Ever wanted to rip open an NFC travel card to see how it all works? One engineer has done just that and it's way cooler than you'd think

They don't require a battery. They don't need to be plugged into anything. You just wave them at a sensor and then you're on your way to pay for goods, travel on a subway, or ride on a bus. NFC cards might appear to work by magic but it's just good old-fashioned electronic engineering. But the scale of what goes on is really incredible, as one distinguished computer scientist discovered.

That person just so happens to be Ken Shirriff, who apart from having a post doctorate in computer science and decades of experience working for Sun, Microsoft, Google, and others, also likes to explore the inner workings of chips by reverse engineering them. On X and his blog, Shirriff took a travel card for the Montreal subway system and delved into how the NFC (near-field communications) card works.

To use the Montreal subway, you tap a paper ticket against the turnstile and it opens. But how does it work? And how can the ticket be so cheap that it's disposable? I opened up the tiny NFC chip inside to find out more… 1/15 pic.twitter.com/OlQkkikp0mJune 23, 2024

The largest part of the whole setup is the antenna—it picks up the 13.56 MHz radio wave signal from the sensor's transmitter and it also provides the means to power the chip. The wave's tiny amount of energy is all that's required. But given that the processor (or rather, the digital controller) is smaller than a grain of salt, it's not surprising that so little power is required.

It's so small that Shirriff ran into all kinds of problems trying to remove it from the card and etch down its layers, to see the logic circuits inside. In his own words, just «bumping the chip or even breathing on it can send the chip flying perhaps never to be seen again.»

Processor die images are things of wonder and we've all gazed and wondered at the work of the likes of Fritchen Fritz. This thing is on another level altogether, though. Not because it comprises billions of transistors (it doesn't) or because it's made on a cutting-edge