US2698917A - Magnetic circuit comprising a ferromagnetic part having high permeability and a substantially flat, thin permanent magnet - Google Patents

Magnetic circuit comprising a ferromagnetic part having high permeability and a substantially flat, thin permanent magnet Download PDF

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Publication number
US2698917A
US2698917A US264984A US26498452A US2698917A US 2698917 A US2698917 A US 2698917A US 264984 A US264984 A US 264984A US 26498452 A US26498452 A US 26498452A US 2698917 A US2698917 A US 2698917A
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United States
Prior art keywords
magnet
dimension
given direction
ferromagnetic
magnetic circuit
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US264984A
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English (en)
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Arend Thomas Van Urk
Rademakers Adriaan
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Hartford National Bank and Trust Co
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Hartford National Bank and Trust Co
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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
    • H01F1/0302—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
    • H01F1/0313—Oxidic compounds
    • H01F1/0315—Ferrites
    • 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
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
    • H04R9/02—Details
    • H04R9/025—Magnetic circuit
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2209/00—Details of transducers of the moving-coil, moving-strip, or moving-wire type covered by H04R9/00 but not provided for in any of its subgroups
    • H04R2209/022—Aspects regarding the stray flux internal or external to the magnetic circuit, e.g. shielding, shape of magnetic circuit, flux compensation coils

Definitions

  • the invention relates to magnetic circuits comprising a ferromagnetic part having a high permeability and a substantially at, thin permanent magnet, magnetized substantially in the direction of its smallest dimension and made of a material having high coercive force BHC of at least 750 Oersted and a comparatively low remanence (for example, less than 5,000 Gauss), the smallest dimension being less than 1A of the largest outer dimension of one pole surface.
  • the ferromagnetic part comprises a portion in which the path of the lines of force is parallel to the lines of force in the magnet and the magnetic circuit comprises atleast one airgap.
  • a magnetic circuit cornprising a ferromagnetic part having a high permeability and a substantially at, thin permanent magnet magnetised substantially in the direction of its smallest dimension, and made of a material having high coercive force, BHC of at least 750 Oersteds and a comparatively low remanence (of, for example, less than 5,000 Gauss), the smallest dimension being smaller than one quarter of the largest outer dimension of one of the pole surfaces, the ferromagnetic part comprising a portion in which the path of the lines of force is parallel to the lines of force in the magnet, whilst in the magnetic circuit at least one airgap is provided, is characterized in that the said portion is spaced apart from the magnet by a distance which is smaller than half, preferably smaller than one quarter the length of the magnet between the poles, the airgap being provided at least in the proximity of an edge of the magnet.
  • the invention is based on the discovery that certain permanent magnetic materials, more particularly those which have a high IHC-value with respect to the coercive force BHC and a permeability u of less than 2, for exam ⁇ ple, l to 1.6, are found to exhibit the property.
  • the number of stray lines of force emanating from the sides between the poles is increased only slightly by arranging ferromagnetic material of high permeability, such as soft iron, on the sides of the magnet, which does occur, on the contrary, for example with the known magnetic steels on an Fe, Aland Ni-basis to which Co, Cu and/or Ti is added. Consequently, the invention is restricted to the use of permanent magnetic materials which exhibit the aforesaid properties.
  • such materials have a further property in that, if desired, the magnet may be magnetised outside the circuit without the risk of real demagnetisation when the magnet is transferred from the magnetising devise to the nal magnetic circuit without any precautions being taken. Consequently, magnetic keeping by means of a soft iron circuit provided between the two pole surfaces during the transfer of the magnet may be dispensed with. It is even found that substantially no change of the working point is produced, if the magnet is taken out of the circuit and reintroduced into it without any precautions being taken. This, consequently, means that the so-called reversible curves substantially coincide with the demagnetisation curve or BH-curve. It is found that, even in the presence of very strong external, opposite magnetic fields, demagnetisation of the material is eifected in practice with great diiiiculty only.
  • the use of the invention has the advantage that, owing to the compact construction obtainable the size of the magnetic circuit may be comparatively small.
  • the magnetic circuit according to the invention is of particular importance, if the permanent magnet is made of a material described and claimed in U. S. application Ser. No. 239,264 tiled July 30, 1951. These materials are characterized by a composition of primarily noncubic crystals of polyoxides of iron and at least one of the metals barium, strontium and lead and, if desired, calcium. Said materials may be a ferromagnetic material having as a component essential for the ferromagnetic properties, single crystals and/or mixed crystals of magnetoplumbite structure of compounds MO-6Fe2O3, where M or MFeiaOzv represents one of the metals Pb, Ba or Sr.
  • the coercive force may amount to, for example, 1,400 Oersteds.
  • the electrical resistance is then more than ohm/cm. at frequencies of a few mcs/sec., so that eddy current losses are very low.
  • the airgap may be arranged such that its operative surfaces are in part bounded by a surface of the magnet. If at least one of the ferromagnetic parts which is parallel to the lines of force substantially touches the magnet, the magnetic circuit has a maximum degree of compactness, so that a minimum of clearance space is left.
  • the magnet may be constituted by such a at body the smallest dimension of which is smaller than one quarter of the smallest outer dimension of one of the pole surfaces.
  • the magnet is made of a solid flat disc and one or both ferromagnetic parts substantially touch(es) the outer edge of the magnet, the operative surfaces of the air-gap being formed in part by the outer edge of the magnet.
  • Fig. 1 shows a disc-shaped permanent magnet 1, which is magnetized in the direction of the arrow.
  • the two pole surfaces 2 and 3 are each adjacent a ferromagnetic (soft iron) part 4 and 5 respectively.
  • the disc 1 has a cylindrical aperture 6, in which is introduced a stud 7 of ferromagnetic material, in which the path of the lines of force is parallel to the direction of the lines of force in the magnet and which is secured to the ferromagnetic part 4.
  • the ferromagnetic portion 7 is arranged at a distance 8 from the magnet 1, which is smaller than half, preferably smaller than one quarter the length 9 of the magnet, for example, equal to the width of the airgap 10.
  • the airgap l0 is annular and is located at least in the proximity of the edge 11 of the magnet 1 and may even be adjacent this edge.
  • the coil 12 secured to a core 13 of an electrodynamic loudspeaker is arranged in the airgap 10.
  • the assembly is very compact, since the stud 7 is at a very small distance 8 from the magnet, so that the clearance space is restricted. It has been found that the two disc-shaped parts 4 and 5 may have a smaller outer diameter than the magnet 1, without a reduction of the field in the airgap.
  • the stray field is materially smaller than with that of Fig. l, since the airgap 10 is formed at the outer edge of the magnet 1 and no central aperture 6 is provided and since the straw field (shown in broken lines) occurring at the outer edge 14 of the magnet 1 (Fig. 1) owing to the small length of the magnet 1 which stray field is not used effectively, is with the construction shown in Fig. 2 concentrated for a large part in the airgap 10 due to the presence of the annular lip on the ferromagnetic part 4 and is thus used effectively.
  • the embodiment shown in Fig. 2 may have a limitation in that the annular airgap 10 has a large diameter, since the latter is determined by the diameter of the magnet 1. This limitation does not apply to the embodiment shown in Fig. l.
  • FIG. 3 A modification of the embodiment shown in Fig. 2 is shown in Fig. 3, in which the soft iron plate 5 has a larger diameter than the magnet 1, the airgap still being in the proximity of the magnet. Referring to Fig. 4, the airgap is provided intermediate the plane surfaces of the magnet 1.
  • FIG. 5 a modification of the embodiment shown in Fig. l, in which the central stud 7 is practically adjacent the magnet 1, without producing appreciably losses and Fig. 6 shows a further modification.
  • Fig. 7 shows a modification of the embodiment shown in Fig. 2, in which part of the soft iron surrounding the magnet is in contact with the magnet and Figs. 8 and 9 show similar modifications of the embodiments shown in Figs. 3 and 4, in which substantially all the stray field is concentrated in the airgap and in which the construction has the maximum degree of compactness, so that no clearance space is left.
  • the operative surfaces of the airgap 10 are in part bounded by a surface of the magnet 1, so that again reduction of the stray field outside the airgap is obtained.
  • Fig. 10 shows a further embodiment in which, in spite of the fact that the soft iron part surrounding the magnet even extends beyond the pole surface 3, no magnetic shortcircuit occurs.
  • the airgap 10 is in part bounded by a surface of the magnet.
  • Fig. l1 shows a U-shaped magnetic circuit, in which the soft iron part 11 is made in one piece and is adjacent the lower pole surface 2, whilst the airgap is formed between the part 13 and the pole surface 3.
  • a system may, for example, be used as a braking magnet for a Ferraris meter.
  • FIG. 12 A modification of this embodiment of Fig. l1 is shown in Fig. 12, in which the airgap is provided between two permanent magnets 14 and 15.
  • the airgap is bordered by an entire pole surface (Fig. 11) and by two pole surfaces (Fig. l2).
  • a simple magnetic filter for example, an oil filter, may be obtained by combining a number of the co-axial circuits shown in Figs. 8, 9 l1 and 12.
  • a magnete circuit having at least one air-gap therein comprising a ferromagnetic part having a high permeability and a substantially fiat thin permanent magnet having a smaller dimension in a given direction than dimensions at right angles thereto and opposed flat faces extending at right anges to said given direction.
  • said magnet being magnetized along an axis parallel to said given direction thereby producing magnetic poles on its fiat faces ⁇ said magnet consisting essentially of non-cubic crvtals of a material selected from the group consisting of MO-6Fe2O3 and MFeiQOzv, M being at least one of the metals selected from the group consisting of barium, strontium and lead, said material having a coercivity of at least 750 Oersted and a low remanence and a permeability of less than 2, said fiat faces having a given dimension at right angles to said given direction which is larger than any other dimension at right angles to said given direction, said smaller dimension in said given direction being smaller than one-quarter of the largest dimension of the fiat faces, said ferromagnetic part having a portion abutting a face of said magnet and another portion extending parallel to said given direction and spaced from said magnet a distance which is smaller than onehalf of said smaller dimension, said air-gap being located at the end of said other portion of said fer
  • a magnetic circuit having at least one air-gap therein comprising a ferromagnetic part having a high permeability and a substantially fiat thin permanent magnet having a smaller dimension in a given direction than dimensions at right angles thereto and opposed flat faces extending at right angles to said given direction, said magnet being magnetized along an axis parallel to said given direction thereby producing magnetic poles on its fiat faces, said magnet consisting essentially of non-cubic crystals of a material selected from the group consisting of MO6Fe2O3 and MFeisOzv, M being at least one of the metals selected from the group consisting of barium, strontium, and lead, said material having a coercivity of at least 750 Oersted and a low remanence and a permeability of less than 2, said flat faces having a given dimension at right angles to said given direction which is larger than any other dimension at right angles to said given direction, said smaller dimension in said given direction being smaller than one-quarter of the largest dimension of the fiat faces, said flat
  • a magnetic circuit having at least one air-gap therein comprising a pair of ferromagnetic parts each having a high permeability and a substantially flat thin permanent magnet having a smaller dimension in a given direction than dimensions at right angles thereto and opposed flat faces extending at right angles to said given direction, said magnet being magnetizcd along an axis parallel to said given direction thereby producing magnetic poles on its fiat faces, said magnet consisting essentially of noncubic crystals of a material selected from the group consisting of MO6Fe2O3 and MFeisOzi, M being at least one of the metals selected from the group consisting of barium, strontium and lead, said material having a coercivity of at least 750 Oersted and a low remanence and a permeability of less than 2, said fiat faces having a given dimension at right angles to said given direction which is larger than any other dimension at right angles to said given direction, said smaller dimension in said given direction being smaller than one-quarter of the largest dimension of the fiat faces
  • a magnetic circuit as claimed in claim 3 in which said other portion of said ferromagnetic parts extending parallel to said given direction abuts said permanent magnet.
  • a magnetic circuit having at least one air-gap therein comprising a pair of ferromagnetic parts each having a high permeability and a substantially fiat thin permanent magnet having a smaller dimension in a given direction than dimensions at right angles thereto and opposed flat faces extending at right angles to said given direction, said magnet being magnetized along an axis parallel to said given direction thereby producing magnetic poles on its fiat faces, said magnet consisting essentially of non-cubic crystals of a material selected from the group consisting of MO-6FezOs and MFeiOzi, M being at least one of the metals selected from the group consisting of barium, strontium and lead, said material having a coercivity of at least 750 Oersted and a low remanence and a permeability of less than 2, said fiat faces having a given dimension at right angles to said given direction which is larger than any other dimension at right angles to said given direction, said smaller dimension in said given direction being smaller than onequarter of the largest dimension of the fiat faces, one of
  • a magnetic circuit as claimed in claim 5 in which said other portion of said cup-shaped member abuts said magnet.
  • a magnetic circuit having at least one air-gap therein comprising a pair of ferromagnetic parts each having a high permeability and a substantially at thin permanent magnet having a central aperture and a smaller dimension in a given direction than dimensions at right angles thereto and opposed flat faces extending at right angles to said given direction, said magnet being magnetized along an axis parallel to said given direction thereby producing magnetic poles on its tlat faces, said magnet consisting essentially of non-cubic crystals of a material selected from the group consisting of MO'FezOs and MFe1sO27, M being at least one of the metals selected from the group consisting of barium, strontium and lead, said material having a coercivity of at least 750 Oersted and a low remanence and a permeability of less than 2, said flat faces having a given dimension at right angles to said given direction which is larger than any other dimension at right angles to said given direction, said smaller dimension in said given directionV being smaller than one-quarter of the largest dimension
  • a magnetic circuit as claimed in claim 7 in which said other projection portion of said one ferromagnetic part abuts said magnet.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
  • Hard Magnetic Materials (AREA)
US264984A 1951-04-23 1952-01-04 Magnetic circuit comprising a ferromagnetic part having high permeability and a substantially flat, thin permanent magnet Expired - Lifetime US2698917A (en)

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NL313462X 1951-04-23

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BE (1) BE505468A (pt)
CH (1) CH313462A (pt)
FR (1) FR1041525A (pt)
GB (1) GB708136A (pt)

Cited By (32)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2778803A (en) * 1953-02-06 1957-01-22 Aerovox Corp Magnetically hard materials
US2920253A (en) * 1956-03-06 1960-01-05 Engineered Products Company Magnetic catch
US2923783A (en) * 1957-06-17 1960-02-02 Stanley F White Electro-acoustical transducer
US2943246A (en) * 1956-02-28 1960-06-28 Howard C Riordan Magnetic detachable holding device
US2966106A (en) * 1957-01-05 1960-12-27 Schneider Co Optische Werke Magnetic system for producing arcuate motions
US2972745A (en) * 1956-04-17 1961-02-21 Hamilton Watch Co Electric wrist watch
US3000016A (en) * 1960-03-03 1961-09-19 Stockwell A Ridge Magnetic securing means
US3022398A (en) * 1959-05-15 1962-02-20 Fluidwick Company Inc Electric control device
US3034320A (en) * 1960-03-21 1962-05-15 Coro Inc Magnetic earring construction including means to concentrate the magnetic force
US3049636A (en) * 1959-06-22 1962-08-14 Chrysler Corp Magnetically driven devices
US3071939A (en) * 1960-05-27 1963-01-08 Coro Inc Magnetic earring with slidably pivoted clamp members
US3090107A (en) * 1958-07-24 1963-05-21 Sylvania Electric Prod Method of making a permanent magnet
US3095525A (en) * 1958-01-20 1963-06-25 Crucible Steel Co America Permanent magnet assembly
US3134057A (en) * 1960-07-11 1964-05-19 Sumitomo Metal Ind Magnetic circuit for the deflection of flux leakage
US3140430A (en) * 1960-07-15 1964-07-07 Radio Frequency Lab Inc Standard magnet structure with predetermined air-gap
US3173067A (en) * 1962-03-22 1965-03-09 Westinghouse Electric Corp Temperature-compensated permanent-magnet devices
US3257586A (en) * 1960-03-03 1966-06-21 Magnetfabrik Bonn Gewerkschaft Flexible permanent magnet and composition
US3304527A (en) * 1965-04-26 1967-02-14 Ibm Magnetic holding and aligning device
US3413551A (en) * 1964-06-22 1968-11-26 Westinghouse Electric Corp Induction devices having low side thrust
US3750068A (en) * 1969-11-28 1973-07-31 Honeywell Inc Magnet actuating arrangement for a magneto sensitive device and method for providing
US4077242A (en) * 1976-12-15 1978-03-07 Sedley Bruce S Metal magnetic key
US4857841A (en) * 1987-12-29 1989-08-15 Eaton Corporation Proximity detector employing magneto resistive sensor in the central magnetic field null of a toroidal magnet
US4911640A (en) * 1987-04-30 1990-03-27 Comadur Sa Magnetic assembly means
US4941235A (en) * 1988-10-14 1990-07-17 Application Art Laboratories Co., Ltd. Magnetic lock closure device
US4991270A (en) * 1988-01-27 1991-02-12 Application Art Laboratories Co., Ltd. Magnetic lock closure
US5125134A (en) * 1985-12-27 1992-06-30 Tamao Morita Magnetic fastener
US5751828A (en) * 1994-05-30 1998-05-12 Matsushita Electric Industrial Co., Ltd. Magnetic circuit unit for loud-speaker and method of manufacturing the same
US6269168B1 (en) * 1998-03-25 2001-07-31 Sony Corporation Speaker apparatus
US20020054690A1 (en) * 2000-11-08 2002-05-09 New Transducers Limited Loudspeaker driver
US20040005074A1 (en) * 2002-07-08 2004-01-08 Sun Technique Electric Co., Ltd. Hi-fi tweeter
US8358801B2 (en) 2007-02-12 2013-01-22 Robert Katz Magnetic circuit for electrodynamic moving voice coil actuators
US10978230B2 (en) * 2018-11-07 2021-04-13 Livivos Inc. Magnet arrangement for producing a field suitable for NMR in a concave region

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1011466B (de) * 1955-06-18 1957-07-04 Philips Patentverwaltung Magnetsystem fuer elektroakustische Wandler
DE1020098B (de) * 1955-10-03 1957-11-28 Stepper & Co Bremsmagnetanordnung fuer eine Laeuferscheibe, insbesondere von Elektrizitaetszaehlern

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB406086A (en) * 1932-11-03 1934-02-22 Darwins Ltd Improvements in or relating to permanent magnets
FR867783A (fr) * 1939-11-24 1941-11-27 Thomson Houston Comp Francaise Perfectionnements aux aimants permanents
US2400662A (en) * 1941-05-27 1946-05-21 Int Standard Electric Corp Telephone transmitter and receiver

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB406086A (en) * 1932-11-03 1934-02-22 Darwins Ltd Improvements in or relating to permanent magnets
FR867783A (fr) * 1939-11-24 1941-11-27 Thomson Houston Comp Francaise Perfectionnements aux aimants permanents
US2400662A (en) * 1941-05-27 1946-05-21 Int Standard Electric Corp Telephone transmitter and receiver

Cited By (37)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2778803A (en) * 1953-02-06 1957-01-22 Aerovox Corp Magnetically hard materials
US2943246A (en) * 1956-02-28 1960-06-28 Howard C Riordan Magnetic detachable holding device
US2920253A (en) * 1956-03-06 1960-01-05 Engineered Products Company Magnetic catch
US2972745A (en) * 1956-04-17 1961-02-21 Hamilton Watch Co Electric wrist watch
US2966106A (en) * 1957-01-05 1960-12-27 Schneider Co Optische Werke Magnetic system for producing arcuate motions
US2923783A (en) * 1957-06-17 1960-02-02 Stanley F White Electro-acoustical transducer
US3095525A (en) * 1958-01-20 1963-06-25 Crucible Steel Co America Permanent magnet assembly
US3090107A (en) * 1958-07-24 1963-05-21 Sylvania Electric Prod Method of making a permanent magnet
US3022398A (en) * 1959-05-15 1962-02-20 Fluidwick Company Inc Electric control device
US3049636A (en) * 1959-06-22 1962-08-14 Chrysler Corp Magnetically driven devices
US3000016A (en) * 1960-03-03 1961-09-19 Stockwell A Ridge Magnetic securing means
US3257586A (en) * 1960-03-03 1966-06-21 Magnetfabrik Bonn Gewerkschaft Flexible permanent magnet and composition
US3034320A (en) * 1960-03-21 1962-05-15 Coro Inc Magnetic earring construction including means to concentrate the magnetic force
US3071939A (en) * 1960-05-27 1963-01-08 Coro Inc Magnetic earring with slidably pivoted clamp members
US3134057A (en) * 1960-07-11 1964-05-19 Sumitomo Metal Ind Magnetic circuit for the deflection of flux leakage
US3140430A (en) * 1960-07-15 1964-07-07 Radio Frequency Lab Inc Standard magnet structure with predetermined air-gap
US3173067A (en) * 1962-03-22 1965-03-09 Westinghouse Electric Corp Temperature-compensated permanent-magnet devices
US3413551A (en) * 1964-06-22 1968-11-26 Westinghouse Electric Corp Induction devices having low side thrust
US3304527A (en) * 1965-04-26 1967-02-14 Ibm Magnetic holding and aligning device
US3750068A (en) * 1969-11-28 1973-07-31 Honeywell Inc Magnet actuating arrangement for a magneto sensitive device and method for providing
US4077242A (en) * 1976-12-15 1978-03-07 Sedley Bruce S Metal magnetic key
US5125134A (en) * 1985-12-27 1992-06-30 Tamao Morita Magnetic fastener
US4911640A (en) * 1987-04-30 1990-03-27 Comadur Sa Magnetic assembly means
US4857841A (en) * 1987-12-29 1989-08-15 Eaton Corporation Proximity detector employing magneto resistive sensor in the central magnetic field null of a toroidal magnet
US4991270A (en) * 1988-01-27 1991-02-12 Application Art Laboratories Co., Ltd. Magnetic lock closure
US4941235A (en) * 1988-10-14 1990-07-17 Application Art Laboratories Co., Ltd. Magnetic lock closure device
US5751828A (en) * 1994-05-30 1998-05-12 Matsushita Electric Industrial Co., Ltd. Magnetic circuit unit for loud-speaker and method of manufacturing the same
US6269168B1 (en) * 1998-03-25 2001-07-31 Sony Corporation Speaker apparatus
US20020054690A1 (en) * 2000-11-08 2002-05-09 New Transducers Limited Loudspeaker driver
US7372968B2 (en) * 2000-11-08 2008-05-13 New Transducers Limited Loudspeaker driver
US20040005074A1 (en) * 2002-07-08 2004-01-08 Sun Technique Electric Co., Ltd. Hi-fi tweeter
US8358801B2 (en) 2007-02-12 2013-01-22 Robert Katz Magnetic circuit for electrodynamic moving voice coil actuators
US10978230B2 (en) * 2018-11-07 2021-04-13 Livivos Inc. Magnet arrangement for producing a field suitable for NMR in a concave region
US20210233692A1 (en) * 2018-11-07 2021-07-29 Livivos Inc. Magnet arrangement for producing a field suitable for nmr in a concave region
US11587707B2 (en) * 2018-11-07 2023-02-21 Livivos Inc. Magnet arrangement for producing a field suitable for NMR in a concave region
US20230360832A1 (en) * 2018-11-07 2023-11-09 Livivos Inc. Magnet arrangement for producing a field suitable for nmr in a concave region
US11887779B2 (en) * 2018-11-07 2024-01-30 Livivos Inc. Magnet arrangement for producing a field suitable for NMR in a concave region

Also Published As

Publication number Publication date
FR1041525A (fr) 1953-10-23
BE505468A (pt)
CH313462A (de) 1956-04-15
GB708136A (en) 1954-04-28

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