NEWS : TECH (NFPC)

Battery 'Sponge' Made from Foam-Like Copper

The humble battery is crucial for technologies ranging from consumer electronics to electric vehicles. But for all of its necessity, it still has major limits. Batteries still take too long to charge, are full of toxic chemicals and typically last just a few hundred cycles. After that, it’s the landfill.

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The Prieto Battery Company wants to change that by building a battery that has a three-dimensional internal structure, allowing them to suck up energy faster and extend their lifetimes. The design is the brainchild of Amy Prieto, a chemistry professor at Colorado State University.

Ordinary batteries are made in layers: the part that provides positive charge, called a cathode, the negatively charged part, called the anode, and the electrolyte between them which is usually an acid. The electrolyte allows electrons to move between the cathode and anode. The layers are either flat, as in a phone battery, or rolled up, as in a AAA for the remote.

The problem is that this design only allows electrons -- the current -- to move from the side of the anode in contact with the electrolyte to the cathode. That provides fewer pathways for the electrons to move, and limits how many can do so, like cramming a crowd of people into a room and only opening the doors on one side. As a result the battery takes a while to charge and loses energy faster.

Prieto’s design does something different: the cathode and anode are like a sponge, with lots of holes. So instead of a solid block, the battery has loads of surface area inside. That allows the electrons to move more easily because they have more points of contact. In the room analogy, it's like opening up the exit doors on all four sides, allowing the people to leave faster.

The Prieto batteries are made with copper. The copper, which takes on a foam-like structure, is then coated with the negative electrode material. That in turn is coated with the electrolyte, which is a solid instead of a liquid. The leftover space is filled with the cathode, which is initially a kind of slurry that then hardens into place.

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The chemicals used are non-toxic -- one component is citric acid as opposed to stronger ones such as the sulfuric acid used in car batteries. The company says they can get it to charge quickly and do so thousands of times, though testing continues and it will be some time before a working version hits the streets.

Via Inhabitat, Prieto Battery

Credit: Prieto Youtube Screengrab

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Coated Sapphire Is Invisible to Infrared Cameras

Infrared detectors are used to see objects otherwise hidden under cover of darkness. The dectors pick up the heat given off by living bodies, warm buildings and vehicles and reveal them as glowing objects when viewed through infrared goggles or cameras. If a building, body or vehicle is cold, the detector typically can't visualize it.

Now new technology from researchers at Harvard School of Engineering and Applied Sciences could turn infrared detection on its head. The technique not only makes hot objects appear cold to infrared detectors -- which could help hide soliders from their enemies at night -- but it can be also used to make an infrared camera so sensitive that even cold objects would look relatively bright.

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The researchers coated a millimeter-thick sheet of sapphire with a 180-nanometer layer of vanadium dioxide, which is used as an insulator. Next, they heated the layered material to 154 degrees Fahrenheit (68 degrees Celsius). At that temperature, the crystal structure of the vanadium dioxide became altered, changing it from an insulator to a metallic conductor.

When the scientists shone infrared light onto the altered material, they found it was a near-perfect absorber, soaking up 99 percent of the infrared light that hit it. It worked because the infrared light waves bounced off the sapphire get absorbed by the vanadium dioxide, and any light waves that escape destructively interfere with each other so that they cancel out.

When the scientists cooled the layers down, the materials returned to their former states.

Mikhail Kats, the lead author of the research, told Discovery News that vanadium dioxide, unlike other materials, absorbs infrared radiation differently depending on its temperature -- it can be tuned.

If one could coat a vehicle or building with this material, it would make the objects invisible -- or at least black -- to an infrared camera, since any infrared radiation emitted by the objects would be absorbed by the material before it could escape.

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And because the material is so sensitive to infrared light, it could also work as a detector. Any imaging device has to absorb light in order to translate it into electrical signals and make a picture. The more sensitive the sensor, the better the detector.

One big challenge was making the vanadium dioxide crystals pure enough. Any flaws would mean it lost its unique reaction to temperature.

The research appears in the latest issue of Applied Physics Letters.

via Harvard University

Credit: Harvard University / Kirill Nadtochiy

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Solar 'Funnel' Could Boost Energy Efficiency

Typical solar cells made of silicon miss out on a wide swath of energy shining from the sun.

But according to calculations made by scientists at the Massachusetts Institute of Technology and China's Peking University and Xi'an Jiaotong University, poking a sheet of material just a molecule thin changes the material's atomic structure and improves its ability to harvest a broader spectrum of sunlight.

Conventional solar panels made of crystalline silicon are most sensitive to wavelengths of sunlight in the red end of the visible range or the near-infrared. Panels made of amorphous silicon are more sensitive to wavelengths of light in the blue range.

But the sun's peak wavelength is in the green part of the spectrum. Photons (light particles) from that wavelength of light do the best job at hitting atoms inside solar panels and knocking out the electrons that ultimately generate an electric current. If solar panels could be tuned to harvest a larger spectrum of sunlight, they'd generate more electricity and be more efficient.

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In this week's issue Nature Photonics, MIT professor Ji Lu and his colleagues have proposed a radical idea that turns a very thin sheet of material into a kind of “solar energy funnel” that takes advantage of elastic strain. The material is molybdenum disulfide, which is not typically made into a solar panel but has been experimented with as a semiconductor material for transistors. It's also in a certain class of substances called 'ultrastrength materials,' which can be stretched out of shape for long periods of time without breaking.

The technique involves poking the sheet of molybdenum disulfide with a microscopic needle. The pressure from the needle causes an elastic strain that not only takes on the shape of a funnel but increases in intensity toward the center.

Like silicon, molybdenum disulfide releases electrons when hit by sunlight. Stretching the material into a funnel shape varies its atomic structure from the edge to the center, and allows different parts of the sheet to respond to photons from different wavelengths of sunlight.

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This means a single sheet of material can actually work harder to collect more energy from the sun. In addition, because the sheet is funnel-shaped, the charged particles will tend to gather at the bottom of it -- moved there by electrostatic energy and not gravity. Having the electric charges all end up in one place is a lot more efficient than having them simply bouncing randomly around the sheet.

All this sounds good, but it hasn't been confirmed by real-world experiments; the calculations are all mathematical models. But the principle has been used before. IBM and Intel have both done experiments with elastic strains in silicon channels in transistors with some success.

Via MIT News

Credit: MIT News/ Yan Liang

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Spray-On Coating Repels Water, Keeps Kicks Dry

Back in high school, I knew a lot of guys who were obsessed with keeping their sneakers white and clean. So, of course, other people did their best to mess up those shoes. Whether it was an "accidental" spill of soda in the lunchroom or a playful nudge off of the sidewalk into the grass, those shoes were the main target. Too bad those obsessive guys didn't have NeverWet, a spray-on coating developed by researchers at Ross Technology in Lancaster, Penn.

The silicon-based aerosol spray is made up of nanoparticles that create a hydrophobic surface when sprayed onto an object. Any liquid that comes into contact with the treated area rolls off without leaving a stain behind. The spray aids in preventing corrosion, icing and bacteria growth. It also helps keep surfaces clean by keeping particles like dust and thick oils on the surface, making them easier to wipe away.

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New Scientist tested out a pair of shoes coated with NeverWet and found that a few things were able to penetrate the water-phobic coating. These included solvents such as acetone and ethanol. The testers were also able to damage the shoes pretty thoroughly with a good ol' can of spray paint. So, it may not be the cure-all for white shoe obsessives, but it does work pretty well on electronics. According to a video on the NeverWet site, an iPhone sprayed with the substance still worked after being submerged in water for 30 minutes.

No official word yet, but the spray is set to hit U.S. shelves soon, with an international release coming later on.

Via: New Scientist TV

Credit: Christine Schneider/cultura/Corbis

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Friction And Static Could Charge Smartphones

Static electricity is good for sticking balloons to walls, but who knew it could be used to prolong the battery life of a smartphone. Sihong Wang and Long Lin, graduate students in Georgia Tech's materials science department have developed a two-layered material that generates power from static electricity and flexing.

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They've used a thin film made of a layer of polymer and another of aluminum. Both layers have tiny structures etched on them at the nanometer scale. When the plastic and the metal come in contact with each other, they accumulate a static electric charge. Flexing them generates a current.

The etched nanostructures increase the surface area, which gives electrons a lot more room to gather and boosts the charge accumulated. The efficiency with which the material turns the mechanical motion of flexing into electricity can go as high as 40 percent, according to the paper.

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Wang has done similar work before: in 2009 he demonstrated that a hamster could wear a jacket that generated power in a similar way.

So how much power can it make? In a paper in the journal Nano Letters, Wang and his team say they have hit 230 volts, at 15.5 microamperes per square centimeter, with a power output of 128 milliwatts per cubic centimeter. That means a sheet the size of the latest iPod Nano –- about three inches by 1.6 inches –- would generate just enough to charge the iPod as it is being flexed.

If it were used in the real world, odds are this wouldn't replace a battery, but it could extend the time between charges.

Via Technology Review

Credit: Danilo Calilung/Corbis

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Conductive Plastic Heals Like Skin

If you want to make artificial skin that works like the real thing (a la Lieutenant Commander Data in "Star Trek") then it's necessary to put together two things: high electrical conductivity that duplicates nerve endings and the ability to self-repair like a skin wound.

The problem is that although metal provides the kind of conductivity necessary to duplicate nerves, it doesn't repair well. And softer materials, like plastic-based ones, can self-repair but don't conduct electricity well.

At Stamford, a research team led by Chemical Engineering Professor Zhenan Bao has found a way to bring those two properties together. The polymer might one day be used to cover prosthetics, or even as a new kind of flexible touch screen -- one that heals itself. Dropping the smart phone might become a bit less nerve-wracking.

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The work builds on experiments conducted last year, in which Bao's team used carbon nanotubes to build a flexible skin-like sensor that could sense pressure. Now the team has found a way to combine the carbon nanotubes with metal atoms. The group worked with a polymer material that had a specific molecular structure -- one where molecules were connected by hydrogen bonds. Hydrogen bonds are relatively weak so they come apart with little force. But unlike other kinds of bonds they can reconnect resulting in a molecular structure that's the same as it was before. This ability to reconnect after damage was an important component of the self-healing material.

The next component was the ability to conduct electricity. For that, the scientists added nanometer-sized bits of nickel to the material. The nickel boosted the material's electrical conductivity, and the more nickel that was added, the stronger the material became.

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In the end, the material Bao and his team developed worked even better than skin: when it was cut with a scalpel it would repair itself in less than a minute; after a half hour, it was back at 100 percent of its strength and electrical conductivity. Skin takes days to do that. 

The new material could work as a sensor because when it's twisted or stretched, the electrical resistance changed. That information could be transmitted to a computer or eventually to a brain, though there isn't yet a reliable brain-computer interface.

The one trade-of was the amount of nickel and the electrical conductivity: an increase in nickel decreased the efficiency of the self-healing. Future work will be geared to finding the optimal amount.

 

Via Stanford University

Credit: Linda A. Cicero, Stanford News Service

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Rinse Cycle Turns Clothing into Pollution Buster

Steadfast environmentalists determined on saving the planet with their greener-than-thou efforts usually wear their heart on their sleeves. But why limit the heart to just the sleeve, especially now that it can be worn on every part of one's clothing?

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Catalytic Clothing has been working on pollution-eating clothing prototypes for a while now, but their new laundry additive is set to hit retail stores soon, although the deal is pending.

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Put the additive in the final rinse cycle of your wash and it'll coat your clothes in nano-sized particles of titanium dioxide that trap and convert nitrogen oxide pollutants in the air into harmless byproducts that can be easily washed away on laundry day.

According the company, one person wearing clothes coated with the additive could remove approximately five grams of nitrogen oxides from the air over the course of a day. That may not sound like a planet-saving number, but considering that's roughly twice the amount that a passenger vehicle gives off in a typical day, I'd gladly step into a wardrobe coated in this stuff.

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The pollution-gobbling threads will be on display at the Manchester Science Festival in Manchester, England from October through November 4.

via Yahoo!

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Clear, Flexible Speakers Made from Graphene

Carbon was first used in microphones and speakers in the form of grains. Now it has a new form: layers only a couple of atoms thick, generating sound from heat.

It's called thermoacoustic sound, and it dispenses with the bulky magnets that ordinary speakers need and allows for speakers that are nearly any shape and size.

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The invention comes from Ji Won Suk at the University of Texas, Austin. He used a principle that has been known for a long time: put a current through most materials and they heat up. Oscillate the current and you get a temperature change that has the same frequency. 

Suk did this to graphene, which consists of carbon atoms arranged in a regular pattern. It's strong and conductive, and also transmits heat very well. Suk made a layer of graphene less than a single nanometer thick and put it on glass and two different types of plastic. He then ran an alternating current through it at various frequencies, from 500 and 22 cycles per second. The result: sound.

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An ordinary speaker uses an oscillating electric current to drive magnets, which then cause a diaphragm to vibrate. In this case, the graphene isn't vibrating. Rather, it is transmitting the heat energy to the air. But transmitting that heat energy moves air molecules around in a way similar to the vibrations of a speaker, so you get sound.

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Suk told Discovery News that he found the best materials to use as substrates are those that are thermal insulators, so more of the energy goes out into the air (where we can hear it). Ideally a graphene speaker would be suspended in the air, but given that it's only a couple of atoms thick that isn't practical, he said.

What's practical is putting the graphene on various substrates, which can be any shape. Suk noted that the sound can also be adjusted by altering the shape of the graphene layer, which itself is flexible. He added that he hasn't tested the limits of the graphene yet -- he used relatively small amounts of current, on the scale of hundreds of milliamps. (He didn't try hooking up an iPod to it yet, but there is no reason that couldn't work).

Suk's experiments appeared in the journal Advanced Materials on Sept. 18.

via Advanced Materials

Credit: University of Texas / Ji Won Suk

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Lens Focuses Light Without Distortion

For centuries, scientists and engineers have pushed the limits of materials to make better lenses. Inventions such as the Fresnel lens made lighthouses visible from further away and plastics made coke-bottle eyeglasses a thing of the past. Now a research team at Harvard has made another leap: a tiny cone-shaped lens that eliminate distortions in everything from cell phone cameras to ligh signals that travel through fiber optic cables.

Ultra-precise lenses are used in telecommunications to focus the beams in fiber-optic systems and in some cell phone cameras. Making them smaller and flatter frees up space and reduces the weight of devices. But existing solid lenses aren't distortion-free, however, and fixing that usually means using multiple lenses, which adds to weight and size. 

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The Harvard team, led by Frederico Capasso, used a kind of lens called an axicon. A normal lens takes on a curved shape, but an axicon is more like a cone. Axicons are used in situations where one needs a steady beam of light that doesn't spread out.

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The axicon lens is made of 60-nanometer thick bits of gold, each shaped like a tiny "V". The gold changes the amount of time it takes for the light to pass through the silicon lens. In fact, the amount they change the focus of the beam is precisely tuned across the surface of the lens.

The precise tuning eliminates the distortions that would ordinarily accompany any lens. For example, a wide-angle camera lens has a "fish eye" effect towards the edge of the image. This design would get rid of that problem.

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Lenses like this could show up in cell phone cameras, where the space is small and it's difficult to make a lens that gathers enough light, or in fiber-optic communications, where focused light has to travel long distances without being distorted.

The work appeared in the journal Nano Letters.

Via Harvard University

Credit: The Capasso Group / Harvard University

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Invisible QR Codes Could Stop Counterfeiters

Counterfeiters date back to at least the 13th Century, when watermarks were invented to authenticate original documents. Ever since then, printers and forgers have been in an arms race to out-do eachother. Now new and simple technology may give printers the upper hand.

A team of researchers from the South Dakota School of Mines and Technology and the University of South Dakota have found a way to print invisible quick response codes onto documents. More frequently referred to as QR codes, these black barcode-like stamps contain digital information in the form of square dots arranged in a square pattern. The codes are commonly used in advertising and may contain a URL to another website or other useful information that can be accessed by scanning it with a camera from a smartphone.

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Instead of making the QR codes with black ink printed on a white background, the researchers found a way to make the codes with invisible ink that's still visible to a smartphone camera.

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The researchers started with ink made with nanometer-sized particles that glow under a laser light. But the way the ink fluoresces is different than expected. Normally, fluorescent ink emits light of a longer wavelength. For example, shine ultraviolet light onto one of those blacklight posters and visible light colors are produced.

But in this case, the nanoparticle ink produces wavelengths that are shorter. Near-infrared light shined onto the ink produces bright blue or green colors. These types of fluorescent inks are a lot harder for forgers to reproduce. A smartphone can read it and know if the document is authentic or not. The laser light reader doesn't have to be a part of the phone either, but can be a separate device that's linked wirelessly to a smartphone's camera.

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A third element in this QR code enhances its security. The team devised a way to embed microscopic image into the code, something forger would have to produce. Without the microscopic image, a close examination would show that the QR code was a fake.

The ink was printed on ordinary paper and the QR codes held up to being folded and unfolded 50 times. Jon Kellar, a professor of materials and metallurgical engineering at the South Dakota School of Mines, told Discovery News that the ink can even work with a desktop printer. And because the code can be printed on plastic or even glass, manufacturers could use it to authenticate other items besides documents -– perhaps as a way of differentiating a real Rolex from a knock-off.

The work appears in the Sept. 12 issue of the journal Nanotechnology.

Credit: South Dakota School of Mines and Technology/Nanotechnology

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