EMI Bites: “We’ve Always Done It This Way”
EMI Bites: “We’ve Always Done It This Way”
We’ve all been trained on simplified models.
- Neatly drawn loops.
- Single-point grounds.
- Capacitors as silver bullets.
Theories that were adjusted to fit everyone—students, beginners, even marketing teams—but no longer fit the complexity of the real systems we’re designing today.
You were told EMI is just “high-frequency noise,” and filtering it is enough.
You were taught that ground is zero volts and that return currents just “find their way,” or that they will eventually "sink back to earth ground."
You were told that if your schematic is right, the layout doesn’t matter that much.
And maybe worst of all, you were made to believe that if it works on the bench, it should pass compliance.
We inherited these shortcuts from textbooks written decades ago.
They were good starting points, but they’re not enough.
- They don’t explain why a trace that looked “short enough” becomes an antenna.
- They don’t show how return current moves when your reference plane is interrupted.
- They don’t teach you how to see the circuit in the frequency domain, where the real EMI demons live.
And no, these are not only techniques for "high-frequency" stuff.
So, when the EMC report comes back full of failures, it’s not just the board that’s broken—it’s the method we used to design it.
We need better tools, but more importantly, we need better understanding.
We need to learn what really drives EMI, current loops, return paths, impedance changes, field coupling, not just component values.
We need to design from the ground up with EMC in mind, not treat it like an afterthought.
Because when you know what’s really going on inside the board, when you see the currents flowing, the fields coupling, the resonances building—then you stop guessing.
You start engineering.
To electromagnetic enlightenment,
Dario
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