Superlensing effect for flexural waves on phononic thin plates composed by spring-mass resonators

This paper demonstrates the superlensing effect of flexural waves by phononic plates with the negative index of refraction. The phononic plate consists of a square lattice of spring-mass resonators attached to an infinite thin plate. The periodic resonator array induces a resonant band gap between the first and second dispersion curves of band structures calculating by a plane wave expansion method. All-angle negative refraction phenomenon has been found for a propagation mode under specific elastic parameters of spring-mass resonators. Furthermore, a flat lens composed by a finite number of spring-mass resonators is designed to focus elastic fields of a point-like excitation operating at this propagating mode. Multiple scattering simulations show that the image resolution of the designed flat lens is about 0.15λ, overcoming the Rayleigh diffraction limit of traditional imaging systems.