Abstract:
A light modulator utilizing the principal of ion injection from a switching electrode into a fluid dielectric to effect turbulent forces and the resultant movement of a light interrupting object into and out of a light path. The fluid dielectric and the movable object have similar values of specific gravity.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This invention is related to our commonly assigned U.S. patent application Ser. No. 167,254 entitled &#34;Reflecting Type Light Modulator&#34; and filed concurrently herewith. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of light modulation and more specifically to the area of electrically controlled display devices. 
     2. Description of the Prior Art 
     In the development of electrically controlled light modulating type displays for automotive applications, much effort and recent attention has been given to those which employ liquid crystal materials. While liquid crystal displays have advantages of high daylight contrast and low power requirements, they have been found to be inoperable at low temperatures without auxiliary heater provisions and have also been found to degrade with age. 
     While others are involved with overcoming the aforementioned problems with liquid crystal type displays, our work has been associated with finding alternatives having the same advantages and none of the disadvantages of the liquid crystal type displays. 
     SUMMARY OF THE INVENTION 
     We have observed that in a fluid dielectric a positive potential applied to a switching electrode, as referenced from a common electrode, causes a suspended object, having a value of specific gravity similar to that of the fluid dielectric and located between the switching electrode and the common electrode, to move to another location in the fluid. Materials such as mica, glass and several plastic dielectric materials have been found to be usable as responsively positionable objects. We have also determined that ions are injected from the switching electrode and create a turbulence in the fluid dielectric. Those turbulent forces effect the physical displacement of the object away from the path of least resistance between the activated switching electrode and the common electrode. 
     The present invention is an outgrowth of our observations and overcomes many of the disadvantages of the prior art displays, while having low power requirements to effect a highly contrasting and responsive light modulator. Modulation is achieved by controlling the movement of a solid opaque element in a fluid dielectric medium. The fluid and movable element are located in a fluid-tight cavity having a pair of chambers, whereby the element is movable between the chambers. One of the chambers has a pair of transparent windows for receiving and transmitting incident electromagnetic radiation. The location of the movable element in the chamber with the windows blocks the transmission of incident light through that chamber. 
     Switching electrodes are provided in each chamber, separated from a common electrode. The switching electrodes are utilized to effect movement of the movable element between the chambers when an appropriate voltage is applied with respect to the common electrode. The fluid dielectric is selected so as to be slightly conductive (ionic) and to allow for ion injection from the switching electrodes when individually activated with respect to the common electrode. Ion injection into the fluid creates a slight turbulence in the fluid and the turbulent forces act on the movable element to push it towards the opposite chamber. Periodic activation of the same electrode insures that the movable element remains in the desired chamber. 
     The fluid dielectric and the movable element are selected so that their values of specific gravity (density) are similar. The movable element has been found to be effected by the turbulent forces when its value of specific gravity is either the same as or slightly greater than that of the fluid dielectric. The selection of a movable element having a slightly higher value of specific gravity allows the element to settle in the fluid dielectric and still be responsive to the turbulent forces. 
     It is, therefore, an object of the present invention to provide a highly responsive light modulator device having low power requirements. 
     It is another object of the present invention to provide an electrically actuated light modulator device that acts as a light valve for selectively transmitting or blocking incident light. 
     It is a still further object of the present invention to provide a highly responsive light modulator device that utilizes a fluid medium and movable solid element having similar values of specific gravity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the present invention as embodied in an X-Y matrix display system. 
     FIG. 2 is a detailed view of the present invention activated to a first light transmission state. 
     FIG. 3 is a detailed view of the present invention activated to a second light blocking state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is illustrated in FIG. 1 as incorporated in an X-Y matrix display system 10. The system 10 includes a translucent light conducting block 12. The block 12 is edge lighted with a light source 20 which is partially surrounded with a reflector 22. The translucent block 12 has metallized reflective edge faces 14, 16 and 18 that reflect light internal to the block 12. The back surface 13 of the block 12 may be either metallized reflective or have a particular color of reflective material coated thereon. The front surface 15 of the translucent block 12 is overlayed with an opaque mask 28 having a matrix of transparent apertures 29 formed thereon. Apertures 29, in this case, respectively form a first window for an associated light modulating cell. In this case, the number of apertures 29 are designated in &#34;n&#34; columns and &#34;m&#34; rows, where &#34;n&#34; and &#34;m&#34; are defined as integers greater than zero. A plurality (2n) of vertically oriented switching electrodes X and X&#39; are arranged overlaying the opaque aperture mask 28 so that each switching electrode corresponds to a single column of apertures 29. For instance, the switching electrode designated as X n  overlies a portion of the nth column of apertures 29 and the X&#39; n  electrode lies adjacent the nth column of apertures 29 over the opaque mask 28. 
     A solid insulator material 30 is laminated over the switching electrodes and the opaque aperture mask 28. The insulator material 30 contains a matrix of individual cavities 31 which form the individual light modulation cells for the display. A plurality of common transparent Y electrodes overlie the individual rows of cells 31 on the material 30. The common electrodes are laminated on the back surface of a light conducting substrate 40; and the light modulator cells 31 are sandwiched between the switching and common electrodes. The substrate 40 is shown as having an opaque mask 42 laminated onto its outer surface. The mask 42 has transparent apertures 44 formed thereon in alignment with the cells 31 and windows 29 in the aperture mask 28. 
     Control circuitry is schematically represented by a control unit 50 which supplies addressing information to the X address circuit 52 and the Y address circuit 54 for gating the appropriate electrodes to be activated with voltage from a source 60. 
     The cell shown in FIG. 2 corresponds to the light transmitting cell designated as II in FIG. 1. The individual light modulation cell 31 is a fluid-tight cavity having a first chamber 32 and a second chamber 34 formed therein. The chamber 32 defines an area of transmission corresponding to the aligned rear window 29 and front window 44. A movable element 48, in this case a sphere, is suspended within a fluid dielectric 36. The material selected for the movable element 48 and that selected for the fluid dielectric have nearly the same value of specific gravity. The relationship of specific gravity of the movable element to that of the fluid dielectric affects the responsiveness of the device. Therefore, the selection of appropriate materials dictates the degree of responsiveness. 
     In the present embodiment, acetone, having a specific gravity of approximately 0.8, is selected as the fluid dielectric material 36. Acetone is a weakly conducting electrolyte having a conductivity of approximately 10 6  Ω cm. 
     The movable element 48 is selected as a sphere of polypropylene having a specific gravity of approximately 0.9. While the polypropylene value of specific gravity is slightly higher that that of the acetone fluid dielectric 36, they are sufficiently similar to allow rapid movement of the element 48 between the chambers of the cell. The slightly higher value for the selected polypropylene allows it to settle in the lower part of its cavity location due to the force of gravity. 
     In FIG. 2, a first thin wire switching electrode X i  is located at one end of chamber 32 and a second thin wire switching electrode X&#39; i  is located at the end of chamber 34. A common transparent electrode Y j+1 , is common to both the chambers 32 and 34 of the cavity 31 and separate from both of the switching electrodes. The movable element 48 in chamber 34 is located and maintained therein by activation of switching electrode X i  and common electrode Y j+1 . The location of the movable element in chamber 34 therefore allows light to be transmitted through window 29, transparent electrode Y j+1  and aperture 44 on front substrate 40. 
     When a voltage on the order of +40 volts is applied between one of the switching electrodes and the common electrode establishing an electric field gradiant therebetween, ions are injected into the fluid dielectric 36 from the activated switching electrode. 
     Protrusions 38 and 39 define the inter communicating limits of respective chambers 32 and 34 of the cavity 31 and also provide a mechanical barrier to prevent the movable element 48 from drifting from one chamber to the other. Another method of retaining the movable element 48 in its selected location is to periodically pulsate the appropriate switching electrode. 
     The cell shown in FIG. 3 corresponds to the light blocked cell designated as III in FIG. 1. The movable element 48 is shown in a light blocking position in chamber 32 and was placed therein by an activation of switching electrode X&#39; i , on the order of +40 volts, as referenced from the common electrode Y j . 
     While the above embodiment has been described as being switchable between light transmissive and light occluding states, we know that by appropriately selecting materials a device may be constructed wherein the movable element 48 is formed of a color dyed cross-linked polystyrene or the like to provide a color filter material when positioned in the path of light transmission. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concept of this invention. Therefore, it is intended by the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.