Nonlinear acoustic phenomena in high amplitude time reversal focusing of airborne sound in a 1-D system

Abstract

Time reversal (TR) is a process that can be used to generate high amplitude focusing of sound. It has been previously shown that using TR in reverberant environments to cause high amplitude foci will in fact have multiple nonlinear properties including waveform steepening and a nonlinear increase in peak pressure compressions. This study investigates the removal of one possible cause for these phenomena: free-space Mach stems. By isolating the focus into a 1-D system, the potential formation of Mach stems is eliminated so that remaining effects can be qualitatively observed. To achieve this, a system of pipes is used to restrict the focused waves to be planar in a 1-D reverberant environment. Preliminary results have shown that waveform steepening effects remain as expected but that the nonlinear increase in compression amplitudes disappears, which is consistent with the idea that free-space Mach stems cannot be formed in a 1-D system.