The invention discloses a permanent
magnet used for a
nuclear magnetic resonance imager. The permanent
magnet comprises upper and lower housing caps and double-columns, wherein the upper and lower housing caps and the double-columns are connected through bolts to form a building block-type assembled H-shaped yoke; two steel magnets, two polar plates, two shimming rings, two
eddy current discs, gradient coils and transmitting coils are respectively and symmetrically arranged on the upper and lower housing caps in sequence to form testing regions; the upper outer end part of each polar plate is provided with the corresponding shimming ring; the two
eddy current discs are respectively arranged in the two shimming rings; the two gradient coils and the two transmitting coils are respectively arranged on the two
eddy current discs in the shimming rings; the
magnetic field intensity of each imaging region (i.e. sphere region, of which the
diameter is 400nm, at the
central region of the permanent
magnet) is between 4000 gauss to 5500 gauss. The eddy current discs respectively manufactured by splicing amorphous sheets of an iron-based amorphous
alloy soft magnetic strip 1K101 is capable of better eliminating or reducing eddy current generated by the polar plates, and therefore, the
signal to
noise ratio is higher, and imaging is clearer; by adopting the N52-N55 high-performance
neodymium-iron-
boron steel magnets and the gradient and transmitting integrated coils, the overall dimension reduction and the total weight reduction of the permanent magnet can be realized, and moreover,
processing is simple, the structure is changeable and shimming is convenient.