Re: [Vo]:Progress in invisibility cloaks
Here's a 1980s idea I never followed up: easy way to make aircraft invisible. I realized this was possible while working with GRIN lenses.
If we were living underwater, we could cover an object with a layer of alcohol or syrup, then adjust the index profile so the object became a mirror via internal reflection, or perhaps even guided the light around the object (the object can never vanish for perpendicular rays, but its perceived optical diameter can grow smaller, perhaps even approach zero.)
In air, the same thing is possible using hot surfaces to heat adjacent air, but only for very low angles (such as a disk-shaped aircraft, or stealth aircraft with sharp-edged wings melded into fuselage.) The craft would be invisible if viewed in the distance, but obviously still be visible when viewed from directly below. The phase velocity of light is higher in the hot air, so from internal reflection, the aircraft acts like a mirror reflecting the sky. Perhaps the heat profile could be sculpted so light is guided around the craft.
Rather than hot surfaces, the air could be heated by surface plasma, thus using less fuel as well as avoiding a bright thermal IR signature. To do this you'd want to cover the aircraft with high-volt insulation. Lowest weight would be thin ferroelectric piezo tiles, allowing the HV generator to run at fairly low freq.
Since the phenomenon is created by air, the aircraft would need to hover or move very slowly, thus avoiding stripping off it's "cloak!" I doubt it would work on a helicopter though. Heh. Best for antigravity vehicles?!
The system would have an interesting side effect: psych warfare issues, we could make the same aircraft *psychologically* invisible by turning on the plasma in the evening. Everyone still sees the aircraft, but since it's flying slow while glowing green and purple with a loud acoustic hum, nobody dares report it, and if they do, they're not believed. (Run a disinfo campaign that stirs up ridicule for any eyewitness reports resembling a plasma-covered disk-shaped military plane.)
Oddest of all: the phenomenon is frequency dependent, so if it was designed for visible light centered at 550nM, the aircraft would probably still show up on UV and infrared cameras.
(((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty http://staff.washington.edu/wbeaty/ beaty chem washington edu Research Engineer billbamascicom UW Chem Dept, Bagley Hall RM74 206-543-6195 Box 351700, Seattle, WA 98195-1700
