1. Field of the Invention
This invention relates to a closure arrangement incorporating an RF seal, i.e. a seal which prevents the transmission of radio-frequency radiation. Such a closure arrangement is particularly useful in a transportable shelter for electrical equipment which is vulnerable to RF radiation.
2. Description of the Prior Art
It has been proposed to provide for such a transportable shelter a closure arrangement comprising a hinged door in a frame in whose rebate is fixed an RF seal. The door, the frame and the rest of the shelter are electrically conductive at least on the outer surface, and the purpose of the seal is to ensure electrical conductivity where the door meets the frame, so that all the incident RF radiation is absorbed.
One problem with such shelters is that the lower, horizontal edge of the door frame is particularly susceptible to contamination and damage in service when operators move in and out of the shelter: the RF seal may be broken or deformed, and may be contaminated with soil or grease or ice, for example. This may significantly impair the RF seal.
A further problem of the transportable shelters described above is the general deterioration of efficiency of the RF seal with use, due to contamination. Moreover, even before the RF seal becomes contaminated, the efficiency of the seal is affected by any irregularity in the surface of the seal or of the edge of the panel member which faces the seal, arising from manufacturing defects or accidental damage.