adio frequency identification (RFID) is an enabling technology. By itself, RFID doesn't provide much value, but it does enable companies to develop applications that create value.

RFID describes systems that use radio waves to transmit an object's identity. There are several methods of identifying objects using RFID, but the most common is to store an ID or serial number that identifies a specific product along with other information, on a tag, which is a small microchip attached to an antenna. The antenna enables the chip to transmit whatever identification information it contains to a reader. The reader converts the radio waves from the RFID tag into digital information that software systems can use for processing.

Typically, when a reader reads a tag, it passes three things to a host computer system: the tag ID, the reader's own ID, and the time the tag was read. By knowing which readers are in which locations, companies can know where a product is, as well as what it is, and by tracking the tag data by time, they can know everywhere it's been.

How RFID Technology Works
The reader sends out electromagnetic radio waves. The tag's antenna is tuned to receive these waves. A passive RFID tag draws power from the electrical field created by the reader and uses it to power the microchip's circuits. The chip then augments the waves to reflect the data it contains back to the reader, which converts them into digital data.

RFID System Components
A complete typical RFID System is composed of the following four components (see Figure 1).

1. RFID tags or transponders
2. RFID readers or transceivers
3. RFID middleware
4. RFID software applications

Figure 1: Typical RFID System Components. To create a complete RFID system, you need tags, or transponders, a reader, some middleware to increase data accuracy and reduce noise, and software applications to manage the data.

The Antenna
Radio waves are transmitted and received by an antenna. The antenna is designed to radiate energy and collect radio energy. The antenna functions for both the transmitter and receiver. Thus, an antenna's tasks are to:

1. Convert electrical signals to radio waves.
2. Collect or receive radio waves and convert into electrical signals.

Tags/Transponders
Tags, also called transponders, are small devices about the size of a grain of rice, containing a microchip attached to an antenna, and placed on or near the objects to be identified. The tags can be programmed with specific items of information, such as an ID or serial number. When a reader transmits an appropriate radio signals the tag reflects energy to the reader, allowing the tag to identify itself and its data.

Tags are typically differentiated and named according to their operating frequency, memory modes, memory size, type, and packaging, however, there are three basic tags/transponders from which to choose:

Active Tags

• Have a battery, which is used to run the microchip's circuitry and to broadcast a signal to a reader
• Usually operate at 455 MHz, 2.45 GHz, or 5.8 GHz, and typically have a read range of 60 feet to 300 feet
• Are usually used on large assets, such as cargo containers, rail cars, and large reusable containers
• Can be always on alert or can be "awakened" when needed

Passive Tags

• Have no power source or transmitter
• Draw power from the reader
• Are cheaper than active tags
• Require no maintenance
• Operate at low frequency, high frequency, and ultra-high frequency

Semi-active Tags

• Combine some traits of both active and passive tags
• Use a battery to run the chip's circuitry, but communicate by drawing power from the reader, and often "sleep" until awakened by a specific reader signal.

Readers
To retrieve the data stored on an RFID tag, you need a reader. A typical reader is a device consisting of one or more antennas that emit and receive radio waves. The reader passes digital information converted from radio waves to a computer system.

RFID readers use a variety of methods to communicate with tags. The most common method for reading tags at close range is "inductive coupling," in which the antenna of the reader interacts with the antenna of the tag to create a magnetic field. The tag collects energy from this field and uses that to send back radio waves to the reader.