High-amplitude focusing of ultrasound in air using time reversal

Abstract

In this study, time reversal (TR) signal processing methods are used to create a focus of airborne ultrasound (between approximately 30 kHz and 50 kHz) in a room. There are unique challenges presented by ultrasonic sources, such as the highly directional nature of the sources, and attenuation of ultrasound in air. The aim of this study is to create a TR focus whose amplitude is as high as possible using the clipping processing method. Because ultrasonic sources tend to be very directional, this study explores the impact of using methods to make the sources more omnidirectional, which increases the number of reflective paths that contribute to the TR focus. This study explores various configurations of source and microphone in the room to determine which configuration yields the highest amplitude. Because thermoviscous loses for ultrasound are higher than for audible frequencies, a smaller room is used in the experiments to increase focal amplitudes.In this study, time reversal (TR) signal processing methods are used to create a focus of airborne ultrasound (between approximately 30 kHz and 50 kHz) in a room. There are unique challenges presented by ultrasonic sources, such as the highly directional nature of the sources, and attenuation of ultrasound in air. The aim of this study is to create a TR focus whose amplitude is as high as possible using the clipping processing method. Because ultrasonic sources tend to be very directional, this study explores the impact of using methods to make the sources more omnidirectional, which increases the number of reflective paths that contribute to the TR focus. This study explores various configurations of source and microphone in the room to determine which configuration yields the highest amplitude. Because thermoviscous loses for ultrasound are higher than for audible frequencies, a smaller room is used in the experiments to increase focal amplitudes.