Faraday screen room

A Faraday screen room is a Enceinte used subsidiarily to protect from the harmful effects electric S and electromagnetic S external or conversely to prevent an equipment from polluting its environment. A Faraday screen room is often used when one wishes to carry out measurement S precise in electronic or electricity.

Principle

Such as she was studied by Michael Faraday during her work on the drivers, the Faraday screen room (i.e. a conducting enclosure connected to the ground in order to maintain its potential fixed) is tight with the electric fields (created by the simple presence of a potential difference, without a current not being necessary) and this, whether the disturbing source is inside or outside the enclosure.

This structure can also have an indirect effect of protection against the disturbances of electromagnetic origin (due to a current). One speaks then rather about electromagnetic Blindage. For this use, it is more necessary only the structure is connected to the ground but the effectiveness is strongly influenced by the frequency of the disturbance and the magnetic Perméabilité of material.

Constitution

The metal enclosure must be closed on each side in theory. But it can also be made up of openwork netting (from where the name of cage). A netting with a mesh of a few centimetres acts like a mirror on a decimetre Onde , as that is used in the Miroir S primary educations of the Radiotélescope S (Effelsberg, Nançay). The higher the Fréquence of the wave is (thus more its wavelength is short), plus the Maille must be small.

There exist three principal techniques of realization of the industrial Faraday screen rooms:

- Modular Cages: They are carried out using folded containers steel . or using panels out of wooden covered on the two faces of a steel sheet. The vats are assembled between them using bolts. The panels wood are assembled using profiles of assembly out of steel. Favors vats: insensitivity to moisture and the hygrometrical variations. Good behavior in the time of the geometry. Favors panels: It can be recut. Dimensions of the room can be modified (in the event of removal for example). The modular cages make it possible to reach performances higher than 100 dB 100 MHz.

- Architectural copper Cages: They are carried out using a strip iron of copper of 2 or 3 tenth of mm (delivered in roller) which is posed in covering and is welded uninterrupted with tin. This technique adapts well to the large-sized buildings and makes it possible to adapt to the complex geometries (corners, setbacks, beams, pillars), which is more complicated, even impossible using a modular cage. There is no loss of place, copper applying directly to the walls. However, it is necessary to envisage a doubling for decoration. The cages coppers make it possible to reach performances higher than 100 dB 100 MHz.

- Architectural metallized fabric Cages: The cage is built using a metallized tapestry posed using adhesive, like a paper paints traditional. This technique has the same advantages as the cages coppers. The performances reached are higher than 60 dB with 100 MHz. These performances are enough in a majority to application. The interest of this technique is that it is possible to associate windows there. Indeed, the principal disadvantage of the Faraday screen rooms is that to preserve the performances, it is impossible to install there windows (80 max. dB). It is thus difficult to consider a permanent work station out of modular Faraday screen room or copper.

It is necessary to recall:

  1. That the performances (and the cost) of a cage essentially hold in its accessories : doors, windows, passages for ventilation (honeycombs), and fluids (waveguides).
  2. That all the drivers penetrating and outgoing of the cage must be provided with radioelectric filters (if not, the drivers behave like antennas and very strongly decreases the total performances of the cage ).

The visitors of the Palate of discovered the, in Paris, can observe a Faraday screen room and its operation.

Examples of applications

  • the Automobile is a current Faraday screen room , which although imperfect cheek often well its role. The use of composite materials not conducting S as well as the glazed openings makes that according to the model, it is only seldom good a Faraday screen room .
  • the metal case of the Ordinateur S also constitutes a Faraday screen room . If this case is nonmetal (plastic), it is, to meet the standards of radio-compatibility, doubled at the strategic places, of a fine metal sheet connected to the electric ground of the machine.
  • In general, much with apparatuses electric household appliances is equipped with shielding internal forming Faraday screen rooms at least for the significant parts. Very often for requirements of costs of construction, the metal sheets of shielding are replaced by a layer of a conducting material applied by projection to the interior of the Carrosserie makes materials insulating.

Related articles

External bonds

  • a video explanatory on the Faraday screen room in electrostatics

Random links:With the guet! | Gordon Brown | Lame Jose | Edgar Bourloton | Joaquim Magalhães Mota | Henry_John_Stephen_Smith