EMC Question of the Week: July 15, 2019

Strong sources of electric-field coupling are circuits that have 

1. rapidly changing voltages
2. rapidly changing currents
3. large capacitors
4. uninsulated wires

Answer

The best answer is "a". Electric fields are proportional to voltage differences, and electric-field coupling (also called capacitive coupling) is proportional to dV/dt. Electric field strengths are independent of current amplitudes, except to the extent that the current produces a corresponding voltage.

Capacitors are good places to find large dI/dts, but not large dV/dts. Capacitors supply current to counter rapid changes in voltage across their terminals. 

In a wire bundle, the permittivity of the insulation between two wires does affect the capacitance between them. So a high-permittivity insulation could increase electric-field coupling between circuits sharing a wire harness. Nevertheless, there is nothing inherent to uninsulated wires that would encourage electric field coupling.

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