How to Classify the Materials Used in Electromagnetic Shielding

The global EMI shielding materials market is expected to hit $10.45 billion by 2023, according to Stratistics MRC. But this growth should not come as a surprise, considering the rising demand among hybrid and electric vehicle manufacturers, the development of the telecom industry worldwide, and the addition of EMI shields to electronic products. Unfortunately, the market is yet to harness its full potential owing to the restrictions relating to the high cost of developing EMI shields as well as the strict regulatory frameworks. However, electrical engineers and designers can save a considerable amount of money by choosing the right material based on their requirements. And, given a large number of shielding materials on offer in the market, they are spoilt for choice. Check out a few standard options available below:

EMI Shielding Metals

Metals conduct electricity extremely well and are capable of absorbing, reflecting, and transmitting electromagnetic interference. Their ability to conduct heat and electricity is the primary reasons why metals are used in multiple applications. Adding metal covers and shields prevents high-frequency electromagnetic radiation from escaping the device.

The most commonly used metal for developing shielding enclosures is mumetal, a high permeability alloy composed of 79.5 percent nickel, 14 percent iron, 5 percent copper, and 1.5 percent chromium. Other metals used in EMI shielding include aluminum, nickel, silver, brass, metalized plastics, stainless steel, and conductive graphite/carbon composites. Many manufacturers, however, hesitate to use metal shields due to the risk of corrosion.

Reflection-based shielding applications generally use lightweight magnesium enclosures that extend across the full frequency spectrum. In case of absorption, die-cast enclosures made of equal weights aluminum and magnesium, offer nominally equivalent SE (shielding effectiveness). That’s because the lower density of magnesium is offset by aluminum’s higher conductivity. On the other hand, EMI shielding enclosures developed from die-cast magnesium alloy provide several advantages compared to both alternative metal and plastic housings.

Plastic Materials

Plastic is a natural insulator, and neither reflects nor absorbs electromagnetic interference. Thermoplastics fail to impede most energy waves entering or exiting the enclosure readily, which leads to interference problems. For this reason, technical methods are used to alter the electrical conductivity of the substances through:

• Conductive Coating: While decorative, plumbing, automotive products, and appliances rely on metallic plating and coating on plastic, conductive applications require metalized plastics. Multiple coating techniques are used, including ion plating, foil tapes and laminates, conductive paints, vacuum metallization, zinc flame spraying, electroless plating, and electroplating.
• Compounding: Traditional plastic materials boast high resistivity and serve as electrical insulators. However, they can be made conducting through the use of conducting materials, especially carbon black. Due to the graphite nature of the material, carbon black is a semiconductor, but when used as filler in plastics and rubbers, it imparts conductive or antistatic properties. Graphite fibers are also commonly used in high-performance applications, normally because of their reinforcing abilities. So, plastic substances that are inherently nonconductive can receive conductive properties through the implementation of different metalized or metal reinforcements and fillers.
• ICPs or Intrinsically Conductive Polymer: The discovery of the metallic properties of molecularly doped polyacetylene in 1977 opened the floodgates for the use of electronically conducting polymers in various applications. Conducting polymers are regularly used as active electrode substances in optoelectronic devices, energy storage, display gadgets, along with their envisaged application to manipulate electromagnetic radiation and dissipate electrostatic charge. Thus, ICPs are used as alternative materials to shield products from the effects of EMI. Among the conducting polymers, polypyrrole (PPY) and polyaniline (Pan) are mainly used in shielding applications.

Studies are underway to find the perfect EMI shielding material across a broad spectrum of applications, but until then engineers and designers have several metallic and non-metallic options at their disposal. The synthetic materials, like PPY and PAn, are especially being considered by many industries due to their commercial viability, less weight, and non-corrosive properties.