Review of Current Test Methods Used to Grade EMI Gaskets by the Industry
The manufacturers of EMI gaskets currently use two test methods to grade their products. These test methods are shielding effectiveness as contained in MIL-DTL-83528, and transfer impedance per SAE ARP-1705. The transfer impedance test method provides accurate test data of ± 2 dB over the frequency range of 10 kHz through 18 GHz. In the performance of the testing, the test plates are constructed from the materials and finishes used by industry. The effects moisture and salt fog have on the shielding can be obtained. The shielding effectiveness test method is a modified MIL-STD-285 (IEEE-299) test. The modifications to the test methods provides levels of shielding or more than 60 dB above that which can be realized in actual use. The force of the gasket against the test plates is uncontrolled and can exceed 400 pounds per inch. The test surfaces are brass and aluminum.
KeywordsShielding effectiveness Transfer impedance MIL-DTL-83528 SAE ARP-1705 EMI gaskets EMI gasketed seam EMI gasketed joint Shielding practice Shielding theory Displacement current Current density
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