Nonlinear acoustic experiments for landmine detection: the significance of the top-plate normal modes

Murray S. Korman; W. C. Kirkpatrick Alberts II; James M. Sabatier

doi:10.1117/12.542574

21 September 2004 Nonlinear acoustic experiments for landmine detection: the significance of the top-plate normal modes

Murray S. Korman, W. C. Kirkpatrick Alberts II, James M. Sabatier

Proceedings Volume 5415, Detection and Remediation Technologies for Mines and Minelike Targets IX; (2004) https://doi.org/10.1117/12.542574
Event: Defense and Security, 2004, Orlando, Florida, United States

Abstract

In nonlinear acoustic detection experiments involving a buried inert VS 2.2 anti-tank landmine, airborne sound at two closely spaced primary frequencies f1 and f2 couple into the ground and interact nonlinearly with the soil-top pressure plate interface. Scattering generates soil vibration at the surface at the combination frequencies | m f₁ +- n f₂ | , where m and n are integers. The normal component of the particle velocity at the soil surface has been measured with a laser Doppler velocimeter (LDV) and with a geophone by Sabatier et. al. [SPIE Proceedings Vol. 4742, (695-700), 2002; Vol. 5089, (476-486), 2003] at the gravel lane test site. Spatial profiles of the particle velocity measured for both primary components and for various combination frequencies indicate that the modal structure of the mine is playing an important role. Here, an experimental modal analysis is performed on a VS 1.6 inert anti-tank mine that is resting on sand but is not buried. Five top-plate mode shapes are described. The mine is then buried in dry finely sifted natural loess soil and excited at f₁ = 120 Hz and f₂ = 130 Hz. Spatial profiles at the primary components and the nonlinearly generated f₁ - (f₂ - f₁) component are characterized by a single peak. For the 2f₁+f₂ and 2f₂ + f₁ components, the doubly peaked profiles can be attributed to the familiar mode shape of a timpani drum (that is shifted lower in frequency due to soil mass loading). Other nonlinear profiles appear to be due to a mixture of modes. This material is based upon work supported by the U. S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate under Contract DAAB15-02-C-0024.

Citation Download Citation

Murray S. Korman, W. C. Kirkpatrick Alberts II, and James M. Sabatier "Nonlinear acoustic experiments for landmine detection: the significance of the top-plate normal modes", Proc. SPIE 5415, Detection and Remediation Technologies for Mines and Minelike Targets IX, (21 September 2004); https://doi.org/10.1117/12.542574

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