Electromagnetic Interference EMI Shielding

Antistatic additives are capable of modifying properties of plastics in such a way that they become antistatic, conductive, and/or improve electromagnetic interference shielding (EMI). Carbon fibers, conductive carbon powders, and other electrically conductive materials are used for this purpose. 

Unfilled skin/core with conductive filler Electromagnetic interference shielding (EMI) Computer housings... 

Electromagnetic interference shielding effectiveness of about 18 dB was achieved with 10 vol% MWCNT-PMMA film which was found to be primarily an EMI absorbing composite material. Figure 7.15 shows the variation of EMI shielding effectiveness due to reflection... 

The low resistivity of a cfrc enables the concrete to be used as an EMI shield and also function as a smart structure, with a direct relationship between the electrical resistivity and compressive stress [56]. Chung and co-workers have investigated carbon filament cement matrix composites for electromagnetic interference shielding. [57,58]. 

The twists of twisted pair cable act as a shield against radio frequency interference (REI), and electromagnetic interference (EMI), and against the cross talk interference that a wire exerts on nearby wires the more twist the less interference. Telephone wires can use large numbers of pairs. In most cases the pairs are not shielded with braiding or foil, as shown in Eigure lb for data communication wire. Data communication wires work at very high... 

Electromagnetic interference (EMI) testing has become more prevalent for materials that either emit or are affected by EMI. Shielding efficiency (SE) of materials is deterrnined by measuring electric field strength between a transmitter and receiver with or without the presence of the material under test. Several researchers have suggested a correlation between volume resistivity and SE values (300,301). 

Fig. 10.4. Mounting of electromagnetic interference (EMI) filters inside a shielding box.

An important application of ferrites is for shielding sensitive equipment (e.g. data-processing, telecommunications and audio-visual equipment) from electromagnetic interference (EMI). Both NiZn- and MZn-based ferrites components are capable of suppressing interference up to the GHz frequency range by virtue of the high impedance they present to high frequency currents. The ferrite parts are made in a variety of shapes to enclose the leads to be shielded, as shown in Fig. 9.17. 

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