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Патент USA US3083278

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March 26, 1963
M. CAMRAS
3,083,268
INTERCHANGEABLE MAGNETIC RECORD TAPE
AND METHOD OF MAKING sAME
Filed May 11, 1954
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United States Patent 0 " ICC
3,083,268
Patented Mar. 26;, 1963’
1
2
3,083,268
1-1 de?ning a non-magnetic gap 12, the machine having
been designed for an existing tape 13 and the bias volt
age of the machine having been established to give op
timum performance with the tape 13, the present inven
tion then contemplates the manufacture of a tape 14
which will give optimum performance with no change
in the bias of the existing machine.
For example,rthe existing tape 13 may have a coat
INTERCHANGEABLE MAGNETIC RECORD TAPE
AND METHDD OF MAKING SAME.
.
Marvin Camras, Chicago, Ill., assignor to Armour Re
search Foundation of Illinois Institute of Technology,
Chicago, 11]., a corporation of Illinois
Filed May 11, 1954, Ser. No. 428,961
6 Claims. (Cl. 179-1002)
ing thickness indicated at 13a of .65 mil (1 mil equals -'
This invention relates to a method of making a high
10
0.001 inch), the coating material having a coercive force
coercive force magnetic tape record member which ‘is in
of 240 oersteds.‘ It is then desired to determine an inter
terchangeable with an existing lower coercive force mag—
changeable tape 14 which may be used with optimum
netic tape record member with respect to a given mag
results on the same ?xed bias machine.
netic recording machine having a given ?xed ‘high fre~
It has 'been discovered that such a tape can be manuJ
quency bias, and to a high coercive force magnetic tape
record member manufactured in accordance with said 15 factured by applying to the tape base a coating 14a of
thickness to have a bias ?eld intensity in the part of the:
method.
magnetizable
coating farthest from the recording gap sub-v
It is an object of the present invention to provide a
stantially equal to the ratio of the coercive force of the
novel method of making a high coercive force magnetic
magnetizable layer 14a, to the coercive force of the mag
tape record member which is interchangeable with an
existing tape for a given magnetic recording machine.
It is a further object of the present invention to pro
vide a magnetic tape record member bearing a novel
netizable layer 13a, the ratio being multiplied by the bias
?eld intensity in the corresponding part of the existing
tape 13.
-
'
In one embodiment of the method, the value of bias
relationship to an existing magnetic tape record member
?eld intensity in the part 13b of the coating 13a is taken"
with respect to a given magnetic recording machine hav
25 as the bias ?eld intensity in air at a distance above the
ing a given ?xed high frequency bias.
poles 10 and 11 equal to the coating thickness. The
Other objects, features and advantages of the present
curve 16 in FIGURE 4 represents the ?eld intensity as a
invention will become apparent from the following de
function of the distance above the poles 10 and 11 along
tailed description taken in conjunction with the accom
the line AA, the distance above the poles being measured
panying drawings, in which; I
‘FIGURE 1 is‘v a diagrammatic view representing an
existing standard tape for use with a magnetic recorder
machine having a given ?xed high frequency bias;
'
in terms of the width of the gap 12. The curve 17 rep;
resents a plot of ?eld intensity along the line BB in terms
of gap widths above the poles 10 and .11; and the curve"
18 represents a similar plot along the line CC in FIG:
FIGURE 2 is a diagrammatic representation of a tape
manufactured in accordance with the present invention 35 URE 3. It will thus be observed from FIGURE 4, that
for points in the magnetizable layer 13a that are closer
which is interchangeable with the tape of FIGURE 1
than about one-?fth of a ‘gap width from the surface
with respect to said magnetic recording machine having
of the head, the maximum ?eld intensity is encountered
the ?xed high frequency bias;
.
near the gap edge provided by the pole 11 (the trailing
FIGURE 3 is a diagrammatic illustration of the ?eld
at the gap of a typical recording head;
FIGURE 4 is a graph representing the total ?eld in
tensity at different points above the head of FIGURE 3
as measured along lines at right angles to the gap and
at successive positions with respect to the gap; and
pole) along the line BB. For points further above the
40 head surface than about one-?fth gap Width, the maxi-
mum ?eld intensity is encountered near the gap center
(along the line AA). The higher of the two 'curves
16 and 17 at any given distance above the head surface
FIGURE 5 is a diagrammatic illustration of a record 45 is taken as the maximum ?eld intensity at that distance,
above the head surface.
ing machine having ?xed bias to which the principles
of the present invention may apply.
Thus, for example, if it desired to ?nd the maximum
?eld intensity in the outer part of a magnetizable layer
of'a tape, the coating having a thickness equal to the
The present invention has for its object the'provision
of a substitute tape which will give substantially the 50 width of the recording head gap with which the tape is
As shown on the drawings:
same performance as an existing standard tape on a
given type magnetic recorder with a given high frequency
used, ‘the point 19‘ represents the maximum ?eld intensity.
along the line CC, the point 20 represents the maximum
?eld intensity along the line BB, and the point 21 rep-"
resents the maximum ?eld intensity along the line AA.
bias, the substitute tape for example having a higher co
ercive force than the standard tape.
Prior to this invention, magnetic recorders were de 55 In this case, the maximum ?eld intensity for a coating
thickness of one gap width would be taken at approxi
signed for optimum performance with a speci?c kind of
mately .31 on a relative basis corresponding to the point
tape. Any other tape required either a change in bias,
or a compromise setting where best performance was
. 21.
For purposes of this invention any arbitrary units
of ?eld strength may be used; actually the values on the,
force was used without increased bias, the result was 60 graph 'of FIGURE 4 are relative to the uniform ?eld
deep inside the gap 12.
poor low frequency response, harmonic and intermodula—
While the values ‘of ?ux density derived from FIGURE
tion distortion especially of the low frequencies, and de
4 are those existing in air, ‘and the permeability of a tape
creased sensitivity. Such recordings had a tendency to
layer is greater than that for air, the relative values of
ward harshness and raspiness that became irritating upon
sacri?ced.’ For example, when a tape of higher coercive
prolonged listening.
?eld intensity in the magnetizable layer will closely ap
Adjustment of bias has not been provided in general
purpose recorders or even in most professional recorders,
proximate those derived by the use of FIGURE 4.
because proper adjustment requires instruments and train
gamma Fe2O3 layer ‘0.65 mil thick with a coercive force.~
ing not possessed by the ordinary operator.
As a practical illustration, suppose that a tape having a ’
of 240 oersteds is used with a standard tape recorder ma
By way of example, if FIGURES 3 and 4 are taken 70 chine having ‘a ?xed high frequency bias. This conforms -_
to represent thev operating conditions for a given existing
closely to present day practice, and a coating material of ,
tape recording machine having recording poles 10 and
these properties may be prepared as outlined in my appli-?
3,083,268
3
,
4
said layer having a substantially uniform coercive force
H02 throughout its volume and having a total thickness
cation Serial No. 763,486, now US. Patent No. 2,694,656
issued Nov. 16, 1954. Taking the recording gap 12 in
FIGURE 3 as having a Width of 0.25‘ mil, a portion of
the layer 13a farthest from the head. is 2.6 gap widths
away, so that referring to FIGURE 4, it encounters
a maximum ?eld of 013 unit. If it is desired to make an
interchangeable tape such as 14 with a layer 14a of the
same chemical composition, but having a coercive force
t2 such that
of 3.3.0. Oersteds, the tape base 140 is coated with a coat
ing having a coercive force of, 330 oersteds and a thick-. 10
ness to have a bias flux density in the outer part of the
magnetizable coating at 14b substantially equal to the
i
'
the coercive force H02 being of the order of 330 oersteds
and the, thickness of the magnetizable layer t2 being of
the order of 0.4 mil.
2. As an article of manufacture, an interchangeable
magnetic record tape for substitution for a conventional
magnetic record tape which has a magnetizable layer of
thickness t1 equal to about .65v mil and a coercive force
He, equal to about 240 oersteds. in a magnetic recording
machine which comprises a ring-type head having a
longitudinal gap and a high frequency bias supply set to
ratio of 330 oersteds to the coercive force of the existing
tape, namely 240 ioersteds, the ratio being multiplied by
the, value of the given maximum bias ?eld intensity name
ly .13 unit, which gives a value of .18 unit of ?eld inten
sity at the layer 14b of the magnetizable coating 14a.
supply an optimum amplitude of bias current to the
Referring to FIGURE 4, it will be observed that this
head to provide an optimum amplitude of bias ?eld in-_
maximum ?eld intensity of .18 is obtained with a coating
tensity for said conventional magnetic record tape, the
20 head, when energized by said optimum amplitude of bias
thickness of 1.7 gap widths or a thickness of 0.425‘ mil.
It has been found that when the maximum ?eld inten
current providing a maximum amplitude of bias ?eld
sities in air for a given head at the outer part of the
intensity H31 in air above said head a distance 21 and
magnetizable layer are proportioned in this manner, that
the, substitute tape functions in an optimum manner with
providing a maximum amplitude of bias ?eld‘ intensity
H32 in air above said head a distance t2 substantially
25 less than .65. mil, said interchangeable tape comprising a
the given head and high frequency bias.
'
,
To illustrate that for typical gaps and coatings in, com
non-magnetic base and a single layer of magnetizable
mercial use, the substitute tape will, have a thickness
material thereon having a substantially uniform, coercive
which is fairly independent, of gap size, the followingv
force H02 throughout its volume and having a total thick:
example may be considered.
,
ness t2 such that
If the gap width had been 0.5 mil instead of 0.25 mil, 30
then, in the above example, the relative ?eld intensity
would be 0.25 unit. The desired relative ?eldstrength in
H32 _'HB1
the outer part of the magnetizab-le layer at 14b would,
the
coercive
force
H02
being,
of the order of, 330 oerjsteds
thenvbe 0.34 unit which occurs at approximately 0.8; g-ap- ~ and the thickness of, the magnet-izable layer being of the
widths above the head ‘or 0.40 mil, which is quite close to
order of 0.4 mil.
the 0.425 mil tape thickness obtained for gap width of
0.25, mil.
-
' 3.. In combination, with a magnetic, recording machine
'
comprising a ring-type head having, a longitudinal 8312'
ltm-ay be noted that “e?ective” gap width tends; to be
somewhat larger than the physical gap width, especially
andra high. frequency bias supply set to supply adopti
mum amplitude of bias current to the head to provide.
for very short- gaps; so that for; example a “one-fourth 40 an optimum amplitude of bias ?eld intensity for a, comv
mil?’ gap may actually behave as if it were a, 0.3 mil or
larger‘ gap. with'the above tapes. The one, half mil gap;
ventional magnetic record tape with a magnetizablelayer
generally shows a less-than proportionally larger e?ective
force H01 equal to about 240' oersteds, said head when
gap.
7
,
‘
.
of thickness :1 equal to about .65 mil and‘ of; coercive
energized. by said. optimum amplitude. oi bias current;
Hmvidiug a maximum amplitude. Qt bias ?eld intensitr
H31 in. air above said; heada distance offtl and, providing;
.
" ,IGURE 5 illustrates diagrammatieally-a tape record
ing: machine having acore 25, providing the poles 10v and;
1A,! and having; an oscillator 26
a,‘ relatively.’ fixed
’ ‘1 mwsimurs- amplitude. of; bias. ?eld. intensity H32 in. air
abovev said head a distance t2, substantially’ less; than; .65,
on. a signal ?ux introduced by a winding 28. The tape
mil, the improvement comprising; an interchangeable
14. will give optimum results when; used with the same 50 magnetic record tape for substitution; for; said, conven
?xed oscillator output as was determined: to ‘be optimum
tional; magnetic.- record. tape in‘ said magnetic. recording
for the. tape 13.
"
'
'
machine,‘ said, interchangeable; magnetic tape having a;
While {have described a preferred embodiment of my
non-magnetic base, and a single layer of magnetiza-ble
invention,‘ it will be apparent that many modi?cations and
thereon, said layer having a substantially uniform
vaniationsmay be made without departing fromthe, scope 55 material
coercive
force H02 throughout its volume and having ‘a
of the novel concepts thereof.
'
.
output the bias ?ux from winding 27 being superimposed;
l-claimgas my invention;
’
total thickness tzsuchthat; '
V,
1. Incombina'tion with a, magnetic recording mgachine
comprising a ting-type head-having a longitudinal gap.
andfa high frequency bias supply set to supply an‘ op
vtiinum, amplitude of bias current to the head to provide
an: optimum amplitude ‘of bias ?eld intensity for a con
ventional magnetic record tape with, a magnetizable layer
of thickness t1 equal to about .65 mil and of coercive
force H61 equal to about 240 oersteds, said head When
energized“ by said optimum amplitude. of bias current
providing a maximum amplitude of bias ?eld intensity
H C2_H Cl .
60
.
HJHB;
greaterthan about 0.4 mil.
65
'
.
.
the coercive force H02 being at least about; 330' oersteds
and the thickness of the'magnetizable layer t2 beinghOt
1
"
'
4. Asan article of manufacture, an interchangeable
magnetic record tape for substitution for a_ conventional
magnetic record tape which has a magnetizable layer of
thickness t1 equal to about .65 mil and a coercive force
Hcl equal to about 240 oersteds in a magnetic recording
H31 in air above said head a distance of t1 and providing
amaximum amplitude ofbias ?eld‘intensity H32 in air .7 machine which comprises a ring-type head having a
above said head a distance t2 substantially less than .65 70 longitudinalgap and a highfrequency biasrsupply set
to' supply an optimum amplitude'of-bias current to the‘,
mil, therimprovement comprising aninterchangeable mag
head to provide an optimum amplitude of bias ?eld‘
netic ‘record tape for substitution for'said conventional '
intensity for said conventional magnetic record tape, the
magnetic record tape in saidmagnetic recording machine, said ‘interchangeable magnetic tape having a non-magnetic ' head'when energized by said optimum amplitude of bias,
base and a single layer of magnetizable material thereon, 75 current» providing, a I maximum amplitude of‘ ‘bias ‘?eld
3,083,268
5
intensity H31 in air above said head a distance t1 and
providing a maximum amplitude of bias ?eld intensity
H32 in air above said head a distance t2 substantially
less than .65 mil, said interchangeable tape comprising a
non-magnetic base and a single layer of magnetizable
material thereon having a substantially uniform coercive
force H02 throughout its volume and having a total thick
ness t2 such that
6
and the thickness of the magnetizable layer t2 being of
the order of 0.4 mil.
6. In the magnetic recording art wherein a magnetic
recording machine comprising a ring-type head having
a longitudinal gap has a non-adjustable high frequency
bias supply set to supply an optimum amplitude of bias
current to the head to provide an optimum amplitude
of bias ?eld intensity for a conventional magnetic record
tape with a vmagnetizable layer of thickness t1 equal to
10 about .65 mil and of coercive force H01 equal to about
240 oersteds, said head ‘when energized by said optimum
amplitude of bias current providing a maximum amplitude
the coercive force HC2 being at least about 330 oersteds
of bias ?eld intensity H31 in air above said head a dis
and the thickness of the magnetizable layer being not
tance of t1 and providing a maximum amplitude of bias
greater than about 0.4 mil.
5. In the magnetic recording art wherein a magnetic 15 ?eld intensity H32 in air above said head a distance t2
substantially less than .65 mil, the improvement com
recording machine comprising a ring-type head having
prising supplying an interchangeable magnetic record tape
a longitudinal gap has a non-adjustable high frequency
as a substitute for said conventional magnetic record tape
bias supply set to supply an optimum amplitude of bias
in said magnetic recording machine, said interchangeable
current to the head to provide an optimum amplitude
of bias ?eld intensity for a conventional magnetic record 20 magnetic tape having a non-magnetic base and a single
layer of magnetizable material thereon, said layer having
tape with a magnetizable layer of thickness t1 equal to
a substantially uniform coercive force H02 throughout
about .65 mil and of coercive force Hcl equal to about
its volume and having a total thickness t2 such that
240 oersteds, said head when energized by said optimum
amplitude of bias current providing a maximum ampli
tude of bias ?eld intensity H31 in air above said head 25
HC2_HC1
HB2_HB1
a distance of II and providing a maximum amplitude of
bias ?eld intensity H32 in air above said head a distance
t2 substantially less than .65 mil, the improvement com
the coercive force HC2 being at least about 330 oersteds
and the thickness of the magnetizable layer being not
as a substitute for said conventional magnetic record tape 30 greater than about 0.4 mil, and subjecting said inter
changeable magnetic record tape to said optimum ampli
in said magnetic recording machine, said interchangeable
magnetic tape having a non-magnetic base and a single
tude of bias ?eld intensity during recording of a sound
signal on said interchangeable tape.
layer of magnetizable material thereon, said layer having
a substantially uniform coercive force H02 throughout
its volume and having a total thickness 12 such that 35
References Cited in the ?le of this patent
UNITED STATES PATENTS
prising supplying an interchangeable magnetic record tape
the coercive force Hcz being of the order of 330 oersteds 40
2,443,756
2,643,130
2,647,954
Williams ____________ __ June 22, 1948
Kornei _____________ __ June 23, 1953
Howell ______________ __ Aug. 4, 1953
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