EMC stands for ElectroMagnetic Compatibility. EMC shielding is a method which is used to protect any sensitive signals from external electromagnetic signals or from preventing the sensitive signal from leaking out and interfering with other surrounding signals. The shield protects PCB elements such as IC chips, connectors, and cables between PCs.
From total disruptions of a signal to simple disturbance in a communication line can be the result of electromagnetic frequencies affecting sensitive signals.
EMC Shield working process:
Preventing ElectroMagnetic Interference (EMI) or Radio Frequency Interference to impact sensitive electronics is the main purpose of the shield. A metallic screen is used to absorb the EMI that is being transmitted through air. The shield here is made up using the principle of Faraday’s cage, i.e., the metallic screen completely absorbs the surrounding transmitted signals resulting in a current production within the body of the screen which is then absorbed by the ground connection (virtual ground plane).
Materials used for EMC shielding:
Multiple processes and methods can be used for shielding, but the type of material depends on the type of electronics and frequencies involved. The size of the shielded volume, amount of signals blocked from transmission are few of the factors that affect the strength and range of frequencies to be absorbed during shielding.
To understand better let us go through few instances:
- Audio speakers have inner metallic casing to block EMI produced by nearby transmitting devices such as TVs.
- PCBs have a built in ground plane and a metal box placed over sensitive elements; and these components are surrounded by a faraday cage’s arrangement.
- Coaxial cables have EMC shield inbuilt wire construction. Other wires can be wrapped in foil. The foil needs to be attached to the metal to provide total coverage.
Magnetic materials can be easily used in environments where the magnetic field is below 100Khz range. Other methods of shielding include sheet metal, metal foam, conductive plastics, and mesh metal screening. The shielding doesn’t have to be a solid metal screen always, the shielding can vary from being regular placed holes, wire fencing. It is important to understand which part of the frequency needs to be particularly guarded against other applications.
There are multiple types of shielding. Let us go through a few:
- Enclosure Shielding: This shielding specialties in providing a comprehensive EMI shielding and Environmental sealing applications. The materials to provide the shielding consists of conductive elastomers, fabric over foam, conductive foam, wire oriented silicone, and combination mesh materials. These materials offer enclosure from abrasion resistance across a broad compression range, economical solution to applications requiring electrical conductivity across substrates, etc.
- Board Level Shielding: Surface mount shielding and through-hole shield configuration are available under one-piece, two-piece, and multi-zone shields – to create a broad specific shield.
Materials that offer excellent thermal properties over a wide range, the silicone based materials displace the air in uneven areas and increase cooling within the appliances are helpful in EMI/EMC shielding. These materials are equipped with features such as soft and excellent compression rates, thermal conductivity, RohS, REACH compliant.