RFID is a generic term for any combination of circuitry that uses RF or microwave energy to provide a means of identification. It could be used to identify people or objects for a number of applications. A typical system uses a microchip that stores information (a serial number, for example, or other information about a person or product) attached to an antenna for transmission. This combination is called an RFID tag. The tag contains a unique serial number but can have other information (account number, license number and so forth). RFID tags can be active, passive or semipassive.

The RFID active tag contains a battery that is used to power the microchip and transmit a signal to a reader. These tags can be read from 300 ft or more and are usually more expensive than other tag types. The military uses active tags to track supplies. The RFID passive tag has no battery. When RF waves from a reader are received by the chip’s antenna, the energy is converted to an electrical signal that can power the chip and enable it to send back information. These tags are very low-priced and lend themselves very well to many commercial applications. The semipassive tag is similar to the active tag except that the battery is used to power the microchip but is not used to communicate with the reader. Many semipassive tags are in a dormant stage until they are activated by a signal. This conserves battery life. Some documents refer to these tags as battery-assisted tags.

Most of the RFID tags hold digital information in a microchip, but there are other chipless tags that use material to reflect back a portion of the signal beamed toward them. These tags use plastic or conductive polymers instead of silicon-based chips. Still others use materials that completely reflect a portion of the wave beamed at them. A computer then generates an image of the reflected energy and uses it like a fingerprint to identify the item incorporating the tag.

RFID tags can be found in various sizes and shapes. Some are readily identified, such as the plastic tags attached to merchandise in stores. Other types are used for animal tracking. These are implanted under the skin to locate family pets or to keep track of endangered species in the wild. They are very small and probably would not be easily recognized. RFID tags have been incorporated in credit cards, as well.

When people hear of RFID, they relate it to bar codes because it is a form of tracking and identification, as well. The bar code has been the traditional method used for both of these functions. The RFID tag, however, is fast becoming the preferred method of identification and tracking because of its read/write capability. This expands identification and tracking to include interactive applications. Also, the RFID tag can be read from a distance away from the product or person, as previously mentioned. It also has the ability to transmit through substances such as snow, fog, ice, paint and other items.

RFID systems can be grouped into categories: electronic article surveillance (EAS) systems, portable data capture systems, networked systems and positioning systems. The EAS system is the most recognizable as the one in retail stores. It uses tags attached to garments with readers by the entry/exit doors. The portable data capture system uses portable readers that enable it to be used at many various locations. The networked system has fixed position readers connected to a centralized information system. The transponders are on people or moveable items, such are trucks and freight cars. The positioning system is for automated location identification of any tagged item.

RFID operates at various frequencies. Common frequencies are 13.56 MHz and frequencies in the UHF frequency band from 0.3 to 3.0 GHz (300 to 3000 MHz). The RFID band used in North America is 862 to 928 MHz (this takes into account the very popular frequency band of 902 to 928 MHz). The European frequencies are 862 to 870 MHz. There are also  microwave tags that operate at 5.8 GHz. These can be read up to 30 ft away, utilize more power, and are more expensive.

Two other types of tags are the read-only tag and the read-write tag. The read-only tag contains data that can be changed only if the chip is reprogrammed. The read-write tag can store new information. This is applicable for reusable containers that must frequently have new information associated with them. This capability is, of course, more costly. The cost of RFID systems is a challenge to widespread adoption.

Another challenge to widespread adoption is privacy and security. The ability to track people, products, vehicles, and currency (such as credit cards) is a concern to many. For example, there are readers now that can read data transmitted by many different RFID tags which means that if a person enters an establishment carrying several tags, one reader can read all of these tags; not only the ones for that business. This might allow that business to put together a profile of that individual, such as their buying habits, currency they carry and their product preferences.