Nonlinear Acoustic Experiments Involving Landmine Detection: Connections with Mesoscopic Elasticity and Slow Dynamics in Geomaterials

The vibration interaction between the top‐plate of a buried VS 2.2 plastic, anti‐tank landmine and the soil above it appears to exhibit similar characteristics to the nonlinear mesoscopic/nanoscale effects that are observed in geomaterials like rocks or granular materials. [J. Acoust. Soc. Am. 116, 3354–3369 (2004)]. When airborne sound at two primary frequencies f₁ and f₂ (closely spaced near resonance) undergo acoustic‐to‐seismic coupling, (A/S), interactions with the mine and soil generate combination frequencies | n f₁ ± m f₂ | which affect the surface vibration velocity. Profiles at f₁, f₂, f₁ −(f₂ − f₁) and f₂ +(f₂ − f₁) exhibit single peaks whereas other combination frequencies may involve higher order modes. A family of increasing amplitude tuning curves, involving the surface vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding resonant frequency. Subsequent decreasing amplitude tuning curves exhibit hysteresis effects. New experiments for a buried VS 1.6 anti‐tank landmine and a “plastic drum head” mine simulant behave similarly. Slow dynamics explains the amplitude difference in tuning curves for first sweeping upward and then downward through resonance, provided the soil modulus drops after periods of high strain. [Support by U.S. Army RDECOM CERDEC, NVESD, Fort Belvoir, VA.]