Comparison among Several Digital Methods of Measuring Time-of-Flight of Ultrasonic Waves in Solids.

Abstract

A digital measurement system for the time-of-flight of ultrasonic longitudinal and transverse waves is constructed in terms of a conventional pulser/receiver, a transducer and a high-speed digital wave memory for material characterization and acoustoelastic stress measurement of solid materials with weak dispersion. Three methods, zero-crossing, cross-correlation and phase spectral methods, are compared from the viewpoint of precision for the time-of-flight measurement. The measurements of aluminum (10 mm in thickness) and acrylic (5 mm) plates have shown that the precision (2σ) of the time-of-flight is estimated to be less than 0.01 ns by the cross-correlation methods, which corresponds to the relative velocity variation of 2×10-6 for the longitudinal velocity of the aluminum plate. The cross-correlation method is found to have the highest stability.