Time reversal focal amplitudes as the focal position approaches boundaries

Abstract

Time reversal (TR) is a signal processing technique that may be used to generate a focusing of waves at selected positions in reverberant environments. This study looks at the increase in the focal amplitude as the distance between the focal location and a boundary is decreased. Previous studies with audible sound in rooms have shown experimentally and numerically that there is a 3 dB increase in focal amplitude if the focal location is positioned 1 cm away from a wall; the numerical model used was a modal summation simulation. It has since been found that using an image source model simulation does not show any increase in focal amplitude as the focal location approaches boundaries. Experiments conducted in solid media with ultrasound showed that focal amplitudes increase by 6 dB at a free boundary. Experiments and modal summation modeling conducted with audible sound in a reverberation chamber also yielded similar results as the focal location reached the wall. The presentation will discuss why the image source model does not yield these results.