US20060018075A1 - Permanent magnet bulk degausser - Google Patents

Permanent magnet bulk degausser Download PDF

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Publication number
US20060018075A1
US20060018075A1 US10/897,882 US89788204A US2006018075A1 US 20060018075 A1 US20060018075 A1 US 20060018075A1 US 89788204 A US89788204 A US 89788204A US 2006018075 A1 US2006018075 A1 US 2006018075A1
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Prior art keywords
magnet
segment
gap
segments
assemblages
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Abandoned
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US10/897,882
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English (en)
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Robert Schultz
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Data Security Inc
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Data Security Inc
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Priority to US10/897,882 priority Critical patent/US20060018075A1/en
Assigned to DATA SECURITY, INC. reassignment DATA SECURITY, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SCHULTZ, ROBERT A.
Priority to JP2005213205A priority patent/JP5042474B2/ja
Priority to DE602005025963T priority patent/DE602005025963D1/de
Priority to EP05016028A priority patent/EP1619667B1/en
Priority to AT05016028T priority patent/ATE496367T1/de
Publication of US20060018075A1 publication Critical patent/US20060018075A1/en
Priority to US12/024,820 priority patent/US7593210B2/en
Priority to JP2012121350A priority patent/JP5550677B2/ja
Abandoned legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/024—Erasing
    • G11B5/0245—Bulk erasing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F13/00—Apparatus or processes for magnetising or demagnetising
    • H01F13/006—Methods and devices for demagnetising of magnetic bodies, e.g. workpieces, sheet material

Definitions

  • This invention relates generally to magnetic degaussers and more particularly to permanent magnet magnetic degaussers for erasing magnetic data storage devices.
  • Magnetic degaussing systems of various kinds are known in the art. Typically, magnetic fields of varying strength and direction are applied to the item to be degaussed forcing the magnetization within the object to change thereby destroying any patterns therein. Magnetic degaussing systems have become increasingly important with the increasing use of magnetic data storage. Data stored magnetically can remain on the storage medium for long periods of time after its use. For example, a computer disk's data can be retrieved even after a user has “erased” the data from the disk because the old data will not be changed until new data is written over that segment of the disk. If another person were to obtain the disk, that person may be able to access information from that disk.
  • rare earth permanent magnets have made the generation of magnetic fields of strengths suitable for bulk media erasure using permanent magnets practical.
  • Such permanent magnets can be arranged with steel elements into magnetic circuits that act much like their electric counterparts.
  • the weight requirements of permanent magnet systems are about equal to the electric systems.
  • the zero power input required by permanent magnets offsets higher production costs as compared to electric systems.
  • Another advantage of permanent magnet systems includes the use of individual elements, which may be off-the-shelf items, rather than trying to fabricate large elements or permanently magnetizing a single large shape.
  • individual elements which may be off-the-shelf items, rather than trying to fabricate large elements or permanently magnetizing a single large shape.
  • NeFeB neodymium-iron-boron
  • Two such “U” shapes can be configured with like poles facing in repulsion across a gap suited to passage of 1-inch thick magnetic media.
  • Such an assemblage can apply a magnetic field with good uniformity and at least 6000 gauss to every point in a common form factor for magnetic data storage media passing through that field. It is understood that at least a second passage of a magnetic storage medium through the field with a different orientation between the storage medium and the magnetic field is necessary to impart the desired change within the storage medium to affect magnetic data storage erasure.
  • any such scaling results in larger volume, increased weight, and greater cost.
  • magnets are attracted to steel plates and to each other when stacked with unlike poles facing.
  • placing magnets adjacent to each other with the same magnetic direction causes repulsion, as does placing like poles facing each other across a gap.
  • framework members must be added.
  • a thick steel plate serves a dual role as a required component of the magnetic circuit and as one of the framework members, but other members generally must be of nonmagnetic materials to avoid undesirable magnetic circuit paths or unnecessary magnetic field fringing effects.
  • prior devices require an attraction-countering member between unlike poles, which experiences extreme compressive force, and this member cannot be magnetic steel.
  • FIG. 1 is a perspective view of a permanent magnet bulk degausser embodying features of the present invention
  • FIG. 2 is a side plan view of a Halbach array of square cross-section permanent magnet elements with directions of magnetizations shown by arrows;
  • FIG. 3 is a perspective view of a preferred permanent magnet element
  • FIG. 4 a is a side plan view of a model of the magnetic fields created by a pair of magnet assemblages in accordance with the array of FIG. 2 ;
  • FIG. 4 b is a side plan view of a model of the magnetic fields created by the pair of magnet assemblages illustrated in FIG. 1 ;
  • FIG. 5 a is a graph showing the magnetic flux density along the gap between a pair of magnet assemblages in accordance with FIG. 4 a;
  • FIG. 5 b is a graph showing the magnetic flux density along the gap between a pair of magnet assemblages in accordance with FIG. 4 b;
  • FIG. 6 is a perspective view of an alternate permanent magnet bulk degausser embodying features of the present invention.
  • FIG. 7 is a perspective view of a prior art permanent magnet bulk degausser
  • FIG. 8 is a side plan view of an alternate permanent magnet bulk degausser embodying features of the present invention.
  • FIG. 9 is a perspective view of a frame structure for use with various embodiments of the permanent magnet bulk degausser.
  • FIG. 10 is a side plan view of the frame structure of FIG. 9 ;
  • FIG. 11 is a side plan view of an alternate permanent magnet bulk degausser embodying features of the present invention.
  • FIG. 12 is a side plan view of a model of the magnetic fields created by the pair of magnet assemblages illustrated in FIG. 11 ;
  • FIG. 13 is a top plan view of an alternate permanent magnet bulk degausser embodying features of the present invention.
  • the apparatus 10 includes a pair of magnet assemblages 14 and 16 arranged so as to define a gap 18 through which magnetic storage media 12 passes in the direction as indicated by arrow 20 across each segment 21 - 25 and 26 - 30 of the assemblages 14 and 16 .
  • the magnetic data storage medium 12 passes through the magnetic field created by the magnet assemblages 14 and 16 thereby facilitating erasure of data on the medium 12 .
  • the magnetic data storage medium 12 can be any medium including magnetic tape, computer disks, hard drives, and the like.
  • the segments 21 - 25 and 26 - 30 are aligned adjacently within each magnet assemblage 14 and 16 with the direction of magnetization of each successive segment rotated by approximately 90 degrees relative to the previous segment. More specifically, the direction of magnetization across successive segments rotates in the same direction so that the direction of magnetization repeats within a magnet assemblage only every fifth segment.
  • This magnetization arrangement is commonly known as a Halbach array.
  • segments 22 and 24 of magnet assemblage 14 with directions of magnetization approximately perpendicular to the gap 18 have two rows of permanent magnets, whereas segments 21 , 23 , and 25 with directions of magnetization approximately parallel to the gap 18 have one row of permanent magnets.
  • the traditional Halbach array ascribed to Klaus Halbach, as conventionally illustrated in two dimensions in FIG. 2 includes a linear sequence of adjacent squares 31 - 35 magnetized such that the direction of magnetization in each adjacent square rotates 90 degrees with respect to its neighbor, with the direction of rotation constant from element to element.
  • the arrows designate a direction of magnetization pointing from magnetic South to magnetic North; however, this convention may be reversed without affecting performance as long as the convention is uniformly applied within a given embodiment.
  • the Halbach array arrangement forms a strongly magnetic side 36 . Neglecting slight imperfections in dimension, shape, and magnetization, side 38 is largely self-shielding and nonmagnetic.
  • Such linear arrays can be illustrated as an unlimited sequence, and the square element construction shown in FIG. 2 typically yields a substantially sinusoidal magnetic field strength along the direction of the array on the magnetic side 36 of the array.
  • the magnet assemblages 14 and 16 of FIG. 1 are arranged with the magnetic side of each assemblage facing the gap 18 .
  • each segment 21 - 30 includes a plurality of permanent magnets arranged in at least one row such that each permanent magnet in the segment has a direction of magnetization pointing in the same direction, substantially perpendicular to the length of the row.
  • the preferred permanent magnet element 40 as illustrated in FIG. 3 is a readily available NeFeB block such as a 2-inch square by 1-inch thick block with a direction of magnetization (as indicated in the figures by an arrow) in the direction of the block's thickness.
  • a magnetization produces a magnetic North pole on one 2-inch square face of the block and a magnetic South pole on the opposite 2-inch square face.
  • Neglecting fringing effects at the ends each preferred permanent magnet generates a 2-inch wide field in the magnetized direction. Placing additional preferred permanent magnets in a row will provide 4-inch, 6-inch, and so on wide fields. As is the case with prior devices, one additional adjacent magnet suffices to counter fringing effects.
  • such elements or segments depicted as having a square cross section may be square plates, cubes, or rods.
  • other permanent magnetic materials may be used.
  • SmCo blocks have aspect characteristics similar to NeFeB and can substitute for it.
  • a particular element size is not necessary.
  • various segments 21 - 25 or 26 - 30 within a magnet assemblage 14 or 16 may have varying sizes and/or shapes.
  • each segment can be an integral permanent magnet with a magnetization in a direction substantially perpendicular to the segment's longest dimension.
  • a complex fixture could magnetize a single large block into a one-piece magnet assemblage with several differently magnetized segments of the block.
  • assembling the invention from individual blocks can introduce acceptable minor field imperfections due to surface roughness, size and shape tolerance, and the common practice of plating NeFeB material.
  • introduction of thin nonmagnetic elements such as shims between permanent magnet elements 40 or segments 21 - 25 or 26 - 30 may introduce some acceptable field imperfections.
  • relatively thin and magnetically soft ferromagnetic materials introduced as shims between permanent magnet elements 40 or segments 21 - 25 or 26 - 30 would hardly disturb the fields.
  • FIGS. 4 a and 4 b model the magnetic flux vectors of two embodiments where the magnet assemblages are arranged in repulsion across the gap 18 .
  • all models disclosed herein use residual flux density (B r ) of 10,000 gauss.
  • B r residual flux density
  • FIG. 4 a demonstrates the magnetic flux for an embodiment using a traditional Halbach array as illustrated in FIG. 2 with square segment cross-sections.
  • FIG. 4 b models the magnetic flux for the preferred embodiment non-traditional Halbach array as illustrated in FIG. 1 .
  • magnetic flux concentrates within the gap 18 , and minimal magnetic flux is present outside the gap 18 .
  • FIG. 5 a illustrates a spatial waveform derived from the internal field of the magnet assemblage pair of FIG. 4 a . It can be seen that the waveform of FIG. 5 a approximates a “windowed” sinusoid.
  • FIG. 5 b illustrates a spatial waveform derived from the internal field of the preferred embodiment model of FIG. 4 b . It can be seen that the waveform of FIG. 5 b has a distinctively triangular characteristic when compared to the waveform of FIG. 5 a.
  • the harmonic content above the fundamental as seen in FIG. 5 b may be detrimental to some Halbach applications, such as for particle beam accelerator components. Peak strength, however, is paramount in the art of erasing magnetic media, and the harmonic content of the numeric analysis given in FIG. 5 indicates a 4% stronger field, nearly a 10,000 gauss peak magnetic field, for the preferred embodiment non-traditional Halbach array when compared to the traditional Halbach array embodiment.
  • prior art magnetic circuits such as illustrated in FIG. 7 , generate only about half this strength, and scaling of the prior art magnetic circuit shown in FIG. 7 by adding additional permanent magnets fails to achieve the field strengths of the embodiments of the invention while using a comparable amount of NeFeB.
  • doubling the NeFeB material in either of two dimensions of the prior permanent magnet degausser of FIG. 7 increases the magnetic strength from about half that of the embodiments of FIGS. 4 a and 4 b to about 70% of that strength.
  • Doubling NeFeB in both dimensions of the prior art degausser uses more material than a non-traditional Halbach embodiment but has several percent less field strength.
  • Halbach-like arrays of more or less than five segments can be utilized.
  • a mirror-imaged pair of three-segment (as illustrated in FIG. 6 ) or five-segment (as illustrated in FIG. 1 ) assemblages with magnetic sides facing in repulsion creates fields much like the prior art permanent magnet facing “U” arrangements (as illustrated in FIG. 7 ), but each embodiment offers respectively improving degrees of uniformity of field.
  • Simulations indicate that the three-segment arrangement of FIG. 6 nearly doubles the field strength of the prior permanent magnet arrangement of FIG. 7 .
  • a seven-segment arrangement not only doubles the prior arrangement's strength, but also produces two magnetic fields of equal strength and opposite direction along a media path 20 .
  • each segment 64 , 65 , and 66 can be arranged within a magnet assemblage 62 in a configuration not generally recognized as a complete Halbach array, but still effective for erasing magnet data storage media.
  • the magnet assemblages 60 and 62 of FIG. 6 each have magnetic sides facing toward the gap 18 through which magnetic data storage medium 12 passes.
  • the segments 64 - 66 of magnet assemblage 62 line up across the gap 18 from the segments 67 - 69 of magnet assemblage 60 such that the directions of magnetization of segments 64 - 66 mirror the directions of magnetization of segments 67 - 69 in what is known as an arrangement in repulsion.
  • the alternative embodiment of FIG. 6 if built using the preferred permanent magnet, saves 28% on material cost and weight as compared to the embodiment of FIG. 1 .
  • the alternative embodiment of FIG. 6 also includes less field strength per unit gap width and slightly less uniformity across the gap, such an embodiment could be applied, for example, with a narrower gap 18 to achieve higher strength for future and continually smaller varieties of magnetic storage media.
  • the overall size of the degausser 10 can be manipulated. For instance, a data processing operation that depends on erasing a large quantity of microminiaturized hard disk drives could benefit from a drastically scaled down version of the invention.
  • PDA personal digital assistant
  • each PDA may include an apparatus for removeably connecting an inexpensive 5 mm thick 4 G Byte disk drive.
  • the PDA could conveniently accompany a patient anywhere in the hospital (except places like MRI imagers) to capture all diagnostic and treatment information on the one drive. Medical records by law, however, must be protected.
  • Halbach arrays are known with magnetization angles of less than 90 degrees between segments. Use of multiple thin plate magnet segments with such reduced angular magnetization yield some further optimization for certain applications. Such approaches trade off some loss at additional contact surfaces between segments for improved harmonic content of the magnetic field profile.
  • a pair of mirror-imaged permanent magnet assemblages 80 and 82 as illustrated in FIG. 8 can be offset from each other by various degrees, generating a magnetic field component in the direction across the gap 18 . By varying the offset, a variety of magnetic field directions are produced within the gap 18 . Offset embodiments of the invention can address various directional erasure characteristics such as perpendicular recording on hard disk drives.
  • gap adjustability can be introduced to trade off field strength against media thickness capacity.
  • Frame structures for manipulating the magnet assemblages to adjust the gap width and to offset the assemblages are known, and an example of such a frame structure 90 is illustrated in FIGS. 9 and 10 .
  • Lower plate 92 supports lower magnet assemblage 16 .
  • Upper plate 94 supports upper magnet assemblage 14 .
  • Pillars 96 are rigidly affixed to lower plate 92 by any conventional method.
  • the pillars 96 include a thick diameter mid-section 98 between upper magnet assemblage 14 and lower magnet assemblage 16 , a smaller diameter upper portion 100 that slip fits through apertures defined (not shown) by upper plate 94 , and a thick diameter top portion 102 fixedly attached to smaller diameter upper portion 100 .
  • the thick diameter mid-section 98 and top portion 102 of the pillars 96 define the limits of the adjustability of the gap 18 .
  • Rods 104 attach to lower plate 92 in a known manner allowing the rods 104 to rotate within and pull on lower plate 92 .
  • At least upper portions 106 of rods 104 have screw threads over the range of adjustability that mate with threaded holes (not shown) defined by upper plate 94 .
  • Crank 108 and lower pinion gear 110 rigidly attach to each other and rotatably attach to upper plate 94 .
  • Lower spur gears 112 and tall upper pinion gears 114 also rigidly attach to each other and rotatably attach to upper plate 94 .
  • Upper spur gears 116 attach rigidly to the partially threaded rods 104 .
  • Turning crank 108 causes lower pinion gear 110 to turn lower spur gears 112 that turn tall upper pinion gears 114 , thereby causing upper spur gears 116 and rods 104 to turn.
  • Threaded portions 106 of rods 104 act on upper plate 94 to selectively raise or lower it, thus affecting the gap 18 between magnet assemblages 14 and 16 for the passage of various magnetic storage media with different thicknesses.
  • FIGS. 9 and 10 The form of gap adjustment shown in FIGS. 9 and 10 is illustrative and not limiting. Similar adjustment apparatuses can be provided for other embodiments of the invention, such as offset forms, attractive forms, and multiple assemblage pairs set at angles to a media path. The various forms of the invention can be combined with each other and with prior art along a media path, with or without a gap adjustment apparatus.
  • two or more pairs of permanent magnet assemblages can provide fields of varying direction along a media path 20 .
  • one pair of magnet assemblages is mirror-imaged across the gap with magnetic sides in repulsion such as the degausser in FIG. 1 forming fields generally in the direction parallel to the gap 18
  • another pair has elements arranged so the magnetic sides are in attraction such as the degausser in FIG. 11 forming two fields generally in opposite directions across the gap 18 .
  • FIG. 11 illustrates a pair of magnet assemblages 118 and 120 arranged in attraction using a basic permanent magnet element with a direction of magnetization different from that of the preferred magnet element.
  • the arrangement illustrated in FIG. 11 can be modified in a number ways including adding or removing segments or by building the pair of assemblages with alternative permanent magnet elements.
  • FIG. 12 models magnetic flux vectors for the pair of assemblages 118 and 120 in attraction illustrated in FIG. 11 showing strong flux projecting across the gap 18 .
  • the assemblages 118 and 120 are also largely non-magnetic and self-shielding outside the gap 18 . It can be seen that the pair of five segment assemblages 118 and 120 produces two fields of opposite direction within gap 18 . The strength of each field peaks near 10,000 gauss, which, like the assemblage pairs arranged in repulsion, constitutes a significant advance beyond the results achievable with prior magnetic circuits. Passage of magnetic storage media 12 through a magnet assemblage pair arranged in attraction before or after passage through a magnet assemblage pair arranged in repulsion provides the exposure to varying fields necessary for erasure of certain varieties of magnetic storage media.
  • two pairs of magnet assemblages 122 and 124 with magnetic sides in repulsion are provided along a media path 20 and oriented with field directions at 45 degree angles to that path and at 90 degrees to each other forming a “one pass” configuration sufficient to erase the magnetic storage media with one pass through the magnet assemblages.
  • Such placement reduces the effective width of the field across the path to approximately 70% of the width achieved in embodiments like FIG. 1 or FIG. 6 .
  • the embodiment of FIG. 13 need only treat media 12 with a single pass in the orientation shown with longest dimension aligned in direction of motion 20 .
  • the magnetic field direction varies by 90 degrees with along the path 20 through the two pairs of assemblages 122 and 124 .
  • Embodiments with a single pair of assemblages generally require two passes, including one pass with the orientation indicated in FIG. 1 and FIG. 6 with longest dimension of media 12 perpendicular to direction 20 to media motion. It can be appreciated that media placement limits 126 reside well clear of the ends of pairs of assemblages 122 and 124 where fringing effects weaken the field strength.
  • This embodiment can be further modified to add cross-gap magnetic fields, forming a “universal” configuration that erases horizontal and perpendicular hard disk drive media in one pass and no media rotation.
  • cross-gap magnetic fields forming a “universal” configuration that erases horizontal and perpendicular hard disk drive media in one pass and no media rotation.
  • FIG. 13 can be added the cross-gap field direction of an array pair with magnetic faces in attraction like that of FIG. 11 , forming a “universal” configuration that erases horizontal and perpendicular hard disk drive media in one pass and no media rotation.
  • not all elements of such multi-gapped embodiments need be Halbach-like arrays.

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  • Magnetic Record Carriers (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US10/897,882 2004-07-23 2004-07-23 Permanent magnet bulk degausser Abandoned US20060018075A1 (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US10/897,882 US20060018075A1 (en) 2004-07-23 2004-07-23 Permanent magnet bulk degausser
JP2005213205A JP5042474B2 (ja) 2004-07-23 2005-07-22 永久磁石バルク消磁装置
DE602005025963T DE602005025963D1 (de) 2004-07-23 2005-07-22 Entmagnetisierungsgerät mit Permanentmagneten
EP05016028A EP1619667B1 (en) 2004-07-23 2005-07-22 Permanent magnet bulk degausser
AT05016028T ATE496367T1 (de) 2004-07-23 2005-07-22 Entmagnetisierungsgerät mit permanentmagneten
US12/024,820 US7593210B2 (en) 2004-07-23 2008-02-01 Permanent magnet bulk degausser
JP2012121350A JP5550677B2 (ja) 2004-07-23 2012-05-28 永久磁石バルク消磁装置

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US10/897,882 US20060018075A1 (en) 2004-07-23 2004-07-23 Permanent magnet bulk degausser

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US12/024,820 Continuation US7593210B2 (en) 2004-07-23 2008-02-01 Permanent magnet bulk degausser

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US12/024,820 Expired - Lifetime US7593210B2 (en) 2004-07-23 2008-02-01 Permanent magnet bulk degausser

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EP (1) EP1619667B1 (enrdf_load_stackoverflow)
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AT (1) ATE496367T1 (enrdf_load_stackoverflow)
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US20070247948A1 (en) * 2006-04-21 2007-10-25 Taeyong Yoon Bulk erase tool for erasing perpendicularly recorded media
US20070247947A1 (en) * 2006-04-21 2007-10-25 Taeyong Yoon Method for utilizing a bulk erase tool to erase perpendicularly recorded media
US20080013245A1 (en) * 2006-07-14 2008-01-17 Schultz Robert A Method and Reciprocating Apparatus for Permanent Magnet Erasure of Magnetic Storage Media
US20080013244A1 (en) * 2006-07-14 2008-01-17 Schultz Robert A Method and Apparatus for Permanent Magnet Erasure of Magnetic Storage Media
US20090284890A1 (en) * 2008-05-16 2009-11-19 Thiel Leroy D Mechanism and Method for Permanent Magnet Degaussing
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US10932027B2 (en) 2019-03-03 2021-02-23 Bose Corporation Wearable audio device with docking or parking magnet having different magnetic flux on opposing sides of the magnet
US11061081B2 (en) 2019-03-21 2021-07-13 Bose Corporation Wearable audio device
US11067644B2 (en) 2019-03-14 2021-07-20 Bose Corporation Wearable audio device with nulling magnet
US11076214B2 (en) * 2019-03-21 2021-07-27 Bose Corporation Wearable audio device
US11272282B2 (en) 2019-05-30 2022-03-08 Bose Corporation Wearable audio device

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CN202631746U (zh) 2009-06-30 2012-12-26 艾斯拜克特磁铁技术有限公司 磁共振装置中带有紧固/削弱系统的笼
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US8339724B2 (en) 2010-11-02 2012-12-25 HGST Netherlands B.V. Induction of magnetic bias in a magnetic recording disk
CZ304444B6 (cs) * 2013-03-27 2014-05-07 Ăšstav struktury a mechaniky hornin AV ÄŚR, v.v.i. Způsob vytváření lineárních protilehlých sestav permanentních magnetů a zařízení k provádění tohoto způsobu
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US10224135B2 (en) 2016-08-08 2019-03-05 Aspect Imaging Ltd. Device, system and method for obtaining a magnetic measurement with permanent magnets
US11988730B2 (en) 2016-08-08 2024-05-21 Aspect Imaging Ltd. Device, system and method for obtaining a magnetic measurement with permanent magnets
US11287497B2 (en) 2016-08-08 2022-03-29 Aspect Imaging Ltd. Device, system and method for obtaining a magnetic measurement with permanent magnets
US10847294B2 (en) 2017-07-10 2020-11-24 Aspect Imaging Ltd. System for generating a magnetic field
CN111627645B (zh) * 2020-06-01 2021-09-07 北京卫星环境工程研究所 利用Halbach永磁阵列减小铁磁性材料磁性的方法
KR102524507B1 (ko) * 2020-06-29 2023-04-21 엘에스일렉트릭(주) 아크 경로 형성부 및 이를 포함하는 직류 릴레이

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EP1619667A3 (en) 2007-05-02
US7593210B2 (en) 2009-09-22
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JP5042474B2 (ja) 2012-10-03
JP5550677B2 (ja) 2014-07-16

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