If your product suddenly fails a compliance test or a sensor starts acting up for no apparent reason, there’s a good chance electromagnetic interference is to blame.

Every electronic device gives off some level of electromagnetic energy, and every device is also sensitive to it. When unwanted signals disrupt normal operation, that’s electromagnetic interference (EMI). Left unchecked, it can cause erratic readings, communication errors, or even prevent a product from passing regulatory testing.

The good news is that with a few smart design and assembly choices, EMI can be managed effectively. In this article, we’ll examine what EMI is, its origins, and how it differs from EMC, as well as eight proven methods to mitigate it, ensuring your electronic designs remain stable, reliable, and ready for certification.

What is Electromagnetic Interference?

Electromagnetic interference (EMI) refers to unwanted disturbances that affect an electrical circuit due to electromagnetic radiation emitted from an external source. Simply, it’s electrical noise that disrupts how signals are supposed to behave. 

Because every circuit both emits and receives electromagnetic waves, EM interference can occur anytime two systems interact unintentionally, with one acting as the source, the other as the victim. The effect may be as subtle as an LED flickering or as serious as a complete communication failure in a control system. 

Engineers generally divide EMI into two main types: 

Common-Mode Interference

This occurs when the same noise signal appears equally on two conductors relative to a shared ground. It often arises from long cable runs, poor grounding, or unbalanced layouts. Common-mode currents tend to radiate strongly, making them a frequent cause of radiated emission test failures.

Differential-Mode Interference

Differential-mode noise appears as opposing signals on paired conductors. It’s usually generated by high-speed switching devices such as DC-DC converters or motor drives. While switching noise radiates less than common-mode noise, it can still distort sensitive data or analog measurements. 

Together, these two forms of interference account for most EMI issues seen in electronic assemblies and guide how engineers select components, lay out printed circuit boards (PCBs), and design enclosures. 

Common Sources of Electromagnetic Interference

If you’re looking for how to reduce EMI interference, it is helpful to understand the sources of electromagnetic emissions. Interference can originate inside a device, from neighboring equipment, or even from natural environmental factors. Broadly, EMI sources fall into two categories: natural and human-made. 

Natural Sources

Not all interference is created by technology. The world itself is full of electromagnetic activity: 

• Lightning strikes release massive bursts of energy that can induce currents in nearby wiring and equipment.
• Solar storms and cosmic radiation can introduce background noise that affects satellite links or long communication lines. 
• Electrostatic discharge (ESD), the tiny spark that occurs when two surfaces touch, can generate short, intense EMI spikes. 

While natural sources are less common in day-to-day electronics assembly, they illustrate that EMI is a universal phenomenon, rather than a manufacturing issue. 

Human-Made Sources

Most EMI problems in electronics stem from human activity. Some of the most common include: 

• Switching power supplies and DC-DC converters, which create high-frequency voltage changes that radiate or couple into nearby circuits. 
• Motors, relays, and solenoids, where brush arcing or coil switching produces bursts of noise. 
• Wireless transmitters, such as Wi-Fi routers, cell phones, and Bluetooth devices, which can couple into sensitive analog or digital lines. 
• High-speed digital circuits, including microcontrollers, FPGAs, and data buses, which generate fast edge transitions that act like miniature antennas. 
• Poor cable management or grounding that allows return currents and loop areas to pick up or emit unwanted energy. 

In modern electronic systems, these sources often interact with each other. For instance, a switching converter inside a product might interfere with its own radio module, or multiple devices on a production line might cross-talk through shared power rails. Identifying and separating these sources early in design is one of the most effective steps toward achieving low-EMI performance. 

Effects of Electromagnetic Interference on Electronic Devices

Electromagnetic interference doesn’t always announce itself with obvious failure. More often, it manifests as inconsistent performance, unreliable communication, or a product that passes testing one day but fails the next. 

Even small amounts of unwanted noise can have a noticeable impact, especially as electronics become smaller, faster, and more densely packed. Some of the most common effects include: 

Signal Distortion or Data Errors

EMI can alter voltage levels or logic timing, leading to corrupted digital data or misread analog signals. 

Component Malfunction

Sensitive ICs, sensors, or amplifiers may exhibit unpredictable behavior when exposed to radiated or conducted noise. 

Communication Dropouts

Wireless modules, serial interfaces, or CAN buses can lose packets or experience reduced range. 

Display Glitches

EMI coupling into LCD or LED driver circuits can cause flickering and visible artifacts. 

Overheating and Power Instability

Noise on power lines can trigger false switching, leading to inefficiency or erratic regulator behavior. 

Test and Certification Failures

Products that exceed regulatory emission limits or fail immunity testing often require costly redesigns or additional filtering. 

8 Ways to Reduce Electromagnetic Interference

While EMI can’t be eliminated entirely, its effects can be minimized through good design discipline. 

The most reliable products use a mix of component-level, board-level, and system-level strategies that work together to control noise at its source and limit how it spreads. 

1. Component Placement & PCB Layout

Strategic printed circuit board (PCB) design is one of the most effective ways to reduce EMI. Keep high-speed or high-current circuits away from sensitive analog or communication traces. Route signal traces and return paths close together, maintain a solid power plane, and minimize each loop area to reduce coupling. A clean, compact layout naturally reduces emissions and susceptibility.

2. Capacitors (Decoupling & Bypass)

Decoupling capacitors stabilize power rails, while bypass capacitors divert high-frequency noise to ground. Choose values based on the circuit’s frequency response and place them close to the IC power pins. Together, they smooth voltage and prevent switching noise from spreading. 

3. Ferrites and Common-Mode Chokes

Ferrite materials absorb high-frequency noise before it radiates or couples into nearby circuits. Clamp-on ferrites work well on cables, while wound common-mode chokes filter noise on power and signal lines. These components improve impedance control and reduce unwanted coupling paths.

4. Cable Routing & Separation

Keep power and signal cables separated wherever possible, and if they must intersect, cross them at right angles. Avoid parallel runs that can act as antennas for conducted or radiated noise. Short, carefully routed cables dramatically reduce interference risk. 

5. Grounding

Grounds provide a return path for noise, but only if they’re well designed. Use solid ground planes for high-frequency circuits and single-point grounds for low-frequency systems to prevent ground loops. Good grounding isolates noisy sections and helps circuits remain highly immune to interference.

6. Shielding

Metal enclosures, shielded cables, and conductive gaskets block external fields from reaching sensitive components. Ensure shields cover critical regions completely and are properly bonded to ground. Even partial shielding can isolate noise and protect system performance.

7. EMI Filters

EMI filters combine capacitors and inductors to block unwanted frequencies from entering or leaving a circuit. They’re often installed on power inputs or communication ports where low-pass filters are most effective. Properly selected filters ensure that the circuit’s characteristics are preserved while blocking unwanted signals.

8. Software Adjustments

Certain firmware changes can help reduce EMI without altering hardware. Techniques like spread-spectrum clocking, slew-rate control, and balanced switching reduce sharp transitions that cause radiation. Small software tweaks can sometimes make the difference in passing compliance testing. 

EMI vs. EMC: What’s the Difference?

All the techniques above share one goal: to keep your design electromagnetically compatible with its surroundings. 

That’s where the term EMC (electromagnetic compatibility) comes in. While EMI describes the noise that causes disruption, EMC is the broader measure of how well a product both controls the interference it creates and resists the interference around it. 

In practice, reducing EMI is how engineers achieve EMC. A design with good EMC meets regulations and performs consistently, even in a noisy environment. 

How August Electronics Builds for Low-EMI Builds

Every product that passes through August’s facility benefits from design for manufacturing (DFM) that includes considerations for EMI and EMC. Our processes are built to minimize interference and ensure compliance. By addressing EMI early, we help clients avoid redesigns, reduce testing delays, and deliver dependable electronic systems at scale. 

Ready to reduce EMI risk on your next build? Contact us today to get started.