Power source

RFID tags need power to perform functions such as sending radio signals to an RFID reader, storing and retrieving data, and performing other computations (e.g., those needed for security mechanisms). Tags can obtain this power from a battery or from electromagnetic waves emitted by readers that induce an electric current in the tags. The power requirements of a tag depend on several factors, including the operating distance between the tag and the reader, the radio frequency being used, and the functionality of the tag. In general, the more complex the functions the tag supports, the greater its power requirements. For example, tags that support cryptography or authentication require more energy than tags that are limited to transmitting an identifier.

Tags are categorized into four types based on the power source for communication and other functionality:


 * Passive tag
 * Active tag
 * Semi-active tag, and
 * Semi-passive tag.