Abstract
Observation of the electric current through the motional admittance of a piezoelectric vibrator is made here by compensating the damped admittance by a condenser with a differential transformer. This current reaches a maximum at the resonant frequency f__0, and its value is remembered by another circuit with a reference resistance. Next, the voltage from a carrier-suppressed balanced-modulator with a carrier frequency f__0 and a modulating frequency f__A is applied on the motioanal admittance. When f__A is adjusted so that the current becomes 1/√2 times the one through the reference resistance, f__A equals to a half of the quadrantal-frequency-difference. The Q value, therefore, is computed from f__0/(2f__A). The wave form of the current is identical with that of the output voltage of the balanced modulator, but, when the carrier frequency deviates from the resonant frequency, its variation becomes very sensitive. The motional admittance at resonance and damped admittance are also known by this procedure, and the electromechanical coupling coefficient can be calculated. Further studies are made on several other points.
