A rich media-animated explanation is available at TECHtionary.com
An RFID system sends data from a transmitter with radio frequency using an antenna via free space (over the air) to other devices known as tags, and to retrieve data with a receiver by machine-readable means at a suitable time and place to satisfy particular application needs. An RFID system requires the means of reading or analyzing the data received with a programmer/interrogator and some means of communicating the data to a host computer or data processing system. A tag (no acronym) is a TRANSPONDER – an electronic TRANSmitter (exciter) – resPONDER (receiver) is attached to the object to be identified, and when appropriate signals are received, it transmits information via radio frequency signals to the reader (receiver).
RFID systems are categorized by their frequency ranges which are related to the cost and distance (read) required. Three carrier radio frequencies are commonly used as representative of the low, intermediate, and high ranges at 125kHz, 13.56 MHz and 2.45 GHz. However, there are eight frequency bands in use around the world.
Passive Tags are powered from the RF (Radio Frequency) transmission signals received from the transmitter. Passive RFID, or read-only tags, operate without a separate external power source and obtain operating power generated from the reader. Passive RFID usually contain 32 to 128 bits (though check with the manufacturer as this is a rapidly changing technology). Active tags are turned on with the RF signals but powered by battery or other sources. Active RFID tags are read/write (can be rewritten and/or modified) powered by an internal battery. An active tag’s memory size and life varies according to application requirements and battery type. Some systems operate with up to 1MB including history and operating other applications, and last an estimated ten years. In general, RFID tags can operate in high/low temperatures and be read through a variety of substances such as snow, fog, ice, paint, crusted grime, and other visually and environmentally challenging conditions such as around corners (not LOS [Line of Sight]), where barcodes or other optically read technologies would be useless. RFID tags typically respond in less than 100 milliseconds. Two methods distinguish and categorize RFID systems, one based upon close physical proximity electromagnetic or inductive coupling (e.g. card reader) and one based upon propagating electromagnetic radio frequency waves. Coupling (connection) is via ‘antenna’ structures forming an integral feature in both tags and readers. While the term antenna is generally considered more appropriate for propagating systems, it is also loosely applied to inductive systems.
Next week, part 2 is an RFID case study.