February 05, 2020 by Abdulwaliy Oyekunle
Digital devices, telecommunication systems and other electronic technologies transmit disruptive electromagnetic energy.
This is known as electromagnetic interference (EMI) and poses harm to the functionality and efficiency of such devices. As will be discussed, electromagnetic shielding and filtering are two chief techniques that electronic engineers adopt to reduce EMI in electronic devices.
Electromagnetic interference, or EMI, is the transmission of electromagnetic waves or energy by one electronic device to another electronic device that disturbs its performance (consider its functionality and efficiency).
All electronic devices are susceptible to EMI and the level of immunity to such interference varies from one device to another. EMI can be transmitted in devices either through conduction or radiation.
One type of electromagnetic interference is radiofrequency interference (aka RFI) is a type of electromagnetic interference that occurs in the radiofrequency range of about 100KHz to 1GHz. Other forms of EMI include electromagnetic pulse and electrostatic discharge.
A major form of electromagnetic interference: electrostatic discharge, or ESD. Pictured: sparks fly from an electronic component due to ESD.
Interference by conduction can happen via power and signal lines connected to a mains supply. This is common in television cables and antennas. Also, conducted EMI can either be differential or common-mode: the transmitted interference in differential mode occurs between conductor pairs, whereas in common mode, the interference happens between a group of conductors and ground. The path of common-mode interference can either be based on inductive or capacitive coupling.
Interference by radiation is the emission of electromagnetic waves by an electronic system or device to interfere with its performance or another electronic device via free-space propagation. The basic component in a radiated EMI is the electromagnetic wave. Such a wave has both electric field and magnetic field components, and they are perpendicular to both each other and to the direction of the propagating wave.
Ensuring electromagnetic compatibility (EMC) is a practical approach to designing an electronic device that is immune to electromagnetic interference and can therefore operate efficiently in its intended environment. It’s a helpful concept associated with the task of addressing concerns of an electronic device’s immunity to various forms of EMI.
There are various standards that exist to ensure an electronic device meets electromagnetic compatibility demands. Two of these standards are covered in the next subsections.
The international standard for EMC is regulated by the IEC (aka the International Electrotechnical Commission). The IEC has three departments or technical committees that make EMC standards for electronic devices. The three committees are CISPR (from the French translation of ‘International Special Committee on Radio Interference’), TC77 and TC65 (each ‘TC’ standing for ‘Technical Committees’ For more terms, check out the full list of TC standards).
The CISPR is responsible for making standards that offer protection of radio reception from interference sources. TC77 makes EMC standards for electronic devices that incorporates a horizontal safety function for devices and has an emission of electromagnetic waves that reach frequencies of up to 9KHz.
The seal of the United States Federal Communications Commission. Image Credit: Extracted from the 1995 FCC Annual Report via Wikimedia Commons.
The Federal Communications Commission (FCC) in the U.S. also regulates interferences from radio frequency devices like radio and televisions. The standard provides safety rules for human exposure to radio frequency. Part 15 of the FCC standard focuses on RF devices and provides policies and guidelines for designing RF devices to meet EMC standards.
There are also EMC standards for electronic devices used in the military. An example of which is the MIL-STD-461, which applies to U.S. military equipment.
Electromagnetic interference has become a major concern for engineers (particularly design engineers) as it undermines the efficiency of manufactured products. Electrostatic discharge destroys integrated circuit, or IC, chips and reduces their potential of being EMC-compliant. Electromagnetic radiation is also associated with health risks for electronic devices consumers.
In addition, EMI undermines the efficiency of communication in the telecommunication devices used in the military.
Components laid on PCBs are also susceptible to EMI. PCBs must be designed expertly to minimise interference. Good circuit designs on PCBs involve careful IC component selection, good cabling, and strong grounding. Each circuit should also have interference suppression components like filters, ferrite beads, and bypass capacitors.
To minimise electromagnetic interference in electronic devices, design engineers have to ensure a proper level of EMI shielding. The use of Faraday’s cage is one way that such shielding can be achieved. Materials suitable for shielding include metal sheets that have high resilience, high fatigue strength, and excellent corrosion resistance.
Apart from shielding, the use of EMI gaskets is another approach to preventing electromagnetic interferences in electronic devices. Gaskets provide continuous conductive paths as they are made of metals, such as beryllium copper (CuBe), and copper-nickel-tin alloy (or CuNiSn). Because of its high conductivity and low inductance, CuBe offers the best EMI reduction, and it also provides better magnetic shielding. (Gaskets can also be used as seals for removable discontinuities.)
Foils and plastic materials with conductive coatings may also be used to minimise interference.
For more techniques to avoid or minimise electromagnetic interference, also see our strategy article for Minimising EMI in Electronic Systems.
