This interference can come from natural sources or things people make. To reduce the effect of EMI, it helps to use good-quality electronics, protective shields, and modern error correction methods.

A common example of EMI is when a cellphone is close to audio equipment or speakers. It can cause weird noises or beeping sounds.

Causes of EMI
EMI happens because electricity and magnetism are closely connected. When electricity flows, it makes a small magnetic field. Similarly, when a magnetic field moves, it creates an electrical current. This relationship is how things like electric motors and generators work. All electrical conductors can also act like radio antennas. Strong electrical and radio sources, both natural and human-made, can affect devices from a distance. As electronics get smaller and more sensitive, they become more vulnerable to these effects, causing EMI issues.

Sources of EMI can be natural, like lightning or solar storms, or human-made, including high-power radio and electrical devices. Malfunctioning consumer devices and intentional actions, like using an electromagnetic pulse, can also cause EMI problems in other devices.

EMI Types
Radiated EMI – Occurs when a powerful transmitter or electrical device produces radio signals that interfere with another device. If the source and the affected device are far apart, it’s likely radiated EMI. For example, a malfunctioning kitchen microwave may cause a computer to restart, or old wireless phones can disrupt Wi-Fi. Radiated EMI can be split into narrowband and broadband interference. Narrowband EMI affects specific radio frequencies, often from radio transmitters. Broadband EMI affects a wide range of radio frequencies and is usually caused by faulty equipment. An example of radiated electromagnetic interference is when wireless phones disrupt Wi-Fi signals, causing connection issues.

Conducted EMI – Occurs when there’s a direct electrical connection from the source to the affected device. This often happens through power lines. For instance, a big motor or power supply can be a source. An example of conducted EMI is when starting a treadmill or clothes dryer causes a computer on the same electrical circuit to restart.

Coupled EMI – Occurs when the source and affected device are close but not directly connected. It can happen through induction or capacitance. Inducted or magnetically coupled EMI occurs when a magnetic field from one conductor induces an unwanted current in another nearby conductor. For instance, if a power cable and an audio cable are close, you might hear a hum in the audio.

Capacitively coupled EMI occurs when two conductors are side by side and store an electrical charge between them. This kind of EMI needs the conductors to be very near each other and often happens on electronic circuit boards or when wires are closely packed together over long distances.

EMI Prevention
To avoid EMI, it’s best to use good-quality electronics from trusted suppliers. In the United States, the FCC requires devices to be tested against emission standards to prevent excessive EMI. Similar rules apply in other countries. Cheap or fake electronics may not be properly tested or shielded, making them more likely to cause EMI in other devices and be affected by it themselves. Modern error correction and filters can also help reduce the impact of nearby EMI sources.

For high-speed networks, separating power lines from data lines, using shielded and twisted pair cables, and considering fiber optic cables can improve signal integrity. In medical devices, there are legal requirements for EMI shielding, and hospitals may ask people to turn off cellphones to avoid EMI in sensitive equipment.

When designing electronics, especially in modern high-speed devices, it’s crucial to consider EMI. Board designers need to think about where components are placed, how they are connected, and may use metal shielding or conductive tape to block EMI. In very sensitive situations, a Faraday cage might be used to shield a device or room from outside EMI. For instance, radio telescopes are often placed in isolated areas to reduce EMI.