Saturday, July 17, 2010

The "Stealth" Dragonfly

One finds interesting memes in the most unexpected places... In this case, the somewhat disappointing sequel to Susan Hubbard's wonderful "The Society of S" (vampire fiction verging on literature, and not to be confused with... uh, the recent spate), "The Year of Disappearances".

In the story, our young, vampire heroine, Ari, is musing about a dragonfly and its "motion camouflage". As I am fascinated with insects, I Googled it. The Wiki entry is, apparently, a stub of a military camouflage-related article, which also cites "active camouflage", and I quote:

"The active camouflage suit by name is credited to science fiction author Philip K. Dick in his 1974 novel A Scanner Darkly. Worn by the narcotics double agent Bob Arctor/Fred, the "scramble suit" is described as a flexible sheath covering the body of the wearer with a reflective/refractive coating on the inside surface that transfers the camouflaging pattern — projected by a holographic lens mounted on the wearer's head — onto the outside surface of the sheath."

For a more concise explanation of motion camouflage, however, I turned to an article in Plus, an online mathematics magazine, entitled: "They Never Saw It Coming" by Lewis Dartnell:

"The word "stealth" is often associated with high-tech bombers built to be invisible to enemy radar. This technology works through the aircraft's surface being specially designed and having a covering of radar-absorbent skin that ensures minimal radio waves are reflected back to the enemy radar transmitter.

There is another kind of stealth, however, that does not rely on hiding the presence of an object, but on masking the fact that it is moving. If the pursuer approaches along a particular trajectory it appears to remain perfectly stationary from the point of view of the target. The pursuer can use this "motion camouflage" to rush right up to the target before it is perceived as a threat. This technique could be used by missiles to remain undetected for as long as possible, and even appears to have been discovered by nature. There is good evidence that hoverflies and dragonflies have evolved this strategy to fly without being detected."

More can be found here... And, for the mathematics behind motion camouflage try here.

But, no, motion camouflage is not the technology which informs the latest attempts at creating "invisibility cloaks", which depend, instead, upon the refractive surface of specific metamaterials.

New: This just found; an invisible hotel for your next vacation... mega-cool!

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