The Magic of Electromagnetic Induction Is Amazing! How Suica, PASMO and Other Contactless Cards Work
Ken Kuwako here, your friendly Science Trainer. Every day is an experiment!
Suica, PASMO, and other transit IC cards are such a lifesaver for commuting, getting to school, and shopping, aren’t they? But have you ever stopped to wonder…
“How does this thing work without a battery?”
It almost feels like magic. What’s really going on inside? My curiosity got the better of me, so this time I decided to take the plunge and take a Suica apart!
Let’s Peek Inside a Suica!
First, I simmered the Suica in hot water for a bit to soften the hard plastic and loosen the adhesive holding the card together. When it seemed ready, I took it out, carefully trimmed around the edges with scissors, and slid a utility knife in from the side. Whoa! It split cleanly into two layers, much more neatly than I expected. And what was inside? I was amazed!
Inside, I found a tiny black IC chip and an antenna (a coil) looping all the way around the edge of the card. There was no sign of a battery anywhere. This coil is the secret behind how a Suica works without one.
Powered by Invisible Energy: The Magic of “Electromagnetic Induction”
That antenna (coil) is the key to unlocking the Suica’s secret.
The keyword is “electromagnetic induction.” You may have run into it in science class.
Put simply, it means that “when the magnetic field (the space where magnetic force acts) around a coil changes, an electric current flows through the coil.” The ticket gate (technically called a reader/writer) gives off an invisible magnetic field. And it’s not just sitting there. It flips direction about 13.56 million times every second, changing at breakneck speed.
When you tap your Suica and bring it close to the gate, the coil inside the card enters this rapidly changing magnetic field. And boom, a current is generated in the coil! That’s electromagnetic induction. The important part is that the magnetic field is changing. If the field stayed constant, the coil wouldn’t produce any current at all. That’s exactly why the gate keeps changing its magnetic field at such incredible speed.
So the “alternating current” you learned about in science class is hard at work here. This current wakes up the IC chip, which then exchanges information with the gate at high speed (checking your balance, deducting the fare, and so on). In other words, your Suica runs on electricity it “borrows” from the ticket gate. No wonder it doesn’t need a battery.
And you never have to worry about it running out of juice, either. That said, the card only gets power when it’s near the gate. With this system, the card and the gate can only communicate from a distance of a few centimeters to a dozen or so centimeters. Now you can see why you’re told to actually tap the card!
Electromagnetic induction was discovered in 1831 by the British scientist Michael Faraday, and it was a landmark discovery. So every time you tap through a ticket gate without a second thought, you’re using cutting-edge technology that traces back to a discovery made nearly 200 years ago. Kind of romantic, isn’t it?
From Cards to Smartphones
Now, this amazing technology isn’t limited to cards. I’m a bit late to the party, but I recently added Mobile Suica to my iPhone. Not having to carry a card and being able to pass through the gate with just my phone is so convenient that I was genuinely impressed!
Seeing my balance update in real time every time I use it feels futuristic and exciting, too.
Of course, there’s the risk of dropping your phone or running out of battery, which would be a real headache, but the convenience more than makes up for it. For a moment I wondered, “Maybe phones don’t use electromagnetic induction?” But it turns out they use the very same principle. The “FeliCa” and “NFC” features built into your phone take over the roles of the card’s coil and IC chip, and communicate with the gate through electromagnetic induction.
The technology that once lived inside that thin card is now built into our smartphones, making our lives even more convenient.Check here for more on Osaifu-Keitai (FeliCa). It’s a fascinating read (in Japanese). By the way, electromagnetic induction is also hard at work in plenty of other everyday places.
Take your smartphone’s wireless charger, for example. It works a lot like a Suica: the changing magnetic field from the charger generates a current in a coil inside your phone. The strength and frequency of the magnetic field are different, but the principle is the same. Be sure to check out my article on phone chargers, too.
A single scientific discovery, reshaped over the years, now enriches our daily lives. Thinking about it that way, doesn’t the science hiding in everyday life start to look even more fascinating? The next time you tap on a ticket gate, try picturing the coil inside your card, quietly collecting power from an invisible magnetic field.
- @IT, “FeliCa Technology” (covers the 13.56 MHz frequency, wireless power supply from the reader/writer, and communication range; in Japanese) https://atmarkit.itmedia.co.jp/frfid/special/felica/felica02.html
- Osaifu-Keitai (Wikipedia, in Japanese) https://ja.wikipedia.org/wiki/%E3%81%8A%E3%82%B5%E3%82%A4%E3%83%95%E3%82%B1%E3%83%BC%E3%82%BF%E3%82%A4
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