State of Protest

This post is one in a series dedicated to deeper analysis of the W1N5T0N annotated version of Cory Doctorow’s Little Brother, particularly to my own annotations.¹

SPOILER WARNING *** If you haven’t read Little Brother, go read it (at least through Chapter 2) first. The following contains spoilers. ***

The chapter 1-2 transition of Little Brother involves Marcus, the main character, trying to skip school with his friend Darryl, who realizes to their dismay that he was still in possession of a library book that contains an RFID (“arphid”) tracking chip. The chip was not only used to keep track of the books, but was also used by the school to identify students who skipped class. Once the book passed through the school perimeter, Darryl’s book would be identified by the arphid as leaving school grounds, and Darryl would eventually get in trouble.²

Marcus determines that he cannot “hide” the chip by way of a Faraday pouch, and in chapter 2, figures that his only option is to “nuke” the chip by popping it in the teacher lounge microwave. Marcus asserts that “30 seconds in a microwave will do in pretty much every arphid on the market.”³

Heliosxx, a commenter on W1N5T0N asked: “Isn’t 30 seconds a bit much? Wont they burn out in just a couple of seconds?”⁴

I immediately thought: “Good questions.” And I set about to try to figure it out.⁵

Here’s the relevant paragraph from the text and the comment I came up with. Enjoy!

Little Brother, Chapter 2, Paragraph 9

That left me with only one option: nuking the thing. Literally. 30 seconds in a microwave will do in pretty much every arphid on the market. And because the arphid wouldn’t answer at all when D checked it back in at the library, they’d just print a fresh one for it and recode it with the book’s catalog info, and it would end up clean and neat back on its shelf.

Procrustes’ comment to Little Brother, Chapter 2, Paragraph 9

According to Instructables, it would only take 5 seconds in a microwave to destroy an RFID chip. However, Little Brother indicates that 30 seconds is sufficient to destroy “pretty much every” RFID on the market. RFID manufacturers often post operating temperature ranges, and one example of a high rated transponder indicates that it can sustain temperatures of 428°F for 30 seconds.

Microwave power/temperature correlations vary by model, but one source sites a model with 650-800 watts of power generating 425-500°F at 90-100% power.

At first glance, to safely assume an RFID chip will be destroyed by a microwave of unknown wattage, 30 seconds appears to be the minimum “safe” time. However, microwave object temperature does not immediately reach the top temperature. Wattage affects how quickly temperatures of materials are reached, and thus 30 seconds is not the literal minimum safe time for the chip linked to as an example above. Instead, it is the minimum safe time once the object has reached that temperature. It’s unlikely that Marcus would have been able to nuke the 428°F rated chip in just a few seconds at what was probably a low-wattage microwave, but that also may depend on exactly how the RFID chip materials are affected by microwaves.

Also, it is questionable whether “temperature” is a good gauge of how a microwave affects its occupants. According to some of the comments on the Built on Facts Science Blog, temperature is not a meaningful measure in microwaves because radiation inside a microwave does not have a thermal spectrum. However, for purposes of determining whether an RFID chip would survive, it should be sufficient that objects subjected to microwaves attain a certain measurable temperature. If the RFID chip in Little Brother was rated to 428°F for 30 seconds, then the microwave holding the chip must cause the temperature of the RFID chip to reach and at least maintain a temperature of 428°F for 30 seconds for the chip to at least void its warranty. But just because a chip is rated such does not mean it will necessarily be fully destroyed after reaching the rating maximum.
It’s quite possible that, depending on the wattage of the microwave, it would require even a longer time in the microwave to “ensure” destruction.

Chip and housing material would also have an effect on whether any microwave would be sufficient. Considering the RFID chips in the book were designed to prevent students from skipping school, it’s unlikely that the school would spend the amount of money necessary to buy chips that could survive nuking for more than a few seconds. Note that the book does not say exactly how many seconds were used to destroy the RFID book chip, though the sparks suggest that the chip died (however, some metals cause sparking in microwaves that may be mistaken for destruction). (The “conscientious” wrapping of a book in paper towels, however, was a tremendous fire hazard unless the paper towels were wet.)

The material of the RFID chip would affect the temperature, as indirectly demonstrated by a patent application for Microwave susceptor film to control the temperature of cooking foods (Under Detailed Description of the Invention, see notes for FIG. 4, describing the author’s representative plot of the coefficients of reflected, transmitted, and absorbed microwave energy as a function of resistivity). The USDA has also noted that wrapping foods in aluminum foil will act as a shield, since microwaves cannot pass through metal. This fact would suggest that if an RFID were wrapped in a similar protective metal that doesn’t interfere with the chip’s ability to operate, it might be extremely resistant to microwaves.

A patent issued in 2001 describes a High temperature RFID tag that, according to the patent, can survive at 275°F, but with a housing that would survive at 572°F “without substantially affecting the intended functions of the tag.”

Thus, there are multiple factors involved in determining whether an RFID chip would become disabled due to exposure to microwaves in a microwave oven.
1. Microwave wattage (relates to the time necessary for an object to reach a certain temperature).
2. Time in microwave (at low wattage, more time may be necessary).
3. RFID chip materials (some chips are designed specifically to survive in harsh conditions).
4. RFID chip housing materials (it’s possible that some chips would be designed with microwave-resistant housing).

In the book’s scenario, the main character is giving a bit of “playing it safe” advice based on that character’s limited knowledge of RFID chips, but it’s likely that there exist chips that would have survived a 30-second nuking, especially considering the microwave and RFID housing used.

For the fun of it, see the USDA’s “Time-to-Boil Test” for microwave ovens to determine wattage:

Measure a cup of water in a 2-cup glass measure. Add ice cubes; stir until water is ice cold. Discard ice cubes and pour out any water more than 1 cup. Set the microwave on high 4 minutes, but watch the water through the window to see when it boils.

* If water boils in less than 2 minutes, it is a very high wattage oven 1000 watts or more.
* If water boils in 2½ minutes, it is a high wattage oven about 800 watts or more.
* If water boils in 3 minutes, it is an average wattage oven 650 to 700 watts or more.
* If water boils in more than 3 minutes or not by 4 minutes, it is a slow oven 300 to 500 watts.

1. Applicable Creative Commons License information. [<]
2. See Chapter 1, paragraphs 102-104. [<]
3. See Chapter 2, paragraphs 8-11. [<]
4. See Paragraph 9 annotations. [<]
5. Disclaimer: I am not a scientist. I do have a healthy technology background, but I’m by far not an expert. Others out there are much more qualified to make such determinations, and I’ve done what I can to seek those determinations out and compile them into an at least somewhat plausible comment. Also, don’t try this at home. [<]