Interpretation of time records and power spectra of scattered ultrasonic pulses in solids

Experiments were conducted to investigate the scattering of a wide bandwidth pulse by a fluid-filled cylindrical cavity in an elastic solid. The pulse amplitude-time record and the corresponding Fourier power spectra of the scattered pulses are analyzed. The sequence of pulses received by a transducer is identified by applying the theory of geometric acoustics and the pulse arrival times are related to the cavity diameter and the wave speed in the fluid. The power spectrum is interpreted in terms of the resonance of the fluid inclusion, the natural frequencies of which also depend on the size and property of the inclusion. Investigations show that both pulse-time record and power spectrum can be utilized to detect the size and the wave speed of a fluid inclusion in a solid.