Highly uniform single-sided portable NMR sensor and its application in assessing the aging level of silicone rubber insulators

摘要

This study presents a high-performance single-sided portable nuclear magnetic resonance (NMR) sensor. The magnet array, which is composed of five identical cuboid permanent magnet blocks and two passive shimming sheets, generates a highly uniform B-0 field in a 10 x 10 mm(2) lateral area. Along the two orthogonal lines in this lateral area, the measured B-0 strength variation is less than 338 ppm. Vertically, the measured B-0 magnitude decreases from 144.387 mT to 130.603 mT, with a constant gradient of 4.6 T/m from 0.15 mm to 3.15 mm above the magnet surface. A planar radiofrequency coil is optimized according to the signal-to-noise ratio level of the coil. A one-dimensional profiling experiment on an oil film shows that a vertical resolution of approximately 1.7 mu m can be achieved. As an application, the silicone rubber insulators are measured using the NMR sensor. Results demonstrate that the silicone rubber insulators with different service times can be distinguished through the transverse relaxation time T-2 of the silicone rubber insulators.