US2567394A - Inductance coil - Google Patents

Description

Sept. 11, 1951 c. w. N UTTMAN INDUCTANCE COIL 2 Sheets-Sheet 1 Filed Aug. 9, 1950 FIG.

X SERIES HW lNl EN TOR C. m NU 7'7'MAN ATTORNEY INDUCTANCE COIL 2 Sheets-Sheet 2 Filed Aug. 9, 1950 0 0 w m 0 0 6 u I 0 7 0 5 M G L o n A 07 M W J, R N M H 6 w m m F M E R W T n w 8 2 10 M a m R m I 0 a P 0 0 0 0 0 0 w m m INVENTOR C. W NUT TMAN B) 5 ATTORNEY "ferromagnetic material, I ceramic ferromagnetic material known as fer- Patentec] Sept. 11, 1951 INDUCTAN CE oQIL p Charles W. Nuttman, East OrangerNrJ assignor to Bell Telephone Laboratories, Incorporated,. New York, N. Y., a corporation of New York Application August 9, 1950, Serial'No.178,40I-Q I 'This invention relates to inductance coils and,

more particularly, to such coils having coupled windings.

In certain types of filters and, particularly,

those employing crystal units as elements of the filter, it is desirable to provide coupling between two of the inductances in the filter sectionin order to attain an additional point of infinite at- .tenuation at a finite frequency. By providing slight changes in the percentage of the coupling between the two inductances in a filter section, the frequency at which the additional infinite attenuation occurs is also changed, and, therefore, a different filter performance characteristic is obtained.

In such circuits and in other circuits where ,-difierent degrees of coupling are required between .windings of the same general characteristics and ,3 form but electrically positioned in difierent parts .of the circuit, it is desirable that a single basic. ,structure be employed and only slight changes be required during the fabrication of this structure to alter the coupling tothe desired percentage In this way, uniformity of the various piece parts required for the difl'erent coupled coils may be obtained with a resultant decrease in the expense of fabricating the different coils.

It is, therefore, one object of this invention to vary the reluctances of the possible flux paths in coils of the general type aforementioned during the fabrication thereof so that asingle basic structure may be employed for coils of any desired inductive coupling. A I

It is another object of this invention to provide a single basic coil structure in which the inductive coupling between the two windings can, be facilely predetermined at any value between approximately zeroand 100 per cent. 7

It is a further object of thisinvention to improve the facility with which such coils are fabricated and to diminish theexpenses of production that have been necessitated by employing different coil structures and difi'erently dimensioned coil parts for coils with different values of inductive coupling between the windings thereof;

A further object of this invention is to provide an'improved inductance coil.

1 These and other objects are accomplished in one specific illustrative embodiment of this invention in which a hollow enclosed casing or a such as a sintered rite, is divided into two sections or cavities by a central ring which forms part of the casing and extends into the casing; A center core, which 7 Claims. (01.171442) also may be of ferrite, is placed in each of these cavities along the axis of the casing, and a winding surrounds each center core. A third center core ispositioned inside the casing medially adjacent the central ring along the same axis as .the other cores andextends slightly into each of the windings. Air-gaps are provided between matelyvzero to per cent.

.each'of' the. three-centercores and between'the twosend center cores and the end sections of the casing by insulating members separating them and between the middle center core and the cen- .tralring. By varying these air-gaps in relation to each other, the inductive coupling between the two windings may be varied from approxi- Specifically,ithere may be altered the reluctances of the paths of" the flux linking each-coil singly and coupling the two coils by varying the air-gap between the central ring and themiddlc center core to particularly affect the individual flux paths, and by varying theair-gaps in the three piece center core, and especially the distance the ;midd1e center core extends into the windings, to particularly aiiect the inductiv coupling between the two windings.

- It is,- therefore, one feature-of this invention that the enclosed casing of thecoil be divided into distinct sections or cavities, each of said cavities having a winding therein, and that said cavitiesbe magnetically linked'by a center core member extending between said cavities and partially into each of said windings.

It is a further feature of "this invention that the casing comprise a central ring or plate adjacent the above-mentioned center core and extending into the casing towards that center core to divide the easing into two cavities and to provide a flux path from the casing to the center core. .1 ij

It isja stillrfurther feature of this invention that the central magnetic path in the casing comprise a plurality of center cores axially aligned and separated from each other and from the end sections of thecasing, the distances between the cores themselves and the end sections providing "from consideration of the following detailed de i n l; thea sgimpan i i n wh h unit |3 between the two windings.

Fig. 4 is a graph illustrating the percentagechange in the inductive coupling in the coil of Fig. 2 with change in the reluctances of the flux paths shown in Fig. 3 by variation of the lengths of the radial and central air-gaps.

Referring now to the drawing, Fig. 1 is a schematic representation of a crystal channelfilter using coils having controlled coupling between the windings of each coil. The first coil comprises a first winding H and a second winding |2 placed in series opposing. and with a crystal Similarly, the second coil comprises a first winding l4 and a second winding |5 in series opposing and with a crystal unit l6 between the two windings. The percentage of coupling between the windings of the two coils may be different; thus, in one illustrative channel filter circuit, the percentage coupling between the windings II and I2 may be 17.09 per cent, and the percentage coupling between the windings l4 and I5 may be 19.10 per cent. However, in accordance with this invention, both' coils may advantageously be constructed in the same general structure and from the same component parts as in the illustrative embodiment of this invention shown in Fig. 2.

As seen in that figure, the coil windings and 2| are completely enclosed within a cylindrical casing, the casing being made up of twocupshaped members 22 and 23 and anannular center plate 24 between them, the casing and other members forming portions of the flux paths of the coil being advantageously of a ferromagnetic material and, particularly, of a sintered ceramic ferromagnetic material known as ferrite. Thus, the magnetic portions of the coil may advantageously be of a manganese-zinc ferrite. In the specific embodiment illustrated in the drawing, the cup-shaped members were themselves constructed of several component parts includingend plates 25 andrings 26; however, the cupshaped members may be made in one piece if desired. Eachend plate 25 has anaperture 21 axially therein, the purpose for which will be discussed below, and apertures 28 through which the leads 29 of thecoils 20 and 2| extend. Insulating grommets 30' are positioned in theapertures 28 around theleads 29.

Theannular center plate 24 extends inwards into the casing further than the sides of thecupshaped members 22 and 23, or, in this specific embodiment, further than therings 26. Theannular center plate 24 thus divides the easing into twoequal cavities 33 and 34.Winding 20 is placed axially incavity 33 and winding 2| axially incavity 34. Threecenter cores 36, 31, and 38, defining a center post, extend axially between the twoend plates 25, being separated 'from them and from each other by air-gap spacers 39, which may be of paper or other insulating material. The spacers 39 are advantageously approximately equal as the maximum Q is attainable when the central air-gaps defined by these spacers are approximately equal. Thespacers 33 and thecores 36, 31, and 3B are axially apertured and provide, with theapertures 21 in theend plates 25, an open path through the casing, the reason for which will be discussed below.

Thewinding 20 is supported on thecenter core 36 in thecavity 33, and the winding 2| is supported on thecenter core 38 in thecavity 34. The middle center core 31 is adjacent the center ring orplate 24 and extends partially into a eachcavity 33 and 34 and into each winding 20 and 2|. The windings may be secured directly to the cores, as shown, or, if it is intended to operate coils constructed in accordance with this invention at higher voltages than those generally encountered in channel filters, the windings may be wound on insulating spools and the spools se cured to the center cores in ways known in the art.

The casing is clamped between two clamping plates 4|, which may be square, by clampingscrews 42 andnuts 43. The clamping plates 4| have apertures centrally therein aligned withapertures 21 in theend plates 25 andapertures 45 aligned withapertures 23 in theend plates 25 and through which apertures 45 the lead .wires 29 extend. The insulating grommets or tubing 35 may also extend into or through theapertures 45.

Referring now especially to Fig. 3. there are three magnetic circuits or paths provided by the above-described arrangement of cup-shaped members, center ring and cores. Magnetic flux may follow the patl 1 5|) defined by thecenter core 36, part ofthe center core 31; the ring-24, and the cup-shaped member 22 and thus not link thecoil 26 with the other coil at all. Similarly, there is a flux path 5| around thecavity 34 for which there is no couplingbetween' the coils. However, there is also a possible flux path- 52 through the threecores 36, 31, and 38, through the rim of thering 24, and the cup-shaped members 22 and 23, all of which flux would link bothwindings 20 and 2|.

It is thus apparent that the flux from each winding that follows the paths 5!! or 5| links only the turns of its own winding, whereas the flux from either winding that follows thepath 52 links the turns of both windings, inductively couplingthem. It has been found that this inductive coupling between the two windings may be varied between approximately zero and 100 per cent by varying the reluctances of these three fiux paths and, specifically, by varying the ratio of the lengths of the air-gaps in the individual winding flux paths 5B and 5| and the lengths oftheair-gaps in thecoupling flux path 52. Thus, the percentage of the inductive coupling between the two windings may be decreased by increasing the air-gaps in the central post of the coil, i. e., between thecenter cores 36, 31, and 38 and between these coils and the ends of the cup-shaped casing members 22 and 23; or the percentage of the inductive coupling may be decreased. by decreasing the radial air-gap between the centralannular plate 24 and the middle center core 31. The first alteration of the air-gaps primarily affects theflux path 52 by increasing the reluctance of that path,as that path includes each of the four air-gaps formed between the center cores and the casing ends. The second alteration of the air-gaps primarily affects the flux paths and 5| by reducing the reluctance of those paths. The per.- centage of coupling can similarly be increased by the opposite of these air-gap variations.

-LIt .has-been found that. in the fabrication 101 these .coils, when both variations. of air-gap spacings from the base value or norm are incorporated in the coil so that their efiects are cumulative, the inductive coupling can be varied 6 Fig. 4 graphically represents this data,curve 56 being drawn for the constant radial air-gap of .007" andcurve 55 being drawn for the constantradial-air-gap of .014", each being a curve in this single structural design from approxi- 5 of total central core air-gap as against the per- .mately zero to 100 per cent and that. any coucentage of inductive coupling. As is readily appling desired within these limits may be obtained. parent, the coupling increases 1 for each curve .The-coil maybe assemblied by a jig having a with-"decrease in the total central air-gap, for n n ma t w l 01 pin t din upwards the reasons explained above. Similarly, curve and onto whichthe various parts are placed, the i0 .51 is a curve of radial air-gap against percentage d0we1 e in hr h he apertres 44 ofthe inductive coupling for a constant total center 'elamping Plates apertures 27 of the end me .core air-gap of .028"; as is also readily apparent s e apertured spacers '39, and therhollow .by. this curve, the percentage of inductive coucenter coremembers-Zili, 31, and 3B.- The rin pling between the coils increases with an in- 26 and annular center pla e a p is crease in the radial air-gap, for the reasons ex.- in place on the jig, as by two semi-cylindrical plajned above I l -D tubes positi d in the j and bearing ,,-It, is to be understood that although these s nst t e coil etw n clamping plates 4| curves have beenplotted in a specific percentage to centrally 'lo ate. thes.e members prior. t0. the range of inductive coupling, the coupling may be fin l cla p f thescrews 42 and nuts predetermined at any value from approximately T e i gs and core.members 36, 31, and 38 zero to 100 per cent by extensions of these -may a be initially Of a standardler base size, curves and of the principles of this invention, which s may he the largest that is expected whereby. difierent curves for different valuesof e n e to obtain any of t e percentages of i air-gap lengths are attainable. Thus, by preduetive coupling desired; I In Order to increase 25 paring a series of curves of, for example, central th length of t e air-gaps in the Center core airegaplength against inductive coupling for difassembimjeach ofv the center cores ,36, 31, and..38 f re t constant radial airflgap lengths the .LWouidthen be. slightly .le d in height. as b gap lengths necessary for any desired coupling gr ndin a the p c c as-by can. be read directly off the chart thus prepared ad ih yfi 0f P- between the cores- As and the parts ground or otherwise slightly varpOinted Out above, tends t0 decrease the into the lengths thus determined In ductive coupling between the twowindings 20 way, the complete range of inductive coupling 1- ,Similariy 9 decrease the s in ,may becovered by a single structure employing th cen er core a t v increase the Couphhgin each instancethe same piece parts but readily h e of thetgprings 24 may be sli yaried during the fabrication in accordance with creased, as y. .s nd n ,-as e total length information easily obtainable from priorly prelof theospacers 9' h thehehtel core members pared charts, thereby allowing a multitude of 3 and 3 equals the h i of the four Outer different coils, as for different locations in filter rings and the center nhg ,circuits, to be fabricated without the equal mul- The radial between the medlahy 40 titude of diiferent parts that must be stored and cated center core member 31 and the annular differently fabri ated Plate ring is determine? by diameter cult is to beunderstood that the above-described of the core member and the Inner dlametelf of arrangements are illustrative of the application the n As t core member 37 h lhto of'the principles of the invention. Numerous ,each of the i and t0 proYlde the other, arrangements may be devised by those w r t n fl P between them its Outer skilled-in .the art without departing from the diameter cannot be altered. Thus,,I have found pirit and cope of the invention it advisable to vary the radial air-gap and thus @What ishclaimed v ev ry the e u tances of thefiux paths 5 0 and 5|. 1. In an inductance coil, a hollow enclosed which link 0 y t pecti wind n by casingsaid casing including a member extendchanging the inner diameter of the annular plate jng t Said casing and dividing Said hoiiow member easing into two sections, a center core in each of In certain l at embodiments of this saidsections, a winding around each of said vention constructed in accordance with Fig. 2 a. middl center core extending withi and described above, different radial and total said member and defining a first air-gap therecentral air-gaps have been employed, and-the .with, said, middle core being in juxtaposition following table is exemplary of the variations in with the first mentioned center cores in said seethe inductive coupling that I have been able to tions, said casing and said cores being of a ferobtain with this single basic structure bymeans romagnetic material, and means providing second 01' these different air-gaps: 6O ,airr aps between said center cores whereby the Inductance and Approximate Turns of Winding Inductive Coupling Total Air-gap Radial up between Windin Central ings in the SeriesCore Assembly gap 20 21 Opposition Connection Per Cent .015" .007" 160 turns, 15.30 mh 47. 0 .028 .007" 160 turns, 7.52 mh 1 21.3 .028 .014" 212 turns, 11.39 mh. 28.2 .040" .014" 212 turns, 12.30 rnh. 18.7

These measurements were made at kilocycles and with .001 ampere through thewindings 20 and 2|.

percentage coupling between said two windings is determined by the relationship between the lengths of said first and second air-gaps.

casing-whereby. the percentage coupling between said twowindingsis determined by the relationship between the lengths of said first and second air-gaps.

, 3.-In an inductance coil, a hollow enclosed casing, said casing including a member extending into-said casing and dividing said hollow easing into twosections, acenter core in each of said sections, a winding aroundeach of said center cores, a middlecenter core extending through said member and defining afirst air-gap therewith, said casing and cores being of a sintered ceramic ferromagnetic material, said middle core extending-into each of said windings and providing a low reluctance flux path between said two windings, and means'providing second airgaps between said center cores and between the outer ofsaid center cores and said casing whereby the percentage coupling between said two windings is determined by the relationship between the lengths of said first and second gaps.

4. In an inductance coil, a hollow cylindrical body closed atboth ends, said bodyincluding a center ringextending into said hollow body and dividing said hollow body into two sections, a central post ins'aid' bodyg-said central postcomprising a center core in each of said sections and a middle center core extending adjacent said center ring and defining a first air-gap'therewith, said body and said cores being of a ferromagnetic material, a winding around, each of said outer cores in said sections, "and means providing second air-gaps in said central post and between said post and said body, the percentage of-inducti've coupling between said windings being determined by the relative widths of said first and the total of said second air-gaps.

5. In an inductance coil, a hollow cylindrical body'closed at both ends, said body including a center ring extending into said hollow body and dividing said hollowbody into two sections, said body being of a ferromagnetic material, a central post in said body, said central post comprising a center corein each of said sections and a middle center core extending adjacent said center ring and defining a first air-gap therewith, said cores being of a ferromagnetic material, a winding around each of said outer cores in said sections, said middle center core extending into each of said windings and providing a low reluctance flux path between said windings, and

means providing second air-gaps .in said central post and between said post and said body, the percentage of inductive coupling between said windings being determined by the relative widths of said first and the total of said second air-gaps. 6. In an inductance coil, a. hollow cylindrical body closed at both ends and having apertures centrally located in said ends, said body including a center ring extending into saidbody and dividing it internally into two sections, a center core --in each of said sections, a middle centerncore' extending between said sections-adjaoent said ring and defining a radial air-gap therewith, saidbody and said cores being of a ferromagnetic material, said cores being aligned axiallyin said body and having apertures there-- through aligned with said apertures i-n said-ends of said body, a winding around each of said outer cores in saidsections, said middle core extend- -ing partially 'into each of said windings, apertured spacers between each of said cores and between said cores and said ends of said body, the apertures of said spacers being axially aligned with said other apertures, said spacers defining a plurality of central air-gaps, the percentage inductive coupling between said windings being determined by the relationship between said radial air-gap and the total of said plurality of central air-gaps, and means clamping said body together.

7 An inductance coil comprising a hollow cylindrical body comprising a pair or end members, each of said members having-an aperture centrally therein, aplurality of ring members,

and a central annular plate member, said annular plate member extending into saidbody and dividing said body into two sections, a center core axially in each section, a winding'around each center core, a middle center core extending axially between said sections adjacent said annular plate member and defining therewith a radial air-gap, said body and said cores being of a sintered ceramic ferromagnetic material, said middle core extending partially into each of said windings, each of said cores being axially apertured, aperture-d spacers between each of said center cores and between the outer center cores and said end members, the apertures of said spacers being axially aligned with said other apertures, said spacer members defining four approximately equal central air-gaps, the lengths of said central air-gaps being determined by the relative lengths of said cores and said rings-the percentage inductive coupling between said windings being determined by the relationship between said radial air-gap and the total of said four central air-gaps, and means clamping said body together. 1

CHARLES W. NUTTMAN.

No references cited.

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