Longer range RFID at HF
Dez 01, 2005
It is popularly believed that HF (13.56 MHz) RFID is limited to one meter range. However, there are many reasons to seek longer range at HF and it has even been available and in use for some time. The reasons for not using UHF, popularly portrayed as "the only way to go" for longer range with a passive tag, include fear of heating and molecule damage in healthcare and the effect of water and metal that can make UHF tags very short range in certain circumstances. Icelandic Fisheries successfully trialled HF for wet fish in pallets and cases because UHF did not work but range was only one meter with the usual credit card sized HF label. More would have been welcome. There are even those who argue that the total cost of ownership can be lower with an HF system working at, say two meters. For example, there are no royalties to pay and ten times as many HF tags have been made, giving economies of scale. (However, the volume story is changing fast in favour of UHF).
Many ways of achieving longer range at HF
There are many ways of achieving longer range at HF. At Metro, one of the world's largest supermarket chains, they want to tag at item level using one frequency and one standard system if possible. For short range smart shelving, HF seems best because range it is smallest, it is controllable (you know exactly what range you are achieving) and there is therefore no problem distinguishing one item from another. A UHF label may be looking at the wrong thing and be too big for small items. The problem lies with large items such as apparel, where most practitioners in Japan, the UK and US see UHF as best because there is no water and little metal to worry about and at two meters range the UHF tags are much smaller than HF tags and potentially cheaper, or so it is argued, because the antenna on the tag can be cruder and of poorer conductivity and still work well. How to make HF work on large items for the sake of standardisation? The Metro approach is not to make the HF tag enormous but to use large interrogatory antennas rather like the anti-theft tag pedestals in stores. Maruetsu in Japan has had a similar approach with their many trails in their food stores at HF.
The large tag option
Others go for large HF tags and more modest interrogators. For example the DHL postal tag covers the whole of the package. Supplied by Denstron, it was so successful in trials that an invitation to tender for one billion has been issued, to test market pricing but not, at this stage, to actually commit. (Another myth is that you cannot have ISO tags at HF - ASK and others happily offer them).
Large HF labels for two meters range are not a new idea. For example, UPM Rafsec of Finland has long sold them at around A5 size to go on the back of the number on the chest of the marathon runner. Miyake of Japan has fitted large numbers of roughly A5 size labels on pipes that see through two meters of soil using frequencies around 13.56 MHz. These use no chip and are a "Swept RF" LC array but the large laminar coil antenna is the same.
Greedy of production capacity
However, these "large antenna" solutions are greedy of production capacity which is area limited in reel to reel processes. Any other approach is also therefore interesting.
Ten meters range?
For example, a French company DAG-System, the electronic branch of the PYGMALYON company, has been developing and manufacturing RFID systems since 1998. Holding several patents, PYGMALYON has developed a unique and very innovative technology of "unconstrained" detection in the band 13.56 MHz for which they claim long distance detection of up to 10 meters through large area or volume (2D or 3D) unlike UHF which usually approximates to a beam, often with blind spots. With antennas able to detect tags within a 60 cubic meter volume, this technology was first developed and sold for sports events. For example it was used in the Rome Marathon.
For the longest ranges, the tags are still large but not as large as they would have to be using conventional means. The company is not prepared to reveal how its interrogatory system achieves this but there are patents that the interested reader can consult. Longer range can also be enjoyed as better range in hostile environments and this technology is no exception.
In addition to this, other companies such as Fractal Systems are exploring the capabilities of fractal RFID tag antennas to achieve long ranges in a smaller form factor.