Electromagnetic interference (EMI) refers to the disturbance caused by electromagnetic radiation on electronic devices, equipment, or systems. This interference can disrupt the proper functioning of electronic devices and cause issues such as signal distortion, data corruption, increased error rates or even complete failure.
EMI can occur through mechanisms such as radiation from electronic devices, power lines, antennas, or other sources of electromagnetic energy. It can also propagate through conductive mediums like wires, cables or PCB traces.
EMI can occur in different forms like conducted interference (transferred through electrical conductors) and radiated interference (propagated through the air as electromagnetic waves). It can affect analog and digital circuits alike.
Common sources of EMI include:
- Switching circuits: Changes in electrical currents like those occurring in switching power supplies or digital circuits.
- Radiofrequency interference (RFI): Signals from radio transmitters, wireless devices, or other communication equipment can interfere with nearby electronic devices.
- Power lines and electrical equipment: Fluctuations in electrical power distribution systems, as well as equipment such as motors, transformers, or lighting fixtures, can emit electromagnetic radiation.
- Natural phenomena: Lightning strikes and atmospheric disturbances can produce electromagnetic radiation that interferes with electronic equipment.
- Man-made sources: Electronic devices, machinery, and appliances can emit electromagnetic radiation unintentionally, causing interference with nearby electronics.
Types of Electromagnetic Interference (EMI)
Conducted EMI
This type of interference occurs when electromagnetic energy is conducted along wires or cables and then unintentionally radiated or coupled to nearby devices or systems. It can result from power lines, signal cables, or ground loops.
Radiated EMI
Radiated Electromagnetic Interference (EMI) is where electromagnetic energy is emitted from an electronic device or system and interferes with the operation of other nearby electronic devices or systems.
Radiated EMI can occur in frequency ranges like radio frequency (RF), microwave, and infrared. It can originate from sources such as digital circuits, power lines, high-frequency oscillators, and switching power supplies. Common examples of devices that emit radiated EMI include computers, mobile phones, Wi-Fi routers, and microwave ovens.
Transient EMI
Transient Electromagnetic Interference (EMI) also known as electrical transients or surges, refers to short-duration bursts of electromagnetic energy that can disrupt the operation of electronic devices or systems. Unlike continuous radiated EMI, which emanates steadily from a source, transient EMI occurs sporadically and lasts for only a brief period, from microseconds to milliseconds. These transient disturbances can originate from sources like switching events, lightning strikes, electromagnetic pulses (EMP), and electrostatic discharge (ESD).
Transient EMI poses a challenge in electronic design and operation due to its unpredictable nature and potential to cause immediate damage or malfunctions in sensitive equipment.
Common Mode Interference
Common mode interference occurs when unwanted electromagnetic energy is present on both conductors (e.g., signal lines or power lines) of a balanced transmission system with respect to a reference point (e.g., ground). It can result from asymmetrical signal paths or external sources.
It (external electromagnetic fields, power supply noise, ground loops, and improperly shielded cables). It usually results from asymmetrical disturbances or noise coupled onto transmission lines or cables.
Differential Mode Interference
Differential mode interference happens when unwanted electromagnetic energy is present on one conductor with respect to another in a balanced transmission system. It can occur due to imbalances in signal paths or coupling from external sources.
External Interference
External interference originates from sources outside of the affected equipment or system. This can include electromagnetic radiation from other electronic devices, power lines, radio transmissions, or natural sources such as lightning.
Internal Interference
Internal interference arises from components within a device or system. This can include switching noise, cross-talk between circuit elements, harmonic distortion, or unintended coupling between circuits.
Intentional Interference
Intentional interference refers to electromagnetic signals deliberately generated to disrupt or interfere with communication systems or electronic devices. Examples include jamming signals used in warfare or intentional electromagnetic interference for testing purposes.