EMI and RFI Shielding Information
Image Credit: Compac Development Corporation; Intermark USA, Inc.
What are EMI and RFI Shielding?
EMI and RFI shielding includes coatings, gaskets, enclosures, sealants, resins and other products or materials that block out electromagnetic interference (EMI) and radio frequency (RF) interference.
EMI and RFI
EMI, also known as RFI, is any electromagnetic radiation or disturbance which is emitted from an electrical circuit or electrical component that causes interference or interruption of other systems. Sometimes EMI is associated with high-frequency interference while RFI is associated with interference of lower frequencies within the electromagnetic spectrum. In the United States, the Federal Communications Commission (FCC) establishes limits for EMI and RFI in order to prevent interference with communications devices and systems.
Selection of Shielding
When selecting EMI and RFI shielding, industrial buyers should consider the different forms of shielding, available, the material types they exist in, and important design features.
Forms of Shielding
The form is integral to a shielding's application, as it determines what system the product is designed to shield or protect. Shielding can be an addition to a system or an added feature of a system that already serves another function.
- Coatings or paints are thin films that can be deposited on materials to add or enhance certain properties. In addition to EMI shielding, they also can provide color, conductivity, corrosion resistance, and various other properties.
- Enclosures are used to house a system or component. In the case of EMI shielding, these are usually electrical or electronic components. In addition to blocking EMI, an enclosure can provide electrical and static insulation as well as protection from harmful environmental conditions.
- Gaskets are used to prevent fluid or gas leaks by providing a barrier between two mating surfaces. EMI gaskets are gaskets used in electrical systems incorporating EMI shielding components.
- Casting resins are plastic or elastomer compounds used to cast parts or molds or to form a structure in place. Casting resins usually consist of two part (A+B) systems that are cast into open molds or forms. EMI shielding casting resin materials can be cast into stock or custom shapes to be used as shielding for a system.
- Encapsulants are compounds used for the sealing or covering of an element or circuit for the purpose of mechanical and environmental protection.Typically, the encapsulant layers are not more than100 millimeters thick.
- Adhesives are organic or inorganic chemical compounds designed for joining components.They require clean surfaces that are compatible with the adhesive.
Selecting the right EMI and RFI shielding involves choosing between different material types. The most commonly used shielding materials are metals, but other types include elastomers, plastics, and composites. Material composition contributes to important design properties including electrical conductivity (or resistivity), strength, hardness, static resistance, and thermal conductivity.
Some specific features of EMI and RFI shielding may be requirements for a particular operation. Since shielding generally protects some type of electrical component or device, conductivity and ESD control are typically important features.
- Electrically conductive shielding materials provide electronic devices protection from EMI while also allowing flow of electrical with less resistance or losses.
- Anti-static or ESD control shielding materials provide protection from electrostatic discharge in addition to EMI shielding, making them ideal for electronic systems in environments where static buildup could occur.