US2895092A - Magnetic circuit - Google Patents

Magnetic circuit Download PDF

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Publication number
US2895092A
US2895092A US653119A US65311957A US2895092A US 2895092 A US2895092 A US 2895092A US 653119 A US653119 A US 653119A US 65311957 A US65311957 A US 65311957A US 2895092 A US2895092 A US 2895092A
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United States
Prior art keywords
magnet
magnetic
auxiliary
fieldstrength
stray
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Expired - Lifetime
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US653119A
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English (en)
Inventor
Cluwen Johannes Meijer
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • 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
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0273—Magnetic circuits with PM for magnetic field generation
    • H01F7/0289—Transducers, loudspeakers, moving coil arrangements
    • 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

  • FIG.4 MAGNETIC CIRCUIT Filed April 16, 1957 Fl GJI awn FIG.4
  • This invention relates to magnetic circuits comprising a permanent main magnet, one or more permanent auxiliary magnets made from different material, and a softmagnetic part for the transmission of the magnetic flux produced by the permanent magnets to an operating or active point.
  • Such circuits are used, for example, in loudspeakers and in magnetic electron lenses respectively, the field set up at the operating point acting upon a loudspeaker moving coil and an electron beam to be focussed, respectively.
  • the invention can generally also be used in bias magnetisation arrangements.
  • This object can be realized by compensating this stray field by a field of the same strength originating from at least one auxiliary magnet made from a different permanent magnet material, having a diiierent operative fieldstrength and being arranged at at least one point at which a comparatively strong stray flux is produced.
  • a magnetic circuit in accordance with the invention is characterized in that the main magnet and the auxiliary magnets are magnetized perpendicularly to each other, and in that the materials from which the magnets are made are different, in the sense that the fieldstrength of the main magnet and the auxiliary magnet respectively at that point of the BH-curve or magnetization characteristic-where the product of the induction B and the fieldstrength H becomes maximum-(BI D is essentially different, and that the fieldstrength of the auxiliary magnet corresponding with its (BH) -product is substantially the. same as the stray fieldstrength produced by the mainmagnet at theplace of the auxiliary magnet,
  • auxiliary magnet in which the auxiliary magnet is arranged so that the stray flux produced by the main magnet is also reduced.
  • this compensation which can only be partial, does not provide any further increase of the effective flux.
  • Fig. 1 shows a magnetic circuit for use in a loudspeaker
  • Fig. 2 is a modification of the circuit shown in Fig. 1,
  • Fig. 3 shows a magnetic circuit for a loudspeaker of different design
  • Fig. 4 shows a third embodiment of such a magnetic circuit
  • Fig. 5 shows a magnetic circuit for an electron lens.
  • the loudspeaker magnetic circuit shown in Fig. 1 comprises a cylindrical axially magnetised permanent main magnet 1 made of a material having a high magnetic output but a comparatively low operative fieldstrength. Use may, for example, be made of the material known under the trade name Ticonal which has an operative fieldstrength H of 500 oersted and an operative induction B of 10,000 gauss.
  • the magnet 1 is provided with a soft magnetic pole hood 2 and a cylindrical soft magnetic shell 3 between which an airgap 4 is produced in which a loudspeaker moving coil can be arranged.
  • stray field is produced, which, particularly in the proximity of the airgap 4, may materially exceed the operative field strength produced within the magnet 1.
  • the provision of an auxiliary permanent magnet made of a similar material would give little advantage, since the operating point of this auxiliary permanent magnet would be highly unfavourable, for, as is well-known, a permanent magnet has its greatest eifect when it is operated at that point of the BH-curve where its energy product is at its peak.
  • an annular radially magnetized auxiliary magnet 5 made of a magnetically stronger material, for example, Ferroxdure, having a fieldstrength of about 1250 oersted and an induction of about 1700 gauss at the operating point Where the product BH of the induction and the fieldstrength becomes a maximum.
  • the auxiliary magnet 5 is operated at substantially its maximum magnetic output, that is to say at its peak energy product, in a manner such that the fieldstrength of the auxiliary magnet 5 corresponding with its (BI-D -product is substantially the same as the stray fieldstrength produced by the main magnet 1 at the place of the auxiliary magnet 5.
  • the field of this auxiliary magnet 5 is added to the field of the main magnet 1 and provides a real increase of, say, from 20% to 30% of the effective field in the airgap 4, and hence of the effective flux.
  • the gain in flux may be eliminated while maintaining the same magnetic potential byan increase in the magnetic reluctance of the main magnet 1.
  • the main magnet 1 is accordingly prolonged and can be made substantially more slender as is shown in Fig. 2. Consequently, a larger space becomes available for the auxiliary magnet 5 in Fig. 2 so that it may be made from Ferroxdure having a field strength of 1000 oersted and an induction of 2200 gauss at its operating point and hence provides an even greater contribution to the effective flux.
  • Fig. 3 shows a loudspeaker magnetic circuit comprising a disc-shaped axially magnetised Ferroxdure main magnet 1 and a soft magnetic part constituted by discs a and 10 and by a central cylindrical core 11 which together with the disc 9 bounds the airgap 4. Between the outer circumferences of the discs 9 and 10 a considerable stray flux is produced, however, its fieldstrength is less than the operative fieldstrength of the main magnet 1.
  • auxiliary magnets 12 and 13 By the provision of two annular radially magnetised auxiliary magnets 12 and 13, made for example from Ticonal', the effective field produced in the air-gap 4 is increased. At the same time the circumferential stray field of the main magnet 1 is partially compensated for by the magnets l2- and 13, so that there is less interference inelectronic apparatus arranged in the proximity of the circuit. Since the auxiliary magnets 12 and 13 lie in an open magnetic circuit, use must be made of a permanent magnet material having an operative fieldstrength which is substantially equal to the total sum of the stray fieldstrength and the natural demagnetisation fieldstrength produced by the cylindrical circumferences. If required, this latter step can be dispersed with or can be assisted by the provision of an annular auxiliary magnet encircling the main magnet 1 and being magnetized in the same direction but having a lower operative field strength.
  • the main magnet 1 of higher operative fieldstrength which may be made from Ferroxdure, is tubular and magnetized radially.
  • the soft-magnetic parts comprise a rod-shaped core 11 and a cylindrical shell 3 the upper ends of which are spaced apart to form an air-gap 4.
  • the stray flux at their lower ends can be materially reduced by the provision of an annular and/or a rod-shaped axially magnetised magnet 16 and/ or 17 respectively of lower operative fieldstrength. (Owing to the lesser concentration of lines of magnetic force, the magnet 16 can usually be dispensed with.)
  • auxiliary magnet 20 of the magnetic electron lens shown in Fig. 5 comprises two disc-shaped main magnets 21 and 22 axially magnetised in opposite directions and soft-magnetic discshaped parts 23, 24 and 25, between which an electrontocussing field is set up along the optical axis 26.
  • the discs 23 and 25 have equal magnetic potentials and consequently do not give rise to a mutual stray flux.
  • stray flux is produced from the discs 23 and 25 to the disc 24, however, this stray flux is at least partially compensated for at the point of highest concentration of the lines of magnetic force by means of the auxiliary magnet 20 having a lower operative fieldstrength.
  • Ferroxdure materials are oxidic permanent magnetic materials, the constituents essential to the permanent magnetic properties of which are compounds having a hexagonal crystal structure and a chemical formula M Ca 0.6Fe O in which 0.6 x l and in which M stands for one or more of the metals Ba (barium), Sr (strontium) and Pb (lead), these materials being more amply described in US. Patent No. 2,762,777.
  • a magnetic circuit comprising main and auxiliary permanent magnets arranged so that their magnetization directions are substantially at right angles to one another and a soft magnetic member for carrying the flux of the magnets to an active point, said main and auxiliary magnets being composed of materials having magnetization characterics such that their field strengths at which their energy products are a maximum are different, said auxiliary magnet being located at a position in the circuit where the sum of its own demagnetizing field strength and the stray field strength produced at that position by the main magnet substantially matches the field strength of the auxiliary magnet at which its energy product is a maximum.
  • a magnetic circuit comprising main and auxiliary permanent magnets arranged so that their magnetization directions are substantially at right angles to one another and a soft magnetic member for carrying the flux of the magnets to an active point, said main and auxiliary magnets being composed of materials having magnetization characteristics such that their field strengths at which their energy products are a maximum are different, said auxiliary magnet being located at a position in the circuit where the sum of its own demagnetizing field strength and the stray field strength produced at that position by the main magnet substantially matches the field strength of the auxiliary magnet at which its energy product is a maximum, said auxiliary magnet having a higher field strength at its operating point than that of the main magnet.
  • a magnetic circuit comprising main and auxiliary permanent magnets arranged so that their magnetization directions are substantially at right angles to one another and a soft magnetic member for carrying the flux of the magnets to an active point, said main and auxiliary magnets being composed of materials having magnetization characteristics such that their field strengths at which their energy products are a maximum are different, said auxiliary magnet being located at a position in the circuit where the sum of its own demagnetizing field strength and the stray field strength produced at that position by the main magnet substantially matches the field strength of the auxiliary magnet at which its energy product is a maximum, said auxiliary magnet having a lower field strength at its Operating point than that of the main magnet.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • Hard Magnetic Materials (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
US653119A 1956-04-18 1957-04-16 Magnetic circuit Expired - Lifetime US2895092A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE860439X 1956-04-18

Publications (1)

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US2895092A true US2895092A (en) 1959-07-14

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US653119A Expired - Lifetime US2895092A (en) 1956-04-18 1957-04-16 Magnetic circuit

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US (1) US2895092A (fr)
BE (1) BE556726A (fr)
FR (1) FR1171263A (fr)
GB (1) GB860439A (fr)

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3120631A (en) * 1960-11-14 1964-02-04 Exxon Research Engineering Co Electromagnet for supporting and dropping weights
US3134057A (en) * 1960-07-11 1964-05-19 Sumitomo Metal Ind Magnetic circuit for the deflection of flux leakage
US3147350A (en) * 1961-12-18 1964-09-01 Lockheed Aircraft Corp Magnetically operated reed switch
US3198254A (en) * 1962-05-08 1965-08-03 Baker Oil Tools Inc Method and apparatus for completing wells
US3454913A (en) * 1966-11-14 1969-07-08 Eriez Mfg Co Permanent magnetic pulley
US3478289A (en) * 1968-02-12 1969-11-11 Robert A Parnell Permanent magnet assembly for a loudspeaker assembly
US3737822A (en) * 1970-06-10 1973-06-05 Magnetics Int Inc Magnetic separator
FR2455792A1 (fr) * 1979-04-30 1980-11-28 Minnesota Mining & Mfg Dispositif electromagnetique, notamment pour un relais a transformateur a basse tension
US4363639A (en) * 1981-03-09 1982-12-14 Iowa State University Research Foundation, Inc. Gas trap for removing atmospheric pollutants and method of operation
US4492827A (en) * 1983-01-31 1985-01-08 Ibuki Kogyo Co., Ltd. Horn speaker with reduced magnetic flux leakage
US4549155A (en) * 1982-09-20 1985-10-22 The United States Of America As Represented By The United States Department Of Energy Permanent magnet multipole with adjustable strength
US4647887A (en) * 1984-12-24 1987-03-03 The United States Of America As Represented By The Secretary Of The Army Lightweight cladding for magnetic circuits
US5142260A (en) * 1991-03-08 1992-08-25 Harman International Industries, Incorporated Transducer motor assembly
US5380430A (en) * 1992-07-24 1995-01-10 Overton; James M. Magnetizing apparatus for treatment of fluids
US5409236A (en) * 1993-12-23 1995-04-25 Therrien; Joel M. Magnetic game or puzzle and method for making same
US6573817B2 (en) 2001-03-30 2003-06-03 Sti Optronics, Inc. Variable-strength multipole beamline magnet
EP1919253A1 (fr) * 2006-10-31 2008-05-07 Sanyo Electric Co., Ltd. Transducteur électroacoustique

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1130517B (de) * 1959-12-22 1962-05-30 Baermann Max Magnetanordnung fuer Grosswinkel-Drehspulmessinstrumente
JP4159184B2 (ja) * 1999-06-25 2008-10-01 株式会社デルタツーリング 磁気ばね
US7705702B2 (en) 2006-08-08 2010-04-27 Selex Galileo Ltd Actuator
GB2440768A (en) * 2006-08-08 2008-02-13 Selex Sensors & Airborne Sys Magnet assembly for moving coil actuator

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2398653A (en) * 1942-10-15 1946-04-16 Gen Electric Magnetic structure

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2398653A (en) * 1942-10-15 1946-04-16 Gen Electric Magnetic structure

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3134057A (en) * 1960-07-11 1964-05-19 Sumitomo Metal Ind Magnetic circuit for the deflection of flux leakage
US3120631A (en) * 1960-11-14 1964-02-04 Exxon Research Engineering Co Electromagnet for supporting and dropping weights
US3147350A (en) * 1961-12-18 1964-09-01 Lockheed Aircraft Corp Magnetically operated reed switch
US3198254A (en) * 1962-05-08 1965-08-03 Baker Oil Tools Inc Method and apparatus for completing wells
US3454913A (en) * 1966-11-14 1969-07-08 Eriez Mfg Co Permanent magnetic pulley
US3478289A (en) * 1968-02-12 1969-11-11 Robert A Parnell Permanent magnet assembly for a loudspeaker assembly
US3737822A (en) * 1970-06-10 1973-06-05 Magnetics Int Inc Magnetic separator
US4321652A (en) * 1979-04-30 1982-03-23 Minnesota Mining And Manufacturing Co. Low voltage transformer relay
FR2455792A1 (fr) * 1979-04-30 1980-11-28 Minnesota Mining & Mfg Dispositif electromagnetique, notamment pour un relais a transformateur a basse tension
US4363639A (en) * 1981-03-09 1982-12-14 Iowa State University Research Foundation, Inc. Gas trap for removing atmospheric pollutants and method of operation
US4549155A (en) * 1982-09-20 1985-10-22 The United States Of America As Represented By The United States Department Of Energy Permanent magnet multipole with adjustable strength
US4492827A (en) * 1983-01-31 1985-01-08 Ibuki Kogyo Co., Ltd. Horn speaker with reduced magnetic flux leakage
US4647887A (en) * 1984-12-24 1987-03-03 The United States Of America As Represented By The Secretary Of The Army Lightweight cladding for magnetic circuits
US5142260A (en) * 1991-03-08 1992-08-25 Harman International Industries, Incorporated Transducer motor assembly
US5380430A (en) * 1992-07-24 1995-01-10 Overton; James M. Magnetizing apparatus for treatment of fluids
US5409236A (en) * 1993-12-23 1995-04-25 Therrien; Joel M. Magnetic game or puzzle and method for making same
US6573817B2 (en) 2001-03-30 2003-06-03 Sti Optronics, Inc. Variable-strength multipole beamline magnet
EP1919253A1 (fr) * 2006-10-31 2008-05-07 Sanyo Electric Co., Ltd. Transducteur électroacoustique

Also Published As

Publication number Publication date
FR1171263A (fr) 1959-01-23
GB860439A (en) 1961-02-08
BE556726A (fr)

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