Patent GB-1207958-A (GB)
Title: Improvements in or relating to devices for the storage of information
Inventor: SMITH ROBIN WYNCLYFFE
IPC: G06V10/88
Filed: 1966-12-16
Abstract: 1,207,958. Data storage and logic operations; pattern recognition. NATIONAL RESEARCH DEVELOPMENT CORP. 15 March, 1968 [16 Dec., 1966], No. 56538/66. Headings G4C and G4R. [Also in Division H1] A vacuum tube comprises means for generating an array of electron beams, output means capable of responding to the individual electron beams, storage means comprising a conductive grid disposed transversely to an electron beam path extending between the generating and output means, the storage means having on the side further from the generating means a coating of insulator with a secondary emission coefficient appreciably greater than unity under specific electron bombardment conditions, and control electrode means between the storage and output means controllable to pass electrons from the storage to the output means or to reflect them towards the storage means. A solenoid 2 produces an axial magnetic field in a glass vacuum envelope 1 containing a photocathode 3, an equi-potential drift space 4, a wire mesh 6, a storage screen 5, a wire mesh 7, an equipotential drift space 8, a wire mesh 9, accelerating electrodes 11 and a display phosphor screen 10. The wire meshes 6, 7, 9 and the photocathode 3 have axial extensions as shown, to act as guard rings. The photocathode 3 otherwise consists of a matrix array of photoelectric areas formed either as separate areas deposited on a transparent conductive substrate or as a transparent insulating (glass) substrate having deposited on it an opaque conductive film with an array of holes and a continuous layer of photo-electric material overlapping the conductive film, so that when an optical image is projected (optionally through a lenticular plate) on to the photocathode, an array of electron beams is produced with a beam present in each matrix position on to which light is shining. The storage screen 5 consists of a metal grid, on the side of which remote from the photocathode 3 is deposited a secondary-electron-emitting insulator (e.g. magnesium fluoride). To record on the storage screen 5, the array of electron beams from the photocathode 3 pass through the screen 5 &c., are reflected by a negative potential on wire mesh 9, and then produce secondary electron emission from the storage screen 5. These electrons are accelerated away by wire mesh 7 and those not absorbed by the latter are reflected back by the field between mesh 7 and drift space 8 arriving with low energy at the storage screen 5 where they are absorbed. A positive or negative electrostatic charge image is recorded in this way, depending on the potential of the storage screen 5. To read out the stored information to the phosphor screen 10 non-destructively, the potential of the storage screen 5 is reduced, the photocathode 3 is illuminated with a uniform beam of light, and a positive potential is applied to the wire mesh 9 to pass the electron beams received. The stored charges may have values O, Q, 2Q ... and it may be arranged, by selection of the storage screen potential, that an output is produced on read-out only if the value reaches a threshold of Q, 2Q ... as desired. The arrays of electron beams can be deflected transversely by electrostatic and/or electromagnetic deflection systems 12, 13 so that a plurality of images can be stored in interleaved form. Movement can be detected by storing a positive charge image of the scene, then later storing a negative charge image on top. They will cancel out only in the absence of movement. By writing two matrices with the same or different sign, on top of one another, addition or subtraction respectively of the matrices is performed. A pattern can be compared with stored patterns, using the selective positive and negative recording facility, for pattern recognition. Performance of crosscorrelation, auto-correlation and standard logical operations are also described, using the transverse deflection, positive and negative recording, and selective threshold facilities described above.