Patent GB-1194304-A (GB)
Title: A Method and Means for Providing a Solid State Electroluminescent Display
IPC: H05B44/00
Filed: 1968-08-26
Abstract: 1,194,304. Electroluminescence. BENDIX CORP. 26 Aug., 1968 [15 Sept., 1967], No. 40722/68. Heading C4S. A solid state display device comprises a closed acoustical loop including a display element of piezo-electric material, means for applying alternating voltages to the p.e. material to set up a standing wave pattern for generating secondary voltages in the material which vary in amplitude above and below a threshold value at points along the display element dependent upon the wave pattern and electroluminescent means on the element to be illuminated at points on the element at which the secondary voltage exceeds the threshold value. The device comprises a bar 12 of Pb zirconatetitanate p.e. material supporting ZnS: Cu e.1. layers 16, 18, interconnected electrodes 22, 24 on the e.1. layers and electrodes 31, 33. The acoustical return path is provided by a member 25 of the p.e. material or of annealed zinc. With an electrode on the underside of the bar 12 earthed, A.C. potentials are applied to electrodes 22, 24, 31, 33. The potentials to electrodes 31, 33 are of the same constant frequency f 1  but 90 degrees out of phase whilst the frequency applied to electrodes 22, 24 can be adjusted by a control 51 above or belowf 1 . The frequency f 1  is chosen to produce standing vibration waves in the bar 12 which induce therein voltages between the top and bottom of the bar, electrode 33 being positioned at a null point of the excitation. The superposition of two such sets of standing waves results in a constant magnitude variable phase voltage transversely across the bar at all points. If electrodes 22, 24 are grounded a constant brightness display is produced. When the A.C. potential is applied to electrodes 22, 24 the effective voltage at any point varies with time and a pattern of light bands is obtained which moves along the bar in a direction depending on whether the frequency applied to electrodes 22, 24 is greater or less than the frequency applied to electrodes 31, 33. The shape of the bands depends on that of electrodes 31, 33. Another embodiment in the form of a toroidal ring comprises a sandwich of an electrode, p.e. material ZnS, Se phosphor and a transparent electrode. Electrodes (83, (85), Fig. 8 (not shown), corresponding to electrodes 31, 33, extend radially in the p.e. material at an angle of 45 degrees apart. Applying frequencies of 35 and 52 kc.p.s. between the radial electrodes produces respectively two and four radial light bands which move round the toroid face. A method of obtaining rotating bands in which no connection is made to the electrode on the e.1. layer comprises feeding the output of two sources having slightly different frequencies of f 1  and f 2 to a frequency mixing network which supplies to electrodes (83), (85) voltages which may vary as a function of the average frequency modulated by half the difference of the frequencies and are 90 degrees out of phase. If the voltages are obtained from a resolver synchro the moving light bands indicate the position and rotation of the synchro. Two synchros may be used, the light bands then indicating the differential rotation between them.