Design, Construction, and Characterization of a Magic Angle Field Spinning RF Magnet

Abstract

Magic angle field spinning (MAFS) is a Nuclear Magnetic Resonance (NMR) spectroscopy technique used in NMR Compact Devices to enhance the spectral resolution. In this technique, the sample is placed inside a magnet which generates a magnetic flux density oriented at 54.74° with respect to the sample main axis and spun at high frequencies. We present here, the design and construction of a novel magnet that generates a magnetic field according to the MAFS technique. The prototype generates two radio frequency and one dc magnetic fields by the combined action of three electromagnets. This combination results in a magnetic flux density of 10 mT, with field deviations ≤1% inside a cylindrical volume of 30\times 30 mm, an orientation easily controlled by field amplitudes and precessing at frequencies up to 12 kHz. The magnet has been characterized by using a novel Flux+Gauss meter (FGM) built and calibrated in-house. The FGM is able to measure ac and dc magnetic fields along seven different longitudinal axes, one of them corresponds to the longitudinal axis of the prototype. The other six axes are placed at six angular orientations on a 30-mm-diameter circumference. The characterization of the magnet includes field profiles of the RF and dc fields along the FGM axes and deviations of the field in the 30\times 30 mm cylinder. The homogeneity is evaluated as the relative differences between the field measured at the centered axis and the field measured along the six extra axes for both RF and dc fields.