Piezoelectric oscillator and ultrasonic motor

1. A piezoelectric oscillator comprising:

an oscillating body having a circumference and first and second surfaces; and

(4/3)n piezoelectric elements secured to the first surface of the oscillating body and configured to generate an n-wave travelling wave that travels in a circular path by combining two B (1, n) mode standing waves that are out of phase with each other by 90° due to oscillation of the oscillating body, the (4/3)n piezoelectric elements being distributed in a circumferential direction of the travelling wave, and where n is a natural number,

wherein, when a central angle around a center of the circumferential direction corresponding to a wavelength of the travelling wave is λθ, each piezoelectric element of the (4/3)n piezoelectric elements has a dimension corresponding to a central angle of λθ/2, and adjacent piezoelectric elements of the (4/3)n piezoelectric elements are spaced apart from each other at intervals each corresponding to a central angle of λθ/4 in the circumferential direction,

wherein each piezoelectric element includes a piezoelectric body polarized in a thickness direction thereof and a pair of electrodes on respective opposite surfaces of the piezoelectric body, and

wherein the (4/3)n piezoelectric elements are arranged such that alternating pairs of piezoelectric elements are polarized in opposite directions.

2. The piezoelectric oscillator according to claim 1 , wherein the oscillating body is formed of a plate-shaped elastic material.

3. The piezoelectric oscillator according to claim 1 , wherein the (4/3)n piezoelectric elements are disposed so as to be positioned on antinodes of oscillation of the B (1, n) mode standing waves.

4. The piezoelectric oscillator according to claim 3 , wherein the (4/3)n piezoelectric elements are disposed on the antinodes of the oscillation of the B (1, n) standing waves, the antinodes positioned inside annular nodes of the B (1, n) mode standing waves.

5. The piezoelectric oscillator according to claim 4 , wherein the (4/3)n piezoelectric elements are disposed inside the annular nodes of the oscillation of the B (1, n) mode standing waves so as not to extend to the outside of the annular nodes.

6. The piezoelectric oscillator according to claim 5 , further comprising a second plurality of piezoelectric elements disposed outside of the annular nodes.

7. The piezoelectric oscillator according to claim 6 , wherein the second plurality of piezoelectric elements are each disposed in a position adjacent to a respective piezoelectric element of the (4/3)n piezoelectric elements, and are polarized in a direction opposite thereto.

8. The piezoelectric oscillator according to claim 1 , wherein the (4/3)n piezoelectric elements each have a rectangular planar shape.

9. The piezoelectric oscillator according to claim 1 , wherein the (4/3)n piezoelectric elements each have a circular planar shape.

10. The piezoelectric oscillator according to claim 1 , further comprising at least one contact that protrudes from the second surface of the oscillating body.

11. The piezoelectric oscillator according to claim 10 , wherein the at least one contact comprises a plurality of contacts that are distributed in an annular area corresponding to where the travelling wave propagates.

12. An ultrasonic motor comprising:

a stator including the piezoelectric oscillator according to claim 1 , and

a rotor that is arranged so as to contact the stator and rotate due to oscillation caused by the n-wave travelling wave.