RFIDbuzz.com

March 03, 2004

As mentioned, someone was microwaving their US 20 dollar bills and claimed that "RFID tags" in the bills caught fire when doing so. Several websites have picked up the news and provided commentary - conspiratorial as well as sceptical; below are some extracts of the current theory(/ies):

BoingBoing reports:

[JC] The same thing happens if you take a stack of copy paper and microwave it. A central point in the stack heats and eventually ignites and burns up and down the stack from that point.

[Alex Q] Also of interest (besides JC's comment) is that they say they are messing with the NEW twenties, but in fact those are the old ones. you can tell because the portrait of Jackson has the circle around it, which is absent in the new twenties.

It is rather obvious that this is nonsense. A bit of knowledge on how microwaves, RFIDs and anti-theft-systems work comes useful here. Lets begin with the anti-theft systems.

The simplest class of anti-theft systems works by measuring the drain on a HF field generator that is caused by introducing a resonant antenna into the field. The antenna is in the small tag thats placed on the protected products. There are various other kind of anti-theft systems, but these are quite frequent. The alarm goes invariably on if something suffiently resonant is in the field. Resonance can also be caused by a simple strip of metal, wire, metallized foil or pattern of conductive ink that has the right measurements.

The new $20 bills apparently does not contain a metal strip like the Euro bills. At least thats what I gather from the US Bureau of Engraving and Printing . The thread on Slashdot suggests that the metal components in the ink of the new bills cause a sufficiently good antenna when stacked. Single bills got no burnmarks.

For research purposes I microwaved a 5 Euro note and got the expected effect. Within a few seconds little sparks where visible on the metal stripe and on the metal printing on the right side and caused the expected burnmarks. From analyzing the note under a microscope it is clear that no RFID is in the Euro note. So much for debunking the "when microwaving makes burnmarks, it must be RFID" myth.

• RFIDbuzz.com: "RFID" tags in new US notes explode when you try to microwave them
• RFIDbuzz.com: RFID in US Postage stamps? Dollar bills? - about US plans to tag dollar bills and other things in the future
• RFIDbuzz.com wiki entry on the US Internal Revenue Service