US3521208A - Reluctance adjustment in electromagnetic devices - Google Patents

Reluctance adjustment in electromagnetic devices Download PDF

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Publication number
US3521208A
US3521208A US730082A US3521208DA US3521208A US 3521208 A US3521208 A US 3521208A US 730082 A US730082 A US 730082A US 3521208D A US3521208D A US 3521208DA US 3521208 A US3521208 A US 3521208A
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reed
flux
gap
reluctance
armature
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Hugh S Knowles
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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
    • H04R11/00—Transducers of moving-armature or moving-core type
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K33/00—Motors with reciprocating, oscillating or vibrating magnet, armature or coil system
    • H02K33/02—Motors with reciprocating, oscillating or vibrating magnet, armature or coil system with armatures moved one way by energisation of a single coil system and returned by mechanical force, e.g. by springs

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  • An electro-magnetic transducer comprising a magnet, a pole piece fiux-conductively engaging each pole of the magnet, an elongated armature, means clamping one end of said armature in spaced relationship to the pole pieces, there being a bending line
  • This invention pertains to the provision of improvements in electromagnetic devices such as transducers employing an armature movable relative to polarized pole pieces, and more particularly, but not exclusively, to that class of transducers used as receivers and microphones in heading aids, and the like, in Which the armature may be a long thin magnetic reed reacting relative to pole pieces conducting the main polarizing flux.
  • One of the principal objects of the invention is the provision of a method and means for adjusting the reluctance at certain gaps in the magnetic circuit in such transducers for the purpose of improving the efficiency and response characteristics of such devices by eliminating troublesome magnetic flux acting along the length of the armature reed, and also by adjusting certain irnbalances in gross polarizing fiux at said gaps.
  • More particular objects are the provision of sim-ple but highly effective paramagnetic adjusting members especially effective and practical in conjunction with miniaturized equipment and situated relative to certain fixed gap portions of a magnetic circuit for transducers of the class described, and characterized in that these members may be moved, as by bending, relative to pole pieces to produce changes in effective reluctance at fixed and working gaps so that the vibratory armature reed may be freed of unwanted flux conditions.
  • This disclosed adjusting means may be singular or plural in number; may
  • FIG. 1 is a magnified top plan View of an improved driver or generator unit of a type adapted for use as a heading aid transducer;
  • FIG. 2 is a greatly enlarged vertical section through a complete transducer, specifically a receiver, as it would appear looking in the direction of lines 2-2 of a driver unit such as shown in FIG. l
  • FIG. 3 is a horizontal section taken to reduced scale along lines 3-3 of FIG. 2;
  • FIG. 4 is a schematic diagram illustrating certain magnetic-circuit conditions relating to the devices shown in FIGS. l to 3;
  • FIG. 5 is a transverse section of a modified form of the pole-piece structure shown in FIG. 2 as would be seen at lines X-X of the latter, parts being shown in elevation;
  • FIG. 6 is a schematic representation of a transverse sectional detail of the clamp gap region of a modified form of magnetic-circuit adjusting means
  • FIG. 6A is a schematic longitudinal plan detail of the armature means employed in the arrangement of FIG. 6, i.e., taken on the line 6A-6A of FIG. 6;
  • FIG. 7 is a schematic representation of a transverse sectional detail of the clamp gap region of another modified form of the invention wherein the tabs are an integral part of the reed;
  • FIG. 7A is a schematic longitudinal plan detail of the armature means employed in FIG. 7, i.e., taken on the line 7A-7A of FIG. 7, and showing the inside edge of the tab positions spaced from the inside, transverse clamping edge of the fixed gap;
  • FIG. 8 is a schematic transverse sectional detail depicting the clamp gap region of another modified form of magnetic-circuit structure and adjusting means therefor;
  • FIG. 9 is a schematic vertical section through parts of a modified transducer motor employing a single corrector for adjusting longitudinal reed and pole piece flux and gross gap flux imbalances simultaneously;
  • FIG. 10 is a schematic diagram of the magnetic circuit for a construction of the class shown in FIGS. 2 and 4 and serving to illustrate theoretically a circulating or longitudinal flux condition in a reed;
  • FIG. 11 is a partial sectional detail through a transducer similar to FIG. 2, but showing changes required where the transducer is utilized as a microphone.
  • the transducer depicted in FIGS. 1 and 2 is of a type intended for use as a receiver (or, with slight modification, as a microphone as in FIG. l1) in a hearing aid, and consists essentially of a coil 20 Wound solenoidfashion on a suitable insulating bobbin 21 and secured between juxtaposed pole pieces 22 'and 23, which are joined in assembly by screws 24 in the manner seen in FIG. 2, wherein the unit of FIG. l is shown secured within a housing 25 on the inner side of an outwardlyrecessed plate member 26 through which said screws are passed, and the recessed portion of which also serves as the basket for a diaphragm mentioned hereafter.
  • An elongated armature reed 27 is clamped at one end between the pole pieces and non-magnetic spacer means, such as brass washers 28W to extend freely for vibratile motion (vertically in FIG. 2) through the core of the coil with the free end of the reed movable in an air gap 29 formed ⁇ between said pole pieces by reason of the presence thereat of a nonmagnetic spacer 30.
  • non-magnetic spacer means such as brass washers 28W
  • a diaphragm 31 (FIG. 2) is suitably secured for vibration in the basket recess of Wall 26', and is drivingly connected to said armature or reed by means of a lightweight drive link 32 slotted transversely at its upper end to interfit snugly with the reed for vibratory displacement by the latter responsive to signal energy acting in coil 20, the working flux of which magnetizes the reed correspondingly, the reed in turn reacting in a polarized field existing across the working gap 29 owing to the provision of polarizing means, such as a pair of elongated transvers'ely magnetized, permanent magnets l33A, 33B,vse I cured- ⁇ between t-he-pole-piecesfonopposite sides of coil (FIG. 3).
  • polarizing means such as a pair of elongated transvers'ely magnetized, permanent magnets l33A, 33B,vse I cured- ⁇ between t-he-pole-piecesfonoppo
  • FIG. 4 a pair of polarized pole pieces A and B, and an armature reed -C- clamped at one end between magnetically inert (e.g. brass) spacers -S- (corresponding to washers 28W) creating a first pair of air gaps G1, G2 (which are called fixed or clamp gaps, because the reed is clamped therein, and are analogous to the gaps existing at 28 in FIG.
  • magnetically inert e.g. brass spacers -S-
  • all longitudinal flux along the armature is, in a manner of speaking, substantially balanced out, at least for the static or resting condition of the reed C-.
  • the permeability of the reed should be high'. High permeability is, however, associated with low saturation densities. To obtain distortion-free reproduction in a receiver the flux through the reed must be proportional to the signal current. This requires that the permeability of the reed be substantially constant for all signal currents. When high permeability materials are used it is therefore essential that there be substantially no flux through the reed when there is no signal current. This permits maximum signal-current amplitudes without distortion.
  • one of themajorobjects of the. present disclosures relates to the provision of 'a simple and highly effective method and means for adjusting a transducer or like device of the general chajracterdes:ribed,"either during or subsequent to vmanufacture, to achieve the aforesaid neutral or magnetically balanced condition4 of the armature reed -C- by making adjustments at"th ⁇ e fixed gaps G1, G2, calculated to render R1/R2 effectively equal to 12a/R4. .j
  • the method in one of its aspects provides for decreasin'g the reluctance at one or the other of the fixed gaps situated on opposite sides of the reed at its clamped end; the means for effectuatingthis method beingthe provision of a paramagnetic member 40, FIGS. ⁇ 1 to l3 (or -T-,'FIG. 4), which may be an integral part ofthe reed and which is an extension of the otherwise normal length thereof beyond the pole pieces at the'physica'l margins of the clamping gaps in a position of access to be bent out of the plane of the reed toward one or the other of the pole pieces, as indicated by the dotted-line positions of part 40 shown in FIGS. 2 and 4.
  • the effect of the various reluctance adjusting means described herein may be more clearly understood by considering the definition of reluctance.
  • the reluctance R l/ua where I is the length of the flux path, a is the arca perpendicular to the lines of uux through which the flux passes and u is the permeability of the material along the length l.
  • I is the length of the flux path
  • a is the arca perpendicular to the lines of uux through which the flux passes
  • u the permeability of the material along the length l.
  • the permeability of air and of what are herein described as non-magnetic metals, such as brass, copper and the like is unity.
  • the reluctance of gaps, or portions of the magnetic circuit in which air or nonmagnetic metals are the materials through whichthe flux flows, is l/a since u is unity. Since u is unity and independent of the number of lines of flux it follows that the reluctance of the gaps is independent of the number of lines of flux.
  • the effect f lengthening the armature reed 27 by adding the extension or tab 40 thereto can therefore be seen to reduce the reluctance of gaps G1 and G2 by adding to and extending the normal clamp gap area. If the tab is in the plane of the reed as shown in the cross hatched section in FIG. 2, this reduction is small because the flux path length from the reed to the pole pieces is long cornpared to length of the gap at the clamp surfaces. The latter gap length in the direction of the flux lines is determined by the thickness of a washer 28W. As the tab is bent toward one pole piece, the reluctance between the tab and pole piece decreases slowly at first and then rapidly as the gap length approaches zero. The reluctance from the tab to the other piece from which it is receding increases only slightly. The tab is most effective when it is close to a pole piece.
  • tab 40 can produce only a decrease in effective reluctance across the fixed gaps G1, G2 (FIG. 4); and corollary to this is the fact that tab 40 primarily effects only the elimination of longitudinal flux in the reed -C-.
  • Longitudinal flux is sometimes arbitrarily referred to as circulating flux, although strictly it does not circulate in the ordinary sense of the word; but this expression when used in connection with a magnetic circuit of the type described is intended to connote the ux which acts longitudinally along the reed due to imbalance from the causes described. This condition is portrayed in the analogous magnetic-circuit diagram of lFIG.
  • one flux path is represented by dotted line arrows as acting from gap G1-, into and along the reed and thence out of the reed again into gap G4, the latter gap in this sense being complementary to gap G1.
  • the dashadot arrow lines show the longitudinal or circulating flux as acting from gap G3 down into and along the reed in the opposite direction, thence out of the reed down into the complementary lower gap G2.
  • the modified tab construction depicted in FIGS. 6 and 6A is capable of manipulation for effecting correction of both kinds of imbalance.
  • the armature reed 50 has no longitudinal extension but is of normal length, that is, it has no tab 40 of a type projecting longitudinally of the reed beyond the geometric margins of the clamp gaps.
  • a thin magnetic shim 51 of preferably rectangular shape and pierced centrally, as at 52, to pass one of the mounting screws 24 for assembly with the reed at the clamp gap.
  • the shim 51 in the assembled condition shown schematically in FIG. 6, is clamped with the reed between a pair of non-magnetic spacers 28W which in turn are disposed between the upper and lower pole pieces 22, 23 in substantially the same fashion as described for the construction of FIGS. l to 3, the shim 51 having opposite sidewise or laterally-projecting tabs 51A, 51B, which can be bent upwardly or downwardly into various positions of adjustment, such as indicated by dotted lines in FIG. 6.
  • the so-called fixed gaps at 28 of G1, G2 are respectively influenced by bending thetabs 51A, 51B toward the appertaining pole piece (i.e. G1 upwardly-G2 downwardly).
  • the total number of lines of flux the permanent magnets supply the magnetic structure depends on the reluctance of the structure viewed from the permanent magnet surfaces. As the reluctance of the structure is raised, the total number of lines of flux supplied by the magnets decreases. This decrease is less than would occur if the magnet had no internal reluctance.
  • This internal magnet reluctance makes it possible to slightly alter the amount of flux through all four gaps, G1, G2, G3, and G4 even though the reluctance of only one is changed. To be useful in practice this effect needs to be augmented by introducing gaps between the magnets and the structure (65 in FIG. 5) as hereinafter described.
  • the reluctance of the total structure viewed from the magnet changes slightly. Since the total structure reluctance and the magnet air gap reluctance are additive, the effect of introducing the latter, which is a fixed quantity, is to minimize the effect of Variations in the former. This results in the magnet more nearly supplying a constant number of lines of flux.
  • the flux through the gap G4 at 29 has its ux decreased for the reason that the lowering of the reluctance at upper fixed gap G1 diverts flux from the reed so that there is then less flux leaving the reed at the other end into the complementary lower working gap G4.
  • the reluctance is directly proportional to the gap length and inversely proportional to the gap area and the permeability of the material in the gap. If the latter is 'air the permeability (in the common system of units) is unity.
  • the permeability of non-magnetic materials like brass, copper, aluminum', etc. is also unity.
  • the reluctance of a gap is however independent of the amount of flux through it.
  • similar results follow the bending of the tab 40 downwardly, that is to say, the reluctance of the lower yfixed gap G2 wouldv be decreased and the flux through it increased, while the apparent reluctance of the complementary upper working gapz G3 would be in effect increased, since less flux can traverse the reed longitudinally from gap G3 toward gap G2.
  • both fixed gaps will be affected, and consequently, in accordance xwith the principles latterly explained, .fiux in both Working gaps would likewise be affected, from which it will now be understood that the dual-tab type of reluctance-correcting or adjusting means can be manipulated to affect the ux in all four gaps, by reason of which an imbalance in gross gap iux, as well as longitudinal flux along the armature reed, can be easily and quickly corrected.
  • the actual armatures or reeds 27 and 50 are preferably fabricated from thin ferromagnetic stock of high permeability and relatively low saturation density (e.g. about 7,0100 to ⁇ 8,000 li./cm.2) in order to have an optimum sensitivity to weak signals; whereas, the metal from which the pole pieces are formed is of lower permeability having, for example, a saturation density of the order of about 14 to 18 thousand li./cm.2 for conduction of the relatively strong polarizing flux supplied by magnets 33A, 33B and adequate conduction of the weak signal flux.
  • high permeability and relatively low saturation density e.g. about 7,0100 to ⁇ 8,000 li./cm.2
  • the metal from which the pole pieces are formed is of lower permeability having, for example, a saturation density of the order of about 14 to 18 thousand li./cm.2 for conduction of the relatively strong polarizing flux supplied by magnets 33A, 33B and adequate conduction of the weak signal flux.
  • the shim 50 can readily be made from different stock having a much higher saturation density and of different thickness and cross-sectional and superficial areas than Vthe reed, with a consequently greater flux-carrying capacity and 'a correspondingly greater control effect, which is augmented by its previously-mentioned capability of controlling both gross and circulating types of ux imbalance.
  • the tabs are preferably made of high-saturation density material so that even if thinner than the reed they can conduct more flux and provide a greater effective control range.
  • the dual lateral-tab type of corrector 51 may be embodied as an integral part of the reed 50, in which case the resulting construction would be substantially identical in appearance to the combination shim and reed structure 50-51 depicted in FIG. 6A, assuming the dotted-line representation to be erased.
  • FIG. 7A the reed 55 is shown in plan view.
  • the bending line of the reed in the fixedrgap is along the dotted line 59 and movement of the tabs 55A and 55B does not have any appreciable effect on the vibratable end of the reed.
  • a reed 60 of normal length (having no integral adjustment tab or extension) is flanked above and below by magnetic shims 61 and 62 in superposed relation and which are respectively spaced from the adjoining pole pieces 22, 23 by non-magnetic spacers 28W.
  • This arrangement affords such possibilities of adjustment as having all tabs 61A, 61B, and 62A, 62B bent in the same direction, all up or all down; or having tabs 61A and 61B bent toward each other and the remaining tabs otherwise, or having tab 61A bent upwardly, 62A downwardly, with 61B bent upwardly and 62B bent downwardly, and so-on.
  • This gap is preferably created by grinding the upper pole faces of each of the two magnets (bearing in mind that the latter are magnetized transversely) to produce a gap the length of which desirably may be approximately 5 percent of the length of the magnets.
  • these gaps 65 are preferably each filled-in by a non-magnetic spacer 66 of brass or the like.
  • the reluctance introduced by the gaps 65 increases the total reluctance into which the permanent magnets work, and the effect of the foregoing reluctance changes at the gaps, resulting from the adjusting and balancing methods recited, consequently produces little change in the total available flux provided by these magnets.
  • FIG. 9 there is shown a further modification of the flux-balancing means in the form of an external magnetic corrector member 70 of high permeability and of approximately Omega-shape in that it has two substantially fiat end portions 71, 72 joined by curved bight or arcuate portion 73.
  • This shunt member is adapted to be mounted at the clamp-gap end of the transducer with the concavity of the bight 73 opposite the fixed end of reed 74 of normal (i.e. non-extended) length. Attachment of the member 70 may be effected by spot-welding one of its legs to one of the pole pieces.
  • the stock of which it is made should be thin enough to permit bending and of high permeability.
  • the operation of the device of FIG. 9 is such that the single corrector 70 will serve to adjust both kinds of gap imbalance at one setting assuming, for example, that gaps G1 and G2 or,G3 and G4 are not identical; that is, by bending the shunt 70 toward or away from the clamp gaps and reed-end, as may be required, both gross ux imbalance at all gaps, and flux traversing the reed longitudinally, will be brought to balance in the sense heretofore explained because, according to this method, the corrector 70 is external in that it by-passes flux wholly around (rather than partially through) the clamped end of the reed, and directly from one pole piece 22 to the other pole piece 23, so that diversion of this flux depends on there being a drop along N or S.
  • the source of flux in the construction of FIG. 9 is regarded as substantially constant, and for this purpose the special gap means 65 is desirably utilized to assure this condition.
  • bending and bendable as used herein in connection with deecting relative to a pole piece, are intended to refer to bending by reasonable manual force, with or without the aid of a tool such as the so-called kniting tool commonly used for deflecting relay springs, switch blades, and the like.
  • the single integral type of corrector means 40 is limited as to permeability by the required moderate permeability in the reed, although its reluctance-modifying effect can be augmented somewhat by enlargement of its supercal area and any special conguration of shape which changes in size or construction of the transducer might permit. But such a corrector is intended to modify primarily the condition of longitudinal or circulating ux imbalance.
  • the multiple-tab type of correctors may require the provision of a constant-ux means such as the flux-source gaps 65, it being understood that the latter may be employed if desired in all forms of transducer, whether a receiver, such as illustrated in FIG. 2, or a microphone, such as shown in part of FIG. 11, it being understood that the only diierence between these two devices resides in the fact that generally a lower value of D.C. current will be present in the coil in a microphone, and the diaphragm cover plate 15 for the microphone may have a large opening covered by grill fabric 16, whereas the receiver of FIG. 2 may have a smaller opening fitted into a so-called Thuras tube adapted to t into the ear.
  • a constant-ux means such as the flux-source gaps 65
  • An electromagnetic transducer comprising a magnet, a pole piece flux-conductively engaging each pole of the magnet, said pole pieces extending laterally of the magnet to form a non-magnetic gap therebetween, an elongated, flux-conductive, elastic armature, means clamping one end of said armature in non-magnetic, spaced relationship to the pole pieces in iixed position in said gap so that the other end of said armature may vibrate in another portion of said gap, there being -a bending line between the clamped end and the vibratable end of the armature, and a bendable tab having a permeability higher than the armature ⁇ and having one end flux-conductively associated with the armature in the clamping means and the other end extending laterally into said gap for varying the reluctance in the air gap between the pole pieces at the xed end of the armature.
  • An electromagnetic transducer comprising a magnet, a pole piece flux-conductively engaging'each pole of the magnet, said pole pieces extending laterally of the magnet to form a non-magnetic gap therebetween, an elongated, ux-conductive, elastic armature, means clamping one end of said armature in non-magnetic, spaced relationship to the pole pieces in fixed position in said gap so that the other end of said armature may vibrate in another portion of said gap, there being a bending line .between the clamped end and the vibratable end of the armature, and an armature projecting beyond its clamp portion on the side opposite to the vibratable end into space adjacent the gap for varying the reluctance in the air gap between the pole pieces at the fixed end of the armature.
  • An electromagnetic transducer comprising a magnet, a pole piece flux-conductively engaging each pole of the magnet, said pole pieces extending laterally of the magnet to form a non-magnetic gap therebetween, an elongated, flux-conductive armature positioned in said gap, a linx-conductive leaf mounted on each side of the same end of the armature with each end of each leaf projecting laterally of the armature into the adjacent portions of the gap, a non-magnetic spacer positioned on each leaf, said spacers, leaves and armature being in a stack clamped between said pole pieces so that the other end of the armature may vibrate in another portion of said gap.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Manufacture Of Motors, Generators (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
US730082A 1958-04-22 1958-04-22 Reluctance adjustment in electromagnetic devices Expired - Lifetime US3521208A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060045298A1 (en) * 2004-09-02 2006-03-02 Patrik Westerkull Vibrator for bone-conduction hearing
US20080205691A1 (en) * 2007-02-20 2008-08-28 Niels Beekman Moving armature receiver with reduced parasitic coupling

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7577269B2 (en) * 2006-08-28 2009-08-18 Technology Properties Limited Acoustic transducer

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Publication number Priority date Publication date Assignee Title
CH217613A (de) * 1940-12-02 1941-10-31 Siemens Ag Albis Vierpolmagnetsystem.
US2443784A (en) * 1943-05-17 1948-06-22 Barber Coleman Company Relay
US2511114A (en) * 1947-06-06 1950-06-13 Bell Telephone Labor Inc Polarized electromagnet
US2912523A (en) * 1955-10-26 1959-11-10 Industrial Res Prod Inc Electro-acoustic transducer
US2912522A (en) * 1954-06-14 1959-11-10 Industrial Res Prod Inc Electro-mechanical transducing device

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Publication number Priority date Publication date Assignee Title
US2245511A (en) * 1937-12-04 1941-06-10 Us Instr Corp Telephone instrument
CH218774A (de) * 1939-09-05 1941-12-31 Fides Gmbh Magnetisches Mikrofon.
DE890992C (de) * 1940-12-23 1953-09-24 Siemens Ag Elektromagnet
DE734040C (de) * 1941-09-24 1943-04-07 Siemens Ag Polarisiertes Relais
CH311081A (de) * 1942-04-07 1955-11-15 Siemens Ag Einrichtung mit steuerbarem Magnetkreis.

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH217613A (de) * 1940-12-02 1941-10-31 Siemens Ag Albis Vierpolmagnetsystem.
US2443784A (en) * 1943-05-17 1948-06-22 Barber Coleman Company Relay
US2511114A (en) * 1947-06-06 1950-06-13 Bell Telephone Labor Inc Polarized electromagnet
US2912522A (en) * 1954-06-14 1959-11-10 Industrial Res Prod Inc Electro-mechanical transducing device
US2912523A (en) * 1955-10-26 1959-11-10 Industrial Res Prod Inc Electro-acoustic transducer

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060045298A1 (en) * 2004-09-02 2006-03-02 Patrik Westerkull Vibrator for bone-conduction hearing
US7376237B2 (en) 2004-09-02 2008-05-20 Oticon A/S Vibrator for bone-conduction hearing
US20080205691A1 (en) * 2007-02-20 2008-08-28 Niels Beekman Moving armature receiver with reduced parasitic coupling
EP1962550A3 (en) * 2007-02-20 2009-03-04 Sonion Nederland B.V. A moving armature receiver with reduced parasitic coupling

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