Electromagnetic interference (EMI), caused by unwanted electromagnetic disturbances, impairs the performance of electronic systems. Therefore, the primary requirement of any material enclosing an electronic device is for it to shield against EMI. A potential source of EMI would include any devices or circuits carrying electric current while barriers placed between emitters and susceptors such that the strength or potential interference caused is diminished are EMI shields. EMI shields work by absorbing, reflecting, or transmitting radiations and their effectiveness depends upon the material used, its design, and the service conditions.
EMI shielding is a significant technology used across industries like the automotive, telecommunications, defence, and aerospace industries. Particularly in Industries with requirements for high performance electronics and accuracy, EMI shields are used in the protection of sensitive components in drones, trucks, helicopters, consumer electronics and control panels and the quality of such shields is considered crucial in combating strong disruptions.
Metal or Plastic - The Better Shielding Material
Given that metals are innately conductive, they can reflect and absorb EMI to a large extent, however, the degree to which a metal can shield against EMI depends on the frequency and nature of the radiation that it is exposed to, the components of the radiation, certain properties of the metal like conductivity and magnetic permeability, and the distance between the source and the shield. Furthermore, the raw material costs are low, structural strength is high even in the case of thin-wall designs, and increased durability.
Plastics, that are inherently insulative in nature, are by themselves ineffective EMI shields. Therefore, there is a dependence of plastic enclosures on surface modification or the integration of metal particles to meet the requirements of shielding. However, it is important to note that both surface modification, as well as the incorporation of metal particles, are expensive to implement, and in the latter case, there would be a resulting decline in tool (die) life.
Magnesium in Die-Cast Shielding Enclosures
Magnesium has a low density, low heat capacity, very low solubility for iron, excellent fluidity. Consequently, it is lightweight, can attain high rates of production, provides a major basis for superior tooling life, and can be cast into thin walls with minimum draft and dimensional accuracy. Moreover, magnesium has its own set of benefits when it comes to shielding by reflection and shielding by absorption. In the case of reflection, the weight-saving benefit of magnesium enclosures is not limited as it extends over the entire frequency spectrum.
When it comes to shielding by absorption, magnesium when compared to aluminum is equivalent in terms of shielding effectiveness on an equal weight basis. This is because the lower density of magnesium offsets the higher conductivity of aluminum. However, with increasing frequencies, the required wall thickness declines progressively with respect to a given level of shielding effectiveness. When the frequency is higher than roughly 1 MHz, the thickness is defined by castability (fluidity) limits and structural integrity requirements. Therefore, the lower density of magnesium becomes advantageous due to its thinner wall casting ability and lower density. As a result, die-cast magnesium is relatively lighter and cost-effective when compared to die-cast aluminum.
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