Electro-Magnetic Interference Shielding: Introduction to and Materials for EMI Shielding
Updated: Dec 17, 2021
EMI shielding allows to protect electronic devices and equipment from external electromagnetic signals. In this post we will answer the following questions: What is EMI shielding? How is it created? Why do we need it? Then, we will introduce the main materials used for EMI shielding applications.
What is EMI Shielding?
EMI shielding aims to protect electronic devices and equipment from external electromagnetic signals. It also avoids generated signals from interfering with nearby components. It is an isolating barrier stopping the leakage of electromagnetic fields capable of interfering with surrounding components, devices, and signals. This protection is made possible by using specific functional materials mainly based on metals and carbon. Non-functional materials, such as ceramics, cement, and polymers, can be used but usually in combination with functional materials.
How is EMI Shielding created?
Electro-Magnetic Interference is translated by the blending of different signals (conductive, capacitive, radiative, magnetic) from multiple systems.
An interference, i.e., a disorder, is created by an external source which is then perceived by the receiver. The disturbance can be due to a natural cause/source (lighting, solar radiation, etc.) or generated artificially (mobile network, radio waves, electronic devices, etc.). Once the interference reaches the receiver, the signal of the concerned device is altered.
This phenomenon leads to the disruption of electronic devices, and equipment in multiple applications such as medical equipment, aeronautic electronics, industry, etc. These phenomena can be continuous or intermittent interferences.
Why EMI shielding?
EMI is becoming a hot subject in electronics development due to the large and spreading use of wireless communication, portable consumer electronics devices, and other electronic devices mainly in industry, medical, aerospace, aeronautics, and automotive domains.
To allow these devices to function properly without signal disruption or disorders generated by interference, EMI shielding solutions must be developed and applied. Furthermore, radiation hazards resulting from the use of electronic devices need to be attenuated and isolated for human health reasons.
Materials usually used for EMI shielding are of relatively high conductivity, i.e., electrical resistivity lower than 10-2 Ohm.cm. Besides, specific surface area also enhances the shielding capacity of a material. EMI shielding can be realized in 2 ways: (i) reflection of the radiation, (ii) absorption of the radiation.
In the first case, radiation is reflected from the shielding material and redirected towards the immediate environment. Absorption is preferred to reflection for multiple reasons:
Radiation may be harmful to the environment and the human body.
In case of stealth applications to avoid that the bounced radiation can become detectable by the radars.
Nowadays, most research and development studies are focusing on nano-structured materials. Indeed, nano-structuring shapes the material in a way that reduces the reflection phenomenon and enhances the absorption shielding mechanism. Furthermore, nanomaterials and/or nano-structures are of higher surface areas compared to micro-structures and thus allow better shielding properties.
Shielding effectiveness is then governed by multiple criteria such as surface area, conductivity, and the dielectric behavior of the shielding material.
Metals are used to absorb, reflect, and transmit EMI. They are mainly used in EMI shielding thanks to their thermal and electrical conductivity. Metals can be used in bulk form (Al sheets), or in coating forms (Al, Cr, Fe, Ni, Cu, Ag, etc.). Coating can be performed by electroless deposition of the metal, thermal treatment, spray coating, printing, metal organic deposition, etc.
Magnetic metals such as Ni/Fe and stainless steel are very useful for EMI shielding by absorption mechanism.
Many types of carbon materials can be used for EMI applications: graphite, graphene, carbon nanofibers, carbon nanotubes, etc. Although they have low conductivities, carbons are excellent absorbers of electromagnetic radiation
Hybrid materials (mixing different shapes and morphologies of carbons or mixing carbons with metals) are being developed nowadays to optimize EMI shielding capacities.
Other materials can also be used for EMI but at a low range and frequency compared to carbons and metals:
✔ Ceramics (silicon and titanium carbides, Fe3O4) mainly combined with metals, carbons, or conductive polymers;
✔ Cement-based materials: those are cement materials with enhanced EMI shielding properties thanks to the incorporation of carbon fibers, conductive particles, etc.
✔ Metal-coated polymers, plastics with embedded metal foils of Al, Cu or Ag, and conductive polymers (Polyaniline, Polypyrrole, etc.)
✔ EMI shielding tapes and laminates.
✔ The EMI shielding market was evaluated at $6.2 billion in 2021 and is expected to reach $7.7 billion in 2026 (CAGR = 4.4%).
✔ Conductive coatings and paint technologies have the largest share of the market.
✔ Asia Pacific (APAC) is expected to have the highest growing range during 2021-2026 period mainly China, Japan, and India.
EMI shielding addresses multiple markets such as:
✔ Consumer electronics
✔ Aerospace and defense
✔ Robotics and industry 4.0
The major players in this market are:
✔ 3M Company,
✔ PPG Industry,
✔ And many others.
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