Nonlinear acoustic techniques for landmine detection: Experiments and theory, Part II

A nonlinear acoustic technique for detecting buried landmines has been suggested by Donskoy [SPIE Proc. 3392, 211 (1998); 3710, 239 (1999)] and verified in a number of experiments by Sabatier et al. [J. Acoust. Soc. Am. 110, 2757, 2758 (2001)]. Airborne sound involving two primary frequencies f1 and f2 undergo acoustic‐to‐seismic coupling which interacts with the compliant mine and soil to generate a difference frequency component that can effect the vibration velocity at the surface. An LDV profile across a buried mine at the difference frequency (chosen at a resonance) showed more relative sensitivity than a linear profile. A layer of soil in a large tube, terminated by an airbacked clamped thin elastic plate, is used to model nonlinear effects including Donskoy’s ‘‘bouncing’’ soil–mine interface. The frequency spectrum of modes of the plate’s response is investigated vs the amount of soil mass loading. In particular, the lowest mode frequency first decreases with loading and then increases. Linear response curves near resonance compare well with the difference frequency response as one primary is varied. [Work supported by the United States Army Communications‐Electronics Command Night Vision and Electronic Sensors Directorate.]