A novel class of acoustic metamaterial is proposed for directional collimation of a cylindrical source into a plane wave beam. The effect is based on transformation acoustics which retains the exact form of the wave equation under conformal mapping from a circular region to a triangular area. The transformation is adjustable, allowing the acoustic energy to be equally radiated in three directions, or preferentially in a single direction. Importantly, the material properties in the physical domain are isotropic and therefore practically realizable. Two example devices are proposed using cylindrical elastic shells in water as the metamaterial elements and demonstrated using full wave simulations. This approach has potential applications beyond acoustic antenna design in beam-steering and wavefront manipulation.
Xiaoshi Su and Andrew N. Norris, "Isotropic transformation acoustics and applications," Proc. SPIE 10170, Health Monitoring of Structural and Biological Systems 2017, 101700M (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 27, 2017; Published: 5 April 2017); https://doi.org/10.1117/12.2259793.
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