Types of RFID Systems
There are two types of RFID systems: passive or active. The tag power system defines which type of system it is.
In a passive RFID system, the tags do not use a battery; instead, they receive their energy to run from the reader. The reader emits an energy field of a few feet, providing the energy for any tag in the vicinity. The tag gathers the electromagnetic energy from the card reader, powers up, and responds with ‘hello world’ and its identification information.
Passive tags have the benefit of being able to be read at a fast rate (10 or more times a second). They are extremely thin (allowing them to be placed between layers of paper) and are extremely cheap (less than $0.05 in 10,000+pcs volumes).
Active RFID systems include tags that have their own internal power supply for increased range. Active tags possess a battery and usually have larger SMD components. After a preset amount of time the tag emits an RF 'chirp'. A reader in the vicinity can listen and hear for this chirp. Because an active tag is they can be read over much larger distances than passive tags (tens of feet).
Downsides to active tags include greater bulk (because of the battery), limited life span (tag is dead when the battery is exhausted), increased cost per tag, and varying report rates.