Classical electromagnetism teaches that current is the flow of charge and charge is the fundamental quantity. A field-centric perspective inverts this — and the inversion is more than philosophical. It changes how you diagnose and fix real circuit behaviour.
The conventional definition: current is the rate of flow of electric charge, expressed as I = dQ/dt. Charge is an intrinsic property of particles — electrons carry it, protons carry it, and it is the source of electric fields. This is the model taught in every introductory physics and engineering course.
It is also the model that creates the disconnect between circuit design and EMC. Here is why.
In a copper conductor carrying 1A of current through a 1mm² cross-section, the drift velocity of the electrons — how fast they actually move — is approximately 73 micrometres per second. The speed of a snail. Yet electrical signals propagate at a significant fraction of the speed of light — typically 0.5–0.7c in PCB dielectrics.
If electrical signals are carried by electrons, how do they propagate at near-light speed when the electrons themselves move at 73 μm/s? The answer: they don't. The electrons are not carrying the signal. The electromagnetic field is.
The energy in an electrical circuit propagates in the electromagnetic field in the space between the conductors — not through the conductors themselves. The conductors are boundary conditions, not carriers.
Rather than treating charge as the fundamental quantity from which fields arise, consider the inversion: the electromagnetic field is the fundamental quantity, and what we call "charge" is a property of the field — specifically, the divergence of the electric field scaled by the permittivity of the medium.
Gauss's law states: ∇·E = ρ/ε. Conventionally, ρ (charge density) is the cause and E (electric field) is the effect. In the inverted formulation, E is the cause and ρ is derived from it. Charge is not a thing that fields surround — it is a mathematical description of where field lines converge or diverge.
This is not just philosophical. The field-centric model changes what you look for when diagnosing circuits. In the conventional model, a PCB trace is a wire with current flowing through it. In the field model, a PCB trace and its reference plane together form a waveguide confining a propagating electromagnetic field. The signal energy is in the dielectric, not the metal.
The Poynting vector S = E × H describes the direction and magnitude of electromagnetic energy flow. In a DC circuit — a battery connected to a resistor by two wires — the energy does not flow through the wires. It flows in the electromagnetic field in the space between the wires, from the battery to the resistor. The wires establish boundary conditions that shape where the field exists and how it flows. This is counterintuitive but experimentally confirmed.
For PCB designers, the implication is direct: the return reference plane beneath a trace is not a return wire. It is the second conductor of a field waveguide. Its proximity, continuity, and impedance determine how well the field is confined and guided — which determines how much of that field escapes into the environment as EMI.
Work directly with Dario to identify EMC risks at the design stage — before a €15,000–40,000 chamber session reveals issues that require a respin.