〕であり、ｃは媒体（例えば空気など）の音速〔単位：ｍ／ｓ〕である。つまり、構造体により内包された空間（例えば壁に囲まれた空間など）である導波路が、空気等の気体媒体で満たされている場合、当該空間の大きさと媒体を伝搬する音波の波長に応じて、気体が音響的に共振する周波数・モードが存在する。そして、導波路を伝搬する音波の周波数ｆがｆ＞ｆ_ｍｎの場合、共振モードｍ、ｎは存在する。

In the above equation, f _mn is the resonance frequency [unit: kHz] of modes m and n (m, n: natural numbers), and c is the sound velocity [unit: m/s] of a medium (for example, air). In other words, when a waveguide that is a space enclosed by a structure (for example, a space surrounded by walls) is filled with a gaseous medium such as air, the size of the space and the wavelength of the sound wave propagating in the medium Accordingly, there are frequencies and modes at which the gas acoustically resonates. When the frequency f of the sound wave propagating through the waveguide is f> _fmn , resonance modes m and n exist.

The resonance space 6 has a dimension such that an acoustic mode having a phase difference occurs at the frequency of the propagating reflected wave, as shown in FIG. 7, for example.

The acoustic mode corresponding to the dimensions of the resonance space 6 can be calculated, for example, by simulation using acoustic analysis software using the finite element method (for example, Ansys (registered trademark), etc.). In FIG. 7, in order to make it easier to understand the regions with different phase differences in the acoustic modes generated in the space, different types of hatching are applied to the regions with different phases, although the cross section is not shown.

In the example shown in FIG. 7, the largest phase difference occurs at points A and B, for example. The resonance space 6 is dimensioned so that an acoustic mode is generated by simulation of acoustic analysis or the like, and the waveguide 511 is connected to the location where the phase difference in the acoustic mode is the largest. In the ultrasonic sensor 1, the plurality of waveguides 511 are each connected to different and independent resonance spaces 6, and the phase difference in the acoustic mode generated at a predetermined driving frequency in the resonance space 6 is maximized. It has a structure in which a waveguide 511 is connected to the position. For example, in the case of FIG. 7, when one waveguide 511 is connected to a position corresponding to point A in the resonance space 6, another waveguide 511 adjacent to the waveguide 511 is It is connected to a position corresponding to point B of another resonance space 6 .

As a result, the phase difference Δx2 in the resonance space 6 is added to the phase difference Δx1 generated at the outer end 511a of the waveguide 511, and finally the reflected wave received by the ultrasonic element 2 is The phase difference becomes larger than Δx1. As a result, the ultrasonic sensor 1 having the resonance space 6 has a larger phase difference Δx with respect to a change in the arrival angle of 1° than the conventional ultrasonic sensor, and the sensitivity to the arrival angle θ is improved. Note that the phase difference of the reflected waves received by the ultrasonic element 2 can be calculated by acoustic simulation, and interaction occurs between the waveguide 511 and the resonance space 6, so it is not Δx1 + Δx2. At least greater than Δx1.

Next, the results of acoustic simulation will be described with reference to FIGS. 8 and 9. FIG.

The inventors designed an acoustic analysis simulation model corresponding to the ultrasonic sensor 1 of the present embodiment, as shown in FIG. 8, for example.

Hereinafter, for the convenience of explanation, as shown in FIG. , y is referred to as a "plane size". Also, the dimension of the resonance space 6 in the z direction is called "thickness", and the simulation model for acoustic analysis is simply called "analysis model". In addition, in FIG. 8, an extension line in the extension direction of the waveguide at the outer end is indicated by a chain double-dashed line. The angle between the direction of the sound wave incident on the waveguide shown in FIG.

In the analytical model, the resonance space 6 is cubic, and the dimensions in the x, y, and z directions are a, b, and c, respectively. In the acoustic simulation, the wavelength corresponding to the drive frequency of the ultrasonic element 2 is λ, a and b are fixed at 4λ/4 and 5λ/4, respectively, and the arrival angle θ and the phase difference for each thickness c of the resonance space 6 are When Δx was calculated, the results shown in FIG. 9 were obtained. Here, two results of c=4 mm and c=8 mm are shown as representative values.

In FIG. 9, the two-dot chain line shows the simulation results for c = 4 mm, the solid line shows the simulation results for c = 8 mm, and the dashed line shows the slope of the phase difference Δx in the range of the arrival angle θ from 0° to 20°. there is

The greater the amount of change in the phase difference .DELTA.x with respect to the arrival angle .theta. of 1.degree. shown in FIG. 9, that is, the greater the slope indicated by the dashed line, the greater the sensitivity to the arrival angle .theta. As a result of the simulation, it was found that the sensitivity to the inclination of Δx, that is, the arrival angle θ, is greater when c=8 mm than when c=4 mm. This indicates that the sensitivity to the arrival angle θ can be improved by adjusting the thickness c of the resonance space 6 .

Therefore, by providing the resonance space 6, it is possible to increase the amount of change in the phase difference Δx with respect to the arrival angle θ without changing the drive frequency of the ultrasonic element 2 and the pitch of the outer end 511a of the waveguide 511, thereby enabling azimuth detection. can improve the accuracy of

When a plurality of resonance spaces 6 are provided, the plane dimensions a and b and the thickness c may all be the same, or part or all of the plane dimensions, thickness dimensions and shapes may be different. The connection positions of the waveguides 511 to each of the plurality of resonance spaces 6 need only increase the phase difference between the different waveguides 511, and are appropriately changed according to the above-described acoustic resonance modes.

According to this embodiment, the ultrasonic element 2 is housed in the case member 5, and the resonance space 6 is provided in the propagation path of the transmitted and received waves connecting the ultrasonic element 2 and the external space, and the arrival angle θ of the reflected wave The ultrasonic sensor 1 has a large amount of change in the phase difference Δx with respect to . Therefore, while protecting the ultrasonic element 2, the degree of freedom in design is high, and the effect of further improving the accuracy of azimuth detection can be obtained.

(Second embodiment)
An ultrasonic sensor 1 according to the second embodiment will be described with reference to FIG.

In FIG. 10, as in FIG. 1, part of the outline of the ultrasonic element 2, the adhesive 3, the mounting substrate 4, and the base material 51 in another cross section is indicated by broken lines. This also applies to FIGS. 11 and 12, which will be described later.

The ultrasonic sensor 1 of the present embodiment differs from the first embodiment in that the waveguide 511 has a shape in which the diameter changes continuously, as shown in FIG. 10, for example. In this embodiment, this difference will be mainly described.

In the present embodiment, the waveguide 511 has an outer space side of the waveguide 511 as an outer end 511a, and an opposite end as an inner end. The shape is larger than the diameter. The waveguide 511 has, for example, a tapered shape in which the diameter continuously increases from the inner end toward the outer end 511a in a cross-sectional view. In this case, the ultrasonic sensor 1 has a narrower transmission wave range and sharper directivity than in the first embodiment.

According to this embodiment, the same effects as those of the first embodiment can be obtained. In addition, since the waveguide 511 has a shape in which the diameter changes continuously, an effect of sharpening the directivity of the transmitted wave can also be obtained.

(Modification of Second Embodiment)
In the ultrasonic sensor 1 of the second embodiment, for example, as shown in FIG. 11, in a cross-sectional view, in addition to the waveguide 511, the through hole 41 of the mounting substrate 4 has a tapered shape having continuity with the waveguide 511. may be In this case, the diameter of the through-hole 41 increases continuously from the ultrasonic element 2 side toward the waveguide 511 side, and the diameter of the opening at the end on the waveguide 511 side increases to the waveguide 511 side. It is substantially the same as the diameter of the inner end of the tube 511 .

12, the waveguide 511 has a tapered shape in which the diameter continuously increases from the outer end 511a toward the inner end. may be In this case, the through hole 41 of the mounting substrate 4 has, for example, a diameter at the opening on the side of the waveguide 511 that is substantially the same as a diameter at the inner end of the waveguide 511, and is continuous toward the ultrasonic element 2 side. It is assumed that the diameter of the Further, the through hole 41 has, for example, substantially the same diameter at the opening on the ultrasonic element 2 side as the diameter of the diaphragm 25 . The through hole 41 may have a shape with a constant diameter. In this case, the ultrasonic sensor 1 has the effect of widening the transmission range of the transmission waves compared to the first embodiment.

This modification can also provide the same effects as the first embodiment. Further, in the case shown in FIG. 11, directivity similar to that of the second embodiment is obtained, and in the case shown in FIG. 12, the effect of widening the transmission range of the transmission wave is obtained. In other words, transmission directivity can be controlled in the second embodiment and its modification.

In the above-described second embodiment and its modification, an example in which the wall surfaces of the waveguide 511 and the through hole 41 are linear in cross section has been described, but the present invention is not limited to this, and may be curved. The shape and the degree of change in diameter may be changed as appropriate.

(Third embodiment)
An ultrasonic sensor 1 according to the third embodiment will be described with reference to FIG.

FIG. 13 shows the state of the case member 5 viewed from the normal direction to the outer surface 51a, and for ease of viewing, only a partial region near the outer end 511a of the waveguide 511 is shown, and other regions are omitted. ing.

The ultrasonic sensor 1 of this embodiment differs from the first embodiment in that outer ends 511a of a plurality of waveguides 511 are linearly arranged along one direction, as shown in FIG. do. In this embodiment, this difference will be mainly described.

In this embodiment, the plurality of waveguides 511 are, for example, n1 (n1: a natural number equal to or greater than 2) or more, and their outer ends 511a are arranged along one direction, so to speak, a "1D array" arrangement. It has become.

According to this embodiment, the same effects as those of the first embodiment can be obtained. Further, the ultrasonic sensor 1 is configured to be able to detect at least one direction (azimuth/altitude) of an external obstacle or the like with respect to the ultrasonic sensor 1 .

(Modified example of the third embodiment)
For example, as shown in FIG. 14, the ultrasonic sensor 1 of the third embodiment has a so-called "2D array" arrangement in which outer ends 511a of a plurality of waveguides 511 are arranged along two orthogonal directions. There may be. In this case, the ultrasonic sensor 1 can detect two directions (azimuth and altitude) of an external obstacle or the like with respect to the ultrasonic sensor 1 .

In addition, the number of outer ends 511a of the waveguides 511 in one row along the left-right direction in FIG. Let the number of outer ends 511a be n2 (n2: a natural number equal to or greater than 2). At this time, the numbers of n1 and n2 may be changed as appropriate.

15, the ultrasonic sensor 1 of the third embodiment may have a structure in which the arrangement of the diaphragm 25 of the ultrasonic element 2 and the arrangement of the outer ends 511a of the waveguide 511 are different. . Specifically, for example, when there are four cells of the ultrasonic element 2 and four waveguides 511, the four cells of the ultrasonic element 2 are arranged in a 1D array along one direction. , the outer ends 511a of the waveguides 511 may be arranged in a 2×2 array. In this case, some or all of the waveguides 511 among the plurality of waveguides 511 have a shape in which the extending direction is changed at least once on the way from the inner end to the outer end 511a (for example, bent, curved, etc.). As a result, even if the plurality of cells of the ultrasonic element 2 are arranged in a 1D array, the outer ends 511a are arranged along two orthogonal directions, so that azimuth detection in two directions is possible.

In FIG. 15, the waveguide 511 connecting the cells and the outer end 511a of the waveguide 511 is indicated by a dashed line in order to facilitate understanding of the relationship between the cell arrangement of the ultrasonic elements 2 and the arrangement of the outer end 511a of the waveguide 511. there is FIG. 15 shows an example in which two waveguides 511 out of four waveguides 511 are bent in the middle from the inner end to the outer end 511a, but it is not limited to this. However, the number and shape of the waveguides 511 whose extending directions change can be changed as appropriate.

This modification can also provide the same effects as the third embodiment. In addition, by arranging the outer ends 511a of the plurality of waveguides 511 in an array of n1×n2, regardless of the cell arrangement of the ultrasonic elements 2, the structure is capable of detecting two directions of an external obstacle or the like. becomes the ultrasonic sensor 1 of

(Fourth embodiment)
The ultrasonic sensor 1 of the fourth embodiment will be described with reference to FIGS. 16 and 17. FIG.

In FIG. 16, as in FIG. 1, part of the outline of the ultrasonic element 2, the adhesive 3, the mounting substrate 4, and the base material 51 in another cross section is indicated by broken lines. In FIG. 17, in order to make it easier to understand the positional relationship between the second resonance space 7 and the waveguide 511 in which it is provided, one of the waveguides 511 in other cross sections communicates with the second resonance space 7. The outline of the part is indicated by a dashed line.

For example, as shown in FIG. 16, the ultrasonic sensor 1 of the present embodiment has a resonance space 7 located directly below the ultrasonic element 2 and a waveguide 511 in addition to the resonance space 7. It differs from the embodiment. In this embodiment, this difference will be mainly described.

A plurality of waveguides 511 have a resonance space 6 immediately below the ultrasonic element 2 as a "first resonance space", and a second resonance space 7 is formed between the inner end and the outer end.

For example, as shown in FIG. 17, the second resonance spaces 7 are provided in the same number as the plurality of waveguides 511, are independent of each other, and have a minimum dimension in the planar direction shown in FIG. larger than the diameter of the part. In other words, like the first resonance spaces 6, the plurality of second resonance spaces 7 have a planar size larger than that of the waveguide 511, and include the outer contour of the communicating portion of the waveguide 511 inside the inner contour. It is arranged to Like the first resonance spaces 6, the plurality of second resonance spaces 7 have plane dimensions and thicknesses that generate acoustic resonance modes. The second resonance space 7 is formed, for example, by dividing the substrate 51 into two members, namely, one member having a portion of the waveguide 511 and a recess communicating therewith, and the other member having the remainder of the waveguide 511. and are formed by connecting them.

The first resonance space 6 is formed by the opening 31 of the adhesive 3 and cannot be larger than the planar size of the ultrasonic element 2, whereas the second resonance space 7 is provided in the base material 51, so the planar size can be made larger than the ultrasonic element 2 . Therefore, one dimension of the second resonance space 7 in the planar direction shown in FIG. not.

From the viewpoint of improving the sensitivity to the arrival angle, it is preferable that a and b have different dimensions and that the shorter dimension is at least 3λ/2. Also, from the same point of view, the dimension of the second resonance space 7 in the thickness direction is preferably smaller than 0.3λ.

According to this embodiment, the ultrasonic sensor 1 can obtain the effects of the first embodiment. In addition to the phase difference between the outer end 511a of the waveguide 511 and the first resonance space 6, the ultrasonic sensor 1 further adds a phase difference occurring in the second resonance space 7, so that the reflected wave It is possible to obtain the effect of widening the adjustment range of the sensitivity with respect to the arrival angle of the . In addition, since the planar size of the second resonance space 7 can be made larger than that of the ultrasonic element 2, the structure has a higher degree of freedom in design.

(Fifth embodiment)
An ultrasonic sensor 1 according to the fifth embodiment will be described with reference to FIG.

In FIG. 18, as in FIG. 1, part of the contours of the ultrasonic element 2, the adhesive 3, the mounting substrate 4, and the base material 51 in another cross section are indicated by broken lines.

In the ultrasonic sensor 1 of this embodiment, for example, as shown in FIG. 18, second resonance spaces 7 are formed in a plurality of waveguides 511 . Further, in the ultrasonic sensor 1, the portion of the waveguide 511 closer to the ultrasonic element 2 than the second resonance space 7 is used as the first waveguide 5111, and are used as a second waveguide 5112, and these are arranged with their axes shifted in cross-sectional view. The ultrasonic sensor 1 differs from the first embodiment in the points described above. Since the second resonance space 7, which is the former difference, is the same as that of the fourth embodiment, the latter difference will be mainly described in this embodiment.

The plurality of waveguides 511 includes a first waveguide 5111 and a second waveguide 5112 in this embodiment. The center position of the wave tube) is shifted, so to speak, an offset arrangement. In this manner, the plurality of waveguides 511 may be arranged with the positions of the two openings connected to the second resonance space 7 shifted.

This embodiment also provides the same effects as the fourth embodiment. Moreover, the ultrasonic sensor 1 has a structure in which the pitch of the waveguides 511 on the outer surface 51 a of the substrate 51 can be arbitrarily adjusted regardless of the pitch of the cells of the ultrasonic element 2 .

(Sixth embodiment)
The ultrasonic sensor 1 of the sixth embodiment will be described with reference to FIGS. 19 to 23. FIG.

In FIG. 19, as in FIG. 1, part of the outline of the ultrasonic element 2, the adhesive 3, the mounting substrate 4, and the base material 51 in another cross section is indicated by broken lines.

In the ultrasonic sensor 1 of the present embodiment, for example, as shown in FIG. 19, the resonance space 6 extends over a plurality of waveguides 511 to form one resonance space 6 common to the plurality of waveguides 511. It is different from the first embodiment in that the In this embodiment, this difference will be mainly described.

In this embodiment, for example, when there are four waveguides 511 , the resonance space 6 straddles all the four waveguides 511 and communicates with all the waveguides 511 . That is, in the present embodiment, the adhesive 3 has a frame shape having only one opening, and is surrounded by the ultrasonic element 2 and the mounting substrate 4 to form one common resonance space 6. there is

The inventors performed acoustic analysis simulations even when the resonance space 6 was a common space communicating with each other, and verified whether the sensitivity to the arrival angle of the reflected wave could be improved.

Specifically, in the acoustic analysis, for example, an analysis model shown in FIG. 20 was designed. In this analysis model, two waveguides extending in a straight line are arranged apart from each other in parallel, and a common resonance space is provided between these receiving points and the external space. A tube communicates through the resonant space. In this analytical model, the dimensions of the resonance space in the x, y, and z directions are a, b, and c, respectively, and the dimension of the resonance space and the reception point in the waveguide in the z direction is d. In this analysis model, a driving frequency of 46.4 kHz (wavelength of 7.4 mm) and a gas medium of air were used to perform an acoustic analysis simulation using the finite element method in the same manner as in the first embodiment.

FIG. 21 shows simulation results when the thickness c is changed. In FIG. 21, the horizontal axis is the angle of arrival, the vertical axis is the phase difference, and the curve based on the theoretical values when there is no resonance space is indicated by the chain double-dashed line. This also applies to FIGS. 22 and 23, which will be described later.

As shown in FIG. 21, the slope of the phase difference in the arrival angle range of 0° to 20° was approximately the same as the theoretical value when c=2 mm. The slope of the phase difference in the range of the arrival angle of 0° to 20° is smaller than the theoretical value when c=3 mm, whereas when c=1 mm, the slope is smaller than the theoretical value when c=2 mm. It was larger than the case and the theoretical value. This indicates that by designing c=1 mm, the sensitivity to the arrival angle of the reflected wave can be made higher than when there is no resonance space. From the viewpoint of improving the sensitivity to the arrival angle of the reflected wave, the thickness c of the resonance space 6 is preferably 0.3λ (unit: m) or less and shorter than the length of the waveguide 511 .

Next, FIG. 22 shows simulation results when the planar dimensions a and b are changed. In this simulation, a=b, and a (=b) was changed in the range of 5λ/4 to 7λ/4. As shown in FIG. 22, the slope of the phase difference in the arrival angle range of 0° to 20° was approximately the same as the theoretical value when a=b=6λ/4. The slope of the phase difference in the range of arrival angles from 0° to 20° is smaller than the theoretical value when a = b = 5λ/4, whereas it is smaller than the theoretical value when a = b = 7λ/4. was larger than This indicates that by designing a=b=7λ/4, the sensitivity to the arrival angle of the reflected wave can be made higher than when there is no resonance space.

Next, FIG. 23 shows simulation results when the distance d between the resonance space 6 and the receiving point is changed in the range of λ/8 to λ/2. As shown in FIG. 23, the slopes of the phase differences in the arrival angle range of 0° to 20° were almost the same and smaller than the theoretical values when d=λ/2 and λ/4. The slope of the phase difference in the arrival angle range of 0° to 20° was larger than the theoretical value when d=λ/8. This indicates that by designing d=λ/8, the sensitivity to the arrival angle of the reflected wave can be made higher than when there is no resonance space.

As described above, even when the resonance space 6 is one common space communicating with a plurality of waveguides 511, each parameter of the planar size, thickness, and distance from the receiving element of the resonance space 6 is appropriately designed. Thereby, it is possible to increase the sensitivity to the arrival angle of the reflected wave.

According to this embodiment, the ultrasonic sensor 1 can obtain the same effects as those of the first embodiment. In addition, since one common opening 31 is provided in the adhesive 3, and the space generated by the opening 31 being surrounded by the ultrasonic element 2 and the mounting substrate 4 is the common resonance space 6, the first The effect of having a structure that is easier to manufacture than the embodiment is also obtained.

(Modified example of the sixth embodiment)
In the ultrasonic sensor 1 of the sixth embodiment, for example, as shown in FIG. A configuration including the space 7 may be employed. In this case, as in the fourth embodiment, the effect of further increasing the sensitivity to the arrival angle of the reflected wave can be obtained.

In this case, the ultrasonic sensor 1 may have a porous member 8 that transmits sound waves in the second resonance space 7, as shown in FIG. 25, for example. The porous member 8 is made of an arbitrary resin or metal material, for example, and has a porosity of about 90%, although not limited thereto. The porous member 8 is fixed in the second resonance space 7 by, for example, an adhesive (not shown). By arranging the porous member 8 in the second resonance space 7, even if a foreign matter enters the waveguide 511 from the outside, it is possible to suppress the foreign matter from adhering to the ultrasonic element 2, thereby improving reliability. An improved ultrasonic sensor 1 is obtained.

Note that the porous member 8 may be a member that transmits sound waves, and the constituent material and structure may be changed as appropriate. In addition, since the porous member 8 transmits sound waves, it has little effect on the acoustic mode in the second resonance space 7, and there is no problem in adjusting the sensitivity to the arrival angle.

For example, as shown in FIG. 26, the ultrasonic sensor 1 may be configured to have only the second resonance space 7 without the first resonance space 6 . Even in this case, since the structure is such that the phase difference occurring in the resonance space 7 can be added to the phase difference at the outer end of the waveguide 511, it is possible to improve the sensitivity to the arrival angle.

These modifications also provide the same effects as the first embodiment. In addition to this, the effect of expanding the range of sensitivity adjustment by having the second resonance space 7 and reducing the influence of foreign matter by the porous member 8 can be obtained.

(Seventh embodiment)
The ultrasonic sensor 1 of the seventh embodiment will be described with reference to FIGS. 27 and 28. FIG.

In FIG. 27, as in FIG. 2, the outline of the diaphragm 25 is indicated by dashed lines, and auxiliary lines indicating the corresponding positions of the ultrasonic element 2, the adhesive 3 and the mounting substrate 4 are indicated by chain double-dashed lines.

For example, as shown in FIG. 27, the ultrasonic sensor 1 of this embodiment is composed of two members separated by an adhesive 3, and the resonance space 6 located directly below the ultrasonic element 2 communicates with the storage space 54. The configuration is different from the first embodiment. In this embodiment, this difference will be mainly described.

In this embodiment, the adhesives 3 are arranged in parallel along two opposite sides of the contour of the ultrasonic element 2 in plan view, as shown in FIG. 28, for example. As a result, the resonance space 6 formed by the adhesive 3 sandwiched between the ultrasonic element 2 and the mounting substrate 4 communicates with the housing space 54 of the case member 5 housing the ultrasonic element 2 . The ultrasonic sensor 1 is configured such that the storage space 54 also functions as the resonance space 6 , and the acoustic resonance mode can be appropriately changed according to the planar size and thickness of the storage space 54 .

According to this embodiment, the same effects as those of the first embodiment can be obtained, and the acoustic resonance mode can be changed by adjusting the dimensions of the storage space 54 regardless of the arrangement of the ultrasonic element 2 and the waveguide 511. The ultrasonic sensor 1 has a structure with a high degree of design freedom.

(Other embodiments)
It should be noted that the ultrasonic sensors shown in the respective embodiments described above are examples of the ultrasonic sensors of the present invention, and are not limited to the respective embodiments described above. For example, the ultrasonic sensor of the present invention can be appropriately changed to various combinations and forms of the above-described embodiments, and other combinations and forms including only one element, more, or less of them. .

For example, the above embodiments and modifications thereof may be freely combined as appropriate within a possible range.

2... Ultrasonic element, 25... Vibrating part (diaphragm), 3... Adhesive material,
4 Mounting substrate 41 Through hole 5 Case material 51 Base material
511... waveguide, 511a... outer end, 5111... first waveguide,
5112 ... second waveguide, 54 ... storage space, 6 ... (first) resonance space,
7 (second) resonance space

Claims (12)

an ultrasonic element (2) having a vibrating portion (25) capable of vibrating at a predetermined driving frequency;
a mounting substrate (4) having a through-hole (41) formed at a position corresponding to the vibrating portion and to which the ultrasonic element is adhered via an adhesive (3);
a case material (5) having a storage space (54) in which the ultrasonic element and the mounting substrate are stored, and a waveguide (511) communicating the through hole and the external space;
At least one of resonance spaces (6, 7) formed between the ultrasonic element and the mounting substrate or in the waveguide,
The ultrasonic sensor according to claim 1, wherein the resonant space has a minimum dimension in a plane perpendicular to the extending direction of the waveguide, which is larger than a diameter of the waveguide. 2. The ultrasonic sensor according to claim 1, wherein a plurality of said vibrating sections and said waveguides are formed apart from each other and arranged along at least one direction. A plurality of the resonance spaces are provided corresponding to each of the plurality of vibrating portions,
3. The ultrasonic sensor according to claim 2, wherein at least one of the plurality of resonance spaces is different in shape or size from other resonance spaces. 4. The ultrasonic sensor according to claim 2, wherein said resonance space spans a plurality of said vibrating portions or said waveguides and is a common space corresponding to at least two or more said vibrating portions. 5. The method according to any one of claims 1 to 4, wherein the resonance space has a thickness of 0.3λ or less, where a dimension of the resonance space along the extending direction is defined as a thickness, and a wavelength corresponding to the drive frequency is defined as λ. An ultrasonic sensor according to any one of the preceding claims. 6. The ultrasonic sensor according to claim 1, wherein said resonance space is provided between said ultrasonic element and said mounting substrate and communicates with said storage space. The resonance space is formed in the waveguide,
A portion of the waveguide positioned closer to the ultrasonic element than the resonance space is a first waveguide (5111), and a portion positioned closer to the external space than the resonance space is a second waveguide. The ultrasonic wave according to any one of claims 1 to 5, wherein, as a waveguide (5112), the second waveguide is arranged at a position different from the extension line of the first waveguide. sensor. 8. The ultrasonic sensor according to any one of claims 1 to 7, wherein the member forming the resonance space is a composite material in which at least one or two or more of the group consisting of resin, metal, and ceramic are combined. . The case material comprises a base material (51) having the waveguide,
9. The ultrasonic sensor according to any one of claims 1 to 8, wherein said base material is a composite material in which at least one or more of the group consisting of resin, metal and ceramic are combined. The end of the waveguide on the side of the external space is defined as an outer end (511a), and the end opposite to the outer end is defined as an inner end. 10. The ultrasonic sensor according to any one of claims 1 to 9, wherein said extension direction changes at least once between said ends. The end of the waveguide on the side of the external space is defined as an outer end (511a), and the wavelength corresponding to the driving frequency is λ, and the linear distance between the outer end and the vibrating portion is nλ/2. 11. The ultrasonic sensor according to any one of claims 1 to 10, which is within ±10% of the value represented by the formula of (n: an odd number equal to or greater than 1). The ultrasonic sensor according to any one of claims 1 to 11, wherein said driving frequency is in the range of 30 kHz to 100 kHz.

Images