MEASUREMENT OF GROUP-VELOCITY VARIATION DUE TO TEMPERATURE USING FREQUENCY-DEPENDENCE OF INTERFERENCE INTENSITY OF ACOUSTIC-WAVES AND ITS FOURIER-ANALYSIS

A measurement theory of variation in group velocity using an interfere nce of acoustic waves is proposed, and an experimental result of a pie zoelectric substrate is discussed, when a variation in temperature;cau ses the variation in group velocity. This method utilizes a periodic f requency characteristic of an acoustic intensity when two acoustic wav es interfere in the substrate. The periodicity is analyzed by fast Fou rier transform (FFT), and the amplitude and phase of the Fourier compo nents which have dimensions of time are calculated. Since the phase sh ifts by the variation in group velocity, the measurement of the former leads to the precise measurement of the latter. The interference of a coustic waves is caused inside an interdigital transducer (IDT) which is used as a reflector for the wave, and the interference intensity is measured using an acoustooptic (AO) interaction.