Perfect transmission through lossy layers via ideal acoustic sources

Abstract

Complementary acoustic metamaterials (CAMMs) have been proposed as a means of enhancing the transmission of acoustic imaging signals through aberrating layers. Aberrating layers with high impedance contrast compared to the surrounding material disrupt the acoustic field and hence distort acoustic images. However, conventional CAMMs are passive and thus unable to compensate for signal distortions associated with loss. This work presents an approach inspired by CAMMs that is not bound by the limits of passivity to compensate for both acoustic scattering and energy attenuation by augmenting a plane wave incident on a lossy material with monopolar and dipolar source fields to allow for perfect transmission, thus rendering the lossy medium acoustically transparent. We present a general approach to derive expressions for source magnitudes that are dimensionless with respect to frequency, system geometry, and the background medium. We validate these results with three-dimensional finite element simulations, where the appropriate monopolar and dipolar source fields are generated by prescribing velocities on finite-dimensional boundaries. We show the limitations of this approach with regard to frequency, system geometry, and lossy material characteristics via a parametric study.