Advanced structured composites as novel phononic crystals and acoustic metamaterials

Abstract

We design and test new periodic materials that can reflect and prohibit the propagation of structural vibrations. These materials are engineered as periodic structures with resonant elements. We rely on recent advances in additive manufacturing to 3-D print composite materials that combine periodically embedded metal resonators within a periodic, truss-like polycarbonate lattice structure, functioning as a support matrix. The polycarbonate lattice geometry allows the matrix to be ultra-low density yet load bearing, and have tunable density and tunable effective elastic modulus. The high acoustic impedance mismatch between this lattice and the metal resonators opens the possibility to create materials with low frequency and wide band gaps, or frequencies where acoustic propagation is forbidden, using a combination of Bragg scattering effects with effects due to the presence of local resonators. Finite element modeling is used to analyze various lattice geometries, lattice densities, and resonator locations to show materials with tunable acoustic properties.