WO2017109013A1 - Method and apparatus for manufacturing 1d and 2d multipole magnet array's - Google Patents

Method and apparatus for manufacturing 1d and 2d multipole magnet array's Download PDF

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Publication number
WO2017109013A1
WO2017109013A1 PCT/EP2016/082269 EP2016082269W WO2017109013A1 WO 2017109013 A1 WO2017109013 A1 WO 2017109013A1 EP 2016082269 W EP2016082269 W EP 2016082269W WO 2017109013 A1 WO2017109013 A1 WO 2017109013A1
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WIPO (PCT)
Prior art keywords
magnet
top surface
magnetic
magnets
manufacturing
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Application number
PCT/EP2016/082269
Other languages
French (fr)
Inventor
Petrus Carolus Maria FRISSEN
Rob Tabor
Angelo Cesar Peter DE KLERK
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Koninklijke Philips N.V.
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Publication of WO2017109013A1 publication Critical patent/WO2017109013A1/en

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    • 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
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets

Definitions

  • the invention relates to a magnet, a method for manufacturing a magnet, an apparatus for manufacturing a magnet, a magnet array and a displacement device.
  • EP 1 135 846 Bl discloses a displacement device comprising a support on which a system of magnets is secured in accordance with a pattern of rows extending parallel to the X-direction, and columns extending parallel to the Y-direction, an equal distance being present between the rows and between the columns, and magnets of a first type, having a magnetization direction which extends at right angles to the support and towards a carrier, and magnets of a second type, having a magnetization direction which extends at right angles to the support and away from the carrier, being alternately arranged in each row and in each column, and a magnet of a third type being arranged in each column between each pair of juxtaposed magnets of the first and the second type, which magnet of a third type has a magnetization direction which extends parallel to the Y-direction and towards the magnet of the first type, and a carrier comprising a first positioning coil and a second positioning coil.
  • EP 0 535 901 A2 discloses a lateral orientation type of anisotropic permanent magnet having a face of magnetic application and at least one lateral face adjacent to the face of magnetic application.
  • An axis of easy magnetization of particles of a magnetic powder constituting the permanent magnet is oriented substantially along lines from the lateral face toward the face of magnetic application to increase the peak value of the surface magnetic flux density at the face of magnetic application. This document does not show a magnetic array.
  • EP 1 548 761 Al shows a method of manufacturing radially anisotropic ring magnets in which a magnet powder packed into a cavity in a cylindrical magnet- forming mold having a core composed at least in part of a ferromagnetic material is pressed under the application of an orienting magnetic field by a horizontal magnetic field vertical compacting process.
  • US 7 207 102 Bl discloses a method for forming a plurality of permanent magnets with two different north-south magnetic pole alignments for use in microelectromechanical (MEM) devices. This method is based on initially magnetizing the permanent magnets all in the same direction, and then utilizing a combination of heating and a magnetic field to switch the polarity of a portion of the permanent magnets while not switching the remaining permanent magnets.
  • the permanent magnets in some instances, can all have the same rare-earth composition (e.g. NdFeB) or can be formed of two different rare-earth materials (e.g. NdFeB and SmCo).
  • the method can be used to form a plurality of permanent magnets side-by-side on or within a substrate with an alternating polarity, or to form a two-dimensional array of permanent magnets in which the polarity of every other row of the array is alternated.
  • this object has been addressed with a magnet, wherein the magnet has a top surface, a bottom surface, and a circumferential surface, wherein the top surface and the bottom surface are parallel to one another, wherein the circumferential surface is perpendicular to the top surface and the bottom surface, wherein the magnet comprises magnetic particles having a preferential direction of magnetization, wherein the preferential direction of magnetization of a first magnetic particle at the top surface is essentially perpendicular to the top surface, and wherein the preferential direction of magnetization of a second magnetic particle at the circumferential surface is essentially perpendicular to the preferential direction of magnetization of the first magnetic particle.
  • the magnetic array according to the invention contains a first sort of magnets having a north pole at the top surface and a second sort of magnets having a south pole at the top surface, and the first and second sort of magnets are mounted on a support to form a line of magnets having alternating poles at the top surface.
  • Essentially perpendicular may encompass an angle from 60° to 120°, in particular from 75° to 105°, more particularly from 85° to 95°.
  • the top surface and the bottom surface may be essentially flat surfaces.
  • the volume of the magnet may be completely defined by the top surface, the bottom surface and the circumferential surface.
  • several circumferential surface parts, which are directly adjacent to one another, may be regarded as one
  • the magnet may, in particular, be formed as a prism or a cylinder.
  • a prism is a polyhedron with an n- sided polygonal top surface and another congruent parallel bottom surface with the same rotational orientation.
  • a circumferential surface of the prism comprises n circumferential surface parts. The circumferential surface parts each join corresponding sides of the top surface and the bottom surface.
  • the magnet comprises more than one circumferential surface.
  • the magnet may be formed as a hollow cylinder or a hollow prism having an inner circumferential surface and an outer circumferential surface not (directly) connected to the inner circumferential surface.
  • a hollow cylinder having a low height compared to the diameter may also be called a ring.
  • the magnet is a rectangular cuboid. Choosing a rectangular cuboid form, may facilitate manufacturing of the magnet, in particular, pressing of the magnetic particles.
  • the magnet is a rectangular cuboid having a quadratic top surface.
  • a quadratic top surface may be advantageous for forming a checkerboard array of magnets showing the same behavior along the lines and the rows of the checker-board.
  • the height of the rectangular cuboid may be selected in view of the desired magnet flux density at the top surface of the magnet.
  • a method for manufacturing a magnet comprising pressing magnetic particles to form a magnet having a top surface, a bottom surface, and a circumferential surface, wherein the top surface and the bottom surface are parallel to one another, and wherein the circumferential surface is perpendicular to the top surface, and applying an external magnetic field during the pressing of the magnetic particles, wherein the magnetic field is oriented perpendicular to the top surface at the top surface, and wherein the magnetic field is oriented parallel to the top surface at the circumferential surface.
  • the method may be adapted to manufacture one of the above- mentioned magnets.
  • the magnetic field may lead to an orientation of the magnetic particles such that the preferential direction of magnetization of a first magnetic particle at the top surface is essentially perpendicular to the top surface, and that the preferential direction of magnetization of a second magnetic particle at the circumferential surface is essentially perpendicular to the preferential direction of the first magnetic particle.
  • Pressing the magnetic particles may include axial pressing the magnetic particles, i.e. pressing the magnetic particles in a direction perpendicular to the top surface and the bottom surface, and transfer pressing perpendicular to the axial pressing.
  • the magnetic field is a static magnetic field. Adjusting the properties and controlling a static magnetic field may require few electronic efforts.
  • Another embodiment of the method for manufacturing a magnet prescribes that the magnetic field is a pulsed magnetic field.
  • a pulsed magnetic field may facilitate a proper alignment of the magnetic particles through vibrational forces.
  • an apparatus for manufacturing a magnet comprising a mold for pressing magnetic particles during the pressing.
  • the apparatus may be adapted to perform an aforementioned method and/or to manufacture an aforementioned magnet.
  • the mold is formed of a material having poor electric conductivity.
  • a material having poor electric conductivity may avoid inducing currents in the mold, when establishing a magnetic field with the first coil.
  • a poor electric conductivity may denote an electric conductivity below 1.5 ⁇ 10 6 S/m, in particular below 1 ⁇ 10 5 S/m, more particularly below 1 ⁇ 10 3 S/m.
  • the apparatus for manufacturing a magnet comprises a second coil for orienting the magnetic particles.
  • Providing a first coil and a second coil may allow for generating a stronger magnetic field having a better defined orientation and being less prone to deviations due to moving walls of the mold.
  • the first coil and the second coil are arranged mirror-symmetrically, and the distance between the surface of the mold forming the bottom surface of the magnet and the mirror plane is less than 2/10 of the height of the magnet to be manufactured, in particular less than 1/10 of the height of the magnet to be manufactured.
  • Such an arrangement of the mold with respect to the coils may allow for an orientation of the magnetic particles, such that their preferred direction of magnetization at the circumferential surface and at the bottom surface is essentially perpendicular to the axis of the first and second coil.
  • the distance between the surface of the mold forming the bottom surface and the mirror plane may, in particular, be essentially zero.
  • the apparatus for manufacturing a magnet further comprises a conducting plate arranged parallel to the surface of the mold forming the bottom surface of the magnet.
  • a conducting plate may have a conductivity above 15 ⁇ 10 6 S/m, in particular above 35 ⁇ 10 6 S/m, more particularly above 55 ⁇ 10 6 S/m.
  • a conductive plate may prevent a magnet field from entering and allowing for a magnetic field during pressing essentially parallel to the bottom surface of the magnet near the bottom surface of the magnet.
  • the apparatus for manufacturing a magnet comprises a capacitance and a thyristor.
  • the capacitance and the thyristor may be used to generate a short very high magnetic pulse in the cavity of the mold.
  • the first sort of magnets and the second sort of magnets are mounted on a support to form a two-dimensional checkerboard pattern of north and south poles at the top surface.
  • a positioning device comprising an aforementioned magnet array and a carrier comprising a first positioning coil having an elongated cross-section and an axis perpendicular to the magnet array.
  • a positioning device may require lower driving currents for the first positioning coil to move the carrier with a predetermined force compared to known positioning devices having the same dimensions. Hence, heat dissipation in the carrier may be reduced.
  • magnets having a lesser volume, i.e. height may be used, if the same current is to be applied.
  • the carrier comprises a second positioning coil having an elongated cross-section and an axis perpendicular to the magnet array, wherein the elongation direction of the first positioning coil is different from the elongation direction of the second positioning coil.
  • Fig. 1 shows a first exemplary magnet
  • Fig. 2 shows a second exemplary magnet
  • Fig. 3 shows a third exemplary magnet
  • Fig. 4 shows a fourth exemplary magnet
  • Fig. 5 illustrates a method for manufacturing a magnet
  • Fig. 6 shows a first apparatus for manufacturing a magnet in a first state
  • Fig. 7 shows the first apparatus for manufacturing a magnet in a second state
  • Fig. 8 shows a second apparatus for manufacturing a magnet in a first state
  • Fig. 9 shows the second apparatus for manufacturing a magnet in a second state
  • Fig. 10 shows a first magnetic array
  • Fig. 11 shows a second magnetic array
  • Fig. 12 shows a first positioning device
  • Fig. 13 shows a second positioning device
  • Fig. 14 shows a comparison between the first positioning device and the second positioning device.
  • Figure 1 shows a magnet 101 composed of several magnetic particles including the magnetic particles 102 and 103.
  • the magnet 101 has the form of a cube having a top surface 104, a bottom surface (not visible) and a circumferential surface composed of four circumferential surface parts, of which the circumferential parts 105 and 106 are visible in figure 1.
  • the top surface 104 and the bottom surface are parallel to one another and the circumferential surface is perpendicular to the top surface and the bottom surface.
  • the magnetic particles have a preferential direction of magnetization indicated by the elongated form of the magnetic particles.
  • the preferential direction of magnetization of the magnetic particle 102 at the top surface 104 of the magnet 101 is essentially perpendicular to the top surface 104.
  • the preferential direction of magnetization of the magnetic particle 103 at the circumferential surface 105, 106 is perpendicular to the preferential direction of
  • the magnetic particles between the magnetic particles 102 and 103 are arranged such that their preferential direction of magnetization essentially follows the continuous curve 107.
  • Figure 2 shows another magnet 201 comprising magnetic particles 202 and 203.
  • the magnet 201 is shaped as a circular cylinder having a top surface 204, a bottom surface (not visible) parallel to the top surface 204 and a circumferential surface 205.
  • the preferential direction of magnetization of the magnetic particle 202 is perpendicular to the top surface and the preferential direction of magnetization of the magnetic particle 203 is perpendicular to the preferential direction of magnetization of the first magnetic particle.
  • the magnet 201 has been magnetized such that the top surface 204 is a magnetic south pole (indicated by arrow 206) and the circumferential surface 205 is a north pole (indicated by arrow 207).
  • the magnetization has been performed to be parallel to the preferential direction of magnetization 206 of the magnetic particles of the magnet 201.
  • Figure 3 shows a further magnet 301.
  • the magnet 301 has a top surface 302, a bottom surface (not visible), a first circumferential surface 303 and a second circumferential surface 304.
  • the magnet 301 like the magnets 101 and 201, comprises magnetic particles 305 and 306.
  • the preferential direction of magnetization of the magnetic particle 305 at the top surface 302 is perpendicular to the top surface 302 and the preferential direction of magnetization of the magnetic particle 306 at the circumferential surface 303 is perpendicular to the preferential direction of magnetization of the magnetic particle 305, i.e. perpendicular to the circumferential surface 303.
  • the magnet 301 has the shape of a ring.
  • Figure 4 shows a still further magnet 401 in form of a prism.
  • the magnetic particles 402 and 403 have been oriented in the same manner as the magnetic particles of the magnets 101, 201 and 301.
  • the magnet 401 has been magnetized such that the magnetic particle 402 has a north pole (indicated by arrow 404) at the top surface 405 and the magnetic particle 403 has a south pole (indicated by arrow 406) at the circumferential surface 407.
  • Figure 5 illustrates a method for manufacturing a magnet.
  • the alloy for manufacturing the magnet is melted under vacuum.
  • the alloy may be a NdFeB- alloy. Having been melted and solidified, the material is crushed (step 502) and milled (step 503) to form fine magnetic particles.
  • the fine magnetic particles are pressed together to form a magnet having a top surface, a bottom surface and a circumferential surface.
  • an external magnetic field is applied, wherein the magnetic field is oriented perpendicular to the top surface and parallel to the top surface at the circumferential surface. Due to the external magnetic field, the magnetic particles may assume an orientation such that their preferential direction of magnetization aligns with the external magnetic field.
  • the pressed green body will be sintered and annealed (step 505) before being machined and coated (step 506). In case of arc magnetization shapes, the risk of crack formation during sintering and annealing may be reduced.
  • an additional magnetization may be performed at the end (step 507).
  • Figure 6 shows a first apparatus 601 for manufacturing a magnet 602.
  • the apparatus 601 comprises a mold 603, 604, 605, 606, 607, 608, 609, 610 surrounding a cavity, wherein the magnet 602 is to be formed by pressing magnetic particles together.
  • the mold 603, 604, 605, 606, 607, 608, 609, 610 is made of a material having poor electric
  • the apparatus 601 furthermore, includes a first coil 61 1 and a second coil 612.
  • the first coil 611 and the second coil 612 are arranged mirror-symmetrically with respect to a mirror plane 613.
  • Energizing the first coil 611 and the second coil 612 with a current leads to a static magnetic field 614 being oriented parallel to the axis of the first coil 611 and the second coil 612 at the interior thereof and parallel to the mirror plane 613 near the mirror plane 613.
  • the magnetic flux density B within the cavity may be selected to be between 0.2 T and 0.8 T, more particularly between 0.4 and 0.6 T.
  • the cavity is provided slightly above the mirror plane 613 such that the bottom surface of the magnet to be pressed essentially aligns with the mirror plane 613.
  • the first apparatus 601 is adapted to apply axial pressure 615, 616 on the magnetic particles encapsulated in the cavity formed by the mold 603, 604, 605, 606, 607, 608, 609, 610.
  • the mold parts 617, 618 of the first apparatus 601 may apply transverse pressure 617, 618 on the magnetic particles encapsulated in the cavity.
  • the transverse pressure 617, 618 may be applied before or after the axial pressure 615, 616.
  • Energizing the coils 611, 612 during the whole pressure process may avoid unidirectional aligning of the magnetic particles according to their preferential direction of magnetization.
  • the apparatus 601 it may be possible to obtain a magnet, wherein the preferential direction of magnetization of its magnetic particles changes continuously from vertical at the top surface to horizontal at the circumferential surface of the magnet 602.
  • Figures 8 and 9 show a second apparatus 801 for manufacturing a magnet 802.
  • the apparatus 801 includes a mold 803, 804, 805, 806, 807, 808 having a cavity for manufacturing the magnet 802.
  • the mold parts 803, 804, 806, 807, 808 are made of a material having very poor electrical conductivity, whereas the mold part 805 is a conductive plate having high electrical conductivity.
  • the conductive plate 805 forms the bottom surface of the magnet 802.
  • the mold part 808 may exert axial pressure 809 on the magnetic particles in the cavity and the mold parts 804 and 806 may apply pressure 811 and 810 in a transverse direction.
  • the apparatus 802 includes a coil 812.
  • the coil 812 may be charged with an external capacitor. With a rectifier, e.g.
  • a short very high magnetic pulse may be generated within the cavity.
  • the pulse length may be between 0.5 ms and 1.5 ms, more particularly between 0.8 and 1.2 ms.
  • the magnetic pulse will induce eddy currents in the electric conductive plate 5 counteracting the B-field, which will, therefore, not pass the conductive plate 5. Accordingly, the magnetic field lines 813 may assume a shape
  • the magnetic pulses may be applied at different times during the axial pressing.
  • Figure 10 shows a first magnetic array 1001 comprising magnets 1002 to 1012.
  • the magnetic array 1001 is a linear magnetic array.
  • the magnets 1002 to 1012 comprise magnetic particles, whose preferential directions of magnetization are collinear to one another and to the magnetization direction of the magnet, which is indicated by an arrow.
  • the magnets 1002, 1006, 1010 have their north pole at the top surface of the magnetic array and the magnets 1004, 1008, 1012 have their south pole at the top surface.
  • the magnets 1003, 1005, 1007, 1009, 1011 are not magnetized vertically but horizontally.
  • the north pole of the magnets 1003, 1005, 1007, 1009, 1011 is directed to the neighboring magnet having the north pole at the top surface, i.e. directed to the magnet 1002, 1006, 1010.
  • the magnetic flux density at the top surface of the magnetic array 1001 starting from a medium value at the center of the top surface of magnet 1002 in a direction to magnet 1012 may increase to a high value just before the interface to the magnet 1003. After the interface to the magnet 1003 the magnetic flux density may have a low value and assume a high value again just after the interface to magnet 1004. At the center of the top surface of magnet 1004, the magnetic flux density may have a medium value again.
  • Figure 11 shows a second magnetic array 1101 comprising magnets 1102 to 1107.
  • the magnets 1102 to 1007 comprise magnetic particles, whose preferential direction of magnetization continuously changes from vertical at the top surface to horizontal at the side surfaces.
  • the preferential direction of magnetization of the magnetic particles corresponds to the magnetization of the magnets, which is indicated by arrows in Figure 11.
  • the curved magnetization of the magnetic array 1101 may be described as having the form of arcs or as sinusoidal.
  • the magnetic flux density first continuously decreases from a maximum value at the center to a minimum value at the interface between the magnet 1102 before rising again to the maximum value at the center of magnet 1103.
  • Figure 12 shows a first positioning device 1201 comprising a magnetic array 1202 and a carrier 1203.
  • the magnetic array 1202 comprises magnets 1204 to 1207.
  • the magnets 1202 to 1207 comprise magnetic particles, whose preferential directions of magnetization are collinear to one another and to the magnetization direction of the magnet.
  • the magnets 1204 and 1205 have a quadratic top surface and are arranged in a checkerboard pattern.
  • the magnets 1204 have a north pole at the top surface and the magnets 1205 have a south pole at the top surface.
  • the north pole of the magnets 1206, 1207 is directed to the neighboring magnet 1204, 1205 having the north pole at the top surface.
  • the carrier 1203 comprises a first positioning coil 1208 and a second positioning coil 1209 each having an elongated cross section and an axis perpendicular to the magnet array.
  • the elongation directions of the first positioning coil and the second positioning coil draw an angle of 90°.
  • a current trough the positioning coils will induce a Lorentz force perpendicular to the elongation directions in view of the magnet field of the magnet array, which Lorentz force may be used to position the carrier with respect to the magnet array.
  • Figure 13 shows a second positioning device 1301 comprising a magnet array 1302 and a carrier 1303.
  • the magnet array 1302 comprises magnets 1304, 1305 having a quadratic top surface and a circumferential surface.
  • the magnets 1304, 1305 comprise magnetic particles, wherein the preferential direction of magnetization of a particle at the top surface is essentially perpendicular to the top surface, and wherein the preferential direction of magnetization of a second particle at the circumferential surface is essentially
  • the magnets 1304 having a north pole at the top surface and the magnets 1305 having a south pole at the top surface are arranged in a checkerboard pattern.
  • the pitch 1306, i.e. the distance between the center of two magnets having a magnetization perpendicular to the top surface, is identical to the corresponding pitch of the magnet array 1202.
  • Figure 14 shows a comparison of the performance of a positioning device according to figure 12 (dashed line, dot-and-dash line) and a positioning device according to figure 13 (dotted line, continuous line) having the same dimensions.
  • the Y-axis shows the force per current experienced by a positioning coil in a horizontal direction transverse to its elongation directions (continuous line, dot-and-dash line) and in a vertical direction transverse to its elongation direction (dotted line, dashed line).
  • the positioning coil is oriented diagonal with respect to the checkerboard pattern.
  • the force has been normalized to 1 for the positioning device pursuant to figure 13.
  • the X-axis shows the horizontal position of the coil.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
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Abstract

The invention relates to a magnet (101), wherein the magnet (101) has a top surface (104), a bottom surface, and a circumferential surface (105, 106), wherein the top surface (104) and the bottom surface are parallel to one another, wherein the circumferential surface (105, 106) is perpendicular to the top surface (104) and the bottom surface, wherein the magnet (101) comprises magnetic particles having a preferential direction of magnetization, wherein the preferential direction of magnetization of a first magnetic particle at the top surface (104) is essentially perpendicular to the top surface (104), and wherein the preferential direction of magnetization of a second magnetic particle at the circumferential surface (105, 106) is essentially perpendicular to the preferential direction of magnetization of the first magnetic particle. The magnetic array according to the invention contains a first sort of magnets having a north pole at the top surface and a second sort of magnets having a south pole at the top surface, and the first and second sort of magnets are mounted on a support to form a line of magnets having alternating poles at the top surface.

Description

METHOD AND APPARATUS FOR MANUFACTURING 1 D
AND 2D MULTIPOLE MAGNET ARRAY'S
FIELD OF THE INVENTION
The invention relates to a magnet, a method for manufacturing a magnet, an apparatus for manufacturing a magnet, a magnet array and a displacement device. BACKGROUND OF THE INVENTION
EP 1 135 846 Bl discloses a displacement device comprising a support on which a system of magnets is secured in accordance with a pattern of rows extending parallel to the X-direction, and columns extending parallel to the Y-direction, an equal distance being present between the rows and between the columns, and magnets of a first type, having a magnetization direction which extends at right angles to the support and towards a carrier, and magnets of a second type, having a magnetization direction which extends at right angles to the support and away from the carrier, being alternately arranged in each row and in each column, and a magnet of a third type being arranged in each column between each pair of juxtaposed magnets of the first and the second type, which magnet of a third type has a magnetization direction which extends parallel to the Y-direction and towards the magnet of the first type, and a carrier comprising a first positioning coil and a second positioning coil.
There is a constant need for faster and stronger displacement device, for example for the positioning of semiconductor wafers for lithography. This may be achieved with higher currents through the positioning coils or improved magnetic alloys. However, the magnetic properties of magnetic alloys only improve very slightly, in particular, compared to the advancements in the semiconductor industry. Increasing the current, on the other hand, leads to undesirable additional heat dissipation.
EP 0 535 901 A2 discloses a lateral orientation type of anisotropic permanent magnet having a face of magnetic application and at least one lateral face adjacent to the face of magnetic application. An axis of easy magnetization of particles of a magnetic powder constituting the permanent magnet is oriented substantially along lines from the lateral face toward the face of magnetic application to increase the peak value of the surface magnetic flux density at the face of magnetic application. This document does not show a magnetic array. EP 1 548 761 Al shows a method of manufacturing radially anisotropic ring magnets in which a magnet powder packed into a cavity in a cylindrical magnet- forming mold having a core composed at least in part of a ferromagnetic material is pressed under the application of an orienting magnetic field by a horizontal magnetic field vertical compacting process.
US 7 207 102 Bl discloses a method for forming a plurality of permanent magnets with two different north-south magnetic pole alignments for use in microelectromechanical (MEM) devices. This method is based on initially magnetizing the permanent magnets all in the same direction, and then utilizing a combination of heating and a magnetic field to switch the polarity of a portion of the permanent magnets while not switching the remaining permanent magnets. The permanent magnets, in some instances, can all have the same rare-earth composition (e.g. NdFeB) or can be formed of two different rare-earth materials (e.g. NdFeB and SmCo). The method can be used to form a plurality of permanent magnets side-by-side on or within a substrate with an alternating polarity, or to form a two-dimensional array of permanent magnets in which the polarity of every other row of the array is alternated.
SUMMARY OF THE INVENTION
Hence, it may be an object of the present invention to provide a magnet, a method for manufacturing a magnet, an apparatus for manufacturing a magnet, a magnet array and a displacement device allowing for higher actuation forces.
According to a first aspect, this object has been addressed with a magnet, wherein the magnet has a top surface, a bottom surface, and a circumferential surface, wherein the top surface and the bottom surface are parallel to one another, wherein the circumferential surface is perpendicular to the top surface and the bottom surface, wherein the magnet comprises magnetic particles having a preferential direction of magnetization, wherein the preferential direction of magnetization of a first magnetic particle at the top surface is essentially perpendicular to the top surface, and wherein the preferential direction of magnetization of a second magnetic particle at the circumferential surface is essentially perpendicular to the preferential direction of magnetization of the first magnetic particle. The magnetic array according to the invention contains a first sort of magnets having a north pole at the top surface and a second sort of magnets having a south pole at the top surface, and the first and second sort of magnets are mounted on a support to form a line of magnets having alternating poles at the top surface. Essentially perpendicular may encompass an angle from 60° to 120°, in particular from 75° to 105°, more particularly from 85° to 95°. The top surface and the bottom surface may be essentially flat surfaces.
The volume of the magnet may be completely defined by the top surface, the bottom surface and the circumferential surface. In this respect, several circumferential surface parts, which are directly adjacent to one another, may be regarded as one
circumferential surface, e.g. the side surface parts of a cube. The magnet may, in particular, be formed as a prism or a cylinder. A prism is a polyhedron with an n- sided polygonal top surface and another congruent parallel bottom surface with the same rotational orientation. A circumferential surface of the prism comprises n circumferential surface parts. The circumferential surface parts each join corresponding sides of the top surface and the bottom surface.
It may be not excluded that the magnet comprises more than one circumferential surface. For example, the magnet may be formed as a hollow cylinder or a hollow prism having an inner circumferential surface and an outer circumferential surface not (directly) connected to the inner circumferential surface. A hollow cylinder having a low height compared to the diameter may also be called a ring.
According to an embodiment of the magnet, the magnet is a rectangular cuboid. Choosing a rectangular cuboid form, may facilitate manufacturing of the magnet, in particular, pressing of the magnetic particles.
In a further embodiment of the magnet, the magnet is a rectangular cuboid having a quadratic top surface. A quadratic top surface may be advantageous for forming a checkerboard array of magnets showing the same behavior along the lines and the rows of the checker-board. The height of the rectangular cuboid may be selected in view of the desired magnet flux density at the top surface of the magnet.
According to a second aspect, a method for manufacturing a magnet is provided, wherein the method comprises pressing magnetic particles to form a magnet having a top surface, a bottom surface, and a circumferential surface, wherein the top surface and the bottom surface are parallel to one another, and wherein the circumferential surface is perpendicular to the top surface, and applying an external magnetic field during the pressing of the magnetic particles, wherein the magnetic field is oriented perpendicular to the top surface at the top surface, and wherein the magnetic field is oriented parallel to the top surface at the circumferential surface. In particular, the method may be adapted to manufacture one of the above- mentioned magnets. The magnetic field may lead to an orientation of the magnetic particles such that the preferential direction of magnetization of a first magnetic particle at the top surface is essentially perpendicular to the top surface, and that the preferential direction of magnetization of a second magnetic particle at the circumferential surface is essentially perpendicular to the preferential direction of the first magnetic particle.
Pressing the magnetic particles may include axial pressing the magnetic particles, i.e. pressing the magnetic particles in a direction perpendicular to the top surface and the bottom surface, and transfer pressing perpendicular to the axial pressing.
In a first embodiment of the method for manufacturing a magnet, the magnetic field is a static magnetic field. Adjusting the properties and controlling a static magnetic field may require few electronic efforts.
Another embodiment of the method for manufacturing a magnet prescribes that the magnetic field is a pulsed magnetic field. A pulsed magnetic field may facilitate a proper alignment of the magnetic particles through vibrational forces.
According to a third aspect, an apparatus for manufacturing a magnet is provided, wherein the apparatus comprises a mold for pressing magnetic particles during the pressing.
The apparatus may be adapted to perform an aforementioned method and/or to manufacture an aforementioned magnet.
According to a first embodiment of the apparatus for manufacturing a magnet, the mold is formed of a material having poor electric conductivity. A material having poor electric conductivity may avoid inducing currents in the mold, when establishing a magnetic field with the first coil. A poor electric conductivity may denote an electric conductivity below 1.5 · 106 S/m, in particular below 1 · 105 S/m, more particularly below 1 · 103 S/m.
In another embodiment, the apparatus for manufacturing a magnet comprises a second coil for orienting the magnetic particles. Providing a first coil and a second coil may allow for generating a stronger magnetic field having a better defined orientation and being less prone to deviations due to moving walls of the mold.
According to a further embodiment of the apparatus for manufacturing a magnet, the first coil and the second coil are arranged mirror-symmetrically, and the distance between the surface of the mold forming the bottom surface of the magnet and the mirror plane is less than 2/10 of the height of the magnet to be manufactured, in particular less than 1/10 of the height of the magnet to be manufactured. Such an arrangement of the mold with respect to the coils may allow for an orientation of the magnetic particles, such that their preferred direction of magnetization at the circumferential surface and at the bottom surface is essentially perpendicular to the axis of the first and second coil. The distance between the surface of the mold forming the bottom surface and the mirror plane may, in particular, be essentially zero.
In another embodiment, the apparatus for manufacturing a magnet further comprises a conducting plate arranged parallel to the surface of the mold forming the bottom surface of the magnet. A conducting plate may have a conductivity above 15 · 106 S/m, in particular above 35 · 106 S/m, more particularly above 55 · 106 S/m. A conductive plate may prevent a magnet field from entering and allowing for a magnetic field during pressing essentially parallel to the bottom surface of the magnet near the bottom surface of the magnet.
According to a further embodiment, the apparatus for manufacturing a magnet comprises a capacitance and a thyristor. The capacitance and the thyristor may be used to generate a short very high magnetic pulse in the cavity of the mold.
In an embodiment of the magnet array, the first sort of magnets and the second sort of magnets are mounted on a support to form a two-dimensional checkerboard pattern of north and south poles at the top surface.
According to a fourth aspect, a positioning device is proposed, comprising an aforementioned magnet array and a carrier comprising a first positioning coil having an elongated cross-section and an axis perpendicular to the magnet array. Such a positioning device may require lower driving currents for the first positioning coil to move the carrier with a predetermined force compared to known positioning devices having the same dimensions. Hence, heat dissipation in the carrier may be reduced. Alternatively, magnets having a lesser volume, i.e. height, may be used, if the same current is to be applied.
In an embodiment of the positioning device, the carrier comprises a second positioning coil having an elongated cross-section and an axis perpendicular to the magnet array, wherein the elongation direction of the first positioning coil is different from the elongation direction of the second positioning coil.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings
Fig. 1 shows a first exemplary magnet;
Fig. 2 shows a second exemplary magnet; Fig. 3 shows a third exemplary magnet;
Fig. 4 shows a fourth exemplary magnet;
Fig. 5 illustrates a method for manufacturing a magnet;
Fig. 6 shows a first apparatus for manufacturing a magnet in a first state;
Fig. 7 shows the first apparatus for manufacturing a magnet in a second state;
Fig. 8 shows a second apparatus for manufacturing a magnet in a first state;
Fig. 9 shows the second apparatus for manufacturing a magnet in a second state;
Fig. 10 shows a first magnetic array;
Fig. 11 shows a second magnetic array;
Fig. 12 shows a first positioning device;
Fig. 13 shows a second positioning device;
Fig. 14 shows a comparison between the first positioning device and the second positioning device.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Figure 1 shows a magnet 101 composed of several magnetic particles including the magnetic particles 102 and 103.The magnet 101 has the form of a cube having a top surface 104, a bottom surface (not visible) and a circumferential surface composed of four circumferential surface parts, of which the circumferential parts 105 and 106 are visible in figure 1. The top surface 104 and the bottom surface are parallel to one another and the circumferential surface is perpendicular to the top surface and the bottom surface. The magnetic particles have a preferential direction of magnetization indicated by the elongated form of the magnetic particles. The preferential direction of magnetization of the magnetic particle 102 at the top surface 104 of the magnet 101 is essentially perpendicular to the top surface 104. The preferential direction of magnetization of the magnetic particle 103 at the circumferential surface 105, 106 is perpendicular to the preferential direction of
magnetization of the magnetic particle 102. The magnetic particles between the magnetic particles 102 and 103 are arranged such that their preferential direction of magnetization essentially follows the continuous curve 107.
Figure 2 shows another magnet 201 comprising magnetic particles 202 and 203. The magnet 201 is shaped as a circular cylinder having a top surface 204, a bottom surface (not visible) parallel to the top surface 204 and a circumferential surface 205. The preferential direction of magnetization of the magnetic particle 202 is perpendicular to the top surface and the preferential direction of magnetization of the magnetic particle 203 is perpendicular to the preferential direction of magnetization of the first magnetic particle. In the embodiment shown in figure 2, the magnet 201 has been magnetized such that the top surface 204 is a magnetic south pole (indicated by arrow 206) and the circumferential surface 205 is a north pole (indicated by arrow 207). The magnetization has been performed to be parallel to the preferential direction of magnetization 206 of the magnetic particles of the magnet 201.
Figure 3 shows a further magnet 301. The magnet 301 has a top surface 302, a bottom surface (not visible), a first circumferential surface 303 and a second circumferential surface 304. The magnet 301, like the magnets 101 and 201, comprises magnetic particles 305 and 306. The preferential direction of magnetization of the magnetic particle 305 at the top surface 302 is perpendicular to the top surface 302 and the preferential direction of magnetization of the magnetic particle 306 at the circumferential surface 303 is perpendicular to the preferential direction of magnetization of the magnetic particle 305, i.e. perpendicular to the circumferential surface 303. The magnet 301 has the shape of a ring.
Figure 4 shows a still further magnet 401 in form of a prism. The magnetic particles 402 and 403 have been oriented in the same manner as the magnetic particles of the magnets 101, 201 and 301. In contrast to the magnet 201, the magnet 401 has been magnetized such that the magnetic particle 402 has a north pole (indicated by arrow 404) at the top surface 405 and the magnetic particle 403 has a south pole (indicated by arrow 406) at the circumferential surface 407.
Figure 5 illustrates a method for manufacturing a magnet. In a first step 501 the alloy for manufacturing the magnet is melted under vacuum. The alloy may be a NdFeB- alloy. Having been melted and solidified, the material is crushed (step 502) and milled (step 503) to form fine magnetic particles.
In the following step 504, the fine magnetic particles are pressed together to form a magnet having a top surface, a bottom surface and a circumferential surface. During pressing an external magnetic field is applied, wherein the magnetic field is oriented perpendicular to the top surface and parallel to the top surface at the circumferential surface. Due to the external magnetic field, the magnetic particles may assume an orientation such that their preferential direction of magnetization aligns with the external magnetic field. After step 504, typically, the pressed green body will be sintered and annealed (step 505) before being machined and coated (step 506). In case of arc magnetization shapes, the risk of crack formation during sintering and annealing may be reduced. Optionally, an additional magnetization may be performed at the end (step 507).
Figure 6 shows a first apparatus 601 for manufacturing a magnet 602. The apparatus 601 comprises a mold 603, 604, 605, 606, 607, 608, 609, 610 surrounding a cavity, wherein the magnet 602 is to be formed by pressing magnetic particles together. The mold 603, 604, 605, 606, 607, 608, 609, 610 is made of a material having poor electric
conductivity.
The apparatus 601, furthermore, includes a first coil 61 1 and a second coil 612. The first coil 611 and the second coil 612 are arranged mirror-symmetrically with respect to a mirror plane 613. Energizing the first coil 611 and the second coil 612 with a current leads to a static magnetic field 614 being oriented parallel to the axis of the first coil 611 and the second coil 612 at the interior thereof and parallel to the mirror plane 613 near the mirror plane 613. The magnetic flux density B within the cavity may be selected to be between 0.2 T and 0.8 T, more particularly between 0.4 and 0.6 T.
The cavity is provided slightly above the mirror plane 613 such that the bottom surface of the magnet to be pressed essentially aligns with the mirror plane 613. The first apparatus 601 is adapted to apply axial pressure 615, 616 on the magnetic particles encapsulated in the cavity formed by the mold 603, 604, 605, 606, 607, 608, 609, 610. As shown in Figure 7, the mold parts 617, 618 of the first apparatus 601 may apply transverse pressure 617, 618 on the magnetic particles encapsulated in the cavity. The transverse pressure 617, 618 may be applied before or after the axial pressure 615, 616.
Energizing the coils 611, 612 during the whole pressure process may avoid unidirectional aligning of the magnetic particles according to their preferential direction of magnetization. With the apparatus 601 it may be possible to obtain a magnet, wherein the preferential direction of magnetization of its magnetic particles changes continuously from vertical at the top surface to horizontal at the circumferential surface of the magnet 602.
Figures 8 and 9 show a second apparatus 801 for manufacturing a magnet 802. The apparatus 801 includes a mold 803, 804, 805, 806, 807, 808 having a cavity for manufacturing the magnet 802. The mold parts 803, 804, 806, 807, 808 are made of a material having very poor electrical conductivity, whereas the mold part 805 is a conductive plate having high electrical conductivity. The conductive plate 805 forms the bottom surface of the magnet 802. The mold part 808 may exert axial pressure 809 on the magnetic particles in the cavity and the mold parts 804 and 806 may apply pressure 811 and 810 in a transverse direction. Moreover, the apparatus 802 includes a coil 812. The coil 812 may be charged with an external capacitor. With a rectifier, e.g. a thyristor, a short very high magnetic pulse may be generated within the cavity. The pulse length may be between 0.5 ms and 1.5 ms, more particularly between 0.8 and 1.2 ms. The magnetic pulse will induce eddy currents in the electric conductive plate 5 counteracting the B-field, which will, therefore, not pass the conductive plate 5. Accordingly, the magnetic field lines 813 may assume a shape
corresponding to the upper magnetic field lines 614 shown in Figure 6. The magnetic pulses may be applied at different times during the axial pressing.
Figure 10 shows a first magnetic array 1001 comprising magnets 1002 to 1012. The magnetic array 1001 is a linear magnetic array. The magnets 1002 to 1012 comprise magnetic particles, whose preferential directions of magnetization are collinear to one another and to the magnetization direction of the magnet, which is indicated by an arrow. The magnets 1002, 1006, 1010 have their north pole at the top surface of the magnetic array and the magnets 1004, 1008, 1012 have their south pole at the top surface. The magnets 1003, 1005, 1007, 1009, 1011 are not magnetized vertically but horizontally. The north pole of the magnets 1003, 1005, 1007, 1009, 1011 is directed to the neighboring magnet having the north pole at the top surface, i.e. directed to the magnet 1002, 1006, 1010.
The magnetic flux density at the top surface of the magnetic array 1001 starting from a medium value at the center of the top surface of magnet 1002 in a direction to magnet 1012 may increase to a high value just before the interface to the magnet 1003. After the interface to the magnet 1003 the magnetic flux density may have a low value and assume a high value again just after the interface to magnet 1004. At the center of the top surface of magnet 1004, the magnetic flux density may have a medium value again.
Figure 11 shows a second magnetic array 1101 comprising magnets 1102 to 1107. The magnets 1102 to 1007 comprise magnetic particles, whose preferential direction of magnetization continuously changes from vertical at the top surface to horizontal at the side surfaces. The preferential direction of magnetization of the magnetic particles corresponds to the magnetization of the magnets, which is indicated by arrows in Figure 11. The magnets
1102, 1104, 1106 have a north pole at the top surface and the magnets 1103, 1105, 1107 have a south pole at the top surface. The curved magnetization of the magnetic array 1101 may be described as having the form of arcs or as sinusoidal.
At the top surface, from the center of magnet 1102 to the center of magnet
1103, the magnetic flux density first continuously decreases from a maximum value at the center to a minimum value at the interface between the magnet 1102 before rising again to the maximum value at the center of magnet 1103.
Figure 12 shows a first positioning device 1201 comprising a magnetic array 1202 and a carrier 1203. The magnetic array 1202 comprises magnets 1204 to 1207. The magnets 1202 to 1207 comprise magnetic particles, whose preferential directions of magnetization are collinear to one another and to the magnetization direction of the magnet. The magnets 1204 and 1205 have a quadratic top surface and are arranged in a checkerboard pattern. The magnets 1204 have a north pole at the top surface and the magnets 1205 have a south pole at the top surface. The north pole of the magnets 1206, 1207 is directed to the neighboring magnet 1204, 1205 having the north pole at the top surface.
The carrier 1203 comprises a first positioning coil 1208 and a second positioning coil 1209 each having an elongated cross section and an axis perpendicular to the magnet array. The elongation directions of the first positioning coil and the second positioning coil draw an angle of 90°. A current trough the positioning coils will induce a Lorentz force perpendicular to the elongation directions in view of the magnet field of the magnet array, which Lorentz force may be used to position the carrier with respect to the magnet array.
Figure 13 shows a second positioning device 1301 comprising a magnet array 1302 and a carrier 1303. The magnet array 1302 comprises magnets 1304, 1305 having a quadratic top surface and a circumferential surface. The magnets 1304, 1305 comprise magnetic particles, wherein the preferential direction of magnetization of a particle at the top surface is essentially perpendicular to the top surface, and wherein the preferential direction of magnetization of a second particle at the circumferential surface is essentially
perpendicular to the preferential direction of magnetization of the first magnetic particle.
The magnets 1304 having a north pole at the top surface and the magnets 1305 having a south pole at the top surface are arranged in a checkerboard pattern. The pitch 1306, i.e. the distance between the center of two magnets having a magnetization perpendicular to the top surface, is identical to the corresponding pitch of the magnet array 1202.
Figure 14 shows a comparison of the performance of a positioning device according to figure 12 (dashed line, dot-and-dash line) and a positioning device according to figure 13 (dotted line, continuous line) having the same dimensions. The Y-axis shows the force per current experienced by a positioning coil in a horizontal direction transverse to its elongation directions (continuous line, dot-and-dash line) and in a vertical direction transverse to its elongation direction (dotted line, dashed line). The positioning coil is oriented diagonal with respect to the checkerboard pattern. The force has been normalized to 1 for the positioning device pursuant to figure 13. The X-axis shows the horizontal position of the coil.
The performance improvement of a positioning device according to figure 13 is comparable to changing the magnetic material from a material with Br = 1.4 T to a material with Br = 1.68, which even surpasses the theoretical Br values for NdFeB materials, i.e. about 1.55 T.

Claims

CLAIMS:
1. Magnet array (1 101) comprising magnets,
wherein the magnets (101) have a top surface (104), a bottom surface, and a circumferential surface (105, 106),
wherein the top surface (104) and the bottom surface are parallel to one another,
wherein the circumferential surface (105, 106) is perpendicular to the top surface (104) and the bottom surface,
wherein the magnets (101) comprises magnetic particles having a preferential direction of magnetization,
wherein the preferential direction of magnetization of a first magnetic particle at the top surface (104) is essentially perpendicular to the top surface (104),
wherein the preferential direction of magnetization of a second magnetic particle at the circumferential surface (105, 106) is essentially perpendicular to the preferential direction of magnetization of the first magnetic particle,
wherein a first sort of magnets (1102) having a north pole at the top surface and a second sort of magnets (1103) having a south pole at the top surface, and
wherein the first (1102) and second sort of magnets (1103) are mounted on a support to form a line of magnets having alternating poles at the top surface.
2. Magnet array according to Claim 1,
wherein the magnets (101) are rectangular cuboids, in particular a rectangular cuboids having a quadratic top surface (104).
3. Magnet array (1302) according to Claim 1,
wherein the first (1304) and second sort of magnets (1305) are mounted on a support to form a two-dimensional checkerboard pattern of north and south poles at the top surface.
4. Method for manufacturing a magnetic array, comprising
pressing (504) magnetic particles to form a magnet having a top surface, a bottom surface, and a circumferential surface,
wherein the top surface and the bottom surface are parallel to one another, and wherein the circumferential surface is perpendicular to the top surface, and applying an external magnetic field during the pressing of the magnetic particles,
wherein the magnetic field is oriented perpendicular to the top surface at the top surface, and
wherein the magnetic field is oriented parallel to the top surface at the circumferential surface, and
wherein a first and a second sort of magnets are mounted on a support to form a line of magnets having alternating poles at the top surface.
5. Method for manufacturing a magnetic array according to Claim 4,
wherein the magnetic field is a static magnetic field.
6. Method for manufacturing a magnetic array according to Claim 4,
wherein the magnetic field is a pulsed magnetic field.
7. Apparatus (601) for manufacturing a magnet for a magnetic array according to Claim 1 or 2 comprising
a mold (603, 604, 605, 606, 607, 608, 609) for pressing magnetic particles; and
a first coil (611) for orienting the magnetic particles during the pressing.
8. Apparatus (601) for manufacturing a magnet for a magnetic array according to Claim 7,
wherein the mold (603, 604, 605, 606, 607, 608, 609) is formed of a material having poor electric conductivity.
9. Apparatus (601) for manufacturing a magnet for a magnetic array according to
Claim 7 or 8, further comprising
a second coil (612) for orienting the magnetic particles.
10. Apparatus (601) for manufacturing a magnet for a magnetic array according to
Claim 9,
wherein the first coil (611) and the second coil (612) are arranged mirror- symmetrically,
wherein the surface of the mold forming the bottom surface of the magnet is arranged parallel to the mirror plane (613) of the first coil (611) and second coil (612), and wherein the distance between the surface of the mold forming the bottom surface of the magnet and the mirror plane (613) is less than 2/10 of the height of the magnet to be manufactured, in particular less than 1/10 of the height of the magnet to be
manufactured.
11. Apparatus (801) for manufacturing a magnet for a magnetic array according to Claim 7, further comprising
a conducting plate (805) arranged parallel to the surface of the mold forming the bottom surface of the magnet.
12. Apparatus (801) for manufacturing a magnet according to any one of Claims 3 to 10, further comprising
a capacitance and
a rectifier.
13. Positioning device (1301) comprising
a magnet array (1302) according to Claim 1 or 3,
a carrier (1303) comprising a first positioning coil having an elongated cross- section and an axis perpendicular to the magnet array (1302).
14. Positioning device (1301) according to Claim 13 ,
wherein the carrier (1303) comprises a second positioning coil having an elongated cross-section and an axis perpendicular to the magnet array, and
wherein the elongation direction of the first positioning coil is different from the elongation direction of the second positioning coil.
PCT/EP2016/082269 2015-12-22 2016-12-21 Method and apparatus for manufacturing 1d and 2d multipole magnet array's WO2017109013A1 (en)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0523002A1 (en) * 1991-07-11 1993-01-13 LAUBE, Hans-Jürgen Compound magnet comprising several individual magnets and a permanent magnetic bearing with a compound magnet comprising several individual magnets
EP0535901A2 (en) * 1991-09-30 1993-04-07 Kawasaki Steel Corporation Lateral orientation anisotropic magnet
WO2001018944A1 (en) * 1999-09-02 2001-03-15 Koninklijke Philips Electronics N.V. Displacement device
EP1548761A1 (en) * 2002-08-29 2005-06-29 Shin-Etsu Chemical Co., Ltd. Radial anisotropic ring magnet and method of manufacturing the ring magnet
US7207102B1 (en) * 2004-04-01 2007-04-24 Sandia Corporation Method for forming permanent magnets with different polarities for use in microelectromechanical devices
US20120256532A1 (en) * 2008-04-04 2012-10-11 Correlated Magnetics Research, Llc Panel system for covering a glass or plastic surface
US20150320168A1 (en) * 2014-05-07 2015-11-12 Dov Hoffman Magnetic case or holder for smartphones and portable electronic devices

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0523002A1 (en) * 1991-07-11 1993-01-13 LAUBE, Hans-Jürgen Compound magnet comprising several individual magnets and a permanent magnetic bearing with a compound magnet comprising several individual magnets
EP0535901A2 (en) * 1991-09-30 1993-04-07 Kawasaki Steel Corporation Lateral orientation anisotropic magnet
WO2001018944A1 (en) * 1999-09-02 2001-03-15 Koninklijke Philips Electronics N.V. Displacement device
EP1548761A1 (en) * 2002-08-29 2005-06-29 Shin-Etsu Chemical Co., Ltd. Radial anisotropic ring magnet and method of manufacturing the ring magnet
US7207102B1 (en) * 2004-04-01 2007-04-24 Sandia Corporation Method for forming permanent magnets with different polarities for use in microelectromechanical devices
US20120256532A1 (en) * 2008-04-04 2012-10-11 Correlated Magnetics Research, Llc Panel system for covering a glass or plastic surface
US20150320168A1 (en) * 2014-05-07 2015-11-12 Dov Hoffman Magnetic case or holder for smartphones and portable electronic devices

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