Acoustic pressure enhancing metamaterials through impedance contrast

Abstract

Acoustic pressure enhancing devices are widely used to extend the range of sensors used for detecting weak and distant sounds. However, conventional sound enhancing devices such as acoustic horns and parabolic reflectors require bulky structures and thus limit miniaturization of sensing systems. To overcome this limitation, metamaterial techniques have been employed and promising results have been reported. However, acoustic pressure enhancing metamaterials reported so far rely on frequency dependent mechanisms to increase acoustic pressure such as resonances or wave compression methods. Therefore, in these approaches, waves are distorted during the enhancement process and this limits their applications considerably. In this presentation, we will show that metamaterials can significantly enhance acoustic waves without wave distortion while keeping the size of the metamaterial subwavelength. Our metamaterial is based on the property of the acoustic waves to increase their acoustic pressure while propagating without insertion loss from a medium of low impedance into a medium of higher impedance. The pressure gain is constant regardless of the frequency, allowing the wave to maintain its shape during enhancement. Here, we will provide the physics of the phenomenon along with numerical and experimental results which were in good agreement with the theoretical prediction.