Elastic metamaterial-based impedance-varying phononic bandgap structures for bandpass filters

In this study, we propose a novel impedance-vaiiation scheme in a half-quarter-wave stack (HQWS) structure to achieve desired bandpass filtering performances such as quasi-flat tops, steep bandedges and wide surrounding bandgaps. Specifically, only the characteristic impedances of constituent half-wave layers are varied without altering the phase shift of it at the center frequency of the target passband that is the Fabry-Perot resonance frequency of the unperturbed original HQWS structure. Because the simultaneous control of characteristic impedance and phase shift in each of the constituent half-wave layers is not achievable only by layer-sizing, the varied layers must be realized by metamaterials. So, specially-configurecl aluminum-based metamaterials having a double-slit void inhomogeneity are engineered and the actual wave transmission performance of the metamaterial-realized HQWS structure is examined numerically and experimentally. (C) 2015 Elsevier Ltd. All rights reserved.