Active RFID vs. Passive RFID

today I'm talking about two kinds of RFID : passive and active RFID and also some differentiation between them.

Active RFID and Passive RFID are fundamentally different technologies that are often evaluated together. While both use radio frequency energy to communicate between a tag and a reader, the method of powering the tags is different. Active RFID uses an internal power source (battery) within the tag to continuously power the tag and its RF communication circuitry, whereas Passive RFID relies on RF energy transferred from the reader to the tag to power the tag.

Passive RFID requires stronger signals from the reader, and the signal strength returned from the tag is constrained to very low levels. Active RFID allows very low-level signals to be received by the tag (because the reader does not need to power the tag), and the tag can generate high-level signals back to the reader. Additionally, the Active RFID tag is continuously powered, whether in the reader field or not. Active tags can also 'beacon,' or initiate communication with a reader (or other tags) when certain conditions are present. Active tags can also contain external sensors to monitor temperature, humidity, motion, and other conditions.

http://www.atlasrfidsolutions.com/active-vs-passive.asp