Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.