SECTION IV: Understanding Radio Frequency IDentification (RFID)
ULTRA HIGH FREQUENCY (UHF) PASSIVE RFID
Ultra high frequency is referred to the frequency range 300 MHz to 3 GHz in the radio spectrum. RFID technology has been developed in different regions using these bands, specifically, 433 MHz, 860 -956 MHz and 2.45 GHz. The focus of this article will be specifically on the 860-956 MHz range due to the fact that this range has attracted most R & D investments and is positioned to dominate the UHF passive RFID market space.
UHF coming to prominence in the RFID market place is a fairly recent phenomena compared to the more established High Frequency (13.56 MHz) and Low Frequency (125-134.2 kHz) technologies. HF is a robust technology, which works well for item management applications, but fails where read ranges of beyond 1m is required. UHF is ideal for applications such as supply chain market where longer read distances are required.
Technologically speaking, RFID in the UHF range differs from High Frequency systems in a number of ways. UHF operates, primarily, in 860-956 MHz range allowing for shorter antennas and longer read distances. Reader-tag communication is implemented using backs-scatter technology. In this method, tag communicates with the reader by modulating the received signal and radiating it back to the reader. This scheme is fundamentally different than the inductive-coupling method used in HF systems. Moreover, the anti-collision (simultaneous reads) feature implementation in UHF is achieved using a protocol based on bit broadcasting as opposed to HF protocol that operates based on the time slot concept. This allows for higher number of tags to be read simultaneously in the UHF range, typically greater than 200 tags as opposed to 50+ tags with HF systems.
Although the UHF RFID addresses some shortcomings of the HF RFID, primarily in terms of read range, it has to contend with its own limitations and challenges. UHF systems do not work well in the presence of liquids whereas HF and LF work fairly well in such environments. Metal poses a challenge for any RFID implementation, more so in the UHF range, however, the advent of UHF on-metal and in-metal tags have largely met this shortcoming. Still, longer read distance becomes a disadvantage in applications such as banking and access control.
Current UHF passive tags are designed for wideband operation. Readers must conform to the regulatory environment in which they operate, but today’s tags may operate unimpeded globally. Inlays are designed to operate globally, delivering global operation from 840 to 960 MHz. This enables the same inlay to be used successfully at the diverse frequencies of the Americas, Europe, Asia, and Africa. World tags allow companies to manufacture products on one continent and ship worldwide utilizing a single RFID inlay.
The following are some of the benefits and limitations of UHF RFID:
- Provides good read distances, up to 10 m
- Tags can easily be embedded into solid non-metallic items such as labels, pallets, cards etc.
- High data throughput and faster anti-collision scheme facilitate higher read rates. 800 reads, per second, is achievable in theory but 200 is the read rate for practical purposes
- UHF transponders cost less compared to HF due to simpler manufacturing processes such as printable antennas
- TAGS – serialized unique TID (tag ID), extended commands (EAS), larger specialized memories (64kByte)
- READERS – reporting tag velocity and directionality
- Poor performance around liquids and metals extended by specialized on-metal, in-metal, balanced in-on metal tags
- Crowded frequency band, 860-960 MHz falls within the ISM (Industrial, Scientific, Medical) band, making it one of the more crowded regions of the spectrum
There are complicating factors that have somewhat hindered faster progress in the UHF RFID market. ISO and EPC Global are the main bodies that work to draw standards and specifications for UHF RFID. The ISO standards for the 900 MHz UHF band are 18000-6-x.
The RFID industry is on the verge of a breakthrough. The market has passed its infancy and there is no doubt that this technology is going to revolutionize the way we live. RFID will add intelligence to objects and that will change the way people interact with them. There is no single RFID technology capable of working in all the applications. Different RFID technologies will be complementing each other, each serving functions that most suit its characteristics.
Continue reading…click here for Section V: RFID STANDARDS