EP0203952B1 - Eisenkernloser elektromagnet - Google Patents

Eisenkernloser elektromagnet Download PDF

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Publication number
EP0203952B1
EP0203952B1 EP85905842A EP85905842A EP0203952B1 EP 0203952 B1 EP0203952 B1 EP 0203952B1 EP 85905842 A EP85905842 A EP 85905842A EP 85905842 A EP85905842 A EP 85905842A EP 0203952 B1 EP0203952 B1 EP 0203952B1
Authority
EP
European Patent Office
Prior art keywords
magnet
coil
rods
current
stack
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.)
Expired
Application number
EP85905842A
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English (en)
French (fr)
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EP0203952A1 (de
Inventor
Guy Aubert
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.)
General Electric CGR SA
Original Assignee
General Electric CGR SA
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Filing date
Publication date
Application filed by General Electric CGR SA filed Critical General Electric CGR SA
Publication of EP0203952A1 publication Critical patent/EP0203952A1/de
Application granted granted Critical
Publication of EP0203952B1 publication Critical patent/EP0203952B1/de
Expired legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/20—Electromagnets; Actuators including electromagnets without armatures
    • H01F7/202—Electromagnets for high magnetic field strength

Definitions

  • the invention relates to a solenoidal magnet, without iron, comprising one or more coils whose technological structure is derived from that of a conventional Bitter coil; the invention more particularly relates to improvements making it possible to improve the homogeneity of the magnetic field generated by such a type of magnet.
  • Bitter coils are well known for the production of strong magnetic fields.
  • the structure proposed by Bitter is a coil made up of metallic annular discs, split to form as many turns and connected to define a substantially helical winding with flat turns.
  • the stacking of the discs is maintained by a plurality of tie rods.
  • This structure is advantageous because it allows efficient cooling of the magnet by making holes in the rings (and in the insulators separating these discs), these holes being arranged in the same configuration from one disc to another to materialize a set of channels parallel to the axis of the coil, in which circulates a cooling fluid, for example deionized water, kerosene or oil.
  • a cooling fluid for example deionized water, kerosene or oil.
  • the invention proposes to perfect such a type of magnet so that the magnetic field generated in a sphere of interest of prescribed radius, the center of which coincides with the center of symmetry of this magnet is of very good homogeneity.
  • a preferred field of application of the invention is indeed that of nuclear magnetic resonance imaging (NMR) where it is necessary to have a relatively high magnetic field (0.15 to 1.5 teslas) with a very high homogeneity, of the order of 1 to 10 parts per million (ppm). With a sufficiently long Bitter coil, a certain homogeneity can be obtained around the center of symmetry of this coil.
  • NMR nuclear magnetic resonance imaging
  • the invention therefore relates to a coiled magnet comprising at least one Bitter type coil, essentially consisting of a substantially helical winding materialized by a stack, with interposition of insulation, of annular discs, each comprising a cut materializing a turn, said turns being connected to each other, characterized in that it comprises one or more conductors ensuring the return of the current to one of the axial ends of the magnet, shaped (s) and / or arranged (s) for distributing the flow of said current longitudinally over a cylindrical surface coaxial with said coil.
  • these rods are preferably the tie rods (or some of them) whose primary function is to maintain the stack of discs of the Bitter coil.
  • the connection of two adjacent turns is simply obtained by shaping each disc of insulation, interposed between the two conductive rings, so that it comprises a sector-shaped cut and by clamping the stack of conductive discs and insulating discs between two end plates, by means of the tie rods mentioned above.
  • the electrical contact between two adjacent turns is thus established through the corresponding cutout. laying under the effect of tightening, the construction of the magnet being greatly facilitated.
  • the fact of posing the problem of obtaining a very uniform field from Bitter coil (s) leads to recognize in this arrangement another cause of disturbance of the magnetic field. Indeed, the variation in current density at each turn in the contact sector is another cause of non-uniformity.
  • the invention also relates to a magnet according to the above definition, characterized in that each end of the turn has a recess and that two adjacent turns are connected end to end by welding of such recesses of complementary shapes.
  • FIG. 1 schematically represents an exploded perspective of a conventional Bitter magnet 11 essentially used to produce an intense magnetic field inside the central hole 12 defined by a stack of annular conductive discs 13 (typically made of copper or aluminum) comprising each a cut 14, here a radial slot, transforming each disc 13 into a turn.
  • the magnetic field generated is oriented along the axis zz '.
  • Thin insulating discs 15 similar to discs 13 are interposed therebetween to isolate the turns. Instead of a fine cut, they each have a large sector-shaped cutout 17, to allow the turns to be connected by simply clamping the stack between two end plates such as 18, by means of a plurality tie rods 19 regularly distributed over a cylindrical surface coaxial with the axis zz '.
  • the conductive discs 13 and the insulating discs 15 are pierced with holes 20 made in the same configuration from one disc to another, so as to define a plurality of channels parallel to the axis zz ', in which a fluid circulates. cooling.
  • the concentration of holes 20 is greater towards the center of the disc because, in a Bitter coil, the current density at a point of a flat turn is inversely proportional to the distance from the point considered to the axis zz '.
  • the heating is therefore greater at the heart of the mass of conductors, hence the need to increase the number of cooling fluid channels in the vicinity of the hole 12.
  • the magnet in FIGS. 2 to 4 is derived from the conventional structure described with reference to FIG. 1.
  • the similar structural elements are identified by the same numerical references increased by 100.
  • the coil of Bitter 111 therefore has a central hole 112, conductive discs 113 and insulating discs 115.
  • the discs 113 and 115 have the same configuration of holes 120 and the stack of discs 113 and 115 is clamped by tie rods 119 between two annular end plates 118a, 118b.
  • the holes 120 made in the discs 113 and 115 are in concordance to define a plurality of longitudinal channels 121, parallel to the axis zz '.
  • the general proportions of the coil have been adapted for application to NMR imaging.
  • the external diameter and especially the internal diameter of the discs are increased to release a sufficient volume to be able to accommodate an elongated human being.
  • the adjacent turns are no longer connected by contact of the faces of the discs in the vicinity of the cuts but by welding of the ends of the turn.
  • the ends of each turn comprise for this purpose recesses of complementary shapes 122, 123 and two adjacent turns (see FIG. 2) are connected end to end by welding two recesses of complementary shapes.
  • an insulating disc 115 is shown between the two adjacent turns connected end to end.
  • the insulating disc is for example cut from a thin dielectric film, but it can be envisaged to remove it if the conductive discs are made of aluminum and the insulator is produced by anodizing these discs. In the case of the use of insulating discs cut from a dielectric material, these are cut radially and connected end to end as the turns are welded.
  • the magnet comprises one or more conductors ensuring the return of the current to one of the axial ends of the magnet, shaped (s) and / or arranged (s) to distribute the flow of said current longitudinally on a cylindrical surface coaxial with the coil or coils constituting the magnet.
  • the configuration which, in theory, best meets this definition is a cylindrical tubular casing, external to the coil, coaxial with the latter and connected by one of its axial ends to one of the end plates, by example plate 118b. It is shown that the flow of current in this tubular casing does not create a disturbing magnetic field in the central hole 112.
  • the abovementioned coaxial cylindrical surface is in this case that of the tubular casing itself.
  • this tubular casing can be replaced by a sufficient number of longitudinal rods, regularly distributed over a fictitious cylindrical surface 124, these rods being connected together so as to define a kind of squirrel cage and this cage being connected in series, as a whole, with said coil. So these rods are traversed by substantially equal fractions of the total current flowing through the coil or coils.
  • the tie rods 119 are used as current return rods. These tie rods are isolated from the conductive discs 113 and it suffices that the tie rods are connected to the end plate 118b if the coil 111 is single or to the corresponding plate of the coil closest to the axial end of the magnet to which none power supply cable is not connected.
  • the plate 118b distributes the current between the tie rods.
  • the tie rods 119 pass through the plate 118a while being isolated from the latter while this plate 118a comprises as many connection terminals 125 as there are tie rods, disposed respectively in the vicinity of each of them to allow the power supply of the magnet from a set of pairs of conductive wires.
  • each pair the conductive wires are arranged parallel to one another so as not to produce a stray field and in the example described, each pair of conductive wires in question forms a cable 126 with a coaxial structure.
  • any disturbing magnetic field (which could have been created by a "sulk including the magnet and its connection wires if these had been respectively connected to the axial ends of the magnet) is eliminated in the vicinity of the magnet. .
  • the fact of using the tie rods (or the tubular casing) to bring the current towards an axial end of the magnet with the additional advantage of compensating for the axial component of the current which circulates in the Bitter coil, due to the pitch d winding propeller.
  • This component is weak and does not create any field along the axis zz '. It modifies little the module of the field but only its orientation. The compensation of this longitudinal component of current by the currents which circulate in the tie rods thus brings back the orientation of the magnetic field along the axis zz '.
  • connection structure illustrated in Figure 3 can be used for the passage of current between the coils if the magnet has more than one.
  • all the end plates of the coils are similar to the plate 118a and two neighboring coils are connected by as many coaxial cables as there are of tie rods.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Claims (10)

1. Elektromagnet, der aus wenigstens einer Spule vom Typ « Bitter besteht, die aus einer im wesentlichen schraubenförmigen Wicklung gebildet und durch einen Stapel von Leiterscheiben (113) mit Zwischenlage eines Isolierstoffes verkörpert ist, von denen jede einen Einschnitt hat, durch den eine Spiralwindung verkörpert wird, wobei die besagten Spiralwindungen miteinander verbunden sind, dadurch gekennzeichnet, daß er einen oder mehrere Leiter (119) enthält, die den Rückfluß des Stromes zu einem der axialen Enden des Magneten sicherstellen und der (die) so gestaltet und/oder so angeordnet ist (sind), daß sie den Fluß dieses Stromes längsgerichtet über eine zylindrische Oberfläche (124) koaxial zur Spule (111) verteilen.
2. Elektromagnet gemäß Patentanspruch 1, dadurch gekennzeichnet, daß er einen einzigen röhrenförmigen Leiter enthält, der die Spule umgibt und mit dieser in Serie geschaltet ist.
3. Elektromagnet gemäß Patentanspruch 1, dadurch gekennzeichnet, daß er mehrere längsgerichtete Stangen (119) enthält, die gleichmäßig über die zylindrische Oberfläche (124) verteilt sind, und daß die Stangen untereinander so verbunden sind, daß sie eine Art Eichhörnchenkäfig definieren, der als Gesamtheit mit der Spule in solcher Weise in Serie geschaltet ist, daß die Stangen von im wesentlichen gleichen Bruchteilen des die Spule durchquerenden Gesamtstromes durchflossen werden.
4. Elektromagnet gemäß Patentanspruch 3, von dem Typ, in dem der besagte Stapel der Scheiben (113) mit Hilfe von isolierten Zugstäben gehalten wird, dadurch gekennzeichnet, daß die besagten längsausgerichteten Stangen durch wenigstens einige dieser Zugstäbe (119) gebildet sind.
5. Magnet gemäß Patentanspruch 3 oder 4, von dem Typ, in dem der besagte Stapel der oder jeder Spule zwischen zwei Endleiterplatten eingespannt ist, dadurch gekennzeichnet, daß die längsgerichteten Stangen, die der Endplatte (118b) benachbart sind und am äußeren axialen Ende des Magneten liegen, elektrisch mit dieser Platte verbunden sind, um die Verteilung des Stromes zwischen besagten längsgerichteten Zugstäben (119) sicherzustellen.
6. Magnet gemäß Patentanspruch 5, dadurch gekennzeichnet, daß die längsgerichteten Stäbe die Endplatte (118a), die am ersten axialen Ende des Magneten liegt, durchqueren, wobei sie elektrisch völlig von dieser isoliert sind, und daß die Endplatte ebenso viele Anschlußklemmen (125) wie Stangen (119) aufweist, die jeweils in der Nachbarschaft jeder von ihnen liegen, um die elektrische Versorgung des Magneten über eine gleiche Anzahl von Leiterpaaren aus parallelen Leiterdrähten zu ermöglichen.
7. Magnet gemäß Patentanspruch 6, dadurch gekennzeichnet, daß jedes Paar von Leiterdrähten ein Kabel (126) von koaxialem Aufbau ist.
8. Magnet gemäß Patentanspruch 6 oder 7, der mehrere entlang einer gemeinsamen Achse ausgerichtete Spulen enthält, dadurch gekennzeichnet, daß zwei benachbarte Spulen durch so viele koaxiale Kabel verbunden sind, wie es vorstehend genannte Stangen gibt.
9. Gewickelter Magnet gemäß einem der vorangehenden Patentansprüche, dadurch gekennzeichnet, daß jedes Ende der Spiralwindung eine Zapfverbindung enthält, und daß zwei benachbarte Spiralwindungen Ende mit Ende durch eine Lötung solcher Zapfverbindungen (122, 123), die von komplementärer Form sind, verbunden sind.
10. Gewickelter Magnet gemäß einem der vorangehenden Patentansprüche, dadurch gekennzeichnet, daß die besagten Leiterscheiben (113) aus Aluminium sind und daß die vorstehend genannte Isolierung durch Anodisierung dieser Ringe realisiert wurde.
EP85905842A 1984-12-14 1985-11-29 Eisenkernloser elektromagnet Expired EP0203952B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8419193 1984-12-14
FR8419193A FR2574982B1 (fr) 1984-12-14 1984-12-14 Aimant solenoidal sans fer

Publications (2)

Publication Number Publication Date
EP0203952A1 EP0203952A1 (de) 1986-12-10
EP0203952B1 true EP0203952B1 (de) 1989-11-02

Family

ID=9310627

Family Applications (1)

Application Number Title Priority Date Filing Date
EP85905842A Expired EP0203952B1 (de) 1984-12-14 1985-11-29 Eisenkernloser elektromagnet

Country Status (5)

Country Link
US (1) US4808956A (de)
EP (1) EP0203952B1 (de)
DE (1) DE3574073D1 (de)
FR (1) FR2574982B1 (de)
WO (1) WO1986003881A1 (de)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2618016A1 (fr) * 1987-07-10 1989-01-13 Thomson Cgr Dispositif de refroidissement d'un aimant resistif
FR2621731B1 (fr) * 1987-10-09 1990-02-09 Thomson Cgr Bobine, aimant comprenant une telle bobine, dispositif d'imagerie par rmn comportant un tel aimant et procede de realisation d'un tel aimant
JPH0245902A (ja) * 1988-08-08 1990-02-15 Kanazawa Univ 交流強磁場用成層渦電流型コイル
US4965521A (en) * 1989-08-11 1990-10-23 Spectroscopy Imaging Systems Method and apparatus for compensating eddy current effects in a magnetic resonance device having pulsed magnetic field gradients
US6876288B2 (en) * 2002-03-29 2005-04-05 Andrey V. Gavrilin Transverse field bitter-type magnet
DE102009016042B4 (de) * 2009-04-02 2011-02-10 Randolf Hoche Voice-Coil-Actuator und Verfahren zum Herstellen desselben
ITRM20130711A1 (it) * 2013-12-20 2015-06-21 Imaging Technology Abruzzo S R L Apparato e metodo di imaging simultaneo tramite risonanza di spin elettronico e risonanza di spin nucleare
CN113539638A (zh) * 2021-07-06 2021-10-22 辽宁意思德电气有限公司 一种大容量电感

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3281737A (en) * 1963-09-26 1966-10-25 Gen Electric Superconductive solenoid
DE3133432A1 (de) * 1981-08-24 1983-03-03 Siemens AG, 1000 Berlin und 8000 München Hochfrequenzfeld-einrichtung in einer kernspinresonanz-apparatur
WO1983002522A1 (en) * 1982-01-15 1983-07-21 Fdx Associates L P Composite coils for toroidal field coils and method of using same
US4517516A (en) * 1983-04-08 1985-05-14 Varian Associates, Inc. NMR Probe coil form structure
US4694255A (en) * 1983-11-04 1987-09-15 General Electric Company Radio frequency field coil for NMR
GB8334374D0 (en) * 1983-12-23 1984-02-01 Picker Int Ltd Coil arrangements
GB8405066D0 (en) * 1984-02-27 1984-04-04 Picker Int Ltd Coil arrangements
US4500860A (en) * 1984-07-05 1985-02-19 General Electric Company Winding support and method for NMR magnet axisymmetric correction coils
FR2567647B1 (fr) * 1984-07-10 1987-12-18 Thomson Cgr Dispositif de creation et/ou de reception d'un champ magnetique alternatif pour appareil exploitant la resonance magnetique nucleaire

Also Published As

Publication number Publication date
WO1986003881A1 (fr) 1986-07-03
FR2574982B1 (fr) 1987-01-16
FR2574982A1 (fr) 1986-06-20
DE3574073D1 (de) 1989-12-07
EP0203952A1 (de) 1986-12-10
US4808956A (en) 1989-02-28

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