The study of acoustic band gaps in 2-D air/aluminum and steel/epoxy phononic structure

Analogous to the photonic band gap structure, phononic band gaps could be found in systems comprised of two materials with different elastic properties called "phononic crystals." Acoustic waves propagating in such structures also exhibit band gaps and may find applications in the high frequency acoustic wave devices. In this paper, the results of acoustic wave propagation in two-dimensional PC calculated with finite-difference time-domain (FDTD) method will be presented. The perfectly matched layer (PML) method was adopted to serve as absorbing boundary conditions (ABC). Band gaps of the 2-D PC were calculated by the FDTD method, and the numerical result has revealed more details of the mixed mode and transverse mode for acoustic wave propagation in isotropic materials. Both the transmission coefficient and images of displacement were obtained from the calculations and the phenomenon of reflection and diffraction can be observed clearly. A phononic structure consists of a square periodic arrangement of cylindrical holes in an aluminum alloy was fabricated and the corresponding band gap measurements were conducted. The experimental results have shown good accordance with those predicted using the FDTD method. It is believed that the proposed numerical formulation can be used to design a phononic crystal and find possible applications in the area of wave-guide channel or filter analyses.