Acoustic Metamaterial Design and Applications By

We proposed an approach to construct a 2D Fresnel lenses by acoustic network. This lens iscomposed of an array of Helmholtz resonators. The resonance at individual resonators results ineffective focusing even the plate has subwavelength thickness. The FEM simulation resultspresented the ultrasonic wave propagation through the lenses together with the resultingdiffraction pattern.INTRODUCTIONThe Fresnel lens was first proposed as viable alternatives to conventional spherical lenses foroptical focusing and has been widelystudied. Planar focusing lens for acoustic wave wasdesigned according to the Fresnel zone plate theory.Since the lens has simple configuration; itcan be fabricated with easy and inexpensive technique. However, the efficiency of Fresnel lensesreported so far is low.In this section, we numerically investigated the planar acoustic Fresnel lens composed of a1D array of Helmholtz resonators using FE method. The Helmholtz resonators are filled withdifferent medium, dividing plate into 29 Fresnel zones. The acoustic wave fields at differentfrequencies are compared from the simulation results.