High-Temperature Shear Ultrasonic Interferometer Using Sensitive Phase-Lock Detection System

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Abstract
A high-temperature ultrasonic interferometer for the study of propagation properties of shear waves through molten glasses below 1600°C and between 3 and 23 MHz is described. Techniques for measuring velocity and absorption of the transmitted echoes are presented with special emphasis on the study of shear waves in the relaxation region of a molten glass. In this case, an absorption per wavelength as high as 5.4 Np/cycle was measured; this is more than twice the capability of previously reported equipment. The use of a lock-in amplifier in the video circuit made this work possible. This method of handling the transmitted echoes not only suppressed noise by 25 dB, but also permitted measurements of pulse heights to better than 0.1 dB. The video circuit is not sensitive to rf values and can be used with most existing pulsed ultrasonic systems.

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