Comparative analysis of different distortion reduction techniques for parametric loudspeaker based on self-demodulation of amplitude modulated ultrasound waves

A highly focused sound beam can be created from the nonlinear interaction of ultrasound waves by using a parametric loudspeaker. An audio signal is produced by the self-demodulation of amplitude modulated sound waves in air. Several preprocessing techniques have been discussed in previous literature to reduce distortion. A comparative analysis of these preprocessing techniques is presented in this paper. Some preceding preprocessing techniques rely on equalization and square-rooting. Newer techniques, instead of using only simple AM, have an additional AM signal with a carrier that is orthogonal to the original one. It will be clearly seen that the distortion of the modified AM is greatly reduced from the normal AM. Simulation results show the effectiveness of the preprocessing techniques.