Nonlinear acoustic techniques for landmine detection: Tuning curves and two-tone tests

Abstract

Measurements of the top surface vibration of a buried (inert) VS 2.2 anti-tank plastic landmine reveal significant resonances in the frequency range between 80 and 650 Hz. Resonances from measurements of the normal component of the acoustically induced soil surface particle velocity (due to sufficient acoustic-to-seismic coupling) have been used in detection schemes. Since the interface between the top plate and the soil responds to pressure fluctuations nonlinearly, characteristics of landmines, the soil, and the interface are rich in nonlinear physics and allow for new methods of buried landmine detection not previously exploited. Tuning curve experiments (revealing ‘‘softening’’ and a back-bone curve linear in particle velocity amplitude versus frequency) help characterize the nonlinear resonant behavior of the soil-landmine oscillator. When two primary waves f1 and f2 drive the soil over the mine, a rich spectrum of nonlinearly generated tones is measured with a geophone on the surface over the buried landmine in agreement with Donskoy [Proc. SPIE 3392 (1998); 3710, 239–246 (1999)]. In profiling, particular nonlinear tonals can improve the contrast ratio compared to using either primary tone in the spectrum. [Work supported by the United States Army Communications-Electronics Command Night Vision and Electronic Sensors Directorate.]