PURPOSE: To change efficiently the center frequency by providing an auxiliary electrode so as to be meandering on a reed screen electrode on the surface of a piezoelectric substrate and impressing a DC voltage to the auxiliary electrode so as to give a bias displacement to the piezoelectric substrate.
CONSTITUTION: The reed screen electrodes 4, 5 and the auxiliary electrodes 8, 9 are formed on the entire face of the piezoelectric substrate 1. The auxiliary electrodes 8, 9 are formed so as to be meandering between the reed screen electrodes 4, 5 and connected to an output terminal of a DC power supply 10. As the DC power supply 10, a power supply generating a variable voltage with an optional polarity is used. Through the constitution above, a stress in response to polarity and magnitude of an output voltage is generated between electrode groups 42, 52 connected to the auxiliary electrodes 8, 9 and a common potential point by changing the polarity and magnitude of the output voltage of the DC power supply 10, and the center frequency is changed in response to the change in the stress.
MIURA AKIRA
MOURI HIROSHIGE
