Description of RFID Technology
Two main components comprise RFID technology: The first is the RFID "tag" or transponder, which contains information about the item to which the tag is attached. The second is the RFID "reader" or "interrogator," a device that is able to locate and activate tags so that the information that has been programmed onto the tag is transmitted back to the reader and subsequently to interfaced computing systems.

RFID tag/transponder
Each RFID tag (sometimes referred to as a transponder) has two components: a chip or integrated circuit (IC) that is programmed with information about the item, and an antenna or coil that transmits this information to a compatible interrogating device. Optionally, a tag may contain a battery that supplies a built-in power source to extend the distance in which the tag can be read.



RFID tags are available in a myriad of shapes and sizes. They can be thick and rigid, or thin and flexible enough to be embedded within an adhesive label and run through a label printer. Animal tracking tags, inserted beneath the skin, have the diameter of a pencil lead. Tags can be screw-shaped to identify trees or wooden items, while credit-card shaped tags are commonly used in security access applications. The hard plastic tags that one sees attached to merchandise in stores to deter theft are often RFID tags. Long paper-thin, disposable tags are typically used to identify pallet loads and caseloads of merchandise to entities in a supply chain. Regardless of the type, the physical elements are similar.

Unlike bar-codes, RFID can be read at any angle as well as through packaging and most other materials. In addition, hundreds of tags can be read simultaneously.

Typically, the larger the tag, the larger the memory capacity and the larger the antenna, thus extending the communication range between the tag and the reader.

Tags can be read-only capable, or can be read-write capable allowing them to be reprogrammed for reuse, although this capability adds cost. There are also tags that are a hybrid of the two; in other words, some data can be permanently written--for instance, a serial number--while other data can be changed or added as needed.

Programming of tags
RFID tags that are read-only capable are either programmed or encoded when they are manufactured or just prior to the tag being attached to an item. The programming is usually done by the same device that detects and reads the tags (the reader).

As already mentioned, tags can be partially coded during manufacture (or afterwards) and then have coding added just prior to installation (or anytime thereafter).

Active vs. passive/read-only vs. read-write
RFID tags come in two types: "passive" or "active." Passive tags are powered by the energy field that is transmitted by the reader, which limits the distance in which they can be located from a reader. Active tags are each powered by their own battery, which adds cost but significantly extends the detection and transmission range beyond that of passive tags. The battery, however, can increase the size and thickness of the tag.

The battery power of active tags also allows for greater read-write capabilities (data on tags can be revised or erased thousands of times). Tags can also be a hybrid of read only and read-write. For instance, when an RFID tag is used for warranty purposes, it may have a serial number permanently written to the tag, but when warranty work is done on the product, repair information would be encoded on the tag. Read-write tags can also be used to record information while the product is being stored or transported. For instance, a tag can be equipped with a sensor to record temperatures to determine if a shipment exceeded temperature tolerances during transit.

Some active tags have a read range of over 100 feet and a battery life of several years. Passive tags have much shorter read ranges, but have the advantage of having a much longer life span than active tags. Active tags can cost several dollars each, while passive tags can be produced for as little as 25 cents (at quantities in the millions). But even at 25 cents each, passive tags are only cost effective at the case and pallet level. It is expected, however, that in the next few years the price of these tags will drop to a few cents each making it economical to replace bar codes on most individual products.

Tag durability
Most tags can withstand an extraordinary amount of abuse. Tags are available that work reliably, whether attached to a side of beef in a freezer, an aircraft part in the desert, or a pallet in a temperature controlled warehouse. The durability of tags has improved to the point that many tags can endure being stomped on, run over by forklifts, and abused in other ways with dirt, water, or chemicals. Tags can be read at remarkable speeds through a variety of substances such as snow, fog, ice, paint, crusted grime and other visually and environmentally challenging conditions, although detection distances may be reduced.

Environmental factors are not only limited to weather and dirt. RFID can be susceptible to interference from metal and water, as well as from other types of radio transmissions, although sensitivity to interference varies by frequency, the usage environment, and the distance between the tag and the interfering material.

RFID Reader-Interrogator
The other key component of RFID technology is the reader. This device is also called an "interrogator" because it sends a signal via an attached antenna, which activates the compatible tag(s) within its range, then "asks" the detected tag to transmit its identity. The information that is received by the reader is then passed to backend computing systems to initiate events, transactions, workflows, etc.

Just like bar code scanners, readers can be fixed or portable. Fixed readers are usually attached to antennas that are designed to detect the tags within a specified area. These units typically collect data on products traveling through loading dock doors, conveyor belts, gates and doorways. In a warehouse situation, a reader antenna will often be placed at the points where tagged items would enter or exit the warehouse. Portable, wireless readers can be brought right to the RFID tag in areas where wiring and/or antenna placement could be difficult, and are also available in models that can be attached to forklifts and collection carts.

Currently fixed readers and hand held mobile readers can cost in the thousands of dollars, but as with all technology, as RFID labeling becomes mainstream those prices will come down.

Not only do readers locate, activate and receive transmissions from RFID tags, a reader-writer has the ability of sending data back to read-write-capable tags in order to append or replace data. Readers exist that can also scan bar-codes in environments where both RFID and bar-codes are required. This capability is more common in handheld readers, and dovetails well in environments where combined bar-code/RFID tags are used.

Managing read areas
Various methods are used in RFID technology to help prevent the "collision" of signals sent by adjacent tags as well as the overlap of reader coverage areas.

Avoiding reader collision
A common problem encountered with RFID readers is the overlap of signals from one reader to another. This is called reader collision. Typically, readers have antennas that are designed to read a clearly delineated area, sometimes with RF shielding materials to prevent other readers from detecting tags in the same area. For instance, a loading dock might be set up as an RFID portal that is protected by RF shields, and has sensors that engage readers when movement is detected.

Additional ways that reader collision can be corrected is by a technology called time division multiple access, or TDMA. In simple terms, readers that are networked together are instructed to read at different times, rather than both trying to read at the same time. This ensures that they don't interfere with each other. Still, it means any RFID tag in an area where two readers overlap could be read twice, but technology also exists to delete the reading of duplicate codes.

Avoiding tag collision
Another challenge is preventing tag collision. This is where more than one chip reflects back a signal at the same time, thus confusing the reader, and is usually resolved by designing readers to ask tags to respond only if their first digits match the digits communicated by the reader. In essence, the reader says to the tags: "Respond only if your code begins with 0." If more than one chip responds, the reader then says: "Respond if your code begins with 00." This process is repeated until only one tag responds. Nevertheless, the reading of tags happens so quickly that even with this technology enabled, a reader can typically read 50 tags in less than a second.

Ranges/Frequencies
The detection range of RFID technology depends on the frequency used, the directional sensitivity of the antenna (both in the tag and the reader), and whether the tag is battery powered. Objects and materials in the environment, such as metal and liquids can also affect the range.

In supply-chain applications, most passive RFID tags operate in two frequency bands: high frequency (HF) at 13.56 MHz, and ultra-high frequency (UHF) band at 860-960 MHz. See the section, "EPCglobal Frequency Specifications for RFID in Supply Chains." Whether HF or UHF, passive tags get the energy needed to operate from the electromagnetic waves transmitted by the reader. HF systems use the magnetic field to transfer power and data whereas UHF systems use the electric field.

HF tags typically cost less and are better suited for tagging water or liquid-bearing objects because the longer wavelengths of HF systems are less susceptible to absorption. A UHF tag can be made to work in these conditions, but its effective read range is dramatically reduced. The HF frequency range is commonly used for library items, laundry linen, supply chain inventory (more about frequency standards for supply chains, shortly), waste management, LPG cylinders, automobile secured ID plates, and numerous other applications.