Electromagnetic Interference Basics: introduction to EMI

With virtually all of our lives connected to some type of electronic device, electromagnetic interference is today a major problem. This is the unwanted energy that disrupts the operation of electronic and electrical systems. Also often referred to as EMI, it results from both natural and manmade sources. Below is all that you may want to know about electromagnetic interference, EMI.

Radiated and conducted electromagnetic interference

Table of Contents


What is Electromagnetic Interference?

So, what is electromagnetic interference? Put simply, this is a form of electrical noise caused by the emission of electromagnetic energy that ends up disrupting the normal operation of other nearby electronic devices. Here is a deeper meaning of EMI and its examples.

Electromagnetic Interference Meaning

Electromagnetic means anything related to electricity and magnetism. In this case, it refers to the radiation that disrupts the performance of electronic devices by interfering with their signals or frequencies. Let’s see how that happens:

Interference electromagnetic waves are composed of two components: an electric field and a magnetic field. These fields travel at right angles to each other. When they interact with electronic and electrical equipment, they cause a coupling of the signals. This interference is known as EMI.

Electromagnetic Interference Frequency Range

Electromagnetic interference is everywhere today, given the sheer number of electronic and electrical devices in our lives. In terms of frequency range, EMI can be classified into two different ranges.

Low-frequency EMI: This covers frequencies caused by electronic motors, transformers, fluorescent lights, and other electric appliances.

High-frequency EMI: This is generally caused by radio broadcast transmitters, TV signals, and frequencies in the microwave range such, cell phone signals, Wi-Fi hotspots, and so on.

Different sources of electromagnetic interference
Different sources of electromagnetic interference
Resource: https://www.researchgate.net

Sources of Electromagnetic Interference

Interference electromagnetic waves can come from both intentional and unintentional sources. Intentional EMI sources include radiated or conducted emissions, while unintentional EMI is caused by the normal operation of electronic systems or natural phenomena. Before we can have a look at these sources, let’s see what causes the interference in the first place.

What Causes Electromagnetic Interference?

An electromagnetic wave carries energy along it in the form of electrical and magnetic fields. When this wave comes into contact with an electronic device, the energy is absorbed by the circuitry, resulting in disruption or interference in its normal operation.

This interference can be caused by either conducted emission, where energy is carried through wires, cables, and other conductive materials, or radiated emission, where energy is transmitted through the air. Common sources of electromagnetic interference are given below.

Electromagnetic interference Sources

The energy of an electromagnetic wave can be expressed in terms of its power, frequency, and distance from the source. The higher the power and frequency, the greater effect it will have on other nearby electronic systems. Common electromagnetic interference sources include:

    • Radio transmitters such as cell phones, walkie-talkies, and two-way radios

    • Radar systems, satellites, and television and radio towers

    • Electric motors, transformers, and lighting systems

    • High-voltage power lines

    • Microwave ovens

    • Computers

    • Portable electronic devices such as phones and tablets

    • Lightning and other natural occurrences

Radiated electromagnetic interference
Radiated electromagnetic interference
Resource: https://www.researchgate.net

Types of Electromagnetic Interference

EMI is mainly categorized based on its transmission or propagation method. In light of that, we have these three types of electromagnetic interference: radiated, conducted, and coupled EMI. Let’s have a look at each of them.

Radiated Electromagnetic Interference

Radiated EMI is the most commonly encountered type of electromagnetic interference. This occurs when energy is transmitted through air or space. It can be caused by intentional sources such as radio transmitters and wireless networks, or unintentional sources like electric motors and lightning strikes.

Conducted Electromagnetic Interference

Conducted EMI happens when energy is carried through a conductor or conducting path. This type of interference can be a common mode where the source is connected to the same return path as the victim device, or a differential mode where the source and victim currents travel in different directions.

Coupled Electromagnetic Interference

Coupled electromagnetic interference refers to when the energy from a conductor couples with the wiring or circuitry of an electronic system, resulting in interference with its normal operation. Coupled EMI happens when two conductors are close together enough to create parasitic capacitance.

Electromagnetic interference between power converter and power line illustrated
Electromagnetic interference between power converter and power line illustrated
Resource: https://www.mdpi.com

Effects of Electromagnetic Interference

EMI can have a wide range of effects on electronic systems, from minor glitches to major disruptions. In most cases, the interference causes data corruption and inaccurate readings. It can also cause system malfunctions and complete shutdowns in extreme cases.

In the worst-case scenarios, interference can cause irreversible damage to electronic components and systems. Examples of electromagnetic interference effects in our daily lives include the following:

    • TV signal interference

    • Electromagnetic interference in cables causing electrical noise and data loss.

    • Wrong readings and operation of medical equipment.

    • An FM radio producing a buzzing sound when using a mobile phone.

    • Poor performance of electronic components such as motor controllers and microprocessors

    • Malfunctioning of telecommunication systems

    • Malfunctions in automated machines, robotic systems, and other industrial equipment

    • Poor reception on cell phones

    • Interference with navigation and control of aircraft

How to Reduce the Effects of Electromagnetic Interference

As we have seen, electromagnetic interference problems can range from the mildly annoying to the seriously disruptive. So, what can we do to prevent or reduce the effects? There are various methods for preventing electromagnetic interference and its effects. They include: shielding, filtering, and grounding. These techniques are further discussed below.

Electromagnetic Interference Filter

An electromagnetic interference filter is a type of circuit that is designed to reduce EMI by blocking unwanted frequencies. The filter is usually placed between two electronic systems or between a power source and an electronic system. It acts as a barrier that prevents unwanted frequencies from passing through.

Electromagnetic Shielding

Shielding is one of the most effective electromagnetic interference suppression methods. It involves the use of materials such as copper, steel, aluminum foil, and other conductive materials to block out unwanted frequencies. Shielding is often the preferred EMI reduction approach in high-frequency applications such as military equipment, medical devices, and aircraft systems.

Electromagnetic Grounding

Grounding is another method of minimizing electromagnetic interference problems. This technique involves connecting an electrical system or component to a ground, which is an electrical reference point that can absorb and disperse any unwanted electrical energy.

Electromagnetic interference measurement
Electromagnetic interference measurement
Resource: https://www.youtube.com/watch?v=J_6JA94pE-Y

Electromagnetic Interference Standards

With EMI becoming an increasingly serious issue, various standards have been developed to ensure the safe and reliable operation of electronic systems. These standards provide guidelines for the design, manufacture, and testing of electronic systems to reduce the effects of EMI.

Some of the most used electromagnetic interference standards are the International Electrotechnical Commission (IEC) 61000 series and the Federal Communications Commission (FCC) Part 15 regulations. These standards outline safety requirements for electrical equipment and impose limits on radiation and conducted EMI levels.

By adhering to these guidelines, manufacturers can ensure their electronic systems are safe and reliable. Additionally, by following these standards, companies that make EMI shielding products can guarantee that their products meet industry requirements and are effective in reducing the effects of EMI.


Electromagnetic interference is a phenomenon that can have serious implications for a wide range of electronics and components. It can result in data corruption, malfunctioning, and system shutdowns if not managed properly. To ensure the safety and reliability of electronic systems, manufacturers should use appropriate methods to reduce EMI. That’s in addition to following industry standards for EMI.

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