Demonstration of nonlinear acoustic landmine detection: Hysteresis effects observed in a soil-elastic plate oscillator

Abstract

In nonlinear acoustic landmine detection the vibration interaction of the top-plate of the buried plastic landmine with the adjacent soil is a subject of interest due to the strong nonlinear coupling. Donskoy discovered the significance of using nonlinear vibro-acoustic two-tone tests to help find buried relatively compliant landmines at certain nonlinearly generated combination frequencies; and that false alarms were reduced due to minimal nonlinear interactions over relatively rigid buried objects. Later, work by Sabatier showed that certain nonlinear experimental results involving tuning curves and profiling at a large number of combination frequencies from two-tone tests (in buried plastic anti-tank inert landmine experiments) revealed that the nonlinear effects were similar to the mesoscopic/nanoscale nonlinear elastic behavior observed in geomaterials like sandstone. Here, an apparatus called the soil-plate oscillator is used to model the nonlinear interaction of a thin clamped vibrating acrylic plate with a small column of dry sifted soil supported over it. Measurements of the effects of tuning curves taken at increased amplitude acoustic drive amplitude (exhibiting softening) can be explained if hysteresis effects (characteristic of the mesoscopic nonlinear) interaction are taken into consideration. Lissajou patterns of the driving force vs. displacement also reveal hysteresis effects. [Work support by ONR.]