Journal
SCIENTIFIC REPORTS
Volume 9, Issue -, Pages -Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/s41598-019-50697-w
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Funding
- Wellcome Collaborative Award in Science [203257/Z/16/Z, 20357/B/16/Z]
- Engineering and Physical Sciences Research Council [EP/M013294/1]
- Medical Research Council [MR/K005464/1, MR/M006301/1]
- Wellcome [203147/Z/16/Z]
- National Institutes of Health [R44HD074495, R44MH110288]
- EPSRC [EP/L016478/1, EP/L016052/1]
- MRC through the Oxford Nottingham Biomedical Imaging Centre for Doctoral Training [EP/L016052/1]
- EPSRC through the Oxford Nottingham Biomedical Imaging Centre for Doctoral Training [EP/L016052/1]
- EPSRC [EP/M013294/1] Funding Source: UKRI
- MRC [MR/K005464/1, MR/M006301/1] Funding Source: UKRI
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To allow wearable magnetoencephalography (MEG) recordings to be made on unconstrained subjects the spatially inhomogeneous remnant magnetic field inside the magnetically shielded room (MSR) must be nulled. Previously, a large bi-planar coil system which produces uniform fields and field gradients was used for this purpose. Its construction presented a significant challenge, six distinct coils were wound on two 1.6 x 1.6 m(2) planes. Here, we exploit shared coil symmetries to produce coils simultaneously optimised to generate homogenous fields and gradients. We show nulling performance comparable to that of a six-coil system is achieved with this three-coil system, decreasing the strongest field component B-x by a factor of 53, and the strongest gradient dB(x)/dz by a factor of 7. To allow the coils to be used in environments with temporally-varying magnetic interference a dynamic nulling system was developed with a shielding factor of 40 dB at 0.01 Hz. Reducing the number of coils required and incorporating dynamic nulling should allow for greater take-up of this technology. Interactions of the coils with the high-permeability walls of the MSR were investigated using a method of images approach. Simulations show a degrading of field uniformity which was broadly consistent with measured values. These effects should be incorporated into future designs.
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