US2469266A

US2469266A - Magnetic transducer having an irregular nonmagnetic gap

Info

Publication number: US2469266A
Application number: US690458A
Authority: US
Inventors: Hugh A Howell
Original assignee: Indiana Steel Products Co
Current assignee: Indiana Steel Products Co
Priority date: 1946-08-14
Filing date: 1946-08-14
Publication date: 1949-05-03
Anticipated expiration: 1966-05-03

Description

May 3, 1949 H. A. HOWELL 2,469,266

MAGNETC TRNSDUGER HAVING AN IRREGULAR NONMAGNETC GAP Filed Aug. 14, 1946 Patented May 3, 1949 MAGNETIC TRANSDUC'ER N "IRREGULAR NONMGNETC Giu 'Hugh A. Howell, Valparaiso., Ind., Jassigner to The Indian-a Steel Products Company, Chicago, vlll., a corporation ofllndiana Application August 14, 1946, Serial No. 699,458

2 Claims. 1

This invention relates to a new magnetic recurdi-ng technique, and .more particularly to a variable gap magnetic :transducer fhead and :novel method.

IOne -of the `,principal features of the :present invention is V-to provide Ean electromagnetic vtransducer head in which the nonmagnetic 'gap thereof varies fromone side to another of the vgapx'so that the .flux density throughout 'the gap is notnniform but varies in a predetermined manner. When :the electromagnetic 'transducer .head .is so .arranged to :provide .a nonmagn'etic :gap which :the -density yvaries la predetermined :manner or pattern, 'a greatly :improved response cha-'racteristic is obtained. Since 'the current 'ontput .fin the pickup -coil of a :magnetic :head `varies 1in Yaccordance with .frequency of the :sig-nal .impressed upon the record vmember and :in accordance 'with ythe iengthof vthegap it is necessary in order to :get a level 'current output to :have a fdiierent 'length 4gap for-each3frequency. By using :an elongated record medi-um having a relatively wide dimension, such as by using a :magnetic :tape and :lay varying the length of the nonmagnetic gap from one iside of the tape to thefother in `a longitudinal direction, the current k'output characteristic curve versus .frequency is `very greatly improved. IIndeed it has been :found that Isuc'h an arrangement gives such a greatly improved result that a reproducing headv may be connected directly into :any home .radio receiver without any special equalizer circuit.

It is an yobject of the'present invention to pro vide a novel method and means for .magnetic recording `and reproducing.

Another obect of the present invention :is to provide a variable gap magnetic transducer head fand method.

A further vobject of the pre'sent .invention is to provide :a novel transducer head yin which 'the nonmagnetic gap is so arranged lthat the flux densi-ty throughout the gap varies from place to place.

A Still further object of th'e :present invention is to provide la 'novel magnetic transducer head in which the 'confronting pole lfaces of the ipolar portions thereof fdo not Tlie vin :spaced .parallel 'planes lbut are of predetermined coniguration Vgiving `a yplurality of ldifferent distances rtif-:tween different confronting portions thereof.

Another and further object yof the present iinven'tion is `to provide a novel method rand means for recording signals on :a .magnetic tape in such a .manner tmat the :so-called constant' current response is more uniform and more easily corrected :j

2 equalization than tthe response hitherto Spossible.

The novel teatures which 'are fbelieved to be characteristic of my `invention are .set :forth `with paiiti'cul'arity in :the appended claims. My invention itself, however., rlootlfi as .to its 4orgam'zation .rand manner :of construction, together with further vobjects and advantages thereof, .may best understood -by reference to the following :de- Jscription, taken in connection xwith the :accompanying fdrawmg, .in which:

Figure i vis la diagrammatic isometric View of an electromagnetic transducer head :embodying 'a inovel feature and characteristic fof 7the present invention;

.Figure '.2 is an A'enlarged .fragmentary isometric `view of fthe confronting lfpolar portions of the :electromagnetic transducer `head :shown .in Figure 1;;

Figure 3 is a graph fsh'owing a typical constant current `response :obtainable from an electromagnetic transducer hea'd 'in which ytheconifronting pole faces lie in :spaced parallel Aplanes;

Figure 4 is fafgraphshowing -a .family-oi curves giving the variations .in the `frequency where the maximum output 'occurs with variations in gap lengths, each curve being -for -fa different `gap length;

Figure :5 is a :graph simi-lar to Figures 3 and 4 but giving :the response 4characteristic when Van yelect'roniagnetic transducer head is employed rsuch as that illustrated in Figures -l and .2 "of the drawing;

Figure 6 is =a fragmentary isometric View fsimilar Ato Fig-ure i2 rbut illustrating a modified form of 4the present invention;

vFigure 7 is 'a iiragmentary isometric view 'similar to Figures y2 and '6 illustrating 'a third embodiment lof the present invention; fand Eig-ure e8 is a .fragmentary iront elevational *view 'of the lpolar Aportion :shown in 4Figure 7,.

The electromagnetic transducer head :shown diagrammen-cally in Figure 1 :of the drawing :includes a core member Irl .a Ipair of -symphonie v:core (portions I2 .and 153 with :a nonmagnetic record member such as a paper tape coated with a permanent magnet material or a Steel tape having a reasonably high coercive force.

It will be remembered that in a conventional electromagnetic transducer head in magnetic recording and reproducing devices the confronting pole faces Il and I8 lie in spaced parallel planes. With such prior art structures the typical constant current response characteristic is illustrated in Figure 3 of the drawing. In this graph the curve I9 shows the relative E. M. F. developed across the terminals 20 and 2l of the winding I5 through the frequency range of 30 to 10,000 C. P. S., when the recording current which impressed the signal on the record member I6 is maintained constant for all frequencies throughout the indicated range during the recording operation. From the curve I9 of the graph in Figure 3 it will be noted that the output rises beginning at the lowest frequency at a rate of about 6 decibels per octave until a certain characteristic maximum has been reached.. The maximum as shown in Figure 3 occurs at about 2,000 C. P. S. After the maximum is passed, the output more rapidly decreases. The rising portion of the curve I9 is due to the fact that the rate of change in flux induced in the transducer head Ic when it is acting as a reproducing head by the tape I6 determines the output. The maximum rate of change for a constant total number of lines is nearly proportional to the frequency. For example a high frequency would produce a aster rate of change than a low frequency at the same tape speed even though the remnant flux on the tape for the two frequencies were of the same value. The characteristic drop after the maximum on the curve is due to a condition imposed by the relation between the gap length and the tape velocity. The particular frequency point where the maximum output occurs increases as the tape speed is increased or as the gap is made shorter.

The characteristic rise in output from the lowest frequency to the maximum will be the range of most interest since it is in this range that the greatest amount of correction is required to get a relatively flat response. It will be noted in Figure 3 that the output at 39 C. P. S. is about 28 db. lower than at the maximum. This means that in order to make the proper correction an overall boost in the base response must he produced in the recording and playback ampliner. A 14 db. boost in the base response of the amplifier would record a higher level in the base region and during playback there would be an equivalent 14 db. boost. It will be here noted that when the proper low frequency boost is used to flatten out the range immediately below the maximum, the response at the extreme low end is still down a few db. and the base response suffers.

In Figure 4 there is a graph giving a family of curves showing the variations in the frequency where the maximum output occurs with variations in gap length, all other conditions being considered constant. More particularly the graph in Figure 4 gives four

curves

22, 23, 24, 25. The curve 22 is for the longest gap and the curve 25 is for the shortest gap. By way of an example and not by way of limitation, the longest gap may be .1" while the shortest gap may be .0015".

In accordance with the teachings of the present invention, a gap is employed which varies in the length across the width of tape and as a result thereof substantially the envelope of the family of curves shown in Figure 4 is obtained, as is shown by the full line 26 in Figure 5. The dotted lines in Figure 5 illustrate the same family of curves as shown in Figure 4. In this manner the maximum output is spread out or flattened over a substantial portion of the operating range. The curve 26 of Figure 5 is obtained from an electromagnetic transducer head having a variable nonmagnetic gap as illustrated in Figure 1 of the drawing. This particular head is shown more clearly in the fragmentary view of Figure 2. More particularly the gap I4 is in the form of a wedge. The pole faces I'I and I8 lie in vertical planes which diverge from the back side of the core II to the front side of the core II. This may be seen clearly by the diverging lines 2t and 21 which are the top edges of the nonmagnetic gap.

Since the length of the nonmagnetic gap from one pole portion to the other, as shown in Figure 2, varies across the width of the tape it will be seen that in effect we have the summation of an innite number of curves making up a family (of which a few are shown in Figure 4). The overall effect is that the current response is the summation of the family of curves and thus a current response characteristic like 2S is obtained rather than a response characteristic like The particular shape of the nal response characteristic 26 as shown in Figure 5 of the drawing may be controlled by the manner in which the gap length varies from one side of the core to the other. Thus instead of using a wedge shaped gap which is not shown in Figures 1 and 2, a gap may be employed in which the

upper lines

26 and 21 of the pole pieces I2 and I3 are curves which gradually flare apart. As shown particularly in Figure 6, the initial portions may be parallel as at 28 and 29 before they start to gradually flare out, depending upon the shape of the final response characteristic desired.

A third embodiment of the present invention is illustrated in Figures 7 and 8 of the drawing wherein the top edges 26 and 2'I not only diverge as in Figure 2 of the drawing but the thickness of the pole pieces I2 and I3 vary from one side to the other. This, when carried out in the manner shown in Figures '7 and 8 of the drawing, produces a much more rapid change in flux density in the gap I4 than is obtained with Figure 2.

While I have shown some particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made, and I, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

l. A magnetic transducer head comprising a paramagnetic core having a pair of confronting pole portions with a nonmagnetic gap therebetween over which a traveling magnetizable tapelike record member is arranged to pass, the confronting faces of said pole portions being shaped to diverge from each other from one side edge of said gap to the other and said pole portions also being decreased in thickness from said first side edge to said second sidel edge, and a signal coil on said core for establishing a fluctuating magnetic eld across said gap.

2. A magnetic transducer head comprising a paramagnetic core having a pair of confronting REFERENCES CITED The following references are of record in the nie of this patent:

Number FOREIGN PATENTS Country Date France June 13, 1924 Great Britain Apr. 28, 1939