Abstract:
A magnetic bubble element which is useful as an image information processing element. A thin film made of a magnetic bubble forming material has a plurality of wedge-formed patterns made of a non-magnetostriction soft magnetic thin film is formed on the upper surface of the thin film 16. A conductor grating comprising two undulating conductor patterns are provided each cycle of the undulation in both conductor patterns defining a wider pitch and a narrower pitch, each of the wedge-formed patterns being disposed over the corresponding part of one of the two conductor patterns defining the narrower pitch in a manner such that the apex portion and the bottom portion of each wedge shaped pattern extend into the parts forming the wider pitch.

Description:
BACKGROUND OF THE INVENTION 
     A bias modulation method utilizing a magneto-static interaction between a wedge-formed pattern made of a non-magnetostrictive soft magnetic material such as Permalloy and magnetic bubbles (cylindrical domains or localized highly stable magnetic states) and operable for conveying magnetic bubbles toward a desired direction is disclosed the article Application of Orthoferrites to Domain Wall Devices by A. H. Bobeck et al in IEEE Trans. on Mag, MAG-5 (1969) PP. 544-553. 
     In this method, a series of wedge-formed patterns made of a non-magnetostrictive high premeability thin film are continuously disposed on a thin plate made of a magnetic bubble forming material such as an orthoferrite and the expansion and contraction of the magnetic bubbles due to the variation of a biasing magnetic field are converted into an effective unidirectional movement of the magnetic bubbles. 
     This method involves a disadvantage in that the wedge-formed patterns are made of a optically opaque material (permalloy) which disturbs the observation of the magnetic bubbles when the latter are used as image forming elements. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides a magnetic bubble element which is useful as an image information processing element. A thin film made of a magnetic bubble forming material has a plurality of wedge-formed patterns made of a non-magnetostrictive soft magnetic thin film formed on the upper surface of the thin film 16. A conductor grating comprising two undulating conductor patterns each cycle of the undulation in both conductor patterns defining a wider pitch and a narrower pitch are provided each of the wedge-formed patterns being disposed over the corresponding part of one of the two conductor patterns defining the narrower pitch in a manner such that the apex portion and the bottom portion of each wedge-shaped pattern enter into the parts forming the wider pitch. 
     It is an object of the present invention to provide a magnetic bubble element which is configured to be particularly useful in image processing applications. 
     It is a further object of the present invention to provide a magnetic bubble element which includes wedge-formed elements made of optically opaque material for displacing the magnetic bubbles in a desired direction, the bubble element being so fabricated that the movement of the bubbles may be observed making the bubble element suitable for image processing applications. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the following drawings wherein: 
     FIG. 1 illustrates the basic configuration of the magnetic bubble element of the present invention; 
     FIGS. 2 and 3 are sectional views along line 2--2 of FIG. 1 showing different embodiments of the present invention; 
     FIGS. 4-6 schematically illustrate the magnetizing state of the magnetic bubbles as the bubble is caused to move; and 
     FIG. 7 shows in a simplified representation of a printer in which the magnetic bubble element of the present invention may be utilized. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is indicated an arrangement of a magnetic bubble element which comprises a series of wedge-formed patterns 11A, 11B, 11C, . . . made in a thin film of, for instance, nickel ferrite (permalloy) constituting a mixture of soft magnetic materials exhibiting no magnetostriction, and a conductor grating 14 made of first and second conductor patterns 12 and 13. Each of the conductor patterns 12 and 13 is made of an electric conductor formed into a rectangular undulation, one cycle of which defines a wider pitch P 1  and a narrower pitch P 2 . Each of the wedge-formed patterns 11A, 11B, 11C . . . underlies a pair of conductor runs defining therebetween the narrower pitch P 2  in the first conductor pattern 12 in a manner such that the apex portion A and the bottom portion B of each wedge-formed pattern intrude respectively into the parts adjacent thereto forming the wider pitch P 1 . The second conductor pattern 13 is disposed to form a grating with the first conductor pattern 12 through the interposition of an insulating layer 15 in the embodiment shown in FIG. 2, or patterns 12 and 13 are arranged on the upper and lower surfaces of the magnetic-bubble forming thin film 16, such as the orthoferrites described in the aforementioned Bobeck et al article, to form the grating as shown in FIG. 3. In either of the embodiments shown in FIGS. 2 or 3; the patterns 13 are placed at positions which never intersect with the patterns 11. 
     The dimensions of the first and second conductor patterns 12 and 13 in one example of this invention are selected in such a manner that when the diameter of the magnetic bubble utilized in this example is assumed to be D, the undulation cycle of the conductor pattern 13 is equal to 4D, the wider pitch P 1  defined between the center lines of respective conductor runs is equal to 3 D, the narrower pitch P 2  likewise defined is equal to 1 D, and the width of the conductors is equal to D/2. 
     However, it should be noted that the first and the second conductor patterns are not necessarily limited to be of the same measurements. 
     In FIG. 2 which is a sectional view along the line 2--2 in FIG. 1, there is shown the wedge-formed patterns 11 at positions closest adjacent to the magnetic bubble forming thin film 16. The second conductor pattern 13 which does not traverse the wedge-formed patterns 11 and the first conductor pattern 12 which traverses the wedge-formed patterns 11 are provided to overlie the same patterns 11 so that an insulating layer 15 is interposed between the first and second conductor patterns 12 and 13. In FIG. 3, the patterns 12 and 13 are arranged on the upper and lower surfaces respectively of film 16, insulating layer 15 not being required. 
     In FIGS. 4, 5, and 6, a fundamental principle of this invention is illustrated schematically. 
     FIG. 4 specifically indicates a state wherein a magnetic bubble C lies directly under the apex portion A of wedge-formed pattern 11A. Fo ease of understanding, it is assumed that the N-pole of the magnetic bubble C is in the plane of paper. That is, the magnetic field bias H B  is directed downwards toward the surface of the paper as shown. 
     In FIG. 5, there is shown a state of magnetization of the magnetic bubble C when electric currents I 1  and I 2  flow through the conductor patterns 12 and 13, respectively, in the arrow-marked directions. Magnetic fields by these currents are formed in three regions formed by the superposition of the two conductor patterns 12 and 13, i.e. a region 17 defined by wider pitch portions P 1  of the two conductor patterns, another region 18 defined by the superposition of a wider pitch portion P 1  and a narrow pitch pattern P 2 , and another region 19 defined by the superposition of narrower pitch portions P 2  of the two conductor patterns 12 and 13. 
     When the magnitude of the electric currents flowing through the two conductor patterns 12 and 13 are equal to each other, a magnetic field of a direction opposing to that of the bias magnetic field is created in the region 17, another magnetic field of a direction equal to that of the bias magnetic field is created in the region 18 because the magnetic field in a narrower pitch portion P 2  is stronger than that created in a wider pitch portion P 1  of the conductor patterns 12 and 13, and still another magnetic field of a direction equal to that of the bias magnetic field is created in the region 19. 
     Because of these magnetic fields, the magnetic bubble C as shown in FIG. 5 is subjected to a contracting force in the region 18 and forced into the region 17 wherein the bubble is subjected to an expansive force. At this time the electric currents flowing through the conductor patterns 12 and 13 are kept to sufficient values for causing the magnetic bubble C to intrude just under the subsequent wedge-formed pattern 11B. After the magnetic bubble C has been expanded and shifted just under the wedge-formed pattern 11B, the electric currents flowing through the conductor patterns 12 and 13 are interrupted and the magnetic bubble C is shifted to the position indicated in FIG. 6. It is to be noted that the magnetic bubble C is visible (using a magnetic-optical effect) to an observer looking on the element (direction of arrows a and b in FIGS. 2 and 3) for almost all of the time that it takes bubble C to move in the sequence shown in FIGS. 4-6 which makes bubble element construction of the present invention ideally suitable for image forming elements. 
     FIG. 7 shows a simplified representation of a printer utilizing the magnetic bubble elements according to this invention each element having a bubble transferring mechanism as described hereinabove. In this figure, numeral 30 designates a conductor pattern terminal, 31 a magnetic bubble generator array, 32 a character generator, 33 a control circuit, 34 bubble transferring channels, 35 bias magnetic field generating coils, and numeral 36 deisgnates bubble erasing coils. 
     In the examples of the printer, the magnetic bubble generating array 31 successively generates magnetic bubbles in accordance with the data concerning a character, figure, or else delivered from the character generator 32 based on a signal from a computer or the like, and the magnetic bubbles are transferred by means of the conductor patterns 12 and 13 (not shown in FIG. 7) which are connected with the control circuit 33 and supplied therefrom with pulse currents. After the character, figure, or else has been converted into a magnetic bubble pattern as described above, the bubbles are expanded as shown in FIG. 5 and the bubbles thus expanded are visualized utilizing a magneto-optical effect. Since the substantial part of the wedge-formed pattern 11 overlies the region 18 formed by the superposition of the narrower pitch portion P 2  and the wider pitch portion P 1  and the apex portion A and the bottom portion B thereof (FIG. 5) intrude into the region 17 formed by the superposition of the wider pitch portion P 1  of the two conductor patterns, the wedge-formed patterns 11, which are opaque, cause no obstacle in optically visualizing the thus expanded magnetic bubbles utilizing a magneto-optical effect (such as Faraday effect). It should be noted that if orthoferrites are used as film 16, they are sufficiently transparent in red light to enable direct visual observation of bubble behavior by means of the Faraday effect. The character of figure displayed by the expanded magnetic bubbles are then developed by electronic photography, for example. After development, the magnetic bubble pattern is erased by interrupting the electric currents flowing through the conductor patterns 12 and 13 and moving the printer through the erasing coils 36. 
     The magnetic bubble element according to this invention can improve the high frequency driving feature in comparison with the conventional bias magnetic field modulating method, and furthermore, the difficulty caused by the requirement of providing a distance in a range of from 3 D to 4 D between each magnetic bubbles for avoiding the repulsive force caused between the magnetic bubbles can be eliminated by expanding the magnetic bubbles. For the latter reason, the ratio between the diameter of the image elements and the distance between the same elements can be substantially improved. 
     While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the present invention without departing from its essential teachings.