What is Electromagnetic Interference?

Electromagnetic interference (EMI) is a phenomenon that occurs when the operation of an electronic device is disturbed by an electromagnetic field and typically occurs when the device is close to an electromagnetic field, which disrupts the radio-frequency spectrum. This can also be referred to as radio-frequency interference (RFI).

EMI can arise from various sources, both natural and man-made, and it can take on a variety of characteristics dependent upon its source as well as the nature of whatever mechanism is giving off the interference. 

In a perfect world, electromagnetic interference would not be present; it is an unwanted signal at the signal receiver.

There are various methods used to prevent and reduce the level of interference with electronic devices because it can affect circuits and prevent them from working correctly.  

TT Electronics is dedicated to staying on top of the competitive landscape engineers are faced with when designing electronic devices and developing new ways to prevent EMI from damaging circuits. 

In this article, we dive into discussing the history of electromagnetic interference and what causes it, best practices to prevent or reduce electromagnetic interference, and the difference between EMI and EMC.


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Chapter 1 

Brief History of EMI

Electronic interference formally gained recognition in 1933 when a subcommittee of the International Electrotechnical Commission (IEC) joined in Paris under the name of CISPR (International Special Committee on Radio Interference). The sub-committee was created with the attempt to gain more information on the long term effects that could arise from radio-frequency technology. 

With the rise in popularity of radio and its debut as a must-have household appliance during the Great Depression, the electronics community began to notice both intentional and unintentional RF transmissions that began affecting electrical systems. 

As a result, not only did awareness of EMI begin to grow in the electronics community, but by 1934, CISPR started producing and distributing specific requirements. 

These requirements consisted of the recommended allowable emissions and immunity limits for electronic devices, which have evolved into much of the world’s EMC regulations, according to EMI Solutions Inc

Following the 1960s, researchers increasingly became more concerned with electromagnetic interference.

For example, in 1967, the US military issued “Mil-Standard 461A,” which set ground rules for testing and verification requirements for electronic devices that were used in any military applications, including emissions and susceptibility limits for any new electronic equipment. [source]

In addition, in 1979, the Federal Communications Commission (FCC) imposed legal limitations on electromagnetic emissions from all digital equipment.

By the mid-1980s, EU member states opted to take a number of new approach directives to standardise technical requirements for various products, so they did not end up creating a trade barrier. 

An example of this is the “EMC Directive 89/336/EC, Article 2” which states it “applies to apparatus liable to cause electromagnetic disturbance or the performance of which is liable to be affected by such disturbance.”

It’s important to note that this was the first time that a legal requirement on immunity was enforced as well as a specific emissions apparatus whose intention was for the general public.

As the years passed and electronic devices became smaller, faster and more powerful, these regulations mentioned above have continued to evolve because with these new systems improvement means they have a greater ability to interfere with operations of other electrical systems. 

Present-day, many countries have similar requirements in place for products to meet some level of electromagnetic compatibility (EMC) regulation. 

Chapter 2

Electromagnetic Interference Causes - What You Need to Know

In all cases, EMI occurs due to a combination of three factors: a source, a transmission path, and a response (at least one response is unplanned).

EMI can occur in many different ways and from various sources. Still, it stems from unwanted voltages or currents that are present, which negatively affects the performance of an electronic system or an electrical device. 

Source: YouTube, Electromagnetic Interference as Fast As Possible, by Techquickie

The different types of EMI can be categorised in several ways... 

1. Source of EMI

One way to categorise EMI types is by the way it was created (i.e. the source of EMI), which can either be naturally occurring or man-made. 

Naturally occurring interference- This type of EMI can arise from various natural sources and phenomena such as atmospheric types of noise like lightning or electrical storms.

Man-made interference- This type of EMI generally occurs as a result of the activities of other electronic devices in the vicinity of the device (also known as the receiver) experiencing the interference. 

2. Bandwidth of EMI

Another way electromagnetic interference can be categorised is through bandwidth. In short, the bandwidth of EMI is the range of frequencies on which EMI is experienced. [source] This can be broken down into two types, Broadband EMI and Narrowband EMI. 

Broadband EMI consists of EMIs that do not occur on single/discrete frequencies, and they take up a large portion of the magnetic spectrum.

Furthermore, they exist in different forms and can arise from both natural or man-made sources.

Common causes of broadband EMIs include arcing, or corona discharge from power lines and it makes up for a large portion of EMI issues in digital data equipment. [source]

Examples of this kind of EMI include faulty brushes in motors/generators, arcing in ignition systems, bad fluorescent lamps, defective power lines and sun outage disrupting the signal from a communication satellite. Luckily, these kinds of issues only last for a few minutes. 

Narrowband EMI conversely is made up of a single carrier source (or narrowband of interference frequencies) that are a result of spurious signals occurring from different kinds of distortion in a transmitter or are generated by a form of an oscillator [source].

It’s important to note that these types of spurious signals will appear at different points in the spectrum and can cause interference to other users of the radio spectrum.

3. Duration of EMI

Finally, EMIs can be categorised into different types based on the duration of interference, also known as the amount of time where interference was experienced. This usually groups EMI in this category in two groups: Continuous and Impulse EMI. 

Continuous EMI, like its name states, is interference that is continuously emitted by a source. The source can be man-made or natural, but it’s crucial to note that the interference is experienced continuously, “for as long as a coupling mechanism exists (Conduction or radiation) between the EMI source and the receiver,” according to Circuit Digest

Impulse Noise is a type of EMI that, like continuous EMIs, can be naturally occurring or made-made. That said, this type of interference occurs either within a very short period of time or intermittently. 

For example, lightning, switching systems and similar sources all contribute to impulse noise that can cause a disturbance in the voltage or current equilibrium of connected systems that are nearby. [source]

Now that we’ve detailed the various types of interference you could run into; it’s crucial to discuss the nature of electromagnetic interference. 

EMIs consist of electromagnetic waves that comprise of both the E (Electric) and H (Magnetic) field components and oscillate at right angles to each other. Check out the graphic below to get a better visual of how the waves interact.


Source: https://circuitdigest.com/article/electromagnetic-interference-types-standards-and-shielding-techniques

These field components respond differently to parameters such as distance, voltage, current, and frequency, which makes it critical to understand the nature of EMI.


By knowing which field is dominant, you can address the problem more clearly and quickly.

Due to technological advancements in recent years in the world of electronic components, the E-field is usually the major component of interference. [source]

Equipment Malfunctions due to EMI

Source: https://www.dau.edu/cop/e3/pages/topics/Electromagnetic%20Interference%20EMI.aspx

Now that we’ve covered the different causes of electromagnetic interference and the nature of EMI, you’re probably wondering how do I mitigate EMI risks? 

We’ll cover some best practices to prevent or minimise risk from electromagnetic interference in the next chapter.

Chapter 3 

Best Practices to Prevent or Reduce Electromagnetic Interference

Managing electromagnetic interference makes up a large number of different solutions at both the emitter and victim devices. 

Occasionally, it can be as simple of a fix as moving devices, so there is more space between the source and victim or even rotating one device can do the trick. 

While the above fixes can get the job done, the better solution, in this case, includes the proper design of all equipment to minimise emissions and/or making the equipment less vulnerable to external interference.

There are three different methods to help reduce EMI:  filtering, grounding and shielding. 

Let’s dive in…

A direct way to get rid of unwanted signals is through filtering them out and in this instance, passive filters work well, and they’re used in most new equipment to minimise EMI.

Filtering usually starts with an AC line filter that prevents any bad signals from entering the power supply or powered circuits, and it keeps internal signals from being added to the AC line. [source]

Filtering is commonly used with cables and connectors on lines into and out of a circuit, and some special connectors can have built-in low-pass filters whose main job is to soften digital waveforms to increase the rise and fall times and reduce harmonic generation, according to Electronic Design.

In our magnetics components product line at TT Electronics, for example, common-mode chokes help reduce EMI through inductive filters that block (choke) unwanted EMI noise while while allowing the desired signals to pass through. 

Shielding, on the other hand, is the preferred way to contain radiation or coupling in source or victim devices, and it usually consists of encasing the circuit inside a completely sealed enclosure, such as a metallic box.

Shielding is crucial because it reflects electromagnetic waves into the enclosure and absorbs waves that aren’t reflected. 

In a majority of cases, a small amount of radiation ends up penetrating the shield if it’s not thick enough. Practically any common metal can be used for shielding (e.g. copper, steel, aluminium). 

Grounding is the establishment of an electrically conductive path between an electrical or electronic element of a system and a reference point or plane referenced to ground, according to DAU, and it can refer to an electrical connection made to Earth as well. 

Some best practices to keep in mind to achieve the best possible ground include: 

  • Keep leads away from internal circuits or any other components to ground as short as possible to reduce inductance.
  • Use multiple grounding points on a large ground plane for best results.  
  • Try to isolate circuits from ground if ground loop voltages can’t be controlled any other way.
  • Maintain separate grounds for analogue and digital circuits-- you can combine them later at a single point.

Utilising any one of these three methods above can help you not only reduce EMI but can help ensure your equipment is less vulnerable to future interference and can assist with reducing emissions.

Chapter 4

What's the Difference Between EMI and EMC?

It’s no surprise that when referring to the regulatory testing of electronic goods and components, the terms of electromagnetic interference and electromagnetic compatibility (EMC) are often used interchangeably.

It can be easy to confuse the two terms, as they are very similar, but they are different.

As we already discussed, EMI is defined as electromagnetic energy that affects the function of an electronic device or system.

Electromagnetic compatibility also referred to as EMC, is a measure of a device’s ability to operate in a shared operating environment while not affecting the ability of other equipment in the same environment.

Two components make up EMC:

  1. Immunity testing - Also known as susceptibility testing, this is the evaluation of how a device reacts when exposed to electromagnetic energy.
  2. Emissions testing - This is the process of measuring the amount of EMI generated by a device’s internal electrical systems.

Both aspects are crucial design and engineering considerations for any system and failing to anticipate the EMC of a device can result in several negative consequences such as product failure or data loss.

Due to this, a wide range of testing equipment for EMC and EMI has been developed to help give engineers a better understanding of how a device will operate in real-world conditions.

For example, emissions testing requires using EMI measurement equipment like amplifiers, receiving antennas, and spectrum analysers. [source]

According to Com-Power, the following rules apply to guidelines for EMC testing:

“FCC Part 15 rules define limits for the amount of unlicensed radio frequency interference that can be produced by consumer electronics and other devices. MIL-STD 461 and MIL-STD 464 outline EMC and environmental requirements for components/subsystems and systems for military applications.”

Outside of the United States, there are various regulations and other standards that define the acceptable limits of EMI and EMC. Still, in some cases compliance with these standards is voluntary. 


Unfortunately, we don’t live in a perfect world, and our electronic systems and devices can be vulnerable to being negatively impacted by electromagnetic interference. 

We’ve come a long way in understanding how electronic devices are impacted by it, measures we can take to reduce or prevent it outright and creating guidelines to regulate acceptable limits of EMI and EMC.

By following the best practices to determine which method(s) fit your electronic system, you can ensure that you’re correctly combatting interference from man-made and naturally occurring sources. 

As a specialist in the development of electromagnetic products for demanding areas of application, TT Electronics is dedicated to staying on top of the rapidly evolving electronics industry. 

Image credit: Photo by israel palacio on Unsplash


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