US1586883A - Loading of signaling conductors - Google Patents

Description

2 Sheets-Sheet l LOADING OF SIGNALING CONDUCTORS June 1 1926.

Patented June 1, 192.6..`

muri?. DI STATES 4PATE/Nr oFFicE.

GUsTAF w. ELMEN, or LEONIA, NEW JEE'sEY, AssIGNoa 'ro WESTERN ELECTRIC colu- EANY, INCORPORATED, or NEW YoEx, N. Y., A coEroEA'rroN or NEW Yoan.

LOADING F SIGNALING CONDUCTORS.

Application nled J'uly 20, 1921. Serial No. 486,009.

, This invention relates to the production and use of a new material orsubstance having certain desirable `magnetic qualities, among-which are high magnetic permeability especially at low magnetizing forces, and W hysteresis loss. It is one object of this invention to provide a suitable loading material for signaling conductors to increase their rangeand speed of operation. Another object relates to applying this loading material to a conductive core in a manner to produce a highly etlicient transmission line for long range, high speed signaling. These objects and other objects will become ap-l parent on consideration of 'exam les of practice thereunder which will be disclosed specifically in this specification, with the understanding that the delinition of rthe invention will be given in the appended claims.

Thisapplication is in part a continuation of application, Serial No. 111,080, filed July 24, 1916.

The importance of iron in the practical application of electricity is Well known and has often been'relnarked upon. Its unique quality of high magnetic .permeability has made it indispensable for the cores of tractive electro-magnets for dynamos, motors, telephone receivers, telegraph relays, etc. For this purpose it may, in certain cases, be advantageously united with a very small proportion of some other element, for example silicon. Vith this qualification it may truly be said that the high permeability1 of iron makes it practically the only medium to be considered for the translation of energy of the electric current into useful mechanical effect, andfor the reciprocal trans- .lation of mechanicalJ energy into electric current. In dynamovelectric machines it is common to have laminated iron cores subject to resultant inagnetizing forces of the orderof 2 to 5 or more c. g. s. units and'to develop magnetic fluxes in these iron cores of the order of 10,000 to 20,0004 lines per square centimeter of cross-section. Muchv attention has been given to obtaining a quality of iron of high permeability for'magnetizing forces and flux densities of. the order here mentioned. On this quality of iron depends its effectiveness in' most electromag-K4 Sil-ico if1i steel: exhibits magnetic qualities.-

' superior toA ordinary iron insome respects,

4should exhibit a lowhysteresisloss.

but its employment is limited by its comparative brittleness and the difficulty of Working it. A good quality of -soft iron has been commonly employed as the best magnetic medium for general use for tractive electromagnets. The principal possi.

ble rivals of iron, nickel andv cobalt, are far below it in ,permeability at the magnetizin forces involved in such apparatus. `.Wit

nickel and cobalt, in this respect,- stands Heuslers f alloy of aluminum, manganese, and copper. It has been found that a composition of about 2/3 nickel and 1/3 copper, when tested at low magnetizing forces, gives a permeabilityv higher than that of iron alone. It will be seen that with the exception of aluminum,- all these metals'stand closetogether in their atomicweights and atomic numbers and in this specification the five elements, manganese, iron, cobalt, nickel and copper, havin the consecutive `atomic numbers 25, 26, 2 `28 and 29 will bereferred to as constituting the magnetic group of elements. v

The criterion of high permeability isv not the onlyone to be considered in seeking the bestmagnetic material.4 If the magnetizing `forces and the resultant liux are changed rapidly, then for most purposes the mate'ilal e development of eddy currents under these conditions may be obviated to a considerable extent by lamination, but the Iresistivity of the material is a factor thatfmay be of im- -portance inthis'connection; the higher the resistivity, the more the eddy current loss l will be kept down.

Magnetic material has important uses aside from its'use in tractive electromagnets. An obvious example is for the cores of alternating current transformers.v In many" situations it is desirable to increase thevinductive reactance Vof an electric conductorand for this purpose magnetic material is' placed in' the'eld of magnetic force asso ciatedwith'the conductor. This is the principle of choke coils, and of the) loading coils" :which are-employed in telephone transmission circuits x, a

In telegraphy and telephony the electric currents are exceedingly smallcomparedto those encountered in the transmission-.and

transformation of power.l lIithertoa-com` :nonrpracti-ce'in increasing-the induetance of', signal-ing conductors has been to wind these conductors many timesin series turns on an iron core, in the form of loading coils.

Since Heaviside discussed the question about 1890, it has been well understood that an ideal way to improve signaling conductors would be by continuous loading, that is, by enveloping the conductor with a layer of magnetic material throughout its length. One trouble has been that with the the present time, although there havebeen many suggestions for continuous loading, it has been found of no advantage for any purl pose except for a few comparatively short,

submarine telephone transmission lines. 1In a few instances .of this class, continuous loading with. iron. has been employed ad vantageously. 'It has not been made useful hitherto in telegraphy.

This invention provides a new magnetic material comprising elements of the magnetic group combined in suitable propormaterial of my invention; Fig. 6 is a curve for hysteresis loss; Fig. 7 is an elevation of a conductor wrapped doubly with the magtions, which, when subjected to a proper heat treatment and guarded against undue stresses and other disturbing causes develops and retains an extremely high permeability at low magnetizing forces, and a low teresis loss. This material has furthermore netic material; Fig. 8 is a curve showing the permeability-temperature characteristic for a variety of the magnetic material; and Fig. 9 shows a loading coil with its core oflthis material and its winding indicated diagrammatically.

Iron and nickel are fused together in an induction furnace in the proportionof about 2li/2 per cent ofiron and 781/2 per cent of nickel.' Good commercial grades. of these two metals are suitable for this purpose. The molten composition is poured in` a mold and cooled .to form a thick bar or rod. -This is subjected to repeated swaging operations by which it is reduced in diameter and correspondingly elongated. The long rod thus formed is then drawn out by repeated wire drawing operations to a size of about No.

20 B. and S. gauge. This wire is then passe'd between flattening rolls, and by several such operations, it is flattened to a tape of the thickness of about 0.006 inch and width a little more than 0.125 inch. "This tape is passed through cutting rolls or discs which trim its edges squarely on both sides and give the tape anexact and uniform width.

This tape of nickel-iron composition is nowV ready for application upon a conductor.'

AThe stranded copper conductor of Figs.

1 and 2 comprises the central cylindrical been applied with advantage to the continubus loading of signaling conductorsin such a manner as to obtain the full benefits of the above noted desirable properties.

The practice of -this invention comprehends considerable variety in the composition and preparation of the magnetic material, the manner of its application for loading material and other purposes, the safeguards against impairment of its magnetic propert etc. An exampleof pro,- cedure, accor 'ng to the invention, will now be disclosedf'by which its utility may be l:realized to advantage.` This disclosure will be made specific to this example, with the understanding that generic as cts of the invention may be comprehende in the terms of the appended claims.

Referrlng to the accompanying drawings, Figure 1 `1s an elevation of a conductor loaded with the improved magnetic material of this invention; F ig. 2 isa cross-section ofthe same; Fig. 3 is a cross-section of the same conductor embodied in a submarine cable; Fi 4 is a section of a. furnace for heating t e loaded conductor; Fig. 5 isa curve showing the relation of resistivity to percentage composition for a certain loading wire 1 enveloped by six equal helical. strands 2, which are shaped to fit together closely to form a cylindrical annulus 'about't-hewire. It is desirable that the conductor assembled in this way shall have a smooth cylindrical contour, and for this purpose it may be drawn through a die or subjected to a swag- 1n o decri ed, has the advantages of flexibility and preservation lof conductive continuity 1n case of a breakage by any` stress not severe enou h to interrupt all the strandsat the same -p ace. This stranded conductor 1T-2 is of size No. 5 B. and S. gauge, and' is to be loaded with the improved magnetic material in the form of the tape heretoore described.

ration. The stranded conductor as lis The nickel-iron tape 3 is wrapped helically on the stranded copper core, care being taken to abut the edges closelv without lap- 1n P Tghe taped conductory is next to .be heat'- treated. For this purpose it is drawn lengthwise straight through the furnace of Fig 4, which is maintained at a temperature of about 875 degrees centigrade. This is a mule Afurnace with the heating elements 20 between the lire clay mule 21 and the vfire brick 22. Around the fire brick 22 is a sheet iron outer wall. The iron. tube 23 has'a the furnace and projects 8 inches beyond ductor should be led away straight from the furnace far enough for it to become Well cooled; bending at this stage may impair its high permeability. Also, the necessary coiling thereafter should be on a large radius, not less than 2 feet: the stresses and strains involved in coiling and uncoiling on a smaller radius may spoil the permeability.

To develop the utmost possible permeability according to'this invention, the rate of cooling after the heating in the furnace is a matter of considerable importance. For the signaling conductor above described, the utmost possible permeability is not particularly desirable, and an eifective permeability of 2400 which is sufficient for the purpose, Will be developed by cooling in air as the taped conductor emerges from the furnace. For some cases, of which an example Will be described later, amore exact procedure With respect to the rate of cooling, is

contemplated. After the heat treatment, the

taped or loaded conductor is insulated, armored, and mechanically reinforced, according to the usual practice for submarine cables, by surrounding it with a layer of gutta percha and the usual Wrapping of jute and the sheath of'adjacent helical tsteel Wires,

gFiying the product shown in cross-section in While a certain speed and temperature with a certain type of furnace have been described to produce the desired results in the case of a particularconductor, it is apparent that these factors may be varied or adjusted to meet different cases, such for egrample, as a conductor of different diameter from that here discussed.

While 781/2 per cent and 211/2 per cent have been mentioned as giving the proportion of the ingredients, nickel and iron, to be employed in making up the improved magnetic material, it Will be understood that the proportion may deviate considerably ffrom these figures when nickel and iron vare the only ingredients, and that when there are other ingredients, this proportion may not apply. Up to the present time, when the only ingredients are nickel and iron, it has been found that a proportion about the same as that named, gives the highest permeability for low magnetizing forces. Other ingredients than nickel and iron may be employed for various purposes, not only to confer high permeability on the product but for other objects; for example, it may be desirable to add chromium for the reason that a comparatively smallquantity of this element Will cause a decided increase in the resistivity of the composition, and this high resistivity may be a desirable factorto cut down the eddy current losses in .the loading material. A composition of nickel `55 per cent, iron 34 per cent, and chromium 11 per cent has been carefully prepared, heat-treated, and tested, and has been found to give a high value of permeability at low magnetizing forces.

7When this material was tested in the form of pancake coils hereinafter described, the permeability of the composition at very low magnetizing forces Was 1000 'or more, which is much higher than the figure for iron. A superior silicon steel gives a permeability for forces approaching zero of only about 400. Thus it Will be seen that With the addition of chromium in considerable quantity, the composition still has a decidedly higher permeability than iron, though perhaps some- What less than might be attained if the chromium Were not present. The resistivity of the`.composition containing chromium, just referred to, is 100 microhms per cu. cm., Whereas the resistivity of iron is only about 11 microhms per cubic centimeter, and the resistivity of the composition of nickel 781/3 per cent and iron 211/2 per cent is about 17 microhms per cubic centimeter (see Fig. 5). Measurements of the permeability of nickel-iron compositions of other proportions than that here stated have shown that the departure may be considerable without serious impairment of the permeability. Thus, using pancake coils, for per cent nickel instead of 7 81/2 per cent, after proper heating and cooling, the permeability at.

forces approaching zero, is about 4100, and at a magnetizing force of 0.2 c. g. s. unit the permeability is about 15,000 Whereas for a percentage of 781A; the respective values of permeability are^7000 and 38,500. It will be seen that these values are much higher than for silicon steel at the same vmagnetizing forces Which has respective permeabilites of only about 400 and 1500. Thus -a Wide departure may be made from the proportion named, yet the permeability at low magnetizing forces will be far greater than for the best materials of the prior art.

'It has already been mentioned that after l the proper heat treatment the composition should be guarded against undue stresses and strains. `When the percentages -`are nickel 78% and iron 211/2, the material 'can be bent With .less impairment of j. pernic-1 ability than when the percentages are respectively 70 and 30. In other \vords,-t he op'tium percentage seems tobe more rugged against impairment of permeability by stresses and strains than the other percentage. However, the difference is not marked and apparently, if the material can be guarded against stresses and strains, this difference is of no great consequence.

The maximum attainable permeability for the nickel-iron composition at percentages of 781/2 and 2li/2 respectively for the nickel and iron has been between 6,000 and 9,000 for zero magnetizing forces. This value which is designated the initial permeability is obtained by determining a series of values for exceedingly low forces, say of the order of 0.01 to 0.05 c. g. s. units. The results plot linearly, and may be extrapelated back to the value for H20, thus giving the value of the permeability at zero magnetizing force. The maximum permeability so far attained is between 45,000 and 60,000. This occurs with the 781/2 per cent nickel composition at a magiietizing force of about 0.1 c. g. s. unit, and the corresponding value of the induction B being from 41,500 to 5,000 c. g. s. units.

- The qualities ofthe new magnetic material exemplified by the nickel-iron compo# sition are evidently not obtained by taking the mere sum or average of the qualities of its components. Not only is the permeability at low forces much greater than for either ingredient (nickel or iron) alone, but the ingredient (nickel) having the lower permeability alone is the major constituent of the composition, while iron, which alone is the 'best magnetic material previously known, here enters into the composition only to the extent of less than a fourth part.

It is worthy of note that the proportion of the ingredients of the nickel-iron composition which gives maximum permeability at low forces and minimum hysteresis loss is also the proportion that gives zero magneto-striction in strong magnetic fields (H250 to H2500). While the heat treatment may not necessarily be the same forl the manifestation of these phenomena, the coincidencegof the proportion is signicant of a fundamental unique character in the composition which attains its maximum expression at that proportion.

The resistivity of the nickel-iron composition of this invention is considerably higher than that of either of its components, and corresponds approximately. to the curve Agiven in Fig. 5. Thus at 781/2 per cent nickel it will be/seen that the resistivity is fully 50 per cent higher than for either nickel or iron alone.

Evidently a smaller proportion of nickel lgives a, decidedly higher resistivity and it may be desirable iii certain cases to sacrifice permeability for the sake of resistivity. Mention has alreadybeen made that for some purposes the utmost attainment of percentages of nickel varying over a wide range. The ordinates in this curve give the work in ergs per cubic centimeter represented by the usual hysteresis loop for a maximum induction of 5,000 c. g. s. units per square centimeter of cross-section.

It will be seen that at 781/2 per cent'nickel, the value is as low at ergs. It will be noted that this percentage for minimum hysteresis loss is the same as for maximum permeability. The low result for the nickel-iron composition at this percentage will be seen to be much lower than the values for other magnetic materials. Thus for a superior quality of iron, the value is as high as 925 and for nickel it is no less than 2,200.

A description has been given of the dimensions of the conductive core and the width and cross-section of the loading tape specifically for a certain contemplated example of a long ocean cable for high speed telegraph transmission. It will be readily understood that the thickness of the tape 100 and other facto-rs may be altered to suit various cases. In some cases where a thicker sheath is desired, it may be best to apply it in the form of two tapes wound in opposite directions, one outside the other as indicated in Fig. 7. Among the advantages of this construction are that it applies the loading sheath in two laminae instead of one, thus reducing the eddy current losses. Also, the opposite winding gives a somewhat more rugged structure for handling, the tape being less likely to slip or buckle. When more than one lamina of loading material 1s used, the thin coating of oxide on each serves as insulation to reduce the eddy currents, 115 but other insulating coatings vmay be applied to the loading material if desired.

An ocean cable, 2000 nautical miles long, and loaded as described, may be operated as a telegraph conductor at a one-way speed, 120 approximately ten times as great as for the present one-way operation of unloaded ocean cables of that length. No ocean telegraph cables have heretofore been loaded, either continuously or by loading coils. With the loading materials heretofore available, it was better to lill the available cable cross-section within a given insulating envelope entirely with copper, rather than to devote part ot that space to loading matebe suificient to cause it to exhibit the useful j property of high permeability at low magnetizing forces to the degree mentioned. Proper heat treatment may be necessary to attain that degree of permeability.

In general, so far as investigations have gone, it has been found preferable to heat the described. nickel-iron composition at least as hot as 825 C. and then cool it down at the proper rate, not too fast but fast enough. This proper rate of cooling is attained in the example described specifically, by a rather ordinary procedure of cooling in The foregoing discussion of the matter of the heat treatment affords guidance by its detailed presentation of alspecific example, but it may be helpful to go over the matter for a different example.

Assume that one has obtained a composition of the desired ingredients in the desired percentage relation, but that he does not know what its previous history has been with respect to heat treatment, and that he wishes to develop the utmost permeability for low forces. It has been found convenient for testing purposes to take lengths of something like 40 feet of tape of cross-section 0.125 inch by 0.006 inch and wind these lengths into pancake coils about three inches in outside diameter with a layer of paper between the successive turns. The. paper may then be expelled with an air blast, thus assuring that the turns of the metal tape are sufficiently loose to guard against undue stresses and strains therein. These pancake coils are evidently conveniently available for testing for permeability by the wellknown method involving the use of a ballistic galvanometer. The first step will be to heat a series of specimensof this composition to a temperature around 900 degrecs centigrade and hold them there for a long enough time to be assured that they have attained this uniform temperature throughout. There will be no objection to heating the specimens somewhat hotter and it may be easier in this way to become assured that the temperature is sufficiently high throughout.

The improved magnetic material here un der .discussion has a so-called critical temperature or magnetic transition temperature, like iron and other magnetic materials. If it is heated from normal temperature to higher and higher temperatures and subjected to low magnetizing forces its permeability increases to a peak and then falls off and vanishes very abruptly and the temperature where -this last change takes place is the so-called critical temperature (page 116 of the 1900 edition of Ewings Magnetic Induction in Iron and Other Metals). -This magnetic transition temperature for the improved magnetic material of this invention will be considerably below the temperature of 900 'degrees that has just been-mentioned in a preceding paragraph, and it willy be different for different compositions, and when the ingredients are nickel and iron it will be different for different proportions of the ingredients. Generally speaking, this magnetic transition temperature will lie around 500 degrees C. or 600 degrees C. and may be somewhat more or less than these figures.

Having heated the specimens thoroughly to a temperature of at least 900 degrees l., they are next cooled down to a temperature near this magnetic transition temperature, preferably a temperature a little higher than the magnetic transition temperature. For a composition of nickel and iron only, with from 55 per cent nickel to 80 per cent nickel, this critical temperature will lie between 550 degrees C. and 625 degrees C. The rate for cooling from 900 degrees C. d'own to this point should be conveniently gradual, say twenty minutes may be required for this stage with a pancake coil of loosely wound nickel iron tape as heretofore described. No harm can be done by cooling too slowly through .this stage from 900 degrees down.

Next the specimens are to be cooled down through a temperature zone that will carry theln distinctly lower than the magnetic transition temperature at a rate which is desired to be fast enough and yet not too fast. They should not be cooled so rapidly as to set up undue stresses and strains, for if this isdone the permeability will be less than the utmost attainable.

On the other hand they should not be cooled too slowly, that is they should be cooled fast enough so that at normal temperatures they will exhibit the highest permeability that can be developed therein.

Assuming as heretofore suggested, that the test is being made with a whole series of like specimens treated alike to the point of cooling down to the magnetic transition temperature, these specimens may be cooled at different rates from that point down to say about 300 degrees, then `cooled at any convenient rate the rest of the way down to normal temperature, and then tested to see which of them has had the highest permeability developed therein. The results obtained will be reproducible, so that in this Way the optimum rate of cooling in the stage from the critical temperature down, may be accurately determined.

. An examination of a series of specimens 'in accordance with Fig. 8 may be helpful.

oped, the curve R will exhibit a high value of inductionfor moderate temperatures but will drop tov an intermediate minimum as at P before going to the Well known maximum Q, that precedes the attainment of the critical temperature, which in this case is about 600 degrees. On the other hand, if the desired permeability has not been developed in this specimen the curve will be like S, showing no such intermediate minimum as at P. I

To sum up briefly, the specimen should be cooled through the stage from the critical temperature down at a rate not too fast and yet fast enough to develop the highest per-` meability at normal temperatures with low magnetizing forces. This rate may be readily determined by testing a series of specimens at different rates, and guidance may be aiforded by noticing whether a test according to Fig. 8 gives a curve similar to R; having an intermediate minimum as at P, instead of such a curve as S, having no such intermediate minimum.

In connection with the foregoing, it should be remembered, (l) that for many purposes the utmost ermeability is not necessary nor desirable; 2) that the rate of cooling that gives the utmost permeability is not exactly and narrowly determined, but that other rates of cooling not Widely different will give almost or quite as great permeability, (3) that a little practice along the line of Fig. 8 will enable one very quickly to recognize the best procedure to obtain the utmost permeability, and (4) that if it is not convenient to carry a plurality of test samples through different rates of cooling, a single sample.

can be taken over the same temperature range in successive trials at the different rates; in this connection it will be noticed that when the optimum rate has been discovered, the reproducibility of the proce.-

dure enables the maximum permeability to.

be re-established in the same sample or a like sample.

` pressure.

found that if an attempt is made to put the A tape through a heating and cooling treatment and thereafter apply it to the conductive copper core, the permeability may be impaired. Apparently, the stresses involved in Winding the tape upon the conductive core have a tendency to destroy the permeability that has previously been conferred upon the material of the tape. Hence it has been found advisable to conduct the heat treatment after the magnetic material has beenassembled in its operative relation to the electric conductor with Which it is to be associated.

For the continuous loading of a signaling conductor it isimportant not only to secure high permeability of the loading material, but it is important that they permeability be uniform. It has required much investigation to determine the necessary conditions of treatment, and these conditions have been presented in this specification.

It has been stated above that it is desirable that the conductor Within the loading envelope shall have a smooth cylindrical contour. One reasonl for this is that the ocean depths, when the cable is subjected to pressures of the order of 5,000 pounds per square inch, if the conductor surface ,were irregular, the magnetic material might be stressed and strained unequally by the great The effect on the material of the sheath might be to impair its permeability. Another advantage of the compact structure shown for the conductor, is that it has less electrostatic capacity than if it consisted of loosely assembled strands.

The improved magnetic material of this invention is useful for other purposes than for the continuous loading of signaling conduotors. It may be used advantageously for relay armatures and for frequency changers and modulators. It is also useful for lumped loading as Well as for continuous loading. Choke coils of very high inductance and 10W resistance, may be made up in remarkably small volume, with consequent savin of material and laboryin manufacture. ils with cores of thls material have been found particularly valuable for use as magnetic shunts in submarine cable telegraph receivare mounted. Such al coil is shown in Fic. 9, with the core 6, on which the coil windings 7 and 8 are indicated diagrammatically. In order to give the core material stability or constancy in permeability, even though large currents are superposed on the loading coil circuit, the core may be provided with gaps filled with nonmagnetic material 9. The use of the improved magnetic material allows the necessary effective permeability to be secured even with these gaps present. The number and length of these gaps may bc regulated as desired. The windings of the wire core G may7 be held together by wrapping the core with tape 1() of non-magnetic material, and the core sections on each side of the non-magnetic gaps, with the windings thereon, may be held together by clamps 11.

Ordinarily, the stresses or strains put upon thenickel-iron wire (assuming that this is the composition of the improved magnetic material employed for the core 6), will not seriously decrease its permeability, provided it has been properly heattreated before winding, so as to develop its possible high permeability. But if it seems desirable, the formed core can be heated and cooled at the proper rate so as then to develop its permeability.

What is claimed is: 1. A magnetic material characterized by higher permeability than that of iron at magnetizing forces around 2/10 c. g. s. unit or less, comprising two elements of the magnetic group and a substance which increases the specific resistance thereof.

2. A magnetic material comprising nickel and at least one other element of the marfnetic group and a substance of high specific resistance, said material having developed therein by heat treatment high permeability at magnetizing forces around 2/10 c. g. s.

unit or less.

`or less comprising nickel, iron, and a substance to increase the specific resistance thereof.

6. A magnetic. material comprising nickel, iron and a substance to increase the specific resistance thereof, and in which the nickel component predominates and having a permeability higher than that of iron at magnetizing forces around 2/10 c. g. s. unit or less.

7. A magnetic material havingl a pernicability higher than that of iron at magnetizing forces around 2/10 c. g. s. unit or less comprising nickel, iron, and a substance to increase lthe specific resistance thereof, and in which the nickelcomponent is 55% or thereabouts of the whole. i

8. A composition of nickel, iron and a substance which increases the specific resistance thereof, in which there is developed by heat treatment a permeability at magnetizingl forces around 2/10 c. g'. s. unit or less higher than is attainable for iron.

9. A magnetic material comprising two elements of the magnetic group and a substance to increase the specific resistance thereof, and having high permeability at low magnetizing forces developed therein by heating above a certain temperature and then cooling past that temperature at a rate intermediate an annealing rate and a rate at which undue'stresses andstrains would be set up in the magnetic material.

10. A magnetic material comprising two elements of the magnetic group having a permeability higher than that of iron at magnetizing forces around 2/10 c. g. s. unit or less and a substance to increase the specilic resistance thereof, and in combination therewith an electric conductor in inductive relation to said material.

11. A transmission line loaded for high speed signaling with a magnetic material, comprising nickel and iron and a substance to increase the specific resistance thereof.

12. A transmission line loaded with a magnetic material comprising nickel, iron and chromium.

13. A magnetic -alloy having a permeability higher than that of iron at magnetizing forces around 2/10 c. g. s. unit or less consisting solely of nickel and iron, both as pure as are good commercial grades, and a substance to increase the specific resistance of the alloy.

14. A magnetic material comprising nickel, iron `and a substance to `increase the specific resistance thereof and having a permeability higher than that of iron at mag-l netizing forces around 2/10 c. g. s. unit or less, and in combination therewith an electrical conductor in inductive relation to said material.

15. A magnetic alloy comprising nickel, iron and a substance to increase the specific resistance thereof and in combination therewith an electrical signalin conductor, in inductive relation yto said alloy, the magnetic field strength set up in saidalloy being of the order of 2/10 c. g. s. unit or less.

16. A magnetic alloy comprising iron, nickel and a substance to increase the specific resistance thereof and having high perso great as to set up undue stresses in the' alloy.

17. A transmission line loaded with a magneticmaterial having a resistivity of range o the order of 100 microhms per cubic centimeter.

18. A transmission li-ne comprising a central conducting core and a layer of magnetic material Wrapped therea'bout, said magnetic material consisting of an alloy of nickel, iron, and chromium having a specific resistance of the order of 100 microhms per cubic centimeter.

19. A magnetic material characterized by higher ermeability than 800 in the entire iimagnetizing forces from 0 to 2/10 gauss, and comprising two elements of the magnetic group and a substantal quantity of chromium.

20. A magnetic material possessing a permeability above 800 in the entire range ot' magnetizing forces from 0 to 2/10 gauss, and comprising nickel, iron. and chromium, in which the nickel component is or more of the total nickel and iron content.

21. A transmission line conductor loaded with a magnetic material comprising an alloy including nickel, iron and chromium, more than 25% of the nickel and iron content being nickel.

22. A transmission line conductor loaded with a magnetic material comprising an alloy including nickel, one other magnetic element, and chromium, more than 25% of the whole material being nickel, said material having an effective initial permeability above 300as applied to the loaded con-l ductor.

23. A magnetic material characterized by higher permeability than that of iron at magnetizing forces in the range between zero and 2/10 gauss comprising nickel, iron and chromium, the chromium being substantially 11% of the entire material.

In Witness whereof, I hereunto subscribe my name this 8th day of July A. D., 1921.

GUSTAF W. ELMEN.

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