Electromagnetic interference and PCB design

Electromagnetic fields exist throughout the universe. Charged particles rearrange the fields, and the fields, in turn, exert forces on the charged particles. This interactive dance is fast but not instant.

The rate at which changes happen is often called the “speed of light,” but it is really the “speed of causality” - the speed at which changes in the conductor cause a change in the electromagnetic field and the speed at which changes in the field cause a change in the conductor.

When a potential difference is established along the length of a conductor, charges begin to migrate. As the charges move, they store potential energy by rearranging nearby electromagnetic fields. The change in the electromagnetic field will cause charges to move in nearby conductors. This is the source of near-end and far-end crosstalk.

When the potential difference is reversed or removed from the conductor, energy from the nearby field can move back into the conductor.

Things get interesting when the changes inside the conductor happen so rapidly that the surrounding electromagnetic field doesn’t have time to establish a steady-state or return field energy to the conductor and the extra energy radiates outwards into space. That energy will eventually find some conductor nearby that can absorb some of the energy. This is the source of electromagnetic interference.

The electrical engineer’s job is to manage the electromagnetic fields in their circuit. Check out this quick video from the PCB experts at Advanced Assembly and learn to design your PCBs around electromagnetic fields.