Electromagnetic interference, or EMI, is a common issue that can affect electronic devices. EMI refers to noise and interference that occurs within a device that’s caused by an external source, such as another piece of equipment or a weather-related event.
EMI can cause electronic devices to stop functioning properly, produce inaccurate readings, and in some cases, even cause safety issues.
In the United States, the Federal Communications Commission (FCC) requires that devices are compliant with electromagnetic compatibility (EMC) rules, such as 47 CFR Part 15, also referred to as FCC Part 15.
These rules place limits on the amount of electromagnetic interference an electronic device can produce, as well as requirements for immunity from interference caused by other devices.
To market your device in the United States, you’ll need to make sure it complies with these rules through lab testing and equipment authorization.
Below, we’ve explained what electromagnetic interference is, as well as the most common types of interference that can affect electronic devices.
We’ve also shared some techniques that you can use to reduce electromagnetic emissions from your device and improve its electromagnetic compatibility.
Need more help complying with EMC regulations? Contact us online or call us at 866-540-5287 to talk to our engineers about EMC compliance, or to request a free quote for EMC testing and certifying your device.
What is Electromagnetic Interference?
The term electromagnetic interference refers to any type of disturbance caused by an external source that affects an electrical circuit via electromagnetic induction, electrostatic coupling, or conduction.
This interference can disrupt, degrade and even stop the proper operation of electrical devices and equipment. You can think of EMI like a form of noise that drowns out the signal of a device, making it difficult to hear the intended message.
For example, imagine you’re trying to listen to a radio station but hear hisses and buzzes rather than music. This annoyance is caused by EMI, which may overwhelm the signal that’s required for a device to function and prevent it from working properly.
Electromagnetic interference can originate from a variety of sources. Some sources of EMI are man-made, such as other electronic devices. Others are natural, such as EMI caused by solar flares, lightning, and other weather-related events.
You can learn more about electromagnetic interference, including why EMI is strictly regulated, in our guide to what electromagnetic interference is.
Types of Electromagnetic Interference
Electromagnetic interference can be classified into several types, each with its own source and characteristics. Understanding the different types of EMI is important for devising a strategy to reduce interference and ensure your device complies with regulations.
Radiated EMI
Radiated EMI spreads through the air, like radio waves. This type of interference can affect any device within its reach, including surrounding devices that share their environment with the key source of radiated emissions.
The emissions that cause this type of interference originate from sources like communications devices, TV broadcasts, and even microwave ovens. These devices can emit radio frequency waves that may interfere with other devices.
Dealing with radiated emissions and the EMI they cause can be challenging, as emissions can penetrate walls and other barriers to affect devices in other rooms.
Radiated EMI is measured through radiated emissions testing — a common process in device compliance testing. This type of testing involves using an anechoic chamber and specialized monitoring equipment to measure radiated emissions from your device.
Conducted EMI
Conducted EMI travels along power lines or signal lines. Conducted emissions affect devices through their power supply or data cables and can cause similar issues to radiated emissions that spread through the air in a shared electromagnetic environment.
Common sources of conducted emissions include electrical motors, power supplies, electrical lighting and other devices. This type of EMI is particularly problematic for devices that connect to a shared power network or data communications lines.
Conducted EMI is measured through conducted emissions testing. This type of testing involves measuring the level of electromagnetic interference that’s emitted via its power lines and signal lines to verify that it operates within regulatory limits.
Transient EMI
Transient EMI, or impulse noise, is a sudden, short-lived form of electromagnetic interference that can affect electronic devices. It occurs as a result of power surges and switching actions that occur in electrical circuits.
Sometimes, transient electromagnetic interference can also occur as a result of natural events, such as lightning strikes.
Although transient electromagnetic interference generally doesn’t last for long, it can result in significant disruptions to electronic devices. In some cases, transient interference may cause lasting damage that affects a device beyond the period of interference.
Common Mode and Differential Mode Interference
Common mode and differential mode interference are two types of interference that can affect electronic circuits.
Common mode interference occurs when the interference signal is present on two or more of the device’s conductors or signal lines and these signals are in-phase (meaning they move in the same direction) with respect to a reference ground.
This means that the unwanted signals on the line are either identical or very similar in phase and magnitude. Common mode interference usually originates from sources such as power lines, radio transmitters and lightning strikes.
One key characteristic of common mode interference is that it usually involves a ground loop that allows the interference signal to enter the system’s ground. This type of EMI can bypass traditional filtering methods, and is often challenging to mitigate.
Differential mode interference, on the other hand, occurs when the interference signal travels in opposite directions on two conductors of a circuit. This type of interference affects the difference in voltage between conductors, rather than the individual voltages with respect to ground.
Differential mode interference is often generated by an electrical device itself, such as switching action from a power supply or digital circuit.
When compared to common mode interference, differential mode interference is usually easier to manage. This is because this type of interference can be filtered effectively using differential mode filters. These filters eliminate signals that have a phase difference, reducing EMI.
EMI and Regulatory Compliance for Electronics
Improving your device’s electromagnetic compatibility is important for reducing interference in a home or workplace environment. It’s also critical for ensuring your device complies with US and EU regulations, such as FCC Part 15 and the European Union’s EMC Directive.
These regulations stipulate that devices need to operate within accepted limits for radiated and conducted emissions. They also impose minimum performance requirements for your device’s level of immunity to emissions that are produced by other devices.
In other words, achieving a high level of electromagnetic compatibility doesn’t just improve your device’s marketability — it’s also mandatory for achieving US and/or EU market access.
How to Reduce EMI in Your Device
Reducing electromagnetic interference is a key step towards ensuring your electronic device is compliant with regulations, including FCC Part 15 and the European Union’s Radio Equipment Directive (RED) and Electromagnetic Compatibility Directive.
Common methods of reducing electromagnetic interference include:
- Using grounding to dissipate electromagnetic interference through a safe path to the ground and reduce your device’s emissions.
- Using conductive or magnetic shielding to encase your device’s components and/or circuits, reducing emissions and interference.
- Using good cable and connector management practices to minimize your electronic device’s cable loop area limit emissions.
- Improving your PCB layout and component placement to reduce emissions that are caused due to internal components.
- Using spread spectrum clocking to spread energy from your device across a wider frequency band and reduce peak emissions.
- Using software to change the way your device operates and limit interference that’s caused by software-manageable functions.
Our guide to reducing electromagnetic interference goes into more detail about the methods listed above. You can also contact us to learn more about steps you can take to reduce your device’s electromagnetic interference and achieve regulatory compliance.
Contact Us About EMC Testing & Regulatory Compliance
Ensuring your device complies with electromagnetic compatibility regulations is a critical step towards gaining market access and selling your device legally.
As an ANSI-accredited electronics testing lab, we can help you lower your device’s emissions and complete testing, allowing you to add the FCC mark, CE mark and/or other legal marks of compliance to your device and gain market access.
To request a quote for testing your device, or to ask our engineers and compliance specialists your questions about electromagnetic interference and regulatory compliance, contact us via our website or call us at 866-540-5287.
