Hosted by IDTechEx
Printed Electronics World
Posted on May 20, 2004 by  & 

Ultra Small UHF Tags

New miniature UHF tags

New miniature RFID tags working at UHF frequencies were demonstrated at the recent Smart Labels USA conference in Boston USA. These tags are of great significance because UHF tags are becoming the de facto standard for pallets and cases worldwide now the Koreans and Japanese are changing their radiation laws to accommodate them. That has resulted in Wal-Mart, Albertsons, Target, Tesco, Metro, Carrefour, the US Military and others specifying them to EPC conventions for pallets and cases. This will lead to global demand of around 40 billion tags yearly, contrasting with the sub 2 billion sales of all types of RFID tags in the last 50 years. Understandably, these companies want to stick to UHF for all applications if possible. They do not want the cost and complexity of multiprotocol, multifrequency readers if they can avoid it.

Many new problems for UHF

However, this poses many problems, because whereas reading pallets is often line of sight or through benign materials such as wood corrugated paper or plastic, the next challenge, which is item level tagging, involves far less favourable obstructions such as water and metal which reflect and absorb electromagnetic radiation, particularly at UHF frequency and above. We have to wait and see whether that can be overcome without the unacceptable extra expense of multiple tags on products.

Size problem overcome?

However, one other concern may now have been addressed satisfactorily and it is size. Because at high frequencies the basic design of antenna has to be a half wavelength, UHF has often given the largest tag. This is no problem on large things such as pallets, cases and vehicles but it is unacceptable on or in small items on the shelves of pharmacies and supermarkets. Enter Matrics and Avery Dennison exhibiting at Smart Labels USA with UHF tags smaller than any seen before - typically about 2.5 centimeters by 3 centimeters. This has been achieved by zigzagging the dipole in the case of Matrics. Their new product is compared with their enormous multiantenna design for pallets in the figure. Avery Dennison showed a similar size of UHF tag but with "paddle" metallization and, although the company is not prepared top say more at this stage, we suspect the physics used involved resonance. Both products have a maximum range in the region of 30-90 centimeters Curiously, no one seems to be using fractal antennas designed by the company of that name despite these being small at UHF - even fitting in a bottle top. Either way, the new tags are no bigger than 13.56MHz ones of similar range.

Small UHF antennas cannot perform as well as large

So do these tags obsolete the large tags they currently sell? We think not, because the larger tags have longer range such as the three meters required for pallets and they are designed to have very little directionality and be damage tolerant. Which raises questions as to whether the small ones are damage tolerant enough (we suspect yes) and omnidirectional enough, particularly when curved around e.g. plastic bottles of pills (we say probably - UHF is quite good for omnidirectionality). Are they small enough for all item level tagging? Probably not. Are they going to have problems with water, metal etc.? Yes, we suspect they will. However, the proximate task is for these companies to help their clients meet the Wal-Mart mandate to tag Class 2 (narcotic) drugs at item level immediately and here there is usually no water or metal or at least minimal amounts as with blister packs.

Optimism at Matrics

Matrics are very optimistic. They have done trials and their interrogators are now installed in a Wal-Mart depot ready to monitor pills down to the 100 pill pack. The Avery Dennison design, if resonant, will have to be different for every UHF frequency around the world but that is not onerous. It may be more omnidirectional. We shall see. Alien Technology and others will have other solutions for small tags at UHF.

Very little track record for UHF tags at item leve

However, almost all item level tagging to date has been at 125-135KHz and 13.56MHz thanks to companies such as Texas Instruments. Some 13.56MHz proponents have expressed their belief that Wal-Mart is coming to terms with having 13.56MHz for item level but whether this is firmly based or just a triumph of hope over reality for these suppliers only time will tell.

The challenge of air baggage

Meanwhile, the most challenging rollout for Matrics is probably the 100 million tag order for McCarran International Airport Las Vegas. Unlike the Wal-Mart requirement for tagging Class 2 drugs where liquids and metals are not usually involved and the packs are in an orderly array, none of this is true with air baggage where the muddle of the average delivery carousel involves a great deal of metal in the carousel and the widely varied shapes and sizes of the baggage itself. Liquids also present as wet bags and beer, whisky and so on in the bags.

Thorough testing

Matrics tell us that, contrary to popular opinion, they have done extensive trials of the UHF tag system in the baggage tagging application at McCarran and all is going ahead. They are not worried that almost all other trials of RFID on air bags over the last ten years have been at other frequencies and are therefore irrelevant. At least they have chosen a good partner. McCarran earns $24 million yearly in profit from 12,000 slots (gambling machines) and its earnings from other non aviation aspects such as parking are also so substantial that landing fees are way down the order of income. It is a wealthy airport that can afford to experiment and correct mistakes.
 
More IDTechEx Journals