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Re: [RFI] Wal-Mart to Put Radio Tags on Clothes - WSJ.com

To: RFI List <rfi@contesting.com>
Subject: Re: [RFI] Wal-Mart to Put Radio Tags on Clothes - WSJ.com
From: Andy <ingraham.ma.ultranet@rcn.com>
Date: Fri, 23 Jul 2010 22:56:02 -0400
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
I'm not very knowledgeable about RFID tags, which is what I think
these are.  But my understanding is that RFID devices have no internal
power; they get their power from the nearby scanner, and otherwise
can't transmit anything.

But I think I've not actually seen one either.  The theft-deterrent
tags I've seen (and taken apart) on purchased items in the past, had
no apparent active circuitry such as an IC in them and seemed to be
just a tuned circuit of some sort.  (I'm sure this shows my ignorance
about them.  Someone will probably point out that they also had
something like a diode, which I didn't see.)

> BTW:  Is an aluminumized static bag sufficient to shield credit
> cards and driver's licenses from undesired scanning or is something
> more robust required?

Good question.  For ordinary credit cards without a smart IC, they use
a magnetic strip, and a static bag provides little if any shielding to
magnetic fields unless it's mu-metal or some other magnetic material,
which I'm sure they aren't.  On the other hand, you've got to be
really close to the magnetic strip to read it.

I really don't know if they shield RFID type signals.  I thought the
conductive substance is a very poor conductor, and rather thin, so it
might not do much to the RF.

My driver's license has optical scan codes on it (1D and 2D barcodes)
and I think that's it.

Andy
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