GB653315A - Improvements in or relating to electron discharge tubes - Google Patents

Abstract

653,315. Electron image tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 7, 1947, No. 21666. Convention date, June 28, 1946. [Class 39 (i)] An electron image tube incorporates a velocity selection arrangement which permits only electrons above, or alternatively below, a predetermined velocity, to impinge on the fluorescent screen. Fig. 1 shows a tube for utilizing thermal image effects, in which the target T is of a material which changes its resistance under the action of heat or other radiant energy. On one side is a thin grounded conductive coating 3, and on the other a mosaic 4 of picture elements capable of producing thermionic, photo - electric or secondary emission. An external heating coil H is used in this instance to cause emission. Rings 6, 7, 8, 9 act as accelerating electrodes, and a magnetic focusing coil 10 surrounds the tube. Initially the potential of a selector grid 5 is adjusted so that no electrons pass through. If now a thermal image is focused on the target, the resistances of the plurality of paths through the target to the mosaic elements 4 will decrease according to the amount of radiation received, and these elements will become more negative to grid 5. The increased velocity enables the electrons to pass the grid, subsequently forming a picture on the fluorescent screen S. Fig. 2 (not shown), is a modification in which the electrons are directed towards an electron mirror, those below a certain velocity being reflected to form the picture on the screen. In this instance, ultra-violet energy causes electron emission from the mosaic elements. If visible light or infra-red radiation is used to produce an image of the object on the target, this may be of lead sulphide or activated cadmium selenide, whose resistance varies with such incident radiation.