Radio frequency identification, or RFID, is a form of automatic identification technology that—much like bar codes and magnetic stripes—can be used to carry data about an object and transfer it to a computer, reducing the time and labor needed for manual data entry.

While most automatic identification technologies require at least some labor (scanning, swiping, etc.), an RFID system can be truly automatic.

A basic RFID system includes an RFID tag, an RFID reader and a host computer. When a reader energizes a tag, the data stored in the tag's memory is transmitted to the reader via radio waves. The reader then communicates the necessary data to the host computer so the computer's software can act on the data. This entire process can be completed with no human intervention.

Common uses of RFID include card keys that control access to buildings, E-ZPass transponders that automatically pay roadway tolls and ID tags for pets and livestock. RFID technology also has many industrial uses, including several materials handling applications.

Most RFID tags have at least two parts:

1. A silicon chip for storing information
2. An antenna for receiving and transmitting a signal

Tags come in various shapes and sizes, depending on the application. The RFID tags typically used in shipping labels combine a tiny square chip (smaller than the head of a pin) with a 3- to 4-inch-wide antenna. Two of the most common antenna shapes for shipping labels are squiggle and double cross (see illustration).

RFID tags can be active, passive or semi-passive.

Active tags include a battery and use the power from the battery to transmit their signal. The battery gives this style of tag an especially long read range. It also increases the price of the tag.

Passive tags have no batteries and instead use energy from an RFID reader to power their transmissions. Passive tags are less expensive than active tags, but they have a limited read range.

Semi-passive tags, also called battery-assisted tags, use a battery to boost the response of a passive tag.

RFID tags can be designed to transmit at one of several frequencies. Generally, higher frequency tags transfer data more quickly but are less able to penetrate water, grease and other obstructions. Two of the most common frequencies are 13.56 mHz and 860-920 mHz:

• 13.56 mHz tags, also known as high frequency (HF) tags, are popular for ID badges, library books and anti-counterfeiting applications
• 860-920 mHz tags, also known as ultra high frequency (UHF) tags, are the most common choice for case, pallet and shipping container tracking

The memory in an RFID tag can be configured in a variety of ways. For example, the data on a reprogrammable tag can be written and rewritten again and again, while a WORM (write once, ready many) tag is programmed at the factory and cannot be written to again.

Information is written to an RFID tag by a device called an encoder. RFID encoders are usually integrated with RFID readers because the two devices use many of the same components. Encoders are also commonly integrated with label printers.

An RFID reader, sometimes also called an interrogator, reads the data stored on an RFID tag and passes it to a host computer for processing. A reader is essentially a small box of electronic components connected to one or more antennas. The antennas emit radio signals to activate RFID tags and to read and write data.

RFID readers range from large tunnel structures to devices small enough to fit inside a cell phone. The major difference is the antenna. The size and shape of an antenna varies by application, frequency and the required read range—the larger the antenna, the longer the range.

Fixed location readers are mounted in one place—near a conveyor line, for example, or surrounding a dock door—while portable readers can be mounted on lift trucks or designed as handheld devices. Handheld readers typically have a short read range because their antennas are small.

Most RFID antennas and readers are not yet “plug-and-play” devices, says Bert Moore, director of communications for AIM Global (724-934-4470, www.aimglobal.org), a trade association representing makers of automatic identification equipment. The radio waves emitted by large antennas, he says, travel in all directions and can bounce off surrounding objects. End users usually work closely with a supplier, he says, to choose and position an appropriate antenna and to install barriers if necessary.

For the data collected from RFID tags to be useful, it usually must be filtered and interpreted by multiple layers of software.

RFID readers usually gather much more data than necessary, explains Moore. They read the same tag multiple times or read all the data stored on a tag when only portions are needed for the application. For this reason, says Moore, most RFID systems require filtering software—often called edgeware or middleware—that recognizes the significant data and filters out the rest. (Bar code readers also require similar filtering software.)

Edgeware can also translate tag data into a format that can be used in other systems. This filtering and translating software can reside on the RFID reader or host computer.

Once the information has been filtered and translated into a usable format, it must be interpreted and applied to business processes. Different uses of RFID require different application software. Using RFID tags to track inventory in a warehouse, for example, requires an RFID-enabled warehouse management system that can identify and track individual cases using the electronic product codes (EPCs) stored on the tags.

Manufacturers have been finding uses for RFID for decades, and the technology is now making its way into warehouses and distribution centers as a potential replacement for bar codes. The following are some of the most common materials handling applications for RFID.

Tracking goods in the supply chain: Thanks to RFID initiatives at Wal-Mart and other major retailers, much attention has been paid in recent years to the use of RFID tags to track goods in the supply chain. These initiatives require suppliers to encode RFID tags with a unique ID number (an electronic product code, or EPC) and place the tags on cases of merchandise before shipping them to the retailer. The passive UHF tags are often embedded in a shipping label.

In theory, the RFID tags can track items more precisely than traditional bar codes, and they can be read faster with less human intervention, increasing visibility and efficiency in the supply chain. The hardware, software and business practices for these applications of RFID, however, are still being refined.

The organization EPCGlobal has been working to standardize the use of tags, readers and software in supply chain applications.

Process tracking: RFID technology can be used to track products throughout the manufacturing process. Automobile manufacturers, for example, often place RFID tags on car bodies and write information to the tags as each task in the manufacturing process is accomplished. Process manufacturers use RFID tags in a similar way to track the ingredients that go into each lot and batch of products.

When defective products are discovered, says Moore, the information captured on these RFID tags can help to make product recalls faster and more specific.

Asset tracking and locating: RFID tags are used to track and locate a variety of expensive assets, from drill bits to lift trucks to railcars. In some systems, readers are mounted above the entrance to a tool crib, monitoring when tools enter and leave. In others, users walk around with a handheld RFID reader, waiting for it to identify a needed item. In some real-time location systems, special active RFID tags act as beacons, broadcasting a signal identifying their location at regular intervals.