Patent GB-1331940-A (GB)
Title: Display apparatus
IPC: G02F1/13
Filed: 1970-11-10
Abstract: 1331940 Measuring voltage, frequency & phase SPERRY RAND CORP 10 Nov 1970 [25 Nov 1969] 53391/70 Heading G1U [Also in Division H4] In a display device a liquid crystal layer 12 which exhibits dynamic or quiescent scattering (i.e. is normally transparent or light scattering respectively, but becomes light scattering or transparent on application of an electric field above a threshold) is disposed between two electrodes 13, 14 at least one of which has  resistance characteristics so that a potential gradient may be applied thereacross to provide a spatially varying electric field which may succeed the threshold value only across some areas of the layer. Thus in Figs. 3 and 10, wherein only electrode 14 has the desired resistance characteristics, a potential source 21 is connected between low resistance contacts 16, 17 on electrode 14, and a potential source 20 is connected between electrode 13 and contact 17. With the polarities shown, and if V14 is twice V13, the field varies between contacts 16, 17 as indicated in Fig. 9, crossing the threshold value Vc twice and giving a band 31 of different optical properties from adjacent areas 30, 32. Altering V13 moves the band, while altering V14 varies the width of the band and may move it. If one of the sources 20, 21 is of reversed polarity, only one boundary at Vc is produced i. e. two adjacent areas variable in size as V13 or V14 is varied, Fig. 6 (not shown). Electrode 17 may have a sheet resistance which is not constant, as has been assumed, e. g. by varying its thickness to give a sheet resistance which varies linearly between contacts 16 and 17 and a corresponding quadratic distribution of potential Figs. 7 and 8 (not shown). This may be useful in sharpening the boundary at which the threshold field Vc occurs, but may reduce the usable area of the display. The electrode may have different shapes. In Figs. 12 and 13 (not shown), electrode 14 is a segment of an annulus with contacts 16, 17 extending radially (meter type display). The sheet resistance of electrode 14 must then be varied radially so that a moving bar with linear boundaries may be displayed. In Figs. 14-16 and 17 (not shown) electrode 14 is circular or part circular and is provided with peripheral and central low resistance contacts so that the potential varies radially and a band is produced between two radii, at least one of which is variable. In Figs.18-20, (not shown) both electrodes have suitable resistance characteristics, and using three voltage sources, bands or areas can be produced with boundaries which can be displaced or rotated  with respect to the electrodes. In Fig. 21, a square high resistance electrode 123 is provided. with four terminals 126-129 and is rotated 45 degrees with respect to a square low resistance electrode 122. Connected to potential sources 130, 131 as shown, the device can be used as for indicating voltage balances or nulls between the sources if the display varies in pattern, Figs. 22a-f (not shown). When V121 is twice V12 a symmetric display comprising four dark semicircles centred on the electrodes 126-129 is obtained. For true null indication V12 is obtained from a divide-by-two potentiometer. The potentials applied to the electrodes may be A.C. potential, and in the device of Fig.21 may be used also as a frequency or phase meter. If the frequencies of V12 and V121 differ, the display pulsates at the difference frequency. The patterns obtained for varying phase differences change in the same manner as those for varying voltage differences. Other devices shown may also be used for indicating voltage e. g. by superemposing a scale composed of masked or shaped nematic cells over the moving band of Fig.10. The display devices may be stacked Figs. 23, 24 (not shown) e.g. to provide sharper boundaries, if the devices are substantially identical, or for multiple colour displays. If unalike, superimposed patterns will produce near patterns and in particular, narrow strips produced by high voltage gradiants and disposed obliquely or at 90 degrees to each other provide a spot which can be scanned over a raster i. e. a flying spot scanner. Polar or other co-ordinate systems may also be used. The devices may be viewed by reflection of ambient illumination, by scattered transmitted light, or by directly transmitted light, Figs.25-27 (not shown), so that the unexcited display is either dark or light.