The gradient coils generate the linear gradient fields that are used for imaging. They produce a magnetic field in the z direction which changes linearly with position. The sensitivity of the gradient coils is 13.7 mT/m/A, 10.4 mT/m/A, and 12.3 mT/m/A for X, Y, and Z, respectively. The gradient coils for this system are contained on a printed circuit board that is inserted into the magnet bore leaving a space just over 1cm for the sample and RF detector/exciter coil.
The gradient coil isocurrent contours were calculated by Maxim Zaitsev and Feng Jia of Univ. Freiburg. The contours were converted to circuitboard traces by Cris LaPierre at MGH. The gradients are implemented as a shielded planar coils, so an inner set of primary coils spaced by about 1cm and the shield coils placed at the magnet poles. The coils are implemented as 8 layer boards with buried vias. Two layers are dedicated to each of the windings (ie. two layers for the x primary on the primary board). The copper was 2oz/ft^2 to allow higher currents.
The inductance and resistance of the final X, Y, and Z coils are:
X: 10.3 uH, 0.385 ohms Y: 10.4 uH, 0.365 ohms Z: 6.4 uH, 0.118 ohms