Improvement of signal intensity using a racetrack-shaped coil on NMR measurement

The measurement technique using a planar surface coil has advantages of acquiring a local Nuclear Magnetic Resonance (NMR) signal in short time from near the coil. This technique is used to measure water-content in polymer electrolyte membrane (PEM) of polymer electrolyte fuel cell (PEFC). Increasing NMR signal intensity obtained by surface coil is required for improvement of measurement accuracy. In this paper, a racetrack-shaped coil was used in order to make signal intensity increase and to keep measurement depth shallow. The detection area and measurement depth of the racetrack-shaped coil at the case of spin-echo measurement were analyzed theoretically. From the analytical result, it was shown that the measurement depth of racetrack-shaped coil is 0.37 time the distance which is between two parallel wires of the coil. And from experimental result, it was shown that the obtained signal intensity was proportional to measurement volume of the coil. Furthermore, in the case that surface coil with small inductance is used, the correction form to be able to compensate the differences of coil geometry and electric conductivity of coil was proposed. (author)