Ultraschallsensor

Abstract

Ultrasonic sensor (1) comprising: an ultrasonic element (5) that converts between an electrical signal and an ultrasonic vibration; and an element receiving housing (6) that has a tubular shape with a base and receives the ultrasonic element therein, and comprising: a side plate section (61) having a tubular shape that surrounds a directional center axis (DA), and a base plate section (62) that closes one end of the side plate section in an axial direction parallel to the directional center axis, wherein the ultrasonic element is attached to the base plate section, a portion of the base plate section within a contour of the ultrasonic element when viewed along the directional center axis contains a space (622) that is bounded by a portion of the ultrasonic element, and the base plate section has a recess (621) formed at a position separate from an inner wall of the side plate section.the space (622) is formed by the ultrasonic element and the recess, the ultrasonic element is arranged with a space between it and the inner wall of the side plate section, and the ultrasonic element (5) is arranged to cover only part of the recess (621).

Description

[Reference to Related Application]The present application is based on Japanese Application No. 2019-82277 filed on Apr. 23, 2019.[Technical Field]The present disclosure relates to an ultrasonic sensor.[Prior Art]Ultrasonic sensors that externally transmit ultrasonic waves as search waves and receive the reflected waves resulting from the transmitted ultrasonic waves are used in object detection devices mounted on vehicles, for example. This type of ultrasonic sensor includes a tubular housing having a bottom and a piezoelectric element mounted on the inner bottom surface of the housing. Studies have been made to provide a single ultrasonic sensor having a plurality of resonant frequencies for this type of ultrasonic sensor, and JP 2010-278 594 A discloses an example of such a structure. The ultrasonic sensor described in JP 2010-278 594 A includes two tubular housings having a bottom of different sizes and a piezoelectric element. The open end of the smaller-bottom tubular housing is attached to the inner bottom surface of the larger-bottom tubular housing, so that a space is formed by the smaller-bottom tubular housing. In this ultrasonic sensor, the piezoelectric element is attached to the outer bottom surface of the smaller-bottom tubular case. When ultrasonic waves are transmitted or received, the bottom end faces of the large and small tubular bottomed housings bulge in the same direction in some cases and in the opposite directions in other cases, whereby the structure can have a plurality of resonance frequencies.DE 20 2007 007 135 U1 discloses a transducer with a cup-shaped housing with an adapted inner contour, which contains a sound-emitting membrane. Furthermore, CN 1 02 873 018 A, DE 10 2012 201 884 A1, DE 10 2015 217 778 A1 and EP 2 592 397 A1 are known.[Summary of the Invention]However, since the large and small tubular housings are connected to the bottom of this ultrasonic sensor, the durability may significantly deteriorate and the manufacturing cost may also increase. The problem is solved by the independent claim. Further aspects of the invention are defined in the dependent claims.The present disclosure relates to an ultrasonic sensor provided with a plurality of resonant frequencies while securing durability.According to an aspect of the disclosure, an ultrasonic sensor includes: an ultrasonic element that converts between an electric signal and an ultrasonic vibration; and an element accommodating case that has a bottomed tubular shape and accommodates the ultrasonic element therein, and includes: a side plate portion that has a tubular shape surrounding a directivity center axis, and a bottom plate portion that closes an end of the side plate portion in an axial direction parallel to the directivity center axis, wherein the ultrasonic element is attached to the bottom plate portion, and a part of the bottom plate portion inside a contour of the ultrasonic element when viewed along the directivity center axis includes a space formed by separating a part of the part inside the contour from the ultrasonic element.This configuration enables the ultrasonic sensor to have two vibration propagation paths, namely, a path on which the vibration propagates from the ultrasonic element directly to the bottom plate portion of the element accommodating case and a path on which the vibration propagates to the bottom plate portion via the space. Thus, a single ultrasonic sensor is provided in which a plurality of vibration modes are generated and which has a plurality of resonant frequencies. The foregoing configuration also eliminates the need to connect another member between the member accommodating case and the ultrasonic member, resulting in improved durability and reduced manufacturing cost.Reference numerals in parentheses assigned to the components or the like indicate examples of correspondence between the components or the like and the specific components described with reference to the embodiments described below.[Brief Description of Drawings]FIG. 1 is a diagram illustrating an installation example of an ultrasonic sensor according to an embodiment. FIG. 2 is a cross-sectional view showing the general device configuration of the ultrasonic sensor. FIG. 3 is a perspective view showing the general configuration of the ultrasonic microphone shown in FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. FIG. 5 is a diagram showing vibration transmission paths between the ultrasonic element and the element accommodating case. FIG. 6 is a diagram showing the acoustic impedance characteristic of the ultrasonic microphone shown in FIG. 3. FIG. 7 is a perspective view showing the general configuration of an element accommodating case according to the first modification. FIG. 8 is a plan view showing the general configuration of an ultrasonic microphone according to the second modification. FIG. 9 is a cross-sectional view showing the recess provided in a bottom plate portion according to the third modification. FIG. 10 is a cross-sectional view showing the cross-sectional shape of a bottom plate portion according to the fourth modification.[Description of Embodiments]Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts of one embodiment that are the same as or equivalent to parts of another embodiment are denoted by the same reference numerals.(Embodiment)An ultrasonic sensor 1 according to an embodiment will be described. The ultrasonic sensor 1 is suitable for use in, for example, an object detection device mounted on a vehicle such as an automobile, but is not limited thereto, and may be applied to other uses. In this embodiment, as a typical example, an example in which the sensor is applied to a vehicle-mounted object detection device will be described.(Installation Example)An example of installing the ultrasonic sensor 1 on a vehicle will be briefly described with reference to FIG. 1. As shown in FIG. 1, for example, a plurality of ultrasonic sensors 1 are installed on a vehicle V having a box-shaped vehicle body V 1. Specifically, the ultrasonic sensors 1 are mounted on a front bumper V 2 attached to the front end part of the vehicle body V 1 and a rear bumper V 3 attached to the rear end part.The front bumper V 2 and the rear bumper V 3 are provided with mounting holes V 4, which are through holes for mounting the ultrasonic sensors 1. The ultrasonic sensors 1 mounted on the front bumper V 2 and the rear bumper V 3 are so-called vehicle-mounted clearance sonars.(Configuration)Next, the configuration of the ultrasonic sensors 1 will be described with reference to FIGS. 2, 3 to 4.Hereinafter, for convenience of explanation, an XYZ rectangular coordinate system is set such that the Z axis is parallel to the directivity center axis DA of the ultrasonic sensors 1, as shown in FIG. 2. The direction parallel to the directivity center axis DA is referred to as an "axial direction". The upper side of FIG. 2, i.e., the side in the positive direction along the Z axis, may be referred to as the "distal end side" in the axial direction. Similarly, the lower side of FIG. 2, i.e., the side in the negative direction along the Z axis, may be referred to as the "proximal end side" in the axial direction. Further, each direction perpendicular to the axial direction may be referred to as an "in-plane direction". That is, an "in-plane direction" is a direction parallel to the XYZ plane in FIG. 2, FIG. 3 shows, in addition to an XYZ coordinate system corresponding to the XYZ rectangular coordinate system of FIG. 2, the contour of a recess 621 having a broken line that is not visible because it is covered with an ultrasonic element 5 described later.Each ultrasonic sensor 1 includes a sensor housing 2, an elastic holding member 3, and an ultrasonic microphone 4. the ultrasonic microphone 4 includes the ultrasonic element 5 and an element accommodating housing 6.As shown in FIG. 2, the sensor housing 2 is a housing of the ultrasonic sensor 1 and is also configured to hold the elastic holding member 3. The sensor housing 2 includes a housing main body part 21, a connector part 22, and a tubular housing part 23.The housing main body part 21 is a box-like part having a substantially rectangular parallelepiped outer shape, and has a bottomed tubular shape with its open end on the proximal end side in the axial direction.The connector part 22 extends outward from the side wall portion of the housing main body part 21 to electrically connect the ultrasonic sensor 1 to an external device such as an electronic control unit.The tubular housing part 23 is a part having a generally cylindrical shape that protrudes from the housing main body part 21 toward the distal end side in the axial direction. The tubular housing part 23 is configured to hold the axially proximal end part of the elastic holding member 3 having a generally cylindrical shape. The central axis of the elastic holding member 3 is the directivity central axis DA. The cylindrical space inside the tubular case member 23 communicates with the substantially rectangular parallelepiped space inside the case main body member 21. Hereinafter, the space inside the tubular case member 23 and the space inside the case main body member 21 are collectively referred to as "space inside the sensor case 2".A circuit board 24, a wiring portion 25 and a shielding portion 26 are accommodated in the space inside the sensor housing 2. The circuit board 24 that controls the operation of the ultrasonic sensors 1 is accommodated in the case main body part 21. The wiring portion 25 electrically connects the ultrasonic microphone 4 and the circuit board 24. The shielding portion 26 is fixed to the inner surface of the sensor housing 2 to electromagnetically shield the circuit board 24 and the wiring portion 25 by covering the circuit board 24 and the wiring portion 25.A damper member 27 is a disk-shaped member and has an outer diameter corresponding to the inner diameter of the elastic holding member 3. That is, the damper member 27 is fitted into the cylindrical space inside the elastic holding member 3 at a position closer to the proximal end side than the ultrasonic microphone 4 in the axial direction. The damper element 27 is provided in order to prevent the transmission of vibrations from the ultrasonic microphone 4 to the sensor housing 2. Specifically, the damper member 27 is formed of, for example, a foamed elastic material such as foamed silicone having insulating and elastic properties.A filler 28 is filled in the space inside the sensor housing 2. The filler 28 is formed of, for example, a synthetic resin material such as silicone rubber having insulating and elastic properties.The elastic holding member 3 is formed of a resin-based elastic material such as silicone rubber having insulating and elastic properties. Synthetic resin-based elastic materials are also referred to as "viscoelastic materials" or "elastomers". The elastic support member 3 is configured to elastically support the ultrasonic microphone 4 by covering the proximal end side of the ultrasonic microphone 4 while exposing the distal end side thereof in the axial direction.The ultrasonic microphone 4 has the ultrasonic element 5 and the element accommodating case 6, and serves as an ultrasonic transmitter / receiver. That is, the ultrasonic microphone 4 is configured to be capable of transmitting and receiving ultrasonic waves.In other words, the ultrasonic microphone 4 is configured to transmit search waves along the directivity center axis DA based on the applied drive signals. The directivity center axis DA is a virtual half line extending from the ultrasonic microphone 4 along the transmission / reception direction of ultrasonic waves and serves as a reference for the directivity angle. The "directivity center axis" may also be referred to as a "detection axis". The ultrasonic microphone 4 is also configured to receive reflected waves from objects in the vicinity thereof and to generate received signals.The ultrasonic element 5 is configured to convert electrical signals and ultrasonic vibrations. The ultrasonic element 5 is, for example, a piezoelectric thin film element, and its thickness direction extends in the axial direction. For example, as shown in FIG. 3, the ultrasonic element 5 is attached to the inner surface of a bottom plate portion 62, which will be described later, of the element accommodating case 6 having a tubular bottomed shape. The inner surface of the bottom plate portion 62 is a surface surrounded by a side plate portion 61 which will be described later.Specifically, in the present embodiment, the ultrasonic element 5 is placed so as to cover the recess 621 formed in the bottom plate portion 62, as shown in FIG. 4, for example, and forms a first space 622 together with the recess 621. The connected surface of the ultrasonic element 5 facing the bottom plate portion 62 has a contact part 51 which is the part attached to the bottom plate portion 62, and a non-contact part 52 which is the rest of the connected surface of the ultrasonic element 5. It can also be said that the non-contact part 52 is the part that is not connected to the bottom plate portion 62.For example, as shown by the white arrows in FIG. 5, the non-contact part 52 is provided to generate two paths having different vibration propagation speeds from the ultrasonic element 5 to the bottom plate portion 62, so that the ultrasonic sensor 1 can have a plurality of resonance frequencies. The two vibration propagation paths include a first propagation path in which the vibration propagates directly from the ultrasonic element 5 to the bottom plate portion 62, and a second propagation path in which the vibration propagates from the ultrasonic element 5 to the bottom plate portion 62 via the first array 622. The effects obtained by such a configuration will be described later. Note that, in order to enhance these effects, the non-contact part 52 preferably occupies an area equal to or larger than that of the contact part 51 in the connected area, in other words, occupies 50% or more of the connected area.The element accommodating case 6 has a tubular shape with a bottom having a central axis coincident with the directivity central axis DA, and has a second space 63 inside capable of accommodating the ultrasonic element 5. The element accommodating case 6 has a side plate portion 61 and a bottom plate portion 62 made of the same material. The element accommodating case 6 is seamless and integrally formed of a metal such as aluminum.The side plate portion 61 has, for example, a tubular shape surrounding the directivity center axis DA, that is, a cylindrical shape having a center axis substantially parallel to the directivity center axis DA. The side plate portion 61 includes a thin-wall part 611 and a thick-wall part 612.The thin-wall part 611 has a partially cylindrical shape having a certain thickness in the radial direction perpendicular to the directivity center axis DA. The "radial direction" is a direction radially extending from the directivity center axis DA. That is, the radial direction is the direction of the radius of a virtual circle drawn on a plane to which the directivity center axis DA is a normal so that the circle center is at the intersection of the plane and the directivity center axis DA. Further, the radial dimension of each of the components of the side plate portion 61 may be referred to as "thickness". In other words, the thin-wall part 611 has a constant thickness smaller than that of the thick-wall part 612.For example, the thickness of the thin-wall portion 611 has a dimension closest to the axial thickness of the bottom plate portion 62, among the radial dimension of the side plate portion 61 and the axial dimension of the bottom plate portion 62. Specifically, the thin-wall portion 611 has a thickness 0.3 to 2.0 times, preferably 0.5 to 1.5 times, more preferably 0.7 to 1.2 times, the thickness (i.e., the axial dimension) of the bottom plate portion 62. Typically, the thin-wall part 611 may have substantially the same thickness as the bottom plate portion 62.The thick-walled part 612 has a thickness (i.e., a radial dimension) larger than that of the thin-walled part 611. Specifically, in the present embodiment, the thick-wall part 612 has an arc-like shape defined by a chord and an arc and extends in the x-axis direction when viewed in a direction parallel to the directivity center axis DA. The thick-wall part 612 abuts on the thin-wall part 611 in the circumferential direction surrounding the directivity center axis DA. The "circumferential direction" is the circumferential direction of the aforementioned virtual circle.In the present embodiment, a pair of thin-wall parts 611 face each other with the directivity center axis DA interposed therebetween. Similarly, a pair of thick-wall portions 612 face each other with the directivity center axis DA interposed therebetween. That is, in the present embodiment, the second space 63 has a rounded rectangular shape or an oval shape consisting of a pair of semi-circles and a pair of line segments when viewed in a direction parallel to the directivity center axis DA. The side plate portion 61 has a pair of thin-wall parts 611 corresponding to the semi-circles and a pair of thick-wall parts 612 corresponding to the line segments. Due to this configuration, the directivity angle of the ultrasonic microphone 4 in the Y-axis direction is smaller than that in the X-axis direction. Since the thick-wall portion 612 may be configured as a portion for adjusting the directivity of ultrasonic waves, it may also be referred to as a "directivity adjustment portion".The bottom plate portion 62 is a flat plate or a thin plate having a thickness direction in the axial direction, and is provided to close one end of the side plate portion 61 in the axial direction. Specifically, the bottom plate portion 62 is smoothly and integrally connected to the axially distal end of the side plate portion 61. As shown in FIG. 3, when the ultrasonic element 5 transmits or receives ultrasonic waves, the bottom plate portion 62 vibrates in the axial direction by ultrasonic wave after being attached to the bottom plate portion 62, while bending with its outer edge connected to the side plate portion 61 serving as a fixed end. The recess 621 is provided on the inner surface of the bottom plate portion 62, i.e., on the end surface facing the second space 63 in which the ultrasonic element 5 is accommodated.The recess 621 is, for example, a syringe-shaped groove and is formed by any suitable method such as a cutting method. In the present embodiment, the recess 621 is completely covered with the ultrasonic element 5. That is, as shown in FIG. 3, the part of the bottom plate portion 62 within the contour of the ultrasonic element 5 when viewed from the directivity center axis DA, that is, the part within the contour forms the first space 622 because a part thereof is separated from the ultrasonic element 5. In the present embodiment, the part of the bottom plate portion 62 within the contour is provided with the recess 621 so that the first space 622 is formed between the bottom plate portion 62 and the ultrasonic element 5.The first space 622 formed by the recess 621 and the ultrasonic element 5 is filled with a medium having a different vibration propagation speed from the material of the bottom plate portion 62, such as air or silicone. In other words, the first space 622 is filled with a substance different from the material of the bottom plate portion 62.The above is the basic configuration of the ultrasonic sensor 1 of the present embodiment.(Effects)Next, the effects provided by the ultrasonic sensors 1 of the present embodiment will be described with reference to FIGS. 5 to 6.In an ultrasonic sensor 1 having the above-described configuration, the ultrasonic element 5 vibrates by ultrasonic when an electric signal is input from a wiring (not shown). When the ultrasonic element 5 vibrates by ultrasonic, the vibration excites the element accommodating case 6 and causes it to vibrate. As a result, the ultrasonic microphone 4 including the ultrasonic element 5 and the element accommodating case 6 vibrates in a certain vibration mode.In the above-described configuration, the bottom plate portion 62 is provided with the recess 621, and the ultrasonic element 5 is mounted so as to cover the recess 621. In other words, the first space 622 formed by the recess 621 is filled with a medium having a propagation speed of the vibration from the ultrasonic element 5 different from that of the material of the bottom plate portion 62.For this reason, as shown in FIG. 5, the ultrasonic microphone 4 has a first vibration mode caused by the vibration from the ultrasonic element 5 propagating directly to the bottom plate portion 62. In addition to the first vibration mode, the ultrasonic microphone 4 has a second vibration mode caused by the vibration from the ultrasonic element 5 propagating to the bottom plate portion 62 via the first space 622. Accordingly, in addition to a first structural resonant frequency generated from the first vibration mode, a second structural resonant frequency is generated from the second vibration mode. The first structural resonant frequency and the second structural resonant frequency have a relationship with each other such that neither is a higher order resonant frequency of the other.A computer simulation of the above-described vibration state was performed to obtain the acoustic impedance characteristic of the ultrasonic microphone 4 shown in Fig. 3, and the result is shown in Fig. 6. In the ultrasonic microphone 4, two significant structural resonant frequencies in the range of 40 to 80 kHz are generated. One of the structural resonant frequencies generated at about 48 kHz corresponds to the first vibration mode described above. The other structural resonant frequency generated at about 73 kHz is caused by the generation of the second vibration mode described above. Specifically, the other structural resonance frequency is considered as a combination of the vibration waves of the first vibration mode and the vibration of the second vibration mode.As described above, the recess 621 has a size and shape that significantly generates a first structural resonant frequency and a second structural resonant frequency that do not have such a relationship with each other that one of the two is a higher-order resonant frequency of the other. For example, the outer shape of the recess 621 is not limited to a substantially cylindrical shape, but may instead be substantially a prism, an elliptic cylinder, or any other suitable shape.According to this embodiment, an ultrasonic microphone 4 can be provided by a simple shape change, i.e., by providing the recess 621 on the inner surface of the bottom plate portion 62, with a plurality of structural resonance frequencies. Further, as compared with the conventional structure in which two tubular housings having bases of different sizes are bonded to each other, it is possible to suppress a decrease in durability and an increase in cost. Thus, a single ultrasonic sensor 1 having a plurality of resonant frequencies is provided while durability is secured.(First Modification)In the ultrasonic sensor 1, as shown in FIG. 7, the element accommodating case 6 may have a side plate portion 61 made of only the thin-walled part 611. Such a structure can also produce the effect with a plurality of resonance frequencies when the recess 621 is formed in the bottom plate portion 62 and the ultrasonic element 5 is placed thereon.(Second Modification)In the ultrasonic sensor 1, as shown in FIG. 8, the ultrasonic microphone 4 may have a structure in which the ultrasonic element 5 covers only a part of the recess 621, i.e., a structure in which the first space 622 and the second space 63 communicate with each other. Even with such a structure, the ultrasonic sensor 1 can have a plurality of resonance frequencies as in the above-described embodiment. Note that FIG. 8 shows a plan view of the ultrasonic microphone 4 as viewed from the directivity center axis, and the broken line represents the part of the contour of the recess 621 that is not visible due to the ultrasonic element 5.(Third Modification)In the ultrasonic sensor 1, as shown in FIG. 9, the recess 621 may be a groove having a wedge-like cross section. In this case, the outer shape of the recess 621 is, for example, a conical or polygonal pyramid as viewed in a cross-sectional view. That is, the recess 621 may have any shape that provides the ultrasonic microphone 4 with the first space 622 serving as a second propagation path of the vibration from the ultrasonic element 5, and the shape is not limited to that of the above-described embodiment and may be changed as appropriate.When the distance between the bottom plate portion 62 and the ultrasonic member 5 in the thickness direction of the bottom plate portion 62 serves as "the depth", an example in which the depth of the first space 622 is constant has been described in the previous embodiment. On the other hand, in this modified example, the depth of the first space 622 varies depending on the position due to the above-described shape of the recess 621, which may allow the ultrasonic sensor to have three or more resonance frequencies. In this case, the recess 621 without the wedge-like cross section may have a shape having a plurality of portions having different depths, such as a stepped shape, and the shape may be determined as needed. In addition, if the recess 621 has a shape whose depth is not uniform, the effect of expanding the resonance band can also be obtained.(Fourth Modification)In the ultrasonic sensor 1, as shown in FIG. 10, the bottom plate portion 62 may have a protrusion 623 having a frame body shape or a partial frame body shape on its inner surface instead of the recess 621. In this case, the ultrasonic element 5 is attached to the distal end surface of the protrusion 623, and forms a third space 624 together with the region inside the protrusion 623 having a substantially frame body shape. In other words, the part of the bottom plate portion 62 within the contour is provided with the substantially frame-body-shaped protrusion 623. The ultrasonic element 5 is attached to the distal end surface of the protrusion 623 so that the third space 624 is formed between the protrusion 623 and the ultrasonic element 5.This allows the ultrasonic microphone 4 to have a vibration mode caused by the vibration from the ultrasonic element 5 propagating to the bottom plate portion 62 via the protrusion 623 and an additional vibration mode caused by the vibration from the ultrasonic element 5 propagating to the bottom plate portion 62 via the third space 624. Therefore, this structure also provides an ultrasonic sensor 1 having a plurality of resonant frequencies.Note that the protrusion 623 has such a size and shape as the recess 621 that the first and second structural resonance frequencies are distinctly generated, which do not have such a relationship with each other that one of the two is a higher-order resonance frequency of the other. Further, the third space 624 may be either a closed space that is not connected to the second space 63 due to the ultrasonic element 5 or a space that communicates with the second space 63 as in the second modification described above.(Other Embodiments)Although the present disclosure is described based on examples, it is understood that the present disclosure is not limited to the examples and structures. The present disclosure encompasses various modifications and variations within the scope of equivalence. Moreover, the scope of the present disclosure and its spirit include other combinations and embodiments, not only various combinations and embodiments, but also those having only one of the components or additional or fewer components.(1) For example, the ultrasonic sensor 1 is not limited to a configuration capable of transmitting and receiving ultrasonic waves, and may have a configuration capable of transmitting ultrasonic waves only. Alternatively, the ultrasonic sensor 1 may be configured to have only a function of receiving the reflected waves of search waves, i.e., ultrasonic waves transmitted from an ultrasonic transmitter and reflected from objects around them. That is, the ultrasonic microphone 4 may be for transmitting and receiving, transmitting only, or receiving only.(2) The outer shape of the ultrasonic microphone 4, that is, the element accommodating case 6, is not limited to a substantially cylindrical shape, but may instead be a substantially regular hexagonal prism, a substantially regular octagonal prism, or the like.(3) The ultrasonic element 5 is not limited to a piezoelectric element, and a so-called capacitive element may be used, for example.(4) Components formed seamless and integrally with each other in the foregoing description can be formed by connecting separate members to each other. Similarly, separate components connected together may be formed seamless and integral with each other.(5) Components formed of the same material in the foregoing description may be formed of materials different from each other. Similarly, components formed from different materials may be formed from the same material.(6) The above-described embodiment and its modifications can be combined with each other. For example, the bottom plate portion 62 may have a shape in which the protrusion 623 is provided and the recess 621 is formed inside the bottom plate portion 62.

Claims

An ultrasonic sensor (1) comprising: an ultrasonic element (5) that converts between an electric signal and an ultrasonic vibration; and an element accommodating case (6) that has a bottomed tubular shape and accommodates the ultrasonic element therein, and includes: a side plate portion (61) that has a tubular shape surrounding a directivity center axis (DA); and a bottom plate portion (62) that closes an end of the side plate portion in an axial direction parallel to the directivity center axis, wherein the ultrasonic element is attached to the bottom plate portion, a part of the bottom plate portion includes, within a contour of the ultrasonic element as viewed along the directivity center axis, a space (622) defined by a part of the ultrasonic element, the bottom plate portion includes a recess (621), which is formed at a position separated from an inner wall of the side plate portion, the space (622) is formed by the ultrasonic member and the recess, the ultrasonic member is disposed with a space from the inner wall of the side plate portion, and the ultrasonic member (5) is disposed so as to cover only a part of the recess (621).The ultrasonic sensor according to claim 1, wherein an end surface of the ultrasonic element facing the bottom plate portion includes: a contact part (51) which is a part attached to the bottom plate portion; and a non-contact part (52) which is the rest of the end surface, and wherein an area of the non-contact part is equal to or larger than an area of the contact part.The ultrasonic sensor according to claim 1 or 2, wherein the side plate portion includes: a thin-walled part (611) having a cylindrical shape or a partially cylindrical shape with a predetermined thickness in a radial direction perpendicular to the directivity center axis; and a thick-walled part (612) provided at a part of the thin-walled part in a circumferential direction surrounding the directivity center axis and having a radial dimension larger than the predetermined thickness.The ultrasonic sensor according to any one of claims 1 to 3, wherein the space is filled with a substance different from a material of the bottom plate portion.The ultrasonic sensor according to any one of claims 1 to 4, wherein, in response to a distance between the ultrasonic element and the bottom plate portion in a thickness direction of the bottom plate portion serving as a depth, the depth of the space is constant.The ultrasonic sensor according to any one of claims 1 to 4, wherein, in response to a distance between the ultrasonic element and the bottom plate portion in a thickness direction of the bottom plate portion serving as a depth, the depth of the space varies depending on the position.

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