Real Life Experiences in the Construction of a Large Laboratory having High Quality Electromagnetic Shielding

This paper describes the shielding behavior of a copper shielded laboratory from surrounding electromagnetic waves with respect to two different techniques used for joining the sheets for shielding. An investigation has also been done to study the effect of a second shielding layer inside the laboratory in the form of a metallic box. The shielded laboratory has been constructed to study the partial discharge and other types of electromagnetic signals, where it is very important to reduce external electromagnetic interference to carry out the investigations properly. The purpose of the shielded laboratory is to attenuate the incoming electromagnetic waves, primarily the communication signals, inside the laboratory and to reduce the external electromagnetic interference to such a level that it would not interfere with the signals to be tested. To study the attenuation behavior of the laboratory with respect to electromagnetic waves, the testing method adopted is the conversion of electromagnetic wave to a voltage level corresponding to the amplitude of the incident electromagnetic signal strength. The signal levels are measured initially at outside and then at different places inside the shielded laboratory to compute the attenuation. The results presented in this paper reflect the attenuation characteristics of the electromagnetic waves in the surrounding neighborhood within the copper shielded laboratory with (i) screwed and overlapped sheet joints, (ii) gas-welded sheet joints using a copper-alloy solder and (iii) a second shielding layer in the form of a box made up of galvanized iron sheet placed inside the laboratory.