Development of a Permanent Magnet With High Uniformity and High Magnetic Field for Miniaturization of Nuclear Magnetic Resonance Measurement System

ABSTRACT We developed a static magnetic field for miniaturization of the nuclear magnetic resonance (NMR) measurement system to measure nutrient solution in agricultural field. Instead of the large electromagnets used in our previous work, a permanent magnet was used to establish a static magnetic field. The design was based on the Halbach array, which allows the magnetic field to be concentrated on one side to increase the magnetic force. To avoid the problem of reducing the magnetic force of the magnets, the array magnets were optimized so that they could be composed of a combination of simple square prism magnets. Observation of the magnetic flux density of the fabricated permanent magnets showed that the magnetic flux density at the center was 0.946 T, and an error of less than 5 mT in magnetic flux density could be achieved. As a result, we succeeded in producing the permanent magnet. NMR measurements of water and air were performed using the produced magnets. When measuring water, a signal at 39.679 MHz was observed, which is the signal of hydrogen. In contrast, no signal was observed in air. Therefore, the NMR signal was successfully measured using the fabricated permanent magnet.