CA1102395A - Magnetic recording head - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A head for producing magnetic images of fine detail, including a group of recording elements spaced perpendicular to the movement of a magnetic tape and a power source that passes current pulses through the recording elements to create magnetic fields that magnetize small regions of the tape. Each recording element includes an elongated conductor with a thin nickel layer nearest the magnetic tape and a thick copper layer on the side of the nickel layer opposite the tape, the copper layer having a small gap therein at a predetermined recording location. Accordingly, the center of current flow is normally through a middle portion of the copper which is too far from the magnetic tape for the resulting magnetic field to magnetize the tape, except at the recording location where the current passes through the nickel layer which is close enough to the tape to magnetize it.

Description

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Bl'.CKGROIJI`~) OF 1'r-lE Ii`~VE'?`lTIOi`J
I'his invention relates to a magnetic recording appard-t us .
In some pr:inting applicat:ions, i-t is necessary -to print alpha-numeric characters or other images of fine detail. A matrix printer w'nich can print a column of about 32 closely spaced do-ts and about the sa~e numb2r oE ro~,7s for each character, can crea-te substantially any style of char-ac-ter. However, where -the charac-ters are -to be of typical print size such as 2.5 mm high, the 32 prln-t or recording elements must be spaced abou-t 0.08 mm apart. It is dlf~icult to manufacture such small elements and mount them at such a small spacing, and it is also difficul-t to do this rela-tively low cost. ~ ~ ~
- ~ , SUI~AR~ OF THE INVE~JTION

In accordance with one embodiment af -the~present invention, a ma~netic recording head is provided which can be utilized in a printing machine of relatively simple con-struction whic}l can print îmages of fine detail. The record-~ ing head includes a group of recording elements which are closely spaced along a line perpendicular to the path of a magnetic recording tape, so that current through the elements produces magnetic flelds that record ma~netic ~pots on the tape. Each recording elemen-t includes an electrical conductor with a cen-ter of conduction spacéd more -than a predeter~ined dis-tance from the magnetic tape path except at a small record-ing location where -the center of conduction lies close enough ~ ' --.3--.

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to the magnetic ~ape path so that a current of predetermined magnetize -through the recording element records a spot on the magnetic tape.
The conductor of each recording element can be formed by a thin layer of nickel whicll extends close to the magnetic tape path and a thick layer of copper lying on a face of the nic~el opposite the tape path, with the copper layer having a gap a~ the recording location. ~hen a current pulse is passed through the recording element, the center of conduction lies near the middle of the copper layer, so that the resulting words magnetlze it. However, at the gap in the copper layer, the current must pass through the nickel layer which lies close enough to the magnetic tape so that the resulting magnetic field is strong enough at the tape to magneti~e it. A series of pulses applied to the recording elements as t~e magnetic tape moves thereby, creates a magnetic image on ~he tape.
Toner ls applied to the magnetic image on the tape, and the toner is transferred to paper or othex print medium to produce a visible image.
According to a broad aspect of the present invention, there is provided in a magnetic recording apparatus wherein a magnetizeable medium extends along a predetermined path, and a magnetic recording head is`posi-tioned along said path, a magnetic recording head comprising: a recording element ~hich includes an elongate electrical conduc~or portion with a center of conduction spaced from said path by more than a first distance ; except along a recording location of limited length wheTe said center of con-duction is spaced from said path by a second distance which is closer than said first distance to said path; and means for passing a current through said conductor portion; said current passing means being constructed to pass a current of an amplitude that will change the magnetization of said magnetizeable medium when said current is a~ said second dis~ance from said path of said medium, but not when said current is at said first dis-tance from said path of the medium.
3a According to another broad aspect of the present invention, there is provided a method for forming a magnetic image on a medium, comprising:

23~5 selectively passing currents along a plurality of substantially parallel pa~hs spaced from said magnetizeable medium by more than a predetermined distance from said medium except along path portions of limited length which are closer to said medium than said predetermined distance, where each of said currents is of a magnitude which causes magnetization of the medium only when moving along one of said path portions but not when moving along the rest of the path which is more than said predatermined distance from said medium.
The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description ~hen read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a simplified perspective view of a printing machine constructed in accordance ~ith one embodiment of the present invention;

-4a-;395 I:igure 2 i.s a pl.an vie~ of the printing machine of Figure 1, and also showing some of -the circuitry thereof;
Figure 3 i.~ a perspect;.ve view of the recording heacl apparatus of -~he rnachine of Figure 1.;
Figure 4 is an underside view of a portion of the recording head of Figure 3, taken on -the line 4-4 of Figure 3;
Figure 5 is an enlarged view taken on the line 5-5 oE Figure 3;
Figure 6 i5 an enlarged view taken on the line ~-6 oE Figure 4;
Figure 7 is an enlarged view showing a portion of a character formed by the machine of Figure l;
Flgure 8~is a~perspective vlew of a printlng system~
: cons~ruc-ted in accordance with another embodiment~o* the in-vention;
- Figure 9 is a~simplif~ied plan view of a recording element array of the type ~hich can ~e utilized in~the system : of Figure 8; and . ~ :
Figure 10 is a more det:ailed view of the recording head of the system of Eigure 8.
~ DESCRIPTION OF THE PREFERRED EMBa~IMENTS
: Figure 1 and 2 illustrate a printing machine 10 which employs a recording head appara-tus 12 of the presen-t invention -to form characters 14 of fine detail on a web of paper 16 or other print medium. The machine includes a~.mag-netic recordin~ -tape :L8 which .i5 guided along a predetermined path by rollers 20, and which is driven along the path by a motor 22 -that turns one of the rollers. The path of the record-ing tape .l~ extends across the recording head apparatus 12, 75/18$?1 23~;

where magnetic images are recordcd on -the tape. T'he tape then passe3 across a toner applying station 26 where -toner is applied to -the tape so -tha-t the rnagne-tized regions receive a coating of -toner particles., l'he tape then moves in fron-t of the paper 16 to which the -toner particles are to be -transferred. A
transfer head apparatus 28 is energi~ed to cause the toner on -the magnetic -tape 18 -to be'transerred to the paper. The paper is advanced by rollers~ and a fuser 30 (Fig. 1) fixes the toner to the paper, so -that a permanent image is formed on the paper~
The particular machine 10 which is illustrated, is designed for printing of lines of characters on paper. Infor-mation which is received in a receiver 32 is delivered .o a signal processor 34 which delivers signals -to the recording head apparatus 12 and to the transfer head ~8~ When signals 1~ represen~ing characters are recelved, signals are delivered ; over line 36 to the recording head apparatus 12 to cause -the recording of magnetic images on the tape. The tape moves past the toner station 26 where the magnetized images are coa-ted with toner 7 and -the toner-coated tape moves in front of the paper 16. When a line of characters lies'in front of the paper, a current pulse is delivered over line 42 to the transfer head 28 which lies behind the paper -to crea-te an elec-tric field which causes the -toner par-ticles on the tape 18 to move from the tape agains-t the paper 16. An electri-cally grounded strip 29 lies opposite -the head 28 -to establish a uniform electric field. After each line ~f characters is printed on the paper~ -the paper is advanced so -that a new llne can be prin-ted, while the previously pr~nted line is fused by th~ fuser 30.

75~1~SI1 Fi.~Ture~ 3~6 ~ strate details oE the recording head 12 ~IhiCll permi t S the reCOrdirlg of` magnetic character :images of fine de-tail on -the magnetic recording -tape l8. As shown in Figure 3, -the recording head apparatus 12 includes a thin sheet~li]ce recording head or device 50 which is mounted on a block~ e support 52 that has a convex face 52f. The recording device 50 (Fig. 4) has a group of -thirty-two record~
ing elements 60a-60ff which each include a recording location 62a-62fE tha-t can magnetize a small area of the magnetic re-cording tape. The recording locations 62 lie side-by-side and are spaced along a recording line 64 which ex-tends trans-verse to the direc-tion of movement~of -the magnetic recording tape l8 past the recording head.
Figures 5 and 6 illustrate addi-tional details of the recording device 50 which records images in a layer 80 of magne*izable material of the magnetic recording tape 18, and showing the details of one of the recording elements 60dd thereof. The recording el~ment 60dd includPs a first or underlayer 70 of moderately good conductivity such as nickel, and a second or overla~er 72 of high conductivity material such as copper. The recording device 50 includes a supporting film 74 of nonmagnetic material such as polyester, which supports -the nickel layer 7n of the recording element 60dd as well as each of -the other recording elernents. When a current is passed lengthwise along the printing elemen-t 60dd, the curreDt flows along a path 76, most of which lies near the center o~ the copper layer 72. This iB because copper has a conductivity abou-t six times grea-ter than nickel, and because -the copper layer is thicker -than the nic]cel layer. Near a plane 6ISp 3~3S

whic'h irlcllldes -the recording line 64, the recording element 60dd has a gap 78 in the copper layer 72. A.5 a result~ -the curren-t pa-th 76 mus-t extend through the nickel''layer ?
Along the current path region 76r ~7here the currerlt passes only through the nickel layer, the center of current flow is located a relatively small distance A froJn a layer of magne-tizable ma-terial 80 on the recording -tape 18. The mag-nitude of -the curren-t pulse passing through the recording element 60dd, is chosen ,so-that the resulting magnetic field ln at the current path portion 76r is strong enough to magne-tize the mater~al 80 of the recording tape. However~ the current magni-tude is small enough that the magnetic field will not magne-tize the material 80 at -the distance B between adjacen-t portions of ~he curren-t path and the tape layer. As a result, only a small region 82 of the magnetizable material 80 of the -tape will become magnetized by the current pulse which is passed longitudinally through the recording element 60dd. It may be noted that the recording tape 18 includes a supporting base 84 of a material suc'n as Mylar which supports the layer 80 of magnetizable material such as chromium dioxide~ and that a thin low friction film 86 of material such as polyester is provided over -the magne-tizable layer 80t The particles of -t'he layer 80 are pre~'erably oriented transverse -to the length of -the tape, and have a highly s~uare hysteresis loop ~haracteristic.
It also may be noted that the supportin~ film 74 of the record-lng head as well as most of the conduct~ve recording èlement extends almost parallel to the tape 18 a~t regions near the recording plane 64p, and ît is only the gap 78 on one side of the recording elem~nt that causes the' cen-ter of the current ~ ~aJ~ ~ r~

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pa-th 76 to suddenly veer cl.ose to the tape.
~ shown in Figure 6, each recordirlg elernent such as 60dd is preferably tapered' in cross-section with -the side nearest -the pa-th of the recording tape, a-t the layer 70, being of' narrowest wid-th. This tapering helps -to assure recording only at the recording loca-tions, in two ways, T'he tapering results in -the center of curren-t at 76 along mos-t o~
the recording elemen-t, lying nearer -the wides-t portion or base 72b of -the copper layer, whic,h resul-ts in ~he distance B from the cen-ter of conduction to the recording material of the mag-netic tape being greater. Additionally, when -the current passes through the recording portion 70r of the nickel layer along -the gap 78 in the copper~ the current flows along a nickel layer of sMall wid~h. This results in higher current intensity, and therefore. greater magnetic intensity immediately opposite -the center of the nickel layer.
The recording device 50 can be cons~ructed at rela--tively low costg ~y well known e-tching o~ deposition processes, although the -tapering may not be as smooth or uniform for elements of small width. The process can involve fo~ming a multilayer sheet that includes two materials of di~ferent conductivity such as nickel and copper, etching grooves across part of the sheet to leave the elongated elements that are connected together at one end to form a common area or base 92 (Figure 4) and e~tching narrow gaps 78 ;n the layer of higher conductivity. ln one method, a layer of copper is deposited over a layer of nickel to form a nickel-copper sandwich. The copper face of the sandwich is then attached to a suppor-t and a resis-t is applied over -the nickel layer in -the pat-tern shown 23~S

in ligur~ 4. Of course, such a pattern can be initiall~ drawn Lo a large scale and photo-reduced~ and then used to expose resist to sensi-tiæe it, all in a well known rnanner. The sand-wich is tihen dipped in an e-tchant tha-t etches bo-th the nickel and copper to produce elernents -tapered in cross~section, of the type shown in Figure 6. The resul-ting etched sandwich is then at-tached to -the polyes-ter sheets 74~ Resist is then utilized over the copper layer except where the gaps 78 are to be formed, and the device is then immersed in an e-tchant -that etches copper but not nickel. Of course 9 a varie~ty of methods can be employed, especially where tapering o~ the recording elemen-ts along their thickness is not require~l, all in accordance with me-thods well known in the art~ The record-ing device 50 then can be moun-ted on the support ~2 in a man-ner shown in Figure 3. One process results in there being an additional nickel layer lying over the copper base 72b (Fig. 6 but which has substantially no effect on the 6ubsequent opera-tion of the device.
In order to facilitate connection6 -to the diEferent recording elernents 60a-60ff, each of the elemen-ts is form~,d with a tail 90a-90f (~ig. 4)~ with the tails being tapered in wid-th and ex~tending in a radiating pa-ttern from the region of the recording location. This proYides relatively wide lead ends which facilitate electrical connections thereto. The end of the recording device 50 opposite the le~ds 90 forms a common base or lead 92 that is coupled -to all of the recording elements.
Along the recording location~ the recording elemen-ts are in the form o~ narrow strips that extend paralleL to one ano-ther and parallel to the pa-th of -the magnetic tape. After -the ~10-7 ~ 5 '3~;

r~cordir.g dsv; e is ~.ounted on l.~e support 52, the leads are coupled to mul-tiple leads of the line 36 (Figure 2) that is connec-ted to the signal processor 34, Figure 7 illustrates -the form of the magnetic image which can be recorded on the magnetic recording -tape 1~ 7 the image 100 representing tlle upper portion of a stylized form of the le-tter "C" ~in practice a mirror image is formed of the desired character to be printed). The image is formed by a series of magnetized areas 102 which are located in columns corresponding to the spacings of the recording loca-tions on the recording elements, and in rows separated from one ano-ther that represent the distance which the tape 18 has moved be-tween repeated current pulses -through the recording elements~ ~hen the magnetic image is dus-ted wi-th toner and the toner is transferred to paper, a continuous image can be formed on the paper ` In one printing machine of the invention, the record-ing elernen-ts are 0,08 mm apart along the recording line 64, with each element being approximately 0.04 mm ln width, and with each element having a nickel layer 70 of 0.005 mm thick-ness, a copper layer 72 of .02 mm thickness, and a gap 78 of 0.02 mm leng-th. It may be not~d that a thicker copper layer may be desirable, but it is di~ficult to etch a much thicker layer, even if both sides of the nickel-copper sandwich are

2~ e-tched, where such close spacing of the recording elements is utilized. A current pulse of 10 ampere and 1 microsecond dura-tion is passed th-rough each recording element, and the fou* groups of pulses for the four groups of eigh-t elements each~ are separated from one another by two microseco-~ds.

7 r)/l~3s ~23~5 Curren-t pul~es with rise times of one microsecond are easi].y ob-tained ln p~ssage through the elements. Of course, the small cross section of -the elements would prevent them from carrying a continuous current of the order of magni-tude of S ten amperes~ but -they can conduct such a current for a micro-second withou-t damage. Each new column of spots is re~orded on -the magnetic recording tape 18 a-t sixty microsecond inter-vals. All of the spots of a column lie almost along a line.
The -tape 18 is moved at a speed of 1.25 meters per second, so that adjacent columns of spots are spaced about at 0. oa mm intervals on the magnetic recording tape.
Figure 8 illustrates a printing sys-tem 110 which utilizes a wide recording head 112 to form lines of magnetlc spots that extend across -the width of a broad magnetic tape lS record 114. Following the head 112, the tape moves past a transfer s-tation~116 where the tape images are transferred~
to a ma-gneti~ drum. The images on the drum are toned by a toner 120 and ~ransferred to a paper web print medium 122.
The recording head 112 may have -to have about two~
thousand recording elements spaced across a tape width or about 20 centimeters. This could make connections to the elements very difficult. For example, if two thousand ele-men-ts had ends tapered to a two millime-ter width and spaced four milliJneters apart, the ends of the 2000 elements would occupy a reglon of a width of eight meters. To minimize the required space, the elemen-ts are arrangecl in an array of the general type illustrated in Figure 9, although with more recording elements in -the array than are shown in Figure 9.
The small array 130 of Figure 9 contains -twenty-four ~lr~2~S

recording e:lemen-ts 132, each elernerl-l having a s-trip-shaped por-tion 1.~'i with a recording location 136 the-realong~ and Wit}l all recording loca-tions arranged along a recording ].ine 168. The elements are arranged in six groups 161-166, each group having four recorder elements 132, -to provide the total of twen-ty-.four elements. The first group o~ elements 161 includes four elements 132a-132d having a cOm~QOn interconnect region 160i on one side of the recording line 168, and wi-th each elemen-t having a separate terminal portion 172 on the other side of the re~ording line. The second and third groups of elements 162, 163 are sirnilarly arranged, with -common interconnect regions 162i, 163i below the recording line 168 and with separate terminals 172 above the line The last three groups 164-166 of elements are symmetric to the first three groups, in tha-t they have common~interconnect regions 164i, 165i, 166i above the recording line 168 and terminals 172 below the line.
Current for operating the .recorder elements 132~ lS
prov;ded by an electricity source 130 with two terminals or ends 18Z~ 184. One end 182 of the source can be connected by any of six switches 16~s-166s to corresponding interconnect regions 161i-166i of the six groups of recorder elements. The other end 184 of the source can be connected by any one of 4 switches 191~194 to cross conductors l91c-198c. Each cross conduc-tor- such as l91c, i.s coupled to three terminals 172 of three recorder e].eme.nts 132a, 132i, 132q that are arranged in a row. I'hus, when -the two switches 161s and 191 are both closed at -the same instant, a current can flow through the element 132a so that its recording location ].36 can record a ~5/185~

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sE,ol: on the magne-t:ic tape. One way of pa~;sing a current -through each o:~ the recordinp elemen-ts 132a-132x woulcl ~e -to :firs-t close one of the group switches such as 161s and leave it closed, while each of the co:lumn swit-hes 191-194 are S closed momentarily in sequence. ~ex-t, sw:itch 161a would be opened, switch 164i closed, and the switches 191-194.again closed momentarily in sequence~ I-t may be noted tha-t each of the recox-der elements 132 is provided with a diode 200 to in-terconnect the cross conductor such as l91c to the strip portion 134 of an element, to allow curren-t flow only in one direc-tion through the element. This is to prevent unwan-ted current flows. For example, at a time that switches 191 and 161s are closed, to energize element 132a, it would otherwise be possible for current -to flow unintentionally down elemen-t 132i, up element 132j, across part of crosa conductor 1.9 and down elemen-t 132b.
The eleJnents 132 can be formed by prlnted circuit methods so that their recording locations 136 are spaced a - small distance apart such as only a few mils. However, such small width would make connection of an element to a cross conductor such as l91c difficult, and also 6uch a small width is too small to provide a region for mounting even a small diode 200 if a separate chip-like d;ode is to be utilized.
The layou-t illustrated in Figure 9 with staggered terminals 172~ enables enlarged -terminal areas to be provided without unduly enlarging the size of the entire array. The -terminals 172 are fo~rned a-t the ends of the recorder elements opposi-te t-he in-terconnect regions such as 161i, and all of the terminals o~ a group such as 161 are arranged in a s-ta~7gered fashion~

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i", -leml.nt :L32d ~-~ on( end of the group 1~17 has a terminal 172 loca-ted imlnediately above the in-terconnect region 16l~i of anot~ler groul). Tlle t-errili.llal of a next element ]32c of -the gr-oup 1~1 is l.ocated irnmedia-tely a~ove and slightly to one side of the terminal of element 13~d. This continues until the terminal of element 132a is loca-ted f~r-thest out and closes-t -to one side of the group. The -terminals of a next adjacen-t group 184 are correspondingly loca-ted, with the -terminal or a firs-t element 132e loca-ted im7nediately under 13 the in-terconnect region 161i of another group, and the ter-minals of the other elements 132f, 132g, 132h are arranged in a staggered fashion wi-th the terminals progressively further from one end oE the group ~eing loca-ted progressively further away from the recording line 168. This arraDgemen-t of the .terrninals allows a large number of terminals to be located in a small space and with all of the terminal regions ~formed primarily by a prin-ted circuit method. Of course, the re-cording loca-tions do not have to be located along a line 68, although it is ofte~ advantageous to do so to avoid -the need for delay circuitry.
In an array similar to that of Figure 9, but with 2048 different elemen-ts arranged in 164 groups af 132 ele-ments each, with the elernen-ts spaced 0.1 millimeter apart at their recording loca-tions, and with terminals tha-t are 1.25 2' millimeters wide and 1.25 millimeters long, the entire array c~n bc contained on an area of only about 2~ centimeters by 5 centimeters. Figure :lO illustrates a portion of an array 270 of this -type, which is construc-ted with éight modules 272 each module contalning eigh-t groups 281-288 of elements witl 391~

c~acOl group conta;ning thirty~two elements with -their termirlals ~52 arr<lllged in a s-taggered ~ashion. The array has been ben-t in a gen-tLe curve so -that the recordi.ng locatlons are arranged along a l:Lne 290, and a covering sheet 250 is shown cut-away to aid in illustra-ting the a-rray.
Although particular emobidments of the invention have been described and illustrated herein, it is recognized -tha-t modifications and variations may readily occur to those skilled in -the art and consequently it is intended that the claims be interpreted to co~er such modifications and equiva-lents.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a magnetic recording apparatus wherein a magnetizeable medium extends along a predetermined path, and a magnetic recording head is positioned along said path, a magnetic recording head comprising: a record-ing element which includes an elongate electrical conductor portion with a center of conduction spaced from said path by more than a first distance except along a recording location of limited length where said center of conduction is spaced from said path by a second distance which is closer than said first distance to said path; and means for passing a current through said conductor portion; said current passing means being constructed to pass a current of an amplitude that will change the magnetization of said magnetizeable medium when said current is at said second distance from said path of said medium, but not when said current is at said first distance from said path of the medium.

2. Apparatus as in claim 1 wherein said electrical conductor portion comprises a narrow strip with a narrow recess therein at said recording location, said recess being formed in the side of said strip which is furthest from said path of said magnetizeable medium and extending only part of the way through the thickness of said strip.

3. Apparatus as in claim 2 wherein said strip comprises a first layer of electrically conductive material positioned near said path, and a second layer positioned directly against a face of said first layer opposite said path, the material of said second layer, and said recess being formed through the thickness of said second layer.

4. Apparatus as in claim 3, wherein said strip is tapered in width along its thickness, with a minimum width at the face thereof which is nearest said path of said magnetizeable medium.

5. Apparatus as in claim 4, wherein the first layer is nickel and the second is copper.

6. A recording apparatus comprising: a magnetizeable tape; means for moving said tape along a predetermined path; and a recording head assembly positioned along said path, for forming magnetic images on said tape; said recording head assembly including a plurality of recording elements having electrically conductive portions in the form of narrow strips that extend parallel to one another in a direction substantially parallel to the length of the tape path portion thereat and that lie close to said tape path, each strip forming a current path extending largely along its length with the center of the current path lying more than a predetermined distance from said tape path except at a predetermined short length portion of said strip where the center of said current path lies closer than said predetermined distance from said tape path; and means for applying current pulses selectively to said narrow strips with each current pulse having an amplitude large enough to magnetize a nearbly portion of said tape as said current moves through the corresponding short length portion of a strip, but small enough so the current does not magnetize said tape as the current moves through the rest of the narrow strip.

7. A method for forming a magnetic image on a medium, comprising:
selectively passing currents along a plurality of substantially parallel paths spaced from said magnetizeable medium by more than a predetermined distance from said medium except along path portions of limited length which are closer to said medium than said predetermined distance, where each of said currents is of a magnitude which causes magnetization of the medium only when moving along one of said path portions but not when moving along the rest of the path which is more than said predetermined distance from said medium.

8. The method described in claim 7, wherein: said magnetizeable medium moves relative to said current paths; and said current is passed in short pulses through alternate groups of said paths, wherein adjacent paths of the same group are spaced apart a distance corresponding to at least twice the width of a path, and then no current is passed through any of said groups for a selected time period which is substantially longer than the duration of said pulses.

9. Recording apparatus as in claim 6 wherein:
said recording head assembly includes a supporting film of electri-cally insulative material, the electrically conductive narrow strips lie on a side of said supporting film which is opposite said tape path, and wherein each strip includes a first layer of a first material and a second layer of a second material, said first layer being positioned between said supporting film and said second layer, and said second layer having a higher conductivity than said first layer;
said second layer of said strips having gaps therein, with said gaps of said strips being arranged substantially along an imaginary re-cording line extending substantially perpendicular to the length of said strips.