IEEE 1302-2008 pdf download IEEE Guide for the Electromagnetic Characterization of Conductive Gaskets in the Frequency Range of DC to 18 GHz
Furthermore. the cross section of the gasket (circular, rectangular) and the mechanical design of applicationflat/flat surfaces, groove structure, compression rate, or closing pressure, etc) may have a dominant effecton the final behavior or the gasketed joint, Also, special care must be taken for the mating surfacesconcerning possible corrosion over the lifetime and the requirements set by the RoHS restrictions.
The gasketed joint can behave like a section of waveguide filled with conductive materials. When thishappens, the gasket and aperture will exhibit complex radiation and transmission properties, and couplingthrough this aperture is likely to be of greater importance to shielding effectiveness (SE) than the enclosureitself. Where the gasket does not appear homogeneous, it is not safe to assume that the current through thegasket is uniform or that it is determined by the shield. The characteristics of the incident field should alsobe considered. the radiation characteristics of the total aperture must be recognized, and the propagation otthe coupled wave through the “loaded”aperture must be taken into account.
Shield current encounters both the contact impedance between the gasket and the impedance of the gasketitself. On the contact surfaces, there are often films of metal oxides and sulfides, paints, cleaners, dust, dirtand environmental deposits. Such films will likely be present on gasket surfaces as well.
NOTE-Many surface films or treatments are nonconductive. Depending on the compression-deflection properties otthe gasket material, the nature of its conductive elements (e.g, “gritty” particles, oriented wires, knitted wires, etc.).and the closure force applied, certain gaskets will bite through such films more effectively than others. This “biting’may or may not be desirable depending on the application environment as it may open a site for corrosion or galvanicaction over the life of the equipment, Environmental testing should be considered for every application.
WARNINGSpecial attention must be given to the requirements as set by the RoHS restrictions.
The path for current from the shield to the gasket will be through the ridges and valleys on the matingsurface that result from machining or casting imperfections to the contacted portions of the gasketmaterials. The contact impedance between the gasket and the parent shield can be a significant factor in theoverall behavior of the gasket. This contact impedance will have reactive components in addition toresistance. For example, there is usually some capacitive coupling between the contact surface and theconductors in the gasket
In addition to the impedance of the gasket and the gaske-to-shield interface, the shield current encountersthe resistive and inductive elements of the shield itself. and a portion flows around the gasket via the straycapacitance between the two pieces of parent material. This capacitor is labeled as shield-to-shieldimpedance”in Figure 2.
In some cases, the gasket characteristics may be masked by the behavior of the test fixtures, and care mustbe taken when making the interpretation about the applicability for an actual design, starting frommeasured data, collected from a measuring setup performing under other electromagnetic conditions.
Thus, the current path through a gasket is a complex network like that illustrated in Figure 2. As complexas this network appears, it is actually somewhat of a simplification. Particularly at very short wavelengths.the gasketed joint will also behave in somewhat the same way as the braid of a coaxial shield, whichpermits energy to “leakthrough. Depending upon the specific configuration of the conducting elements ofthe gasket, these openings can render the gasket practically transparent at particular frequencies or overcertain frequency ranges (see Quine [B28)
IEEE 1302-2008 pdf download
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