Misconceptions about electron flow cause EMC test failures.

Engineers often view signals as electrons moving through traces.

This overlooks the propagation of electromagnetic fields.

An ineffective stackup allows fields to radiate as EMI.

A well-designed stackup channels electromagnetic fields efficiently.

Some engineers delay electromagnetic interference (EMI) considerations until compliance testing, assuming issues can be resolved with quick fixes.

This approach often leads to costly redesigns and project delays.

EMI is best addressed early in the design phase through:

- Optimized PCB Layout: Minimize the area enclosed by current loops to reduce antenna-like structures that radiate or conduct high-energy harmonic content.

- Strategic Component Selection and Placement: Choose components and arrange them to limit EMI risks.

When you flip a light switch, the bulb lights up instantly.

You might think electrons flow through the wires, carrying energy from the battery to the bulb.

That’s a common idea, but it’s not quite right.

The Old Idea: Electrons Moving Inside Wires

Traditionally, electricity is like water in pipes: the battery pushes electrons inside wires to the bulb (the "load") and back.

One of the biggest game-changers for me in EMI control is visualizing the EM fields as signals propagate.

Too often, we focus only on the signal path and treat the return path as an afterthought, just to close the current loop at the end of the design.

In reality, the loop is closed as the signal travels (yes, displacement current in the dielectric magically closes it!), so any gaps or breaks in the return path—like splits in the reference plane—can mess with your signals, causing crosstalk or turning cables into antennas.

How bad? It depends on frequency (high-speed signals are pickier!), but it’s always better to know it’s coming.

I like to think of the PCB as a set of channels for guiding EM fields exactly where I want them.

Most engineers miss the real answer.

In circuits, signals travel at 150 million m/s, but electrons crawl at 73.4 μm/s. Why?

It’s not electrons pushing energy, it’s electromagnetic fields.

My latest article, "Redefining Current and Charge," explains this.

Fields carry energy outside wires, in the space between PCB traces or cables.

Understanding why this is critical unlocks many other fundamentals of EMI control.

It requires shifting your mindset from thinking about charges flowing in conductors to understanding electromagnetic field propagation.

By building structures to channel and redirect these fields, you can harness them to do useful work.

If you think EMI is too complex or even 'black magic,' I’m here to tell you it’s actually simpler than it seems—but it demands a change in perspective on the fundamentals.

-Dario

Most EMI issues we encounter in design stem from a lack of planning.

The good news is that the most common issues can be addressed before the design phase is complete.

You need to know what to look for, but once you do, it’s a game-changer.

I say this because I learned the hard way.

The biggest hurdle is unlearning the misconceptions that keep us thinking of electricity as electrons flowing from point A to point B in a conductor.

What is ground, anyway?

Power ground? Earth ground? Digital ground? Zero-volt reference?

So many variants, each with distinct roles, yet lumped under one confusing term.

How do we connect them, and how can we tame EMI with smarter “grounding”?

In my latest article, I dive into why “ground” needs a serious rethink to master EMI control in electronics design.

If you are still using two-layer PCBs without "Ground" planes for your awesome electronic design and you're planning to test for EMC, then this is for you.

At a fundamental level, something just doesn’t add up.

The reason is simple: it's in how the signal propagates in the PCB.

The "water flowing through pipes" analogy to describe how signals propagate in a PCB no longer works.

It fails to explain how electromagnetic fields actually travel through the dielectric medium (not the conductors), which is key to understanding signal propagation—especially in high-speed designs.