How do contactless smart cards work?
Contactless smart card systems are closely related to contact smart card systems. Like contact smart card systems, information is stored on a chip embedded within the contactless smart card. However, unlike the contact smart card, the power supplied to the card as well as the data exchanged between the card and the reader are achieved without the use of contacts, using magnetic or electromagnetic fields to both power the card as well as to exchange data with the reader.
The contactless smart card contains an antenna embedded within the plastic body of the card (or within a key fob, watch or other document). When the card is brought into the electromagnetic field of the reader, the chip in the card is powered on. Once the chip is powered on, a wireless communication protocol is initiated and established between the card and the reader for data transfer.
The following four functions describe at a high level the sequence of events that happen when a contactless smart card is brought near a card reader:
Energy transfer to the card for powering the integrated circuit (chip)
Clock signal transfer
Data transfer to the contactless smart card
Data transfer from the contactless smart card
Hence, once the card is brought within range of an electromagnetic field of the required frequency, the card will be powered up, ready to communicate with the reader. Since the contactless smart cards described in this FAQ are based on the ISO/IEC 14443 standard, this frequency is 13.56 MHz and a reader that complies with the standard would have an activation field (range) of about 4 inches (approximately 10 centimeters). In other words, the card needs to be within 10 centimeters of a reader for it to be effectively powered; however, the effective range for communications for the card to be read will depend on a number of factors like the power of the reader, the antenna of the reader and the antenna of the card.