Ring Magnet Design Considerations for Obtaining Magnetic Resonance Signals in Low Non-Uniform Fields

Use of low static magnetic fields for nuclear magnetic resonance (NMR) signal detection remains a challenge due to low signal-to-noise ratio, low energy difference between energy levels, and less spin transitions due to limited availability of spins. Despite these challenges, different measurement techniques based on low static magnetic fields, stray magnetic fields, and non-uniform fields have been implemented. In this paper, an approach toward using low static fields generated by permanent magnets for portable magnetic resonance applications is described. Finite element simulation models of different magnet geometries are used to develop an estimate of the magnetic field distribution exterior to the magnet. A concentric ring magnet geometry is selected to obtain flexible control of localized regions of uniform magnetic field. An estimate of the NMR voltage for different magnet sizes and orientations is presented. It is expected that the findings of this paper would be valuable for design of future portable magnetic resonance systems.