Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
. . .
Field of the Invention
The present invention relates to an image pickup
element and system for converting an optical image of character
or the like into a magnetic-bubble pattern.
Heretofore, image pickup tubes using photoelectric
transducers have been principally employed. In this type of
pickup tube, however, there exist certain disadvantages such
as susceptibility to mechanical shock, a complicated structure,
and difficulty in attaining a compact structure. Further, the -`
output signal obtained is serial.
Recently, attempts have been made to eliminate
such disadvantages, and, in particular, an image pickup -~
element of photomagnetic-effect substance using magnetic-
bubbles has been proposed. However, in this image pickup
element a bubble propagation element for propagating the
bubbles from a sequential bubble generator through a photo-
magnetic substance such as silicon-added yttrium iron-garnet
is required. Therefore, the above element is disadvantageous
in that it involves intricate processes such as the setting
of the propagation circuit with the photomagnetic-effect sub-
stance and the setting of the bubble generator. Further, the'
bubble propagation method is limited only to the utilization
of a rotating magnetic field.
SUMMARY OF THE IN~7ENTION
In accordance with one aspect of this invention
there is provided a photomagnetic image pickup element com-
pri~sing a thin film of magnetic material capable of having
magnetic-bubbles formed therein where the intensity of the
magnetic-bubble collapse field varies with temperature; a first
conductor set disposed on said one side of said thin film; and a
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second conductor set disposed either on said one side or on
the other side of said thin film; said first and second con-
ductor sets being orthogonal with respect to one another;
each of said sets c~mprising a plurality of parallel conductor
elements, the pitch between successive elements of each set
being Pl and P2 where P2 is greater than Pl.
In accordance with another aspect of this invention
there is provided an image pickup system comprising an image
pickup element including a thin film of magnetic material
capable of having magnetic-bubbles formed therein where the
intensity of the magnetic-bubble collapse field varies with
temperature; first conductor pattern disposed on one side of :
said thin film; and a second conductor pattern disposed
either on said one side or on the other side of said thin
film, said first and second conductor patterns being so dis-
posed with respect to one another as to form a lattice shape ~:
on sald thin film; said first and second conductor patterns
being orthogonal with respect to one another and each com- ~:
prising a plurality of parallel conductor elements disposed :~.
in a first direction, the pitch between succèssive elements
alternately being Pl and P2 where pitch Pl is substantially
greater than pitch P2; means for respectlvely applying first
and second current pulses to said first and second conductor
patterns to establish insular magnetic domains having a pre-
determined direction of magnetization only where said P2 pitch
portions of said first and second.conductor patterns overlap;
means for applying a bias magnetic field to said thin film,
the direction of said bias magnetic field being opposite to
said magnetization of said insular magnetic domains to
thereby create a magnetic-bubble lattice in said thin film
and (HCo)Kl~HB>(~co)K2 where ~ is the intensity of said bias
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magnetic field, (HCo)Kl is the field intensity required to
extinguish magnetic-bubbles in said thin film at temperature
Kl and (HCo)K2 is the field intensity required to extinguish
said magnetic-bubbles at temperature K2 where K~>Kl; and
means for projecting an image of light and dark on one face
of said thin film to thereby selectively raise the temperature
at the light irradiated portions from Kl toward K2 and thus
selectively annihilate the light irradiated bubbles to form
a magnetic-bubble pattern in the thin film corresponding to
said image.
By way of added explanation, the image pickup element
of this invention utilizes magnetic bubbles to convert an
optical image into a magnetic-bubble pattern. In particular,
a magnetic thin film is employed, the intensity of the film's
magnetic-bubble collapse field changing in accordance with
temperature rise resulting from the absorption of irradiated
light. The film is covered with a minute, lattice-shaped
conductor pattern for forming a magnetic domain lattice
therein, the domains being formed by the magnetic fields
corresponding to the current passing through the conductor
pattern, A magnetic-bubble lattice is then created by the
application of a bias magnetic field. An optical image may
be then projected onto the magnetic~bubble lattice to select-
ively annihilate the magnetic bubbles and thus produce a
1 magnetic-bubble pattern corresponding to the optical image.
l This invention will be more apparent from a reading
of the following specification and claims taken with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plane view of a conductor pattern in
accordance with the invention.
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Figure 2 is a sectional view of an image pickup
element in accordance with the invention.
Figure 3 is a magnetic field distribution in a
magnetic thin film produced by an application of current
pulse applied to conductor patterns.
Figure 4 is a plane view of a magnetic image pickup
element, showing a setting of seed bubbles.
Figure 5 is a plane view of a magnetic image pickup
element, showing a production of strip domains from the seed
bubbles in Fig. 4.
Figure 6 is a plane view of a magnetic image pickup
element illustrating three area groups for explanation.
Figure 7 is a plane view of a magnetic image pickup
element, showing insular domains produced from the strip -
domains by di~iding the latter.
Figure 8 shows a resultant magnetic bubble lattioe.
Figure 9 illustrates the timing of application of
current pulses to the conductor patterns and of biasing
current.
~igure 10 is a plane view of a magnetic bubble
pattern propa~ation circuit,
Figure 11 is an example of the conductor pattern
driving methods.
DETAILED DESCRIPTION OF THE PREF~RRED EMBODIMENT
7 In this specification and the following claims, a
magnetic bubble denotes cylindrical magnetism existing under
a bias magnetic field exerted in the direction perpendicular
to the surface of a thin film of suitable magnetic material ~ -
such as a rare earth orthoferrite, plumbite or rare earth
iron-garnet. Various properties of magnetic bubbles are
discussed in "Properties and Dev1ce Applications of Magnetic
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Domains In Orthoferrites" by A.H. Bobeck, The Bell System
Technical Journal, Vol. XLVI, No. 8, October, 1967, pp. 1901 -
1925 and "Propagation of Cylindrical Magnetic Domains in
Orthoferrites" by Anthony J~ Perneski, IEEE Transactions on
Magnetics, Vol. Mag -5, No. 3, September, 1969. The magnetic
bubble diameter changes with film thickness, bias magnetic
field intensity or temperature, and the magnetic field in-
tensity for annihilating the magnetlc bubbles changes with
film thickness or temperature.
As an example of the magnetic materials usable in
the present invention, samarium-terbium mixed orthoferrite
~$m0 55 Tbo 45 EeO3) is considered. In the magnetic bubble
device, it is known on BSTJ. Dec., 1969, pages 3287 to 3335
that the properties of bubble can be represented, in the
standardized form, by the characteristic material length 1,
the thickness h and the saturation magnetism 4~Ms and these
properties do not change even when the magnetic material is
chan~ed,
For SmO 55 Tbo 45 FeO3~ the bubble diameter d and
the collapse magnetic field Hco are changed with temperature
in which Hco is abruptly decreased with increase of temp-
erature in a normal temperature range (290K to 350K).
See "Temperature Dependence of Rare-Earth Orthoferrite
Properties Relevant to Propagating Domain Device Application"
by Rossol, IEEE Transaction on Mag., vol. MAG-5, No. 3, ~ -~
September, 1969. In this paper, it is shown that at the
normal temperature (300K), the diameter of bubble having
characteristic material length of 4 jU under a bias magnetic
field H bias being 58 oe is about 30 ~ and the bubble collapse
magnetic field Hco and the strip-out magnetic field Hs are
64 oe and 50 oe, respectively. The collapse field Hco at
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320K decreases to 55 oe. This means that when the bias field
H bias at a normal temperature (300K) is 58 oe, the bubble
existing in the magnetic thin film is disappeared upon in-
crease of temperature of the film to 320X. Further, at the
normal tempera~ure, the bias field H bias is reduced to a
value lower than 50 oe due to same external magnetic field,
the bubble is stripped-out, resulting in a strip domain the
thickness is about 40 ,u ! in the above case.
When a pair of bubbles are coexisting with a small
distance therebetween, an expelling force acts on the both
bubbles. The distance by which the bubbles are not given a
mobility force is larger than 3d where d is the diameter of
the bubble. Therefore, by setting the bias field H bias to
58 oe so that the diameter d becomes 30 ~ and by seiecting
the distance between the adjacent bubbles forming the bubble
lattice as 3d, a sum of the narrow pitch portion P and the
wide pitch portion of P2 of the pattern 10, or 12 becomes
3d, This will be described in detail with Pl and P2 being
30,u and 60 ~, respectively.
In this case, the width of the conductor is
determined as 15 ~ according to Goldstein et al. "Bubble
Forces in Cylindrical Magnetic Domain Systems", J. Appln.
Phys. vol. 44, No~ 11, November, 1973, In this case, the
thickness of the conductor is several microns.
In the image pickup element according to the present -~
inVention, a conductor pattern 10 such as shown in Figure 1
may be proviqed on both sides of a magnetic thin film in an
orthogonal relationship with each other as shown in Figure 2
to form a lattice structure. As will be explained in furthér
3a detail hereinafter, when a current is applied to the ortho-
gonal conductor patterns, a magnetic field configuration
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corresponding to the patterns is produced. Each conductorpattern comprises a plurality of parallel conductor elements
lOa, lOb, lOc, lOd, lOe, lOf, lOg, lOh,...lOx, the pitch
between successive elements alternately being Pl and P2 where
pitch P2 is substantially greater than pitch Pl. Although
conductor patterns 101 and 12 are each shown as single con-
ductors, the conductor elements lOa - lOx may each be driven
by separate current sources if desired. Since each conductor ~-
pattern is cyclical having a narrow-pitch portion Pl and a
wide-pitch portion P2, a striped means magnetic field con-
figuration, which is produced by one conductor pattern and
is perpendicular to the surface of the magnetic thin film,
intersects a striped mean magnetic field configuration in
the opposite direction caused by the other conductor pattern,
thereby producing insular magnetic fields in the magnetic
thin film, As will be explained in detail hereinafter, the
fields are acted upon by a bias field to establish the
magnetic-bubble lattice, In Fig. 1, the conductor pattern
10, is to form an 11 x 11 bubble lattice and the member of
20 the parallel conductor elements lOa to lOx is twenty-four. ~ ~-
This~conductor pattern is formed on a substrate of such as
glass by using the etching technique. The resultant pattern
is put on an upper surface of the magnetic thin film in an
intimate contact therewith. Thereafter, when an electric
current is supplied, a magnetic field is produced in the -
magnetic thin film.
Fig, 3 shows a magnetic field distribution in the -
film. The vertical axis is the magnetic field component Hz
in the normal direction to the film surface, averaged with
30 respect to the film thickness. As shown in Fig. 3, the `
direction of the bias magnetic field is denoted as the plus
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direction. The peak values of the magnetic fields produced
in the respective narrow and wide pitch portions Pl and P2
are ~ 73 oe and - 41 oe, respectively, when a current of one
ampere is flown through the conductor pattern. That is, the
value of the magnetic field produced in the narrow pitch
portion Pl is about 1.8 times that produced in the wide pitch
portion P2.
The directional relation between the external
magnetic field including the bias magnetic field and the field `~
produced by the current flowing through the conductor pattern
and the magnetization in the magnetic thin film is in just
reverse to that between the bias magnetic field and the
magnetization of the cyllndrical magnetic domain (bubble).
The bias magnetic field range within which the bubble is
stabilized is from the strip-out magnetic field + 50 oe to
the bubble collapse magnetic field + 64 oe. In this range the
bubble diameter is reduced with increase of the bias magnetic
field. The direction of the bias magnetic field H bias is
shown as coming in through the paper sheet, in Fig. 4 and, in this
case, the upper portion and the lower portion or the bubble
in the magnetic film become S and N poles respectively.
The method of producing the bubble lattice will be
described with reference to the drawings. Firstly, a biasing
magnetic field + 58 oe which is within the bubble stabilizing
range is applied to the surface of the magnetic thin film in
the direction normal to the surface by a Helmholty coil to
set up seed bubbles in an end area of the wide pitch portions
P2 of the conductor pattern 10, as shown in Fig. 4. The
sètting up may be performed by applying the bias magnetic
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field (+ 58 oe) to form bubbles and guiding them to the seed
bubble setting positions respectively by means of magnetic
needles of polarity (N pole) capable of attracting the
bubbles. The guiding may be performed visually by the use
of polarization microscope, in the simplest case, or by the
utilization of magneto-optical effect. As to the stabiliza-
tion of the seed bubbles,`it is advisable to provide thin
film (5000~ ~) of high permeable magnetic material on
the magnetic bubble film by etching to provide bubble
stabilizing position on the magnetic bubble film. This is
shown as four PERMALOY* dots in "Theory of Single - Current
D~main Propagation Circuits" by Copeland, IEEE Traus. on Mag.,
Letters, June U972~ pages 241 to 243. It is also described
in ~'~pplication of Orthoferrites to Domain-Wall Devices" by
Bobeck et al, IEEE Traus. on Mag., MAG-5, No. 3, Sept., ~
1969, that with a presence of a magnetic bubble in the~ -
stabilizinq position, the bubble collapse magnetic field
becomes larger than that required to collapse free bubble
by several Oersteds.
~fter the seed bubbles are set up, a current of -
about 0.5 ampereS is flown to the conductor pattern 10, in
the arrow direction in Fig. 5 by closing a switch Sw of a ! ~' '
pulse current source 22. Due to the current, the magnetic
field is produced in the magnetic thin film in the distribution
` shown in ~ig. 3~ In this case, the magnetic field produced
in the wide pitch portion P2 of the conduction pattern 10,
has a direction reverse to that of the bias magnetic field
(+ 58 Oersteds~. Therefore the bias magnetic field in
this portion becomes 38 Oersteds because the field in the
pitch portion P2 is - 20 Oersteds. Since the strip out
* trade mark for a nickel-iron alloy containing more than
30% nickel
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magnetic field Hs is 50 Oersteds, the bias magnetic field
is smaller enough than the strip out field, and therefore,
the seed bub~les are stripped out to positions in the magnetic
thin film corresponding to the wide pitch portions P2 of the
conductor pattern 10, as shown in Fig. 5. The distance of
extension of the stripped-out domaln depends upon the wave
height of electric current pulse flowing through the conductor
pattern 10, and the width of the pulse. The distance required
for the 11 x 11 bubble lattice is about 1 mm where the wave
height is 0.5 ampere and the width is 10 3~ 10 5 seconds.
After the strip domains are aligned as shown in
Fig. 5, a current is flown through the conductor pattern 12
in the direction as shown in Fig. 6 by closing a switch Sw
of a pulse source 24. In the magnetic bubble device, a
production of new bubbles are made by dividing the seed
bubbles as is well known. For samarium-terbium mixed ortho-
ferrite, it is shown in the article of Bobeck et al that the
bubble dividing magnetic field is 37.5 Oersteds. The dis-
tribution of the magnetic field produced in the magnetic
film by the current flowing through the conductor pattern
12 is shown in Fig. 3. Since the patterns 101 and 12 are
orthogonal, the distribution of the composite magnetic field
becomes complicated. For explanatory purpose, overlapping
portions of the two patterns are shown by portions A, B and
C. The portion A shows a portion where the wide pitch
portion P2 of the pattern 101 and the narrow pitch portion P
of the pattern 12 are overlapped, the portion B shows a
portion where the wide pitch portions P~ of the patterns 101 -
and 12 are overlapped and the portion C is a portion where
the narrow pitch portion Pl of the pattern 101 and the wide
pitch portion P2 of the pattern 12 are overlapped. The
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magnetic fields produced in the magnetic film portions
corresponding to these overlapped portions by the currents
flowing through the patterns 101 and 12 are denoted by HA,
HB and Hc. When a current of 0.9 amperes flows through the
pattern 102, HA is a subtraction of 20 Oersteds (the field
produced in the wide pitch portion of the pattern 101) from
66 Oersteds (the field produced in the wide pitch portion of
the pattern 102) and, therefore, becomes 44 Oersteds. The
latter is larger than the bubble dividing magnetic field,
so that each of the aligned strip domains are cut at the
respective portions A causing insular domains as shown in
Fig. 7. The reason for that there is no bubble produced even
when the bias magnetic field is applied is that the field
in the portion B when the land domain exist becomes - 57
Oersteds which substantially cancels the biasing magnetic
field therein. A magnetic field HC in the portion C is sub-
stantially zero and, therefore, there is the bias magnetic
field H bias as it is. The width of the current pulse flow-
` ing through the pattern 10~ is 10 3 - 10 6 seconds. After
the production of the insular domains in this manner, the
currentS flowing through the patterns 101, and 12 respect-
ively are cutout, resulting in a bukble lattice shown in Fig.
The amount of image radiation light is about 50mJ/-
mm2 and the wave length is within the absorption range of
the magnetic thin film (equal to or shorter than about 6000A).
It is easy to increase the number of lattice points,
i.e., bubbles, in the bubble lattice. For example, if the
number of the conductive elements of the conduction pattern
is increased to 66, the active area of the lattice becomes
.: . ~ . .
about 3 mm X 3 mm and the bubble lattice is 32 X 32. ~he ~
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bias field may be applied via a loop or the like, the plane
of which is parallel to the thin film. For example, the
techniques disclosed in the articles cited hereinbefore may
be employed or any conventional technique may be used.
The timing of the current pulses applied to the
upper and lower conductor patterns lOl and 12 is adjustable
although a preferred effect is achieved, as shown in Figure 3,
by delaying application of a current pulse to either con-
ductor pattern (for example, 101) and increasing its magnitude.
In Figure lO, Il is a current pulse applied to upper con-
ductor pattern 10l, I2 is a current pulse applied to lower
conductor pattern 12 and IB is a current applied to a loop
or the like to generate a bias magnetic field. The duration
of IB is indefinite and depends on the length of time the
bubbles are to be maintained. -
Although the above description refers to an embodi-
ment where upper and lower conductor patterns lOl and 12
sandwich the top and bottom surfaces 2Oa and 2Ob of magnetic
thin film 20, it is of course possible to attain the above
results by a pair of orthogonal conductor patterns lOl and 12
disposed on only one surface of magnetic thin film 20.
The magnetic thin film~of the present invention is
made of a material such as samarium-terbium-mixed ortho-
~errite in which the magnetic field, intensity needed to
annihilate magnetic bubbles changes sha~rply with temperature
~luctuation. Assuming the magnetic bubble extinction field
intensitY at temperature Kl is (HCo)Kl and the magnetic
bubble extlnctlon field intensity at temperature K2 is
~HCo~K2, the bias magnetic field intensity HB is so set as
to satisfy the following relationship assuming K1 is lower
than X2; ~
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i.. . . . .. . ~ . ,. . . . : :,. . :
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(Hco)Kl ~ HB (HCo)K2 , ................. (1)
By selective raising of the temperature from Kl to K2, the
magnetic bubbles are selectively annihilated in the portions
where the temperature has been raised.
Therefore, after magnetic bubbles are generated as
aforesaid on the above-stated image pickup element, an
optical image of a character, figure or the like is focused
by projector 28 on the surface of the magnetic thin film as
shown in Fig. 11. By the selective temperature rise resulting
from the selective absorption of irradiated light, magnetic
bubble collapse field in the light-irradiated portion is
lowered in intensity compared to the bias magnetic field.
Hence, in accordance with Equation ~1) annihilation of the
light-irradiated magnetic bubbles is effected and the optical
image ls converted into a magnetic-bubble pattern. -
The magnetic-bubble pattern thus formed can be
propagated in any direction desired through a propagation
circuit 30 shown in Figure 11 and is usable also as an input
to a device utilizing magnetic bubbles. Furthermore, the
magnetic bubble pattern can be converted into an electrical
signal by the Hall effect or the magnetic reluctance effect.
Also easy conversion into a serial or p~arallel signal is
~chieved, The aforementioned articles disclose various
devices for propagating and utilizing magnetic bubbles.
When the number of the conductive elements is in- -
creased and the length of the conductive element is increased,
the resistance of the conductor is increased accordingly.
However, by dividing the conductor pattern into a plurality
of conductor segments and drlving these segments in parallel,
` 3Q the increase of electric resistance may be avoided.
The resolution of the image pickup element using
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magnetic bubble depends upon the bubble diameter and there-
fore, in order to increase the resolution it is usual to
make the bubble diameter as small as possible and to use a
bubble material having properties that the bubble collapse
magnetic field is reduced with temperature increase. As
an example, a mixture garnet represented by Eul 7 Erl 3Alo 7-
GaO 8Fe3 5 12 is suitable as the bubble material. The
characteristic material length of the mixture garnet is 0.75
at 25C and the bubble diameter is about 6 ~. The bubble
collapse magnetic field is about 52 Qersteds at 300K and
about 37 Oersteds at 313~K, showing a large dependency on
temperature. ~-
It becomes possible, when this material is used,
to form a 56 X 56 bubble lattice in a magnetic thin film
having area of 1 mm2, as described in "The temperature
dependence of the Auisotropy field and Coercivity in epit- -
axial films of mixed rare-earth iron garnets", by Shumate,
Jr. et al, J. Appl. Phys., vol. 44, No. 1, January, 1973.
By virtue of the above-described structure, the
, 20 present invention requires no sequential generation of
magnetic bubbles by a magnetic bubble generator, the botch
processing is possible to form a magnetic-bubble lattice by
the application of current pulses to the conductor pattern
10 thereby attaining the advantages peculiax to the present
.
' invention including the reduction of processing time and less - -
'~ limitation on the method for transferring of the magnetic-
bubble patterr.
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