The Invisible Cloak

A very cool story in today’s Washington Post.

My under­stand­ing is that early attempts at this “light bend­ing” tech­nique required bulky power sources and crazy optics. But from this Washington Post piece, it looks as if mate­ri­als sci­ence is begin­ning to catch up.

Seems to me at least in the early stages, vehi­cles and air­craft could use the tech­nol­ogy since they can carry more weight and gen­er­ate a lot of power.

And heck, I could sure use some of this stuff on my hunt­ing forays…those damned deer keep spot­ting me…

From the Post…

Their Deepest Darkest Discovery

Black is get­ting blacker.

Researchers in New York reported this month that they have cre­ated a paper-​​thin mate­r­ial that absorbs 99.955 per­cent of the light that hits it, mak­ing it by far the dark­est sub­stance ever made — about 30 times as dark as the government’s cur­rent stan­dard for black­est black.

The mate­r­ial, made of hol­low fibers, is a Roach Motel for pho­tons — light checks in, but it never checks out. By vora­ciously suck­ing up all sur­round­ing illu­mi­na­tion, it can give those who gaze on it a dizzy­ing sen­sa­tion of nothingness.

“It’s very deep, like in a for­est on the dark­est night,” said Shawn-​​Yu Lin, a sci­en­tist who helped cre­ate the mate­r­ial at Rensselaer Polytechnic Institute in Troy, N.Y. “Nothing comes back to you. It’s very, very, very dark.”

But sci­en­tists are not sat­is­fied. Using other new mate­ri­als, some are try­ing to man­u­fac­ture rudi­men­tary Harry Potter-​​like cloaks that make objects inside of them lit­er­ally invis­i­ble under the right con­di­tions — the pin­na­cle of stealthy technology.

Both advances reflect researchers’ grow­ing abil­ity to manip­u­late light, the fleetest and most evanes­cent of nature’s offer­ings. The nascent invis­i­bil­ity cloak now being tested, for exam­ple, is made of a mate­r­ial that bends light rays “back­ward,” a weird phe­nom­e­non thought to be impos­si­ble just a few years ago.

Known as trans­for­ma­tion optics, the phe­nom­e­non com­pels some wave­lengths of light to flow around an object like water around a stone. As a result, things behind the object become vis­i­ble while the object itself dis­ap­pears from view.

“Cloaking is just the tip of the ice­berg,” said Vladimir Shalaev, a pro­fes­sor of elec­tri­cal and com­puter engi­neer­ing at Purdue University and an expert in the fledg­ling field. “With trans­for­ma­tion optics you can do many other tricks,” per­haps includ­ing mak­ing things appear to be located where they are not and focus­ing mas­sive amounts of energy on micro­scopic spots.

U.S. mil­i­tary and intel­li­gence agen­cies have funded the cloak­ing research “for obvi­ous rea­sons,” said David Schurig, a physi­cist and elec­tri­cal engi­neer at North Carolina State University who recently designed and helped test a cloak­ing device. In that exper­i­ment, a shielded object a lit­tle smaller than a hockey puck was made invis­i­ble to a detec­tor that uses microwaves to “see.”

The first work­ing cloaks will be lim­ited that way, he said — able to steer just a lim­ited part of the light spec­trum around objects — and it could be years before sci­en­tists make cloaks that work for all wave­lengths, includ­ing the vis­i­ble spec­trum used by the human eye.

But even cloaks that work on just a few key wave­lengths could offer huge ben­e­fits, mak­ing objects invis­i­ble to laser beams used for weapons tar­get­ing, for exam­ple, or ren­der­ing an enemy’s night gog­gles use­less because objects would be invis­i­ble to the infrared rays those devices use.

The Defense Department did not fund devel­op­ment of the new blacker-​​than-​​black mate­r­ial, cre­ated by Lin and his col­leagues. But mil­i­tary offi­cials were among the first to call after a descrip­tion of the work appeared in this month’s issue of the jour­nal Nano Letters, Lin said in an interview.

Substances that absorb every smidgeon of incom­ing vis­i­ble light could com­ple­ment exist­ing stealth coat­ings that absorb radar waves, Lin said. He and oth­ers empha­sized, how­ever, that there are also peace­ful and more imme­di­ate appli­ca­tions for the black­est stuff on Earth.

Solar pan­els coated with it would be much more effi­cient than those coated with con­ven­tional black paint, which reflects 5 per­cent or more of incom­ing light. Telescopes lined with it would sop up ran­dom flecks of inci­den­tal light, pro­vid­ing a blacker back­ground to detect faint stars.

And a wide array of heat detec­tors and energy-​​measuring devices, includ­ing climate-​​tracking equip­ment on satel­lites, would become far more accu­rate than they are today if they were coated with energy-​​grabbing superblack.

That helps explain why Lin has been field­ing queries from solar-​​energy com­pa­nies such as SolFocus of Mountain View, Calif., and the European Space Agency.

“The more black the mate­r­ial the bet­ter,” said Gerald Fraser, a physi­cist at the National Institute of Standards and Technology, the fed­eral agency that spe­cial­izes in fine mea­sure­ments and indus­trial standards.

That agency offers sci­en­tists a chem­i­cal mix it calls “stan­dard black,” which for years has been the defin­ing mea­sure of black­ness. Photographers and print­ers use it to cal­i­brate their gray scales. Industrial radi­ol­o­gists use it to cal­i­brate X-​​ray imag­ing sys­tems that detect radi­a­tion or hid­den defects in build­ing materials.

That black reflects about 1.4 per­cent of incom­ing vis­i­ble light, and in recent years it has become some­what out­moded. In 2003, sci­en­tists devel­oped a sub­stance made of nickel and phos­pho­rus that reflected just 0.17 per­cent of vis­i­ble light, win­ning it a Guinness World Records list­ing and kudos in Time mag­a­zine as one of that year’s 300 “coolest inventions.”

The newest black — which when held next to some­thing con­ven­tion­ally black, such as a tuxedo jacket, is notice­ably blacker — reflects just 0.045 per­cent of vis­i­ble light.

It is made of car­bon nan­otubes: micro­scopic, hol­low fibers whose walls are just one atom thick. Importantly, the fibers are widely spaced, pro­vid­ing plenty of space to allow light in and almost no sur­faces to bounce it back out.

“There are a lot of mate­ri­als that are very absorb­ing of light so that once the light gets in, very lit­tle is reflected. That is not the big issue,” said John Pendry, a physics pro­fes­sor at Imperial College London. “The big issue is per­suad­ing the light to go in there in the first place” — some­thing the New York team accom­plished by spac­ing the nan­otubes so widely… 

While Lin and his col­leagues, includ­ing Pulickel Ajayan, now at Rice University, pur­sue appli­ca­tions for their superblack, Pendry and oth­ers are hop­ing to go fur­ther by per­fect­ing com­plete invis­i­bil­ity. The big dif­fer­ence is that a superblack object, even if invis­i­ble to the eye, still casts a shadow behind it, while an object shielded by an invis­i­bil­ity cloak does not.

Pendry pio­neered much of mod­ern think­ing about how to attain full invis­i­bil­ity using “meta­ma­te­ri­als” — sub­stances engi­neered to man­han­dle light. Ordinary mat­ter, such as glass or water, slows and bends light as it passes through. Metamaterials con­tain bits of metal or other sub­stances embed­ded in pre­cise pat­terns to make the light bend in an oppo­site direc­tion from nor­mal paths.

“In a sense you have some neg­a­tive space,” Pendry said. “The light appears to go back­ward in space.”

The first gen­er­a­tion, meta­ma­te­r­ial “cloaks” are not thin and flex­i­ble like Harry Potter’s imag­ined ver­sion but are inches thick and solid, resem­bling can­is­ters, mak­ing them able to hide a sta­tion­ary object but not a mov­ing per­son. But the sci­ence is pro­gress­ing quickly, physi­cist Schurig said.

To make a thin, flex­i­ble meta­ma­te­r­ial cloak, Schurig said, “is tech­ni­cally chal­leng­ing but not fun­da­men­tally impos­si­ble.” And although no cloak can yet make objects fully invis­i­ble to the human eye, he added, it may not be long before sci­en­tists can bend the vis­i­ble spec­trum enough to make an object hard to see… 

Read the rest of this fas­ci­nat­ing story at Washingtopost​.com.

– Christian

February 20th, 2008 | Bizarro | 384692 Comments »http://defensetech.org/2008/02/20/the-invisible-cloak/The+Invisible+Cloak2008-02-20+12%3A35%3A30Ward You can skip to the end and leave a response. Pinging is currently not allowed.