Radio Frequency Identification (RFID) is an automatic identification method often used in the manufacturing, packaging and logistics industries. RFID systems allow companies to store and retrieve data, such as product information, storage location, and even specific product information such as color and style, using devices called RFID tags or transponders.

An RFID tag is a small tag or label that can be attached to or incorporated onto a product, or package. RFID tags contain small chips and antennas to allow them to receive and radio signals from an RFID transceiver.

The antenna emits radio signals to activate the tag and read and write data to it. Antennas are the conduits between the tag and the transceiver, which controls the system's data acquisition and communication. Antennas are available in a variety of shapes and sizes; they can be built into a door frame to receive tag data from persons or things passing through the door, or mounted on an interstate toll booth to monitor traffic passing by on a freeway. The electromagnetic field produced by an antenna can be constantly present when multiple tags are expected continually. If constant interrogation is not required, the field can be activated by a sensor device.

Often the antenna is packaged with the transceiver and decoder to become a reader (a.k.a. interrogator), which can be configured either as a handheld or a fixed-mount device. The reader emits radio waves in ranges of anywhere from one inch to 100 feet or more, depending upon its power output and the radio frequency used. When an RFID tag passes through the electromagnetic zone, it detects the reader's activation signal. The reader decodes the data encoded in the tag's integrated circuit (silicon chip) and the data is passed to the host computer for processing.　(From Wikipedia)