JP2020102659A - Ultrasonic transducer - Google Patents

Abstract

To provide an ultrasonic transducer with an arbitrary directivity.SOLUTION: An ultrasonic transducer 100 includes a diaphragm 2 in which the outer surface 20 is formed as a curved surface, and a piezoelectric element 1 is bonded to an inner surface 21, and on the outer surface 20, an intersection line L1 that intersects an imaginary plane including an axis P of a main beam M when the diaphragm 2 radiates ultrasonic waves W due to the vibration of the piezoelectric element 1 is an arc that is convex outward.SELECTED DRAWING: Figure 1

Description

The present invention relates to an ultrasonic transducer used as a sensor.

Patent Document 1 discloses ultrasonic waves used in a vehicle (vehicle-mounted) clearance sonar used for a device that detects a possibility of contact with an obstacle on a road surface when the vehicle is parked, turns, or the like and warns a driver. A sensor (an example of an ultrasonic transducer of the present application) is described. This ultrasonic sensor has a piezoelectric vibrator and a sensor housing having a substantially circular cross section and having an inner bottom surface. The piezoelectric vibrator is fixed to the center position on the inner bottom surface with an adhesive or the like. The vibration surface (diaphragm of the present application) of this ultrasonic sensor is a part of the bottom surface of the sensor housing to which the piezoelectric vibrator is fixed. A hollow portion is formed inside the sensor housing, and one surface is open. The outer shape of the sensor housing is formed by cutting off a part in an arc shape on the left and right sides of the opening to form an outer step. The hollow portion is formed by cutting the inside into an oval shape (oval shape) along the outer shape of the sensor housing, and an inner step portion is formed at a substantially middle portion in the axial direction. .. The outer step portion and the inner step portion are provided along the oval side surface. This narrows the directivity of ultrasonic waves from the vibrating surface. As the oval shape, an oval shape whose major axis extends in the vertical direction is shown.

In Patent Document 2, a conical focusing is formed by forming three mutually independent circular and concentric annular piezoelectric transducers (an example of the piezoelectric element of the present application) directly on a concave lens provided on an end surface of an acoustic lens on the object side. Type ultrasonic probe (an example of the ultrasonic transducer of the present application) is described. An ultrasonic probe converts an electrical input into ultrasonic waves, focuses a beam on the surface of or inside a subject, and irradiates it. The ultrasound is partially scattered and absorbed by the subject and then reflected by the ultrasound. It has a function of detecting a beam, converting it into an electric signal again, and outputting it. These functions are performed by the acoustic lens and the piezoelectric transducer, which are components of the ultrasonic probe. The piezoelectric transducer performs electric/ultrasonic conversion and ultrasonic signal detection. The acoustic lens focuses the ultrasonic beam.

JP, 2002-058091, A JP-A-6-281634

On-vehicle ultrasonic transducers, especially ultrasonic transducers for sonar applications, which are sensors for detecting obstacles on the road surface, require countermeasures against flying stones. In addition, for the ultrasonic transducer mounted on the vehicle, directivity control such as narrowing the vertical directivity of the vehicle and widening the horizontal directivity is desired.

As a countermeasure against the above flying stones, for example, a thick diaphragm plate can be considered. In the ultrasonic transducer described in Patent Document 1, when the diaphragm has a thick plate, it is necessary to increase the area of the diaphragm in order to correct the change in the resonance frequency corresponding to the thick plate. Since the ultrasonic transducer is usually formed to have a circular outer shape (cylindrical shape), the diaphragm of the ultrasonic transducer described in Patent Document 1 approaches an oval shape to a circular shape as its area increases. There is no choice but to form. Then, the ultrasonic transducer described in Patent Document 1 cannot control the directivity. That is, the ultrasonic transducer described in Patent Document 1 cannot obtain arbitrary directivity.

The ultrasonic transducer described in Patent Document 2 focuses ultrasonic waves in a conical shape, but has different directivities in two orthogonal directions, for example, the vertical direction (vertical direction) and the horizontal direction (horizontal direction) of the vehicle. It is not considered to have.

The present invention has been made in view of such circumstances, and an object thereof is to provide an ultrasonic transducer having an arbitrary directivity.

The characteristic configuration of the ultrasonic transducer according to the present invention for achieving the above object, at least, the outer surface is formed as a curved surface, a piezoelectric element is bonded to the inner surface of the diaphragm, the outer surface, An intersecting line portion that intersects an imaginary plane including the axis of the main beam when the diaphragm radiates ultrasonic waves due to the vibration of the piezoelectric element is at a point including a curved curve on the outer side or the inner side.

According to the above configuration, the outer surface of the diaphragm serves as a surface on the ultrasonic wave transmitting/receiving side. Further, the intersecting line portion that intersects the virtual plane including the axis of the main beam corresponds to the outer shape of the cross section of the diaphragm on the virtual plane. The intersecting line portion corresponding to the outer shape of this cross section has a convex shape (convex outward) or a concave shape (convex inward).

In this way, by making the intersecting line portion concave, compared to the case where the intersecting line portion is linear, the ultrasonic beam emitted from the diaphragm (in the present application, so-called main beam) The directivity is narrowed. By adjusting the concave shape, the directivity of this beam can be sharply included.

By thus forming the intersecting line portion in a convex shape, the directivity of the beam of ultrasonic waves transmitted from the diaphragm is made wider than in the case where the intersecting line portion is formed in a straight line shape. By adjusting the convex shape, it is possible to make the beam directivity extremely wide.

As described above, in the diaphragm whose outer surface is formed by the curved surface, by forming the intersecting line portion into a concave shape or a convex shape, it is possible to provide an ultrasonic transducer having an arbitrary directivity. ..

A further characteristic configuration of the ultrasonic transducer according to the present invention is that the curved line includes an arc line.

According to the above configuration, at least a part of the curve of the intersecting line portion can have a shape along the arc. This facilitates the design and manufacture of the shape of the outer surface of the diaphragm. For example, the outer surface of the diaphragm can be easily processed.

A further characteristic configuration of the ultrasonic transducer according to the present invention is a first curve that is the curve corresponding to the first virtual surface that is the virtual surface, and the virtual surface that is orthogonal to the first virtual surface. This is that the concavo-convex relationship with the second curve corresponding to the two virtual surfaces is opposite to each other.

According to the above configuration, the outer surface of the diaphragm has a so-called saddle shape. As a result, the directivity in one direction can be narrowed and the directivity in the other direction can be widened with respect to the two orthogonal directions, compared to the case where the surface of the diaphragm is flat.

For example, when the first virtual plane is a horizontal plane, the first curve is convex outward, and the second virtual plane is a vertical plane, and the second curve is convex further inward, the outer surface is It is possible to widen the horizontal directivity while narrowing the vertical directivity as compared with the case where the plane is flat.

That is, when it is desired to obtain directivity that narrows the directivity in one direction (for example, the vertical direction) and widens the directivity in the other orthogonal direction (the horizontal direction orthogonal to the vertical direction), The dimension of the diaphragm in one direction (vertical direction) can be shortened, and the dimension of the diaphragm in the other direction (horizontal direction) can be lengthened as compared with the case where the surface of the diaphragm is flat.

Explaining in comparison with the ultrasonic transducer described in Patent Document 1, the diaphragm of the ultrasonic transducer described in Patent Document 1 has an oval shape whose long axis extends in the vertical direction. The diaphragm of such an ultrasonic transducer can have a more circular shape. That is, the outer diameter of the ultrasonic transducer can be reduced by making the diaphragm into an oval shape or a circular shape that fits within a smaller circle. By reducing the outer diameter of the ultrasonic transducer, the sensor using the ultrasonic transducer can be downsized, and the mountability on the vehicle and the design of the vehicle can be improved.

A further characteristic configuration of the ultrasonic transducer according to the present invention is that the curved line has a central curved line portion that intersects the axis and end curved portions at both ends of the central curved line portion, and the curved line is outside. In the case of being convex, the end curved portion has a smaller curvature than the central curved portion, and in the case of the curve being convex inward, the end curved portion has a larger curvature than the central curved portion.

According to the above configuration, it is possible to adjust the ultrasonic waves radiated at the end portion of the diaphragm so as not to spread too far to the outside in the radial direction of the diaphragm. In other words, it is possible to prevent the ultrasonic beam from becoming wider than necessary. This improves controllability of the detection range when the ultrasonic transducer is used as a sensor such as sonar. As an example of improving controllability of the detection range, setting of the detection range is facilitated or simplified. As another example, the detection accuracy becomes uniform in the range set as the detection range.

An ultrasonic transducer having an arbitrary directivity can be provided.

Schematic diagram of sonar and ultrasonic transducer Front view of the diaphragm from the outer surface side Sectional drawing in the 1st virtual surface of the main body containing a diaphragm (III-III cross section) Sectional drawing in the 2nd virtual surface of the main body containing a diaphragm (IV-IV cross section) Perspective view of the diaphragm from the outer surface side Side view conceptual diagram showing an example of mounting a sonar on a vehicle Top view conceptual diagram showing an example of mounting a sonar on a vehicle Another cross-sectional view of the body including the diaphragm in a first virtual plane. Another cross-sectional view of the body including the diaphragm in a second virtual plane.

An ultrasonic transducer according to an embodiment of the present invention will be described with reference to the drawings.

[Overall configuration of sonar]
FIG. 1 illustrates a sonar 200 that detects a detection target B such as an obstacle. The sonar 200 includes an ultrasonic transducer 100 as an ultrasonic sensor that emits an ultrasonic wave W to detect a detection target B, a power supply circuit 9 that supplies an alternating current to the ultrasonic transducer 100 to emit an ultrasonic wave W, and an ultrasonic wave. The sound wave transducer 100 has a detection device 90 that specifies the position and size of the detection target B based on the current change of the alternating current that the reflected wave R is received and converted. The reflected wave R is an ultrasonic wave reflected by the detection target B of the ultrasonic wave W. The power supply circuit 9 is an AC current source or an AC voltage source that generates a desired AC current or AC voltage.

[Configuration of the entire transducer]
The ultrasonic transducer 100 has a diaphragm 2 to which the piezoelectric element 1 is attached (an example of joining) by adhesion, and a bottomed cylindrical main body 3 having the diaphragm 2 as a bottom. The ultrasonic transducer 100 is electrically connected to the power supply circuit 9 and the detection device 90 via a pair of signal lines 91. The detection device 90 is connected to the ultrasonic transducer 100 via a pair of signal lines 92 branched from the pair of signal lines 91.

〔Piezoelectric element〕
The piezoelectric element 1 is a member that produces a strain when a voltage is applied. The piezoelectric element 1 generates vibration that repeatedly expands and contracts due to the supply of alternating current (application of alternating voltage). Examples of the material of the piezoelectric element 1 include PZT (lead zirconate titanate) and BaTiO ₃ (barium titanium(IV) oxide). One electrode of the piezoelectric element 1 is attached to the inner surface 21 of the diaphragm 2 and electrically connected to the diaphragm 2. The piezoelectric element 1 is electrically connected to one of the signal lines 91.

[Body]
The main body 3 is formed in a bottomed tubular shape having a cylindrical tubular portion 30 and a diaphragm 2 serving as a bottom that closes one end of the tubular portion 30. The main body 3 houses the piezoelectric element 1 inside the bottomed cylinder.

The tubular portion 30 and the diaphragm 2 are formed of a conductive material mainly composed of metal such as aluminum, and the tubular portion 30 and the diaphragm 2 are electrically connected. The tubular portion 30 is formed in a straight tubular shape. The tubular portion 30 is electrically connected to the other one of the signal lines 91. The signal line 91 electrically connected to the tubular portion 30 is connected to the ground G and grounded. That is, the other electrode of the piezoelectric element 1 is electrically connected to the ground G via the diaphragm 2, the tubular portion 30, and the other of the signal lines 91.

The diaphragm 2 is a member that vibrates due to the inverse piezoelectric effect of the piezoelectric element 1 and transmits an ultrasonic wave W from the outer surface 20 to the outside. The diaphragm 2 is a member that receives an ultrasonic wave (reflected wave R) from the outside and causes the piezoelectric element 1 to be distorted. From the diaphragm 2, a main beam M and, as the case may be, side lobes (not shown) directed to the outside in the radial direction of the main beam M are emitted as a beam of the ultrasonic wave W. In this embodiment, as shown in FIG. 2, the diaphragm 2 has a circular outer shape in a front view on the outer surface 20 side.

The axis P in FIG. 1 is the axis of the main beam M. The axis P is the center of the half-value angle in the radial direction of the main beam M. In the present embodiment, the extending direction of the axis P coincides with the center of the outer shape of the diaphragm 2 on the outer surface 20 side in a front view. Further, it coincides with the axial center of the tube portion 30 of the main body 3 in the extending direction of the tube.

An intersection with the outer surface of the diaphragm 2 when the axis P is extended will be referred to as an intersection Q below. In the present embodiment, hereinafter, the main beam M will be simply referred to as the ultrasonic wave W.

The diaphragm 2 of the present embodiment is formed integrally with the tubular portion 30 and has a bottomed tubular shape with the diaphragm 2 serving as a bottom portion, and is electrically connected to the tubular portion 30. In the present embodiment, the outer peripheral portion of the outer surface 20 of the diaphragm 2 is the end portion of the tubular portion 30. Thereby, the main body 3 such as the diaphragm 2 and the tubular portion 30 can be easily processed, and the cost can be reduced.

The piezoelectric element 1 is attached to the inner surface 21 of the diaphragm 2.

[Shape of diaphragm]
As shown in FIG. 1, at least the outer surface 20 of the diaphragm 2 is formed as a curved surface. In addition, in the present embodiment, the inner surface 21 of the diaphragm 2 is also a curved surface.

In this embodiment, as shown in FIG. 2, the diaphragm 2 has a circular outer shape in a front view on the outer surface 20 side. FIG. 2 shows an intersection line (an example of an intersection line portion) as an imaginary line that intersects the outer surface 20 with the virtual surfaces S1 and S2 different from each other (parallel to the axis P) including the axis P (see FIG. 1). ) Are shown as intersection lines L1 and L2 (an example of a first curve and an example of a second curve, respectively). The line of intersection L1 is a line of intersection between the outer surface 20 and the first virtual plane S1 that is a virtual plane including the axis P. The line of intersection L2 is a line of intersection between the outer surface 20 and the second virtual surface S2 that is the virtual surface that includes the axis P and is orthogonal to the first virtual surface S1.

In the diaphragm 2, the intersecting lines L1 and L2 as intersecting line portions that intersect the virtual planes S1 and S2 including the axis P include a curved line that is convex outside or inside. In the present embodiment, on the outer surface 20 of the diaphragm 2, the intersecting lines L1 and L2 that intersect the virtual plane including the axis P are arcs that are convex outward or inward (one example of a curved line, one example of an arc line). Note that the inward convex means a concave portion when viewed from the outer surface 20 side. The intersection lines L1 and L2 pass through the intersection Q, respectively. The intersection lines L1 and L2 are orthogonal to each other at the intersection point Q.

FIG. 3 illustrates a cross section of the ultrasonic transducer 100 including the line of intersection L1 in the case where the line of intersection L1 is one arc that is convex outward. The cross section of the ultrasonic transducer 100 shown in FIG. 3 corresponds to the cross section of the first virtual surface S1 (see FIG. 2).

More specifically, when the intersecting line L1 is one arc that is convex outward, the cross section of the diaphragm 2 formed by a plane parallel to the intersecting line L1 is convex with respect to the radiation direction of the ultrasonic wave W (direction along the axis P). Be in shape.

FIG. 4 illustrates a cross section of the ultrasonic transducer 100 including the line of intersection L2 when the line of intersection L2 is one arc that is convex inward. The cross section of the ultrasonic transducer 100 shown in FIG. 4 corresponds to the cross section of the second virtual surface S2 (see FIG. 2). The relationship between the intersecting line L1 and the intersecting line L2 may be reversed.

More specifically, when the intersecting line L2 is one arc that is convex inward, the cross section of the diaphragm 2 formed by a plane parallel to the intersecting line L2 is concave with respect to the radiation direction of the ultrasonic wave W (direction along the axis P). Be in shape.

FIG. 5 shows a perspective view of the ultrasonic transducer 100 as viewed from the outer surface 20 side. The outer surface 20 has a so-called saddle shape. The line of intersection L1 runs along the bottom of the valley on the outer surface 20. The line of intersection L2 is along a ridge or ridgeline on the outer surface 20.

Virtual lines on the outer surface 20 and lines (not shown) other than the intersecting line L2 orthogonal to the intersecting line L1 are convex downward with the intersection point with the intersecting line L1 as the summit, like the intersecting line L2. Is the curve of.

Virtual lines on the outer surface 20 and lines (not shown) other than the intersecting line L1 orthogonal to the intersecting line L2 are convex upward with the intersection point with the intersecting line L1 as the summit, like the intersecting line L1. Is the curve of.

[Example of using sonar]
6 and 7 show a front portion including a front F of a vehicle C equipped with a sonar 200 using the ultrasonic transducer 100. FIG. 6 is a schematic diagram of a side view of the vehicle C. FIG. 7 is a schematic diagram of the top view of the vehicle C. An ultrasonic transducer 100 is attached to the front F of the vehicle C at a position displaced toward the ground, with the diaphragm 2 facing the front side in the traveling direction of the vehicle.

In other words, the ultrasonic transducer 100 is attached so that the axis P (radiation direction of the ultrasonic wave W) is along the traveling direction of the vehicle and is slightly upward from the horizontal. 6 and 7, the ultrasonic transducer 100 is fixed to the vehicle C so that the line of intersection L2 is along a plane perpendicular to the ground. A cross section of a plane parallel to the intersection line L1 (see FIG. 3) of the diaphragm 2 has a convex shape in the radiation direction of the ultrasonic waves W (direction along the axis P). A cross section of a plane parallel to the intersection line L2 (see FIG. 4) of the diaphragm 2 has a concave shape with respect to the radiation direction of the ultrasonic wave W (direction along the axis P).

The angle Q1 shown in FIG. 6 is a half-value angle of the ultrasonic wave W on a plane parallel to the axis P and perpendicular to the ground (corresponding to the second virtual plane S2 shown in FIG. 2).

The angle Q2 shown in FIG. 7 is a half-value angle of the ultrasonic wave W on a plane parallel to the axis P and orthogonal to the plane perpendicular to the ground (corresponding to the first virtual plane S1 shown in FIG. 2). The angles Q1 and Q2 are half-value angles of the ultrasonic wave W. As shown in FIGS. 3 and 4, the intersecting line L1 is convex outward and the intersecting line L2 is convex inward. Therefore, in the present embodiment, the angle Q1 (see FIG. 6) is equal to the angle Q2 (see FIG. 6). The angle is smaller than that of (see 7).

A portion of the outer surface 20 of the ultrasonic transducer 100, which is convex outward, has a greater radiation angle of the ultrasonic wave W and a reflected wave R (see FIG. 1) than in the conventional structure in which the intersection line L1 is a straight line. Since the reception angle can be widened to the angle Q2, the directivity can be widened. Further, in the portion of the outer surface 20 of the ultrasonic transducer 100 that is convex inward, the emission angle of the ultrasonic wave W and the reflected wave R (see FIG. 1, respectively) compared to the conventional structure in which the intersection line L2 is a straight line. Since the reception angle of) can be narrowed to the angle Q1, the directivity can be narrowed.

As a result, the ultrasonic transducer 100 narrows its directivity in the direction perpendicular to the ground with the direction of travel of the vehicle C suppressed, and suppresses the influence of unnecessary reflected waves from the road surface. Only obstacles in the vicinity can be detected accurately. Further, the ultrasonic transducer 100 can detect an obstacle in front of the vehicle C in a wide range by widening its directivity in the left-right direction in the traveling direction of the vehicle C in a state where the directivity is oriented in the traveling direction of the vehicle C. ..

As described above, it is possible to provide an ultrasonic transducer having an arbitrary directivity.

[Another embodiment]
(1) In the above embodiment, the case has been described as an example where the line of intersection L1 is one arc that is convex outward. However, the intersecting line L1 may include one arc that is convex outward. For example, both ends of the intersection line L1 may be linear. In this case, the portion including the center of the line of intersection L1 (the point of intersection with the axis P) may be an arc.

(2) In the above embodiment, the case has been described as an example where the line of intersection L2 is one arc that is convex inward. However, the intersecting line L2 may include one arc that is convex inward. For example, both ends of the intersection line L2 may be linear. In this case, the portion including the center of the line of intersection L2 (the point of intersection Q with the axis P) may be an arc.

(3) In the above embodiment, the case has been described as an example where the line of intersection L1 is one arc that is convex outward. However, the line of intersection L1 may include a plurality of arcs that are convex outward. For example, as shown in FIG. 8, a portion including the center of the intersection line L1 (intersection point Q with the axis P) is defined as a first curved portion that is convex outward (hereinafter referred to as a central curved portion F1), and the central curved portion is formed. At both ends of F1, a second curved portion having a curvature smaller than that of the central curved portion F1 and protruding outward (hereinafter, referred to as end curved portion F2) may be provided. It is preferable that the boundary between the central curved portion F1 and the end curved portion F2 be smoothly continuous. As a result, it is possible to suppress the unnecessary spread of the directivity of the radiation or reception of ultrasonic waves in the outer peripheral portion of the diaphragm 2. In addition, the controllability of directivity can be improved.

(4) In the above embodiment, the case where the intersection line L2 is one arc that is convex inward has been described as an example. However, the line of intersection L2 may include a plurality of arcs that are convex inward. For example, as shown in FIG. 9, a portion including the center of the intersection line L2 (intersection point Q with the axis P) is defined as a third inwardly convex curved portion (hereinafter referred to as central curved portion F3), and the central curved portion is formed. A fourth inwardly convex curved portion (hereinafter, referred to as end curved portion F4) having a larger curvature than the central curved portion F3 may be provided at both ends of F3. It is preferable that the boundary between the central curved portion F3 and the end curved portion F4 be smoothly continuous. As a result, it is possible to suppress the unnecessary spread of the directivity of the radiation or reception of ultrasonic waves in the outer peripheral portion of the diaphragm 2. In addition, the controllability of directivity can be improved.

(5) In the above embodiment, the intersecting line L1 is one arc that is convex outward, the intersecting line L2 is one arc that is convex inward, and the intersecting lines L1 and L2 are orthogonal to each other at the intersecting point Q. As shown in FIG. 5, the case where the outer surface 20 has a so-called saddle shape is illustrated. Then, a virtual line on the outer surface 20 that is orthogonal to the intersection line L1 (not shown) is a downwardly convex curve having the apex at the intersection point with the intersection line L1 as with the intersection line L2. I explained a case. Further, a virtual line on the outer surface 20 that is orthogonal to the intersection line L2 (not shown) is an upwardly convex curve with the apex at the intersection line L1 as at the intersection line L1. I explained a case. However, a shape in which one of the intersecting lines L1 and L2 is linear, that is, a shape in which the outer surface has only convex inside (intersecting line L1 is linear) or a shape having only convex outside (intersecting line L2) May be linear).

Note that the configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in other embodiments, as long as no contradiction occurs. The embodiments disclosed in the present specification are exemplifications, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within a range not departing from the object of the present invention.

The present invention can be applied to an ultrasonic transducer used as a sensor.

1 :Piezoelectric element 2 :Diaphragm 3 :Main body 9 :Power supply circuit 20 :Outer surface 21 :Inner surface 30 :Cylinder part 90 :Detecting device 100 :Ultrasonic transducer 200 :Sonar B :Detection target F1: Central curve part F2 :End Part curve part F3: central curve part F4: end curve part L1: intersection line (intersection line part, first curve)
L2: Line of intersection (line of intersection, second curve)
M: Main beam P: Shaft (axis center)
Q: intersection R: reflected wave S1: first virtual surface (virtual surface)
S2: Second virtual surface (virtual surface)
W: Ultrasound

Claims (4)

At least, the outer surface is formed as a curved surface, the inner surface is provided with a diaphragm to which a piezoelectric element is bonded,
The outer surface is an ultrasonic transducer in which an intersecting line portion intersecting an imaginary plane including an axis of a main beam when the diaphragm radiates an ultrasonic wave by the vibration of the piezoelectric element includes a curve which is convex outward or inward. .. The ultrasonic transducer according to claim 1, wherein the curved line includes an arc line. A first curve that is the curve corresponding to the first virtual surface that is the virtual surface, and the virtual surface, the uneven relationship between the second curve that corresponds to the second virtual surface orthogonal to the first virtual surface The ultrasonic transducer according to claim 1 or 2, which are opposite to each other. The curved line has a central curved line portion that intersects with the axis, and end curved line portions at both ends of the central curved line portion,
When the curve is convex outward, the end curve portion has a smaller curvature than the central curve portion,
The ultrasonic transducer according to any one of claims 1 to 3, wherein when the curve is convex inward, the end curve portion has a larger curvature than the central curve portion.

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