In an ultrasonic vibrator of structure in which an electro-mechanical energy conversion element for generating a vibration is held by and between electrically conductive blocks and in which a mechanical-electrical energy conversion element for detecting the vibration state of the vibrator is inserted between the blocks, the potentials of the blocks are made different from each other by various means. Therefore, the detection of the vibration state becomes possible, for example, by a detecting element.

A hand held device for generating ultrasonic vibrations comprises an elongate tubular casing having therein a piezoelectric vibratory element comprising an elongate bar of piezoelectric material and a generator that develops an electrical signal having a predetermined ultrasonic frequency that excites the piezoelectric vibratory element into ultrasonic vibration. The piezoelectric vibratory element also functions as the dielectric of a capacitor which constitutes part of the generator and which determines the ultrasonic frequency of the electrical signal output of the generator. A work tool protrudes from the casing and is vibrationally coupled to the piezoelectric vibrator element by a vibratory rod which transmits the vibrations from the piezoelectric vibratory element to the work tool. A cooling system is disposed within the casing and flows a cooling agent through the device to cool both the piezoelectric vibratory element and the generator and the cooling agent is discharged from the device in atomized form through an opening in the work tool. Manually operable control means on the casing controls the generator and the cooling agent.

A method for flating the phase characteristic of a differential detection signal in one higher and lower regions thereof relative to its resonance frequency by controlling a differential characteristic. A searching, over a range, which is wider than the width of the flat region, is accomplished prior to phase characteristic being effected thereby discriminating a fundamental resonance frequency. After this discrimination of the fundamental resonance frequency, automatic tracking is effected under stable corrected phase characteristics for the fundamental resonant frequency whereby high electro-mechanical conversion efficiency can be maintained.

A control system for a Tonpilz transducer which is positioned between the transducer and the transducer drive amplifier. The control system determines the head velocity of the transducer from the input current and voltage and utilizes this determination in a feedback arrangement to maintain proper transducer excitation.

A piezo-resonator included in a filter and/or an AM signal receiving circuit eliminates unwanted signals produced as a result of the piezo-resonator experiencing a mechanical impact. The piezo-resonator includes a piezoelectric substrate and first and second electrodes provided on opposite surfaces of the substrate. The first electrode is divided into three portions along its width by grooves extending along the longitudinal substrate. The grooves are formed so that the resulting divided portions are substantially symmetrical to each other with respect to the central axis extending along the longitudinal substrate. The peripheral portions of the divided electrode are used as one input/output terminal, while the central portion is used as the other input/output terminal. The piezo-resonator can be provided in at least the last stage of a plurality of resonators for use in a filter. Further, such piezo-resonators or filter can be used in an intermediate frequency filter contained in an AM signal receiving device.