FR2765069A1 - DEVICE FOR PROTECTING AN ELECTRICAL CIRCUIT AGAINST INTERFACE MICRODECHARGES - Google Patents

Abstract

The invention concerns a device for protecting an electric circuit against interface micro-discharges and corresponding radio interference, comprising, in the proximity of the electric circuit (10), an element (2, 20) attenuating/absorbing the electromagnetic wave generated by said micro-discharges and vibrations affecting the electric circuit. The invention is applicable to all types of electric circuits, in particular in the field of Hi Fi.

Description

~~ ~ PROTECTION DEVICE OF AN ELECTRICAL CIRCUIT
AGAINST INTERFACE MICRODECHARGES.

 The invention relates to a device for protecting an electrical circuit against interface micro-discharges and the application of this device to specific electrical circuits.

 The phenomenon of electrical micro-discharges has been highlighted in the context of the proven deterioration in the quality of sound reproduction of the musicality of high-fidelity channels.

When, in this type of device, an electrical conductor-insulator interface is subjected to a variable electric field, electric discharges occur at this interface, even in the case where these electric fields are generated from low voltages. value, of the order of a millivolt, very common voltage values when implementing audio frequency signals. These discharges, although very fast, 0.1 Ps, and at relative levels of -80 dB compared to the audio frequency signal, are however likely to generate significant radiated electric fields that are not negligible. They are more particularly designated by the expression micro-interface discharges. In particular, they have recurrence frequencies belonging to the frequency domain of the audible spectrum and are correlated with the audio frequency signal, which makes the latter particularly harmful as regards the quality of sound reproduction and the musicality of this type of device.

 Technical elements relating to their mode of production, with a view to better musicality, have been described in particular in a French patent application No. 96 12369 filed on October 10, 1996 and incorporated in the present patent application for reference.

 Thus, when an isolated electrical conductor is subjected to a variable electric field, discharges occur at the dielectric / insulating electrical conductor interface, according to a relaxation process according to the most likely hypothesis, see figure Oa. The electric fields radiated with respect to the reference mass or voltage of the device can however be significant, in any case not negligible.

 Within the framework of a modeling of the phenomenon as represented in figure Ob, based on the hypothesis of disruptive discharge or breakdown of an insulating layer immediately in contact with the electrical conductor, C denotes the electrical capacity of the insulating layers immediately in contact with the electrical conductor, C2 the conductor capacity - reference voltage or ground, e designates a spark gap "causing" the phenomenon of micro-discharge.

 The variable voltage measured across the electrical capacitance C of the layers immediately in contact with the electrical conductor is shown in Figure Oc.

This tension testifies to the existence of very rapid relaxation oscillations whose frequency of recurrence disturbs the audio frequency signal.

Micro-discharges therefore have an origin, behavior and primary effect which directly relate them to partial discharges (DP) well known in isolation
High Voltage, or even to the corona effect which manifests itself in a gas around conductors brought to high potentials.

 However, work and investigations carried out on the phenomenon of micro-discharges in ELECTRICITE DE FRANCE laboratories by Mr. T. JOOET have made it possible to specify certain characteristics.

micro-discharges appear for voltages
very weak medium electrics, less than
millivolt. They don't seem to have an effect
threshold.

the breakdown voltage of these micro-discharges is very
weak, probably between 1, uV and 1 mV.

the discharge fronts are very fast, lower
at 1 ns.

micro-discharges necessarily generate local
an electromagnetic wave which constitutes, in particular
ment for electrical or electronic circuits
audio frequencies, a major disturbing element.

In addition, discharges of the same type can appear on the external surface of the insulation covering the conductor, in fact at the insulation-air interface. This phenomenon is in particular justified by the Maxwell-Wagner effect according to which concentrations of electric charges at the interface between two layers of insulating materials can occur.

 Additional investigations have shown that these micro-discharges are eminently sensitive to the vibratory state, in the mechanical sense of the term, of their support. This phenomenon therefore appears, moreover, the phenomenon of electrical micro-discharges to known triboelectric phenomena, with however the additional existence of one or more harmful electromagnetic waves, due to their direct effect on the electronic audio-frequency signals generated, transmitted or processed by these circuits.

 Their mode of action with respect to the support electrical conductor can, with reference to FIG. Od, be established in the following manner.

Corresponding in fact to a phenomenon of conductive - insulating microclacking, they disturb the electric current flowing in the electrical conductor support by taking electrical energy there. The importance of this disturbance depends of course on the local conditions of the supportive conducting medium. Given the very small electrical capacity values involved, some picofarads, their local mode of action is weak.

However, their overall mode of action cannot be overlooked.

Indeed, the phenomenon of micro-discharges is generally reflected by an electromagnetic wave, like any discharge, which can be guided by the conductive parts. The wavelength associated with the phenomenon of micro-discharges is between 1 and 30 cm in a vacuum, which corresponds to radio frequencies between 3 and 30 GHz.

 Direct confirmation of the aforementioned phenomena and characteristics could be obtained, on the one hand, by highlighting the transmission of such an electromagnetic wave, by the insulating interval, of a few millimeters, existing between the output terminal d 'a power supply and the housing of this power supply, itself connects to the earth, and, on the other hand, by the attenuation likely to be brought to this electromagnetic wave according to one of the very objects of the present invention.

 When the wave associated with the interface micro-discharges reaches an electronic circuit, part of this is picked up by the elements of the circuit, which, because of their nonlinear transfer characteristic at the frequencies considered - this is in particular the welds and contacts - proceed to a detection phenomenon generating parasitic voltages.

 This phenomenon is further aggravated by the fact that the micro-discharges are frequently correlated with the transmitted electronic signal BF or even with the mechanical vibrations generated or introduced by the latter, which can then be strongly disturbed.

Thus, taking into account the aforementioned phenomenon and more particularly of the microwave character, of SHF type, of the parasitic electromagnetic wave, because associated with the interface micro-discharges, thus generated, the paradoxical action of this one on the circuits can be summarized below
- the discrete electrical components are likely to serve at the same time of transmitters and receivers.

As receivers, they can receive their own emission, and thus amplify it, or that of external components.
- the influence of the electromagnetic wave associated with the interface micro-discharges on the useful signal occurs by intermodulation and detection, taking into account the non-linearities of transfer existing at such radio frequencies:
- the arrangement of the components is very important because it conditions the ability of the latter to pick up or not this electromagnetic wave. Thus, it may seem more advantageous to arrange these components in any directions ...

- the wiring, for this same reason, is critical as well as the composition and structure of the printed circuits, because each conductor constitutes, at the aforementioned frequencies, a transmitting receiving antenna. The presence of insulation on the wiring leads also promotes the generating process of this electromagnetic wave
- a seemingly harmless component, such as a bypass or a plug socket, can be disastrous
- electrical insulators or other absorbent screens exhibit very variable behavior at the above frequencies and can for example focus, reflect or diffract the waves giving totally unexpected results
- the wave associated with the interface micro-discharges can be guided outside the conductors and is therefore perfectly able to pass through a socket, transformer or other component such as winding
- the rack or other packaging of models, working perfectly on a study table, can prove to be catastrophic for the musicality of the audio-frequency devices, whereas conventional electronic measurements, such as the signal to noise ratio, have not been significantly modified, or even appear better. In fact, such conditioning had the unexpected effect of creating a resonator or even a "microwave oven" for the electromagnetic wave associated with the interface micro-discharges.
- the electromagnetic wave resulting from micro-discharges can itself trigger other micro-discharges on the insulating - conductive or insulating - insulating interfaces where there are electric fields of the electrostatic type associated with the audio signal, by an effect of the avalanche effect type
- the mains supply appears to be a major source of micro-discharges - high voltage, 230 V - propagation of micro-discharges generated by the assembly
receivers connected in the vicinity.

 The present invention relates to the implementation of a device for protecting an electrical circuit against interface micro-discharges.

 Another object of the present invention relates more particularly to the implementation of means for attenuation of the electromagnetic wave associated with the interface micro-discharges of any electrical circuit.

 Another object of the present invention also relates, more specifically, to the use of means for absorbing the electromagnetic wave associated with the interface micro-discharges of any electrical circuit.

 Another object of the present invention is also, more specifically, the use of means for absorbing mechanical vibrations capable of affecting the electrical circuit in order to reduce the triboelectric contribution to the electromagnetic wave associated with interface micro-downloads.

The device for protecting an electrical circuit against interface micro-discharges and radioelectric interference generated by these interface micro-discharges, object of the present invention, incorporating such means, will be better understood on reading the description and on observation of the drawings below, in which, in addition to the figures Oa to Od relating to technical elements known to the inventor, Mr. P.JOHANNET
- Figure la shows a device for protecting an electrical circuit against interface micro-discharges, according to the object of the present invention, in a first embodiment
- Figure lb shows a device for protecting an electrical circuit against interface micro-discharges, according to the object of the present invention, in a second embodiment
FIG. 2 represents a device for protecting an electrical circuit against interface micro-discharges, in accordance with the object of the present invention, in the case where the electrical circuit consists of a loudspeaker,
FIGS. 3a, 3b and 3c represent a device for protecting an electrical circuit against interface micro-discharges, in accordance with the object of the present invention, in the case where the electrical circuit is constituted by the reading cell and the electrical connection conductors of a phonosensor
- Figures 4a and 4b show a device for protecting an electrical circuit against interface micro-discharges, according to the object of the present invention, in the case where the electrical circuit is constituted by a transformer and a transformer isolation respectively
- Figures 5a and 5b show, in a first and a second variant embodiment, a device for protecting an electrical circuit against interface micro-discharges, in accordance with the object of the present invention, in the case where the circuit electrical consists of a circuit of discrete components wired on a printed circuit board
- Figures 6a, 6b, 6c and 6d show a device for protecting an electrical circuit against interface micro-discharges, in accordance with the object of the present invention, in the case where the electrical circuit consists of an electrical outlet or special electronics
- Figures 7a and 7b show a device for protecting an electrical circuit against interface micro-discharges, according to the object of the present invention, in the case where the electrical circuit consists of discrete elements wired on a wafer circuit board
- Figure 8 shows a device for protecting an electrical circuit against interface micro-discharges, in accordance with the object of the present invention, in the case where the electrical circuit is constituted by a stabilized supply.

 The different figures are shown in section, at least partially, in order to better highlight the different constituents.

 A more detailed description of a device for protecting an electrical circuit against interface micro-discharges and radio interference generated by these interface micro-discharges, in accordance with the object of the present invention, will now be given in a first then in a second embodiment in relation to Figures la and lb.

 In general, it is indicated that the device for protecting an electrical circuit against interface micro-discharges and the radio interference generated by these interface micro-discharges, object of the present invention, is intended for an application of all types electric circuit, the concept of electric circuit covering a field as wide as that relating to electric conductors, or simple electric cables, much more elaborate electric circuits such as transformers, electric circuits with discrete components or in the form of components with integrated circuit wired to a printed circuit board, electrical and / or electronic sockets, electrodynamic devices such as loudspeakers or phonosensor reading cells for example.

 In general, the device for protecting an electrical circuit against interface micro-discharges and radio interference generated by these interface micro-discharges, object of the present invention, is remarkable in that it comprises, in the vicinity of this electrical circuit, an attenuation element of the electromagnetic wave generated by these interface micro-discharges.

 With reference to FIG. 1a and by way of nonlimiting example, the electrical circuit, in this figure, is deemed to be constituted by a plurality of electrical conductors such as enameled wires 5 / 10ths of a mm in diameter, these conductors carrying the reference 1 in FIG.

 The attenuation element of the electromagnetic wave generated by these interface micro-discharges, normally present at the interface between the above-mentioned electrical conductors 1 and the surrounding space, or even the insulating constituent enamel covering these wires or electrical conductors, bears the reference 2 in Figure la.

 In the embodiment as shown in FIG. 1 a, the attenuation element 2 of the electromagnetic wave generated by these interface micro-discharges advantageously comprises a coating of semiconductor material applied to the external surface of the electrical conductor 1.

Thus, the element 2, in accordance with a particularly advantageous aspect of the present invention, consists of this semiconductor material whose linear resistivity is chosen within a suitable range of values, so as to allow both the maintenance of the external surface of the electrical conductor at a static electrical potential of constant local value, close to that of the electrical conductor 1, and absorbing all of the erratic electrical discharge currents caused by the interface micro-discharges, and thus attenuating the wave electromagnetic generated by them.

 More specifically, it is indicated that the semiconductor coating constituting the element 2 for attenuation of the electromagnetic wave has a linear resistivity of value p between 0.1 Qm and 10 Qm.

 In a non-limiting embodiment of the device for protecting an electrical circuit against interface micro-discharges and radio interference generated by these interface micro-discharges, in accordance with the object of the present invention, it is indicated that the element 2 absorbing the electromagnetic wave generated by these interface micro-discharges can consist of a liquid saline solution or a gel thereof having a resistivity close to 0.7 Qm corresponding to that of physiological saline for example, this solution s 'being shown to be particularly effective.

 Of course, as shown in the aforementioned figure, it is then necessary, in order to constitute this absorbent element in a sleeve coating the electrical conductors 1, to provide an enclosure formed for example by a plastic tube made of polyethylene or polytetrafluoroethylene for example , bearing the reference 2o in the same figure la.

 The enclosure thus produced can be closed in leaktight manner by means of end sealing sleeves, denoted 2. in FIG. 1a, the sealing being able moreover to be perfect by means of a silicone seal, bearing the reference 22 in the same figure la, the aforementioned silicone seal / sealing sleeve assembly, 22, 2, allowing the sealed passage of the electrical conductors 1 for example. Finally, a heat-shrinkable sheath 23 can be provided at each end of the enclosure or plastic tube 2o so as to constitute a cabal protected in accordance with the object of the present invention and bearing the reference CP later in the description. The passage of the electrical conductors i through the sealing sleeve 2: can be sealed with a poxy resin for example, referenced 2 in FIG.

 Finally, in a preferred embodiment, it is indicated that the attenuating element 2 can for example be constituted by a sodium chloride solution NaCl at 0.9t or also by physiological saline.

 According to a particularly advantageous aspect of the protection device, object of the present invention, it is indicated that the attenuation element 2 of the electromagnetic wave generated by the interface micro-discharges comprises an element absorbing this electromagnetic wave generated by these micro-discharges interface.

 Thus, it turned out, as will be described in more detail later in the description, that, in addition to the attenuation and the absorption of all the erratic electric currents of discharges caused by the interface micro-discharges , this attenuation having the effect according to Maxwell's laws of consequently attenuating the amplitude of the electromagnetic field thus radiated, this same element of attenuation 2 of the electromagnetic wave also made it possible to ensure absorption of the electromagnetic wave generated by these interface micro-discharges by an attenuation of the electric field propagated by radiation due to the semiconductor property of the abovementioned attenuation element 2.

 It is recalled in fact that for a guided propagation of an electromagnetic wave in a waveguide, the boundary conditions of the electrically conductive walls of the waveguide impose a field value substantially zero in the vicinity of these walls. In the same way, the attenuation element 2, because of its semiconductor properties, has the effect of reducing the value of the electromagnetic field thus radiated due to the appearance of the phenomenon of interface micro-discharges.

 A second alternative embodiment of the device for protecting an electrical circuit against interface micro-discharges and radio interference generated by these interface micro-discharges, in accordance with the object of the present invention, will now be described in conjunction with the figure. lb.

 In the case of FIG. 1b, it is indicated that, by way of nonlimiting example, the electrical circuit can for example be constituted by an electrical transformer.

In such a case, it has proven to be particularly advantageous to constitute the element 2 for attenuation of the electromagnetic wave generated by the interface micro-discharges in the form of an element absorbing mechanical vibrations liable to affect the electrical circuit considered. . It is in fact understood that an electrical transformer, bearing the reference 1 in FIG. 1b, is the seat of electromechanical vibrations, these electromechanical vibrations being capable of causing the appearance of electrical micro-discharges and, consequently, the appearance of radio interference consecutive to the existence of these micro-discharges.

 In FIG. 1b, the reference 2 thus designates the element for attenuating the electromagnetic wave generated by the micro-discharges, this element constituting an element absorbing the above-mentioned mechanical vibrations. Preferably, it can then consist of a pulverulent element having semiconductor properties as mentioned above.

 In the same figure 1b, the reference 2o designates a box in which the electrical circuit 1, constituted by a transformer, immersed in the powdery element 2, and this powdery element, are contained, as shown in the aforementioned figure 1b.

 Of course, other measures can be provided in order to minimize the influence of the interface micro-discharges, measures such as for example graphiting of the transformer windings by means of a very thin graphite layer and graphiting of the electrical conductors intended to ensure the connection with the outside between the transformer, constituting the electrical circuit 1, and the external circuits. The housing 20 may be constituted by any housing made of suitable plastic material which is sufficiently rigid.

 In a preferred embodiment, it is indicated that the pulverulent element 2 was constituted by silica sand to which 0.1% by mass of powdered graphite had been added.

 The effects of interface micro-discharges are similar to electromagnetic interference.

However, it stands out most clearly because of its particularly complex mode of action, which requires corresponding specific protection.

This mode of action is in fact linked to the various sources of interface micro-discharges.

Among these, there are
- powerful sources, but not correlated with the disturbed audio signal: essentially the sector at 50 Hz (and its harmonics ...) and its transformers, transformers, motors
- powerful sources correlated with the disturbed audio signal: loudspeakers and ampli-HP cables
- weak sources not correlated with the disturbed audio signal: neighboring conductors of the chain, they are generally neglected vis-à-vis other sources
- weak sources correlated with the disturbed audio signal: mainly electronics and associated wiring, assumed to be sheltered from vibrations, which is not always the case and explains the advantage of spikes and other anti-vibration supports. .

The modes of action on the audio signal of the micro-discharges and their associated wave can consist, without exclusion
- By a direct action on the current of the useful signal at the moment when the micro-discharges occur. The modeling shows that this effect is probably negligible, given the very low capacity values involved.

- In the detection by non-linear elements of the circuit of the electromagnetic wave emitted by the micro-discharges: this mode of action is more likely, the detection being able to be carried out by partially rectifying elements such as welds or bi-metallic contacts: the welding problem has been raised many times by Audiophiles. Note that at the frequencies envisaged, all the conductive elements are more or less rectifiers. It is conceivable that a wave strongly correlated with the audio signal, rectified and reinjected into the circuits, could effectively degrade the musicality
- In the action of external sources not correlated with the useful signal (sector), although more difficult to grasp. However, the efficiency of the mains filters designed by supposing the existence of micro-discharges - and by seeking to eliminate them - provides a probable mode of action.
the sector at 50 Hz and the associated transformers
provide a micro-discharge wave not correlated with
the audio signal but of significant amplitude,
this wave is likely to favor even trigger
micro-discharges on the audio circuits which are
polarized by the signal itself,
we are then in the presence of an avalanche phenomenon
or the triggering element is the sector at 50 Hz and where the
triggered signal is going to be a wave of micro-discharges on
useful signal, with a whole set of intermodulations
between this and the 50 Hz signal and its harmonics.

 The effectiveness of the device for protecting against micro-discharges, object of the present invention, indirectly confirms their existence.

- Basic protection consists in surrounding the supposedly insulated conductors with a semiconductor material
conductive enough to promote equipotentiality
local, sufficiently resistant to dissipate and absorb the wave
associated with micro-discharges.

 - the micro-discharges being generated at the conductor - insulator interfaces, the capacitors themselves produce micro-discharges. Only air (or vacuum) capacitors can have a certain efficiency.

 - the protection of transformers against the emission of micro-discharges consists in coating them in a mechanical absorbent making it possible at the same time to dissipate the electromagnetic wave.

- In differential mode, the absorption of micro-discharges can be carried out preferentially by circuits
RC
R: non-inductive resistance, preferably carbon, of
value close to the characteristic impedance of the conduits
tutors considered,
C: air or vacuum capacity.

 - In common mode, the absorption of the electromagnetic wave associated with micro-discharges is delicate and involves the coating of circuits in a semiconductor medium, also absorbing vibrations in the case of vibrating elements (motors, transformers).

 A more detailed description of a device for protecting an electrical circuit against interface micro-discharges and parasites generated by these interface micro-discharges, in accordance with the object of the present invention, when this electric circuit consists of a loudspeaker, will now be given in connection with FIG. 2.

Conventionally, the loudspeaker shown in the above-mentioned figure comprises a magnetic yoke, noted
CU, provided with an air-gap housing LE and an electric coil integral with a loudspeaker diaphragm, the diaphragm being denoted M in FIG. 2 above. Conventionally, the membrane M is secured at its periphery to the frame A, the frame A having substantially the shape of a bowl itself secured to the magnetic yoke CU. An electric coil distributed at the base of the membrane M is engaged in the air gap housing LE, the coil being connected to output terminals BSl and BS2 and to cables connecting these terminals to the output terminals of a electric amplifier.

 In general, and in order to ensure the protection of the entire loudspeaker shown in FIG. 2 against the phenomenon of interface micro-discharges, it is indicated that, firstly, the coil placed at the base of the membrane v, may be provided with a coating of a thin layer of graphite, the coil for this reason bearing the reference 1 in FIG. 2.

 In addition to the graphitation of the aforementioned loudspeaker coil, it is indicated that the device, object of the present invention, represented in FIG. 2, includes a foam lining of semiconductor material, bearing the reference 20, this lining being placed at the bottom of the LE air gap housing. In addition, the walls of the air gap housing also have a coating of semiconductor material, for this reason bearing the same reference 20.

 Finally, it is indicated that a protective coating of the terminals BS1 and BS2 can be provided, this coating ensuring protection of the terminals and of the connection cables of these terminals, this protective coating being able to consist of a semiconductor material covering the latter on at minus part of their length.

 It is thus understood that the booine coated with a layer of graphite lo is thus provided with a coating of semiconductor material and that the protective coating of the terminals BS1 and BS2 and of the connection cables of these terminals can be produced by means of the same conductive foam as that which is used and placed at the bottom of the LE air gap housing.

In a nonlimiting embodiment, it is indicated that the connection cables between the terminals BS1 and
BS2 and the terminals of the aforementioned electric amplifier can be produced in the form of protected cables CP as described above in connection with FIG.

 In addition, at the end of the aforementioned connecting cables, that is to say protected cables CP for example, a filter rejector of very high radio frequencies can be provided, this filter rejector being connected to the end of the cables or the part of the connecting cables covered by the semiconductor material.

 In a nonlimiting embodiment, it is indicated that the rejection filter can be constituted by a resistor of low value in series with the central core of the cables, the resistors designated by R in FIG. 2 being connected by a capacitance C of low value. It is indicated that, in a nonlimiting exemplary embodiment, the resistors R had a value between 0.1 and 2.5 Q, while the capacitance C had a value between 30 and 100 pF and the resistance R ' a value between 10 and 50 Q.

 More specifically, it is indicated that in the context of the device which is the subject of the present invention, proof of the implementation of this device as described in connection with FIG. 2 will be given below.

The loudspeaker coils consist for example of one or two layers of enamelled electrical conductor wires on an insulating tube, integral with the membrane
M and which, due to their position in the air gap housing LE, thus bathe in a uniform magnetic field.

 The boxes are therefore subject to intense vibrations due to their essential function and thus generate a large amount of micro-discharges which can disturb the output amplifier through the aforementioned connection cables.

 The device which is the subject of the present invention, as described in connection with FIG. 2, makes it possible to substantially reduce the micro-discharges created at the source of the circuit formed by the speaker coils by absorbing in particular the electromagnetic wave emitted by these micro-discharges.

 The emission level of the micro-discharges is reduced by means of a controlled application of a semiconductor material such as graphite on the coil itself, the coil being thus graphitized to constitute the graphitized coil 1o previously mentioned in the description.

The application of graphite can be carried out by spraying a graphite film on a support separate from the coil, the graphite used being for example the
Graphit 33, or the commercially available Blindotub.

 After the graphite film has completely dried on the aforementioned support, a dry graphite is removed using a tool such as a pad, so as to blacken the aforementioned pad.

 The graphite is thus regularly applied to the loudspeaker coil by means of the buffer over the entire surface of the above-mentioned coil.

 A polishing can be carried out with a graphite-free pad, the polishing appearing suitably carried out when the loudspeaker coil takes on a slightly gray glossy appearance.

 The absorption of the electromagnetic wave emitted by the micro-discharges is carried out by means of the semiconductor foam 2 placed at the bottom of the air-gap housing LE, in the vicinity of the coil, and, in any event, in the parts of the cylinder head CU not impeding the movement of the membrane, that is to say the bottom of the cylinder head, core cover constituted by a dome for example, which, in FIG. 2, also bears the reference 20 for this right.

 With regard to the foam used, this semi-conductive foam can for example be constituted by the high density Vermason and Vitec foam with a resistivity less than or equal to 15 Qm, such foam having the particularity of being constituted by open cells.

A foam suitable for carrying out the above operation may consist of Vermason and Vitec foam bearing the reference 167-848 from the FARNELL catalog. However, a more conductive foam whose resistivity is substantially equal to 1 Qm may be preferred.

 As regards the graphitization operation of the coil, it is indicated that the coating thus formed forms, in accordance with the object of the present invention, a semiconductor coating making it possible to create local equipotentiality and regularization of the field. surface, this coating however being sufficiently resistant to avoid enclosing the micro-discharges in a resonant cavity. In other words, it is indicated that the excess graphite layer on the coil is likely to degrade the results obtained.

 The wavelengths brought into play by the phenomenon of interface micro-discharges are centimetric wavelengths. Consequently, the semiconductor foams intended to absorb the electromagnetic wave generated by the interface micro-discharges at these wavelengths can advantageously have irregularities or indentations of this order of magnitude of length, so as to be effective from the point of absorption and avoid any phenomenon of reflection of this electromagnetic wave.

 However, with regard to the capacities C used to constitute the filter for rejecting very high radio frequencies, it is indicated that these capacities can preferably be constituted by air capacities, in which the phenomenon of micro-discharges is weak, or, preferably, by capacities encapsulated under vacuum or in a neutral gas, if necessary in air. The fact of using encapsulated capacities is particularly advantageous, since encapsulation under vacuum, in an atmosphere constituted by a neutral gas or even in air, constitutes a protection against variations in the surrounding atmosphere, the rejection filters as well constituted thereby retaining very high frequency stability, in particular in the cutoff frequencies of the very high frequencies transmitted.

 Finally, in the case of loudspeakers using ferrofluid in the air gap, in particular in the case of loudspeakers known under the name of "tweeters", the device, object of the present invention, can then also consist of incorporate 0.1 to 1% by mass of colloidal graphite in the ferrofluid, in order to absorb the electromagnetic wave generated by the phenomenon of micro-discharges.

 A more detailed description of the device for protecting an electrical circuit against interface micro-discharges and radio interference generated by these interface micro-discharges, in accordance with the object of the present invention, will now be described in conjunction with FIGS. 3a to 3c when the circuit consists of cells for reading discs or phonograms still designated by microgrooves.

 A brief reminder of the operation of a reading cell of a conventional phonosensor will be given below.

 A phonosensor usually comprises a read tip electrically connected to two moving coils, the two moving coils being 90 "to constitute in fact a stereophonic reading cell. The moving coils are movable around a pivot axis in a magnetic field, noted H.

 In such a case, as shown in particular in FIGS. 3a and 3b, the device, object of the present invention, comprises a coating of semiconductor material covering the wires making up the voice coils as well as the electric cables.

 As shown in the aforementioned figures, the coating of semiconductor material covering the wires making up the moving coils can be produced by graphitizing these coils according to the process previously described in connection with the speaker coils. However, such an operation requires special care due to the fineness of the conductive wire used to make these moving coils.

 In addition, an absorbent foam of semiconductor material is introduced at the level of any circuit and of any housing or gap when this introduction is not liable to hinder the movement of the above-mentioned moving coils. In Figures 3a and 3b, there is thus shown, in addition to the graphitation of the moving coils, the presence of a cap m of semiconductor foam surrounding the read head itself, and of a sleeve surrounding the cables connecting the coils mobile amplifiers of the signal delivered by the mobile coils. For this reason, and in the same manner as in the case of the preceding figures, in FIGS. 3a and 3b, the graphite voice coils bear the reference 1G, the conducting wires connecting the voice coils to the amplifier bear the reference 1; and the cap m and the sleeve of semiconductor foam attached to the read head itself and to the cables 1. graphitized bear the reference 20.

 Special precautions must be taken with regard to the protection of the conductors connected to the reading cell, that is to say to the above-mentioned moving coils and passing through the reading arm as shown in FIG. 3a or in FIG. 3b.

In general, it is advantageous to rewire the arm in the following manner
- choice of conductors 1: enameled wire from l / lOème to 2 / 10th of a mm in diameter, double high temperature polyurethane enameling for example
- replacement of existing conductors with this graphite conductor as described previously in the description relating to the speaker coils
- Coating of the aforementioned graphical electrical conductors in semiconductor foam 20, so as to constitute a protective sleeve along the tonearm.

 It is indicated in particular that the wiring can be carried out, either inside the tonearm, as shown in FIG. 3a, the sleeve being inserted inside this arm, or, on the contrary, as shown in FIG. 3b, outside the tonearm, the sleeve and electrical conductor assembly can then be maintained by means of ligatures or cable ties made of polytetrafluoroethylene ribbons. These tightening tapes bear the reference 2 in FIG. 3b.

Of course, at the output of the aforementioned connection cables 1, that is to say in fact at the input of the read amplifier, a filter for rejection of high radio frequencies is provided, this filter being constituted by a resistor R and a capacitance C of value comparable to that previously mentioned in the description relative to the loudspeakers. It is of course understood that in the context of a stereophonic read head, which has a left channel G and a right channel D, a rejection filter is provided for each left and right channel, as shown in FIG. 3c. In this case, the rejector filter can be placed under the reading table itself
TL, as shown schematically in Figure 3c. The resistors and capacitors R, C used are resistors of the same nature and of the same value as those indicated previously in the description relative to the constitution of the rejection filter for the loudspeaker.

 A more detailed description of a device according to the object of the present invention, implemented when the electrical circuit is that of a supply voltage transformer, will now be given in conjunction with FIGS. 4a and b.

 As shown in FIG. 4a, the supply voltage transformer comprises a primary winding, denoted 1, and a secondary winding, denoted 12.

 The device, object of the present invention, comprises, similarly to the device shown in FIG. 1b, a box 2 constituting a sealed enclosure provided with sealed bushings, as shown schematically in FIG. 4a. Sealed bushings are marked with the reference 2 ,. The sealed enclosure formed by the housing 2c comprises and contains the primary winding 11 and the secondary winding 1 and is also filled, as in the case of FIG. 1b, with a semiconductor material absorbing the mechanical vibrations of the transformer. In addition, the primary 1: and secondary 12 windings are interconnected to the watertight crossings by means of connection cables bearing in the reference numbers 13 and 1 ;.

 Preferably, and analogously to the electrical circuits previously described in the description, on the one hand, to the loudspeaker coil, and, on the other hand, to the read head moving coils, the electrical wires constituting the primary and secondary windings 1: and 1 as well as the electrical wires making it possible to ensure the connection of the primary and secondary windings to watertight bushings 1; and 14 advantageously comprise a coating of semiconductor material. This semiconductor material may consist of a graphite film deposited and polished in accordance with the indications given previously in the description.

 In addition, the sealed enclosure formed by the housing 20 is filled with semiconductor material, an element absorbing mechanical vibrations, the aforementioned primary and secondary windings 1 and 1 thus being embedded in the aforementioned semiconductor material 2.

 In the same way as in the case of FIG. 1b, the semiconductor material element absorbing mechanical vibrations consists of a pulverulent material such as graphite sand under the conditions which will be given below in the description.

 Proof of the implementation of such a device relative to the protection of transformer circuits against the phenomena of interface micro-discharges will now be introduced.

In general, after the loudspeakers and the phonocaptric cells, the transformers constitute a major source of interface micro-discharges
- insulated windings under voltage are generally accessible on the external surface of these transformers, the external surface of the toroidal transformers also being entirely made up of windings
- the electrodynamic forces and the constraints of magnetostriction induce a high level of vibration, multiplying the micro-discharges, and this, all the more since the external winding is connected to the phase rather than to the neutral of the AC supply network.

Thus, the measures making it possible to attenuate or substantially eliminate the phenomenon of interface micro-discharges at the level of a circuit such as a transformer consist
- to create local equipotentiality at the level of the external windings
- to prevent or absorb mechanical vibrations as much as possible
- to absorb the electromagnetic wave emitted by micro-discharges and the currents generated by it.

 In the same way as in the case of loudspeaker coils for example, or mobile undines of phonosensor cell, the creation of a local equipotential layer at the level of the external windings of the transformer can be carried out by spraying of graphite Blindotub or Graphit 33 on the exterior surface of the transformer under the conditions described above in the description.

 In order to achieve attenuation and absorption of mechanical vibrations, the primary windings 11 and 12 of the transformer are placed in the above-mentioned waterproof housing 2o, the transformer - housing space preferably never being less than 1 cm, so to allow the insertion of an adequate layer of powdery semiconductor material of sufficient thickness, in order to allow the absorption of the above mechanical vibrations.

 When the transformer windings have been placed in the housing, the free space is then filled by means of a damping powder mixture, containing a suitable proportion of graphite powder or, for example of colloida graphite used for the lubrication of mechanical parts. in the proportion of 0.1 to 0.8t by mass.

 It is indicated in particular that as regards the percentage of graphite or colloidal graphite added to the pulverulent element, the substantially homogeneous mixture thus formed must have an electrical resistivity of between 0.1 and 10 Qm as mentioned previously in the description.

 As regards the base of pulverulent material used, it is indicated that this can be constituted by siliceous sand to which is added powdered graphite or colloidal graphite in the proportions indicated above. It is indicated in particular that the percentage by mass of graphite depends on the resistivity of the silica sand or of the pulverulent material used, due to the fact that when silica sand is used, this material is naturally semiconductor.

 As regards the filling of the entire enclosure containing; the primary and secondary windings, it is indicated that the filling is carried out by means of the mixture consisting of silica sand and graphite in the absence of compaction, the mixture thus introduced slightly covering the upper part of the transformer proper.

 As regards the output of the watertight bushings 21, it is indicated that the connection can be made by connection by means of protected cables CP, as described previously in the description relative to FIG.

 In the case where CP protected cables are not used to make these connections, in accordance with the device which is the subject of the present invention, it is advantageous to provide a sleeve of conductive foam, as shown for the connection of the secondary winding 14, this sleeve surrounding the aforementioned connection cable over a major part of the length thereof. In addition, in all cases, it is also advantageous to maintain, both the conductive foam sleeve bearing the reference 22 in FIG. 4a, as the cables protected CP by means of ferrite cores, bearing the reference 2j, as shown for the connection of the primary winding in Figure 4a. The ferrite cores, which are particularly suitable for this purpose, can consist of ferrite cores marketed under the reference 3E25 of the SELECTRONIC catalog and manufactured by the company PHILIPS. The aforementioned ferrite toroids make it possible, due to the electromagnetic stress imposed by the latter on the connection cables, to fight by attenuation against the parasites resulting from micro-discharges in common mode likely to be propagated on the aforementioned connection cables.

 Other materials, constituting an element absorbing mechanical vibrations, can be used if necessary, insofar as these prove to be more efficient or more practical to use depending on the applications considered.

Thus, it is possible to fill the sealed enclosure formed by the casing 2 by means of a liquid or a gel, that is to say a viscous liquid, such as
- physiological serum,
- a mixture of insulating oils containing from 1 to a few% by mass of colloidal graphite in suspension, insulating oils which may be included in the group of paraffin oil, vaseline oil, insulating oil
DIALA marketed by the company SHELL, graphitized lubricating oils normally used in mechanics,
- a mixture of silica sand / physiological serum,
- pouring a coating of molten paraffin containing a suitable percentage of graphite, the cooling of the paraffin thus bringing the whole to a homogeneous block maintaining the transformer,
- low melting point waxes,
- polyurethane, epoxy or silicone compound coating resins, these different products can be loaded with graphite and can be used when the interior disassembly of the transformer is not necessary.

 In general, it is indicated that the housing 23 can be constituted by an insulating material, such as a conventional ABS or other material, or if necessary a metallic conductor according to the desired protection and the conditions of use. When the box is metallic, experience has shown that the subsequent earthing of this box does not bring any improvement, or even is likely to introduce a degradation of the protection of the circuit against the phenomenon of micro-discharges of interface.

 As regards the housing 20, it is indicated that it can advantageously be constituted by a double-walled enclosure the gap formed between the double wall then being folded over with a semiconductor material such as a liquid semiconductor material . In such a case, the saline solution previously mentioned in the description or the physiological saline previously cited will be preferred as the liquid semiconductor material. The gap may then have a dimension in the direction orthogonal to the surface of the housing of the order of approximately 2 cm, in order to ensure sufficient protection.

 A particularly advantageous embodiment of a device for protecting an electrical circuit against interface micro-discharges and parasites generated by these interface micro-discharges, in accordance with the object of the present invention, will be given in connection with the figure. 4b, in the case where this electrical circuit is constituted by an isolation transformer.

First of all, it is recalled that the isolation transformer consists of a first and a second transformer interconnected by their secondary windings, the primary winding of one of the transformers being connected to the supply network, for example transformer
T1, and the primary winding of the second transformer, transformer T2, being connected to output terminals and delivering a supply voltage substantially equal to the mains supply voltage, in the absence of direct galvanic connection with the mains network cited above.

In such a case, as shown in FIG. 4b, the device which is the subject of the present invention comprises, in a sealed housing 2, the first Tl and the second T2 transformer interconnected by their secondary windings, the primary winding of each transformer being interconnected with input / output terminals via watertight bushings, noted 2
Of course, the primary and / or secondary windings of the transformers Tl and T2 can be subjected to a deposition of semiconductor material such as graphite deposition, as mentioned previously in the description relative to the winding of the loudspeaker or to the moving coils of the sensor-probe head for example. It is the same for the connection wires connecting the primary windings of the first and second transformers to the aforementioned sealed bushings 2.

 With regard to the connecting wires of the primary windings of the transformers, these connection wires bearing the reference 2 in FIG. 4b, these can also be provided with a coating of semiconductor material such as a graphite film deposition, as mentioned previously in the description. In addition, and in a particularly advantageous manner, a capacity resistance attenuation circuit, bearing the reference 23 in FIG. 4b, is provided, this attenuation circuit being interconnected in parallel between the interconnected secondary windings of the transformers T1 and T2. Finally, the transformers T1 and T2 and the attenuation circuit 23 are buried in a semiconductor material 2 contained in the housing 2c.

 As regards the attenuation circuit 23, this can include at least one matching resistor, denoted R, and, connected with this resistor, in series with it, at least one electrical capacity encapsulated under vacuum, in air or in a neutral gas, this encapsulated capacity, denoted C, which can be doubled in parallel by a capacity C 'of higher value.

 In an effective embodiment, it is indicated that the transformers T1 and T2 were toroidal transformers, primary voltage 110 V or 240 V, secondary voltage 2x40 V, 250 VA, marketed under the reference 432453 in the FARNELL catalog. Capacity C was an air capacity of value between 60 to 100 pF and capacity C 'a polypropylene capacity of value between 0.47 to 2.2 pF. Resistor R was a resist case where the electrical circuit protected against the phenomena of interface micro-discharges, in accordance with the object of the present invention, is a discrete or integrated multicomponent electrical or electronic circuit, mounted on a printed circuit board by example.

 In Figures Sa and 5b, the symbolic representation of the profile of discrete components such as transistor, resistor, capacitor or the like can be recognized on one of the faces of the printed circuit board, the printed circuit naturally being drawn in the conventional manner. and engraved on the other side.

 As shown in FIG. 5a, the device, object of the present invention, comprises at least one box 2o open at one of its ends, this box containing a semiconductor material in liquid form for example, this seii- conductor bearing the reference 2 in FIG. 5a and constituting the element absorbing the electromagnetic wave generated by the phenomenon of micro-discharges from the interface.

 In addition, as shown in FIG. 5a above, a protective envelope of flexible plastic material, bearing the reference 2, is provided in order to allow protection of the electronic circuit from the medium or semiconductor material 2 under liquid form.

The assembly constituted by the electronic circuit CE and the aforementioned protective envelope 2. is then immersed in the liquid semiconductor material 2 contained in the housing 20 open at its upper end according to the embodiment of FIG. 5a.

 Of course, a closure seal, bearing the reference 2w, is provided, this seal making it possible to seal the envelope 2 at the periphery of the open housing, as shown in FIG. 5a above.

 Of course, the embodiment as shown in FIG. 5a is not limiting. In particular, it is indicated that the plastic envelope 2, at least in the upper part thereof, can be stiffened so as to ensure the mechanical maintenance of the electronic circuit CE in a substantially vertical position as shown in FIG. 5a. In addition, the upper part of the electronic circuit CE, that which is exposed beyond the free surface of the liquid semiconductor material in the open air, can advantageously be provided with a radiator R making it possible to dissipate the thermal release generated by the operation of the CE electrical or electronic circuit. Of course, the connection cables of the entire electronic circuit CE can then be connected to connection terminals of the electronic circuit CE and protected in the same way as mentioned above with respect to the connection cables of the loudspeakers. , transformers or moving coils of phonosensors. It is of course understood that the connecting cables as well as the electrical or electronic circuit CE are further protected from contact with the liquid semiconductor material via the plastic casing 2 ..

 The embodiment shown in FIG. 5a gives satisfaction. It is particularly simple to make and inexpensive. The liquid semiconductor material 2 can for example consist of the saline solution or physiological saline previously mentioned in the description.

In such a case, the liquid semiconductor material, by the static pressure exerted by the latter on the protective plastic envelope 2, presses it against the electronic circuit CE, which is then particularly well protected against the phenomenon of interface micro-downloads. The saline solution, or physiological saline, can of course be replaced by a semiconductor gel of equivalent properties, or, if necessary, by graphite sand impregnated with physiological saline for example.

 The embodiment of the protection device, according to the object of the present invention, as shown in Figure Sa, gives satìsfac asn.

 However, a simplified variant is shown in FIG. 5b, this simplified variant possibly being of interest to the extent that it is particularly quick and simple to implement, and where, on the other hand, the concept of bulk and portability of the assembly is improved taking into account the fact that the liquid semiconductor element is added in the form of an independent discrete element, and therefore much easier to implement and / or to handle.

In such a case, as shown in FIG. 5b, the device which is the subject of the present invention comprises, in addition to the box open at one of its ends, bearing the reference 2c, the multi-component electronic circuit CE as well as a plurality timing cushions for this circuit
CE, each cushion consisting of an envelope formed of plastic material filled with the semiconductor material as described above in connection with FIG. 5a. In FIG. 5b, each cushion, with reference to FIG. 5a, bears the reference 2, 2 .., and, where appropriate, higher indices when more than two cushions are used. It is understood in particular that it is possible to use four cushions, two cushions making it possible to protect the electronic circuit CE and the timing thereof so as to prevent any movement in the plane of the sheet in which the Figure Sb, and two cushions, not shown, being used to protect the electronic circuit CE and the timing thereof in a plane orthogonal to the plane of the sheet in which is shown in Figure Sb.

 With regard to the implementation of the various aforementioned cushions, it is indicated that, in an advantageous embodiment, the electronic circuit CE is placed in the open housing 2 as shown in the initial state in FIG. 5b, while the empty cushions 21 and 22 are introduced, as shown in the above figure, so as to protect the electronic circuit CE and the setting of the latter in the plane of the sheet in which Figure 5b is shown. In the initial state, the two cushions 2. and 2 are empty. The final state shown in FIG. 5b is then obtained by filling each cushion 2.l and 212 with absorbent liquid semiconductor material, such as physiological saline, then sealing the cushions by heat-sealing for example, bearing the reference 22 in FIG. 5b. Of course, the two side cushions allowing protection and wedging in a plane perpendicular to the plane of the sheet in which the figure Ss is represented can be produced in a similar manner.

 We understand on that instead of the saline solution or physiological serum 2 used, it is also possible to fill the aforementioned cushions with graphite oil, graphite silica sand, silica impregnated with serum, particularly effective in the fight against vibrations. In the latter case, the different cushions are first filled with silica sand, then the serum is poured until the sand is completely impregnated.

 Other materials, such as conductive gels of suitable resistivity, these spongy materials making it possible to stabilize the physiological serum or foams such as polyurethane foams made semi-conductive by the addition of graphite, can also be used.

 The device, object of the present invention, can be applied to any type of electrical circuit, as mentioned previously in the description. In addition to the various electrical circuits already mentioned, the device which is the subject of the present invention can of course be applied to all electrical or electronic sockets, which constitute a privileged passage for the electromagnetic waves generated by the interface micro-discharges.

 In fact, years of research carried out in ELECTRICITE DE FRANCE's laboratories have clearly shown that the parasites thus generated, radioelectric parasites, pass through the insulating / chassis mass / socket interval.

 A first exemplary embodiment of a device for protection against interface micro-discharges and against radio interference generated by the latter, will first be given in connection with FIG. 6a in the case where the electrical outlet is constituted by a RCA socket for chassis for example.

 In Figure oa, there is shown in section an RCA type socket mounted on a CH chassis. Conventionally, the socket comprises an RCA socket head comprising a coaxial type conductor whose central core constitutes the hot spot, the assembly of the socket head being mounted through the chassis and fixed to the latter by the through an EC nut in a conventional manner. The central core AC is surrounded by a dielectric material ensuring with the external metallic envelope a transmission of coaxial type.

As shown in FIG. 6a, the device which is the subject of the present invention comprises a sleeve of semiconductor foam surrounding the whole of the external envelope.
Ee of the RCA plug on a determined length thereof.

The sleeve of semiconductor foam bears the reference 20 in FIG. 6a.

As also shown in the above figure, the sleeve 2 of semiconductor foam can be held at its ends and in particular in the vicinity of the chassis CH by means of a ferrite ring 2i, sold under the reference 3E25 by the society
PHILIPS, this ferrite ring having, as mentioned previously in the description, a parasite suppression function in common mode.

In the same way and placed outside the chassis
CH, that is to say on the right part of FIG. 6a, a cover of self-conducting foam is provided, which is intended to cover the whole of the superstructure emerging from the chassis CH, superstructure formed by the end male of the RCA socket shown in FIG. 6a, the nut EC and the conventional fixing means such as a metal washer or the like. The cover shown in FIG. 6a bears the reference 23.

 In some cases, it may be advantageous, as shown in FIG. 6b, to move the sockets outside the CH chassis in order to provide better protection, in particular when it is desirable to provide connection to the electrical or electronic circuits. internal by means of CP protected cables previously mentioned in the description.

 Such an embodiment is shown in the aforementioned FIG. 6b in which the connection being made at the level of an electrical or electronic circuit CE by means of a protected cable CP as described above, the external part of the chassis CH, therefore located to the left of the plane materializing the chassis Cn in FIG. 6b, can advantageously include for this purpose a section of tube welded to the substantially metallic chassis, bearing the reference TU, this section of tube comprising a filling of semi-foam conductive, bearing the reference 20 in Figure 6b. The assembly constitutes a particularly efficient and rigid sleeve in which the protected cable CP, connected to the circuit CE, is then traversing with respect to the aforementioned sleeve. A ferrite core with the reference 2: can also be placed inside the chassis CH so as to provide additional protection from parasites in common mode, as mentioned previously in the description.

 Of course, the length of the protected cable CP can a priori be arbitrary. However, in the case of very long cables, it is preferable, as shown in FIG. 6c, to provide protection in the vicinity of the socket itself as represented in FIG. 6b, which corresponds, in the above-mentioned figure, to an RCA socket for example.

As shown in FIG. 6c and in such a case, in the vicinity of the aforementioned female socket, the device, object of the invention, can consist of placing a sleeve on the protected cable CP itself in the vicinity of this socket. of semiconductor foam, bearing the reference 20, and on this sleeve, a ferrite torus, bearing the reference 2 :, this ferrite torus may correspond to that already mentioned in the description, marketed by the Company
PHILIPS, the aforementioned ferrite toroid 2 being itself protected by means of a semiconductor foam coating bearing the reference 2t, this coating covering not only the ferrite toroid 2 but also the sleeve 2o previously mentioned. Thus, the coating 22 can be maintained by means of links 23 such as clamps or the like as shown in Figure 6c.

 This protection can, for example, be associated with, or supplemented by the installation, on the power cord 1 corresponding to the devices to be supplied and as close as possible to their power outlet, of a sleeve 20 of semiconductor foam suitably tightened around of the cord by collars 21 made of metallic adhesive copper tape, for example 3M ref. 1181 9.5 to 12.7 mm wide, spaced 15 to 25 mm apart, as shown in Figure 6d. One or two copper rings 2 at the ends can be replaced by a ferrite toroid 2, as shown previously in FIG. 6c.

 Of course, the implementation of the device, object of the present invention, involves some modifications of the circuits subject to the protection of this device.

When the modifications necessary for existing devices cannot be easily introduced, in particular with regard to electrical or electronic circuits with discrete components as shown for example in FIG. 5a or 5b, a preferred non-limiting embodiment of the device, object of the present invention, making it possible to introduce a minimum of modifications at the level of the circuit itself, will now be described in conjunction with FIGS. 7a and 7b.

 As shown in the aforementioned figures, the device, object of the present invention, comprises at least one housing open at one of its ends, this housing constituting a chassis comprising at least one upper part, denoted CH,, and one part lower, denoted CH2, metallic parts electrically insulated from each other.

 As shown in the aforementioned figure, the housing comprises at least one chassis subdivided between the two upper CH and lower CH2 parts, the multicomponent electronic circuit CE, the printed circuit side of the latter, that is to say the underside of this in FIG. 7b, comprising a coating of insulating dielectric material, bearing the reference 2D This protective insulator can be constituted by the varnish of the printed circuit itself or an added varnish.

 In addition, the device which is the subject of the present invention comprises an internal lining made of a material of the semiconductor foam type, bearing the reference 21, placed on the internal face of the housing, that is to say on the internal face of the upper part CH: and the lower part CH2. The printed circuit face comprising the coating 20 of insulating dielectric material is placed in the vicinity of the internal lining of material of the semiconductor foam type.

 As shown in FIG. 7b in particular, the two opposite faces forming the upper part CH: and CH2 of the chassis comprising the internal lining of semiconductor foam constitute in fact internal linings with corrugated face, as shown in the abovementioned figure.

The corrugations introduced have a depth h in the direction perpendicular to the upper parts CH; and lower CH and a spacing d in a second direction perpendicular to this -remire direction.

 In FIG. 7a, there are shown different embodiments of the corrugations that can be used to produce the internal linings by means of the semiconductor foams 2 previously mentioned.

Different forms of corrugations can be used, pyramidal corrugations at point A in Figure 7a, dihedrons at point B in this same figure a, and finally of accordion and spring type respectively, as shown in points C and D of the same figure 7a above. In the case of corrugations of the accordion type, it is indicated that a sheet of foam of sufficient thickness can be subjected to an accordion folding, as shown in FIG. 7a, the accordion structure then being maintained by means of insulating holding rods, marked 22.

 In the case of point D of FIG. 7a, the spring can be produced by means of preformed elements of foam of semiconductor material, these preformed elements being successively assembled in head-ceche symmetrically with respect to a vertical plane and subjected to suitable bonding, the assembly being held in place by holding rods 22.

 With regard to the dimensioning of the abovementioned corrugations, it is indicated that the sheets or linings of foam of semiconductor material can be produced in a similar manner to that used in anechoic chambers, the average height of the indentations or corrugations being of the order of h = 5 cm + 3 tsp.

 As a general rule, for a height h equal to 5 cm + 3 cm as mentioned above, '' spacing b is then taken to be substantially equal to the value n / 2.

 Of course, the pointed face of the corrugations is directed towards the circuit to be protected at a short distance from it, that is to say a few centimeters.

 In addition, it is indicated that the upper and lower plates CH, and CH- electrically isolated can then, in a particularly advantageous manner, be used so as to create an electrostatic field making it possible to block the micro-discharges.

 For this purpose, the two aforementioned external faces CH1 and CH2 opposite the aforementioned corrugated internal faces play the role vis-à-vis the latter of an electrically conductive coating, this electrically conductive coating being brought to a determined difference in static electric potential. by means of a DC voltage generator E, as shown in FIG. 7b. The voltage applied to create the electrostatic field is of the order of 80 to 100 V, this voltage being applied to the plates CH and CH2 via a resistance R of value 100 KQ at 1 .Y in order to limit the residual intensity in the event of accidental contact.

 In general, it is indicated that the corrugated foams must have teeth of length at least equal to the lowest wavelength to be absorbed which can reach, or even exceed, 30 cm.

 Preferably, the coating 2: of corrugated semiconductor foam sees its efficiency improved in the case where it adheres to the conductive surfaces of the chassis, that is to say the CH plates. and CH2. In such a case, the absorption appears more complete due to the fact that the wave is subjected to reflection on the corresponding metal wall.

 In a preferred embodiment, it is indicated that the covering 2 was constituted by several semi-conoucting foam plates, glued together with the interposition of graphite cardboard, only the internal face turned towards the electronic circuit CE presenting of course the corrugations. The graphite cardboard can be replaced by a copper plate 0.1 to 0.2 mm thick.

 Finally, a particular rea saton node of the device, object of this int-end, more particularly intended for protection against radioelectric disturbances generated by the phenomenon of interface micro-discharges when these radioelectric disturbances are guided, will now be described in the case where the protected circuit is a power supply.

 The phenomenon of guiding the electromagnetic wave generated by the phenomenon of interface micro-discharges is particularly troublesome when a device not protected against the phenomenon of interface micro-discharges is connected to the system, although this device also has qualities of perfect performance at low frequencies. In such a case, the ounce associated with micro-discharges propagates on the connection conductors and thus disturbs the connected device.

 In such a case, the device, object of the present invention, comprises, as shown in FIG. 8, a set of protected cables CP, each cable being used to ensure the connection vis-à-vis one of the positive, negative terminals or mass of the stabilized power supply proper, and the protected cables CP being combined in a bundle, the bundle itself: itself surrounded by a foam sleeve made of semiconductor material, bearing the reference 20 in FIG. 8 The sleeve is itself enclosed at its ends by ferromagnetic material rings or toroids bearing the reference 2 in FIG. 8. A ferrite torus 2; can also be inserted on the connection cable of the stabilized power supply to the mains.

In a preferred embodiment, it is indicated that this cord may have a ground conductor connected to the ground of the power outlet by an appropriate impedance, shock inductance or carbon resistance of 270 Q.

 In addition, as shown diagrammatically in FIG. 8, each protected cable C? is connected via an RC attenuation circuit to the cable constituting the earth connection of the device to be supplied with the stabilized supply. It is recalled that the attenuation circuit RC can be constituted by an air capacitor or vacuum-encapsulated with a value of the order of 100 pF, while the terminals themselves of the stabilized supply can advantageously be connected by capacitors air or vacuum encapsulated, of greater value between 100 and 500 pF. Finally, the ground conductor of the stabilized supply, at the level of the connection to the device to be supplied, can be connected to earth via a resistor R of the same value, substantially.

 Thus, the attenuation circuits R, C 'constitute an impedance adaptation for the micro-discharges in differential mode, while the resistance R plays the same role for the common mode.

 In order to reduce the disturbances due to interface micro-discharges in common mode, it is advantageous, on each device, to find the correct direction of connection of the mains socket, in particular so that the sector neutral connection is connected to the appropriate terminal of the supply voltage, to isolate the earths from the sources and to connect the earth alone of the amplifier to the local earth by a resistance, the resistance R of value previously mentioned, ranging between 5 and 270 Q.

 In order to find the correct direction of connection of the mains socket, in which direction the external surface of the transformer is connected to the neutral, which makes it possible to reduce the level of mains interference, it is then possible to proceed according to the conventional ways known from the art. 'man of art'

 Tests of implementation of the devices in accordance with the object of the present invention were carried out within the laboratories of ELECTRICITE DE FRANCE.

 These tests made it possible to demonstrate that the subjective rendering of a high-fidelity system for example could be considerably modified by the simple displacement of the screens intended to protect the electronic circuits with discrete components, as represented in FIGS. 7a and 7b.

When moving these screens, it was successively obtained
- a particularly dull, even muted sound, with rapid note extinctions and a hushed overall appearance in the wrong sense of the term,
- high quality sound with extended note extinctions and excellent signal separation with a particularly pleasant overall feeling of space,
- a sound which one can qualify as aggressive when the extinctions of notes are well prolonged and then seem difficult to separate. The overall experience of the listener is then a feeling of distortion quickly unbearable which then encourages the latter to lower the volume quickly.

 A global interpretation of the phenomenon will be given below.

 The audio signal transmitted and processed for example in a high fidelity chain generally consists, when it is a musical signal, of an attack, of the body of the signal itself and of a trail or extinction of the note. , this drag can be at a noise level of the order of -20 to -40 dB relative to the signal body.

 This trail, fundamental for the quality of musicality of the signal perceived by the listener, sees its perception seriously disturbed by the radio interference generated by the interface micro-discharges. Indeed, the rest of the signal, or even external causes, generates an electromagnetic wave due to micro-discharges, which is rectified or demodulated by the non-linear elements of the circuit, non-linear elements such as solders and other bimetallic contacts, which leads to the creation of a broad spectrum background noise which exists only in the presence of the audio signal.

 The protection against the phenomena of interface micro-discharges implemented using the device, object of the present invention in the various situations previously described in the present description, makes it possible to ensure such protection by attenuating or eliminating the effects of the electromagnetic wave generated by the aforementioned micro-discharge phenomenon.

The solutions recommended and previously described then allow
to prevent the production of micro-discharges when this production can be prevented without harming the operation of the aforementioned circuit,
- prohibit access of the electromagnetic wave generated by the interface micro-discharges to sensitive circuits,
- of

Claims (20)

 1. Device for protecting an electrical circuit against interface micro-discharges, and radio interference generated by these interface micro-discharges, characterized in that said device comprises, in the vicinity of said electrical circuit, means for attenuating the electromagnetic wave generated by these interface micro-discharges.  2. Device according to claim 1, characterized in that said means for attenuating the electromagnetic wave generated by these interface micro-discharges comprise means absorbing the electromagnetic wave generated by these interface micro-discharges.  3. Device according to claim 1 or 2, characterized in that said means for attenuating the electromagnetic wave generated by these interface micro-discharges comprise means absorbing mechanical vibrations capable of affecting said electrical circuit, which makes it possible to reduce the triboelectric contribution to said electromagnetic wave generated by these micro-discharges.  4. Device according to one of claims 1 to 3, characterized in that said means for attenuating the electromagnetic wave generated by these interface micro-discharges comprise a coating of semiconductor material applied to the external surface of the electrical conductor , the linear resistivity of said semiconductor material being chosen within a range of values adapted so as to allow both the maintenance of the external surface of the electrical conductor at a static electrical potential of constant local value close to that of the electrical conductor and d 'absore: -' all the erratic electric discharge currents caused by the interface micro-discharges and, thus, attenuate the electromagnetic wave generated by them.  5. Device according to claim 4, characterized in that said selai-conductive revetelnent has a linear resistivity of value p between 0.1 Q x m and 10 Q x m.  6. Device according to one of the preceding claims, characterized in that, when said electrical circuit is that of a loudspeaker, this loudspeaker comprising a magnetic yoke provided with a gap housing, an integral electrical coil a loudspeaker diaphragm, this electric coil being engaged in the air gap housing, and terminals and cables for connecting these terminals to the output terminals of an electric amplifier, this device comprises at least:  - a foam lining of semiconductor material placed at the bottom of said air gap housing, the walls of said air gap housing further comprising a coating of semiconductor material  - a coating of semiconductor material covering the conductors forming said electric coil  - a protective coating of said terminals and connecting cables of these terminals, said protective coating consisting of a semiconductor material covering these terminals and these connecting cables on at least part of the latter  - a very high radio frequency rejector filter connected to the end of the cables or of the part of the connection cables covered by the semiconductor material.  7. Device according to one of claims 1 to 5, characterized in that, when said electrical circuit is that of a reading cell of a phonosensor, comprising a reading arm equipped with a reading head with moving coils , connected by electric cabals to an output connector, said device comprises at least  - a coating of semiconductor material covering the constituent wires of said moving coils and the electric cables  - a foam lining of semiconductor material coating the whole of the read head substantially and said electrical cables along the length of the read arm  - a very high radio frequency rejector filter ensuring the connection between the free end of said electrical cables and said output connector.  8. Device according to one of claims 1 to 5, characterized in that, when said electrical circuit is that of a supply voltage transformer, comprising a primary winding and a secondary winding, said device peddles at least one enclosure watertight provided with watertight bushings, said watertight enclosure containing said primary winding and said secondary winding being filled with a semiconductor material, absorbing mechanical vibrations, the primary and secondary windings being interconnected with said watertight bushings.  9. Device according to claim 8, characterized in that the electrical wires constituting the primary and secondary windings comprise a coating of semiconductor material.  10. Device according to one of claims 8 or 9, characterized in that said semiconductor material, absorbing mechanical vibrations, is a pulverulent material comprising from 0.2 to 0.8% by mass of graphite.  11. Device according to one of claims 8 to 10, characterized in that said sealed crossings are formed by electrical conductors provided with a coating of semiconductor material extending outside the sealed enclosure , each conductor further comprising outside the enclosure seals a ferrite toroid surrounding the conductor and the coating.  12. Device according to one of claims 8 to 11, characterized in that said sealed enclosure is a double wall enclosure, the gap formed between the double wall being filled with a liquid semiconductor aterlau.  13. Device according to one of claims 8 to 12, characterized in that, when the electrical circuit is that of an isolation transformer consisting of a first and a second transformer interconnected by their secondary winding, this- this includes, in a waterproof case  - Said first and second transformers interconnected by their secondary winding, the primary winding of each transformer being interconnected at input-output terminals by means of sealed bushings;  - a capacity resistance attenuation circuit interconnected in parallel between the interconnected secondary windings of said transformers;  - a semiconductor material burying said first and second transformers and said attenuation circuit.  14. Device according to claim 13, characterized in that said attenuation circuit comprises at least  - an adaptation resistor, and, connected in series with this resistor,  - at least one electrical capacity encapsulated under vacuum, in air or in a neutral gas.  15. Device according to one of claims 1 to 5, characterized in that, said electrical circuit being a discrete or integrated multicomponent electronic circuit mounted on a printed circuit board, said device comprises at least  - a shoemaker open at one of its ends containing said semiconductor material in liquid form  a protective casing for the electronic circuit, made of plastic material, the assembly consisting of the electronic circuit and the protective casing being immersed in the liquid semiconductor material, said casing ensuring the tightness of said container to said semiconductor material liquid.  16. Device according to one of claims 1 to 5, characterized in that said electrical circuit being a discrete or integrated multi-component electronic circuit mounted on a printed circuit board, said device comprises at least one housing open to one from its ends, this housing containing  - said multi-component electronic circuit  - A plurality of cushioning wedges of this circuit, each cushion consisting of an envelope formed of plastic material filled with a semiconductor material.  17. Device according to one of claims 1 to 5, characterized in that said electrical circuit being a discrete or integrated multicomponent electronic circuit mounted on a printed circuit board, said device comprises at least one housing open to at least one from its ends, this housing containing  - Said multicomponent electronic circuit, the printed circuit face comprising a coating of insulating dielectric material;  an internal lining made of semiconductor foam type material placed on the internal face of the housing, said printed circuit face comprising the coating of insulating dielectric material being placed in the vicinity of said internal lining made of semiconductor foam type material.  18. Device according to claim 17, characterized in that at least two opposite faces of the internal lining are corrugated faces.  19. Device according to one of claims 17 or 18, characterized in that two external faces of the housing opposite to the corrugated internal faces of the internal lining include an electrically conductive coating, said electrically conductive coatings being brought to a difference in static electric potential determined.  20. Device according to one of claims 1 to 5, characterized in that said electrical circuit being constituted by a socket comprising in the nuions a ground connection plug or by an electric cable, said device comprises at least  - a sleeve forming a guard ring placed around the connection plug or the electric cable, this sleeve being made of a semiconductor foam  - at least one toroid or ferrite ring in the vicinity of this sleeve.