Time-delay estimation and correlation analysis of acoustic signals in granular media using wavelet decomposition

The transmission of pulsed ultrasonic signals along a chain of spheres has been studied experimentally, with a view to determine the exact nature of propagation along such chains at ultrasonic frequencies. The transmitted signals were measured using a laser vibrometer, and the resultant waves were analyzed using wavelet decomposition. This allowed the frequency components and the first arrival time to be examined. The propagation velocity along the chain was found to be much smaller than the bulk sound speed of the sphere material. Increased non-linearity also led to higher frequencies being present at higher input levels.