Physical Form Factor (Tag Container)
A tag can take almost any form desired to perform required functions. The design may be influenced by the type of antenna, which in turn may be dependant on the frequency used for the system. The tags may be standalone devices, or integrated into another object such as a car ignition key. Systems parameters, such as whether active or passive tags are required and whether a battery is on a tag, can also influence the design.
Figure 24.1 shows that tags can be put into packages of almost every conceivable shape. The rule is: The larger the tag, the further distance it may be "read."
The following sections discuss some typical tags.
RFID tags in a "credit card" physical format are usually used for purposes such as building access. This type typically involves security. Personnel that are allowed to enter, or restricted from entering, certain areas of the building are a given encoded cards. Readers are typically mounted next to a door where access is controlled. The reader relays the cardholder information to a database and the database determines whether the cardholder has line access to that particular area. If access is allowed, an electronic door lock is disengaged, allowing access to the building or to a particular room.
Some of the first commercial RFID applications were card-controlled entry systems using "proximity cards." Proximity cards do not carry as much information as newer RFID units and are about double or triple the thickness of a credit card. Newer RFID cards are the same thickness as a credit card.
The white rectangles seen in Figures 24.1 and 24.3 are RFID cards, each containing an electronic microchip with a serial number encoded.
Credit cards are seen as potential RFID tags. In late 2005, television viewers saw new credit card commercials showing the PayPass system and their "Tap 'N'Go" Tag line. The credit card becomes a tag, because it has an integral RFID chip. Instead of swiping the card through a traditional magnetic card reader, the user holds the credit card containing the RFID chip near the reader at the POS. The transaction is completed in a matter of seconds. According to the RFID Gazette, the tag conforms to the International Organization for Standardization (ISO)/IEC 14443 standard, uses Triple Data Encryption Standard (DES) and SHA-1 cryptography, and operates at 13.56 MHz.
The RFID technology is being pushed to the extent that the latest "dummy" cards used for American Express advertising show a fake RFID chip and antenna. The newest design calls for the card plastic to be clear. Figure 24.7 depicts a replica card recently received in a credit card application. The fake RFID chip and antenna are pointed out with arrows.
Figure 24.7: Fake credit card showing the RFID chip and antenna
24.7.2 Key Fobs
Key fobs are also popular for POS systems. The RFID tip is encapsulated in a small cylinder or other container designed to use on a key ring. This allows the tag to be conveniently located (e.g., the passive key fobs used as part of the ExxonMobil SpeedPass system are approximately 1-1/2" long and 3/8" in diameter). The internal electronics are even smaller; the glass-encased RFID chip and antenna assembly is approximately 7/8" long by 5/32" in diameter. Figure 24.8 shows an example of a passive tag's internal components.
Figure 24.8: A passive tag's internal components
The ExxonMobil SpeedPass is a passive tag, designed to be held in the user's hand, and waved within close proximity (>1") in front of the gas pump's integral reader. ExxonMobil also makes active SpeedPass tags designed to be vehicle mounted.