Mhlnews 1422 Trans03 00

A Fresh Look at RFID Temp Sensors

Jan. 1, 2007
For those concerned with the transportation climate of perishables, pharmaceuticals, or humidity-sensitive materials, new RFID tags may have something to offer.

Listen Closely.... No, those aren't the voices in the head of the person sitting next to you thinking too loudly, they're your products telling you about their day. To hear what they're saying don't get out the aluminum foil hat; get out your RFID reader.

If you're concerned with the transportation (either to market or from suppliers) of perishables, pharmaceuticals, or even certain humidity-sensitive electronics or raw materials, these new tags may have something to offer. Sensor-enabled RFID tags aren't anything new. Semi-disposable sensor-enabled RFID tags with data loggers are. While still in the early stages of introduction, these battery-assisted passive tags offer temperature and humidity logging at a fraction of the cost of older tags.

A study using this new generation of data logging RFID tags was conducted by Michigan State University to determine temperature variation in different size refrigerated trailers. Temperature-loggers were placed on every pallet and on some of the cases themselves. The study uncovered a wide variation in the temperature in these trailers, far beyond what the researchers expected from air circulation patterns. While the study did not purport to offer conclusive data on the potential effects of these variations on food product expiration dates, it did show that "micro-logging" could make it possible to develop models that do.

Many distributors and retailers of perishable goods would like to create an effective "FEFO" (First Expire First Out) inventory management system. While they can do this in a general sense with existing data, in-transit data down to the case level has been impossible to gather. And that leads to waste.

Here's an example. Two different truckloads of bananas could arrive two days apart. All the cases in the first load have been maintained at a consistent optimal temperature. Some of the cases in the second trailer, however, experienced above optimal temperatures for a significant period of time. Since the variation was localized, the temperature logger in the trailer did not detect or record it. Thus, the affected fruit in the second load could well spoil before it's even put out for sale.

The tags used in this study are currently only semi-disposable. That is, they're thin, flexible, rewritable, and suitable for insertion into a packing list pouch. They have a thin film battery that will last for more than one use and are not really inexpensive enough that you would want to use them only once and throw them away.

However, for the purposes of performing tests on your in-transit products, they could be either considered disposable (in limited quantities) or reclaimed and reused on a limited basis. Otherwise, reusing these tags in a true open system would create a logistics nightmare.

For returnable shipping containers that come back to your facility (or your suppliers'), they could easily be used to monitor the supply chain environment for sensitive materials. Because of the thin film battery, they are not intended for very long-term use.

The Michigan researchers found that refrigerated trailers have micro-climates that exist even when a trailer is properly loaded. These micro-climates lead to noticeable (although not always significant) temperature variations that had not been predicted. This research could lead to further study of refrigerated trailer air circulation systems or improved pallet and trailer loading configurations. But that's in the future.

In the short term, you can use these tags to see how your products "feel" at any part of their trip either by implementing a test of your own distribution chain or, if you discover that conditions warrant it, implementing their use on a full-time basis.

Bert Moore is a 20-year veteran of the AIDC industry. He is director of IDAT Consulting & Education, Alpharetta, Ga.

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