Sunday, August 17, 2008

Stealth Suits and how they work

Irreconcilable Differences makes extensive use of stealth suits, and I've already gotten questions on how they work. Before I go on at length about what chameleopoly is and how it works, there's this video I found on youtube that shows what it *does*.

(If you can't see the video, it's of a laptop rigged with a camera looking out the back of the screen being displayed on the front of the screen. If you can't see the video, you'll have to trust me that it's an effective illusion that the screen is transparent.)

From the glossary of Irreconcilable Differences:
Chameleopoly: Short for chameleopolymer, a family of polymer products whose color, pattern, and reflectivity is variable. The most common types are passive matrix, which requires no external power, and which gradually assumes the pattern on its darker side, and active matrix, which will digitally generate and display anything that would have been in the environment, were the chameleopolymer not there. One can, for example, watch TV through someone wearing a chameleopolymer suit, and in fact, most modern roll-up TVs are made of chameleopolymer.

I envision a layer of video sensors and some active processing that ensures that what is on the front of the suit looks just like what's on the back of the suit, and vice versa. Obviously this works better the less there is to see of the suit, which is why people wearing them tend to hug the walls. (Hugging the walls also reduces your chances of being walked into whilst invisible, and gives you some natural cover as well.)

It bears noting that the idea isn't original to me, particularly. Gibson's mimetic polycarbon suits did approximately the same thing, as does thermoptic camouflage in Ghost in the Shell. It's a common meme. My addition was to deal with the problem of body heat, by adding (in later versions of the suit) what amounts to a sponge layer saturated in liquid nitrogen, which is insulated from the body. Body heat is transfered to the liquid nitrogen layer and absorbed by the state change of some of the nitrogen from a liquid to a gas. The gas emerges from vents in the suit at ambient temperature. Given that nitrogen makes up 78% of Earth's atmosphere, this small amount of extra nitrogen would be devilishly hard to detect in the air space of a building. And yes, I did calculate how much heat the body produces, and how much heat a given volume of liquid nitrogen requires at sea level to vaporize and rise to room temperature, and those factors were all considered.

The result is a suit which is reasonably invisible to the naked eye, and exactly the same temperature as ambient air, making it invisible to infrared sensors.

I would have loved to see the Mythbusters try the liquid nitrogen idea in their Mega Movie Myths episode, and they did try hosing the wetsuit down with a fire extinguisher, which worked until it warmed up. The idea of carrying liquid nitrogen in the suit would have been interesting to see them explore, but the possibility of freezing Tori solid probably would have made it impractical. It was, in any case, gratifying to see that the basic premise of the suit's thermal control was workable in the real world. :)


1 comment:

JRS said...

After a long discussion with the guy who originally asked me how the stealth suit works, it becomes apparent that the simple front-to-back mapping I was imagining fails miserably in 360 degree viewing, due to not constraining the viewing angle enough.

Obviously the suit would have to do much more sophisticated mapping and modeling, perhaps even projecting light interference patterns to produce a hologram of the empty space the suit is in, for true invisibility.

As written, the suit assumes the color and patterns of the background, and is normally used against walls and such in well lighted areas, so perhaps simple camouflage is all that is required. All the suit really needs to do is remove the visual cues your brain uses to know that something is there.


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