JP7627110B2 - Piezoelectric transducers and ultrasonic transducers - Google Patents

Description

The present invention relates to a piezoelectric vibrator and an ultrasonic transducer.

The following Patent Document 1 discloses an ultrasonic transducer that uses a piezoelectric vibrator. Such an ultrasonic transducer outputs ultrasonic waves and receives ultrasonic waves reflected by the object to be detected.

JP 2014-82655 A

The inventors discovered that detection directionality can be achieved by adjusting the directional angle depending on the direction, rather than outputting ultrasonic waves with the same directional angle in all directions. As a result, they conducted extensive research into adjusting the directional angle and discovered a new technology that can achieve detection directionality.

The present invention aims to provide a piezoelectric vibrator and ultrasonic transducer with directional detection.

A piezoelectric vibrator according to one embodiment of the present invention has a piezoelectric layer having a first main surface and a second main surface facing each other, a first electrode provided on the first main surface, and a second electrode provided on the second main surface and having the opposite polarity to the first electrode, and an active region defined as a region in which the piezoelectric layer is sandwiched between the first electrode and the second electrode includes a narrowing portion in which the width of the active region narrows and a widening portion in which the width of the active region widens are aligned along a first direction perpendicular to the thickness direction of the piezoelectric layer, as viewed in the thickness direction of the piezoelectric layer.

When the above piezoelectric vibrator is applied to an ultrasonic transducer, the active region includes a narrowing section in which the width of the active region narrows along the first direction and a widening section in which the width of the active region widens, so that vibrations in the first direction and in a direction perpendicular to the thickness direction of the piezoelectric layer are restricted. Therefore, with the above piezoelectric vibrator, the directivity angle in the first direction and in a direction perpendicular to the thickness direction of the piezoelectric layer is narrowed, and detection directionality can be achieved.

In another embodiment, the active region of the piezoelectric vibrator is composed of a first region and a second region that are separated from each other, and the first region has a narrowing portion and the second region has a widening portion.

In another embodiment of the piezoelectric vibrator, the second electrode has an extended end that is extended through the side surface of the piezoelectric layer to the first main surface, and when viewed in the thickness direction of the piezoelectric layer, the extended end of the second electrode is adjacent to the narrowed portion of the active region.

In another embodiment, the active area of the piezoelectric vibrator has a square outer shape.

In another embodiment, the active area of the piezoelectric vibrator has a perfectly circular outer shape.

In another embodiment, the active region of the piezoelectric vibrator has a rectangular outer shape, and the long side of the rectangle is aligned along the first direction.

In another embodiment of the piezoelectric vibrator, the width of the active region gradually decreases in the narrowed portion of the narrowed portion, and gradually increases in the widened portion of the narrowed portion.

In another embodiment of the piezoelectric vibrator, the second electrode is provided over the entire area of the second main surface of the piezoelectric layer, and the shape of the first electrode and the shape of the active region are the same when viewed in the thickness direction of the piezoelectric layer.

An ultrasonic transducer according to one embodiment of the present invention includes the above-described piezoelectric vibrator, which outputs ultrasonic waves in response to an input voltage signal.

An ultrasonic transducer according to another embodiment further includes a bottomed cylindrical case in which the piezoelectric transducer is housed, and the second main surface of the piezoelectric layer of the piezoelectric transducer faces the bottom surface of the case.

The present invention provides a piezoelectric vibrator and an ultrasonic transducer with directional detection.

1 is a schematic configuration diagram illustrating an ultrasonic detection system according to an embodiment. FIG. 2 is a schematic cross-sectional view showing the ultrasonic transducer of FIG. 1. FIG. 3 is a schematic perspective view showing the piezoelectric vibrator of FIG. 2 . 4 is a diagram showing an active region of a piezoelectric layer of the piezoelectric vibrator of FIG. 3. 1A-1C are diagrams showing different aspects of active regions. 1A-1C are diagrams showing different aspects of active regions. 1A-1C are diagrams showing different aspects of active regions. 4 is a schematic perspective view showing a piezoelectric vibrator according to a different embodiment from that shown in FIG. 3. 9 is a diagram showing an active region of a piezoelectric layer of the piezoelectric vibrator of FIG. 8 . 4 is a schematic perspective view showing a piezoelectric vibrator according to a different embodiment from that shown in FIG. 3. 11 is a diagram showing an active region of a piezoelectric layer of the piezoelectric vibrator of FIG. 10. 1A-1C are diagrams showing different aspects of active regions.

Below, an embodiment of the present invention will be described in detail with reference to the attached drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference numerals, and duplicate descriptions will be omitted.

In this embodiment, we will explain an ultrasonic detection system that uses ultrasonic waves to detect objects.

As shown in FIG. 1, the ultrasonic detection system 1 outputs ultrasonic waves to a specific object 10 and receives ultrasonic waves reflected by the object 10. The ultrasonic detection system 1 can detect the presence of the object 10 and the distance to the object 10 from the received ultrasonic waves.

The ultrasonic detection system 1 is configured with a control circuit 20 and an ultrasonic transducer 30.

The control circuit 20 is a circuit that generates a signal of a specific frequency and inputs the signal to the ultrasonic transducer 30 via the signal line 25. The control circuit 20 is also a circuit that appropriately amplifies and detects the ultrasonic signal received by the ultrasonic transducer 30. The control circuit 20 can include an LC circuit.

The ultrasonic transducer 30 oscillates in response to a signal input from the control circuit 20 and outputs an ultrasonic signal. When the ultrasonic transducer 30 receives an ultrasonic signal from the outside, it transmits the signal to the control circuit 20.

As shown in FIG. 2, the ultrasonic transducer 30 is configured with a piezoelectric vibrator 40 and a housing 50 that holds the piezoelectric vibrator 40.

The piezoelectric vibrator 40 has a generally square, flat plate-like outer shape, and is configured with a piezoelectric layer 41, a first electrode 42, and a second electrode 43, as shown in Figures 2 to 4.

The piezoelectric layer 41 has a generally square plate-like shape and has an upper surface 41a (first main surface) and a lower surface 41b (second main surface) that face each other. The piezoelectric layer 41 can be made of a piezoelectric ceramic material such as PZT. In the following description, for convenience of explanation, the thickness direction of the piezoelectric layer 41 is also referred to as the Z direction. In addition, the two directions that are perpendicular to the Z direction and perpendicular to each other are also referred to as the X direction and the Y direction. In this embodiment, the X direction is a direction parallel to one side of the piezoelectric layer 41, and the Y direction is a direction parallel to a side that is perpendicular to that side (the side parallel to the X direction).

The first electrode 42 is partially provided on the upper surface 41a of the piezoelectric layer 41, and one of the wirings (or leads) 26 extending from the signal line 25 is connected to the first electrode 42. The first electrode 42 extends along the X direction (first direction). The first electrode 42 has an electrode pattern that is linearly symmetrical with respect to a virtual line L that bisects the piezoelectric layer 41 in the X direction. Specifically, the electrode pattern of the first electrode 42 includes a first pattern 42a and a second pattern 42b, both of which are trapezoidal, and the upper bases of the trapezoids are aligned with each other on the virtual line L. Therefore, the electrode pattern of the first electrode 42 has a maximum width (i.e., Y-direction length) at both ends in the X direction and a minimum width on the virtual line L. In this embodiment, the first electrode 42 has an electrode pattern that is linearly symmetrical with respect to a virtual line (not shown) that bisects the piezoelectric layer 41 in the Y direction.

The second electrode 43 is connected to the other wiring (or lead) 27 extending from the signal line 25, and has the opposite polarity to the first electrode 42. The second electrode 43 is provided over the entire lower surface 41b of the piezoelectric layer 41. The second electrode 43 has an extended end 43a that is extended through the side surface 41c of the piezoelectric layer 41 to the upper surface 41a. The extended end 43a of the second electrode 43 is provided away from the first electrode 42 so as not to be conductive with the first electrode 42. The extended end 43a of the second electrode 43 is adjacent to the first electrode 42 when viewed from the Z direction. In the embodiment, the extended end 43a of the second electrode 43 is provided along one side of the upper surface 41a.

When a voltage signal is input from the signal line 25 through a pair of wirings 26 and 27, the active region S, in which the piezoelectric layer is sandwiched between the first electrode and the second electrode, expands and contracts, generating vibrations according to the input signal. The piezoelectric vibrator 40 vibrates in the plate thickness direction and can also vibrate in a direction perpendicular to the plate thickness direction.

As shown in FIG. 4, the active region S of the piezoelectric vibrator 40 according to this embodiment coincides with the region of the electrode pattern of the first electrode 42 when viewed in the thickness direction of the piezoelectric layer 41, and has a substantially square outer shape. That is, the active region S is linearly symmetrical with respect to the imaginary line L, and is configured to include a first region S1 corresponding to the first pattern 42a and a second region S2 corresponding to the second pattern 42b. In addition, the first region S1 and the second region S2 of the active region S are both trapezoidal, and the upper bases of the trapezoids are aligned on the imaginary line L. Like the electrode pattern of the first electrode 42, the active region S has a maximum width at both ends in the X direction and a minimum width on the imaginary line L.

The active region S has a narrowed portion 44. The narrowed portion 44 according to this embodiment is composed of a reduced width portion 45, the width of which gradually decreases corresponding to the first region S1, and a widened width portion 46, the width of which gradually increases corresponding to the second region S2, and the reduced width portion 45 and the widened width portion 46 are adjacent to each other in the X direction. In this embodiment, the reduced width portion 45 has a gradually decreasing width, and the widened width portion 46 has a gradually increasing width. The reduced width portion 45 may have a gradually decreasing width (i.e., in a step-like manner), or the widened width portion 46 may have a gradually increasing width (i.e., in a step-like manner). The extended end portion 43a of the second electrode 43 may be provided adjacent to the narrowed portion 44 of the active region S when viewed from the Z direction.

The housing 50 is composed of a cup portion 52, a frame portion 54, and a lid portion 56.

The cup portion 52 (case) has a bottomed cylindrical shape. The cup portion 52 includes a bottom cover 53 that extends parallel to the piezoelectric vibrator 40 (i.e., perpendicular to the Z direction). The above-mentioned piezoelectric vibrator 40 is housed in the cup portion 52 and placed on the bottom cover 53. The piezoelectric vibrator 40 is fixed to the bottom cover 53, for example, by an adhesive, so that the lower surface 41b of the piezoelectric layer 41 faces the bottom surface of the bottom cover 53. When the second electrode 43 is provided over the entire lower surface 41b of the piezoelectric layer 41, there are no irregularities on the lower surface 41b of the piezoelectric layer 41, so that high adhesion to the bottom cover 53 can be achieved. The cup portion 52 is made of resin and can be made of polybutylene terephthalate (PBT) or LCP.

The frame 54 is provided at the upper end of the cup 52 and has an annular shape. The lid 56 is provided at the inner opening of the frame 54 and cooperates with the frame 54 to close the upper opening of the cup 52. The lid 56 is coupled to the end of the signal line 25 and is provided so as to be able to hold the end of the signal line 25. The frame 54 can be made of, for example, nitrile rubber (NBR), and the lid 56 can be made of, for example, urethane.

In the ultrasonic transducer 30 described above, when a signal is input from the control circuit 20 via the signal line 25, the piezoelectric vibrator 40 vibrates and an ultrasonic signal is output from the bottom cover 53 side of the cup portion 52. In addition, when the ultrasonic transducer 30 receives an external ultrasonic signal at the bottom cover 53 of the cup portion 52, the ultrasonic signal is converted into a voltage signal in the piezoelectric vibrator 40 and sent to the control circuit 20 via the signal line 25.

The active region S of the piezoelectric vibrator 40 of the ultrasonic transducer 30 includes a narrowed portion 44. The inventors have newly discovered that when the active region S includes the narrowed portion 44 described above, the vibration of the piezoelectric vibrator 40 in the Y direction is restricted, and as a result, the directional angle in the Y direction is narrowed. At this time, the directional angle in the X direction of the piezoelectric vibrator 40 is not narrowed and is maintained as it is. That is, in the ultrasonic transducer 30, the directional angle in a specific direction is narrowed while the directional angle in other directions is maintained. Therefore, the ultrasonic transducer 30 realizes detection directivity. For example, when the ultrasonic transducer 30 is used to detect an object in front of a car, it is possible to adjust the directional angle in the vertical direction (for example, the Y direction in FIG. 1) to narrow the directional angle while maintaining the directional angle in the vehicle width direction (for example, the X direction in FIG. 1) so as not to detect obstacles on the roadway or in the air more than necessary.

In the above-described embodiment, the shape of the active region S of the piezoelectric vibrator 40 can be variously configured as shown in Figures 5 to 7.

For example, in FIG. 5(a), the portion where the contour line of the first region S1 of the active region S of the piezoelectric vibrator 40 and the contour line of the second region S2 are connected form a curved line without corners. In FIG. 5(b), the contour line of the first region S1 of the active region S of the piezoelectric vibrator 40 and the contour line of the second region S2 are curved over the entirety. When the contour of the active region S has no corners as in FIG. 5(a) and FIG. 5(b), the first electrode 42 and the second electrode 43 forming the active region S can be designed to have a shape with few corners, and the occurrence of cracks in the piezoelectric layer 41 due to stress concentration can be suppressed. In FIG. 5(c), the first region S1 and the second region S2 of the active region S are both isosceles triangular, and the vertices of the isosceles triangles are butted against each other on the virtual line L. In this case, the active region S is divided into a first region S1 and a second region S2, and the first pattern 42a and the second pattern 42b of the corresponding first electrode 42 are separated and not electrically connected. Therefore, the wiring 26 can be connected to each of the first pattern 42a and the second pattern 42b of the first electrode 42. The first region S1 and the second region S2 may be separated from each other.

In FIG. 6(a), the active region S includes a first region S1, a second region S2, and a rectangular third region S3 of equal width in the X direction. The narrowed portion 44 of the active region S is composed of a reduced width portion 45 corresponding to the first region S1, a widened width portion 46 corresponding to the second region S2, and an equal width portion 47 corresponding to the third region S3, and the reduced width portion 45, the equal width portion 47, and the widened width portion 46 are arranged adjacent to each other in this order along the X direction.

In FIG. 6(b), the contours of the first region S1, the second region S2, and the third region S3 of the active region S of the piezoelectric vibrator 40 are connected to each other in a curved line with no corners. In this case, as with the active region S in FIGS. 5(a) and 5(b), the first electrode 42 and the second electrode 43 can be designed to have a shape with few corners, and the occurrence of cracks in the piezoelectric layer 41 due to stress concentration can be suppressed.

In FIG. 7(a), the active region S includes a first region S1, a second region S2, and a fourth region S4 and a fifth region S5 that extend in a strip shape in the Y direction at the end of the piezoelectric layer 41 in the X direction. The fourth region S4 is located at the end of the piezoelectric layer 41 on the first region S1 side, and the fifth region S5 is located at the end of the piezoelectric layer 41 on the second region S2 side.

In FIG. 7(b), the active region S includes a first region S1 and a second region S2 each having an isosceles triangular shape, as well as a fourth region S4 and a fifth region S5 that extend in a strip shape in the Y direction at the end of the piezoelectric layer 41 in the X direction.

In FIG. 7(c), the active region S includes a first region S1, a second region S2, a fourth region S4, and a fifth region S5, as well as a rectangular third region S3 having an equal width in the X direction.

All of the active regions S shown in Figures 5 to 7 include a narrowed portion 44 in which a narrowed portion 45 corresponding to the first region S1 and a widened portion 46 corresponding to the second region S2 are arranged along the X direction with or without an equal-width portion 47 corresponding to the third region S3. Therefore, similar to the above-mentioned embodiment, it is possible to achieve detection directionality in the ultrasonic transducer 30.

The piezoelectric layer 41 of the piezoelectric vibrator 40 is not limited to a square plate shape, but may be a rectangular plate shape as shown in FIG. 8, or a circular plate shape as shown in FIG. 10.

The piezoelectric vibrator 40A shown in FIG. 8 has a rectangular flat piezoelectric layer 41 extending in the X direction. The first electrode 42 and the second electrode 43 of the piezoelectric vibrator 40A are the same as or similar to the first electrode 42 and the second electrode 43 of the piezoelectric vibrator 40 described above, and therefore will not be described.

9, the active region S of the piezoelectric vibrator 40A coincides with the region of the electrode pattern of the first electrode 42 when viewed in the thickness direction of the piezoelectric layer 41, and has a substantially rectangular outer shape. That is, the active region S is linearly symmetrical with respect to the imaginary line L, and is configured to include a first region S1 corresponding to the first pattern 42a and a second region S2 corresponding to the second pattern 42b. In addition, the first region S1 and the second region S2 of the active region S are both trapezoidal, and the upper bases of the trapezoids are aligned on the imaginary line L. Like the electrode pattern of the first electrode 42, the active region S has a maximum width at both ends in the X direction and a minimum width on the imaginary line L.

The active region S has a narrowed portion 44, similar to the piezoelectric vibrator 40 described above. The narrowed portion 44 according to this embodiment is composed of a narrowed portion 45, which corresponds to the first region S1 and has a gradually narrower width, and a widened portion 46, which corresponds to the second region S2 and has a gradually wider width, and the narrowed portion 45 and the widened portion 46 are adjacent to each other in the X direction.

Therefore, even with an ultrasonic transducer 30 equipped with a piezoelectric vibrator 40A, the directivity angle in a specific direction is narrowed while the directivity angle in other directions is maintained, achieving detection directionality.

The width may be gradually decreased at the narrowing portion 45 and gradually increased at the widening portion 46, or the width may be gradually decreased (i.e., stepped) at the narrowing portion 45 and gradually increased (i.e., stepped) at the widening portion 46. The extended end 43a of the second electrode 43 may be provided adjacent to the narrowing portion 44 of the active region S when viewed from the Z direction.

The piezoelectric vibrator 40B shown in FIG. 10 has a circular flat piezoelectric layer 41, a first electrode 42 partially provided on the upper surface 41a of the piezoelectric layer 41, and a second electrode 43 provided over the entire lower surface 41b of the piezoelectric layer 41.

The first electrode 42 has an electrode pattern that is linearly symmetrical with respect to a virtual line L that divides the piezoelectric layer 41 in the X direction. The electrode pattern of the first electrode 42 includes a first pattern 42a and a second pattern 42b, both of which are substantially trapezoidal, and the upper bases of the trapezoids are aligned with each other at the virtual line L. In the first pattern 42a and the second pattern 42b, the lower bases of the trapezoids are curved to follow the edges of the piezoelectric layer 41. Therefore, the electrode pattern of the first electrode 42 has a maximum width (i.e., Y-direction length) near both ends in the X direction and a minimum width on the virtual line L. In this embodiment, the first electrode 42 has an electrode pattern that is linearly symmetrical with respect to a virtual line (not shown) that divides the piezoelectric layer 41 in the Y direction.

The second electrode 43 is provided over the entire lower surface 41b of the piezoelectric layer 41, and has an extended end 43a that is extended through the side surface 41c of the piezoelectric layer 41 to the upper surface 41a. The extended end 43a of the second electrode 43 is provided away from the first electrode 42 so as not to be electrically connected to the first electrode 42. The extended end 43a of the second electrode 43 is adjacent to the first electrode 42 when viewed from the Z direction.

As shown in FIG. 11, the active region S of the piezoelectric vibrator 40B coincides with the region of the electrode pattern of the first electrode 42 when viewed from the thickness direction of the piezoelectric layer 41, and has an approximately perfect circular shape. That is, the active region S is linearly symmetrical with respect to the imaginary line L, and is configured to include a first region S1 corresponding to the first pattern 42a and a second region S2 corresponding to the second pattern 42b. In addition, the first region S1 and the second region S2 of the active region S are both approximately trapezoidal, and the upper bases of the trapezoids are aligned with each other on the imaginary line L. In the first region S1 and the second region S2, the lower bases of the trapezoids are curved so as to follow the edge of the piezoelectric layer 41. As with the electrode pattern of the first electrode 42, the active region S has a maximum width near both ends in the X direction and a minimum width on the imaginary line L.

Like the piezoelectric vibrators 40 and 40A described above, the piezoelectric vibrator 40B has an active region S with a narrowed portion 44. The narrowed portion 44 includes a narrowed portion 45 that corresponds to a portion of the first region S1 and gradually narrows in width, and a widened portion 46 that corresponds to a portion of the second region S2 and gradually widens in width, and the narrowed portion 45 and the widened portion 46 are adjacent to each other in the X direction.

Therefore, even with an ultrasonic transducer 30 equipped with a piezoelectric vibrator 40B, the directivity angle in a specific direction is narrowed while the directivity angle in other directions is maintained, achieving detection directionality.

The shape of the active region S of the piezoelectric vibrator 40B can take various forms, as shown in FIG. 12.

In FIG. 12(a), the contour line of the first region S1 and the contour line of the second region S2 of the active region S of the piezoelectric vibrator 40B are curved over the entire area. In this case, like the active region S in FIG. 5(a) and FIG. 5(b), the first electrode 42 and the second electrode 43 can be designed to have a shape with fewer corners, and the occurrence of cracks in the piezoelectric layer 41 due to stress concentration can be suppressed.

In FIG. 12(b), the first region S1 and the second region S2 of the active region S are both fan-shaped, and the central angles of the fan shapes are abutted against each other on the virtual line L. In this case, the active region S is divided into the first region S1 and the second region S2, and the first pattern 42a and the second pattern 42b of the corresponding first electrode 42 are divided and not electrically connected. Therefore, the wiring 26 can be connected to each of the first pattern 42a and the second pattern 42b of the first electrode 42. The first region S1 and the second region S2 may be separated from each other.

In FIG. 12(d), the active region S includes a first region S1, a second region S2, and a rectangular third region S3 of equal width in the X direction. The narrowed portion 44 of the active region S is composed of a reduced width portion 45 corresponding to a part of the first region S1, a widened width portion 46 corresponding to a part of the second region S2, and an equal width portion 47 corresponding to the third region S3, and the reduced width portion 45, the equal width portion 47, and the widened width portion 46 are arranged adjacent to each other in this order along the X direction.

All of the active regions S shown in FIG. 12 include a narrowed portion 44 in which a narrowed portion 45 corresponding to the first region S1 and a widened portion 46 corresponding to the second region S2 are arranged along the X direction with or without an equal-width portion 47 corresponding to the third region S3. Therefore, similar to the above-mentioned embodiment, it is possible to achieve detection directionality in the ultrasonic transducer 30.

Although the preferred embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-mentioned embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in order to realize a desired shape of the active region, an embodiment in which the shape of the first electrode is made to match the shape of the active region is shown, but it is also possible to make either one of the first electrode or the second electrode, or both the first electrode and the second electrode, match the shape of the active region. Furthermore, the second electrode does not necessarily have to have an extended end, and may be provided only on the lower surface of the piezoelectric layer.

1...ultrasonic detection system, 10...object, 20...control circuit, 30...ultrasonic transducer, 40, 40A, 40B...piezoelectric vibrator, 41...piezoelectric layer, 42...first electrode, 43...second electrode, 44...narrowed portion, 45...reduced width portion, 46...widened portion, 47...equal width portion, 50...housing, 52...cup portion, 53...bottom cover, S...active region, S1...first region, S2...second region, S3...third region.

Claims (11)

a piezoelectric layer having a first main surface and a second main surface opposed to each other, a first electrode provided on the first main surface, and a second electrode provided on the second main surface and having a polarity opposite to that of the first electrode;
an active region defined as a region in which the piezoelectric layer is sandwiched between the first electrode and the second electrode includes, when viewed from the thickness direction of the piezoelectric layer, a narrowed portion in which a width of the active region narrows and a widened portion in which a width of the active region widens are arranged side by side along a first direction perpendicular to the thickness direction of the piezoelectric layer, and is symmetrical with respect to a virtual line that divides the piezoelectric layer in half in the first direction;
A piezoelectric vibrator, wherein the active region is composed of a first region and a second region that are separated from each other, the first region having the reduced width portion, and the second region having the increased width portion . the second electrode has an extended end portion that extends through a side surface of the piezoelectric layer to the first principal surface,
2. The piezoelectric vibrator according to claim 1 , wherein the extended end of the second electrode is adjacent to the narrowed portion of the active region when viewed in a thickness direction of the piezoelectric layer. 3. The piezoelectric vibrator according to claim 1, wherein the active region itself has a square outer shape. 3. The piezoelectric vibrator according to claim 1, wherein the active region itself has a perfectly circular outer shape. 3. The piezoelectric vibrator according to claim 1, wherein the active region itself has a rectangular outer shape, and a long side of the rectangle is oriented along the first direction. 6. The piezoelectric vibrator according to claim 1 , wherein the width of the active region is gradually decreased in the narrowed portion, and the width of the active region is gradually increased in the widened portion. the second electrode is provided over the entire second main surface of the piezoelectric layer,
7. The piezoelectric vibrator according to claim 1 , wherein a shape of the first electrode and a shape of the active region are the same when viewed in a thickness direction of the piezoelectric layer. 8. An ultrasonic transducer comprising the piezoelectric vibrator according to claim 1 , wherein the piezoelectric vibrator outputs ultrasonic waves in response to an input voltage signal. The piezoelectric vibrator further includes a cylindrical case having a bottom, the cylindrical case being configured to accommodate the piezoelectric vibrator.
The ultrasonic transducer according to claim 8 , wherein the second main surface of the piezoelectric layer of the piezoelectric vibrator faces a bottom surface of the case. a piezoelectric layer having a first main surface and a second main surface opposed to each other, a first electrode provided on the first main surface, and a second electrode provided on the second main surface and having a polarity opposite to that of the first electrode;
an active region defined as a region in which the piezoelectric layer is sandwiched between the first electrode and the second electrode includes, when viewed from the thickness direction of the piezoelectric layer, a narrowed portion in which a width of the active region narrows and a widened portion in which a width of the active region widens are arranged side by side along a first direction perpendicular to the thickness direction of the piezoelectric layer, and is symmetrical with respect to a virtual line that divides the piezoelectric layer in half in the first direction;
A piezoelectric vibrator, wherein an end of the active region in the first direction is along an edge of an end of the piezoelectric layer in the first direction. The piezoelectric vibrator according to claim 10 , wherein the width of the active region is maximum at an end in the first direction along an edge of the end of the piezoelectric layer.

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