Ultrasonic sensor

1. An ultrasonic sensor comprising:

a case having a bottom portion; and

a piezoelectric element bonded to an inner surface of the bottom portion, the piezoelectric element including:

a piezoelectric layer having a transmission region and a reception region;

a common electrode having at least one portion facing or disposed within both the transmission region and reception region of the piezoelectric layer;

a transmission electrode opposed to the common electrode with the transmission region interposed therebetween; and

a reception electrode opposed to the common electrode with the reception region interposed therebetween, wherein an impedance between the transmission electrode and the common electrode is lower than an impedance between the reception electrode and the common electrode.

2. The ultrasonic sensor according to claim 1 , wherein the reception electrode comprises at least one disk and the transmission electrode comprises a plurality of intermediate portions disposed in the transmission region of the piezoelectric layer, wherein the number of intermediate portions is greater than the number of the at least one disk.

3. The ultrasonic sensor according to claim 1 , wherein the transmission region and the reception region are arranged at positions adjacent to each other in a direction perpendicular to the inner surface of the bottom portion.

4. The ultrasonic sensor according to claim 1 , wherein the transmission region and the reception region are arranged at positions adjacent to each other in a direction parallel to the inner surface of the bottom portion.

5. The ultrasonic sensor according to claim 1 , wherein the reception region is disposed at a center portion of the piezoelectric element in a planar view of the ultrasonic sensor, and the transmission region is disposed on a peripheral portion of the piezoelectric element relative to the reception region in a radial direction.

6. The ultrasonic sensor according to claim 5 , wherein the transmission region surrounds the reception region.

7. The ultrasonic sensor according to claim 5 ,

wherein the transmission electrode comprises at least one inner electrode that is laminated in a direction of being distanced from the bottom portion, and

wherein the at least one inner electrode comprises a ring-like shape that is arranged on the peripheral portion of the piezoelectric element.

8. The ultrasonic sensor according to claim 1 , wherein the common electrode is a common bus having a shape extending over both the transmission region and the reception region in a planar view of the ultrasonic sensor.

9. The ultrasonic sensor according to claim 2 ,

wherein the transmission region of the piezoelectric layer includes a plurality of first piezoelectric layers electrically connected in parallel and that are laminated in a direction being distanced from the bottom portion so as to be interposed, respectively, between the plurality of intermediate portions of the transmission electrode, and

wherein the reception region of the piezoelectric layer includes one second piezoelectric layer disposed between the common electrode and the reception electrode.

10. The ultrasonic sensor according to claim 2 ,

wherein the transmission region of the piezoelectric layer includes a plurality of first piezoelectric layers electrically connected in parallel and that are laminated in a direction being distanced from the bottom portion so as to be interposed, respectively, between the plurality of intermediate portions of the transmission electrode,

wherein the reception region of the piezoelectric layer includes a plurality of second piezoelectric layers electrically connected in parallel and that are laminated in a direction being distanced from the bottom portion, and

wherein the number of first piezoelectric layers is equal to or greater than the number of second piezoelectric layers.

11. The ultrasonic sensor according to claim 1 , wherein a surface area of a surface of the transmission region at a side bonded to the inner surface of the bottom portion is equal to or larger than a surface area of a surface of the reception region at a side bonded to the inner surface of the bottom portion.

12. The ultrasonic sensor according to claim 1 , wherein a thickness of the transmission region in a direction orthogonal to the bottom portion is smaller than a thickness of the reception region in the direction orthogonal to the bottom portion.

13. The ultrasonic sensor according to claim 1 , wherein the piezoelectric element is configured to perform bending vibration together with the bottom portion of the case.

14. The ultrasonic sensor according to claim 1 , wherein the common electrode includes a plurality of surface layers disposed on opposing outer surfaces of the piezoelectric layer and at least one intermediate layer disposed within the piezoelectric layer.

15. The ultrasonic sensor according to claim 14 , wherein the transmission electrode comprises a plurality of intermediate portions disposed between the at least one intermediate layer of the common electrode and the plurality of surface layers of the common electrode, respectively.

16. A ultrasonic sensor comprising:

a case having a bottom portion; and

a piezoelectric element that is bonded to an inner surface of the bottom portion, the piezoelectric element including:

a piezoelectric layer having a transmission region, a reception region, and an isolation region disposed between the transmission region and the reception region in a direction orthogonal to the bottom portion of the case;

a common electrode having at least one portion facing or disposed within the transmission region, the reception region and the isolation region of the piezoelectric layer;

a transmission electrode opposed to the common electrode with the transmission region interposed therebetween; and

a reception electrode opposed to the common electrode with the reception region interposed therebetween,

wherein the common electrode does not oppose either the transmission electrode or the reception electrode where the common electrode faces or is disposed within the isolation region in the direction orthogonal to the bottom portion of the case, and

wherein at least one of the transmission electrode and reception electrode extends into the isolation region in a direction parallel to the bottom portion of the case.

17. The ultrasonic sensor according to claim 16 , wherein the common electrode extends into the isolation region in the direction parallel to the bottom portion of the case.

18. The ultrasonic sensor according to claim 16 , wherein the transmission electrode extends into the isolation region in the direction parallel to the bottom portion of the case.

19. The ultrasonic sensor according to claim 16 , wherein the reception electrode extends into the isolation region in the direction parallel to the bottom portion of the case.

20. An ultrasonic sensor comprising

a case having a bottom portion; and

a piezoelectric element that is bonded to an inner surface of the bottom portion, the piezoelectric element including:

a piezoelectric layer having a transmission region, a reception region, and an isolation region disposed between the transmission region and the reception region in a direction orthogonal to the bottom portion of the case;

a common electrode having at least one portion facing or disposed within the transmission region, the reception region and the isolation region of the piezoelectric layer;

a transmission electrode opposed to the common electrode with the transmission region interposed therebetween; and

a reception electrode opposed to the common electrode with the reception region interposed therebetween,

wherein the common electrode does not oppose either the transmission electrode or the reception electrode where the common electrode faces or is disposed within the isolation region in the direction orthogonal to the bottom portion of the case, and

wherein the reception electrode comprises at least one disk and the transmission electrode comprises a plurality of intermediate portions disposed in the transmission region of the piezoelectric layer, wherein the number of intermediate portions is greater than the number of the at least one disk.