Maxime Van Landeghem, PPMD-ESPCI et Saint-Gobain recherche

Jeudi 16 décembre 2010, 16h00
Amphi Boreau, Esc C, 2ème etage

Depth profiling with single-sided NMR sensors

Maxime Van Landeghem1,2,3, Ernesto Danieli1, Federico Casanova1, J. Perlo1 and Bernhard Blümich1

1 ITMC - RWTH-Aachen Worringer Weg 1, D52056 Aachen, Germany
2 ESPCI - PPMD, UMR 7615 CNRS UPMC, ESPCI ParisTech, 10 rue Vauquelin, 75005 Paris, France
3 Saint-Gobain Recherche, 39 quai Lucien Lefranc, BP 135, 93303 Aubervilliers cedex, France

Nuclear Magnetic Resonance (NMR) methods have been initially developed to work in the homogeneous fields of strong magnets, but the limited volume of these devices restricts the applications of NMR, in particular for in situ studies of large objects. But in addition to conventional NMR, where samples are adapted to fit into the probe, there is single-sided NMR, which uses open magnets specially adapted to the object under study. Such open magnets can be low in cost and portable. However, the open geometry of the magnets brings associated a number of challenging limitations. To be usable, the magnetic field needs to be shimmed by moving the magnets from each other. This is a reminiscence of the old style of improving the field inhomogeneity in NMR magnets. Typical magnet geometries provide the best performance for large magnetic field values (typically 0.5T) when also a large gradient (typically 20 T/m) is obtained. In this limit, the thickness of the excited slice becomes extremely thin (of the order of 100 μm) requiring mechanical or electronic slice repositioning to profile large depth range into the sample, which leads to an important restriction to the experimental time required to profile large depth ranges into the sample. To avoid this, a U-shape permanent magnet was equipped with extra shim magnets to strongly reduce the magnetic field gradient along the depth direction while keeping under control the lateral components. Under these conditions depth profiles over a range of two millimeters are measured with a resolution of 50 µm in a single-shot. The increment in the thickness of the sensitive volume eliminates the need for repositioning the sensor with respect to the object allowing us to cover the whole depth range in a single measurement.

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