Patent US4812797A successfully refreshed from Google Patents.
US4812797A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Compensation coil for temporal drift of a superconducting magnet
Assignee: General Electric Co
•
Filing: 1988-03-22
•
Granted: 1989-03-14
•
Expires: 2008-03-22
Abstract
Abstract A superconducting coil assembly for a nuclear magnetic resonance imaging system has a main coil for producing a static magnetic field within a cylindrical volume. a conventional set of active correction coils are provided to spatially homogenize the magnetic field. A pair of passive compensation coils are electrically connected in series and shorted together. The compensaton coils are inductively coupled to the main coil so that the temporal decay of the current in the main coil induces current in the compensation coils. The magnetic field harmonics produced by this induced current is opposed to the magnetic field harmonics produced in the correction coils by main coil decay. The compensation coil thereby counteracts the inhomogeneity effects from the main coil current decay.
Inventors
- 👤 Raghavan Jayakumar
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 14:57
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/38; G01R33/389; G01R33/381; G01R33/3815; G01R33/387; G01R33/3875
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
101 words
A coil assembly for an NMR imaging system comprising: a main coil means for producing a magnetic field within a region; a correction coil means for correcting spatial inhomogeneity in the magnetic field produced by said main coil means, said correction coil means being inductively coupled to said main coil means; and a compensation coil means inductively coupled to said main coil means so that temporal decay of the main coil current produces a magnetic field harmonic component from said compensation coil means that is opposed to a magnetic field harmonic component produced by the correction coil due to the decay.
Claim 2
Dependent Claim
101 words
A coil assembly for an NMR imaging system comprising: a main coil means for producing a magnetic field within a region; a correction coil means for correcting spatial inhomogeneity in the magnetic field produced by said main coil means, said correction coil means being inductively coupled to said main coil means; and a compensation coil means inductively coupled to said main coil means so that temporal decay of the main coil current produces a magnetic field harmonic component from said compensation coil means that is opposed to a magnetic field harmonic component produced by the correction coil due to the decay.
Claim 3
Dependent Claim
23 words
The coil assembly as recited in claim 1 wherein said compensation coil means comprises two windings electrically connected in series and shorted together.
Claim 4
Dependent Claim
25 words
The coil assembly as recited in claim 2 wherein the two windings are axisymmetric with respect to the longitudinal axis of said main coil means.
Claim 5
Dependent Claim
19 words
The coil assembly as recited in claim 2 wherein the two windings are colocated with said correction coil means.
Claim 6
Dependent Claim
87 words
A coil assembly for establishing a static, highly uniform magnetic field comprising: an active main magnetic coil means for producing a magnetic field within a cylindrical volume having a longitudinal axis; an active correction coil means for correcting spatial inhomogeneity of the magnetic field within the volume; and a passive compensation coil means for compensating for the inhomogeneity of the magnetic field within the volume that results from temporal drift of the magnetic field, said compensation coil means being inductively coupled to said main magnetic coil means.
Claim 7
Dependent Claim
87 words
A coil assembly for establishing a static, highly uniform magnetic field comprising: an active main magnetic coil means for producing a magnetic field within a cylindrical volume having a longitudinal axis; an active correction coil means for correcting spatial inhomogeneity of the magnetic field within the volume; and a passive compensation coil means for compensating for the inhomogeneity of the magnetic field within the volume that results from temporal drift of the magnetic field, said compensation coil means being inductively coupled to said main magnetic coil means.
Claim 8
Dependent Claim
30 words
The coil assembly as recited in claim 5 wherein said compensation coil means includes two coil windings coaxial about the longitudinal axis, the windings being connected in series and shorted.
Claim 9
Dependent Claim
24 words
The coil assembly as recited in claim 6 wherein the two windings are symetrically located with respect to a median of the cylindrical volume.
References Cited (Backward Citations)
US4398150A
Cited
US4581580A
Cited
US4701736A
Cited
US4656447A
Cited
US4500860A
Cited
US4689591A
Cited
US4647858A
Cited
US4680551A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-03-13 | 1992-09-12 | 1993-03-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-03-13 | 1996-09-12 | 1997-03-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-03-13 | 2000-09-12 | 2001-03-14 | $7700.00 | Window Closed / Lapsed |