Wideband nonlinear time reversal seismo-acoustic method for landmine detection

Abstract

Acoustic and seismic waves provide a method to localize compliant mines by vibrating the top plate and a thin soil layer above the mine. This vibration is mostly linear, but also includes a small nonlinear deviation. The main goal of this paper is to introduce a method of processing that uses phase-inversion to observe nonlinear effects in a wide frequency band. The method extracts a nonlinear part of surface velocity from two similar broadcast signals of opposite sign by summing and cancelling the linear components and leaving the nonlinear components. This phase-inversion method is combined with time reversal focusing to provide increased seismic vibration and enhance the nonlinear effect. The experiments used six loudspeakers in a wood box placed over sand in which inert landmines were buried. The nonlinear surface velocity of the sand with a mine compared to the sand without a mine was greater as compared to a linear technique.

Imaging of human tooth using ultrasound based chirp-coded nonlinear time reversal acoustics

“…6c has the advantage to show the amplitude referenced image of the nonlinear effects induced by the focusing of ultrasound at the surface of the tooth. The measured vibrations velocities of the nonlinear signature and previously validated with other samples coming from the aeronautic industry are in the order of 1 mm/s which is compatible with nonlinear effects also measured with the same TRA method in landmine detection (0.2 mm/s in [17]). …”

“…During experimental TR-NEWS validations [12,[15][16][17][18] in various medium (simple and complex), side-lobes effects leading to ''phantom images'' have been identified and associated to virtual sources coming for multiple scattering and multiple reflections. As described schematically for a simple medium (Fig.…”

“…Using symbiosis of these systems, symmetry analysis (TR, reciprocity, chirpcoded PI, etc.) and NEWS methods, TR-NEWS fundamental experimental demonstration [16] have been conducted with applications in the improvement of nonlinear scatterers identification, such as bubbles [15], landmines [17], cracks in complex aeronautic materials [18] and is now highly recognized as extremely reliable [19, p. 14].…”

Nonlinear Time Reversal Tomography of Structural Defects

“…This procedure requires measurement of inter-element response matrices for excitations necessary for ESAM application (Eqs (6-9)). From these matrices K (E) (t), K (A) (t), K (B1) (t) and K (B2) (t), the nonlinear terms corresponding to each trajectory |T k R m | are extracted according to Eqs (13)(14)(15). Matrices K (1) (t), K (2) (t) and K (3) (t) are obtained on which DORT is applied, as described previously.…”

“…For the extraction of nonlinear parameters corresponding to the scatterers S 1 and S 2 , DORT is applied on the separated nonlinear terms of direct responses provided by ESAM (Eqs (13)(14)(15)). This procedure requires measurement of inter-element response matrices for excitations necessary for ESAM application (Eqs (6-9)).…”