Camouflaging the location of a sound source via topology-optimized source-shifter

We demonstrate numerically an inverse design of a structure for camouflaging the location of a sound source as if the sound emanated from a different location. Employing a topology optimization approach used in acoustic-elastic coupled problems, the difference between the sound pressure fields emanating from an actual source and a virtual source, one that is not physically present at the location, is the objective function infimized in camouflaging the sound source. Optimal topologies of elastic structures made of acrylonitrile butadiene styrene were designed for the camouflaging purpose; moreover, no acoustic metamaterials are used. Our metastructures, so-called source-shifters, are expressed at the design stage using a level-set method, which generates sharp interfaces between acrylonitrile butadiene styrene and air. These source-shifters are modeled in finite-element analyses as acoustic-elastic coupled systems and incorporate acoustic fluid-structure interaction. From studies of the underlying camouflaging mechanism and the dependence of camouflaging performance on the distance between actual and virtual locations, we evaluate the effectiveness of our scheme in camouflaging the location of sound sources.