The tag and reader communicate with one another over an RF channel. In some systems, the link between the reader and the computer is wireless. RFID systems can further be broken down according to some characteristics of the tags being used, namely, whether the tags are active or passive. The classification of RFID systems is best summarized by the figure below. The major frequency bands in which most RFID systems operate, along with some of their respective characteristics and applications are summarized in the table below.
Active tags have an on-board power source, such as a battery.
The advantage of active tags is that they reduce the power requirements of the reader, and they can transmit their information over relatively far distances. The disadavantages are that they have a limited operating life, can only be used in certain environments, and are more expensive than passive devices. Passive tags operate without an on-board power source. They obtain their operating power from energy generated by the reader. They are smaller, lighter, and less expensive than active tags.