Transfer Impedance testing of EMI gasketed joints to 10 GHz for cost effective design

There are presently two (2) methods used by industry to grade the ability of EMI gaskets to seal seams in the chassis used to house Electronic equipment. These are the “Shielding Effectiveness” test method contained in MIL-DTL-83528 and the “Transfer Impedance” test method contained in SAE, ARP-1705. This paper describes (1) the development of the two methods for testing gaskets; (2) the faults and advantages of the two methods, (3) provides mathematical equations that can be used to predict the actual shielding obtained from a gasketed maintenance cover as a function of the transfer impedance of the gasketed cover; (4) illustrations that show that the shielding obtained from a gasket is a function of the joint surfaces as well as the conductivity of the gasket; (5) the effects a moisture soak has on the shielding offered by gasketed joints; and (6) the effect the storage in an office environment can have on the conductivity of a silver elastomeric gasket.