EMI Gaskets Research Articles

Study on Corrosion-Induced Shielding-Degradation of EMI Gaskets

The deterioration of the shielding performance of electromagnetic interference finger stock gaskets in a corrosive environment is investigated. The visualization of the real contact area shows a drastic reduction of the engaged active contact region between fingers and their mating surfaces in presence of corrosives residues. In fact, additional openings occur besides the “T-like” holes due to the porous nature of gaskets. This leads to a strong degradation of the shielding effectiveness. Modified Bethe's theory is used to estimate the equivalent circuit parameters while the shielding effectiveness in terms of ratio between two transfer functions is obtained upon applying the filter theory. Quantitative measurements carried out for different gasket types show a good agreement with calculated results, demonstrating thus the validity of the approach.

Solderable EMI gasket and grounding pad

Solderable EMI gasket and grounding pad

EMI gasket for plug connector with latch mechanism

EMI gasket for plug connector with latch mechanism

Electromagnetic Interference Shielding Reaching 130 Db Using Flexible Graphite

AbstractElectromagnetic interference (EMI) shielding effectiveness reaching 130 dB at 1 GHz was achieved by using flexible graphite (Grafoil). Due to the resilience of flexible graphite, it is particularly attractive as an EMI gasket. The high shielding effectiveness is due to the large specific surface area and large skin depth. In contrast, the shielding effectiveness was only 90 dB for polycrystalline graphite of low specific surface area.

Design, Analysis and Fabrication of a Graphite/Epoxy Electronics Enclosure Flanged Aperture, with Supporting Electromagnetic Interference Test Data

The structural design of a rectangular metal electronics enclosure for airborne or space applications is straightforward and contained in a number of texts. However, the design of a composite electronics enclosure, optimized for weight and structural and thermal load paths, has not been addressed. In particular, the design of flanges that attach the walls to one another or the enclosure to its cover is an important topic because of the need for EMI shielding and flange structural stability in a random vibration environment. Several carbon fabric/epoxy flanged aperture (two overlapping flanges with gap) designs were considered for integration into a composite electronics enclosure. The design evaluation was based on structural integrity, EMI shielding effectiveness, ease of fabrication, development time, number of parts, total cost, and total weight. The most promising design consisted of two overlapping "L" flanges with a double EMI gasket in the aperture. This design was analyzed for instability of the flanged aperture, local buckling of the individual flanges between fasteners, and bearing and shearout of the flanged aperture. Laminate configurations used in the structural analysis consisted of [(0°)]3, [(0°), (45°)] s, and [(0°), (45°), 0.076 mm thick syntactic foam core, (45°), (0°)]. The preliminary analysis indicated that the [(0°)] 3 laminate configuration would fail by local buckling between flanges. The [(0°), (45°), 0.076 mm thick syntactic foam core, (45°), (0°)] laminate had the highest margins of safety in overall flanged aperture instability, local buckling, bearing, and shearout. This configuration was thought to be the best lay-up because large margins of safety would be needed in random vibration to compensate for the unknown torsional and bending loads in the flanges. EMI shielding tests on a Ni plated carbon fabric flanged aperture from 200 MHz to 40 GHz showed that the geometry of the flange alone provided significant shielding over that of an open hole. The shielding effectiveness of the Ni plated carbon fabric/epoxy flanged aperture with EMI gasket was equivalent to that of a continuous solid Ni plated carbon fabric/epoxy panel. The [(00), (450)], and [(00), (450), 0.076 mm thick syntactic foam core, (45°), (00)] laminate configurations are currently being incorporated into a finite element model of the electronics enclosure.

Design of a cyclic contact resistance test device

The design and operation of a cyclic contact resistance test device for electromagnetic gasket materials is described. The device and associated instrumentation provide unique capabilities to measure electrical contact resistance for up to ten gasketed test assemblies as a function of make-and-break cyclic loading of the contacts. Resistance results for a custom gasketed contact design demonstrates that the test method is sensitive to both materials and lubrication used in the contact joint. The gasket cycler test system was designed and constructed to simulate the closure forces and mating action encountered by EMI gaskets in shielded facility access doors, hatchways, and cover panels.

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.