This technique is used in many contactless cards in order to deliver power to the card and to allow it to communicate with the outside world. Same technique used to interrogate early types of in-car tag
. A coil is embedded within the surface of the card or the road and a card is placed in or connected to the read-write unit. When the current is passed through one coil, say the read-write unit, magnetic field is created and, if the second coil, say in the contactless card, is bought close enough to it, this magnetic field leads to current being delivered to that coil as well. Once this occurs, the card has sufficient power to function and data can be exchanged between the card and the read-write unit.