Passive shims for correction of (3,2) and (3,-2) harmonic terms

Details Passive shims for correction of (3,2) and (3,-2) harmonic terms Passive shims for correction of (3,2) and (3,-2) harmonic terms

1988-12-22

1989-08-01

Harris, George

Electricity: magnetically operated switches, magnets, and electr

Magnets and electromagnets

Magnet structure or material

324320, H01F 700

Patent

active

048536636

ABSTRACT:
A shim set for passively shimming (3,2) and (3,-2) harmonic terms in the field of the magnetic resonance magnet having a cylindrical bore, is provided. Four shims of ferromagnetic material, all of the same size, are secured to the interior of the bore of the magnet. The length of each of the shims is greater than its width. The first two of the shims are secured diametrically opposite one another, near one end of the magnet, with the length of the shims extending circumferentially. One of the first two shims is situated so that a polar angle is created between the axial centerline of the cylindrical bore and an imaginary line extending through the center of the cylindrical bore and the center of the shim, at about 30.degree.-44.degree. with 38.degree. being the most desirable location. The second two of the four shims are positioned symmetrically about the axial midplane of the cylindrical bore from the first two of the four shims and rotated 90.degree. circumferentially relative to the first two shims.

REFERENCES:
patent: 4698611 (1987-10-01), Vermilyea
patent: 4743853 (1988-05-01), Frese
patent: 4771243 (1988-09-01), Vreugdenhil et al.

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