INTRODUCTION TO RFID
UHF (Ultra High Frequency) RFID Standards and Frequencies
In the UHF (Ultra High Frequency) band, where RFID tags work according to the principles of the electromagnetic coupling, the most popular technology at the moment is the one based on the ISO 18000-6C protocol, best known as EPC Class 1 Gen 2 or for short Gen 2. The EPC Class 1 Gen 2 standard was proposed by the private organization EPCGlobal and then adopted in 2006 as the ISO 18000-6C standard by the International Standards Organization (ISO).
The EPC Class 1 Gen 2 standard was created to address some issues of previous UHF RFID standards conceived for logistics applications (such as the ISO 18000-6a and the ISO 18000-6b). The new standard was developed specifically to track fluxes of goods between different companies and across all world regions with good read performance in environments with a high density of tags.
According to the standard specifications, EPC Class 1 Gen 2 tags have four memory banks: reserved, EPC, TID and user memory. The EPC bank, typically 96 bit in size, is the one that mainly characterizes EPC Gen 2 tags. It allows to univocally identify an enormous number of objects and controls anti-collision and wake-up functions. Since the EPC number is programmed by the user, more and more Gen 2 RFID tags in the market, as well as tags of other technologies, have a unique serial number that is set at the factory by the IC manufacturer and is inalterable in order to make the tag really unique. This feature is particularly important in applications where counterfeiting is an issue.
EPC Gen 2 RFID tags work in the frequency band that goes from the 860 MHz to the 950 MHz, but there are three main frequency sub-bands used in different geographical regions:
– Europe, India, Middle East, Africa: 865-868 MHz (ETSI)
– US (plus South America and some regions of Asia): 902-928 MHz (FCC)
– Japan: 950-956 MHz (JPN)
There are EPC Gen 2 tags that are designed to work well across the entire 860-950 band and others that are optimized to provide the best performance in a specific sub-band.
The majority of EPC Class 1 Gen 2 tags on the market are passive tags, but Gen 2 BAP tags and semi-passive Gen 2 RFID tags are also available.
Passive UHF Gen 2 RFID tags – Common advantages:
– Global functioning.
– Read range from a few centimeters (UHF near field) to more than 10 meters.
– Lower costs of labels in comparison to HF labels in good volumes.
– Good performance in data transmission and in environments with high tag density.
Passive UHF Gen 2 RFID tags – Common disadvantages:
– Difficulties with liquids (absorbing materials) and as well as in proximity to animals and the human body.
– Problems in the presence of metals (reflecting/detuning materials) and when attached to metal surfaces if not specifically designed for this kind of usage.
– Smaller memory sizes in comparison to passive HF RFID tags.
BAP and semi-passive UHF EPC Gen 2 RFID tags – Common advantages in comparison with passive UHF Gen 2 RFID tags:
– They offer longer read ranges (BAP tags, few dozens of meters).
– The battery power helps with liquids.
– Extra sensors (semi-passive RFID tags).
BAP and semi-passive UHF EPC Gen 2 RFID tags – Common disadvantages in comparison with Passive UHF Gen 2 RFID tags:
– Higher costs than “comparable” passive technologies.
– The battery can limit their usage in some extreme environmental conditions.
Thanks to their common characteristics and the wide variety of models designed for specific applications, passive UHF tags are those that can be used in the largest range of applications: retail, pharmaceutical item tracking, books and media management and above all, warehouse management, industrial supply chains and many other applications where long read ranges, resistance to harsh environments and low costs are required.
UHF BAP tags are a good choice when longer read ranger are needed or when the presence of liquids can make it difficult to use passive UHF tags.
Semi-passive UHF tags are used when there is a need for extra sensors in order to measure environmental condition parameters. Their most common application is for temperature monitoring in cold-chain applications.
Another standard that works in the UHF frequency band is the ISO-18000-6b. It is falling into disuse in favor of Gen 2 standard because of the way the memory is organized. ISO-18000-6b RFID tags are not suitable for tracking goods moving from one company to another with high speed read. Nevertheless, they continue to be used in several closed-loop applications where UHF read ranges and great quantity of user memory are required.
Another RFID standard in the UHF frequency band is the ISO-18000-7, an active RFID protocol that works at 433 MHz that is also promoted by the DASH7 Alliance, a consortium that is working to create a new wireless sensor networking technology that has evolved from a combination of existing radio-frequency identification and sensing technologies.
ISO-18000-7 active RFID tags – Common advantages:
– Global functioning.
– Thanks to their working frequency, they have less problems with metals and liquids in comparison to UHF passive RFID tags.
– Long read ranges.
– Low battery consumption for longer durability.
ISO-18000-7 active RFID tags – Common disadvantages:
– As all tags with a battery, ISO-18000-7 RFID tags have higher maintenance costs than “comparable” passive technologies.
– The battery can limit their usage in some extreme environmental conditions.
Like other active RFID tags that work at higher frequencies (usually at 2.45 GHz and 5.8 GHz) and are based on proprietary protocols, ISO 18000-7 RFID tags are used in indoor and outdoor Real Time Location Systems, in applications where long read ranges are required and where measurements of environmental conditions have to be made.