Bruschini, Claudio

Cattin, V.

Guiga, A.

Ittel, J.-M.

Léger, J.-M.

Vidal, J.-C.

Infoscience - École polytechnique fédérale de Lausanne

LANDMINE DETECTION SYSTEM WITH NMR GRADIOMETER V. Cattin*, C. Bruschini1, A. Guiga, J.M. Ittel, , J.M. Léger, J.C. VidalLETI (CEA - Technologie Avancées) DSYS CSME, CEA/G17 Avenue des Martyrs, 38054 Grenoble Cédex 9 – France1EPFL – LAMI & VUB-ETRO-IRIS, EPFL-LAMICH-1015 Lausanne – SwizerlandDuring the last 5-10 years, landmine problems became increasingly urgent.Since detection and clearance are very often carried out using manualmethods, new systems are being studied to provide safer and more powerfuldetection and localisation functions. In this context, we have implemented amine detection system based on high resolution scalar magnetic sensors.Passive magnetic sensors detect the presence of ferromagnetic material. Theymeasure both the remanent magnetization and the magnetization induced bythe earth magnetic field in such materials. Most land mines contain enoughmetal to be detected by this method even if their metallic pieces are often verysmall (<1g). We propose to use a Leti NMR scalar magnetic sensor (Abragam-Overhauser effect). Such a sensor measures the module of the ambient field, orthe projection of the magnetic response of the mine on the earth fielddirection. Its main advantages compared to other magnetic sensors are higherresolution (pT/Hz1/2), especially in the DC band, its robustness andinsensitivity to movements. The high-resolution demonstration system we setup consists of a vertical gradiometer composed of two NMR sensors. The firstsensor is moved along a profile at about 10 cm from the ground and measuresthe magnetic mine effect. The other is about 1.5 m above the ground and isused as a reference to measure the ambient electromagnetic noiseperturbations, both industrial and geological, which may screen the targetresponse. This gradiometer concept ensures a large noise reduction, fromabout 1000 pTpp down to less than 10 pTpp. The distance between the twosensors has to be matched to the depth of investigation and the sensitivity.This system was tested to measure magnetic effects of several common APlandmines provided by the EPFL. We have first verified that the geologicalenvironment and the industrial magnetic perturbations are efficiently reducedby the gradiometer. We then performed static measurements and the obtainedmagnetic effects range between 50 pT up to 7.5 nT for the smaller and largermetallic components of the different mines. By moving the gradiometer abovethe targets, we obtain a profile which characterises the magnetic signature ofthe target. In the future, such a system could be used either to build a reliablemagnetic effect database of mines, or to design a new handheld or vehicle-integrated detection device. In the next step, signal processing can be used toextract specific parameters of each target like distance, size or magneticmoment.

Landmine Detection System with NMR Gradiometer

http://infoscience.epfl.ch/record/257008/files/2000_Cattin_LandmineDetNMRgradiometer_absLetiEUROEM.pdf

LANDMINE DETECTION SYSTEM WITH NMR GRADIOMETER

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