EMC FLEX BLOG A site dedicated to Automotive EMC Testing for Electronic Modules

Capacitive Coupling vs Inductive Coupling

13. December 2020 19:29 by Christian in EMC/EMI, Noise Coupling, Troubleshooting
Electromagnetic fields and how they propagate and couple together. Conductive coupling is usually lo

How Electromagnetic Fields are propagated and coupled together.

Conductive coupling is usually low frequency noise traveling along a pair of wires due to a common resistive path, which form a loop. Breaking the connection stops the interference (“ground loops”).

Radiated coupling represent EM waves propagating through space from one point to another, whose coupling factor reduces by a factor of 1/r.

Inductive and Capacitive couplig refers to near field effects, which are reduced rapidly with separation (near field terms of 1/r^2 and 1/r^3). 

Inductive coupling requires two "loops" coupled together, with the field of the one inducing noise into the other (think transformer).

Example: one cable inducing noise into an adjacent cable.

Inductive coupling is a high di/dt phenomenon.

Capacitive coupling requires two “plates” with the noisy plate inducing a voltage change in the other due to dispersion effects (think capacitor).

Example: heat sink from a switched mode power supply inducing voltage changes in a nearby cable or chassis.

Capacitive coupling is generally a high dv/dt phenomenon.

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