Topology Optimized Cloak for Airborne Sound

Abstract

Directional acoustic cloaks that conceal an aluminum cylinder for airborne sound waves are presented in this paper. Subwavelength cylindrical aluminum inclusions in air constitute the cloak design to aid practical realizations. The positions and radii of the subwavelength cylinders are determined by minimizing scattering from the cloakstructure and cylinder using the gradientbased topology optimization method. In the final optimization step, the radii of the subwavelength cylinders are constrained to three discrete values. A nearperfect narrowbanded and angular cloaking effect is obtained by optimizing for one target frequency. To get a larger bandwidth, the acoustic cloak is optimized for three frequencies at the cost of reduced peak cloaking performance at the center frequency.