EMC Question of the Week: July 15, 2019
Strong sources of electric-field coupling are circuits that have
- rapidly changing voltages
- rapidly changing currents
- large capacitors
- 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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