Electromagnetic or radio frequency interference is a disturbance that occurs in electrical circuits due to either electromagnetic induction or radiation from a secondary source. This can interrupt or degrade the performance of any circuitry. Also, it may result in data degradation or complete and total data loss.
To prevent EMI or RFI, shielding must be used to protect systems from these interferences. Examples of EMI or RFI that everyone has experienced, at one point or another, is when a mobile device causes interference with speakers producing a choppy noise. Or when WI-FI signal interferes with a speaker system. Shielding can correct this problem by providing a barrier that isolates the internal components from external signal interference.
Electromagnetic waves consist of two oscillating fields. One of these is the electric field and the other a magnetic field. Every device is either an emitter (external device) or susceptor (primary device). The external device generates noise and the primary device is susceptible to that noise. Any system can be either or both an emitter or susceptor. Any barrier placed between an emitter and a susceptor can diminish the strength of the interference and can be thought of as an EMI shield. The losses in field strength from a shield are a function of the material (permeability, conductivity, and thickness), frequency and distance from the external source to the actual shield.
EMI shielding materials are used to provide an electrically conductive seal for electronic equipment opening and housing covers to prevent or limit electromagnetic interference in EMI shielding gaskets. There are many types of EMI shielding and some of the mainstream materials include conductive silicone rubber and conductive nickel-graphite filled with silicone.
The Silicone rubber EMI shielding gasket’s main advantage is its environmental sealing over a broad temperature range. The EMI gasket is typically silicone rubber or fluorosilicone rubber with embedded silver plate aluminum particles. Silicone rubber has high resilience, high temperature stability, and are generally unaffected by aging and degradation from sunlight and ozone.
A conductive Nickel-Graphite filled silicone gasket is a compressible 30 to 40 durometer material. EMI shielding integrity and dimensional stability reduce wear and tear during handling and assembly.
Other options for dealing with electromagnetic interference are EMI absorbing materials. This thin flexible material absorbs EMI by converting the EMI energy into heat that with dissipate to its surrounds.
Material & design selection will Depend on what you are shielding and how much signal interference you wish to limit. Options are available from EMI shielding to simply connecting the primary device to a filter to eliminate unwanted noise. Whatever the chosen method, eliminating noise is a must when designing a system to operate properly without data obstruction or total data loss.
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