Use of a microcomputer for studying the rapid changes of attenuation and velocity of ultrasonic waves

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Abstract
A new instrument has been developed for continuously recording rapid changes in ultrasonic relative velocity ( Delta v/v0) and attenuation ( Delta alpha ) in a solid under the effect of a uniaxial stress. The system is built around a microcomputer with a parallel interface port. The computer permits the simplification of the ultrasonic receiver which includes an amplitude detector for Delta alpha measurement and a product detector for measurement of Delta v/v0 by a comparison with a reference sample; the microprocessor operates calculations and corrections in order to plot directly Delta alpha and Delta v/v0. The performances obtained in the range 5-20 MHz are as follows: resolution of 10-3 dB mu s-1 in attenuation changes, of 10-5 in relative velocity changes (corresponding to a time propagation change of 100 ps); the time constant of the whole system is 20 ms.