Evaluation of parametric acoustic array technology in application to the acoustic landmine and improvised explosive device (IED) detection problems

There has been recent interest in using the parametric acoustic array for obtaining highly directional low frequency sources in acoustic landmine and IED detection. Experiments (using a commercial parametric array (0.5 m diam) located 1.5 m directly over the target and driven by a swept sine audio modulated 60 kHz tone) were performed to compare the ‘‘on’’ to ‘‘off’’ target soil surface particle velocity of an inert VS 1.6 (plastic) anti-tank landmine buried 2.5 cm deep in masonry sand in a concrete box located in the anechoic chamber facility. The laser Doppler vibrometer response (normalized to the microphone) was measured from 100–1,100 Hz using a spectrum analyzer. A SPL of 40 dB re 20 μ rmPa at 150 Hz was insufficient, where the mine was known to have its largest resonance. Resonances between 300–600 Hz also went undetected, but amplitude contrast ratios of 20 and 3 were measured at 850 and 1,050 Hz, respectively, upon signal averaging. Limitations in carrier SPL, auditory damage, saturation effects, distortion, and low efficiency need to be addressed to achieve the required 60–80 dB SPL needed near 100 Hz. Mines or IEDs buried at 15 cm require more SPL. [Work supported by ARL.]