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 used much more widely than active tags.