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Agence Nationale De Valorisation De La Recherche (anvar)

Didier Perino

Jacques Lewiner

Gerard Dreyfus

Claude Hennion

To manufacture a thin sheet electret of small size having charge distributed in very uniform manner, even at its edges, use is made of a device comprising a grounded electrode (2) for supporting a dielectric (1) to be charged, means for generating ions (3) in the vicinity of the dielectric, a grid (4) extending parallel to the surface to be charged of the dielectric, at a small distance from said face, and raised to an electric potential different from ground potential and a conductive frame (7) that is insulated from the electrode and that is electrically connected to the grid, said frame surrounding the dielectric and forming a single block with the electrode.

Devices for manufacturing electrets, and electrets obtained thereby

For making an SiO.sub.2 electret, a layer of SiO.sub.2 is formed on a solid substrate (5) by chemical vapor deposition in a vapor phase starting from a plasma containing silicon and oxygen and the layer so formed (10) is subjected to a thermal treatment by raising its temperature to above 100.degree. C. during a time period longer than 1 hour, before being electrically charged.

SiO.sub.2 electrets and process of making it

The invention provides a device for measuring ionizing radiations, comprising a Geiger-Muller tube (1) whose high supply voltage is obtained from pulses which are emitted (by 6,7) at a constant relatively low frequency as long as a predetermined threshold is not exceeded by the intensity of the radiation and (by 6,7,4 and 32) at an increasing frequency depending on the output of the tube, after said threshold has been exceeded. Thus, alarm dosimeters having very long independent operation may be formed.

Devices for measuring ionizing radiations

The invention relates to a circuit breaker for cutting off the two AC supply leads of an electrical receiver from the time of creation of a leakage current F between said receiver and ground through a human body. This circuit breaker comprises a differential transformer generating a faulty voltage V.sub.O, a relay with contacts open when it is not energized, and means (A.sub.1,A.sub.2, . . . A.sub.n ; R.sub.1,R.sub.2 . . . R.sub.n) supplied by the system, adapted to exploit the voltage V.sub.O for the purposes of energizing the relay if the current F is dangerous or at least unpleasant in its intensity and/or its duration, without however being sensitive to disturbances.

Circuit breakers sensitive to leakage currents

The device comprises, on the one hand, a cassette containing an electret between two electrodes and, on the other hand, a fixed reader adapted to receive the cassette in a pocket, to identify it, to measure the charge of its electret and to display data relating to this charge. This reader comprises also a head adapted to record the data on an area (or strip) of the cassette and there are provided readers independent of the aforesaid reader adapted to subsequently receive the cassette, to measure the charge of its electret, to read the data and, by difference between the measured value and that read, to display the radiation dose received by the cassette since its recording.

Electret devices for measuring ionizing radiation

The invention relates to a device for measuring irradiation capable of modifying the charge of an electret. It is arranged in a portable cassette, between two electrodes held separated by a part and connected to a measuring circuit. A conductive shutter is movable parallel to itself and to the electret between this electret and than electrode, so as to alternately mask this electret with respect to this electrode and to render the electret visible to the electrode. The measurement exploits differences in charge of the electret read according to the movements of the shutter.

Devices for measuring parameters which can modify the charge of an

The device detects variations in magnetic flux so that the passage through a given threshold by the amplitude of such a variation per unit time is manifested by the movement of an element adapted to trigger an action. It comprises a practically closed electrical circuit, such as a winding, arranged and mounted so that the variation in magnetic flux to be detected generates by induction at the terminals of this winding an electrical voltage V, two electrodes forming a capacitor, one of which is movable with respect to the other, an electret interposed between these two electrodes and whose charge produces a field exerting on these electrodes an electrostatic force H tending to bring them mutually together, means for forming a rectified voltage U from said voltage V and for applying this voltage U between the two electrodes in a direction such that the field which results therefrom is opposite that generated by the electret and hence tends to reduce the force H, and means urging the movable electrode scarcely reversibly in the opposite direction to the force H. The force G of these urging means and the charge of the electret are selected so that the overshoots by the voltage U of a predetermined threshold U.sub.o corresponding to the level to be detected of the magnetic flux-generating phenomenon cause swings of the movable electrode from its vigilance position to its active position, the triggering of said action being servocoupled to said swings.

Devices adapted to detect variations in magnetic flux notably circuit

The device comprises means for applying a DC voltage U as a function of the voltage taken from the terminals of a fuse between a fixed electrode and a movable electrode forming together a capacitor. The movable electrode is urged towards the fixed electrode by an electret fast to the latter and in the opposite direction by a magnet and by the voltage U. As soon as this voltage exceeds a threshold corresponding to the rupture of the fuse, the movable electrode swings over and closes a switch for warning purposes.

Devices for detecting the rupture of an electrical circuit element

The device is able to detect the exceeding of a given threshold by a parameter, other than an electric voltage, capable of affecting the electrostatic force of attraction exerted between a charged electret and one, of two electrodes between which said electret is placed, said parameter being for instance an ionizing radiation. The two electrodes are at the same electric potential and the device also comprises return means for urging the first electrode and the electret permanently apart, and means for using the relative displacement of said elements, when it occurs, for desired detection purposes.

Detectors of parameters adapted to act on the force of attraction

The invention concerns a switching device using electrets. It comprises at least two electrodes and at least two electrets; control signals are applied between electrodes to cause a mobile element carrying an electret to pass from one rest position to the other. Application to electrical, pneumatic and optical switching.

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Suresnes, France

Didier Perino