Abstract: The invention relates to electret bistable systems comprising two fixed electrodes forming a capacitor. A sheet of electret material is inserted for creating holding forces in two rest positions of a moving element located in the capacitor gap. In accordance with the invention, the electret sheet is separated from the corresponding fixed electrode by a layer of dielectric which can be an air gap. As a variant, the charge density of the electret sheet may be concentrated in islands for reducing the holding forces.

Abstract: A reflecting electrostatic display cell comprising a dihedral block having two surfaces departing from an edge, two electrodes extending onto respectively said two surfaces, and an electret sheet secured to said edge. One electrode and one face of the sheet are painted with a first color; and the second electrode and the remaining surface of the sheet are painted with a second color. Under the control of a temporary voltage applied between the electrodes, the electret sheet sticks to one electrode, the cell thus presenting one of the two colors. Under the control of a temporary reversed voltage, the electret sheet sticks to the other electrode, the cell thus presenting the other colors.

Abstract: The invention relates to bistable systems using electrets. The invention provides a three-electrode system in which the movement of the moving armature is obtained by means of biasing voltages applied to the fixed electrodes. A switching voltage applied between the moving electrode and one of the fixed electrodes releases the electrostatic holding forces generated by the electrets.

Abstract: A holographic storage cell for storing volume holograms wherein a plate of either Bi.sub.12 SiO.sub.20 or Bi.sub.12 GeO.sub.20 is provided with electrodes producing an electric field transversed to the plate. These electrodes may be on opposite ends of the plate, or in the form of interdigitated combs. In one embodiment, such a cell is utilized as a holographic memory wherein the modulation of the object beam and the deflection of the reference and object beams are controlled electronically. The cell may also be utilized to perform calculations by superpositioning data to perform addition and substraction.

Abstract: The object of the invention is to provide a device for storing and selectively erasing information in electrooptical photoconductive materials in which selective recording and erasure are obtained by identical optical devices which project the same distribution of light onto the zone to be recorded and then erased. Recording and erasure differ solely in the direction of the electrical field applied to the material.

Abstract: The invention relates to loud-speaker enclosures comprising a sealed box with several loud-speakers. More particularly, the invention relates to a sealed box enclosure comprising an amplifier and in which the loud-speakers form two groups which, connected in series, constitute the first two arms of a bridge circuit. The other two arms of said bridge circuit form a voltage divider. A negative feedback loop is connected to the node of the first two arms while a positive feedback loop is connected to the node of the other two arms.

Abstract: The invention relates to electrically controlled switching devices in which a movable member can occupy at least two stable positions. The invention has for its object to provide a switching device in which the movable member is a dielectric body having received a persistent electric charge. This body can occupy stable positions defined on an insulating support by conductive pads. The switching is produced by a potential difference applied between the conductive pads.

Abstract: The invention relates to X rays detection devices, either for dose metering purposes or for display purposes. The device in accordance with the invention comprises a thin plate of ferroelectric material upon the faces of which electrical charges are deposited. X ray radiation produces an increase in the conductivity of the material and, consequently, modulation of the distribution of the charges, determination of which furnishes the desired detection.

Abstract: The present invention relates to a holographic optical storage device utilizing a material in which the transfer of photo-induced charges is orientated along the cristallographic axis C of the material. On the faces of the material perpendicular to said axis, two transparent electrodes connected together are arranged so that the field developed between said two faces is zero whatever the uniform illumination superimposed upon the modulation. The selective erasing of a first induced spatial variation in refractive index is achieved by recording a second spatial variation which is the complement of the first, the number of successive record-erase cycles being unlimited.

Abstract: For amplifying the photosensitivity of a ferroelectric crystal in which information is to be stored, an external field applied to the crystal is created by means of a heavily doped, reduced photocell crystal illuminated uniformly by radiation within the absorption band of the crystal. The photocell crystal connected to the terminals of the lightly doped, non-reduced ferroelectric crystal, of which the resistivity is very much higher than that of the photocell crystal, develops a very high voltage which relaxes with a high time constant. Such a voltage increases the variations in the birefraction of the ferroelectric crystal.

Abstract: The present invention relates to optical systems for the storage in the form of elementary holograms, of pages of binary data, said elementary hologram being stored in a two-dimensional or three-dimensional photosensitive medium. The system in accordance with the invention makes use of a photosensitive storage medium lending itself to the selective erasure of binary data, and which contains optical phase-shift devices which enable a phase-shift of 0.degree. or 180.degree. to be produced between the object beam and the reference beam depending upon whether it is desired to record or to erase the data.

Abstract: The present invention relates to photo excitable ferroelectric optical memory system designed to store, erase, and display light traces. In accordance with the invention, there is provided a system wherein a photo-ferroelectric plate is placed between a polarizer and a polarization analyzer. Under the combined action of a recording radiation and an external electric field, a photo induced electric is formed in the illuminated zones of the plate. Erasure is obtained by re-illuminating the plate without applying any external field. The optical display is achieved by means of an electric read-out field.

Abstract: The device comprises a flexible magnetic sheet reflective on one side, at least one magnetic circuit associated with at least one zone of the sheet for deforming the sheet by a modification of the magnetic flux in the magnetic circuit. Exciting means controlled by electrical data vary the magnetic flux so as to modify the reflecting conditions in said zone as a function of the electrical data.A unit for recording holographical optical memories is disclosed which employs this device.

Abstract: A high operational reliability modulator, constituted by a mosaic of elements having variable double-refraction properties. It comprises, on a flat ferro-electric ceramic structure and in respect of each element, a first conventional pair of transparent electrodes and a second pair of distinct electrodes, made of transparent photoconductive material; by the application of illumination, the second electrodes are rendered conductive exclusively at the required instant, thus avoiding any interim disturbance to the action of the first electrodes and enabling the change of double-refraction properties of the ceramic.