Interested to know how a card only needs to be in close proximity to send a signal to the terminal yet doesn’t appear to have any internal power of its own to send the signal? Could understand if contact was necessary to complete a circuit and data could transfer but don’t quite get how it can wirelessly send/receive data with no power source?
In: Technology
It is the radio waves from the terminal that provide the power that that card use.
When an antenna picks up a radio signal it creates an electrical current in the wire. In most situations that is too little power to do anything useful so let it be the input to an amplifier.
But for a short distance where the power can be relatively high and low power requirement lithe the card has it is enough. You send out a radio signal that is used to power the card, the card can store the power in a capacitor and use it to do the operation and transfer data back.
The technology a type of RFID. IT is a quite common technology. There are standards with passive (in internal power) RFID tags that can be read from 10 meters.
There is another example of this being used and that is in a [Crystal_radio](https://en.wikipedia.org/wiki/Crystal_radio) where you can demodulate a AM radio signal and power headphones with the energy in the radio signals.
They have been used since 1902 and was popular in the early day of radio as the was very simple to build at home and not radio is required.
You can compare it to a wireless phone charger. That user changing magnetic field instead of radio waves but is another application of wireless power at a short distance.
Energy is transferred from the reader to the card. There’s a circuit with an antenna and capacitor that absorbs energy from the radio waves and give the card enough power to do what it needs to do.
They simply use RFID chips, which are small little devices that communicate with each other over very short ranges. There’s one in the card and an RFID reader in the pay terminal that authenticates it and competes the transaction.
So, without getting into to much details, but the chip on your card IS actually powered.
The chip on your card is relatively simple, as it doesn’t store a load of data. It’s basically pre-written code that will do something whenever it get enough energy to power. In this case, it will emit to the best of its abilities a signal saying “Hey, I’m haribo001. I am the real card.”
The card reader is in fact a mini radio tower. It will send a very short radio pulse when asked to read. It will send the pulse and see if a message comes back. That radio pulse carries energy (not much, but a little bit).
The full thing thus go with the card reader sending a bit of energy through the air, if any card gets close enough, it’ll receive that energy and immediatly send a signal saying which card it is, and include a bit of security (like encryption and stuff). While its sending its pulse, the reader will also start listening for answer fitting whatever type of message it’s trying to get (in our case, a debit card). When the card sends the message, the reader stop emitting pulses and just carries on with whatever it is supposed to do with that info. In the example, sending a message to the bank like “Greetings CorporateBank, I’m reader from RandomCompany, your client [haribo001] wants to make a purchases of 0.99$. Confirmation code is 10110101. Do you copy?”
The confirmation code is the encryption and stuff, just to make sure you’re not just using the name, but you actually have the right card. So you can’t bill someone without having access to his card.
Latest Answers