Characterization of Piezoelectric Ceramic Transducer for Accurate Speed-of-Sound Measurement

Piezoelectric ceramics mounted on the endplates of a cylindrical resonator were used as the source and detector for speed-of-sound measurements. The perturbations of the longitudinal gas modes of the cavity due to the compliance of the diaphragms (10 mm diameter, 0.3 mm thick) and the attached transducers were estimated from first-order perturbation theory. The fractional shift of the resonance frequencies in argon caused by the source and detector was 0.03 x 10(-6) at 0.1 MPa and 273.16 K. The high signal-to-noise ratio (up to 1 x 10(4) with a 6 s integration time) that was obtained with these transducers makes them suitable for acoustic thermometry. The heat dissipation in the source transducer was measured to be only 0.7 mu W at the working voltage (7 V) and frequency (1 kHz).