Focusing of spoof surface-acoustic-waves by a gradient-index structure

We have investigated the focusing of the spoof surface acoustic waves (SSAWs) on a rigid surface engraved with array of cylindrical holes. To focus the SSAWs launched along x direction, the holes array, with a shape of rectangle as a whole, is fabricated to possess gradient index of refraction along both the +y and −y directions, which is achieved by varying linearly the radii of the holes along the corresponding directions. Good focusing performance has been demonstrated experimentally, which is in good agreement with the numerical simulations. This acoustic system is believed to have potential applications in acoustic field such as high resolution detecting.