US3855691A - Method of making a magnetic material part with spatial distribution of the permeability - Google Patents

Method of making a magnetic material part with spatial distribution of the permeability Download PDF

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US3855691A
US3855691A US00337308A US33730873A US3855691A US 3855691 A US3855691 A US 3855691A US 00337308 A US00337308 A US 00337308A US 33730873 A US33730873 A US 33730873A US 3855691 A US3855691 A US 3855691A
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permeability
initial
manufacture
magnetic article
solid magnetic
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US00337308A
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A Deschamps
G Faye
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Lignes Telegraphiques et Telephoniques LTT SA
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Lignes Telegraphiques et Telephoniques LTT SA
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Priority claimed from FR7207816A external-priority patent/FR2174683A1/fr
Priority claimed from FR7210779A external-priority patent/FR2177508A1/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/34—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials non-metallic substances, e.g. ferrites
    • H01F1/36—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials non-metallic substances, e.g. ferrites in the form of particles
    • H01F1/37—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials non-metallic substances, e.g. ferrites in the form of particles in a bonding agent
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/265—Compositions containing one or more ferrites of the group comprising manganese or zinc and one or more ferrites of the group comprising nickel, copper or cobalt
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2675—Other ferrites containing rare earth metals, e.g. rare earth ferrite garnets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/0302—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity characterised by unspecified or heterogeneous hardness or specially adapted for magnetic hardness transitions
    • H01F1/0311—Compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/32—Non-reciprocal transmission devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/4902—Electromagnet, transformer or inductor
    • Y10T29/49075—Electromagnet, transformer or inductor including permanent magnet or core
    • Y10T29/49076—From comminuted material

Definitions

  • ABSTRACT A part made of ferrimagnetic material with a spatial Forelgn Apphcatlon Prlomy Data variation of the permeability value is obtained through Mar. 7, 1972 France 72.07816 heat treatment of a body of ferrimagnetic material at Mar. 28, 1972 France 72.10779 the temperture such that the free energy of the material is low and that a transformation into a material [52] US. Cl 29/608, 252/6257, 252/6262, with higher free energy is obtained, stopping said heat- 336/233 ing before complete transformation and further ma- [51] Int. Cl.
  • the present invention concerns a process for the preparation of homogeneous articles of the ceramic type, of which the magnetic properties vary from point to point. Magnetic circuits whose permeability varies spatially are usually built up of different materials chosen for the appropriate value of their permeability.
  • a chemical composition differing from that of the solid and the third case is achieved through solid phase diffusion of a salt or oxide of the substituting ion into the isting in the structure does not modify the chemical machining of said piece to obtain the required spatial distribution.
  • the material When this sum is zero, the material is non-magnetic (its permeability is near that of the vacuum). Change of ion in the sites may change the value of the sum and therefore of the permeability.
  • soft magnetic materials have been obtained essentially from structures of the spinel type, that is to say, those belonging to the space group 0;, F 3 dm, and from structures of the garnet type, belonging to the group 0;, l a 3 d.
  • the change may be summed up either as a suppression of ions from some sites, as the introduction of foreign ions into the lattice or as a substitution of ions at some of the lattice sites.
  • the second case will not be taken into consideration due to the fact that too little vacancies are available in current soft magnetic materials for easy fill up of the lattice introducing an important change in the magnetic properties.
  • the invention therefore is based on the first and third type of modifications.
  • the first case consisting of locally depriving the lattice of ions through heating the material will be used when the phase diagram of the material shows the formation of a liquid phase corresponding to composition and may result in a deformation of the crystal lattice, and the ion driven off is accumulated in the form of an oxide or of another salt at the grain boundaries;
  • the substitution reaction is accompanied by a modification of chemical composition since the previous ions are evaporated as oxide or salt or the substitution is only a change in the valency of a polyvalent metal (such as iron for instance) with evaporation of molecules corresponding to the anions of the lattice.
  • the electrostatic energy U, of a spinel is expressed as a function of the distribution of the ions between the sites A and B (parameter A) and of the position of the oxygens (parameter u 3/8 8). )t and 6 are determined for each structure by X-ray analysis. The usual values of 8 are comprised within the range (0 8 0.01).
  • the repulsion energy U can be calculated from the Born- Mayer formula.
  • the covalence energy U is zero in the absence of a covalent bond. When covalent bonds exist, U may be high and, as a result of the decrease of the ionic charge, it may become the preponderant factor of U.
  • the change in the magnetic properties of a magnetic material F is obtained by heating a piece of said magnetic material at a temperature such that the free energy of the F material is much smaller than the free energy of another ferrimagnetic material F into which F is transformed at said temperature, this change is stopped before it has been carried out completely and the piece of material is machined so that at least one part of the outer surface of said machined piece consists of the initial F material.
  • a body of a material of complex structure having the magnetic properties required to constitute a fraction of the solid magnetic article is subjected to a thermal treatment in vacuo at a temperature several degrees higher than the solidus-liquidus equilibrium temperature that is at a temperature where the free energy is near zero for a period such that the magnetic properties of the external fraction of the body only are modified by evaporation of the liquid phase, the initial magnetic properties of the central fraction of the body being retained.
  • a thermal treatment in vacuo facilitates the evaporation of the liquid phase formed.
  • a diffusion is effected in a crystal structure of an initial magnetic material, that is to say, the replacement of an ion M in one site by a different ion M corresponding to a second structure of magnetic material by heating the material in presence of a M salt or oxide at a temperature such that E E where E, is the internal energy of the initial'maten'al (M Fe O and E is the energy of the second material (M Fe O and such that E is very low.
  • E is the internal energy of the initial'maten'al (M Fe O and E is the energy of the second material (M Fe O and such that E is very low.
  • U TS U, T5 is higher than 850 C for the spinels usually used as soft magnetic materials and about l200 C in the case of garnets.
  • the thermal treatment may have the ef fect of increasing or reducing the permeability of the material, depending upon the initial composition of the latter. Similar treatments may have either effect.
  • the temperature'of the thermal treatment is fixed by the above conditions for the free energy.
  • the liquid phase intermediate it can be selected on the phase diagram of the constituents of the body.
  • the application of a reduced pressure in the course of the thermal treatment generally results in a reduction of the temperature at which the liquid phase is formed, as compared with its value at atmospheric pressure. This point is particularly favourable to maintenance of the mechanical cohesion of the body.
  • FIG. 1 is a known phase diagram of the mixture of iron and yttrium oxides
  • FIG. 2 shows experimental curves representing the value of the saturation magnetisation as a function of the space co-ordinates of a cylindrical block of an ironyttrium-aluminium-gadolinium garnet treated in accordance with the invention
  • FIG. 3 is a diagram of the block of material corresponding to the above curve
  • FIGS. 4 to 7 inclusive are micrographic views of different sections of the material from which the curves of FIG. 2 were obtained.
  • FIG. 8 is a diagram representing the saturation magnetisation of ferrites of Ni and Zn as a function of the composition.
  • FIGS. 9 and 10 are micrographs of a specimen of Ni-Zn ferrite treated in accordance with the invention.
  • FIG. 11 is a nickel ferrite specimen which has undergone a heat treatment
  • This material which is green in colour, has good magnetic properties (41rMs of the order of 900 to 1,000), and is particularly adapted to operate in the frequency range of 9GHz (linewidth between 70 and 80 oersteds tangent of the loss angle of the order of I 10"). It is commonly used in the production of circulators, isolators, etc., based upon the propagation of elec tromagnetic microwaves in a high-permeability material.
  • FIG. 1 shows the phase diagram, at atmospheric pressure, of the iron oxideyttrium oxide mixture, as published in the Journal of American Ceramic Society 1961 Vol. 5, No. 44, page 2l 3.
  • the quaternary diagram of the iron-yttriumgadolinium-aluminium oxide mixtures cannot be represented in a simple form on the same diagram. Since aluminium oxide is more refractory than iron and yttrium oxides the appearance of an aluminium-rich liquid phase takes place only at temperature higher than those at which the iron (or yttrium) oxide liquid phase appears. At the temperatures indicated in the diagram of FIG. 1", the presence of the other two constituents has scarcely any effect on the phase diagram.
  • a solid body for example of cylindrical form, consisting of a garnet obtained by any known method, such as for instance by that described in the British application filed by the Applicants on theFeb. 2nd, 1973 for: Improved production process of fine grained ferrites, which body is coated in alumina powder and disposed in a vacuum oven whose temperature is brought to l,300 C after out-gassing for about 1 hour at a pressure of 10' cm.Hg. The temperature rise takes place in about minutes.
  • the garnet follows a course similar to AB on the phase diagram.
  • the curves of FIG. 2 show the variation of the saturation magnetisation of the body subjected to two successive series of machining operations, the first being a plane grinding having the effect of eliminating fragments parallel to the base of the cylinder and reducing the height of the body, while the second is a cylindrical grinding having the object of eliminating a cylindrical film and reducing the diameter of the body.
  • FIG. 3 illustrates these successive operations.
  • the overall saturation magnetisation of the article after thermal treatment is gauss/cm.
  • discs such as l, 2, etc. in a direction parallel to one of the terminal faces of the cylinder are successively eliminated. These successivediscs have a thickness of 1 mm.
  • the initial height of the article is 10 mm and its diameter is 2.75 mm.
  • the elimination of a fragment of 1 mm, such as the fragment 1' at one of the ends of the cylinder results in a considerable increase in the saturation magnetisation, which changes to 735 gauss/cm (origin of the curve h 9 mm).
  • FIG. 4 is a micrographic view of the section of the body of FIG. 2 before the heat treatment, with a magnification of 50.
  • the lower part corresponds to the peripheral zone and has relatively coarse grains.
  • the central part of the micrograph corresponds to a bright zone and the upper part corresponds to the centre of the body and to a green zone.
  • Larger-scale micrographs of the three zones appearing in FIG. 4 form the subject of FIGS. 5, 6 and 7 which correspond respectively to the peripheral zone, to the bright intermediate zone and to the central zone.
  • the magnification of these micrographs is 1,000.
  • the dimensions of the grains constituting the peripheral zone are much greater than those of the grains constituting the central zone.
  • the black portions of the photographs correspond to grains torn out in the course of the polishing treatments and to the chemically attacked grain junctions.
  • the average dimensions of the grains change from 20 microns in the peripheral zone to 6 microns in the central zone.
  • the starting ferrite has a saturation magnetisation of 4760 gauss/cm which value is reduced to 3800 gauss/cm after the thermal treatment.
  • the measured loss angles show that the body thus obtained cannot be used in a microwave circuit owing to the presence of F8304. 7
  • the initial material is a nickel ferrite of spinel structure, NiFe O in which 2 l, the nickel ions occupying only the octahedral sites B.
  • Cupric ions are diffused into this structure under the following conditions: after sintering and optional grinding, the spinel is disposed in a non-porous sintered and crystallised alumina boat provided with a lid. A few grammes of copper oxide CuO are added and the temperature is raised to 900 C and maintained for 48 hours. The saturation magnetisation of the material after treatment is substantially nil.
  • copper oxide CuFe O has a structure such that 2) ⁇ 0.88 and 8 0.005.
  • the copper ions occupy the octahedral sites in a majority, and they have strong square covalent bonds in the spinel structure, which even produce a quadratic deformation of the mesh.
  • the covalence energy of copper is therefore very high.
  • Nickel ferrite does not exhibit any covalent bonds. If the nickel ferrite is denoted by F, and the copper ferrite by F then at 900 C E, is in the neighbourhood of zero, while the free energy E is distinctly higher.
  • nickel ions become concentrated in the form of oxide in the grain boundaries.
  • nickel ferrite was treated under the same conditions at l,250 C for 48 hours in the presence of zinc oxide. There was again obtained a substitution of the nickel ions by Zinc ions. Under the above conditions, an increase of the saturation magnetisation of the nickel ferrite from 3,300 to 4,300 gauss/cc was obtained. It is known that, in zinc ferrite, the zinc ions occupy the tetrahedral sites A (2% 0), while the nickel ions of the initial structure occupy the sites B. The diffusion is therefore accompanied by a transfer of the metallic ions in addition to their substitution.
  • the zinc ions in the final structure exhibit strong tetrahedral covalent bonds, which explains why the free energy of the zinc ferrite is higher at l,250 C than that of nickel ferrite. Account must also be taken, in evaluating the free energy, of the energy variation resulting from the transfer of the ions between the sites B and A, which variation may be evaluated, as a first approximation, by the electrostatic energy difference between a normal and 9 an inverted spinel (cf the above mentioned book by Lax and Button page 115).
  • the same nickel ferrite was subjected to the same experimental conditions in the presence of boron oxide and heated at l,300 C for 48 hours. The saturation the electrostatic attraction forces are higher than in the case of nickel.
  • the component U, of the internal energy is increased at a given temperature, which clearly corresponds to a value of E E,.
  • the diffusion temperature is so chosen that the nickel ferrite has under these conditions a low internal energy.
  • the micrograph shows that the grain junctions have substantially disappeared.
  • the magnification of the latter micrograph is 150, and that of the preceding ones 1,000.
  • This diffusion is accompanied, as in the previous case, by a change of chemical composition due to formation of yttrium borate YBO
  • the electrostatic energy of the borate is substantially higher than that of the garnet. The free energy of the second ferrite is therefore considerable.
  • a process for the manufacture of a solid magnetic article with a spatially uneven distribution of permeability which comprises:
  • a process for the manufacture of a solid magnetic article with a spatially uneven distribution of the permeability according to claim 1 in which a liquid phase of different chemical composition develops at the heating temperature, the chemical composition of which differs from that of the initial l material.
  • a process for the manufacture of a solid magnetic article with a spatially uneven distribution of permeability according to claim 3 in which said initial F material is an yttrium iron Gd, Al substituted garnet and said heating temperature is between l,250 and 1350 C.
  • a process for the manufacture of a solid magnetic article with a spatially uneven distribution of permeability according to claim 3 in which said initial F material is a Ni Zn spine] ferrite and said heating temperature is between 1,270 and l,3l0 C.
  • a process for the manufacture of a solid magnetic article with a spatially uneven distribution of the permeability according to claim 1 in which said heating is carried on at a temperature lower than the liquefaction of the F material in presence of a salt of a foreign metal which constitutes the F material through substitution.
  • a process for the manufacture of a solid magnetic article with a spatially uneven permeability distribution according to claim 6 in which said initial material is nickel spinel, the metal ion of said salt of foreign metal is divalent zinc and said heating temperature is above 850 C.
  • a process for the manufacture of a solid magnetic article with a spatially uneven permeability distribution according to claim 6 in which said initial material is nickel spinel, the metal ion of said salt of foreign metal is divalent copper and said heating temperature is above 850" C.
  • a process for the manufacture of a solid magnetic article with a spatially uneven permeability distribution according to claim 6 in which said initial material is nickel spinel, the metal ion of said salt of foreign metal is divalent boron and said heating temperature is above 850 C.
  • a process for the manufacture of a solid magnetic article with a spatially uneven permeability distribution according to claim 6 in which said initial material is an yttrium-iron garnet the metal ion of said salt of foreign metal is divalent boron and said heating temperature is above l,200 C.

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US00337308A 1972-03-07 1973-03-02 Method of making a magnetic material part with spatial distribution of the permeability Expired - Lifetime US3855691A (en)

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FR7207816A FR2174683A1 (en) 1972-03-07 1972-03-07 Integrated microwave circuit substrate - by heating polycrystalline magnetic starting material and mechanically working
FR7210779A FR2177508A1 (en) 1972-03-28 1972-03-28 Integrated microwave circuit substrate - by heating polycrystalline magnetic starting material and mechanically working

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4142728A1 (de) * 1991-12-21 1993-07-01 Ant Nachrichtentech Ferritkoerper
US5446459A (en) * 1991-08-13 1995-08-29 Korea Institute Of Science And Technology Wide band type electromagnetic wave absorber
US20070210274A1 (en) * 2004-08-27 2007-09-13 Fraungofer-Gesellschaft Zur Forderung Der Angewandten Ferschung E.V. Magnetorheological Materials Having Magnetic and Non-Magnetic Inorganic Supplements and Use Thereof
US20070252104A1 (en) * 2004-08-27 2007-11-01 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological Materials Having a High Switching Factor and Use Thereof
US20080318045A1 (en) * 2004-08-27 2008-12-25 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological Elastomers and Use Thereof
US20100193304A1 (en) * 2007-04-13 2010-08-05 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Damping device with field-controllable fluid
US20190219188A1 (en) * 2018-01-17 2019-07-18 Nextern, Inc. Solenoid operated valve with flux density concentration ring and molded-in valve seat

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2982948A (en) * 1957-11-01 1961-05-02 Ibm Multi-material ferrite cores
US3057802A (en) * 1958-02-13 1962-10-09 Lignes Telegraph Telephon Magnetic materials of the high permeability ferrite type
US3132105A (en) * 1962-03-14 1964-05-05 Sperry Rand Corp Temperature compensated yttrium gadolinium iron garnets
US3457174A (en) * 1964-12-29 1969-07-22 Itt Ferromagnetic materials and processes for their manufacture
US3763045A (en) * 1970-04-03 1973-10-02 Nippon Electric Co Calcium-vanadium ferrimagnetic garnets

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2982948A (en) * 1957-11-01 1961-05-02 Ibm Multi-material ferrite cores
US3057802A (en) * 1958-02-13 1962-10-09 Lignes Telegraph Telephon Magnetic materials of the high permeability ferrite type
US3132105A (en) * 1962-03-14 1964-05-05 Sperry Rand Corp Temperature compensated yttrium gadolinium iron garnets
US3457174A (en) * 1964-12-29 1969-07-22 Itt Ferromagnetic materials and processes for their manufacture
US3763045A (en) * 1970-04-03 1973-10-02 Nippon Electric Co Calcium-vanadium ferrimagnetic garnets

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5446459A (en) * 1991-08-13 1995-08-29 Korea Institute Of Science And Technology Wide band type electromagnetic wave absorber
DE4142728A1 (de) * 1991-12-21 1993-07-01 Ant Nachrichtentech Ferritkoerper
US20070210274A1 (en) * 2004-08-27 2007-09-13 Fraungofer-Gesellschaft Zur Forderung Der Angewandten Ferschung E.V. Magnetorheological Materials Having Magnetic and Non-Magnetic Inorganic Supplements and Use Thereof
US20070252104A1 (en) * 2004-08-27 2007-11-01 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological Materials Having a High Switching Factor and Use Thereof
US20080318045A1 (en) * 2004-08-27 2008-12-25 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological Elastomers and Use Thereof
US7608197B2 (en) 2004-08-27 2009-10-27 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological elastomers and use thereof
US7708901B2 (en) * 2004-08-27 2010-05-04 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological materials having magnetic and non-magnetic inorganic supplements and use thereof
US7897060B2 (en) * 2004-08-27 2011-03-01 Fraunhofer-Gesselschaft Zur Forderung Der Angewandten Forschung E.V. Magnetorheological materials having a high switching factor and use thereof
US20100193304A1 (en) * 2007-04-13 2010-08-05 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Damping device with field-controllable fluid
US20190219188A1 (en) * 2018-01-17 2019-07-18 Nextern, Inc. Solenoid operated valve with flux density concentration ring and molded-in valve seat
US10619755B2 (en) * 2018-01-17 2020-04-14 Nextern, Inc. Solenoid operated valve with flux density concentration ring and molded-in valve seat

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GB1428000A (en) 1976-03-10

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