World’s first 3D acoustic cloaking device created

Metamaterials are already being used to create invisibility cloaks and “temporal cloaks,” but now engineers from Duke University have turned metamaterials to the task of creating a 3D acoustic cloak. In the same way that invisibility cloaks use metamaterials to reroute light around an object, the acoustic cloaking device interacts with sound waves to make it appear as if the device and anything hidden beneath it isn’t there.

Steven Cummer, professor of electrical and computer engineering, and his colleagues at Duke University constructed their acoustic cloak using several sheets of plastic plates dotted with repeating patterns of holes. The plastic sheets, which were created using a 3D printer, were stacked on top of each other to form a device that resembles a pyramid in shape. The geometry of the sheets and the placement of the holes interact with sound waves to make it appear as if the device and anything sitting underneath it isn’t there.

Despite its apparent simplicity, the device’s construction was far from a haphazard affair, with a lot of time and research going into calculating how sound waves would interact with it. As Cummer puts it, “we didn’t come up with this overnight.”

To work effectively, the cloak needs to alter the trajectory of the sound waves so they behave as if they had reflected off a flat surface. To achieve this, the device needs to slow down the speed of the sound waves to compensate for the fact that they aren’t traveling as far.

To test the effectiveness of the cloak, the researchers took a small sphere and covered it with the cloak. They then “pinged” the sphere with short bursts of sound from various angles and mapped how the sound waves responded using a microphone. The team then produced videos of the sound waves traveling through the air and compared them to videos produced with the cloak removed and another showing the sound wave behavior with an unobstructed flat surface.

The results showed that the acoustic cloak made it appear as if the sound waves were being reflected off a flat surface with no sign the sphere was there. Unlike the “silence cloak” developed at Germany’s Karlsruhe Institute of Technology that worked only in two-dimensions, this held true no matter which direction the sound originated from or where the observer was located, prompting the team to call their creation the “world’s first 3D acoustic cloaking device.”

Cummer believes the technology has numerous potential commercial applications.

“We conducted our tests in the air, but sound waves behave similarly underwater, so one obvious potential use is sonar avoidance,” he said. “But there’s also the design of auditoriums or concert halls – any space where you need to control the acoustics. If you had to put a beam somewhere for structural reasons that was going to mess up the sound, perhaps you could fix the acoustics by cloaking it.”

The team’s acoustic cloaking device is detailed in a letter published in the journal Nature Materials.

Source: Duke University

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Need to filter some water? Just go peel a pine tree

In many parts of the world, the presence of harmful bacteria makes it vitally important that water from lakes or rivers be thoroughly filtered before being consumed. While materials such as silver nanoparticles and titanium dioxidewill do the job, people in developing nations or rural settings typically need something a lot cheaper and easier to manufacture. As it turns out, wood from pine trees works great.

More specifically, it’s pine sapwood that traps bacteria.

It’s made up of a porous material known as xylem, that is used to draw sap up from the roots and into the rest of the tree. Xylem’s internal structure consists of a series of microscopic vessels, which are linked together by pores in their walls. These pores, called pit membranes, allow sap to flow from vessel to vessel along the length of the tree. They’re too small for air bubbles to pass through, though – that’s a good thing, as bubbles in the “sapstream” can kill a tree.

As discovered by scientists at MIT, the pit membranes also let water pass through, yet are small enough that they block the passage of bacteria. In lab tests, pieces of the sapwood were glued into the inside of rubber tubes, which E. coli-contaminated water was then flowed through. When the wood was subsequently examined, approximately 99 percent of the bacteria that had been in the water was found to be trapped around the pit membranes in the first few millimeters of the filter.

According to the researchers’ calculations, a single 1.5-inch-wide (38 mm) sapwood filter could be used to produce up to four liters (1 US gal) of drinking water per day. It couldn’t be allowed to dry out when not in use, however.

Additionally, although the wood can catch most types of bacteria, it likely cannot filter out viruses, due to their smaller size. Sapwood from some other types of trees has smaller pores that could presumably trap smaller microbes, however, so the scientists are planning on conducting more research.

In fact, it’s not just the wood from trees that can stop bacteria. A previous study indicated the seeds of the Moringa tree are also highly effective.

A paper on the MIT research was recently published in the journal PLoS ONE.

Source: MIT

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Powerful artificial muscles made from … fishing line?

Artificial muscles could find use in a wide range of applications, including prosthetic limbs, robotics, exoskeletons, or pretty much any situation in which hydraulics or electric motors just aren’t a practical means of moving objects. Scientists have been working on such muscles for a number of years, using materials like vanadium dioxide, graphene, carbon nanotubesand dielectric elastomers. Now, however, some of those same scientists have discovered that very powerful artificial muscles can be made from much more down-to-earth materials – regular polymer fishing line, and metal-coated nylon sewing thread.

The research was led by The University of Texas at Dallas, but involved the input of partnering universities in Australia, South Korea, Canada, Turkey and China.

To make the muscles, the team started by attaching one end of a piece of fishing line to the tip of a power drill, with the other end hanging below it, held in place by an attached heavy weight. A piece of the thread hung with the line, joined to it along one side. As the drill was powered up and its end started spinning, the line initially responded by twisting along its length. Once it had twisted as much as it could, it then proceeded to bunch up into a series of coils, like a land-line telephone receiver cord.

The scientists then heated that coiled line with a hair dryer, causing the coils to set permanently – even once the weight was removed, the line remained coiled.

When heat is subsequently applied to one of those lines, it will respond by coiling tighter, thus contracting like a muscle. According to a recently-published paper on the research, “Extreme twisting produces coiled muscles that can contract by 49 percent, lift loads over 100 times heavier than can human muscle of the same length and weight, and generate 5.3 kilowatts of mechanical work per kilogram [2.2 lb] of muscle weight, similar to that produced by a jet engine.”

While the heat could be applied electrically (via the metal in the thread), it could also take the form of exposure to light, or a chemical reaction. This means that the muscles wouldn’t necessarily require an electrical power source, and could be used for things like automatically opening and closing window shutters based on time of day or air temperature.

The paper was published on Feb. 21, in the journal Science. The following video, from Australian project partner the ARC Centre of Excellence for Electromaterials Science, illustrates the production process – it also shows how a number of the artificial muscles could be weaved together, for extra power.

Sources: University of Texas at Dallas, ARC Centre of Excellence for Electromaterials Science, University of British Columbia

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Spongy material could charge phones using vibrations from cars

While it’s already possible to wirelessly recharge smartphones in cars, those cars need to be equipped with a special charging pad that the phone has to be placed on. Thanks to a newly-developed “nanogenerator,” however, it might eventually be possible to place the phone anywhere in any car, letting the vehicle’s vibrations provide the power.

Developed by a team of scientists from the University of Wisconsin-Madison, the University of Minnesota Duluth, and China’s Sun Yat-sen University, the nanogenerator could be incorporated directly into a phone’s housing.

It’s made from a piezoelectric polymer known as polyvinylidene fluoride, or PVDF. Like other piezoelectric materials, PVDF generates electricity when subjected to mechanical strain.

The scientists deposited nanoparticles of zinc oxide into a thin film of the polymer, but then etched those particles out again, leaving tiny interconnected pores where they had been. The presence of those pores caused the ordinarily rigid PVDF to take on a sponge-like consistency, allowing it to flex and thus generate electricity when subjected to even slight vibrations – having the weight of a phone pressing down on it would amplify the effect.

That film is sandwiched between two electrode sheets, the whole multilayer nanogenerator still remaining quite thin and flexible. Because of this quality, it could conceivably conform not just to the flat, rigid housings of phones or other devices, but also to a variety of irregular surfaces including human skin.

Source: University of Wisconsin-Madison

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Stretchable optical circuits could find use in robot skin and more

If flexible electronic devices are ever going to become practical for real-world use, the circuitry incorporated into them will have to be tough and resilient. We’re already seeing progress in that direction, including electrical wires that can still carry a current while being stretched. However, what if the application calls for the use of fiber optics? Well, scientists from Belgium may have that covered, too. They’ve created optical circuits utilizing what they believe are the world’s first stretchable optical interconnections.

The idea is that devices such as wearable sensors or touch-enabled robot skin could utilize standard glass fiber optic cables for the most part, but could use the interconnections to bridge gaps between those cables, allowing the device to bend or lengthen at those locations.

Made from a clear rubbery substance known as PDMS (poly-dimethylsiloxane), the interconnections feature a transparent core through which the light travels, that’s surrounded by an outer layer of the same material. Because light doesn’t move as easily through that outer layer due to its lower refractive index, the design keeps the light signals contained within the core.

In lab tests, the interconnections were able to guide light signals when stretched by up to 30 percent, or when bent around an object with a diameter as small as that of a human finger. What’s more, they maintained that functionality after being mechanically stretched by 10 percent a total of 80,000 times.

The interconnections were developed at the Centre for Microsystems Technology, which is a laboratory associated with Belgium’s Ghent University and the imec micro-electronics research center. A paper on the research was recently published in the journal Optics Express.

Source: The Optical Society

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“Living liquid crystal” could be used to detect diseases earlier.

With any medical condition, the earlier it’s detected, the better the chances are of successfully treating it. When assessing biological samples from a patient, however, it’s often quite difficult to see the indicators of a disease when it’s still in its early stages. That could be about to change, thanks to the development of a solution known as “living liquid crystal.”

The biomechanical hybrid substance consists of a water-based nontoxic liquid crystal, combined with live, swimming bacteria. It possesses “highly desirable optical properties,” and moves in a very easy-to-see fashion in response to external stimuli such as the amount of oxygen available to the bacteria, the concentration of given compounds within a sample, or the temperature.

In this way, it serves as a sort of visual amplifier, allowing clinicians to see reactions or other images that might ordinarily be too subtle to detect.

The research was conducted by scientists at Ohio’s Kent State University and Illinois’ Argonne National Laboratory.

Source: American Institute of Physics

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New laser shines a light on breath testing for disease

Various institutes around the world have long touted the potential of breath testing as a form of early and non-invasive disease detection. Now a research team from Australia’s University of Adelaide has developed a new kind of laser with the ability to detect low concentrations of gases, opening up even more possibilities for disease diagnosis and other applications such us measuring the concentration of particular greenhouse gases in the atmosphere.

The erbium-doped zirconium-fluoride-based glass fiber laser operates in the mid-infrared frequency range, which is the range where many hydrocarbon gases absorb light. The laser can produce 25 times as much light as lasers operating at a similar wavelength according to the researchers, paving the way for the detection of previously obscured, low concentrations of gases.

“This laser has significantly more power and is much more efficient than other lasers operating in this frequency range,” says Ori Henderson-Sapir, PhD researcher and one of the study’s authors. “Using a novel approach, we’ve been able to overcome the significant technical hurdles that have prevented fiber lasers from producing sufficient power in the mid-infrared.”

The researchers report a light emission of 3.6 microns, what they say is the deepest mid-infrared emission from a fiber laser operating at room temperature.

“Probing this region of the electromagnetic spectrum, with the high power we’ve achieved, means we will be able to detect these gases with a high degree of sensitivity,” says Project Leader Dr David Ottaway. “For instance, it should enable the possibility of analyzing trace gases in exhaled breath in the doctors’ surgery.”

Detecting certain particles and gases through breath-testing has proven valuable in the diagnosing of particular illnesses. In December 2013 a team of UK-based researchers began trialling a device designed to recognize certain chemicals in the breath of early lung cancer patients, while systems to detect asthma have been in use for some time.

As far as alternative potential applications for the laser go, the sky is the limit. The researchers cite the detection of the greenhouse gases methane and ethanol in the atmosphere as another use for their system due to its power, efficiency and ability to be easily transported.

“The main limitation to date with laser detection of these gases has been the lack of suitable light sources that can produce enough energy in this part of the spectrum,” says Dr Ottaway. “The few available sources are generally expensive and bulky and, therefore, not suitable for widespread use.”

The team’s findings were recently published in the journal Optics Letters.

Source: University of Adelaide

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Artificial graphene could outperform the real thing

Graphene is truly a 21st-century wonder material, finding use in everything from solar cells to batteries to tiny antennas. Now, however, a group of European research institutes have joined forces to create a graphene knock-off, that could prove to be even more versatile.

Conventional graphene takes the form of a one-atom-thick sheet of carbon atoms, linked together in a honeycomb pattern. Along with being transparent and conductive, it is also both the world’s thinnest material, and the strongest.

The artificial graphene has the same honeycomb structure, but is made from nanometer-thick semiconductor crystals instead of carbon atoms. The chemical makeup, size and shape of those crystals can be tweaked, essentially custom-tuning the properties of the material to the desired application.

It could conceivably be used in many of the same places in which graphene is currently utilized, but with even better performance. According to project partner the University of Luxembourg, “’Artificial graphene’ should lead to faster, smaller and lighter electronic and optical devices of all kinds, including higher performance photovoltaic cells, lasers or LED lighting.”

Other institutes helping to develop the material include the Institute for Electronics, Microelectronics, and Nanotechnology (IEMN) in France; the Debye Institute for Nanomaterials Science and the Institute for Theoretical Physics of the University of Utrecht, in The Netherlands; and Germany’s Max Planck Institute for the Physics of Complex Systems. A paper on the research was recently published in the journal Physical Review X.

Source: University of Luxembourg

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Scientists announce breakthrough in quest for fusion power

In a perfect example of beating swords into plowshares, a team of scientists at the Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF) in California reached a milestone in the quest for practical fusion power using a process designed for the development and testing of nuclear weapons. The announcement in the February 12 issue of Natureclaims that the team used the world’s most powerful laser barrage to produce a controlled fusion reaction where more energy was extracted from the fuel than was put into it.

If there is an ultimate engineering dream, then nuclear fusion is about as close as close as one can get. By literally harnessing the power of the stars, it holds the promise of what is, for all practical purposes, unlimited clean energy. Since man-made fusion was first demonstrated in 1951 with aboosted fission weapon, scientists and engineers have worked on some way to produce a practical fusion reactor instead of a hydrogen bomb.

The story of the fusion reactor is one of both great progress, but also constant frustration. When work began, the first reactor was predicted to be 25 years away. Since then and up until today, it’s still 25 years away. That’s because although nuclear fusion is relatively simple in theory, getting a controlled reaction started outside of the heart of a star is extremely difficult. The trick is to reach the “ignition” point, where the energy released by the reactor is greater than what’s put into it and the reaction becomes self-sustaining.

A fusion reactor works by simulating the conditions inside the Sun. Put simply, hydrogen atoms fuse in the Sun because its huge mass squashes the atoms together to form helium, releasing huge amounts of energy as the strong nuclear force that keeps them apart is overcome. A hydrogen bomb does the same thing, only with a fission bomb creating the necessary conditions for a millionth of a second.

A fusion reactor creates the right pressures and temperatures by taking an ionized plasma of the hydrogen isotopes deuterium or tritium and squeezing it using magnetic fields or lasers to set off the reaction. Not surprisingly, this requires huge amounts of energy, which set off various processes that heat the plasma to incredible temperatures.

The NIF breakthrough isn’t ignition, but it is a significant waypoint. The NIF team achieved what is called a “fuel gain”. Using an array of 192 high-energy lasers aimed at one tiny plastic sphere filled with a mixture of deuterium and tritium, the scientists subjected the droplet of cryogenic fuel to 1.9 megajoules of light to produce sun-like temperatures for a tiny fraction of a second. The result was a fusion reaction where the energy put into the fuel was exceeded by the energy that came back out – something that until now has never been achieved anywhere outside of a star or a hydrogen bomb, and is ten times greater than anything previously seen. The key to this is something called “boot-strapping”.

Boot-strapping works by using alpha particles, which are helium atoms stripped of their electrons. Normally, when a fusion reaction produces such particles, they shoot off, carrying energy with them. In bootstrapping, the deuterium/tritium mixture is made to capture the alpha particles, which heats the plasma more and releases more alpha particles to increase the reaction.

According to the team, the key to boot-strapping was to keep the plastic shell that contains the fuel from disintegrating during compression under a high-energy laser pulse by altering the timing of the pulse to “fluff up” the ablative plastic, making it more resilient. The team believes that this disintegration in previous tests hindered the reaction and by modifying the laser they were able to prevent this.

“What’s really exciting is that we are seeing a steadily increasing contribution to the yield coming from the bootstrapping process we call alpha-particle self-heating as we push the implosion a little harder each time,” says Omar Hurricane, lead author of the team’s report.

Ironically, power generation wasn’t the team’s primary goal. The NIF is designed to provide hard data for computer models that simulate the explosion of a nuclear warhead as part of the US program to produce new warheads and to ensure that the existing stockpiles remain safe and reliable. Up until the comprehensive nuclear test ban treaty, this would have been done using underground test explosions, but the US government now relies on lasers and supercomputers for the National Nuclear Security Administration’s Stockpile Stewardship Program.

Eventually, the scientists hope the boot-strapping process will lead to ignition, but that remains in the future, as does practical application in a working commercial reactor. Currently, the experiment is only able to produce of net gain of about one percent. “There is more work to do and physics problems that need to be addressed before we get to the end,” said Hurricane, “but our team is working to address all the challenges, and that’s what a scientific team thrives on”.

The team’s results were published in the journal Nature.

Source: Lawrence Livermore National Laboratory

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Your next fridge could keep cold more efficiently using magnets

The fridge is the most common of common household appliances. Despite improvements in efficiency over the years, they remain one of the biggest users of electricity in the home, relying on chemical refrigerant and a compressor to transfer heat from the inside to the outside of the fridge. GE researchers have now developed a new type of refrigeration technology using magnets that is more environmentally friendly and is predicted to be 20 to 30 percent more efficient that current technology … and it could be in household fridges by the end of the decade.

Magnetic refrigeration is not a new idea. Ever since German physicist Emil Warburg observed in the 1880s that certain materials changed temperature when exposed to a changing magnetic field – known as the magnetocaloric effect – there have been efforts to create refrigerators based on the technique.

Such magnetic refrigeration systems were developed as far back as the 1930s, and researchers at the Los Alamos National Laboratory (LANL) in New Mexico successfully achieved a few degrees of refrigeration in the 1980s. However, the technology has failed to make it into household refrigerators as it relies on superconducting magnets that themselves need to be cooled to extremely low temperatures, making it not cost- or energy-efficient for household use.

GE teams in the US and Germany turned their collective efforts to the task a decade ago and built a cascade from special magnetic materials. Each step of the cascade lowered the temperature slightly but after five years of work they were only able to realize cooling of just 2° F with a prototype that Michael Benedict, design engineer at GE Appliances, describes as a “huge machine.”

A breakthrough then came courtesy of the research team’s materials scientists who developed a new type of nickel-manganese alloys for magnets that could function at room temperatures. By arranging these magnets in a series of 50 cooling stages, the team have managed to reduce the temperature of a water-based fluid flowing through them by 80° F with a device that is, according to Benedict, “about the size of a cart.”

“Nobody in the world has done this type of multi-stage cooling,” said Venkat Venkatakrishnan, a leader of the research team. “We believe we are the first people who shrunk it enough so that it can be transported and shown. We were also the first to go below freezing with the stages.”

The team has demonstrated the system for experts from the Department of Energy (DoE), White House staffers and the EPA and is now working to further refine the technology. They hope to achieve a 100° F drop in temperature at low power, with the ultimate goal of replacing current refrigerator technology, possibly before the end of the decade.

“We’ve spent the last 100 years to make the current refrigeration technology more efficient,” said Venkatakrishnan. “Now we are working on technology for the next 100 years.”

The magnetocaloric refrigeration technology is explained in the following video.

Source: GE

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