ALLPCB
Definition
Electromagnetic interference (EMI) refers to electromagnetic interactions between electronic devices, or between electronic devices and their surrounding environment, that degrade or damage the performance of one or more devices.
Basic concept
EMI denotes unintended interference in electronic devices, circuits, or systems caused by the radiation or conduction of electromagnetic fields. Such interference can affect normal operation, resulting in signal quality degradation, malfunctions, data errors, or complete device failure.
Mechanism
EMI generation and propagation involve electromagnetic wave behavior. When electronic devices operate, internal components such as circuits, wiring, and chips generate electromagnetic fields. These fields can radiate as radio-frequency (RF) signals or be conducted through connecting wires and power lines to other devices or systems. The radiated or conducted fields can interact with the normal operation of nearby devices or systems, producing EMI.
Common EMI sources
Typical sources include high-frequency oscillators, switching power supplies, motors, and wireless communication devices. Device layout, wiring quality, and grounding methods also influence EMI levels.
Mitigation measures
- Enclosure shielding: use metal housings or shields to block radiated fields.
- Filters: add filters in circuits to suppress high-frequency interference and preserve signal integrity.
- Grounding design: proper grounding can reduce conduction and reflection of electromagnetic waves, lowering interference.
- EMC testing: perform electromagnetic compatibility testing during the design phase to ensure compliance with relevant standards.
- Wiring practices: careful routing and power-line management reduce coupling and conducted interference.
Propagation paths
- Radiated propagation: currents in conductors, cables, or antennas produce electromagnetic radiation that propagates as radio waves to other devices or systems.
- Conducted propagation: EMI can be transmitted between devices via conductors, cables, or shared ground connections.
- Coupling: electromagnetic coupling between nearby devices allows fields from one device to affect another via current induction, capacitive coupling, or inductive coupling.
Summary
EMI arises from multiple factors related to device design, layout, grounding, routing, and filter use. Reducing EMI requires implementing appropriate electromagnetic compatibility (EMC) measures during both design and engineering implementation stages.
