Apparatus for the continuous measurement of changes in ultrasonic velocity

Abstract
In measuring the velocity of sound in materials with plate-like of fibrous geometries, in thin foils, or in materials with high attenuation, the only clear signal is often after a single transit through the sample. A system is described which allows continuous measurements of changes of acoustic propagation time through such samples with a resolution of 0.2 ns. In some circumstances, the resolution can be improved to 15 ps.