Electromagnetic interference (EMI) is a common problem which occurs with electronic devices when the performance of a device is disturbed or interrupted by electromagnetic radiation or conduction. The source of EMI can be natural or artificial in origin, and it can become a very serious problem in some situations. In addition to appearing accidentally, electromagnetic radiation can also be created deliberately, as is done by military aircraft which wish to jam the electronic signals of enemy forces.
Solar flares and the Northern Lights are two common natural causes of electromagnetic interference. Both of these phenomena cause radiation which can interfere with electronic devices. Many people with radios have noted that sometimes the signal experiences a profound decline in quality as the result of increased solar activity, making it difficult to hear radio stations through static and other signal interruptions. Solar activity can also disrupt the function of satellites and aircraft.
Any electronic device can potentially create interference. They may cause narrowband or broadband interference which can do everything from creating wiggles on a television screen to causing phone calls to be heard over baby monitors. Wireless devices like cell phones, cordless phones, and wireless Internet routers in particular tend to be prone to generating electromagnetic interference. Anything which draws large amounts of energy, like a refrigerator or air conditioner, can also be responsible for interference.
Manufacturers of electronic devices must usually conform with regional laws which are designed to prevent electromagnetic interference. These measures include proper grounding of electrical circuits, and shielding of devices so that they will be less prone to emitting radiation. People may also be required to use dedicated circuits for particular devices, both as a safety precaution and to reduce electromagnetic conduction between these devices and devices on the same circuit.
Before they are sold, electronic devices are usually tested for compliance with laws regarding electromagnetic radiation. People can reduce the amount of EMI they experience in their homes and businesses by keeping items which are likely to cause interference isolated, and making sure that devices are used as directed. Computers, for example, should be left shielded in their cases.
The deliberate generation of electromagnetic interference is a tactical tool utilized by some law enforcement agencies and militaries for the purpose of jamming signals. Individuals such as criminals and terrorists may also build jammers for the purpose of blocking signals or interfering with the function of electronic devices.