EMC – Electromagnetic Compatibility

Electromagnetic compatibility is the control of Electromagnetic Interference (EMI) so that unwanted effects are prevented. Electromagnetic compatibility (EMC) is the ability of an electrical system or equipment to function as designed whilst exposed to an electromagnetic environment. This is achieved by limiting the unintentional generation, propagation and reception of electromagnetic energy, which may cause unwanted effects such as Electromagnetic Interference (EMI) or physical damage to a piece of equipment.

EMC – Issues

Electromagnetic Compatibility has four main issues: Emission, Susceptibility, Immunity and Coupling. The study of EMC looks at the unwanted emissions and countermeasures which can be taken to reduce unwanted emissions.

    • Emission refers to the generation of electromagnetic energy, this may be either deliberately or accidental. This energy is then passed into the surrounding environment.
    • Susceptibility is the tendency of electrical equipment to malfunction or break due to the presence of unwanted emissions which is known as Radio Frequency Interference (RFI).
    • Immunity is the opposite of susceptibility, being the ability of electrical equipment to function as designed in the presence of RFI.
    • Coupling is the mechanism by which the emitted interference reaches the system or component.

Electromagnetic Compatibility mitigates interference by addressing any of these issues. In practice engineering techniques, such as grounding and shielding apply to all areas.

Electromagnetic Interference (EMI)

Electromagnetic interference divides into several categories and can be generated from:

  • Continuous Interference: audio frequencies, radio frequencies, broadband noise
  • Pulse or Transient Interference which are usually isolated or repetitive such as: switching actions, power line surges, electrostatic discharge, lightning, nuclear magnetic pulse, non-nuclear electromagnetic pulse (usually a weapon) and electric motors.

EMC Controls

The effects of electromagnetic interference are often damaging and pose an unacceptable risk to electrical systems and technology. EMC control is necessary to control these interferences and reduce risks to an acceptable level. A single design improvement often will reduce both emissions and susceptibility. Below are common controls used to mitigate interference:

  • Grounding earthing
  • Shielding cables
  • Shielding housings: A conductive metal housing will act as an interference shield however, to access the housing internal space, it will usually be comprised of a box and a lid. This may provide a space for interference to leak through. To stop this from occurring an RF gasket may be used.

A combination of these controls may all be used at once however, often one approach will suffice to reduce the risks to an acceptable level.

EMC History

The earliest Electromagnetic Compatibility (EMC) issues where related to lightning strikes on ships and buildings, prompting the introduction of lightning rods and conductors around the mid-18th century. Providing basic protection against Electromagnetic interference (EMI)During the 19th century the widespread use of electricity generation and power lines saw problems arise with equipment short circuiting, fires and shock hazards when the power supply lines where struck with lightning. As a rectification power stations where supplied with circuit breakers to further protect these systems and equipment.Electrostatic Discharge (ESD) began to present as an issue with accidental electrical spark discharges occurring in coal mines and during aircraft refuelling often with devastating results including fire and explosions. Static dischargers where developed to dissipate built up static electricity back into the atmosphere or ground to prevent accidental discharge.From the 1970’s modern circuitry grew rapidly, which increased switching speeds (increased emissions) and lower circuit voltages (increase susceptibility). This lead to nations to issue directives to manufacturers that set out the specific requirements of electrical equipment, that needed to be met before they could be sold on markets.From then to know there has been several major technological advancements including, mobile communications, Wi-Fi and broadcast media channels which has led to further regulation and information regarding modern Electromagnetic Compatibility.

Whilst there have been many developments in technologies throughout these years, the underlying need to protect electrical equipment and systems has never been more vital. Modern systems are more precise and expensive than ever and must still be protected against unwanted interference and failure. When complex electrical systems are engineered adequate controls must be designed in to mitigate unwanted risks and failures.