RFID tags are of two types: passive and active. A
passive RFID tag is a chip incorporating memory
and a microwave transmitter that is embedded
in a product or in the product’s packaging. The
memory contains the identification number of
the tag and may also contain physical specifications
of the product using PML, Physical Markup
Language (York, 2003). In order to read the tag
an RFID reader sends out a burst of microwave
energy, which is picked up by the tag and is sufficient
to allow the tag to transmit the contents
of its memory, which is received by the reader.
Since the tag receives power from the reader, it
does not need to have its own battery, and is called
a passive RFID tag for that reason. Passive tags
cost about US$0.20 in large volumes, and are