Solid–liquid interface reconstructions from ultrasonic time-of-flight projection data

Abstract

The large difference in the ultrasonic velocity of solid and liquid semiconducting materials results in significant ray refraction and pulse time delays during propagation through solid–liquid interfaces. This has led to an interest in the use of ultrasonic time-of-flight (TOF) measurements for deducing the interfacial geometry. A ray-tracing analysis has been used to analyze two-dimensional wave propagation in the diametral plane of model cylindrical solid–liquid interfaces. Ray paths, wavefronts, and TOFs for rays that travel from a source to an arbitrarily positioned receiver on the diametral plane have been calculated and compared to experimentally measured TOF data obtained using a laser generated/optically detected ultrasonic system. Examinations of both the simulations and the experimental results reveals that the interfacial region can be identified from transmission TOF data. When the TOF data collected in the diametral plane were used in conjunction with a nonlinear least-squares reconstruction algorithm, the interface geometry (i.e., axial location and shape) were precisely recovered and the ultrasonic velocities of both solid and liquid phases were obtained with error of less than ∼3%.