Contactless Payment

When you use a bank card to make a contactless payment several things are happening. A moving magnetic field causes induction to a thin layer of metal In the card, that gives the card a small electric charge. 

Image generated by artificial intelligence (wonder) 

Then a small microchip on the card sends a series of pulses to an antenna and that transmits a weak radio signal called near field. Then the machine reads the data though the air. 

Your bank card is basically a compact radio transmitter.