This Letter presents the design, fabrication, and experimental characterization of a directional three-dimensional acoustic cloak for airborne sound. The cloak consists of 60 concentric acoustically rigid tori surrounding the cloaked object, a sphere of radius 4 cm. The major radii and positions of the tori along the symmetry axis are determined using the condition of complete cancellation of the acoustic field scattered from the sphere. They are obtained through an optimization technique that combines genetic algorithm and simulated annealing. The scattering cross section of the sphere with the cloak, which is the magnitude that is minimized, is calculated using the method of fundamental solutions. The low-loss fabricated cloak shows a reduction of the 90% of the sphere scattering cross section at the frequency of 8.55 kHz.

Design of an acoustic metamaterial lens using genetic algorithms

A three-dimensional acoustic cloak has been designed, fabricated, and experimentally characterized. The cloak is made of 60 concentric tori acoustically rigid that surround a sphere of radius 4 cm, which is considered as the cloaked object. The major radii and positions of the tori along the symmetry axis are determined by a cancelation condition; i.e., the scattering cross section by the sphere and the tori must be zero. An optimization algorithm that combines a genetic algorithm and simulated annealing is employed to satisfy such a condition. The operational frequency of the one-directional cloak is 8.67 kHz with a bandwidth of about 120 Hz.