Types of RFID
RFID tags can be either passive, semi-passive (also known as semi-active), or active.
Passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for the CMOS integrated circuit (IC) in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier signal from the reader. This means that the aerial (antenna) has to be designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. The response of a passive RFID tag is not just an ID number (GUID): tag chip can contain nonvolatile EEPROM(Electrically Erasable Programmable Read-Only Memory) for storing data.
Lack of an onboard power supply means that the device can be quite small: commercially available products exist that can be embedded under the skin. As of 2006, the smallest such devices measured 0.15 mm × 0.15 mm, and are thinner than a sheet of paper (7.5 micrometres). The smallest EPC chips (the one used by Wal-Mart and the Department of Defense) are measured at 0.25 millimeters square, such devices are practically invisible. Passive tags have practical read distances ranging from about 2 mm (ISO 14443) up to about few metres (EPC and ISO 18000-6) depending on the chosen radio frequency. Due to their simplicity in design they are also suitable for manufacture with a printing process for the antennae. A development target are polycarbon semiconductor tags to become entirely printed. Passive RFID tags do not require batteries, and can be much smaller and have an unlimited life span.
Because passive tags are cheaper to manufacture and have no battery, the majority of RFID tags in existence are of the passive variety. As of 2005, these tags cost an average of Euro 0.20 ($0.24 USD) at high volumes. Today, as universal RFID tagging of individual products become commercially viable at very large volumes, the lowest cost tags available on the market are as low as 7.2 cents each in volumes of 10 million units or more. Current demand for RFID integrated circuit chips is expected to grow rapidly based on these prices.
Semi-passive RFID tags are very similar to passive tags except for the addition of a small battery. This battery allows the tag IC to be constantly powered. This removes the need for the aerial to be designed to collect power from the incoming signal. Aerials can therefore be optimised for the backscattering signal. Semi-passive RFID tags are faster in response and therefore stronger in reading ratio compared to passive tags.
Unlike passive and semi-passive RFID tags, active RFID tags (also known as beacons) have their own internal power source which is used to power any ICs and generate the outgoing signal. They are often called beacons because they broadcast their own signal. They may have longer range and larger memories than passive tags, as well as the ability to store additional information sent by the transceiver. To economize power consumption, many beacon concepts operate at fixed intervals. At present, the smallest active tags are about the size of a coin. Many active tags have practical ranges of tens of metres, and a battery life of up to 10 years
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "RFID".