Ultrasonic Phase Velocity by the Pulse-Echo-Overlap Method Incorporating Diffraction Phase Corrections

Abstract

The pulse‐echo‐overlap method for ultrasonic time‐delay measurements is reviewed. In this method, pairs of echoes are compared by driving the x axis of a viewing oscilloscope at a frequency equal to the reciprocal of the travel time between the echoes. A method for choosing the correct cyclic overlap for the rf within the echoes is given. Utilization of the proper cyclic overlap permits the accurate measurement of ultrasonic phase velocity. When corrections for the phase advance due to ultrasonic diffraction are applied to the travel times between various pairs of echoes, the accuracy of the average round‐trip travel time is improved. Experimental verification of this is presented for longitudinal waves in isotropic materials and in the pure mode directions in cubic crystals. Delay times are accurate to 0.2 nsec or better.