Patent GB-597525-A (GB)
Title: Improvement in or relating to television receiving devices
IPC: H04N5/74
Filed: 1945-05-23
Abstract: 5 9 7 , 5 2 5 . Television ; cathode-ray tubes. SCOPHONY, Ltd., and WIKKENHAUSER, G. May 23, 1945, No. 12891. [Classes 39(i) and 40(iii)] A television receiving device comprises a cathode-ray tube having a deformable body which is provided, on the side opposite to that scanned by the cathode ray, with a highly reflecting metal layer so disposed in the optical path between a light source and an image screen that when elemental areas of this metal layer are deformed in accordance with image signals the light reflected by these areas on to the image screen is correspondingly varied in intensity. The deformable body 19, which is of insulating material and mounted inside the cathode-ray tube 10, has, on its scanned surface, :a mosaic of conducting and mutually insulated particles 20 and, on the opposite surface, a metallic reflecting layer 21. Light from a source 23 is directed by lens 24 and concave mirror 25 on to the field lens 22 which is supported within the envelope. The layer 21 is arranged to be substantially flat in the absence of distortion of 19 and under these conditions light from 23 is reflected back on to 25. When elemental areas of 21 are distorted, light from these areas passes around 25 and is focused by lens 26 on to the image screen 27. One way of producing distortion of 19, and hence of 21, is to utilize the secondary emission :from the scanned surface 20 to stabilize the potential of the particles of this surface at a value at which the number of primary electrons from the cathode-ray beam which reach -the particles is equal to the number of secondary electrons emitted by -the particles as a result of bombardment by the cathode ray so-that, when the potential of each particle, as it -is scanned, differs from that of the metal layer 21, to which the image signals are applied across impedance 28, an electrostatic stress is set up in the body 19 in the region of the particles. If the insulation of the particles -is sufficiently high the deformation produced by one scanning will remain until the mosaic 20 is again scanned. A conducting coating 29 is provided to collect the secondary electrons. Another way of producing the desired distortion of 19 is to velocity-modulate the cathode ray with the image signals so that the secondary emission from the particles, and consequently their potential, varies with the velocity of the impinging electrons. In this arrangement, 21 is maintained at a fixed potential and the impedances 28 and 30 are replaced by direct connections. A further method of operating the arrangement is to vary the intensity of the cathode-ray beam by applying the image signals across 30 to the control electrode 12 and arranging the velocity of the beam so that. secondary emission is negligible and the particles therefore, when scanned, become more negative in accordance with the intensity of the impinging beam. To enable the charge acquired during one scan to dissipate before the next scans the spaces between the particles may be made slightly conductive, by treating with a liquid suspension of graphite which is connected to a point of suitable fixed potential. The material of 19 should have a high S.I.C. and a high-breakdown voltage, e.g. "polythene," and the conducting particles and reflecting layer may be of silver. The silver is deposited on both sides of a polythene foil by known means, one side being sub-divided to form the required particles by rubbing the silver away along two mutually perpendicular sets of parallel lines. An alternative method is to evaporate the silver on to the foil through a suitable marking grid which is subsequently removed. Specification 543,485 is referred to.