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Details of Grant 

EPSRC Reference: GR/L17443/01
Title: DIRECT METHODS FOR FIELD HOMOGENEITY OPTIMIZATION IN NMR SPECTROSCOPY
Principal Investigator: Morris, Professor GA
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Department: Chemistry
Organisation: Victoria University of Manchester, The
Scheme: Standard Research (Pre-FEC)
Starts: 03 December 1996 Ends: 02 December 1998 Value (£): 138,035
EPSRC Research Topic Classifications:
Instrumentation Eng. & Dev.
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Summary on Grant Application Form
Shimming, the adjustment of the magnetic field to very high homogeneity, wastes many hours of spectrometer time in NMR spectroscopy. Despite much effort, existing automatic shimming methods based on blindfold simplex optimisation using free induction decay area or lock signal amplitude criteria perform poorly. A new approach is proposed which uses direct measurements of field distribution followed by iterative field correction in a highly convergent process. The existing spectrometer hardware is used without the need for pulsed field gradient facilities. The magnetic field distribution is mapped by measuring the signal profile in the presence of strong additional linear field gradients provided by the normal shim coils, and extracting from the profiles a field distribution map. An approximate correction field is then synthesised using individual shim coil field distributions determined by the same process, and the cycle repeated with smaller applied gradients until the required field homogeneity is obtained. Three cycles should typically suffice, taking well under a minute for a complete shim of a spinning sample.
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