| 摘要 |
PROBLEM TO BE SOLVED: To reduce a power to be consumed when driving a piezoelectric element. SOLUTION: An on signal is output to a switch 10 to drive a piezoelectric element 7 with an a.c. current from a piezoelectric element-driving circuit 12. After a connection time has passed, the output of the on signal to the switch 10 is stopped. As a result, the switch 10 is turned off to free connection between the piezoelectric element-driving circuit 12 and a lower electrode 8. Although the supply of the a.c. current from the piezoelectric element-driving circuit 12 to the piezoelectric vibrator 7 is stopped, the piezoelectric vibrator 7 is driven with an electricity stored in a resonance circuit constituted of an inductance 9 and the piezoelectric element 7. In other words, even when the supply of the a.c. current from the piezoelectric element-driving circuit 12 to the piezoelectric vibrator 7 is stopped, the piezoelectric vibrator 7 is vibrated with the electricity from the resonance circuit, thus continuously generating ultrasonic waves.
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