Almost perfect: A breakthrough in superlens development

ScienceDaily (Jan. 9, 2012) — A superlens would let you see a virus in a drop of blood and open the door to better and cheaper electronics. It might, says Durdu Guney, make ultra-high-resolution microscopes as commonplace as cameras in our cell phones.

No one has yet made a superlens, also known as a perfect lens, though people are trying. Optical lenses are limited by the nature of light, the so-called diffraction limit, so even the best won't usually let us see objects smaller than 200 nanometers across, about the size of the smallest bacterium. Scanning electron microscopes can capture objects that are much smaller, about a nanometer wide, but they are expensive, heavy, and, at the size of a large desk, not very portable.

To build a superlens, you need metamaterials: artificial materials with properties not seen in nature. Scientists are beginning to fabricate metamaterials in their quest to make real seemingly magical phenomena like invisibility cloaks, quantum levitation -- and superlenses.

Now Guney, an assistant professor of electrical and computer engineering at Michigan Technological University, has taken a major step toward creating superlens that could use visible light to see objects as small as 100 nanometers across.

The secret lies in plasmons, charge oscillations near the surface of thin metal films that combine with special nanostructures. When excited by an electromagnetic field, they gather light waves from an object and refract it in a way not seen in nature called negative refraction. This lets the lens overcomes the diffraction limit. And, in the case of Guney's model, it could allow us to see objects smaller than 1/1,000th the width of a human hair.

Other researchers have also been able to sidestep the diffraction limit, but not throughout the entire spectrum of visible light. Guney's model showed how metamaterials might be "stretched" to refract light waves from the infrared all the way past visible light and into the ultraviolet spectrum.

Making these superlenses would be relatively inexpensive, which is why they might find their way into cell phones. But there would be other uses as well, says Guney.

"It could also be applied to lithography," the microfabrication process used in electronics manufacturing. "The lens determines the feature size you can make, and by replacing an old lens with this superlens, you could make smaller features at a lower cost. You could make devices as small as you like."

Computer chips are made using UV lasers, which are expensive and difficult to build. "With this superlens, you could use a red laser, like the pointers everyone uses, and have simple, cheap machines, just by changing the lens."

What excites Guney the most, however, is that a cheap, accessible superlens could open our collective eyes to worlds previously known only to a very few.

"The public's access to high-powered microscopes is negligible," he says. "With superlenses, everybody could be a scientist. People could put their cells on Facebook. It might just inspire society's scientific soul."

Guney and graduate student Muhammad Aslam published an article on their work, "Surface Plasmon Diven Scalable Low-Loss Negative-Index Metamaterial in the visible spectrum," in Physical Review B, volume 84, issue 19.0

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The above story is reprinted from materials provided by Michigan Technological University. The original article was written by Marcia Goodrich.

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Journal Reference:

Muhammad Aslam, Durdu ?. Güney. Surface plasmon driven scalable low-loss negative-index metamaterial in the visible spectrum. Physical Review B, 2011; 84 (19) DOI: 10.1103/PhysRevB.84.195465

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New Wireless Breakthrough Allows Simultaneous Two Way Communication

Stanford researchers have developed new technology that allows wireless signals to be sent and received simultaneously on a single channel. The breakthrough could lead to faster and more efficient wireless networks.

Until recently radio traffic was only able to travel in one direction at a time on any given frequency. You will probably remember using the infamous 'over" and "over and out" when using a walkie talkie as a kid?

Being able to communicate in both directions at the same time, not surprisingly, makes it twice as fast as current technology.

"Textbooks say you can't do it," said Philip Levis, assistant professor of computer science and of electrical engineering. "The new system completely reworks our assumptions about how wireless networks can be designed," he said.

Mobile phones currently allow two way communication using a complicated work around that is expensive and needs careful planning, making it unfeasible for wireless networks like Wi-Fi.

A small group of Standford graduates began working on the project after coming up with what seemed like a fairly simple concept "What if radios could do the same thing our brains do when we listen and talk simultaneously: screen out the sound of our own voice"?

In most wireless networks, each device has to take turns speaking or listening. "It's like two people shouting messages to each other at the same time," said Levis. "If both people are shouting at the same time, neither of them will hear the other."

Over a period of several months, and with the help of professor Levis the group figured out how to build the new radio device.

The most difficult obstacle to overcome was that incoming signals tend to be overpowered by outgoing signals, preventing the device form 'listening' while 'talking.

The group hypothesized that if the receiver could filter out the signal from its own transmitter then incoming signals should be easier to pick up. This works because a radio 'knows" what it is transmitting and consequently what should be filtered out. The principle is the same as used in noise cancelling headphones.

The breakthrough is making 'big noise' and has already won the researchers an international award. Prior to the demonstration no-one in the field believed that it was possible. One researcher even told the trio that it wouldn't work "something so simple could not work, if it was that obvious, someone must have tried it already".

The implications for future networks is phenomenal, the most obvious benefit is that being able to send and receive at the same time doubles the amount of information transferred over an given time period. This would lead to faster and less congested networks in both the office and at home.

The group has a provisional patent on the technology and is working to commercialize it. They are currently trying to increase both the strength of the transmissions and the distances over which they work. These improvements are necessary before the technology is practical for use in Wi-Fi networks.

Brendan Wilde writes about a range of technology and computer issues with a specific focus on managed wireless networks and local loop unbundling.

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Breakthrough could double wireless capacity with no new towers

ScienceDaily (Sep. 7, 2011) — The days of waiting for smartphones to upload video may be numbered. Rice University engineering researchers have made a breakthrough that could allow wireless phone companies to double throughput on their networks without adding a single cell tower.

Rice's new "full-duplex" technology allows wireless devices like cell phones and electronic tablets to both "talk" and "listen" to wireless cell towers on the same frequency -- something that requires two frequencies today.

"Our solution requires minimal new hardware, both for mobile devices and for networks, which is why we've attracted the attention of just about every wireless company in the world," said Ashutosh Sabharwal, professor of electrical and computer engineering at Rice. "The bigger change will be developing new wireless standards for full-duplex. I expect people may start seeing this when carriers upgrade to 4.5G or 5G networks in just a few years."

In 2010, Sabharwal and Rice colleagues Melissa Duarte and Chris Dick published the first paper showing that full-duplex was possible. That set off a worldwide race to demonstrate that the technology could actually be used in a real network. This summer, Sabharwal and Rice's Achaleshwar Sahai and Gaurav Patel set new performance records with a real-time demo of the technology that produced signal quality at least 10 times better than any previously published result.

"We showed that our approach could support higher throughput and better link reliability than anything else that's been demonstrated, which is a plus for wireless carriers," Sabharwal said. "On the device side, we've shown that we can add full duplex as an additional mode on existing hardware. Device makers love this because real estate inside mobile devices is at a premium, and it means they don't have to add new hardware that only supports full duplex."

To explain why full-duplex wireless was long thought impossible for wireless networks, Sabharwal uses the analogy of two people standing far apart inside an otherwise empty arena. If each shouts to the other at the same time, neither can hear what the other is saying. The easy solution is to have only one person speak at a time, and that's what happens on two-way radios where only one person may speak at a given time. Cell phones achieve two-way communications by using two different frequencies to send and listen.

Rice's team overcame the full-duplex hurdle by employing an extra antenna and some computing tricks. In the shouting analogy, the result is that the shouter cannot hear himself, and therefore hears the only other sound in the arena -- the person shouting from far away.

"We send two signals such that they cancel each other at the receiving antenna -- the device ears," Sabharwal said. "The canceling effect is purely local, so the other node can still hear what we're sending."

He said the cancellation idea is relatively simple in theory and had been proposed some time ago. But no one had figured a way to implement the idea at low cost and without requiring complex new radio hardware.

"We repurposed antenna technology called MIMO, which are common in today's devices," Sabharwal said. "MIMO stands for 'multiple-input multiple-output' and it uses several antennas to improve overall performance. We took advantage of the multiple antennas for our full-duplex scheme, which is the main reason why all wireless carriers are very comfortable with our technology."

Sabharwal said Rice is planning to roll its full-duplex innovations into its "wireless open-access research platform," or WARP. WARP is a collection of programmable processors, transmitters and other gadgets that make it possible for wireless researchers to test new ideas without building new hardware for each test. Sabharwal said adding full-duplex to WARP will allow other researchers to start innovating on top of Rice's breakthrough.

"There are groups that are already using WARP and our open-source software to compete with us," he said. "This is great because our vision for the WARP project is to enable never-before-possible research and to allow anyone to innovate freely with minimal startup effort."

Sabharwal's team has gone one step further and achieved asynchronous full-duplex too -- that is one wireless node can start receiving a signal while it's in the midst of transmitting. Asynchronous transmission is import for carriers wishing to maximize traffic on their networks, and Rice's team is the first to demonstrate the technology.

"We've also developed a preliminary theory that explains why our system is working the way that it is," Sabharwal said. "That's also important for carriers and device makers, because engineers aren't likely to implement something like this without a clear understanding of fundamental tradeoffs."

Rice's research has been funded by the National Science Foundation, the Roberto Rocca Education Program and Xilinx Incorporated.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rice University.

Journal Reference:

Achaleshwar Sahai, Gaurav Patel, Ashutosh Sabharwal. Pushing the limits of Full-duplex: Design and Real-time Implementation. arXiv, 4 Jul 2011 [link]

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Sketching with superconductors: Breakthrough in controlling defects could lead to new generation of electronic devices

ScienceDaily (Aug. 22, 2011) — Reporting in the journal Nature Materials, researchers from the London Centre for Nanotechnology and the Physics Department of Sapienza University of Rome have discovered a technique to 'draw' superconducting shapes using an X-ray beam. This ability to create and control tiny superconducting structures has implications for a completely new generation of electronic devices.

Superconductivity is a special state where a material conducts electricity with no resistance, meaning absolutely zero energy is wasted.

The research group has shown that they can manipulate regions of high temperature superconductivity, in a particular material which combines oxygen, copper and a heavier, 'rare earth' element called lanthanum. Illuminating with X-rays causes a small scale re-arrangement of the oxygen atoms in the material, resulting in high temperature superconductivity, of the type originally discovered for such materials 25 years ago by IBM scientists. The X-ray beam is then used like a pen to draw shapes in two dimensions.

A well as being able to write superconductors with dimensions much smaller than the width of a human hair, the group is able to erase those structures by applying heat treatments. They now have the tools to write and erase with high precision, using just a few simple steps and without the chemicals ordinarily used in device fabrication. This ability to re-arrange the underlying structure of a material has wider applications to similar compounds containing metal atoms and oxygen, ranging from fuel cells to catalysts.

Prof. Aeppli, Director of the London Centre for Nanotechnology and the UCL investigator on the project, said: "Our validation of a one-step, chemical-free technique to generate superconductors opens up exciting new possibilities for electronic devices, particularly in re-writing superconducting logic circuits. Of profound importance is the key to solving the notorious 'travelling salesman problem', which underlies many of the world's great computational challenges. We want to create computers on demand to solve this problem, with applications from genetics to logistics. A discovery like this means a paradigm shift in computing technology is one step closer."

Prof Bianconi, the leader of the team from Sapienza, added: "It is amazing that in a few simple steps, we can now add superconducting 'intelligence' directly to a material consisting mainly of the common elements copper and oxygen."

The X-ray experiments were performed at the Elettra (Trieste) synchrotron radiation facility. The work is published in Nature Materials , 21 August 2011 (doi:1038/nmat3088) and follows on from previous discovery of fractal-like structures in superconductors (doi:10.1038/nature09260).

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Journal References:

Nicola Poccia, Michela Fratini, Alessandro Ricci, Gaetano Campi, Luisa Barba, Alessandra Vittorini-Orgeas, Ginestra Bianconi, Gabriel Aeppli, Antonio Bianconi. Evolution and control of oxygen order in a cuprate superconductor. Nature Materials, 2011; DOI: 10.1038/nmat3088Michela Fratini, Nicola Poccia, Alessandro Ricci, Gaetano Campi, Manfred Burghammer, Gabriel Aeppli, Antonio Bianconi. Scale-free structural organization of oxygen interstitials in La2CuO4+y. Nature, 2010; 466 (7308): 841 DOI: 10.1038/nature09260

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