Shielding Effectiveness of EMI Gasketed Joints

EMI gaskets are used extensively by the electrical/electronic engineering community to assist in inhibiting the flow of radiated electromagnetic fields into and out of electronic equipment. Shielding effectiveness tests are used extensively by the manufacturers of EMI gaskets to grade their products. The assumption made by the design engineering community is that the shielding effectiveness as presented in the data is what they will receive in their equipment. This assumption is not true due to the errors associated with the shielding effectiveness testing of the gaskets where errors of as much as 80 dB (10 000 times) can be represented. The paper describes briefly the problems associated with the shielding effectiveness test methods currently used and provides a detailed method of calculating the shielding effectiveness of an EMI gasketed joint using transfer impedance test data.