Infrasound amplification using simple strongly nonlinear granular metamaterials

Monodispersed and inverse tapered granular chains with grain sizes varying uniformly from small to large under external harmonic excitations are numerically investigated. The control parameters are the number of granules, driving amplitude, driving frequency, and tapering parameter. The frequency response is analyzed using the transfer function, where properties of transmission, amplification, and filtering of signals are observed. For monodispersed chains, amplification peaks are described by functions of the control parameters. For sufficiently long monodispersed chains, signals at low frequencies (≈10Hz) are amplified. Inverse tapered chains exhibit similar behavior with shorter chain lengths, as do monodispersed chains modeled with forces between granules with nonlinearity greater than that of the Hertzian contact law. Potential applications are in the fields of geosciences and oceanography, life sciences, military applications, and environmental monitoring.