Have you ever heard of electromagnetic interference? It’s the force that could be causing all your cell phone calls to drop or your PCB board to malfunction—but what is it, and what causes electromagnetic interference?

Before we get into what causes electromagnetic interference (EMI), let’s learn what exactly EMI is, and why we should know about it. EMI comes from the close relationship between electricity and magnetism and the disruption that comes from these two forces interacting.

All electrical flow—from natural electricity to the cell phone in your pocket—emits a moving magnetic field with an electrical current. The magnetic field from other sources interacting with the electrical flow of a device can cause severe interference and disrupt the device’s circuits—leading to lost signals, connections, or outright device failures.

Where does all the EMI come from? Essentially, there are two main sources: natural and human-made EMI.

Although it’s not as common as its artificial counterpart—natural EMI can come in many forms and disrupt our electronic equipment. When you think of natural electricity, what do you imagine? A thunderstorm, a rainstorm?

Those are both common causes of EMI. The static electricity from those weather phenomena builds up and, in the right conditions, causes severe disruption in electronic devices. Other natural EMI comes from off-planet in the form of solar flares, storms, and cosmic radiation from other planets.

The EMI we’re most likely to run into is from human-made equipment and devices. Artificial EMI can come from direct contact with an electronic conductor (conducted EMI) or by induction (radiated EMI).

Radiated EMI is most common, in which an electronic device’s electric flow is disrupted by a magnetic field emitting from a nearby device. Common sources of natural EMI you might run into every day include:

As you can see, there are many potential sources for EMI. Now, let’s learn how we can prevent it from upsetting our necessary equipment.

Thanks to modern advancements in EMI shielding, EMI is something that most ordinary people don’t have to worry about. EMI shielding uses various techniques like shielded cables and metalized EMI filters to prevent devices from emitting EMI and absorbing any potential EMI before it disrupts the machine circuits.

Without EMI shielding, our personal electronic devices, vital communications, and medical technology would be far less effective. We rely on EMI shielding every day, even if most people have never heard of it.