Electromagnetic Shielding

    Electromagnetic shielding

    This is not normally a consideration for architectural applications but there are projects where the choice of glass is important to either let signals through the glass or to prevent them.  An example of an installation where the transmission is required to be high is the building of an envelope protecting a transmitter.  An example of the opposite is where sensitive data is held in a building and there is a concern for electronic eavesdropping. 

    With architectural glass the opportunity to vary the thickness away from the standard product qualities is very limited.  The thickness and tolerance of glass is determined within BS EN 572.  Float glass depending on its thickness can have an attenuating effect on a narrow frequency band and if this is critical for the location advice should be sought to ensure the chosen glass thickness does not coincide with the required transmission.

    For most installations using insulating glass units at least one of the panes has a coating to control thermal losses or to provide solar control.  The coatings tend to be conductive and also affect radio wave transmission.  The coatings are varied in their chemical composition and depending on the construction there can be a capacitance effect.  These effects can be harnessed to stop electromagnetic signals penetrating the building through the glass.  A basic common product used in buildings of all sorts is  Pilkington K Glass™ .
     
    Pilkington K Glass™ and radio waves

    Pilkington K Glass™ is float glass with a low emissivity coating applied to one surface. The product is designed to be used in insulating glass units to achieve substantially better performance than ordinary insulating units by reflecting long wave electromagnetic radiation (I.e. heat radiated by objects in a room at ordinary temperatures), back into the room.

    The type of coating which performs this task is normally an electrical conductor, and the Pilkington K Glass™ coating is no exception. In addition to operating as a good heat reflector, low emissivity coatings also tend to reflect parts of the electromagnetic spectrum used for radio transmissions, particularly those in the VHF and UHF bands.

    If Pilkington K Glass™ insulating units are glazed into a structure which contains large quantities of electrically conducting material, for example a steel frame building with metal sheet formers for concrete floors or to a lesser extent, reinforced concrete frame buildings, the overall effect can be to reduce considerably the penetration of radio waves into and out of the building. This, effect may interfere with the transmission of radio signals, although not to an extent which would be regarded as electromagnetic security.

    Normally there would be other, non-vision, areas of the cladding which would be transparent to radio waves, but if aluminium or steel cladding or over cladding is installed, the overall effect on radio transmission may be considerable.

    Multiple Pilkington K Glass™ coatings in a single glass or insulating unit can be used to effectively prevent the passage of radio waves when the building or rooms are deliberately designed as a Faraday, Cage (all surfaces conductive and electrically connected).  The use of two panes of Pilkington K Glass™ for the deliberate control of signals relies on other factors within the building to ensure that the system works as a whole.  Please seek further advice if this is a requirement.