Shielding Computers With Metal-Coated Glass

54 EE September COMPUTERS WITH METAL-COATED GLASS by Bill Pressdee, BSc, CEng, MIEE Shielding for electromagnetic and radio-frequency interference (EMI/RFI) has two distinct functions. In the first instance, its purpose is to keep unwanted electromagnetic fields and unwanted transmission from interfering with sensitive electronic equipment. A second reason that has come about in recent years is keeping transmissions inside a given system. For many years a shielded room, or Faraday cage, has been a prerequisite for exact setting up of electronic circuitry in conditions free from extraneous inter- ference. Early shielded rooms, totally enclosed by an earthed metallic mesh frame were, however, often expensive to construct and claustrophobic. The puncturing of the screen to in- troduce ventilation often created ad- ditional problems with the result that air flow was minimal. As a result of these indifferent working conditions much of the purpose of the Faraday cage was fre- quently co...