Refractive and focusing behaviours of tunable sonic crystals with dielectric elastomer cylindrical actuators

The refractive and focusing behaviours of a tunable sonic crystal (SC) consisting of air and dielectric elastomer (DE) cylindrical actuators are investigated. The refractive direction of the acoustic wave in SCs is predicted from the equivalent frequency surface obtained by the plane-wave expansion method. The inner and outer radii of the cylindrical actuators are increased with the electric field which is applied between the electrodes on the internal and external lateral surfaces. Therefore, the dispersion relation is varied with the geometric adjustment of the DE tubes and the refractions of acoustic wave in SCs are changed from positive to negative with the increase in the applied electric field. Based on the geometry adjustment of the cylindrical actuator, a tunable acoustic superlens could be proposed by a SC slab with DE tubes. The distance from the surface of the slab to the centre of the image spot can be changed with different electric fields. Thus, extensive applications of such a phenomenon to acoustic devices are anticipated.