Design and simulation of broadband multiphase pentamode metamaterials

Pentamode metamaterial (PM) has great potential in controlling underwater waves due to its broadband and solid-state merits. The reported underwater PM devices were all designed with single metallic materials, which largely limited the realizable properties range of PM. Pentamode metamaterials for simulating water with dual phase and triple phase were proposed and investigated in this article. It was revealed that the acoustic scattering of the proposed PM in water is very weak within the simulation frequency range except at some resonance frequencies. The mean total scattering cross section of the proposed pentamode metamaterials is about two orders smaller than that of the titanium alloy block, while the far-field sound pressure of pentamode microstructures was only about 1/3 of that of titanium alloy block. It also illustrates that the second and third phase of the unit cell could not only broaden the realizable properties range of PM but also suppress the bending and rotational vibration modes, demonstrating the efficacy and broadband characteristic of the multiphase pentamode metamaterial.