The Generation of Heat and the Acoustic Radiation Resistance of Ultrasonic Transducers Employing Barium-Titanate Ceramics

Abstract

Barium titanate ceramics accompanies the generation of a considerable amount of heat when used as generators of high power ultrasonics. The temperature rise of the ceramics during ultrasonic radiation was measured for the purpose of elucidating the mechanism of the heat generation. When the frequency was varied at constant voltage, large temperature rise was found in the neighbourhood of its resonance. When the specimen was not polarized, it showed no anomalous temperature rise. Accordingly it was concluded that heat is generated by large internal friction. A phenomenological treatment was performed by choosing the strain and the polarization as independent variable and introducing a frictional term proportional to the strain velocity in the piezoelectric equations. Acoustic power and the distribution of heat generation in the ceramics were calculated and the resistance term in the equivalent electric circuit was found to be the sum of the acoustic radiation resistance and the internal friction resistance. Experimental results are explained qualitatively by this theory.