Patent GB-1124678-A (GB)
Title: Electrically responsive light controlling devices
IPC: G02F1/17
Filed: 1966-03-04
Abstract: 1,124,678. Light modulators. A. M. MARKS. 4 March, 1966, No. 9616/66. Heading H4F. A light controlling device which may reflect, transmit or absorb light upon application of an electrical potential comprises a transparent sheet of glass or plastic 10, Fig. 4, spaced from a second sheet of material 11 which may be transparent or light absorbing, both sheets being covered with an electrically conductive transparent coating 14, and a fluid-tight sealing means such as flexible bellows 23 or gasket (12), Fig. 1, not shown, between the sheets to form a tank-like space 13 which is filled with a fluid 17 in which there is carried a suspension of thin and flat light reflecting di-pole particles 18. The particles 18 are disorientated by Brownian motion and light incident on sheet 10 is reflected diffusely by the particles. Fig. 1, not shown. When an electric field is imposed across conductive coatings 14 the particles become aligned parallel to the field and normal to the surface of the sheets so that the light passes between them and reaches the second sheet 11 which may be transparent, light absorbing or made of a coloured reflecting material so that the light is reflected from the coloured surface and emerges in a coloured beam. When the field is decreased or reduced to zero the di-pole particles 18 again become disorientated by Brownian motion, but in order to quicken this disorientation and cause the device to become reflective in a shorter time the sheets 10 and 11 are displaced with respect to each other by means of a vibrator 24 which may comprise a small motor having an eccentrically mounted flywheel or a piezoelectric or magnetostrictive oscillator. A protective layer such as a transparent silicon monoxide layer (22, Fig. 3, not shown), may be applied to the conductive coatings 14, and several devices may be arranged on top of each other to provide a series of flat tank-like spaces (13, Fig. 5, not shown), the di-pole particles in each space being differently coloured so that the reflected light has the colour of the di-poles within the tank space from which it was reflected. Conductive coatings 14 may be replaced by a network or spacer grid of parallel conducting wires (26, 25<SP>1</SP>, Fig. 6, not shown), which enables small areas of the device to be activated. In addition to mechanical disorientation the space 13 may be radiated with infra-red radiation if the suspending liquid is capable of absorbing such radiation. The sheets 10 and 11 may be circular and mounted in a holder so that they may be rotated or displaced with respect to each other (Figs. 7 and 8, not shown). The di-pole particles may comprise vanadium pentoxide, tungstic acid, certain proteins (see Specification), anisotropic birefringent elongated di-pole particles and absorptive di-pole particles such as herapathite crystals (see Specification). Alternatively the particles may comprise anisotropic crystal needles coated with silver or platinum films, or flake-like particles such as glass flakes or natural or synthetic pearlescence, e.g. bismuth or lead carbonate crystals. The liquid for the di-pole suspension may comprise plasticizers such as the silicone fluids, dibutyl phthalate or disphenyl. The transparent conductive coatings may comprise stannic oxide films. In a further embodiment, Fig. 9, the device comprises a transparent plastic film strip 31 having a plurality of small drops 32 of silicone oil in which lead carbonate crystal flakes 33 of high refractive index are suspended, such that when a field is applied via transparent electrodes 34, 35 the particles 33 are aligned. Electrodes 34 and 35 may be strip electrodes of large area.