Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2003-02-13
2004-10-12
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
Reexamination Certificate
active
06804040
ABSTRACT:
FIELD OF THE INVENTION
The present application relates to a power-efficient and low-cost method and device for controlling an AC voltage applied to a suspended particle device (SPD). The present application also relates to methods and devices for shock prevention, detecting forced entry, and reducing the manufacturing costs of SPD film.
BACKGROUND OF THE INVENTION
Light valves have been in use for more than sixty years for the modulation of light. As used herein, a light valve is defined as a cell formed of two walls that are spaced apart by a small distance, at least one wall being transparent, the walls having electrodes thereon, usually in the form of transparent, electrically conductive coatings. The cell contains a light-modulating element (sometimes herein referred to as an “activatable material”), which may be either a liquid suspension of particles, or a plastic film in which droplets of a liquid suspension of particles are distributed.
The liquid suspension (sometimes herein referred to as “a liquid light valve suspension” or “a light valve suspension”) comprises small, anisometrically shaped particles suspended in a liquid suspending medium. In the absence of an applied electrical field, the particles in the liquid suspension assume random positions due to Brownian movement, and hence a beam of light passing into the cell is reflected, transmitted or absorbed, depending upon the cell structure, the nature and concentration of the particles, and the energy content of the light. The light valve is thus relatively dark in the OFF state. However, when an electric field is applied through the liquid light valve suspension in the light valve, the particles become aligned and for many suspensions most of the light can pass through the cell. The light valve is thus relatively transparent in the ON state. Light valves of the type described herein are also known as “suspended particle devices” or “SPDs.” More generally, the term suspended particle device, as used herein, refers to any device in which suspended particles align to allow light to pass through the device when an electric field is applied.
Light valves have been proposed for use in numerous applications including, e.g., alphanumeric and graphic displays; television displays; filters for lamps, cameras, optical fibers, and windows, sunroofs, sunvisors, eyeglasses, goggles and mirrors and the like, to control the amount of light passing therethrough or reflected therefrom as the case may be. As used herein the term “light” generally refers to visible electromagnetic radiation, but where applicable, “light” can also comprise other types of electromagnetic radiation such as, but not limited to, infrared radiation and ultraviolet radiation.
For many applications, as would be well understood in the art it is preferable for the activatable material, i.e., the light modulating element, to be a plastic film rather than a liquid suspension. For example, in a light valve used as a variable light transmission window, a plastic film, in which droplets of liquid suspension are distributed, is preferable to a liquid suspension alone because hydrostatic pressure effects, e.g., bulging, associated with a high column of liquid suspension, can be avoided through use of a film, and the risk of possible leakage can also be avoided. Another advantage of using a plastic film is that in a plastic film, the particles are generally present only within very small droplets, and hence do not noticeably agglomerate when the film is repeatedly activated with a voltage.
As used herein, the terms “SPD film” or “light valve film” mean at least one film or sheet comprising a suspension of particles used or intended for use by itself or as part of a light valve. The light valve film or SPD film includes either: (a) a suspension of particles dispersed throughout a continuous liquid phase enclosed within one or more rigid or flexible solid films or sheets, or (b) a discontinuous phase of a liquid comprising dispersed particles, the discontinuous phase being dispersed throughout a continuous phase of a rigid or flexible solid film or sheet. The light valve film or SPD film may also include one or more other layers such as, without limitation, a film, coating or sheet, or combination thereof, which may provide the light valve film or SPD film with (1) scratch resistance (2) protection from ultraviolet radiation (3) reflection of infrared energy, and/or (4) electrical conductivity for transmitting an applied electric or magnetic field to the activatable material.
U.S. Pat. No. 5,409,734 illustrates an example of a type of light valve film that is formed by phase separation from a homogeneous solution. Light valve films may be made by cross-linking emulsions such as those described in U.S. Pat. Nos. 5,463,491 and 5,463,492, both of which are assigned to the assignee of the present invention.
The following is a brief description of liquid light valve suspensions known in the art, although the invention is not limited to the use of only such suspensions.
1. Liquid Suspending Media and Stabilizers
A liquid light valve suspension for use with the invention may be any liquid light valve suspension known in the art and may be formulated according to techniques well known to one skilled in the art. The term “liquid light valve suspension”, as used herein, means a “liquid suspending medium” in which a plurality of small particles is dispersed. The “liquid suspending medium” includes one or more non-aqueous, electrically resistive liquids in which there is preferably dissolved at least one type of polymeric stabilizer, which acts to reduce the tendency of the particles to agglomerate and to keep them dispersed and in suspension.
Liquid light valve suspensions useful in the present invention may include any of the liquid suspending media previously proposed for use in light valves for suspending the particles. Liquid suspending media known in the art which are useful herein include, but are not limited to the liquid suspending media disclosed in U.S. Pat. Nos. 4,247,175 and 4,407,565. In general, at least one of the liquid suspending medium and the polymeric stabilizer.dissolved therein is chosen in a manner known in the art so as to maintain the suspended particles in gravitational equilibrium.
The polymeric stabilizer, when employed, can be a single solid polymer that bonds to the surface of the particles, but which also dissolves in the non-aqueous liquid or liquids of the liquid suspending medium. Alternatively, two or more solid polymeric stabilizers may serve as a polymeric stabilizer system. For example, the particles can be coated with a first type of solid polymeric stabilizer such as nitrocellulose which, in effect, provides a plain surface coating for the particles, after which they are re-coated with one or more additional types of solid polymeric stabilizer that bond to or associate with the first type of solid polymeric stabilizer and which also dissolve in the liquid suspending medium to provide dispersion and steric protection for the particles. also, liquid polymeric stabilizers may be used to advantage, especially in SPD light valve films, as described in U.S. Pat. No. 5,463,492.
2. Particles
Inorganic and organic particles may be incorporated into a light valve suspension useful in forming a switchable suspended particle device. Such particles may be either light-absorbing or light-reflecting in the visible portion of the electromagnetic spectrum. For some particular applications the particles can be reflective at infrared wavelengths.
Conventional SPD light valves have generally employed polyhalide particles of colloidal size, that is the particles generally have a largest dimension averaging about 1 micron or less. As used herein, the term “colloidal”, when referring to particle size, shall have the meaning given in the preceding sentence. Preferably, most polyhalide or other particles used or intended for use in an SPD light valve suspension used in accordance with the invention will have a largest dimension which averages less than one-half o
Harary Joseph M.
Malvino Albert P.
Saxe Robert L.
Epps Georgia
Hasan M.
Research Frontiers Incorporated
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