The RFID tag is a carrier of numeric information hidden in a miniature chip connected to a small antenna. It is not connected to any power source in the passive design. The power is created when the tag is read by an antenna connected to the RFID reader. The energy emitted by this antenna induces the antenna in the tag and the chip can send its code back to the reader. All this is done in seconds for all tags that are in an area covered by the reader. The reader can read hundreds of tags in a second.
Passive tags are cheap to manufacture, often in the form of self-adhesive labels supplied in a roll. They are powered only when communicating with the reader, which induces energy from the transmitting antenna. Active tags are more robust, often in a plastic case and have a built-in battery. The tags may have different shapes depending on the way they are used, from small flat stickers to large square or round tags that can be mechanically affixed for example to shipping containers.
