Passive RFID tags
RFID passive standards
by passive on Sep.08, 2009, under Overview, Passive RFID tags
There is no international body governing the use of RFID frequencies. Each country decides its own practices, usually the national communications authority. This introduces some restrictions on the use of RFID tags. For example, ultra high frequency tags cannot be used on a global basis without common standard. Frequencies licensed for RFID use in one country might conflict with ranges allocated to civilian or military use in another country.
Despite this, a number of standards are in place dealing with specific aspects of RFID technology.
The International Standards Organisation (ISO) lists over 30 current standards covering areas such as reader protocols, performance test methods, guidelines for use in item management and in animals. Over 20 additional standards are currently at various pre-issue stages.
EPCglobal is a venture founded by the global standards organisations GS1 and its American member organisation, GS1 US, who are primarily involved in the development of standards for supply chain management, and previously set global standars for barcodes. EPCglobal’s brief is to provide similar standard for commercial applications of RFID technology, and works with both suppliers and end users to set standards benefitting both.
EPCglobal was responsible for developing the EPC Gen 2 standard in 2004, which provides a protocol for communication for UHF RFID tags operating in the 860-960MHz range. This standard was subsequently ratified by the ISO and incorporated into ISO 18000-6. This standard provides for uniquely numbered RFID passive tags acting as an Electronic Product Code (EPC), which can be read globally by any EPC-compliant RFID reader.
The benefits of a guaranteed unique EPC serial number are obvious – any such RFID passive tag can be tracked worldwide. The EPC also provides a specification for a network through which this tracking can be done – the RFID reader passes the information to a computer which queries a name service to determine where to access further details on the tagged object, in a similar fashion to how a DNS resolves a web address. Together with standards for how data is stored, read and updated, EPC Gen 2 provides a complete framework for international use of RFID passive tags for supply chain management.
The issue of available UHF frequencies in different coutries is still present, however. EPCglobal maintains a list of UHF RFID regulations in both GS1 member countries and major non-members, which includes permitted frequencies and power levels in each country.
EPCglobal also provides a set of recommendations on how RFID passive tag use should respect consumer privacy, making consumers aware of the presence of RFID passive tags on products, advising them on how to disable or remove them or learn more about them, and ensuring that personally identifying information is not retained.
Passive RFID tag cost factors
by passive on Sep.02, 2009, under Cost, Overview, Passive RFID tags
Active RFID tags generally cost at least double figures, although they provide greater range and typically more functionality than their passive counterparts. RFID passive tags cost far less, although price can vary depending on a range of factors.
The amount of memoryon the chip is a major factor, and different sizes are suitable for different applications. Lower cost tags might only offer 96 bits of storage. That’s 12 characters, assuming 8 bits per character. While this might be enough to hold a product key or a unique serial number, it will need an external database to hold further details, which your reader will need to be able to connect to. A tag with 512 bits providing 64 characters might negate the need for database connectivity, while larger chips storing 1-8 Kb could store both current and historical data directly on thechip without ever needing to refer to an external source.
High frequency tags can cost from twice to four times as much as ultra high frequency tags with the same characteristics.
The tag housing needs to be considered: tags embedded in fobs or cards will cost more than a simple tag mounted on a substrate. Another common tag format is smart labels: RFID passive transponders inserted between printed labels and an adhesive backing.
Tags which are shielded to function in harsher conditions, or to work near metal surfaces which would normally interfere with the signal, will be more expensive.
Increasing the range of the transponder will add to the expense, particularly as RFID passive tags have a much shorter range than active tags, due to their need to draw their power from the RFID reader.
Quantity, as always, can be a major factor. Bulk order of hundreds of thousands might save as much as 20% against order measured in the tens ofthousands.
These are some of the main factors influencing the cost of passive RFID tags. The other side of the RFID cost equation is the cost of RFID readers.
Passive RFID tag types
by passive on Aug.19, 2009, under Overview, Passive RFID tags
Modern RFID passive tags all share certain basic characteristics. They are composed of an antenna and a microchip, and a battery for active and semi-passive tags. They work in the same manner:
The passive tag remains dormant until activated by energy from an RFID reader’s antenna. The tag then sends the data stiored on the microchip as radio waves to the reader, powered by energy derived from the reader’s electromagnetic field. The reader interprets the radio waves as data, and can also update the data on the chip.
With decreasing production costs, and without the need for their own power source, passive RFID tags have now reach the point where they can be used disposably.
While the word “tag” is generally used when talking about RFID systems, an RFID tag is specifically an RFID transponder (the microchip and antenna) mounted on an underlying layer. While this is the cheapest option, other possibilities exist:
- the transponder can be placed within a printed adhesive label to form a smart label, which can be used like a barcode, but with the ability to be read without line of sighth and have its data modified;
- it can be embedded in a plastic card, and used in access control or transport pass systems;
- it can be integrated into a container to enable tracking of the contents;
- the transponder can be protected by special packaging to withstand extremes of temperature or other harsh conditions which would otherwise damage it.
The production cost will obviously increase if the transponder is packaged in such a manner.
We will continue to use the term “tag” as an inclusive reference to any of these alternatives.
Whether tag data can be updated is another point of differentiation.
- Read only tags can’t be updated and store a unique serial number, which can be used to uniquely identify them but will need to reference an external database to find more information about the tag.
- Read/write tags can have their information updated many times.
- Write once, read many, or WORM, tags can only be written to once, after which the stored data cannot be updated.
Thus there are a variety of passive RFID tag types, with the most appropriate dependent on the nature of the application in question.
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