Everday we come across many electronic devices like radio, television, smartphone, computer, tablets, speakers, headphones, chargers, etc. All these devices are the source of radiated electromagnetic fields called radiated emissions. These radiated emissions are the accidental by-product of the device design.
Electromagnetic Interference (EMI)
It is the degradation in performance of a device due to fields making up the electromagnetic environment.
Television broadcasting stations, radio, mobile towers, etc. radiate electromagnetic energy as they operate. Every electronic device is susceptible to EMI. EMI is the problem that occurs when unwanted voltages or currents are present to affect the performance of a device. But EMC is the solution for this problem.
The origins of EMI are basically undesired conducted emissions (voltages and/or currents) or radiated emissions (electric and/or magnetic fields).
The conducted emissions are those currents that are carried by metallic paths and placed on the common power network where they may cause interference with other devices that are connected to this network. Example: Lightning strokes affecting radio receivers.
The radiated emissions concern the electric fields radiated by the device that may be received by other electronic devices causing interferences in those devices. Example: ECG measurement is affected by the inferences due to nearby power lines and devices.
Electromagnetic Compatibility (EMC)
It is achieved when a device functions satisfactorily without introducing intolerable disturbances to the electromagnetic environment or to other devices in its neighborhood.
The purpose of EMC is to ensure system or subsystem works properly during normal operation according to the system design and that ensures a system relatively free of EMI problems.
Sources of EMI
Any electronic device may be the source of EMI. As mentioned earlier it is the accidental by-product of the device. It is not the intention of the designer.
When the cause of the EMI problem is within the system then it is called as Intrasystem EMI problem.
When the cause of the EMI problem is outside the system then it is called as Intersystem EMI problem.
The source of EMI is called as the Emitter. The victim device affected by EMI is called as the Susceptor.
The following table presents emitters and susceptors of intrasystem EMI problem.
| S.No. | Emitters | Susceptors |
| 1 | Radar transmitters | Radar receivers |
| 2 | Power supplies | Relays |
| 3 | Fluorescent lights | Ordnance |
| 4 | Mobile radio transmitters | Mobile radio receivers |
The following table presents emitters and susceptors of intersystem EMI problem.
| S.No. | Emitters | Susceptors |
| 1 | Computers | Television sets |
| 2 | Aircraft transmitter | Ship receivers |
| 3 | Power Lines | Heart Pacers |
| 4 | Radar transmitter | Aircraft navigation systems |
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