Shielding effectiveness evaluation of metalised plastics with signal source inside test console

Present generation electronics is found to replace metallic enclosures with moulded plastic ones for obvious advantages. On the other hand, radiation hazards from commonly used electronic equipment like TVs, computer monitors, etc. and their immunity to external electromagnetic (EM) fields has become more serious due to their proliferation into every walk of life. To comply with regulations, related to radiation hazards to ensure safety for the users and EM immunity, plastic/glass materials used for making commercial equipment enclosures are coated with conductive material for achieving electromagnetic shielding. In this context, a simple low cost test method for measuring the shielding effectiveness (SE) of metalised plastics become essential. The paper analyses the standard test procedure in use for the above-said SE measurement and brings out the difficulties in following the same. It describes a simple alternative based on the same principle. The test method has been validated up to 1 GHz. The method can be used to measure the shielding effectiveness of any specimen like glass, plastics, leather, etc. with conductive coating.