Nelson N. Hsu
NIST, Gaithersburg, MD 20899
The use of plane-wave ultrasound to probe interface properties based on angular spectrum analyses is common in the nondestructive testing of materials. Space-time domain Green's function modeling is an alternative approach to frequency domain modeling. it is better suited for the implementation of short duration pulses, small aperture transducers, and time-resolved pulse-echo methods. However, a computation based on the Green's function, though conceptually simple, is more involved than a computation based on the model of a plane wave of fixed frequency. Recently, an explicit Green's function for layered media has been derived. Efficient computer programs have also been developed for cases which can be easily tested experimentally and have immediate applications. As examples, comparison results between theory and experiment are reported here for three test configurations: (1) a solid plate on a half-space with different interface conditions, with a point step-function source and a point detector located on top of the plate; (2) a liquid/solid interface, with both the point source and point detector in the liquid; and (3) a line focus transducer probing a liquid/solid interface. Practical applications to laser ultrasound, simulated acoustic emission, and the acoustic microscope are illustrated.