This Letter presents practical realization of a two-dimensional low loss acoustic cloak for airborne sound obtained by inverse design. The cloak consists of 120 aluminum cylinders of 15 mm diameter surrounding the cloaked object—a cylinder of diameter 22.5 cm. The position of each cylinder in the cloak is optimized using the data from two different techniques: genetic algorithm and simulated annealing. The operation frequency of this cloak is 3061 Hz with the bandwidth of about 100 Hz. Being a multi-step approach to the desired cloaking, the inverse design is also valid, in principle, for non-symmetric cylinders and even for three-dimensional objects.
A team of researchers from the Universitat Politecnica de Valencia and the Universidad de Valencia have created a prototype of an acoustic cloak by using a 2-D mathematical model. Unlike sound-canceling technologies that eliminate noise by creating the exact-but-opposite waveform, an acoustic cloak would enable sound waves to travel around an object without changing their shape or direction.
According to the researchers, the narrow operating band of the cloak can be overcome by increasing the number of cylinders used to create the cloak. If such a technique could be applied in real-world designs, it could enable better soundscapes in urban environments, better acoustics in performance halls, and quieter helmets that protect the ears from extreme noises, the researchers speculate.