Image storage matrix
United States Patent 1 1 Norman et al.  
 [451 Apr. 15, 1975 1 I IMAGE STORAGE MATRIX [76] Inventors: Ralph L. Norman, 3644 Marymont Dr., N.W., Huntsville, Ala.; Jerry W. Hagood, 307 Mountain Gap Rd., S.E., Huntsville, Ala. 35803; Joe Shelton, 700 Tatom St., N.W. Huntsville, Ala. 35805 [22] Filed: Oct. 10, 1973 [21] Appl. No.: 405,230  
 [52] US. Cl. 313/376; 313/391 [51] Int. Cl. H0lj 31/28 [58] Field of Search 313/65 A, 65 T, 66, 67,  
 [56] References Cited UNITED STATES PATENTS 10/1941 Lubszynski et al. 313/66 V 11/1952 Boer et al. 313/67 3,067,348 12/1962 Ochs ..3l3/67 Primary E.\-aminer.lames B. Mullins Attorney, Agent, or FirmRobert P. Gibson; Nathan Edelberg [57] ABSTRACT 4 Claims, 3 Drawing Figures PATENTED APR 1 s 575 IMAGE STORAGE MATRIX DEDICATORY CLAUSE The invention described herein may be manufactured, used, and licensed by or for the Government for Governmental purposes without payment to us of any royalty thereon.  
 BACKGROUND OF THE INVENTION Images are stored in various forms. One method widely used in electronic image storage, such as that used in the image orthicon, employes a very thin sheet of a material such as glass as a target. The thin sheet of glass is subjected to sodium doping which gives it a characteristic of being more conductive from one face to the other than it is between edges, with distances normalized. An electronic image can be received and stored on the glass since the electrons can flow through the glass from face to face but cannot flow toward its edges. The less resistance from face to face and the greater the resistance laterally, from edge to edge, the more perfect is the sheet for electron image storage. At lower light levels lateral target leakage results in loss of resolution in image orthicons, greatly limiting their usefulness.  
  In image storage, impinging electrons cause secondary emission from a coated face of the target, depleting the electrons. For retrieval the removed electrons are replaced on the other face of the target by a scanning electron beam, with the sodium ions conducting the charge between faces of the target. In a typical image orthicon an incoming optical image is focused on a photocathode, stimulating electron emission therefrom in proportion to the photon density. The electrons are directed toward the glass target with suitable means, such as focusing coils, reducing divergence of the beam. A screen grid, disposed between the photocathode and the target, collects secondary electrons emitted by the target when the photoelectrons impact the target. The opposite side of the target is scanned by an electron beam. The target, when depleted of electrons, draws electrons from the scanning beam to restore the target. The scanning beam returns to a multiplier stage in the area surrounding the source, minus these electrons, producing a signal indicative of the original optical input signal. This signal is then enhanced in the multiplier stage of the tube and coupled out as a video signal. Further and more detailed background on electrooptical imaging devices is available in such publications as Electro-Optical Photography at Low Illumination Levels by H. V. Soule, 1968.  
 SUMMARY OF THE INVENTION An image storage matrix is disclosed having improved resolution for providing an improved image output and having excellent face-to-face conduction for restoring to normal or zero potential when the stored image is retrieved. A metal-oxide matrix material allows this versatile&#39;image storage. The material comprises a matrix of continuous, parallel, metal fibers embedded in an oxide insulating material. The matrix material may comprise several million fibers per square centimeter which are coated with an electron emitting surface to enhance secondary emission..The oxide insulation between fibers may be any one of several combinations, affording a selectable resistance between adjacent fibers for controlling the lateral restance per unit area. An electron emissive coating over one surface of the matrix allows signal amplification through secondary emission of electrons.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified diagrammatic drawing of three basic sections of an image tube employing the image storage matrix and omitting the normal, typical circuit components such as deflection coils and housing assembly therefor.  
  FIG. 2 is a simplified sectional drawing of an image storage matrix showing the electron emissive coating on one end surface of the conductive fibers.  
  FIG. 3 is a simplified schematic of an image scanning section of an image tube showing field emission control for obtaining an output image from the target.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT In the image storage matrix, a thin slice of an ultrahigh density metal-oxide matrix is used for storage of an image and from which the image may be electrically read. Metal fibers of the matrix store the electrical images until the matrix is read and insulation characteristics of the matrix oxide prevent image destruction by isolating the charges stored on respective fibers.  
  The high density, metal-oxide matrix may be similar to that disclosed by Shelton et al in US. Pat. No. 3,745,402, issued July 10, 1973. Shelton et al disclose that the metal-oxide composite can comprise more than a million emitting fibers per square centimeter of emitter surface area. The device is capable of emitting electrons at ambient temperatures when subjected to an electric field. The quantity of electrons emitted depends on the field since thermionic emission is not required. Similarly, a field effect electron gun is disclosed in US. Pat. No. 3,783,325 by Shelton, a co-inventor in the present invention. Shelton discloses the electron gun can be shaped to produce a desirable electric field and current path for electron tubes.  
  The image-storage matrix of the instant invention may be best disclosed in reference to the drawings wherein like numbers represent like parts throughout the several drawings. FIG. 1 discloses a section of an electron tube employing the image storage matrix while excluding the extraneous portions of the tube; i.e. that part of the device which does not apply directly to the inventive area. An image storage matrix 10 is coaxially disposed between an electron gun l2 and a photocathode l4. A fine mesh screen grid 16 is disposed between photocathode l4 and matrix 10, the grid being positioned close to matrix 10 to capture secondary electrons emitted by the matrix. Matrix 10 functions as a target for photoelectrons accelerated from the photocathode. The target matrix includes parallel conductive fibers 20 which may be tungsten and may vary from one to several million per square centimeter; an insulating oxide 22 grown with the fibers provides insulation between fibers 20, providing high resistance from edge to edge per unit area; and an electron emissive coating 24 covers the surface of target 10 facing the grid 16. Typical insulators 22 for target 10 include zirconium oxide and uranium oxide. A typical secondary emitter capable of functioning as the emissive coating 24 is magnesium oxide (MgO) or silver magnesium oxide (AgMgO).  
  In typical operation of the image storage matrix, an optical image from an input lens 28 is projected onto photocathode 14 which emits electrons in proportion to the intensity of the light received in the photon image from the lens. The emitted electrons form an electron image on material 24 allowing secondary electrons to be emitted on impact. The secondary electrons are collected by grid 16, leaving the image on the target as a charge distribution across the fibers. The image in the form of the charge distribution can then be read by an electron scan. The scan beam electrons from electron gun 12 will deposit on the metal fibers where the fibers are charged positive due to the prior loss of electrons from the electron-emissive face 24. For fibers 20 that are not charged, the scan beam returns to its source unmodulated. For fibers that are charged, the scan beam gives up electrons, restoring the target to its normal or zero potential state and the scan beam returns, modulated, to the vicinity of source 12. The return beam provides the output video signal when processcd.  
  As shown in FIG. 2, electron-emissive coating 24 need not cover the entire surface of target 10. Because of the high packing density of fibers 20, photoelectrons will impact the nearest surface 24 without loss of resolution. The system operation is further enhanced by the greater resistance of oxide 22 between electronemissive surfaces 24. In providing this particular embodiment of target matrix 10, the metal fibers 20 can be etched a minimal distance below surface 30 of the oxide. The electron emissive coating 24 is deposited over surface 30 and the ends of fibers 20. The face of matrix 10 is then polishe to remove coating 24 from insulator 22 while leaving it on emitters 20.  
  FIG. 3 schematically shows image storage matrix 10 disposed for reading by use of an electric field. The electron gun and associated image multiplier section of the tube is replaced by one or more fine mesh grids 32 coupled to a source of positive direct current B+. Grids 32 allow an electric field to be developed between target 10 and the grids. This is accomplished by develop ing the electric field between photocathode 14 and a photon emissive surface 34. The photon emissive surface 34, such as a phosphor, is disposed on the other side of grid 32. Electrons, freed from matrix 10 and accelerated through grids 32, impact the photon emissive surface. Light is emitted across the surface and the amplified image may be viewed or imprinted. In this mode, the electron emissive coating 24 is omitted from the face of matrix 10. This allows the electron image to be stored directly in the metal fibers as a momentary surplus of electrons. The image is then read out of the matrix by application of the electric field drawing the excessive electrons away from the matrix. Since the field is already established between grids 32 and matrix target 10 and is critically adjusted to the threshold of conduction, the added electrons on the matrix result in instantaneous conduction of the electrons through grids 32 to surface 34. For more intensified imaging of a target signal under reduced input signal conditions, the electric field is increased, increasing sensitivity of response.  
  The image storage matrix provides a versatile image storage sheet which is extremely sturdy since it is a ceramic reinforced with metal and produced at high temperature. This greatly reduces the fragile nature of devices such as the image orthicon, which employ an image plate of this nature. Resolution is limited only by the electron beam capability since the matrix employs millions of fibers per square centimeter for image capture and storage. Since the resistance between fibers is controlled by a high resistance oxide preventing charge migration, image storage time is increased with minimum deterioration of the original image.  
  It is to be understood that the form of the invention, herewith shown and described is to be taken as a preferred example of the same, and that various changes in the arrangement of parts may be resorted to, without departing from the spirit or scope of the invention. Accordingly, the scope of the invention is to be limited only by the claims appended hereto.  
 We claim:  
  1. In an image device for converting an optical image into video signals and having an imaging section and a thin film target section, the improvement comprising: an image storage matrix target for providing enhanced face to face conduction, electrical energy storage, and high resistance to lateral charge migration, said matrix target being a thin sheet of oxidemetal composite having several million parallel metal fibers per square centimeter disposed normal to the sheet surfaces for conducting electrons between surfaces of said sheet, and an oxide insulator between respective fibers for resisting lateral charge migration; a photocathode aligned on a first side of said target for directing photoelectrons thereto; and a signal sensing means aligned on a second side of said target for scanning the second surface of said target to obtain said video signal, said signal sensing means is an electron gun for generating an electron scan beam; and wherein a screen grid is disposed between said photocathode and said target for attracting secondary emission electrons, and an electron emissive coating covers the entire first surface of said sheet for providing secondary emission amplification.  
  2. In an image device for converting an optical image into video signals and having an imaging section and a thin film target section, the improvement comprising:  
 a metal-oxide, image storage matrix target for providing enhanced face to face conduction, electrical energy storage, and high resistance to lateral charge migration, said matrix target being a thin sheet of oxide-metal composite having several million parallel metal fibers per square centimeter disposed normal to the sheet surfaces for conducting electrons between surfaces of said sheet, and an oxide insulator between respective fibers for resisting lateral charge migration; a photocathode aligned on a first side of said target for directing photoelectrons thereto; and ascreen grid disposed on a second side of said target for developing an electric field across said target to enhance electron migration from the target toward the grid.  
  3. In an image device as set forth in claim 2 the further improvement of a photon emissive surface aligned with said target, said grid disposed between said photon emissive surface and said target for enhancing electron flow by field effect emission from the target; and wherein said target fibers are charged with an increase in electron density due to impact of said photoelectrons; said field effect emission from said target being directly coupled to said photon emissive surface without further amplification.  
  4. In an image device&#39;for converting an optical image into an electron image and having an imaging section and a target section, the improvement comprising: a  
  metal-oxide, image storage matrix target for providing enhanced face to face conduction and high resistance to lateral charge migration, said target being a sheet of I metal-oxide composite having several million parallel metal fibers per square centimeter disposed normal to the sheet surfaces for conducting electrons between surfaces of said sheet, and an oxide insulator between respective fibers for resisting lateral charge migration; a photocathode aligned on a first side of said target for