TYPES OF RFID
RFID tags are generally classified under two heads: active and passive.
• Active RFIDs have a source of power in the form of a battery embedded in them. This implies they are always active being powered by a constant source of energy. These tags generally have a higher read range and offer read/write facilities. The pitfalls of this are these tags are generally more bulky in size and weight compared to the passive tags (due to the weight of the battery) and are more expensive.
• Passive RFIDs: Passive RFIDs are cheaper compared to active RFIDs. They do not have any external source of power and hence most of the times they are passive. These tags are activated whenever it comes within the electromagnetic range of a RFID reader. The frequency generated from the reader activates the passive device and it reflects back the information stored in the tag. However these tags have a comparatively lesser read range and are not writeable. The lack of need of an external power source makes these tags virtually of unlimited life.
Each type has its own set of uses: active RFIDs are mostly used in expensive items where there is a need to store a lot of information. For low cost-high volume items passive tags make more sense.
Tags can be either read only or WORM (Write Once Read Many) or complete read/write enabled depending on the usage requirements.
RFIDs are also classified based on the frequency band they operate in for example HF, UHF, LHF etc. Low frequency lags have lower read ranges and lower system costs. Generally the range and cost goes up with the increase in frequency. LF tags are in the range of 30 KHz to 500 KHz. The frequency also determines the range and usability, for example UHF tags are not suitable for pharmaceutical products etc.
RFID CLASSIFICATION BASED ON FREQUENCIES
1. Low Frequency (LF): These tags typically have a frequency of 125 KHz and 134 KHz. These tags have the benefit of minimum interference in-case the product contains liquids or metals compared to other higher frequencies. This property makes it ideal for use in animal tracking where the tag is embedded into the body of the animal (since most of the animal body is water, other frequencies which cannot penetrate water are unable to detect). However the limited read range and slow data read speed limit its applications and usability. Hence these tags are commonly used in operations which do not require a higher read range and which contain higher amount of liquid/metal. Typically these tags are more expensive compared to the HF and the UHF tags described below.
2. High Frequency (HF): The popular frequency in this spectrum is 13.56 MHz. This has been in use since almost the last 15 years. The coupling between the tag and the reader is inductive in nature, also known as near field coupling since the tag is detected at a fraction of the wavelength of the RF waves. Antennas for HF tags can be printed and are flexible enough for different form factors. This makes it ideal for smart card applications.
3. Ultra High Frequency (UHF): The frequency band is in the range of 860-960 MHz and has recently found widespread acceptance. This is the frequency in which a lot of investment is being made by global giant Wal-Mart and US Department of Defense. This technology forms the basis of the EPCGlobal Gen 2 Standards. It is the most popularly used frequency for supply chain/logistics and distributions mainly because of its better read range, faster data identification/transfer, good anticollision capability and high future potential of cost reduction compared to LF and HF frequency tags. This frequency operates in the “far field” since the wavelength of these waves is in inches whereas the detection range is in metres. The UHF frequency used in the
a. US is 915 MHz
b. Europe is 868 MHz
c. Korea: 908.5 – 914 MHz
d. Singapore: 866-869 MHz and 923-925 MHz
e. Japan: 950 MHz
4. Microwave: This frequency range offers the highest data transfer rate and faster identification compared to all other frequencies. However the factors limiting its usability are the higher cost (twice as costly compared to other frequencies), inability to penetrate metals/liquids and lower read range. This frequency is used in limited supply chain applications where higher amount of detail is required to be stored. The silicon technology for this frequency tags is still at a very infant stage of development and much change is not expected in the near future.