Varied amplitude nonlinear acoustic method of landmine detection

Abstract

Acoustic methods of land mine detection are being developed for nonmetal mines where conventional electromagnetic methods fail. Nonlinear acoustic methods have shown higher sensitivity than linear methods. In previous studies, the nonlinear methods, based on interaction of two frequency waves and phase inversion of two pulses, were investigated. We propose an alternative nonlinear method based on the use of wide‐frequency pulses with different amplitude and subtraction of the normalized received signals. This method evaluates the nonlinear effects in a wide‐frequency band similar to the phase inversion method and it detects nonlinear components that are lost in the phase inversion method. In our tests, the suggested method was combined with time reversal acoustic focusing to concentrate seismic wave energy in proximity to the mine, which increased nonlinear effects. Experiments with various types of mines were conducted at Fort Belvoir using six loudspeakers in a box for excitation in the frequency band 50–500 Hz. The nonlinear mine response measured by the varied amplitude method provides the highest mine/no mine contrast among all the experiments performed using linear and nonlinear techniques. [Work was supported by the U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate.]