Modeling acoustic landmine detection using a soil-plate oscillator

Abstract

In laboratory acoustic landmine detection experiments a plastic cylindrical drum-like simulant is buried in a soil (or sand) tank. Airborne sound, generated from two subwoofer loudspeakers (located above the soil), drive the soil particles and subsequent particle vibration over the compliant top plate of the simulant. Measurements of tuning curve soil surface vibration particle velocity versus frequency are recorded for various scan locations across the soil surface in an effort to profile the buried simulant. Measurements of resonances “off the target” are also included in this study. The results can be modeled using a soil-plate-oscillator (SPO) apparatus. The SPO involves a vertical thick-wall cylindrical column of granular medium (sand, soil, pebbles, light density edible granular material like wheat germ or even uncooked brown rice) that is supported by a thin circular elastic (acrylic) plate (8 in. diameter, 1/8 in. thick) that is rigidly clamped at the bottom of the column. A small accelerometer placed on the granular surface (or a laser Doppler vibrometer) measures tuning curve results across the surface using a sweep spectrum analyzer. Profiles are compared for both the SPO and the simulant in an effort to model the results in the later—more complicated case.