Experimental considerations on water-couplant temperature for accurate velocity measurements by the LFB ultrasonic material characterization system

The line-focus-beam ultrasonic material characterization (LFB-UMC) system can measure the phase velocity of leaky surface acoustic waves (LSAWs) excited on the water-specimen boundary. The temperature distribution in the water-couplant, however, is the source of some measurement errors in the LSAW velocity. A method for obtaining the proper water-couplant temperature and longitudinal velocity has been developed using the measured temperature distribution and the small interference signals between the V(z) curve signals and the carrier leakage signals arising from the RF tone burst pulse generation circuit used in the system. A procedure to obtain the LSAW velocity accurately is established and the system achieves relative accuracy of LSAW velocity better than ±0.002% at a single chosen point and better than ±0.003% in two-dimensional measurements