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Acoustic-like behavior in periodic metal structures

Pentamode materials are of interest for acoustic metamaterials because of their property of having only one elastic mode, similar to the hydrostatic response of an acoustic fluid. This static property does not take into account dynamic frequency dependent effects related to the necessary spatial inhomogeneity in the structural realization. In this talk, we argue that pure pentamode behavior is not desirable, and instead AMM users should focus on the one-wave dynamic response. Experience with metal structures designed to provide acoustic properties close to those of water using metal structures, e.g., Su et al. (JASA 2017, doi: 10.1121/1.498519), shows that the most useful response is in a one-wave band gap in which shear waves are non-propagating. Surprisingly, the one-wave region is generally broadband relative to the cutoff frequency of the shear waves at low frequencies, and is non-dispersive, with constant phase speed over the one-wave gap. The talk will attempt to explain these surprising and unexpected features using numerical and analytical results. The latter include an approximation of the dynamic effective properties of 2D and 3D metallic structures displaying broadband one-wave regions using simplistic models.Pentamode materials are of interest for acoustic metamaterials because of their property of having only one elastic mode, similar to the hydrostatic response of an acoustic fluid. This static property does not take into account dynamic frequency dependent effects related to the necessary spatial inhomogeneity in the structural realization. In this talk, we argue that pure pentamode behavior is not desirable, and instead AMM users should focus on the one-wave dynamic response. Experience with metal structures designed to provide acoustic properties close to those of water using metal structures, e.g., Su et al. (JASA 2017, doi: 10.1121/1.498519), shows that the most useful response is in a one-wave band gap in which shear waves are non-propagating. Surprisingly, the one-wave region is generally broadband relative to the cutoff frequency of the shear waves at low frequencies, and is non-dispersive, with constant phase speed over the one-wave gap. The talk will attempt to explain these surprising and unexpec...