# US 5,706,575 A · Method of making eddy current-less pole tips for MRI magnets

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- Number: US 5,706,575 A
- Document ID: US5706575A
- Status: Granted
- Kind: A
- Application number: 08/700,995
- Filed: 1996-08-21
- Granted: 1998-01-13
- Earliest claimed: 1994-09-22
- Assignees: The Regents of the University of California
- Inventors: Leon Kaufman; Joseph W. Carlson
- Web page: https://patentgrep.com/patent/US5706575A

## CPC

- G01R 33/385: using gradient magnetic field coils
- G01R 33/383: using permanent magnets
- H01F 2007/1676: {Means for avoiding or reducing eddy currents in the magnetic circuit, e.g. radial slots}
- Y10T 29/49075: including permanent magnet or core
- Y10T 29/49078: Laminated
- Y10T 29/49796: Coacting pieces
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Static magnet pole tips for a MRI system in which the static magnet pole tips are cut from a slug of spirally wound ferromagnetic material. The static magnet pole tips are cut from the spirally wound slug such that the static magnet pole tips have no or few semi-closed loops of ferromagnetic material. The static magnet pole tips can be used individually, or can be stacked for strength and symmetry.

## Claims

### Claim 1

A method of manufacturing a static magnet pole tip of a predetermined size for an MRI system, comprising the steps of:
1) winding ferromagnetic tape into a spiral slug of electrically insulated layers having a slug size larger than the predetermined size of the static magnet pole tip; and
2) cutting the static magnet pole tip from the spiral slug, whereby the approximate center of the static magnet pole tip is apart front the approximate center of the spiral slug.

### Claim 2 (depends on 1)

A method of manufacturing a static magnet pole tip according to claim 1, wherein:
the spiral slug and static magnet pole tip are generally in the form of circles,
the spiral slug having a diameter D.sub.s and the static magnet pole tip having a diameter D.sub.p, and
D.sub.s >D.sub.p.

### Claim 3 (depends on 1)

A method of manufacturing a static magnet pole tip according to claim 1, wherein step 2 includes cutting the static magnet pole tip from the spiral slug whereby the static magnet pole tip does not include the approximate center of the spiral slug.

### Claim 4 (depends on 2)

A method of manufacturing a static magnet pole tip according to claim 2, wherein:
D.sub.s >2D.sub.p ; and
step 2 includes the step of cutting two static magnet pole tips from the spiral slug.

### Claim 5 (depends on 4)

A method of manufacturing a static magnet pole tip according to claim 4, whereby the static magnet pole tips each include an orientation point that is closest to the approximate spiral center of the slug during step 2, the method further including:
3) stacking the two static magnet pole tips together oriented such that the respective orientation points on the static magnet pole tips are approximately 90 degrees apart relative to each other; and
4) bonding the two static magnet pole tips.

### Claim 6 (depends on 1)

A method according to claim 1, wherein step 1 includes the step of winding ferromagnetic tape into an spiral oval slug.