Advances in RFID help food traceability

IT is sometimes said that RFID at more than one metre’s range is impossible under the radio regulations of most countries other than at UHF, a band of license free frequencies around 900MHz.

It is true that longer range is available if a battery is present in the RFID tag, and this is a viable solution for vehicles and trailers. However, these so-called “active” tags have limited life, are expensive, relatively large and have more parts to potentially fail.

This has meant UHF passive tags have been standardised for pallets and cases of food at the behest of leading US and European retailers and the US military.

UHF RFID not ideal for all food applications

However, although UHF RFID works reasonably well with nothing in the way, it can behave very unpredictably when water or metal is nearby, let alone in the way.

Sometimes the proximity of water or metal can prevent any reads taking place. At other times, things can be unexpectedly sensed 50 meters away, creating confusion about what one is sensing.

Improvements to UHF systems are occurring, but there have also been recent advances in the traditional HF (13.56MHz) and microwave (2.45GHz) systems, making them longer range and more suitable for traceability applications.

Password protected HF tags

Texas Instruments has released a password-protected, standards-compliant write mechanism for HF tag data, introduced a quality control inlay-manufacturing process, and offered a unique solution for pharmaceutical tagging that will be relevant to food.

Eventually, item level tagging of food in the supermarket will have to involve tags staying on after the till and not being deactivated. IDTechEx finds that 30% of the potential benefits and paybacks at item level occur after the till including better recalls, fraud reduction and consumer rewards.

Longer range RFID at HF

Icelandic Fisheries successfully trialled HF for wet fish in pallets and cases because UHF did not work, but the range was only one metre with the usual credit card sized HF label.

There are those who argue that total cost of ownership can be lower with an HF system working at two meters.

There are many new ways of achieving longer range at HF without necessarily having very large tags and readers.

For short range smart shelving, HF seems best because at short range it gives the smallest tag, is controllable, and there is therefore no problem distinguishing one item from another.

A UHF label may be looking at the wrong thing and the tag can be too big for small food items.

For large items, one approach is to use large interrogatory antennas rather like anti-theft tag pedestals in stores.

The large tag option

One option is to adopt large HF tags and more modest interrogators.

Large HF labels for two meters range are not a new idea, such as those at A5 size used on the back of the number on the chest of marathon runners.

Japan’s Miyake has also fitted large numbers of roughly A5 size labels on pipes that see through two meters of soil using frequencies around 13.56 MHz.

Smaller HF tags for long range

However, such large antenna solutions require larger production capacities, and are area limited in reel-to-reel processes.

Other approaches being developed include French company DAG Systems’ technology of “unconstrained” detection in the band 13.56 Mhz, for which they claim long distance detection of up to ten metres through large area or volume (2D or 3D), unlike UHF which usually approximates to a beam, often with blind spots.

The current DAG tag for ranges of many meters is rather large, but other companies have developed so-called fractal antennas to reduce the size of such tags for a given range.

Energy harvesting can also be used to keep tag size small. None of these tags have any problem with the water associated with most foodstuffs.

Breakthroughs in SAW RFID

Surface acoustic wave (SAW) RFID has been around for some time, benefiting from reliability and cost reduction that comes from the billions of non-RFID SAW applications in mobile phones, pagers and so on.

To this day, no one knows how to make SAW RFID that is active or read-write, though RFSAW of Dallas has shown how it can sense strain or temperature without extra sensors and even give position.

Both functions are possible with silicon chips and separate sensors but only at considerable cost. For example, there are instances of cattle and food with temperature-monitoring RFID today, but only in limited numbers.

While a disadvantage with SAW RFID is that it still employs a brittle chip like silicon, processing steps are fewer and less precise, giving the promise of lower cost than silicon chip based RFID.

The unique physics of SAW ID chips is said to solve major RFID issues and achieves reliable reading at large separation between tag and reader, surmounts the tendency of liquids and metals to block reading signals, and supports commercial full pallet reading which is a vitally important RFID capability.

In many applications, SAW tag read range is sufficiently large so that passive tags can replace high-cost battery-powered active tags.

SAW-based RFID systems have the inherent ability to measure tag position, direction of travel, and tag temperature, which are costly or difficult to implement with competing technologies.

Furthermore, SAW tags can withstand security and safety related processes that involve elevated operating temperatures, high energy x-rays, or gamma ray sterilisation as is used with some food and medical supplies.