IDTechEx recently published a highly technical, yet extremely interesting, article in its Smart Labels Analyst publication, about how some companies are achieving longer read ranges with HF (13.56 MHz) tags. The article provides in part:

"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 to drugs 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 to Intermec 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). More importantly, UHF can give interference between interrogators and it is only approved in Europe for narrow bandwidth and low power, restricting its range to one meter or so, and then only if water and metal are not causing problems. For that reason alone, although some 15 million RFID air baggage tags were sold in 2005 and 60 million will be sold in 2006, almost none will appear in Europe. That is leading some European retailers and airports to look at HF. Indeed, Airport World recently reported that Symbol Technologies had achieved a satisfactory 2 to 3 meters range with air baggage tags working at HF in Europe.

Many ways of achieving longer range at HFThere are many ways of achieving longer range at HF and some are shown in the table.

At Metro, the world's third largest supermarket chain, 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 of the small size of the tag, so it fits easily on even the smallest container such as drugs. Also valuable is the fact that that the range is controlled (you know exactly what range you are achieving) and there is therefore no problem distinguishing one item from another. A UHF label may have long or short range depending on what is near to it at the time so it may be looking at the wrong thing. UHF labels have been too big for small items.

However, in any attempt to standardise on HF for item level tagging, 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 have been much smaller than HF tags (the opposite of the situation with short range 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.

The large tag optionOthers go for large HF tags and more modest interrogators. For example the DHL postal tag covers the whole of the package as shown below. 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."

Smart Labels Analyst normally is a paid subscription publication. However, on its website IDTechEx is offering a free sample of the December issue in which the full article appears. Go here to download the free issue and read the entire article (PDF file).