A design of permanent magnet array for unilateral NMR device

We have designed a three-dimensional magnetic circuit consisting of various pieces of magnetic blocks for a unilateral MRI device, which generates a homogeneous magnetic flux density at a remote region. The direction of the remanent flux density of the main outer magnetic blocks is parallel to the surface of the device; hence the direction of the magnetic flux density in the remote region is also parallel to the surface of the device. The magnitudes of the remanent flux density of the magnetic blocks are adjusted so as to minimize the variation of the magnetic flux density in the remote region. This magnetic circuit, with an outer dimension of 400 mm x 400 mm x 200 mm, produces a magnetic flux density in a 20 mm x 20 mm x 5 mm region of interest at a distance of 55 mm from the surface of the device with a magnitude of 64.5 mT (2.75 MHz in resonant frequency) and a uniformity of 275 ppm (755 Hz in band width).