RFID tags in Arctic conditions?

I have an application in which RFID tags need to respond and send data while at very cold (10 deg F to -30 deg F) temperatures. They will have been put in place for up to one year. While not exactly the application, it's as if I were attaching RFID tags to the entrances of Arctic Fox dens - a very cold environment with the possibility of deep and total snow cover.

Readers would be protected and would have minimum exposure to the cold.

In such cases I would need to find certain ones of such a hidden collection. I suspect the reader would need to be of special design, needing proximity sensing as well. While GPS could get us in the approximate vicinity of a known object, this special reader would need more exact proximity capability that resembles some metal detectors and emit some sound that increases in intensity the closer you get to the object.

Distance range, reader to tags, could vary to, say, 60".

Before contacting some development firm for price quotations, is what I've described well within the realm of feasibility? Len Miller

Reply to
Fatfreek
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Sounds more like an application for radio direction finding. At 60" plus snow cover it would almost have to be active. For example transmitters that emit only brief bursts so the battery lasts a long time. Since this makes direction funding tougher you might consider equipping the motes with receivers so that they can turn to higher duty cycle or a timed continuous transmission when the guy with the reader presses the "Mote number 17 - please answer now for 5 minutes" button.

You could experiment with low power modulated AM transmitters, go up into the mountains, throw some snow on them, try to find them using a portable AM radio that has a good clean ferrite antenna. There are tricks to overcome the 180 degree ambiguity to some extent but first I'd try to locate a few hidden motes. Have someone else bury them so you really don't know where they are. But mind the FCC limits on low power AM. This can also be a concern depending on the jurisdiction in your planned deployment area. Last but not least mind the animals. If arctic foxes are anywhere as curious as the gray foxes that live near the office here they'll try to "reverse engineer" anything that looks interesting or unusual. Especially their kits.

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Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

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Some good thoughts there, Joerg.

Ah, yes, those curious foxes. Thanks for that alert.

Len

Reply to
Fatfreek

I get the impression the tags are static and possibly buried in snow for a year, the readers are mobile but probably have to withstand the same temperatures albeit not for a year at a time. If I have misread your intentions well, alas. Soldiering on...

  1. Battery types: this will be critical to the readers as many types have reduce capacity below 0C (uh, 32F), significantly lower at -10C and freeze at almost exactly -20C (-10F). So avoid normal alkalines, lithium ion etc. Special alkaline types for low temperatures are available from one of the big battery manufacturers, Duracell I think, but for non rechargeables you'll need to be careful about circuit current consumption. Lead Acid may be your only option for rechargeable cells (heavy!). I strongly recommend you do far more testing than you originally assumed because batteries are often the Achilles Heel of instruments when operated in extreme environmental conditions; the battery manufacturers may CLAIM operation at -20C but capacity will be way down and they may gradually degrade if left that way for months.

  1. However I have good news! I was looking into RFID tags myself recently and discovered SAW types are excellent at extreme environmental conditions, PLUS they can be self powered from the incoming RF pulse, PLUS their range is generally better than other types. Have a look at this page...

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If you scroll down to figures 21 and 21a you'll see the implementation of these things as tags is pretty straightforward, and already in use.

See the comparison between SAWs and different RFID technologies on page

4 of this document:

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I would be interested to hear others' views of this technology. I'm a newbie to RFID. Have I missed something or is it really rather good?

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Nemo
Reply to
Nemo

That's right, materials is a very important consideration. Many Lithium batteries are spec'd down to -20C but will work further down. It is important to have an indepth conversation with an engineer from a company such as Duracell.

Other parts are of concern, too. For example, I would not use electrolytics. This means you either have to have the space for lots of ceramic caps to bridge the transmit current surges or the battery has to be large enough so the voltage won't collapse.

Passive sensors would be a stretch here, I don't think it'll work in this case. IIUC the distance can be tens of meters and the devices may have a thick layer of snow over them.

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Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

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