GB2199448A

GB2199448A - Radio screened enclosures

Info

Publication number: GB2199448A
Application number: GB08627017A
Authority: GB
Inventors: Jeffrey Park; Peter Richard Brown
Original assignee: Airtech Ltd
Current assignee: Airtech Ltd
Priority date: 1986-11-12
Filing date: 1986-11-12
Publication date: 1988-07-06
Also published as: GB8627017D0

Abstract

A closure for an aperture (12) in a radio screened enclosure comprises a pivotable door (14) for closing the aperture (12). The door (14) has a first metal screening member (20) with a first edge flange (22) extending around the periphery of the door (14). A second metal screening member (24) with a second edge flange (26) extends around the periphery of the aperture. Further screening members (28, 30) are formed on the inside of the door and around the aperture, these members (28, 30) having edge flanges (32, 34). In the closed position of the door (14), the metal screening members and the flanges overlap around the periphery of the aperture (12) to prevent leakage of incident low frequency fields in the enclosure. <IMAGE>

Description

Title: Radio Screened Enclosures Field of the Invention This invention relates to radio screened enclosures, and in particular to closures for apertures in radio screened enclosures, such as cabins and containers.

Background to the Invention Radio screened enclosures such as cabins or containers are used for accommodating communications equipment. Such cabins or containers should attenuate incident electromagnetic radiation by more than 60dB, and it is found convenient to split the frequency spectrum of the incident electromagnetic radiation into three bands when assessing performance. For the high frequency band, covering 100 MHz to 10 GHz, the wavelengths involved approach the physical dimensions of the components used in the container construction. Radiation can be channelled round the structure in wave guides formed by cavities in the cabin walls, and leakage is frequently found to come from joints in the structure. Any discontinuity in the structure can act as an efficient slot aerial but these problems are relatively easy to overcome.The midfrequencies, covering 100 KHz to 100 MHz are similarly dealt with by conventional screening and shielding methods. The low frequency band, covering 10 KHz to 100 KHz, is more of a problem because any discontinuity in the structure is likely to lead to the leakage of magnetic fields into or from the internal volume of the cabin or container. The conventional method for dealing with this problem is to make the cabin or container walls conform as closely as possible to a continuous sheet of material. To do this, all doors and hatches require to be close fitting and all contact points have to be kept scrupulously clean and under significant pressure. To achieve these aims add considerably to the complexity, weight and cost of the structure. Also, to maintain the integrity of the closure often requires expensive inspection and maintenance.The invention aims to provide a closure for an aperture in a radio screened enclosure which reduces the problem of leakage of low frequency fields, whilst still maintaining excellent high frequency performance.

Summary of the Invention According to the invention a closure for an aperture in a radio screened enclosure comprises a closure member movable between an open position in which the aperture is open and a closed position in which the closure member closes the aperture, the closure member having a first metal screening member with a first edge flange extending around the periphery of the closure member and the enclosure having a second metal screening member with a second edge flange extending around the periphery of the aperture, in the closed position the metal screening members overlapping around the periphery of the aperture with the first flange extending towards the second metal screening member and the second flange extending towards the first metal screening member in such manner that the flanges overlap around the periphery of the aperture, whereby the overlapping metal screening members substantially prevent leakage of incident low frequency fields in the enclosure.

The first and second metal screening members thus form a metal "skin" which may be on the inside surface or the outside surface of the enclosure. In a preferred embodiment, two such metal skins are provided, on the inside and outside respectively of the enclosure, each skin having the overlapping metal screening members and flanges of the invention.

The flanges preferably overlap by at least 40mm.

A container according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a horizontal sectional view through a closure of the container, and Figure 2 is a vertical sectional view through the same closure.

Referring to the drawings, the container has a vertical wall 10 with a rectangular door aperture 12 therein. The door aperture 12 is closable by a closure member in the form of a door 14 pivotally mounted by a hinge 16 about a vertical pivot axis 18 disposed on one side of the aperture 12.

The door 14 has a first metal screening member 20 with a first edge flange 22 extending around the periphery of the door 14 this screening member 20 effectively forming an outer skin for the door 14. The edge flange 22 extends towards a second metal screening member 24 forming an outer metal skin for the wall 10, this outer skin having a flange 26 set back a short distance around the periphery of the aperture 12. The flange 26 extends towards the first metal screening member 20 and overlaps the flange 22 of the first metal screening member 20. The first and second metal screening members 20, 24 and the flanges 22, 26 in effect provide an outer metal skin for the closure.

The closure also has an inner metal skin provided by an inner screening member 28 on the inside of the door 14 and an inner screening member 30 on the inside of the wall 10.

The screening member 28 has a flange 32 extending towards the screening member 30 and the member 30 has a flange 34 extending towards the member 28. The two flanges 32, 34 overlap so that the screening members~28, 30 and the flanges 32, 34 provide an inner skin for the closure. It will be noted from Figure 2 that the flanges are angled for rain drainage where they extend above and below the aperture 12. Also, the extremity of the flange 22 has a radio frequency seal or gasket 36 to seal against the member 24 and prevent the ingress of high frequency fields, and the extremity of the flange 34 has a further radio frequency seal or gasket 38 which seals against the member 28 and presents the ingress of high frequency fields. The hinge 16 is spring-loaded to urge the door to the closed position illustrated in Figures 1 and 2, to ensure engagement with the seals 36, 38.

It has been found that the overlapping arrangement of the metal screening members and the flanges screens the inside of the enclosure from fields having frequencies in the range 10 KHz to 100 KHz.

The invention removes the need for the contunity of a low impedance path (as in the prior art), thus avoiding the complexity, rigidity and weight of doors and frames to be reduced and allowing mechanical tolerances to be considerably less critical.

Claims

1. A closure for an aperture in a radio screened enclosure, comprising a closure member movable between an open position in which the aperture is open and a closed position in which the closure member closes the aperture, the closure member having a first metal screening member with a first edge flange extending around the periphery of the closure member and the enclosure having a second metal screening member with a second edge flange extending around the periphery of the aperture, in the closed position the metal screening members overlapping around the periphery of the aperture with the first flange extending towards the second metal screening member and the second flange extending towards the first metal screening member in such manner that the flanges overlap around the periphery of the aperture, whereby the overlapping metal screening members substantially prevent leakage of incident low frequency fields in the enclosure.

2. A closure according to claim 1, wherein the first and second metal screening members form a metal skin which is on the inside surface of the enclosure.

3. A closure according to claim 1, wherein tthe first and second metal screening members form a metal skin which is on the outside surface of the enclosure.

4. A closure according to claim 2 or 3, wherein two such metal skins are provided, on the inside and outside respectively of the enclosure, each skin having the overlapping metal screening members and flanges.

5. A closure according to any of the preceding claims, wherein the flanges overlap by at least 40mm.

6. A closure constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.