WO1994018682A1 - Aimant permanent - Google Patents

Aimant permanent Download PDF

Info

Publication number
WO1994018682A1
WO1994018682A1 PCT/GB1994/000227 GB9400227W WO9418682A1 WO 1994018682 A1 WO1994018682 A1 WO 1994018682A1 GB 9400227 W GB9400227 W GB 9400227W WO 9418682 A1 WO9418682 A1 WO 9418682A1
Authority
WO
WIPO (PCT)
Prior art keywords
magnet
magnets
main body
magnetic
ferromagnetic material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB1994/000227
Other languages
English (en)
Inventor
Paul Beasley
Peter Hanley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Oxford Instruments UK Ltd
Original Assignee
Oxford Instruments UK Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oxford Instruments UK Ltd filed Critical Oxford Instruments UK Ltd
Publication of WO1994018682A1 publication Critical patent/WO1994018682A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3808—Magnet assemblies for single-sided MR wherein the magnet assembly is located on one side of a subject only; Magnet assemblies for inside-out MR, e.g. for MR in a borehole or in a blood vessel, or magnet assemblies for fringe-field MR
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/383—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using permanent magnets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0205—Magnetic circuits with PM in general
    • H01F7/021—Construction of PM
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0273—Magnetic circuits with PM for magnetic field generation
    • H01F7/0278—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles

Definitions

  • the invention relates to permanent inagnets.
  • a permanent magnet comprises a main body of a first magnetically hard ferromagnetic material, at least one pole of the main body carrying an auxiliary body of a second magnetically hard ferromagnetic material, the first material being magnetically softer than the second material.
  • soft and hard for ferromagnetic materials are well known and are defined for example in “Electricity and Magnetism” by W J Duffin, published by McGraw Hill, 2nd Edition 1973, pages 336-337.
  • a "soft" ferromagnetic material can be considered as one with a zero remanence and coercivity.
  • soft ferromagnetics have a small coercivity, a low loss because of a narrow loop, and a high permeability. Pure iron and 3% S:Fe are typical soft ferromagnetic materials.
  • the invention is concerned with the use of hard ferromagnetic materials which should have a relatively large remanence and coercivity.
  • Examples include alloys of Fe, Al, Co and Cu, known generically as Alnico alloys (which comprise a group of "softer", hard ferromagnetic materials) and cobalt-rare earth materials such as cobalt-samarium and NdFeB which constitute "harder” hard ferromagnetic materials.
  • the first material may comprise Alnico and the second material Ne-Fe-B or SmCo.
  • the invention could be used in the arrangement of US-A-4350955 or in the invention of WO-A-93/14413.
  • Figure 2 is a view similar to Figure 1 but showing an example of a magnet assembly according to the invention
  • Figure 3 illustrates the variation of radial field with radius for the Figure 1 and Figure 2 examples respectively;
  • Figure 4 illustrates the variation of magnetic potential for different types of magnet.
  • the magnet or probe assembly shown in Figure l comprises a pair of main, permanent magnets l which are aligned and spaced apart along a Z axis. The poles of these magnets 1 facing each other are of the same sense. Arranged between the main magnets 1 is a set of permanent shim magnets 2.
  • a line 4 in Figure 3 illustrates the variation in the magnetic field due to the assembly shown in Figure 1 and it will be seen that a substantially homogeneous region 5 is generated radially spaced from the magnet assembly itself. In practice, this region would be arranged to fall within an area to be examined using a NMR process and have sufficient homogeneity or uniformity for such a process, e.g. better than 100 ppm.
  • the ferromagnetic material used to make up the main magnets 1 will typically be a "hard” material which is not easily magnetised but at the same time is difficult to demagnetise.
  • This material should be contrasted with a "soft” magnetic material which usually has a very narrow hysteresis loop, that is, low values of coercive force and high permeabilities.
  • a "soft” magnetic material which usually has a very narrow hysteresis loop, that is, low values of coercive force and high permeabilities.
  • there are relatively soft materials, for example alnico which would generate a field profile of the type shown by the line 4 in Figure 3.
  • the advantage of this material is that it is cheap and readily available but it has a relatively low magnetic energy and is relatively easily demagnetisable.
  • the magnets 1 could also be made of a magnetic material at the harder end of the group of hard ferromagnetic materials, for example Ne-Fe-B or SmCo which have high magnetic energy and are difficult to demagnetise but which are very expensive.
  • a magnetic material at the harder end of the group of hard ferromagnetic materials for example Ne-Fe-B or SmCo which have high magnetic energy and are difficult to demagnetise but which are very expensive.
  • FIG 2 illustrates an example of a magnet assembly according to the invention which it can be seen is generally similar to the Figure 1 example.
  • each of the magnets 1 is made of a relatively softer, hard magnetic material and is tipped with a magnetic material 3 which is relatively harder than the magnetic material making up the main body of the magnet 1.
  • the main body could be made of alnico while the tips 3 are made of Ne-Fe- B or SmCo.
  • the invention provides a much more cost effective magnet with the relatively harder, hard magnetic material of the tips 3 only being used where it is actually required, i.e. at the ends of the main body of the permanent magnet 1 where the material is demagnetising.
  • Figure 4a illustrates one end of a permanent magnet 1 of the type shown in Figure 1 and made of a soft ferromagnetic material where it can be seen that the magnetic potential is not confined to the pole face of the magnet.
  • Figure 4b illustrates the same magnet made throughout of a much harder magnetic material and in this case the magnetic potential is confined to the pole face.
  • Figure 4c illustrates the end of a magnet 1 of the type shown in Figure 2 and it can be seen here that the diverging magnetic potential shown in Figure 4a has been redirected so that the majority of the magnetic potential is confined to the pole face thus achieving substantially the effect of the Figure 4b example but without the need to make the entire permanent magnet from the expensive, harder hard magnetic material.
  • a line 6 indicates the magnetic field profile and it can be seen that the radial extent of the homogeneous region has significantly increased over the untipped version.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Vascular Medicine (AREA)
  • Hard Magnetic Materials (AREA)

Abstract

Aimant permanent comprenant un corps principal (1) constitué d'un premier matériau ferromagnétique magnétiquement dur. Au moins l'un des pôles du corps principal porte un corps auxiliaire (3) constitué d'un second matériau ferromagnétique magnétiquement dur. Le premier matériau est magnétiquement moins dur que le deuxième matériau.
PCT/GB1994/000227 1993-02-12 1994-02-07 Aimant permanent Ceased WO1994018682A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB939302843A GB9302843D0 (en) 1993-02-12 1993-02-12 Permanent magnet
GB9302843.9 1993-02-12

Publications (1)

Publication Number Publication Date
WO1994018682A1 true WO1994018682A1 (fr) 1994-08-18

Family

ID=10730345

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1994/000227 Ceased WO1994018682A1 (fr) 1993-02-12 1994-02-07 Aimant permanent

Country Status (3)

Country Link
GB (1) GB9302843D0 (fr)
IL (1) IL108517A0 (fr)
WO (1) WO1994018682A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0653096A4 (en) * 1992-07-27 1995-06-21 New York University High field magnets for medical applications.
WO1999008126A1 (fr) * 1997-08-11 1999-02-18 Oxford Instruments (Uk) Limited Ensemble generateur de champ magnetique pour appareil a resonance magnetique nucleaire (rmn)
GB2355800A (en) * 1999-10-29 2001-05-02 Oxford Magnet Tech Laminated ferromagnetic structure for improved field homogeneity
US6400149B1 (en) 2001-05-24 2002-06-04 Schlumberger Technology Corporation Nuclear magnetic resonance apparatus and method for generating an axisymmetric magnetic field having straight contour lines in the resonance region
GB2380309A (en) * 2001-08-20 2003-04-02 Richard Wolfe Magnetic device for reduction of EMI in audio circuitry
US7501817B1 (en) 1998-03-03 2009-03-10 Schlumberger Technology Corporation Method and apparatus for generating an axisymmetric magnetic field
FR3012263A1 (fr) * 2013-10-23 2015-04-24 Schneider Electric Ind Sas Ensemble de prises electriques

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3768054A (en) * 1972-04-03 1973-10-23 Gen Electric Low flux leakage magnet construction
JPS61170004A (ja) * 1985-01-24 1986-07-31 Namiki Precision Jewel Co Ltd 永久磁石体
EP0479278A1 (fr) * 1990-10-04 1992-04-08 Shin-Etsu Chemical Co., Ltd. Aimant cylindrique approprié pour l'imagerie à résonance magnétique nucléaire

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3768054A (en) * 1972-04-03 1973-10-23 Gen Electric Low flux leakage magnet construction
JPS61170004A (ja) * 1985-01-24 1986-07-31 Namiki Precision Jewel Co Ltd 永久磁石体
EP0479278A1 (fr) * 1990-10-04 1992-04-08 Shin-Etsu Chemical Co., Ltd. Aimant cylindrique approprié pour l'imagerie à résonance magnétique nucléaire

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 10, no. 376 (E - 464) 13 December 1986 (1986-12-13) *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0653096A4 (en) * 1992-07-27 1995-06-21 New York University High field magnets for medical applications.
WO1999008126A1 (fr) * 1997-08-11 1999-02-18 Oxford Instruments (Uk) Limited Ensemble generateur de champ magnetique pour appareil a resonance magnetique nucleaire (rmn)
US7501817B1 (en) 1998-03-03 2009-03-10 Schlumberger Technology Corporation Method and apparatus for generating an axisymmetric magnetic field
GB2355800A (en) * 1999-10-29 2001-05-02 Oxford Magnet Tech Laminated ferromagnetic structure for improved field homogeneity
GB2355800B (en) * 1999-10-29 2004-10-27 Oxford Magnet Tech Improved magnet
US7071694B1 (en) 1999-10-29 2006-07-04 Oxford Magnet Technology Limited Magnet assembly of an MRI system with concentric annular ferromagnetic laminations
US6400149B1 (en) 2001-05-24 2002-06-04 Schlumberger Technology Corporation Nuclear magnetic resonance apparatus and method for generating an axisymmetric magnetic field having straight contour lines in the resonance region
GB2380309A (en) * 2001-08-20 2003-04-02 Richard Wolfe Magnetic device for reduction of EMI in audio circuitry
GB2380309B (en) * 2001-08-20 2005-04-06 Richard Wolfe Magnetic device for reduction of electromagnetic interference (EMI) in audio circuitry
FR3012263A1 (fr) * 2013-10-23 2015-04-24 Schneider Electric Ind Sas Ensemble de prises electriques

Also Published As

Publication number Publication date
IL108517A0 (en) 1994-05-30
GB9302843D0 (en) 1993-03-31

Similar Documents

Publication Publication Date Title
US3768054A (en) Low flux leakage magnet construction
US4994777A (en) Enhanced magnetic field within enclosed cylindrical cavity
US5886609A (en) Single dipole permanent magnet structure with linear gradient magnetic field intensity
US5635889A (en) Dipole permanent magnet structure
EP0964263A3 (fr) Aimant supraconducteur ouvert et blindé
US4122386A (en) Uniform magnetic field generating device
GB2355799B (en) Magnet with improved access
GB1110172A (en) Improvements in or relating to magnet structures
Leupold et al. Applications of yokeless flux confinement
Peng et al. Axial magnetic field produced by axially and radially magnetized permanent rings
GB1139112A (en) Magnet structure
WO1994018682A1 (fr) Aimant permanent
EP1603142A4 (fr) Aimant permanent destine a un accelerateur de faisceaux de particules et generateur de champs magnetiques
JPH02246102A (ja) 磁気回路
US4761584A (en) Strong permanent magnet-assisted electromagnetic undulator
US5075662A (en) Enhanced magnetic field within enclosed annular cavity
Gould Permanent magnet applications
US6538432B1 (en) Hysteresis loop tracer with symmetric balance coil
GB2319844A (en) Prepolarising MRI magnet with powdered iron poles
JPS62139304A (ja) 磁界均一性のよい磁気回路
Peng et al. Cylindrical permanent-magnet structures using images in an iron shield
US5218333A (en) Magnetic field generating device for use with ESR device
US3740683A (en) Electromagnetic turnoff system for permanent magnets
EP0940687A3 (fr) Structure ouverte d' aimant blindé
Andrews Understanding permanent magnets

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB GR IE IT LU MC NL PT SE

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
121 Ep: the epo has been informed by wipo that ep was designated in this application
122 Ep: pct application non-entry in european phase