The branch of electrical sciences that studies inadvertent generation, propagation and reception of electromagnetic energy as it applies to the unwanted effects that such energy has is called Electromagnetic compatibility or EMC. What EMC attempts to do is to determine how items can function properly when exposed to other objects that use similar technology that might generate fields that interfere with them. This is done by looking a emission properties that produce unwanted electromagnetic fields and the countermeasures that can reduce them in addition to determining the susceptibility or immunity of an object to such disturbances created outside the item. This can be looked at as the reduction of "noise" or static by addressing both areas of concern.
There are a number of types of electromagnetic interference sources. These can be natural or man made. The sources are divided by signal characteristics. CW interference is from a continuous emission of a set range of frequencies and is also called "DC to daylight". These range from audio frequencies of very low to 20-100kHz. RFI ranged for 20kHz and up as tecnhology expands that direction. Broadband noise is spread across this in a wider range then the other two. Pulse interference, or EMP, is from short duration pulses of energy, typically broadband in nature with the ability to excite a narrow-band damped sine wave response in the item impacted. These can be isolated or repetitive types of events. This can also be called Radio frequency interference (RFI).
Although EMI can be used for intentional radio jamming and electronic warfare it is far more common as an unintentional byproduct of modern society. In urban areas EMI causes major interruption, obstruction, and degradation to AM radio transmissions and to a lesser degree cellular phones, FM radio, and television reception. Older analogue amplitude modulation technology and other older radio technologies tend to have more difficulty with interference then newer systems.
This is because they have no way to filter out wanted and unwanted signals from those sent by the omnidirectional dipole antennas that are part of broadcast systems. Newer technologies have a number of ways to improve filtering. Wi-Fi, for example, uses error correction techniques like spread-spectrum and frequency hopping to improve performance under conditions where there might be interference. Using a parabolic antenna or a diversity receiver can also help in selecting one signal over the others. Ultra wideband or UWB is a new proposed technology that uses large sections of radio spectrum at low amplitudes for the transmission of high bandwidth digital data. The goal is to allow for extremely efficient use of the spectrum, however older technology would be subjected to substantial interference.
Consumer devices today present far more interference potential then previously. To combat this there are several laws in place to regulate what types of emissions are allowed from each device. In the case of the United States these regulations are developed by equipment makers and part of a voluntary compliance program. Following this most countries have legal restrictions that mandate electromagnetic compatibility. In Europe this problem was noticed back in 1933. The laws there have been compiled over time and form many of the regulations on EMC that exist now.
It is well known that many devices using intergrated circuits demodulate high-frequency carrier signals that exist in the environment because of cellular phones. These devices manifest this low-frequency demodulated signal as a unwanted audible buzz on things like microphone and speaker amplifiers, car radios, and ground phones. To combat this on-board EMI filters have been added or in newer system special layout techniques are used to bypass this EMI. ICs are tested to measure their ability to reject RF as part of their design process. These tests are done inside special anechoic chambers that allow specific test vectors to be used in controlled simulation of actual environmental situations.
In controlling EMC, one needs to understand the impact that the damaging effects it has and that this is considered unacceptable. The steps taken to reduce this include knowing the characteristics of the threat, knowing the standards for emission and susceptibility limits, and design and testing for fitting those standards. More complex items may require dedicated EMC control plans. Once the design is made and the threats understood the testing is vital in confirming that standards have been met. Both emissions and susceptibility needs to be determined. This usually is done with a physical prototype inside a radio-frequency anechoic chamber. When necessary simulations can be made with Virtual models.