Radio frequency identification (RFID) is a technique that uses radio waves to track and identify people, animal, objects, and shipments. This is done by the principle of modulated backscatter. The term “backscatter” is referring to the reflection of the radio waves striking the RFID tag and reflecting back to the transmitter source with its stored unique identification information.
What makes up the RFID System?
The RFID system consists of two things:
- An RFID tag (also called the RF transponder) includes an integrated antenna and radio electronics.
- A reader (also called a transceiver) consists of a transceiver and an antenna. A transceiver is the combination of a transmitter and receiver.
The reader (transceiver) transmits radio waves, which activates (turns on) an RFID tag. The tag then transmits modulated data, containing its unique identification information stored in the tag, back to the reader. The reader then extracts the data stored on the RFID tag. The RFID idea dates back to 1948, when the concept of using reflected power as a means of communication was first proposed. The 1970s saw further development in RFID technology—in particular, a UHF scheme that incorporates rectification of the RF signal for providing power to the tag.
Development of RFID technology
Development of RFID technology significantly increased in the 1990s. Applications included toll collection that allowed vehicles to pass through tollbooths at highway speeds while still being able to record data from the tag.
Today, RFID technology is being used to track inventory shipments for major commercial retailers, the transportation industries, and the Department of Defense. Additionally, RFID applications are being used in Homeland Security in tracking container shipments at border crossings. Additionally, RFID is being incorporated into WLAN computer networks to keep better track of inventory. Wireless technologies are becoming more important for the enterprise. RFID technology is being used as a wireless means for asset tracking and as a result is placing more importance on its role in the network. The tracking technology is even being extended to tracking Wi-Fi devices within the WLAN infrastructure.
There are three parameters that define an RFID system. These include the following:
- Means of powering the tag
- Frequency of operation
- Communications protocol (also called the air interface protocol)
Powering the Tag
RFID tags are classified in three ways based on how they obtain their operating power. The three classifications are passive, semi-active, and active:
Passive: Power is provided to the tag by rectifying the RF energy, transmitted from the reader, that strikes the RF tag antenna. The rectified power level is sufficient to power the ICs on the tags and also provides sufficient power for the tag to transmit a signal back to the reader. The tag inlays include both the RFID chip and the antenna mounted on a substrate.
Semi-active: The tags use a battery to power the electronics on the tag but use the property of backscatter to transmit information back to the reader.
Active: Use a battery to power the tag and transmit a signal back to the reader. Basically this is a radio transmitter. New active RFID tags are incorporating wireless Ethernet, the 802.11b–Wi-Fi connectivity.
Frequency of Operation
The RFID tags must be tuned to the reader’s transmit frequency to turn on. RFID systems typically use three frequency bands for operation, LF, HF, and UHF:
Low-frequency (LF) tags typically use frequency-shift keying (FSK) between the 125/134KHz frequencies. The data rates from these tags is low (~12Kbps), and they are not appropriate for any applications requiring fast data transfers. However, the low-frequency tags are suitable for animal identification, such as dairy cattle and other livestock. The RFID tag information is typically obtained when the livestock are being fed. The read range for low-frequency tags is approximately .33 meters.
High-frequency (HF) tags operate in the 13.56MHz industrial band. High-frequency tags have been available commercially since 1995. It is known that the longer wavelengths of the HF radio signal are less susceptible to absorption by water or other liquids. Therefore, these tags are better suited for tagging liquids. The read range for high-frequency tags is approximately 1 meter. The short read range provides for better defined read ranges. The applications for tags in this frequency range include access control, smart cards, and shelf inventory. The data rate for high-frequency (HF) tags is 26Kbps.
Ultra-high frequency (UHF) tags work at 860–960MHz and at 2.4GHz. The data rates for these tags can be from 50–150Kbps and greater. These tags are popular for tracking inventory. The read range for passive UHF tags is 10–20 feet, which make it a better choice for reading pallet tags. However, if an active tag is used, a read range up to 100 meters is possible.
Communications (Air Interface) Protocol
The air interface protocol adopted for RFID tags is Slotted Aloha, a network communications protocol technique similar to the Ethernet protocol. In a Slotted Aloha protocol, the tags are only allowed to transmit at predetermined times after being energized. This technique reduces the chance of data collisions between RFID tag transmissions and allows for the reading of up to 1000 tags per second. (Note: This is for high-frequency tags.) The operating range for RFID tags can be up to 30 meters. This means that multiple tags can be energized at the same time, and a possible RF data collision can occur. If a collision occurs, the tag will transmit again after a random back-off time. The readers transmit continuously until there is no tag collision.
Published on Tue 21 August 2012 by Rolf Gupta in Networking with tag(s): rfid