A proximity card or prox card is a smart card which can be read without inserting it into a reader device, as required by earlier magnetic stripe cards such as credit cards. To use, the proximity card is held near an electronic reader unit for a moment. The reader usually produces a beep or other sound to indicate the card has been read. Proximity cards typically have a range of around 5 cm (2 inches) for reading. The card can often be left in a wallet or purse, and read by simply holding the wallet or purse near the reader. The term "proximity card" can refer to the older 125 kHz devices or the newer 13.56 MHz contactless smartcards.
Passive cards, the more widely used type which were described above, are powered by radio frequency signals from the reader device and so have a limited range and must be held close to the reader unit. They are used as keycards for access control doors in office buildings, library cards, contactless payment systems, and public transit fare cards.
Active cards, sometimes called vicinity cards, are powered by an internal lithium battery. They can have a greater range, up to 150 meters (500 ft), and are often used for applications where the card is read inside a vehicle, such as security gates which open when a vehicle with the access card inside approaches, or automated toll collection. However the battery eventually runs down, and the card must be replaced after 5 to 7 years.
Method of operation
The card and the reader unit communicate with each other through radio frequency fields of either 125 kHz, or 13.56 MHz for the newer cards, by a process called resonant energy transfer. Passive cards have three components, sealed inside the plastic: an antenna consisting of a coil of wire, a capacitor, and an integrated circuit (IC), which contains the user's ID number or other data. The reader unit has its own antenna, which continuously transmits a short range radio frequency field.
When the card is placed within range of the reader, the antenna coil and capacitor, which form a tuned circuit, absorb and store energy from the field, resonating like an electrical version of a tuning fork. This energy is rectified to direct current which powers the integrated circuit. The chip sends its ID number or other data to the antenna coil, which transmits it by radio frequency signals back to the reader unit. The reader checks whether the ID number from the card is correct, and then performs whatever function it has been programmed to do. Since all the energy to power the card comes from the reader unit, passive cards must be close to the reader to function, and so have only a limited range.
An active card contains a flat lithium cell in addition to the above components, to power it. The integrated circuit contains a receiver which uses the battery's power to amplify the signal from the reader unit so it is stronger, so it can detect the reader at a greater distance away. The battery also powers a transmitter circuit in the chip which transmits a stronger return signal to cover the greater distance.
Modern proximity cards are covered by the ISO/IEC 14443 (proximity card) standard. It defines two types of card ("A" and "B", with different communications protocols), which typically have a range up to 10 cm (4 inches). There is also a related ISO/IEC 15693 (vicinity card) standard, which typically works up to a longer range of 50 cm (19 inches)
The card readers communicate in various protocols, for example the Wiegand protocol that consists of a data 0 and a data 1 circuit (or binary or simple on/off (digital) type circuit). The earliest cards were 26 bit. As demand has increased bit size has increased to continue to provide unique numbers. Often, the first several bits can be made identical; these are called facility or site code. The idea is that company A has a facility code of xn and a card set of 0001 through 1000 and company B has a facility code of yn and a card set also of 0001 through 1000. Numbering system is internationally harmonized and allocated by Netherlands based NEN (registration authority) as international registration authority according to ISO/IEC 6523 and ISO/IEC 15459 standard.
- Access badge
- Access control
- Common Access Card
- Identity document
- Magnetic stripe card
- Photo identification
- Physical security
- Smart card
- Wiegand interface