FR2842916A1 - OPTICALLY ACTIVE GLAZING - Google Patents

Abstract

Optically active glazing, comprising two plates of glass or the like (10, 12) parallel and delimiting between them a closed volume containing dielectric particles (20) suspended in a fluid, and electrodes (22, 24) formed on the plates and connected to a power supply (26, 28) to move and organize the particles by means of dielectrophoretic forces and particle interactions.

Description

I

OPTICALLY ACTIVE GLAZING

  The invention relates to an optically active glazing, the transmission, diffusion, reflection and / or color characteristics of which are variable in a controlled manner. Glazing of this type can be used in particular in the automotive industry and in construction and have other applications, very

diverse and numerous.

  Glazing has already been proposed using direct electrical effects such as electrochromic effects, but which have not made it possible to obtain the expected results. Other known systems are based on electrooptical effects of liquid crystals and are complex and expensive. Display systems based on electrophoretic effects are also known, in which charged particles are displaced by electric control fields, as described for example in the articles by John Rogers et al. Proc. Nat. Acad. Sc. 48, 4835-4840 (2001) and d'Albert, Comiskey et al., Nature 394, 253-255 (1998) and in documents US-A-6120588 and US-A-5961804. These known systems however have some drawbacks, such as a defect in

  long-term stability of particle charges.

  The object of the invention is in particular to provide active glazing which does not have these drawbacks and which is simple, inexpensive and very

  reliable over a long period of time.

  To this end, it offers optically active glazing, the optical characteristics of transmission, diffusion, reflection and / or color of which are variable in a controlled manner, characterized in that it comprises two plates of material such as for example glass or the like, parallel and delimiting between them a closed volume, a fluid contained in said volume between the plates, a suspension of dielectric particles in the fluid, and controlled means of applying electric field gradients to said particles, making it possible to move them and organize them using dielectrophoretic forces and

interactions between particles.

  The invention is therefore based on the controlled movement of dielectric particles suspended in a fluid. These uncharged particles are displaced by an electric field gradient which acts on the electric dipole of the particles (dielectrophoretic effect) and they are gathered or agglomerated by interactions between particles leading to electro-rheological properties. The use of non-electrically charged particles makes it possible to avoid the problems of charge stability inherent in electrophoretic systems. The aggregation of the particles makes it possible to store them in zones chosen between the plates in order to obtain overall optical effects, for example coloring or high contrast transmission. By modifying the gradients of the electric field applied to the particles, these particles can be separated and reorganized into other zones between the plates, to modify the overall optical effect and alternately obtain a display and the

suppression of the display.

  In addition, variations in dielectrophoretic or interaction forces depending on the size of the particles, their dielectric properties, the frequency of the electric field and the effects of entrainment by the fluid allow specific separations of particles and effects of contrast and of multiple colors, when using particles

  with different dielectric properties.

  In addition, long particle retention times after the power supply has been cut off make it possible to envisage a

  very low power consumption.

  According to another characteristic of the invention, the means for applying electric field gradients comprise electrodes placed in said volume, and means for connecting these electrodes to

a power supply.

  The electrodes can be arranged according to any

  desired configuration for obtaining the desired optical effects.

  They can be formed on the plates by various means, by

  for example by deposition and engraving, by inkjet, by stamping or others.

  These electrodes can be either opaque or semi-transparent depending on

the desired effects.

  In a preferred embodiment of the invention, each

  plate carries at least two groups of electrodes.

  The particles in suspension in the fluid can be of very diverse types and can be made of any dielectric material depending on the desired optical effects and the required dielectric properties. They typically have dimensions between 10 nm and pLm and can be of simple or composite structure based on inorganic or organic materials, polymers, dyes, metals, etc. The fluid used is preferably a dielectric or weakly electroconductive liquid, for example water or a silicone oil, having dielectric properties and a viscosity selected by

depending on the desired effects.

  The power supply can be direct current, or

  fixed or variable frequency alternating current.

  According to yet another characteristic of the invention, the volume between the plates is partitioned into a plurality of small volumes separated in a substantially leaktight manner from each other, to avoid the effects of long-distance sedimentation which would prevent short-distance movements under the effect of dielectrophoretic forces and interactions. These small volumes typically have dimensions of between a few gm and 1 cm. The partitions are made of any dielectric material, for example glass or polymer and are formed by any suitable means, for example by stamping or

other.

  The glazing plates are identical or not and are made of any suitable material, in particular glass or plastic. One of the plates can be transparent and the other opaque, for

  metallic example, in the case of reflective operation.

  In general, the invention is applicable to glazing

  active as well as passive (non-emissive) displays.

  The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading

  the following description, given by way of example with reference to the drawings

  attached in which: - Figure 1 is an enlarged partial schematic view, in cross section, of a glazing according to the invention; - Figure 2 is a top view of an elementary cell of the glazing; - Figures 3, 4 and 5 are schematic partial views illustrating modes of operation of a glazing according to the invention. The glazing unit of FIG. 1 comprises two plates 10, 12 of a transparent dielectric material such as glass or a plastic material, which are parallel and separated by a small distance, for example between approximately 0.01 and 1 mm, these two plates 10, 12 being

  identical or different from each other.

  The internal volume defined between these plates is divided into a plurality of small independent volumes or elementary cells 14 separated in a substantially sealed manner by partitions 16 made of materials

  dielectrics, for example plastic.

  The elementary cells 14 are filled with a fluid, preferably a dielectric or weakly electroconductive liquid 18, which contains a suspension of identical or different particles 20 of dielectric material, these particles having a size of between 0.01 and

pim approx.

  The facing faces of the plates 10, 12 carry electrodes 22, 24 which are for example of the same kind and arranged face to face as shown in FIG. 1, but which can be different or arranged in an offset manner in certain areas of the glazing or in some achievements. These electrodes are made of a suitable electroconductive material and have dimensions (thickness, width) which are typically between 1 μm and a few mm approximately. They have any desired configuration (threads, ribbons, combs, etc.). They are formed on the plates 10, 12 by any appropriate means (deposition and etching, jet

ink, stamping, etc.).

  These electrodes are connected to power supply means 26 associated with control means 28. The power supply means 26 may be direct or alternating current at variable frequency. Typically, the supply voltages are between 0.5 and 500 V and the frequency is between 0 and 1 MHz. When the electrodes 22, 24 are supplied with direct current, the particles 20 all move in the same direction in the absence of convection movements of the fluid with different speeds depending on their nature and size, and with thresholds different (value of the electric field from which the particles begin to move). If certain particles contained in the fluid are not electrically neutral, an electrophoretic effect depending on the polarities of the charge and the field

  electric is added to the aforementioned dielectrophoretic and interaction effects.

  When the electrodes are supplied with alternating current, the particles can move in different directions according to their nature and their size, according to the frequency of the current because of the frequency dependence of the factor of Clausius Mosotti which gives the effective dipole of a particle immersed in a dielectric fluid (see for example FIG. 4 of the article by NG Green and H. Morgan in J. Phys. D: Appl. Phys. 31, 1998, L25-L30). If certain particles contained in the fluid are electrically charged, no electrophoretic effect

  adds to the dielectrophoretic effect.

  In general, the electrodes 22, 24 can be opaque or semi-transparent. The fluid (liquid) 18 can be transparent or colored, depending on the applications. The particles 20 can be identical or not, they have the same color or different colors and optical characteristics of transmission, reflection and diffusion which are selected according to the applications. They can also be subjected to specific treatments intended to make them independent of each other or on the contrary to promote their agglutination. Finally, it is possible to add charged particles to the

  dielectric particles suspended in the fluid.

  In the embodiment of Figure 2, the electrodes of each plate are formed by combs 22, 23 and 24, 25 respectively nested in each other, the electrodes of two nested combs can be at electrical voltages of identical polarities or opposite. In addition, depending on the desired overall effects (display, opacity, reflection, scattering or transmission effects), the sets of electrodes 22, 23, 24, 25 may be the same or different. In particular, the electrodes 22, 23, 24, 25 may differ from one another by their natures, their shapes, their dimensions, their locations and / or by the polarities of the electrical voltages which are applied to them. Three possible operating modes of active glazing

  according to the invention are shown diagrammatically in FIGS. 3, 4 and 5.

  In FIG. 3, the electrodes 22, 23, 24, 25 of the plates 10, 12 are identical and transversely aligned from one plate to another, the distances between the electrodes formed on the same plate being

  greater than the widths of the electrodes.

  When the electrodes are not supplied, the particles suspended in the fluid are dispersed in a more or less uniform and random manner between the plates and give an overall optical effect which is determined by their nature and their properties (the glazing being by globally reflective example when the particles 20 have reflective properties, or more or less opaque in the case of

non-reflecting particles).

  When the electrodes are supplied with direct current, the electrodes 22, 23 being for example at a positive voltage and the electrodes 24, 25 at a negative voltage, the particles 20 are collected between the aligned electrodes of opposite polarity and form webs 30 between these electrodes as shown, the webs 30 being perpendicular to the plates. The particles release most of the volume between the plates and an overall "transparent" effect is obtained (or the color of the fluid 18 in which the particles

are suspended).

  In FIG. 4, only the electrodes 22 and 23 of the plate 10 are electrically supplied and each electrode 22 has a polarity opposite to that of the two neighboring electrodes 23. It then forms webs 32 of particles between the electrodes 22 and 23, these webs being parallel to the plate 10, and the overall effect obtained is due to the properties

  optics of the particles (reflective or opaque appearance for example).

  As a variant, when the electrodes 24, 25 are supplied in the same way as the electrodes 22, 23 and when the electrodes 24 which are opposite the electrodes 22 have a voltage of the same polarity as these electrodes 22, it also forms particle sails between

  electrodes 24, 25 along the plate 12.

  In FIG. 5, the arrangement and the supply of the electrodes 22, 23, 24, 25 correspond to those described with reference to FIG. 3, but the width of the electrodes is greater than the distance between electrodes formed on the same plate. When these electrodes are supplied as shown, dense layers 34 of particles are formed between the electrodes opposite the two plates, with an overall effect which is for example more or less opaque or reflecting or diffusing depending on the nature of the particles. and the width of the electrodes, this width possibly further varying from one zone to another in the glazing. In this

  case, the electrodes are semi-transparent.

  It is therefore possible to obtain very different overall effects, in particular of display, by controlling the power supply of the different groups of electrodes 22, 23, 24, 25, and these effects can be reinforced and refined by differentiating electrodes, by their shapes, dimensions, locations, etc. By using different electrode supply frequencies, it is possible to separate different particles and store them separately on sets of electrodes, then release them selectively to obtain a display with particular effects.

  desired (absorption, diffusion, color, metallic reflection, etc.).

  The results obtained in Figures 3, 4, 5 can also be obtained when the electrodes are supplied with alternating current, with variations due to the frequency dependent effects (sign of the dielectrophoretic force d to the sign of the Clausius-Mosotti factor, effects electromechanical on different particles between electric field

  continuous and alternating electric field, etc ...).

Claims (16)

  1 / Optically active glazing, the optical characteristics of transmission, diffusion, reflection and / or color of which are variable in a controlled manner, characterized in that it comprises two plates (10, 12) of material such as, for example, glass or the like, which are parallel and delimit between them a closed volume, a fluid (18) contained in said volume between the plates, a suspension of dielectric particles (20) in the fluid (18), and controlled means (26, 28) applying electric field gradients to said particles enabling them to be displaced and organized by means of forces   dielectrophoretics and interactions between particles.   2 / glazing according to claim 1, characterized in that the means for applying electric field gradients comprise electrodes (22, 23, 24, 25) placed on said plates in said volume, and means for connecting these electrodes to a power supply (26, 28).   3 / glazing according to claim 2, characterized in that each plate (10, 12) carries at least two groups of electrodes (22, 23; 24, 25).   4 / Glazing according to claim 2 or 3, characterized in that the electrical supply is direct or alternating current of fixed frequency or variable.   / Glazing according to one of claims 2 to 4, characterized in   that at least some of the electrodes (22, 23, 24, 25) are opaque.   6 / Glazing according to one of claims 2 to 5, characterized in   that at least some of the electrodes (22, 23, 24, 25) are semitransparent.   7 / Glazing according to one of claims 2 to 6, characterized in   what the electrodes are wires, ribbons or combs.   8 / Glazing according to one of claims 2 to 7, characterized in   that said electrodes are mutually parallel from one plate to another.   9 / Glazing according to one of claims 2 to 8, characterized in   that the electrodes are identical to each other.   10 / Glazing according to one of claims 2 to 8, characterized   in that the electrodes are of at least two different types and differ from each other by their dimensions and / or by their locations from one plate to another and / or by the polarities of the electrical voltages which are applied to them.   11 / Glazing according to one of the preceding claims,   characterized in that the particles (20) are all of the same type.   12 / Glazing according to one of claims 1 to 10, characterized   in that the particles (20) are at least two different types.   13 / Glazing according to one of the preceding claims,   characterized in that the particles (20) have optical characteristics   determined by color, reflectivity and / or diffusion.   14 / Glazing according to one of the preceding claims,   characterized in that the fluid (18) also contains particles electrically charged.   15 / Glazing according to one of the preceding claims,   characterized in that the fluid (18) is dielectric or weakly electrically conductive.   16 / Glazing according to one of the preceding claims,   characterized in that the volume between the plates (10, 12) is partitioned into a plurality of small volumes (14) separated in a substantially sealed manner one another.   17 / Glazing according to one of the preceding claims,   characterized in that one of said plates (10, 12) is opaque, by metallic example.