Abstract: An apparatus equipped with annular electrostriction elements each having four divided segmental electrodes with the respective polarities reversed alternately in the direction of thickness thereof. The annular electrostriction elements are so disposed that the center lines of division are positionally coincident with diagonal lines of a square plate resonator while passing through the surface center point thereof, whereby the corner portions of the resonator can be vibrated effectively at an ultrasonic frequency.

Abstract: The present invention deals with an ultrasonic wave generating apparatus with voltage controlled filter, comprising a phase comparator which detects a shifted value from a predetermined phase difference between a driving voltage or a driving current of an ultrasonic transducer and a vibratory velocity signal, and a voltage-controlled band-pass filter which is controlled by the output of the phase comparator and which is provided in a feedback loop from the vibratory velocity signal to an input of a driving amplifier of the ultrasonic transducer, wherein the oscillating frequency is changed while following the resonant frequency of the ultrasonic transducer, so that stable operation is materialized without developing abnormal oscillation in subresonant frequencies and permitting very small following error.