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Stretchable Antenna Boosts Range for Wearable Devices

Imagine a flexible antenna attached to a sports shirt wirelessly sending health and fitness data from sensors on the body to a smartphone hundreds of meters away. Such a vision for wearable devices has proven impractical—that is, until now. But a new antenna design has proven its ability to withstand the bending and stretching that garments endure, while steadily communicating via Wi-Fi.

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Acoustic Holograms Form Ultrasonic Tractor Beams for Tiny Objects

You've seen holograms before: they're images that seem to jump out of a flat surface, full of depth that you can experience through perspective changes and parallax cues. The three-dimensional effect that a hologram creates comes from the three dimensional light field that's created when photons diffract through the interference pattern on a holographic plate. It's essentially a structure made of light that gets projected out into space when the seemingly random pattern of features on the plate interact with each other.

Light isn't the only wave that can be manipulated to create structures in space; the same thing goes for sound waves. The structures generated by constructively and destructively interfering with ultrasonic waves are tangible things that can exert force on objects. Researchers at the Public University of Navarre in Spain have used ultrasonic acoustic holograms to manipulate things just like the tractor beam used by the crew of the USS Enterprise on the TV show Star Trek.

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NASA Satellites Will Use GPS to Boost Hurricane Forecasts

Eight small NASA satellites and the existing GPS network could provide the first serious upgrade for hurricane intensity forecasting in decades. Once launched in a little less than a year, the mission’s boost to extreme weather prediction would go a long way toward giving authorities more time to plan coastal evacuations and prepare for the onslaught of 21st-century storms.

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Megapixel CCD Can See Terahertz

Terahertz waves, a frequency band squeezed in between the far infrared and the very short-wave radio frequency region of the electromagnetic spectrum, are not only difficult to create but also difficult to detect. So making a good imager for them is quite a difficult task.  Still, in 2012 researchers reported an experimental 1000-pixel CMOS terahertz camera.

The SwissFEL laser team led by Christoph Hauri at the Paul Scherrer Institute near Zurich has now shown that you can use a common megapixel  CCD device, as found in electronic cameras or in smartphones, to capture images produced by terahertz waves.

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Spider Silk Sensors Could Search for Life on Mars

Ziggy Stardust would love this: Spiders could help find life on Mars.

That is, optical sensors made with spider silk could be used to look for trace gases produced by biological processes, according to a researcher who showed how silk could be used in place of conventional optical fibers, under a grant from the European Space Agency. The scientists hunting for life on Mars would like to be able to test for small amounts of ammonia, which might be emitted by the metabolism of microbes, so they need a sensor that can detect that while remaining insensitive to the large amounts of carbon dioxide in the Martian atmosphere.

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Ultra-Sensitive Magnetic Sensors Don't Need Ultra Cold

Newly developed magnetic sensors not only perform better than most standard commercial devices, but also can operate at temperatures well above absolute zero, say UK researchers.

Superconducting quantum interference devices, or SQUIDs, can detect minute magnetic fields, making them useful for applications such as analyzing brain activity, medical imaging, and oil prospecting. SQUIDs work by converting magnetic flux—a measure of magnetic intensity—into a voltage.

The most sensitive commercial magnetic sensors are single SQUIDs that need to be kept at 4.2 Kelvin. Such incredibly cold temperatures, within a hair’s breadth of absolute zero, require expensive and difficult to handle liquid helium.

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Zero-Index Metamaterials Open New Possibilities for Optical Chips

One class of metamaterials, with a refraction index of zero [pdf], was first created in 2013 and quickly caught the interest of scientists because of the materials’ unique properties. Such a material, when irradiated with light, behaves in a peculiar way, explains Eric Mazur, who leads a team of researchers investigating metamaterials at  Harvard University in Cambridge, MA.  For example, light directed at a planar slab can only pass when its incident angle is exactly 90 degrees. Says Mazur:

The light sets up a response in the material so that combined with the incident electromagnetic field the field in the material has the same phase throughout the material—not unlike the wheels of a carriage in a movie can appear at rest due to the interplay of the frequency of rotation and the frequency of the movie. This complete coherence in space, results in light with infinite wavelength and infinite phase velocity.

Since the phase of the light is the same in all of the metamaterial, it looks like the sinusoidal field has a wavelength that is streched to infinity and the phase propagates instantaneously. These two properties allow the light to be controlled in an unprecedented way in the very small space available on optical chips; it can travel through exteremely narrow channels or waveguides, and go around sharp corners without losing energy. 

Now Mazur and his team at Harvard, working with researchers at Peking University in Beijing, report in the 19 October online edition of Nature Photonics the creation of an on-chip metamaterial with a refractive index of zero.

Fabricating such a metamaterial on a chip allows integration with other nanofabrication techniques for on-chip light manipulation, says Mazur.  He and his collaborators created a metamaterial layer consisting of silicon pillars embedded in a polymer matrix and covered on both sides with gold film, deposited on a silicon substrate.

Such a zero-index metamaterial layer can fill in many of the potholes engineers might otherwise face on the road to future photonic chips. One of those bumps in the road is is the coupling of light into the small structures—smaller than the diffraction limit of light—on optical chips. The team devised the concept of a "super coupler” [pdf] in which light is transported through zero-index materials that can deal with small sizes and sharp angles. This will reduce the size of optical connections, and eliminate losses in the transmission of light, says Yang Li, a member of Mazur's research team. 

“If we put a zero-index metamaterial into a waveguide made of mirrors, we can achieve a high-efficiency transmission, regardless of the length, squeeze, shape, twisting, or bending of the waveguide. These are phenomena that we are not able to achieve in the microwave and optical regimes by using regular waveguides,” says Li. A demonstation of a super coupler is next on the books, says Li. 

A second application is phase matching in nonlinear optics, which is the study of phenomena in matter caused by light that are not proportional to the intensity of the light. Optical processing will require separate light beams to interact with each other. Two light beams can only interact with each other by nonlinear processes, and only when the momentum of the outgoing photons matches the momentum of incoming photons, says Mazur. 

“Zero-index materials make this particularly easy because the momentum vector of light in a zero-index material is zero. This relaxes some of the constraints on nonlinear optical processes at the nanoscale,” says Mazur.

Applications in optical quantum computers may be promising because all the light emitters in a zero-index material must oscillate in phase. “Take quantum emitters, such as erbium ions, and you can have them entangled over much larger distances that you can have in any other type of environmemt,” says Mazur. 

Artificial Intelligence Outperforms Human Data Scientists

Artificial intelligence may be poised to ease the shortage of data scientists who build models that explain and predict patterns in the ocean of “Big Data” representing today’s world. An MIT startup’s computer software has proved capable of building better predictive models than the majority of human researchers it competed against in several recent data science contests. 

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Light Where the Sun Don't Shine

An optical fiber made mostly of water could be used to zap tumors with light-activated drugs, continuously monitor a patient’s health, or trigger genetically modified cells with a laser beam, according to the scientist developing the fiber.

“We can reinvent optical components with biologically compatible materials,” says Seok-Hyun (Andy) Yun, an associate professor of biomedical optics at the Wellman Center for Photomedicine at Massachusetts General Hospital and Harvard Medical School. He presented the results of his recent work at the 2015 IEEE Photonics Conference in Reston, Va., earlier this month.

Yun and his colleagues have created a thin optical fiber from a hydrogel made of polyethylene glycol-diacrylate. They pour a solution of the material into a thin, transparent tube then cure it with ultraviolet light. Once they’ve formed the fiber, they coat it with alginate, a natural polymer derived from brown seaweed and commonly used in wound-healing dressings. The coating acts as a cladding similar to that used in typical silica fibers; the difference between the index of refraction of the two materials keeps the light traveling down the fiber instead of escaping through its transparent surface.

The fiber can carry blue-green laser light (wavelengths around 492 nanometers) for about 10 centimeters, a distance sufficient to reach from the surface of the skin to various organs. Visible light can normally only penetrate tissue to depths of a few millimeters, limiting the use of optical techniques to natural cavities such as the gastrointestinal tract.

Because the hydrogel is 80 to 90 percent water and very porous, it’s easy to dope it with various drugs that could be delivered to where they’re needed and then turned on with a beam of light. The fiber, which could carry molecules that would act as sensors for glucose, pH levels, or various biomarkers, would fluoresce in the presence of a target molecule. Yun’s team has even shown that they can infuse the fibers with genetically modified cells that stimulate insulin production in mice when the fibers are hit with a laser beam.

Clinical use of the fiber would probably require approval of the U.S. Food and Drug Administration (FDA), Yun says, but he’s using materials on the FDA’s list of items generally recognized as safe. One of the ingredients, for example, is the same one used to make biodegradable sutures.

Yun says his fiber has two advantages over conventional silica fibers. It’s much more flexible. “You can insert it like a needle into the body, with less worry about fiber breakages,” he says. And it’s biocompatible, so it could be left in for days or weeks with no immune reaction. One use he imagines is long-term monitoring of organ transplants. And even if a fiber were to get stuck, it would eventually be harmlessly absorbed by the body. It’s possible, by manipulating the chemistry of the fiber, to make it biodegrade in less than an hour or have it last for months, says Yun.

                

European Laser Facility Opens in Prague

A new laser research center in Europe, which will house the most powerful laser in the world, officially opened on 19 October.

The new ELI (Extreme Light Infrastructure) Beamlines facility, located in Prague, will be the world's first international laser facility when completed in 2018. The strongest of the four lasers housed there will reach intensities 10 times as great as any currently achievable; it will have a peak power of 10 petawatts, or 10 million billion (1015) watts.

The ELI center’s lasers will be used for research into material sciences, medicine, biology, chemistry, pharmaceuticals, astrophysics, and nuclear physics. Researchers noted that laser-driven particle acceleration could ultimately find use in cancer treatments and extremely compact electron-positron colliders. It is also hoped that the center will be the site of discoveries leading to improved contrast and resolution in medical X-ray imaging. That, in turn, could lead to early detection of small tumors. Research into plasma physics at the complex might also shed light on phenomena such as controlled nuclear fusion, ultra-high energy cosmic rays, and the Hawking radiation given off by black holes.

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