US2488717A - Magnetizable wire recording system and method - Google Patents

Description

Nov. 22, 1949 s. D. EILENBERGER 2,488,717

' MAGNETIZABLE WIRE RECORDING SYSTEM AND METHOD Filed Nov. 19, 1945 2 Sheets-Sheet 1 FIG-u l-A INVENTOR F Ga sta'nleg DEilen berser- ATTORNEYS.

1949 s. D. EILEYNBERGER 2,483,717

MAGNETIZABLE WIRE RECORDING SYSTEM AND METHOD Filed Nov. 19, 1945 2 Sheets-Sheet 2 14;; /5Q All INVENTOR Stan Le z D. Eilenberger BY M w ATTORN EYS.

Patented Nov. 22 1949 umrszo: PAI M;

v znssam MKGNETI'ziiBLEiWiRE RECDBDINGSYSTEM ANWMETHDU StanlewDsrEilenberger, Kenosha, Wis, assignor, by mesne': assignments, toql ljoago coin Machine :Co., ;at.oorporatin of'Illinois z Applicationwoveniller -ls, 19453 serialnotezoisoo sac'laiinsa f (o1. 179-1062) U. is. Eaten-ti No.-.,2 ,43'3;20 7; granted Decr123o 194-7; eandnreference should ber-maideztdstheseacdspending; applications for -a; betterrunderstandinga of the present invention.

For the purposezof-this;application, a FIGtHilFlflT-l polerpiece is rdefined-zas :one: having: a; thickness aon therord'er o-fsound .track-diameterza relativelyrlongi width;in'zthe:- direction-50f soundetrackztizavels'and' heighth in aaccordancevwithncoil desist-1:2, Imp ticular, this definition has; been: appliedn to: a: Teshapedpole@ piece where-'zthe' head aof thee inverteda-Tdsiin magnetic relatiomto;thesoundtracks 'I'heuoperational l principles; of such: an pole pieoee have -been-described in detail dmtheeaboveacitect coependin applicationsaandaforzthe pnrposeseofi the-present invention; it maysimply bestatedcthati sucha pole 'piece' r-istrelatively independent Ilfhigh; frequency; cut-off as l a, functiorrfi. oie sound-i: traolei speed;1 tthuscmakin-gg possible :relativelydow: sound? track speedsfor-agiven high frequency-responses The presentdnventiorr is :sizmilar-' to one-winner cot-pending applications:a'bovercitedaentitledaR tilinearpole piece for wire recordingd? file'dsMa m 9;; 1945 Seriah iNumloer 592,811,: now abandoned; intgeneral form; but certain improvementsi have? been made=.,which result :in aradicaliimprovements. in-efliciency and the slgna'lsto noise-oration,- Cone sidering; efficiency: in terms-toil: the outplrt leveir 40%;

of the magnetic; head duringn the-- reproducing? cycle the gain in efii'ciency; oi -la system operating-.1 accordingatothe present invention overra System41 operated according: to my: previously, cited: cos-' Bit-,wayi-oi ifartherzclarificatiomit maysbes brieie: 1y? statedithatethe: outputlevel; of; the magnetic; head operated in accordance With;mm'previ0ns-@- 1y;citedgcoependinggapplication was; on :the order of microphonesoutpnt levelslwhichtxmayebreirtakem as ;'502 d-b., while-fthe output ota headioperatedfinr accordance with l the present -inventionglis sonother order of piclr-uprlevelror approximately .zerogclbrn.

further: feature of; the}? present inventi'on is thatwthe fidelity is greatlygimprovedfio errthessysa' tem-idisclosedrbp previously citedacoepcndingr application, as vvi'llebe shown fartherz below:

- Ehe objectssofuthis invention arefiv 1 To 'provide a magnetic recording lreproduow inggsystem whichshallobe relatively free from:

thealimitations of -finite;pole piecev dimension-and: sou-11d traek speed asz'a function of llrigfih frequency; response, i to. provide relatively; good; high: free; quency: response I at relativelylow sound track; speeds;

To:- provide aom-a'gnetic;recording reproduca ing; .system which shall ;op erate= at relatively hih efficiency as compared-to previously-v known: sys:- tems.

3-. To provide-za-magnetic -recordingr/reproduc-fi ing system ;which .shall I have a1-favorab-le:-. signah to-1noise ratio--as compared :=to-;-previou'sly knownz systems.

7 42 Y T02: provide a magnetic recording /reproduce ineczsystemawhich-shall .-essentia1ly; reproducew-thez recorded-wave form with a m-inimhrnaof frequency! response correction'toprovide a relatively? high-. fidelity system.-

This-inventionwillnbe' best understood? rfIiOllI a2 consideration 1 of l the". following detailed: descrip tionfln viewof 'the'accompanyi-ng drawingsiionm ing appa-rt of"; the specificationsnevertheless; i understoodwthat the inventionis :not confinednto: thesdisclosure beingv isusoeptibletoesuclr changes; and-modificationsas definerno material-departure:- fromnthe sa-lient featur estoftth'e :invention -as exw pressed in the appended claims.-.-

Inthee-drawings Figure: l represents 2.71 schematic view or; as

pending; application; is on-the %order {of '50 d-bz;z and) 45s magnetizablewire recording reproducing; systenri this (radical 1 improvement in efficiencyi' I'B'SlliilSPiIt? argreatly improved :signai tOuIlOiSG patio.

The. signal tonoise: ratio isrgenerally definedrasr theratio ofthe signal voltage to, thenoisevoltsagar-and in thepresent instance; the :1noise;levelil50 remainsessentially constant, if- 'compared toi thef= system described-Jammypreviouslvjrcitedtcomend? in'g application; fwh-ilet the-:signaleleveh isrup t apsproximately *d-b's; thus -'.resulting-;in a:. '50i-dbs im-x' provement insignalsitosnoise ration operated in a-ccordancei-withi'previouslin citedr (impendingapplication: entitled Rectilin'eari pole piece "for: Wire: recordi-n-g=,; and :a-lli reference? numerals are :the' same as in Figure l .-;of this co-" pendingivapplication, this drawing being 'included'a" for -reference purposes only;

\ Figure 1a is QACIOSS: section-:schem-atictviewrofi Figured through-line-JQQ and is againeid'enticalc with Eignre 2? of! my coependings application?! 1 1 our cited'just Fabove:

Figure 2 represents a simplified view of the magnetic field associated with the pole piece the same as in Figure 1.

Figure 3 shows a modification of part of Figure 1, where the sound track position is in accordance with this invention, all other components being the same as in Figure 1.

Figure 4 represents a simplified field configuration for the sound track position of Figure 3.

Figure 5 is a grossly exaggerated section of sound track with a grossly exaggerated and simplified magnetic field configuration as it appears to the sound track passing by the pole pieces in Figure 3.

Figure 6 represents a modified pole piece shape for use in the arrangement of Figure 3.

Figure '7 represents a farther modified pole piece shape for use in the pole piece arrangement of Figure 3, and is the preferred form.

Figure 8 represents a modification of Figure 3 incorporating the pole piece shape illustrated by Figure 7, wherein both pole pieces are formed as a unit section.

Figure 9 is similar to Figure 8, except that the pole pieces are formed in two sections with a magnetic joint to facilitate construction of a complete recording/reproducing head, and this arrangement represents the preferred form.

' Referring now to Figure 1, the magnetizable sound track is represented by I, sound track I being Wound from wire reel 2 onto wire reel 3 in the direction of motion as indicated by the arrows, for the recording of reproducing cycle, it being understood that the wire may be rewound from reel 3 onto reel 2 and that during the rewinding process the direction of motion will be opposite that shown by the arrows. The recording or reproducing pole pieces are represented by 4 and 5, having coils 6 and I associated therewith, said coils being connected in series aiding and having leads brought out to terminals 8, it being understood that terminals 8 are connected to a suitable recording or reproducing amplifier.

The novel feature of pole pieces 4 and 5 is that the dimension in the direction of sound track travel is on the order of or greater than the lowest frequency it is desired to record. This is in total disagreement with the previous conception of magnetic recording, where it had generally been accepted that, in order to carry out the recording/reproduction process, it was necessary to have a finite dimension in the direction of sound track travel on the order of one-half wave length of the highest frequency it was desired to record, thus necessitating an exceedingly small dimension, usually on the order of .001". The operational principle for rectilinear pole pieces, as

represented by 4 and 5, has been more fully disclosed in my co-pending application hereinbefore referred to, but it may be briefly stated that pole pieces 4 and 5 should have a dimension Z at least equivalent to a full cycle of the lowest frequency it is intended to record, and preferably a dimension Z on the order of two cycles of the lowest frequency it is intended to record, where dimension is a function of frequency and sound track speed. It has been experimentally determined that a practical dimension for Z is on the order of to /2". A dimension smaller than fails to fulfill the requirements of a system operated in accordance with this invention, and a dimension much greater than /2", while theoretically sound, operates at low emciency due to the relatively large mass of pole piece material. obliteration is carried out by obliteration pole piece 9 and its associated obliteration coil I0, having terminals I I connected to a suitable source of obliterating current, which is usually a source of D. C. voltage, the magnitude of which is determined by obliteration head design. Air gaps I2 and I3 are shown between sound track I and pole pieces 4 and 5.

Referring now to Figure 1a, a cross section view of Figure 1 is shown through the line XX, all reference numerals being the same as in Figure 1. The dimension V of pole pieces 4 and 5 is non-critical and may be equal to or greater than the diameter of sound track I. For reasons of mechanical conveniences dimension V is usually made much greater than the diameter of sound track I. For example, assuming that sound track I has a diameter on the order of .004", then it would be satisfactory to make dimension V of pole pieces 4 and 5 on the order of thus removing the necessity for extremely accurate guiding means.

It is understood that Figures 1 and 1a are included in this specification for reference purposes only, and do not disclose the novel features of this invention, such novel features being represented by Figures 2 through 9 inclusive.

Referring now to Figure 2, a partial view of pole pieces 4 and 5 is shown, and it may be assumed at a given instant, pole piece 4 represents a north pole and pole piece 5 represents a south pole, and that pole pieces 4 and 5 are unit poles, so that the lines I4 would represent the normal path of the transverse magnetic flux, it being understood that this picture is over simplified, as in actual practice the magnetic flux lines will not be exactly straight, and that in a dynamic system there will be leakage flux at both the leading and trailing edges, but for the purpose of this invention, it introduces no error to assume the flux lines are straight and to ignore the leakage flux known to exist at the leading and trailing edges of the pole pieces.

Referring now to Figure 3, the conditions are essentially the same as in Figure 1, except that sound track I has been made to pass obliquely between pole pieces 4 and 5, so as to be in relatively close magnetic relation to pole piece 4 at leading edge A and also to be in relatively close magnetic relation to trailing edge D of pole piece 5, at the same time maintaining relatively distant magnetic relation to trailing edge 13 of pole piece 4 and leading edge C of pole piece 5. As a matter of physical practice, it has been found satisfactory to allow sound track I to travel obliquely between pole pieces 4 and 5 in magnetic contact with pole piece 4 at point A and pole piece 5 at point D. Ihis arrangement does not result in undue pole piece wear, the wear being taken up by guides normally associated with any wire recording system. As a matter of mechanical convenience and improved preformance, dimension Y is now made relatively great in comparison to the diameter of sound track I. For example, assuming that sound track I has a diameter on the order of .004", it has been experimentally determined that a practical dimension for Y would be on the order of .025", which would give an air gap on the lines BD and AC of .025 minus .004" or .021, with air gaps between sound track I and point A and D approximating zero. The dimension Y is variable within limits, the lower of which is critical at twice sound track diameter, or in the example as given, at approximately .008". The upper limit is less critical and desirable results have been obtained with this dimension in excess of ten times sound track diameterv or, inthe exof the fiu'x path is shown, where we may again assume that at a given instant, pole piece 4 is a unit north poleand pole piece 5 is a unit south pole, and that flux-lines 14' result from this con- ,dition, thus producing, to some degree, transverse polarization of soundtrack I. At the same instant, we have a closed magnetic circuit between points A and D, so that there is produced longitudinal polarization of sound track l, as represented by the flux path I5.

Referring now to Figure 5, the condition illustrated by Figure 4 isexaggerated, la representing a section of the sound track I, where joint AA is the instantaneous north pole and point DD the instantaneous south pole, with flux lines l4a representillg the transverserpolarization of; sound ra k mend flux lines .1 4 rep senting he l gitudinal polarization of sound track la, it being understood that these flux lines will not be perfectly straight as represented in Figure 5, and this is particularly so in a dynamic system where sound track la is moving in respect to its associated pole pieces, thus bending flux lines Ma to a degree partly determined by the speed of sound track la in respect to its associated pole pieces. However, it is believed, that flux path l5a will be largely confined to the sound track due to the relatively low reluctance of a closed magnetic path.

Referring now to Figure 6, a modified pole piece structure is shown in the form of a T, having a pole piece face It and coil ll associated with pole piece body I 8 and connected to a suitable recording/reproducing amplifier at terminals 8. While the pole piece illustrated by Figure 6 may assume various modified forms, it has been experimentally determined that practical dimensions would be pole piece body width W equal and pole piece face width Z equal /2", the practical thickness for such a pole piece being on the order of .025" and the length of pole piece body l8 being determined by coil design.

Referring now to Figure 7, a farther modification of pole piece design is represented, where pole piece face I9 is shown with triangular leading and trailing edges, all other conditions being the same as represented by Figure 6. I

Referring now to Figure 8, a complete schematic view of a recording/producing head is shown, where pole piece 22 has faces 24A shaped in accordance with Figure 7 and coil 23 connected to a suitable recording/reproducing system at terminal 8, the design being such that guiding means normally associated with sound track I causes said sound track to move obliquely between pole piece faces 24A in accordance with Figure 3.

Referring now to Figure 9, a modification of Figure 8 is shown, where pole pieces 25 and 26 are two separate pieces mechanically, having pole piece faces 27A and 28A and a magnetic joint at 29, where said magnetic joint 29 may be either a butt joint or lap joint, but 29 is intended to represent a closed magnetic circuit without introducing an air gap. This is the preferred design, as the two piece construction allows easier assembly of a complete recording/reproducing head, and in practice it has been found satisfactory to allow pole pieces 25 and 26 to over lap each other about A," inside of the coil associated with pole pieces 25 and 26.

of the liigh'permeabflity,alloys such as mix-metal or Permalloy, have-beenfound satisfactory as pole piece nmterial,v themechanical design being a function of .goodengineering practice. r W

The present system disclosed bythis inventicn, differs from the-system-disclosed by my. previously mentionedco-pe'nding applications, in the method of passing the sound track. through the head, and the results obtained may. he briefly :sunnnarized as follows:

The output level for a constant amplitude recording is approximately 50 db. higher for a system operated in accordance with Figure :3, as compared to a system operated in accordance with Figure 1-.

The signal to noise ratio is also approximately 50 db. better forthesystem of Figure 3 over the system of Figure 1.

The fidelity is much better in that the arrangement of Figure :1 tends to distortthe lower frequencies, where such lower frequencies approximate a full wavelength as a function of .9 piece dimension and sound etraekspe d a d a s tends to distort the even harmonics of this fundamental frequency. This distortion is absent in a system operated according to Figure 3 and lower frequencies are produced with a fidelity equivalent to the high frequency fidelity, the high frequency fidelity being good for both systems.

The reason for this is not entirely known. It is not a function of the closed magnetic circuit as compared to an open magnetic circuit. For example, in a system operated in accordance with Figure 1, all magnetic dimensions may be closely adjusted to provide a closed magnetic circuit with a result that the system is essentially inoperative. It is believed that the combination of transverse polarization and longitudinal polarization produces a result not obtainable with either polarization alone and this is in accordance with recent magnetic theory. For example, assuming that we record a single frequency of 5,000 O. P. S., we will record a great number of transverse magnets in sound track I and simultaneously a number of longitudinal magnets in sound track I These cross magnets interfere with each other to a degree not yet determined, but the end result is a longitudinal polarization, where the trailing edge of the pole piece face acts as an infinitely fine point. The details of this process have been fully explained by one of my co-pending applications previously cited entitled Rectilinear pole piece. In certain recently developed magnetic devices, auxiliary means are used to superpose a second frequency on the sound track in addition to the recorded frequency and such systems have been tentatively explained as producing better fidelity at higher eificiency due to the presence of many minor descending loops in the hysteresis loop, and it is believed that the present invention accomplishes the same end result by a simpler means, and that the cross polarization produces numerous minor descending loops in comparison to the normal hysteresis loop, thus resulting in a longer and straighter descending limb, which may be used for recording. In additionto these advantages, the present system includes all of the advantages offered by the rectilinear process, as set out by my previously mentioned co-pending applications, in that good high frequency re sponse is obtained at relatively low sound track.

76 speeds.

The above examples are for the purpose of i1- lustrating some of the methods and means by which the broad purposes of this invention may be carried out and are not to be deemed as restrictive in any manner. Other modifications and alternatives will occur to those skilled in the art without departing from the scope of this invention as defined by the following claims.

Having thus described the invention, what is claimed as new is:

1. In a magnetic system of the type having a sound track transversely magnetized for recording and reproducing complex sound waves covering a broad range of frequencies, a recording and reproducing head providing spaced magnetic pole faces transversely aligned on opposite sides of the track having a dimension along the path of sound track travel of the order of the speed of the sound track divided by the lowest frequency to be recorded and means for moving a sound track obliquely through the normal flux path between the pole faces.

2. The system of claim 1 wherein said sound ing edge of one pole face and the trailing edge of the other pole face.

3. The system of claim 1 wherein the distance between opposed pole faces is in excess of twice 5 the transverse dimension of the sound track.

STANLEY D. EILEN'BERGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 873,078 Pederson Dec. 10, 1907 15 2,300,320 Swartzel Oct. 27, 1942 2,351,003 Camras June 13, 1944 2,351,007 Camras June 13, 1944 FOREIGN PATENTS 0 Number Country Date 590,330 Germany Feb. 24, 1928 594,991 Germany Mar. 15, 1934 638,930 Germany Nov. 5, 1936 track is in magnetic engagement with the lead-

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