June 24, 2010 feature
Researchers design more reliable invisibility cloak
(PhysOrg.com) -- Researchers have proposed a new design for an invisibility cloak - a device that could make objects invisible by guiding light around anything placed inside the cloak.
In the study, Elena Semouchkina from Michigan Technological University and Pennsylvania State University and her coauthors designed an invisibility cloak made of glass for the infrared range. Currently, most metamaterial cloak designs require that the metamaterial response be homogeneous. However, the new design relies on simulations of a true multi-element cloak structure and takes into account the inhomogeneity of a real metamaterial response.
“This is one of the first designs of an optical cloak, in particular, of a cylindrical shell,” Semouchkina told PhysOrg.com. “This is a non-metallic low-loss all-dielectric cloak. ... In contrast to the previous designs, the design of our cloak has been developed at a careful control of interactions between resonators, since a true multi-resonator structure has been simulated. It makes the design essentially more reliable.”
The structure of the proposed cloak consists of identical nanosized chalcogenide glass resonators arranged in a concentric pattern. In simulations, the researchers found that glass resonators in the shape of a cylinder with a diameter of 300 nm and a height of 150 nm provided the best results for the light wavelength of 1 micron.
“The design employs identical resonators in all layers of the cloak, which, from the point of view of fabrication tolerance, presents a tremendous advantage versus fabricating nano-sized elements of different prescribed dimensions,” Semouchkina said.
The spoke-like configuration of the resonators forms radial magnetic moments despite different incidence angles of incoming light. As Semouchkina explained, the magnetic resonance response creates the desired effective parameters of the medium.
“Our cloak is based on the magnetic resonance in dielectric resonators,” Semouchkina said. “This resonance is used to obtain the desired values of the effective permeability of the medium. The simulations of real 3D resonators, and not of effective medium layers, allowed us to find optimal resonator shapes and their arrangement to assure the magnetic moment formation in resonators illuminated under different incidence angles.”
The researchers simulated cloaked cylindrical objects of infinite lengths and of diameters ranging from 5 to 15 wavelengths. Simulations also showed that objects could be cloaked over a wide range of infrared frequencies at the manipulation of inter-resonator distances.
Overall, the new design is one more example of the progress made in invisibility cloaks since they were first designed in 2006. Since then, researchers have been working on different design approaches in an attempt to expand the cloaking spectrum, simplify fabrication, and make other improvements.
“We are currently performing detailed investigations of the interactions between the resonators in metamaterials and their role in controlling the wave propagation, as well as working on the experimental demonstration of an all-dielectric cloak operation at microwaves,” Semouchkina said.
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User comments
I'd speculate that it should be possible, but not withing the next few years, anyway. There's a lot of work being done on engineering refractive indicies in materials, which would probably be necessary. However, most metamaterials research is being done on monochromatic light/radio waves.
It does make me wonder. How long was the stealth in service before it was officially revealed to the public? I would like to know exactly how far ahead the highest tech of the tech is compared to what we know about. 10 years, 15? And as far as the cloak goes, the Romulans aren't gonna like this.
It's actually a trick. While her scantily clad assistants distract the press, Elena Semouchkina from Michigan Technological University and Pennsylvania State University quickly removes the object from behind the "cloak". The US military has already contracted David Blaine to mass-produce fighter planes that function on the same principle.
1) if light is bent around the object then no light will hit the object (i.e. the object will be unable to 'see' the outside). So if we get an invisibility cloak then it will make the wearer also blind.
2) these methods only work at selected frequencies - you'd still be able to see the object at all other frequencies. Also the phase shift will give a cloaked object away (since the 'bent' rays will travel longer paths)
3) Invisibility cloaks are interesting for applications in optical switches - not making battleships invisible.
Stuff that is published in conference proceedings is at the forefront of reesearch (i.e. the result of the last 1-2 years of work which has just been completed). Journals lag, usully, 6 months to a year behind.
Now that is a very good question. I wonder if this could one day be adapted as a form of heat shield as well. Afterall heat is just a different wavelength on the scale?
The frequency range of cosmic radiation is very big. 'Invisibility cloaks' only work for very narrow frequency ranges. So no: There is not going to be a cosmic ray shield based on this technology.
Then again, if I could see it,that would mean it doesn't work.
So to make a ship or station 'invisible' to most cosmic rays should require a rather powerful magnetic field like that used for a particle accelerator, correct? Still require some protection from the magnetic field, though. As for the metamaterial cloak, we will probably have to invent some sort of non-Newtonian fluid inside a clear restraint. The object would be visible for a moment until the fluid adjusted to the 'pressure' of the ambient background light. However, it's unlikely to be damage-resistant unless we invent some form of plastalloy first...
Spaceships just need to be able to deflect and/or absorb the radiation before it impacts on the biological entities aboard.
Invisibility cloaks are special because the metamaterials used can have negative refraction indices. To deflect oncoming radiation that is not needed.
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