Chemnitz University of Technology, Research Center MAIN
Abstract:
Based on extensive numerical simulations and first validating experiments, we present a two-dimensional phononic crystal
design that exhibits exceptionally large complete band gaps, comparable to those of bubble crystals. Building on the analogy
between electronic band structures in solids and acoustic wave propagation in periodic media, we introduce the concept of
Function Phononic Crystals: a bulk structure characterized by spatially continuous material parameters rather than discrete
boundaries. Numerical simulations reveal that a sawtooth-like variation of these parameters produces extensive frequency
gaps and flat bands. Remarkably, this band structure can be closely replicated by a much simpler geometry composed of
cylindrical inclusions that touch at single points, effectively forming a broadband acoustic filter. Analysis of the acoustic density
of states shows that even minor deviations from the conventional step-function profile lead to rapid convergence toward the
continuous case. Experimental acoustic frequency response measurements on an easy-to-assemble two-dimensional array of
parrafin candles confirm the predicted broadband sound isolation and validate the numerical results. Our findings demonstrate
that complex continuous material distributions can be replaced by simple discrete structures with equivalent spectral
properties, enabling efficient, experimentally accessible phononic crystal designs with the potential of a strong sound
attenuation and a practical application potential.