Mechanically Tuned Gradient-Index Phononic Crystal Lens

A two-dimensional gradient-index phononic crystal composed of aluminum scatterers in air matrix for frequency ofλ=6.1a is designed and simulated. We gradually change the radiuses to make a hyperbolic secant refractive index profile. Then the path of waves inside the structure is shown by analytical solutions. In this work, filling factor is mechanically increased which results in a shift in the focal point whereas the spot size remains almost constant. In order to enable the structure to be mechanically tuned, the conservators have been utilized and changed the circular cross section of scatterers slightly. However, due to this fact that the results of circular and non-circular structures do not show any differences, we used the circular scatterers for calculating the refractive indices. However, the amount of focal pressure can be slightly changed. The calculation of band structure as well as the simulation of acoustic waves’ propagation inside the structure has been accomplished using the finite element method.