FR2741504A1 - Ventilation panel for enclosure containing VHF equipment - Google Patents

Abstract

The ventilation panel is made up from a frame (2) fixed by one edge to the wall of the enclosure to be ventilated. The frame contains a large number of tubes (3,4) which lie parallel and are fastened together, absorbing very high frequency electromagnetic radiation. An individual tube (5) may be provided with a coating on part of its internal surface, the coating being of ferrite which is able to absorb the VHF radiation. The coating may be applied by means of a paint which includes some ferrite material. The diameter of each tube is greater than that which would provide cut-off for the radiation, but the internal coating ensures the absorption of the radiation which may otherwise pass through the tube.

Description

Ventilation duct impervious to very high frequency electromagnetic radiation
The present invention relates to a ventilation duct through the wall of an enclosure comprising sources of very high frequency electromagnetic radiation, for example from 10 to 20 GHz, and impermeable to this radiation, comprising a network of parallel tubular openings honeycomb, with walls formed over at least part of their length of a magnetic material.

 Such ventilation ducts have already been formed by joining metal tubes side by side, each of which, welded to its neighbors, functions as a waveguide of transverse dimension less than that corresponding to the cutoff frequency of such a guide. waves.

 The stacking of such tubes being difficult, they are often replaced by corrugated blades arranged face to face, constituting half-tubes which are welded together, for example by immersing them in a hot-dip galvanizing bath.

 However, in the case of enclosures containing sources of very high frequency electromagnetic radiation, of the order of 10 to 20 GHz and above, the transverse dimensions required for the tubes become too small and their resistance to the passage of l the air becomes too strong.

 Document SU-A 965981 has also proposed a ventilation duct opaque to electromagnetic radiation of high frequency, constituted by a block pierced with square openings provided on a fraction of their length with inserts of magnetic material, such as 'a ferrite, each pierced with a circular bore, the bores of the different inserts being different to avoid the effects of resonance. However, such sheaths are complex to manufacture and require significant machining operations.

The object of the present invention is to provide a ventilation duct for enclosures containing sources of very high frequency electromagnetic radiation, of the order of 10 to 20.
GHz or above, which is simple to manufacture and low cost.

 The ventilation duct according to the invention is characterized in that its tubular openings are of transverse dimension greater than that corresponding to the cut-off frequency of electromagnetic radiation, and in that their internal wall and coated on at least part of its length of a magnetic material, or in that they are provided with longitudinal spacers or fin bars made of magnetic material.

 Alternatively, the openings are provided with cross-section fin bars in the shape of a spoke wheel.

 The magnetic material used will generally be a ferrite.

 There is described below, by way of examples and with reference to the figures of the appended drawing, an air duct and tubular openings according to the invention.

 Figure 1 shows in perspective an air duct consisting of multiple cylindrical honeycomb tubes welded to each other.

 Figure 2 shows in diametral section on a larger scale a tube coated with absorbent magnetic material over part of its length.

 FIG. 3 shows in large-scale diametral section a tube with an internal surface provided with a layer of paint with radiation absorbing properties.

 FIG. 4 shows in perspective a tube provided with a bar with longitudinal fins made of radiation absorbing material.

In Figure 1, the ventilation duct is constituted by a box 2 fixed by a flange 1 on the wall of the enclosure. The box contains a large number of tubes such as 3, 4 welded to each other absorbing very high frequency electromagnetic radiation
According to the variant of FIG. 2, an individual tube 5 is provided over a part of its length with an internal coating 6 of ferrite, a magnetic material which absorbs electromagnetic radiation well. The diameter of the tube 5 is greater than that corresponding to the cut-off frequency of the radiation, but the internal coating 6 ensures the absorption of the radiation likely to pass through the tube.

According to the variant of FIG. 3, an individual tube 7 is coated with a layer of paint containing ferrite, so as to absorb the radiation liable to pass through the tube
According to Figure 4, each tube is provided with a bar 10, comprising an axial core 1 and fins in the shape of a spoke wheel 12, 13, 14, 15 made of ferrite.

 Although the tubes described with reference to the drawing are circular, it will be understood that they could also be of different cross sections. in particular be rectangular or square.

Claims (2)

1 / Aeration duct through the wall of an enclosure comprising sources of very high frequency electromagnetic radiation impermeable to this radiation, comprising a network of parallel tubular honeycomb openings (3, 4), with walls made up of at least part of their length of magnetic material, characterized in that the tubular openings are of transverse dimension greater than that corresponding to the cut-off frequency of electromagnetic radiation, and in that the internal wall of the openings is coated over at least part of its length of magnetic material (6, 8) / or in that the openings are provided with longitudinal spacers or bars (10) with fins (12, 13, 14, 15) of material magnetic. 2 / ventilation duct according to claim 1, characterized in that the wall (7) of the openings is coated with a paint (8) containing a magnetic material 3 / ventilation duct according to claim 1, characterized in that the cross section of the finned bar (10) is in the form of a spoke wheel (12, 13, 14, 15).