CommunicationA low-field, low-cost Halbach magnet array for open-access NMR
Section snippets
Overview
In conventional NMR spectrometers the sample is enclosed by the magnet, shim and RF coils which typically prevent the sample from being readily studied by other, non-NMR spectroscopic, and/or mechanical probes. In many situations, such as food processing, the sample undergoes rapid and irreversible changes and it would be advantageous to be able to monitor these changes with a variety of complementary spectroscopic methods. Of course, one-sided magnet systems, such as the NMR-MOUSE offer easy
Magnet and RF coil design
The Halbach array was composed of a set of four strong composite permanent magnets. These were neodymium-ferrite-boron, type NdFeB N38H, 200 mm long by 18 × 18 mm square, fabricated by Magnet Sales and Service Ltd of Highworth, UK. The magnetic axis of each magnet runs parallel to one of the 18 mm dimensions. An aluminium frame held the magnets in a square array 200 mm long by 74 mm square, in such a way that they could be rotated about their long axes, and then locked in position with their short
Results and conclusion
Experiments were performed using Hahn echo or CPMG pulse sequences on samples in conventional NMR tubes ranging over 5–18 mm diameter. To illustrate the open-access aspect of the instrument, whole fruit and eggs were also scanned by simply resting them on the RF coil, as well as a human finger (inserted through the coil) and a gel sample in a 2 cm diameter impedance cell. Considering the limitations of the design, especially low S/N ratio, the results were considered satisfactory and capable of
Acknowledgment
The authors gratefully acknowledge funding of this work by a Small Business Research Initiative award from the EPSRC.
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