Design of Broadband Acoustic Cloak Using Topology Optimization

A procedure for broadband topology optimization is applied to the design of acoustic cloaking. An acoustic cloak conceals a given object with arbitrary shapes. That is, the object can be made undetectable with respect to acoustic wave propagation in a specific frequency range. The guided acoustic wave in a given direction will re-attach in the incident direction, leading to a minimized norm of the scattering field. Gradient-based topological optimization is accomplished using a time-dependent adjoint formulation for sensitivity analysis. Results indicate that the current methodology produces improved cloaking performance for narrowband near a target frequency, and as expected less than optimal performance is observed away from this frequency. For topology optimization over a broadband, improved performance is realized over the entire frequency range, but not necessarily optimal at any given target frequency.