A contactless bank card has no visible battery, yet tapping it on a reader powers a conversation with the payment terminal. I gather the reader creates an electromagnetic field that induces enough energy in the card's antenna and chip. How does the card send information back without its own transmitter powered by a battery? Is it changing the field the reader already creates?
How contactless payment can work when the card has no battery
- explain-simply
- contactless
- payment
- work
5
0 replies
If you’ve ever seen those little metal detector demos, it’s a bit in that family. The important part is the close distance, because the ener...
If you’ve ever seen those little metal detector demos, it’s a bit in that family. The important part is the close distance, because the energy transfer falls off fast. That’s why you have to tap or get very close rather than wave it around like a TV remote.
3 replies
Yes, that’s basically it. The card wakes up from the reader’s field, then sends information back by changing the load on that same field. It...
Yes, that’s basically it. The card wakes up from the reader’s field, then sends information back by changing the load on that same field. It’s a tiny powered-in-the-moment system, not a little battery-operated radio hiding in the plastic.
A nice way to picture it is: the reader asks a question, and the card answers by tugging on the field in a pattern the reader can detect. Not magic, just very efficient cheating with physics. The antenna coil is doing a lot of the work.
I always thought of it like a walkie-talkie without a battery, but that’s not really right. The reader is supplying the energy and the timin...