You have probably heard the acronym "RFID," which stands for radio frequency identification. You may know that RFID tags can contain unique information that identifies whatever they are attached to, and can share that information wirelessly with computer databases and networks so items can be tracked efficiently.
What you may not know is how far the technology has come and what is being developed right now that could help your warehouse or distribution center. To help decide if RFID would be beneficial, consider if any of the following statements apply to your business:

• Processing speed is essential or could provide a competitive advantage
• We deal in high-value assets that need to be protected
• A bar code cannot physically survive our processes
• Areas of our facilities need to be protected from unauthorized access
• We need more unique information on each item than a bar code can contain
• We are highly automated and need to minimize human intervention
• We could benefit by knowing where products are at all times in the supply chain, in real time.

If any of these statements apply to your business, RFID should be given serious consideration in your system design.

How RFID Works
First, the basics: RFID is a means of uniquely identifying an object through a wireless radio link. The identification is accomplished by an interrogator, also called a reader or "master," and a tag, also called a transponder or "slave" that has a unique identification code. Data is exchanged between tags and readers using radio waves between the tag and interrogator, and no direct line of sight is required for the transaction. The interrogator asks the tag for the code, or processes the signal being broadcast by the tag, decodes the transmission and transfers the data to a computer. The computer, in turn, may simply record the reading, or look up the tag ID in a database to direct further action, and may also direct the interrogator to write additional information to the tag.
The latest generation of RFID allows the dozens of individual objects within a group to be uniquely identified at the same time. This is in contrast to bar codes, which must be read one by one, and can be very advantageous in high-speed reading, sorting and material handling applications. Because no line of sight is required between the reader and the tag, unattended reading stations can be set up to identify objects on a conveyor belt or within a transport container. Fast simultaneous processing and unattended reading are the main performance characteristics that set RFID apart from bar code.
This advanced functionality comes with a price, which in the past often made RFID systems cost-prohibitive. Today, however, pricing has come down considerably, with many tags suitable for warehouse and distribution operations costing are often reusable and can be packaged to be extremely durable, which helps amortize the initial system cost and provides strong total cost of ownership (TCO) advantages compared with identification methods that must continually be replaced.

Tags
The lower-cost tags generally are passive (meaning they have no internal power source), have limited data storage capacity (typically 32 to 128 bits), are read-only (not rewritable), and have limited read range. Like bar codes, they are usually used as "license plate" identifiers, i.e., they hold little actual data but serve to identify the object to a database containing larger amounts of information. For example, a tag attached to a product in a work-in-process application would uniquely identify the product each time it passed by a reader. The reading, and any work performed on the assembly, would be recorded in a database. In turn, a conveyor-based sortation system could identify the item and receive routing instructions from a database application, allowing products to reach their loading destination without human intervention.
Higher-cost tags are available for many more complicated longer read applications. They often have their own power source (these are known as active tags), making them heavier than passive tags, and large data storage capacities (upwards of 1M), making them essentially self-contained databases. These higher-capacity tags could, for example, monitor temperature through a process or give operational instructions to a robotic workstation when they arrive attached to their item, then have updated status information appended to the tag when the task is complete. This flexibility does have a cost, however; the internal power source can burn out, giving these tags a life span of 5-10 years.

Frequencies
RFID systems are available in a wide range of frequencies to suit various performance needs. Frequency is an important factor in transmission range and speed.  This is an important consideration when planning logistics and supply chain applications. Most tag frequencies share the ISM (Industrial, Safety and Medical) bands.
Most RFID technology used in warehousing and distribution operate at 13.56 MHz (high frequency), 860-930MHz (ultrahigh frequency, or UHF) or the 2.45GHz (microwave) band. Still in use are 125 KHz low frequency tags, which are used for access control and vehicle identification. Standards that have been ratified or are in development for material handling, logistics and supply chain applications are concentrated in the UHF band and 13.56MHz.
Wal-Mart, which will begin requiring its 100 largest suppliers to tag shipments with RFID, has specified the use of draft standards in these frequency bands. Here is a very brief overview of different RFID frequencies and their performance characteristics.

Frequencies - High Frequency
The high frequency, which some call intermediate, band encompasses the 10 to 15MHz range, with 13.56MHz being the most common. Read range with a fixed station reader is around 1 to 3 meters (3 to 10 feet), although the reading speed is higher than the low-frequency band. Sizing of the antennas and tags becomes more critical. More expensive than low frequency, this band has the potential to become more cost-competitive through volume purchase of tags. Typical applications here include access control and smart cards. The first "smart labels" which are RFID tags embedded within adhesive bar code labels, were produced at 13.56MHz, but are now also available in other frequencies.

Frequencies - Ultrahigh Frequency (UHF)
Ultrahigh-frequency RFID encompasses the 850 to 950MHz band and is frequently championed for distribution and logistics applications. The American National Standards Institute (ANSI) standard for RFID identification of returnable transport items, which complements the ANSI MH10.8 bar code shipping label standard, specifies the 902-928MHz band for item identification.

Frequencies - Microwave
Some RFID products are also produced in the microwave bandwidth, typically at either 2.45GHz or 5.8GHz. These products offer the highest data read rates, but are also more expensive and have higher power requirements. These are often appropriate in specialized applications.

Read/Write Capabilities.
When considering what RFID technology is right for your warehousing or distribution application, it's important to understand the difference between the various types of writing capabilities available. In general, the more versatile, or the more stand alone a system is, the more memory needed, which increases both the size and cost of the tag. Read-only tags have fixed information securely programmed into them when they are manufactured. Write once, read many (WORM) tags may have data written to them once only post-manufacture and are the most popular kind of tag currently used. Rewritable tags are the most memory- and cost-intensive, but provide flexibility to update data. Rewritable tags have a shorter writing range than reading range, which must be considered when planning the application.