RFID Cards and Tags

An RFID card or tag (commonly known as a transponder) can come in many sizes and shapes, but they all contain these common elements: a) a coil or coils, which act as an antenna; b) a silicon chip, which contains a radio transceiver, an analog to digital converter, a computer and memory; c) a core of air or ferrite (rod).

Tags can also contain a battery, which provides additional operating power for the IC. These tags are known as active tags. The battery also provides power to operate sensitive reader detection and data transmission circuits. This allows the tag to begin sending its data at a considerably greater distance away from the reader than its "passive" counterpart. Additionally, an active tag uses battery energy to produce a much stronger electromagnetic return signal than its passive counterpart. All of this results in a significantly greater read range than a passive tag.

Active tags do not require special readers and can therefore readily satisfy applications that require a mix of both passive and active tags. Active tags usually have a 3-10 year life, the shelf life of the battery.

Read-Only or Read-Write

Besides being active or passive, RFID cards and tags are typically broken into two categories; read-only (RO) and read-write (RW).

Read-only cards and tags are programmed during the manufacturing process and cannot be altered. Read-only cards and tags offer an inexpensive means for the basic identification requirements of access control and industrial tracking and management.

Write-once, read many (WORM) formatted cards and tags are essentially read-only. They can be programmed one-time after manufacture by the user.

Read-write cards and tags possess memory types and operational architectures that allow the memory contents to be "written to" as well as "read from" by the user. Since tag memory contents may be changed at will by the user via commands sent to the reader, the reader must also be a "writer." Read-write technology is used in applications such as smart cards, prepaid value cards, toll collection and industrial compliance marking.

RFID Readers

All RFID readers have the same basic architecture: an antenna (a coil of wire in a housing with a driver board), reader electronics (decoder, data converter, computer interface) and a power supply. Computer interfaces available from vendors are usually RS-232, RS-422 and RS-485 and Ethernet communications are also possible. Typically plug compatible interfaces that emulate other technologies are common. These include bar code wand, ISO card and magnetic stripe emulation. Ease of connectivity allows RFID readers to input into virtually all popular data collection terminals, computers and networks.

Portable readers have the same basic architecture as RFID readers, but the elements are typically enclosed in a single hand-held unit. The portable readers often draw power from their host. RS-232, bar code wand emulation or keyboard emulation are configurable in portable units.

Read Range

Read range, or the maximum distance away from the reader at which a card/tag may be read, is generally a function of the antenna size within the reader and/or the tag for a given operating frequency. Larger readers and/or larger tags usually have greater read range.

Active tags (those powered by a battery) can be beneficial in applications that have limited reader areas along with high tag travel speeds. Because active tags begin transmitting farther away from the reader than passive tags, the use of an active tag effectively increases the size of the read zone.

High Frequency vs. Low Frequency

Operating frequency is the determining factor for the type of application an RFID system is best suited for. These frequencies include high frequency (850-950 MHz and 2.4-5 GHz), intermediate frequency (10-15 MHz) and low frequency (100-500kHz).

• High-frequency RFID systems are suitable for applications requiring a longer read range such as supply chain, inventory, assembly lines, toll-collection systems and railroad car and intermodal container tracking.

• Intermediate-frequency RFID systems are just now beginning to emerge in the financial transaction processing areas of smart card use.

• Low-frequency systems are used for applications requiring shorter read ranges. These include access control, work in process tracking and asset management.

As you move up in frequency, tag and reader costs move up as well. Tags at 125 kHz operating frequency have ICs costing tens of cents as compared to 2.4 GHz tag ICs costing several dollars.

Also, as you move up in frequency, you not only receive an increase in passive read range but also an increase in the speed at which the device can operate. Longer range tags in the hundreds of MHz and GHz are measured in yards and miles. Lower frequency tags in the 125 kHz and 13.56 MHz range have read ranges measured in inches and feet.

Application requirements for minimum read range, cost ceilings, speed of operation and communications complexity drive the decision as to which frequencies to deploy.

More About RFID

• How RFID Works

• More about RFID

• The EPC Network