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Magic carpets can hide objects in plain sight
TECHNOLOGY
Magic carpets can hide objects in plain sight THE latest twist on invisibility cloaks won’t hide Harry Potter in the middle of a room, but it might just let spies conceal microphones under the rug or the wallpaper. So called “carpet cloaks” are the first technology to succeed in hiding objects by deflecting light across a range of wavelengths. Two groups described different cloaks last week at the International Quantum Electronics Conference in Baltimore, Maryland. Invisibility cloaks work by deflecting light waves so the light that reaches the eye shows no trace of the hidden object. Conventional optical materials can’t do this, but a dozen years ago John Pendry of Imperial College London showed it was possible to bend light around objects by building materials made of components smaller than the wavelength of the light. In theory, the principle will work across the electromagnetic spectrum, but early experiments with invisibility cloaks have been done at microwave frequencies,
which have wavelengths in the centimetre range, meaning subwavelength components are relatively easy to make. Both new carpet cloaks work in infrared light, which has a wavelength far shorter than microwaves, and provide the first demonstrations of optical cloaking. As they are not limited to a narrow range of wavelengths, in principle the cloaks could hide objects in normal light. Other cloaks, even if scaled down to the optical range, would work only in rooms lit with a single-colour lamp.
20 | NewScientist | 13 June 2009
50-nanometre silicon posts into silicon dioxide. So far the carpet cloaks only work in two dimensions, but the results are encouraging because the cloaks use only well-known materials and production methods. The demonstrations are “very charming”, says Georg von Freymann of the Institute of Nanotechnology at the University of Karlsruhe in Germany. “It looks like real-world applications may come from this.” In the short term, such materials could be used to create new optical devices such as super-lenses for concentrating sunlight. In principle the cloaks might one day hide objects on walls and floors or in satellite images. Jeff Hecht ■
Now you see it... A “carpet cloak” laid over a bumpy surface reflects light in a way that makes it look flat NO CLOAK
NO CLOAK
WITH CLOAK
LIGHT SOURCE
Light bounces off a flat surface with uniform brightness
Could a ‘lung-on-a-chip’ replace countless lab rats? “MICROLUNGS” grown from human tissue might one day help to replace the vast numbers of rats used to check the safety of drugs, cosmetics and other chemicals. The work is part of a growing drive to develop toxicology tests based on human cells as a replacement for animal testing. Such efforts are made partly for ethical concerns, and partly because animal testing is so time-consuming and expensive. For example, the European Union’s REACH regulations require about 30,000 chemicals to be tested for toxicity over the next decade. Yet testing the effects of inhaling a single dose of a particular
The cloaks were made at the University of California, Berkeley, and at Cornell University in Ithaca, New York. Instead of deflecting light waves around an object, both set-ups involve hiding bumps on a thin layer of material. Illuminating the bump from the side would normally cast a dark shadow. But with the cloaks, the light is reflected uniformly so that there is no shadow, and the cloaked surface appears flat (see diagram). At Berkeley, Jensen Li and colleagues made their invisibility cloak by drilling nanoscale holes into a micrometre-thick layer of silicon. At Cornell, Lucas Gabrielli and colleagues achieved a similar effect by embedding
chemical typically requires more than 200 rats, while testing the chronic effects of breathing it in over time can take more than 3000. Meanwhile the EU Cosmetics Directive – which covers items from deodorants and perfume to air-fresheners – seeks to ban all tests of cosmetics on animals by 2013. The obvious alternative is to test chemicals on human cells grown in the lab. The difficulty, however, lies in enticing those cells to form complex tissue that responds as our organs do. Cell biologist Kelly BéruBé at the University of Cardiff, UK, has managed to grow human lung cells into flat differentiated layers that resemble
Bump forms a shadow
the inner lining of the lungs. Her method is already being used for drug testing by companies such as Unilever and AstraZeneca. But when allowed to grow in three dimensions, as in the body, cells arrange themselves very differently, and this can change how they respond to chemical stimuli. “We need to move from something
“Cells grow on little plastic spheres, essentially producing a tiny insideout lung around each bead” flat to 3D structures,” says BéruBé. A popular approach is to seed plastic scaffolds with stem cells to grow artificial “organs”, but BéruBé and her colleagues have found an alternative which could allow thousands of drugs to be screened at once.
Cloak alters the angle at which light bounces off the bump, so the surface looks flat
Instead of large scaffolds, BéruBé has grown lung cells on the surface of plastic spheres half a millimetre in diameter, essentially producing a tiny inside-out lung around each bead. The ultimate aim is to develop a chip on which thousands of microlungs can be grown then tested simultaneously, she told the Cheltenham Festival of Science in the UK last week. The big challenges will be getting the technique accepted by regulatory authorities and convincing academia that tiny globs of lab-grown tissue can tell us as much in tests as whole animals. But BéruBé points out that rat models are less relevant to humans than most people realise. Chocolate, for example, is lethal to rats and their anatomy is such that they can only breathe through their noses. Duncan Graham-Rowe ■
Magic carpets can hide objects in plain sight THE latest twist on invisibility cloaks won’t hide Harry Potter in the middle of a room, but it might just let spies conceal microphones under the rug or the wallpaper. So called “carpet cloaks” are the first technology to succeed in hiding objects by deflecting light across a range of wavelengths. Two groups described different cloaks last week at the International Quantum Electronics Conference in Baltimore, Maryland. Invisibility cloaks work by deflecting light waves so the light that reaches the eye shows no trace of the hidden object. Conventional optical materials can’t do this, but a dozen years ago John Pendry of Imperial College London showed it was possible to bend light around objects by building materials made of components smaller than the wavelength of the light. In theory, the principle will work across the electromagnetic spectrum, but early experiments with invisibility cloaks have been done at microwave frequencies,
which have wavelengths in the centimetre range, meaning subwavelength components are relatively easy to make. Both new carpet cloaks work in infrared light, which has a wavelength far shorter than microwaves, and provide the first demonstrations of optical cloaking. As they are not limited to a narrow range of wavelengths, in principle the cloaks could hide objects in normal light. Other cloaks, even if scaled down to the optical range, would work only in rooms lit with a single-colour lamp.
20 | NewScientist | 13 June 2009
50-nanometre silicon posts into silicon dioxide. So far the carpet cloaks only work in two dimensions, but the results are encouraging because the cloaks use only well-known materials and production methods. The demonstrations are “very charming”, says Georg von Freymann of the Institute of Nanotechnology at the University of Karlsruhe in Germany. “It looks like real-world applications may come from this.” In the short term, such materials could be used to create new optical devices such as super-lenses for concentrating sunlight. In principle the cloaks might one day hide objects on walls and floors or in satellite images. Jeff Hecht ■
Now you see it... A “carpet cloak” laid over a bumpy surface reflects light in a way that makes it look flat NO CLOAK
NO CLOAK
WITH CLOAK
LIGHT SOURCE
Light bounces off a flat surface with uniform brightness
Could a ‘lung-on-a-chip’ replace countless lab rats? “MICROLUNGS” grown from human tissue might one day help to replace the vast numbers of rats used to check the safety of drugs, cosmetics and other chemicals. The work is part of a growing drive to develop toxicology tests based on human cells as a replacement for animal testing. Such efforts are made partly for ethical concerns, and partly because animal testing is so time-consuming and expensive. For example, the European Union’s REACH regulations require about 30,000 chemicals to be tested for toxicity over the next decade. Yet testing the effects of inhaling a single dose of a particular
The cloaks were made at the University of California, Berkeley, and at Cornell University in Ithaca, New York. Instead of deflecting light waves around an object, both set-ups involve hiding bumps on a thin layer of material. Illuminating the bump from the side would normally cast a dark shadow. But with the cloaks, the light is reflected uniformly so that there is no shadow, and the cloaked surface appears flat (see diagram). At Berkeley, Jensen Li and colleagues made their invisibility cloak by drilling nanoscale holes into a micrometre-thick layer of silicon. At Cornell, Lucas Gabrielli and colleagues achieved a similar effect by embedding
chemical typically requires more than 200 rats, while testing the chronic effects of breathing it in over time can take more than 3000. Meanwhile the EU Cosmetics Directive – which covers items from deodorants and perfume to air-fresheners – seeks to ban all tests of cosmetics on animals by 2013. The obvious alternative is to test chemicals on human cells grown in the lab. The difficulty, however, lies in enticing those cells to form complex tissue that responds as our organs do. Cell biologist Kelly BéruBé at the University of Cardiff, UK, has managed to grow human lung cells into flat differentiated layers that resemble
Bump forms a shadow
the inner lining of the lungs. Her method is already being used for drug testing by companies such as Unilever and AstraZeneca. But when allowed to grow in three dimensions, as in the body, cells arrange themselves very differently, and this can change how they respond to chemical stimuli. “We need to move from something
“Cells grow on little plastic spheres, essentially producing a tiny insideout lung around each bead” flat to 3D structures,” says BéruBé. A popular approach is to seed plastic scaffolds with stem cells to grow artificial “organs”, but BéruBé and her colleagues have found an alternative which could allow thousands of drugs to be screened at once.
Cloak alters the angle at which light bounces off the bump, so the surface looks flat
Instead of large scaffolds, BéruBé has grown lung cells on the surface of plastic spheres half a millimetre in diameter, essentially producing a tiny inside-out lung around each bead. The ultimate aim is to develop a chip on which thousands of microlungs can be grown then tested simultaneously, she told the Cheltenham Festival of Science in the UK last week. The big challenges will be getting the technique accepted by regulatory authorities and convincing academia that tiny globs of lab-grown tissue can tell us as much in tests as whole animals. But BéruBé points out that rat models are less relevant to humans than most people realise. Chocolate, for example, is lethal to rats and their anatomy is such that they can only breathe through their noses. Duncan Graham-Rowe ■