Quantifying nonlinear characteristics in time reversal focusing of airborne sound

Abstract

Time reversal can be used to focus sound to a chosen location within a reverberant environment. Virtual sources in the reverberant environment increase the amplitude of the focusing. Recent investigations into the focusing of high-amplitude sound waves, up to peak levels of 200 dB, has led to the observation of nonlinear characteristics in the focus event. This study investigates these nonlinear characteristics, including distortion of the focus wave, shift in harmonic content, and nonlinear increase in the peak pressure compressions. This study also attempts to quantify a threshold where the focus events begin to transition from a linear to the nonlinear regime. Additionally, a comparison of the microphones and transducers used to record these focus events is made in order to both verify the levels of pressure attained, and to ensure that microphone distortion is not the cause of the nonlinear features in the focusing.