Three-dimensional ultra-broadband focusing flat mirror for airborne sound

We report the theoretical design, numerical simulation, and experimental demonstration of a flat mirror capable to efficiently focus the reflected sound in three-dimensional space within an ultra-broad band. The proposed mirror is implemented with a textured rigid surface, enabling simple design and easy fabrication. We analytically derive the distribution of geometric parameters needed for producing ultra-broadband focusing, and verify the performance of resulting mirror both numerically and experimentally. Furthermore, our scheme allows further extending of the working band by resizing individual elements. Our design with simplicity and capability may promote the application of focusing devices generally subject to limited bandwidth. Published by AIP Publishing.