Wednesday, November 14th, 2012

Time	Event
5:00a	New metamaterial lens focuses radio waves In many respects, metamaterials are supernatural. These manmade materials, with their intricately designed structures, bend electromagnetic waves in ways that are impossible for materials found in nature. Scientists are investigating metamaterials for their potential to engineer invisibility cloaks — materials that refract light to hide an object in plain sight — and “super lenses,” which focus light beyond the range of optical microscopes to image objects at nanoscale detail. Researchers at MIT have now fabricated a three-dimensional, lightweight metamaterial lens that focuses radio waves with extreme precision. The concave lens exhibits a property called negative refraction, bending electromagnetic waves — in this case, radio waves — in exactly the opposite sense from which a normal concave lens would work. Concave lenses typically radiate radio waves like spokes from a wheel. In this new metamaterial lens, however, radio waves converge, focusing on a single, precise point — a property impossible to replicate in natural materials. For Isaac Ehrenberg, an MIT graduate student in mechanical engineering, the device evokes an image from the movie “Star Wars”: the Death Star, a space station that shoots laser beams from a concave dish, the lasers converging to a point to destroy nearby planets. While the researchers’ fabricated lens won’t be blasting any planetary bodies in the near future, Ehrenberg says there are other potential applications for the device, such as molecular and deep-space imaging. “There’s no solid block of any material in the periodic table which will generate this effect,” Ehrenberg says. “This device refracts radio waves like no other material found in nature.” Ehrenberg published the results of his research in the Journal of Applied Physics. His co-authors on the paper are Sanjay Sarma, the Fred Fort Flowers and Daniel Fort Flowers Professor of Mechanical Engineering at MIT, and Bae-Ian Wu, a researcher at the Air Force Research Laboratory. Shaping a cell A metamaterial’s extraordinary properties are determined largely by its structure — similar to how a diamond’s crystals impart strength. A material can refract light differently depending on the shape of individual units within a material, and the arrangement of those units as a whole. Prior to this recent paper, Wu and others have studied how certain shapes of metamaterials can affect the propagation of electromagnetic waves. The team came up with a blocky, S-shaped “unit cell” whose shape refracts radio waves in particular directions. Ehrenberg used the unit shape as the basis for his concave lens, creating the rough shape from more than 4,000 unit cells, each only a few millimeters wide. To fabricate his design, Ehrenberg utilized 3-D printing, building a lens layer by intricate layer from a polymer solution. He then washed away any residue with a high-pressure water jet and coated each layer with a fine mist of copper to give the lens a conductive surface. To test the lens, the researchers placed the device between two radio antennae and measured the energy transmitted through it. Ehrenberg found that most of the energy was able to travel through the lens, with very little lost within the metamaterial — a significant improvement in energy efficiency when compared with past negative-refraction designs. The team also found that radio waves converged in front of the lens at a very specific point, creating a tight, focused beam. Imaging space and beyond Sarma says the combination of the device’s “low loss” and tight focus is a promising step toward engineering practical metamaterial lenses. “There are a lot of phenomena in the world that you can demonstrate, but whether you can achieve it at scale is the issue,” Sarma says. “We’ve taken the negative refraction concept from the realm of proof-of-concept to the realm of practicality.” The device, which weighs less than a pound, may be used to focus radio waves precisely on molecules to create high-resolution images — images that are currently produced using bulky, heavy and expensive lenses. Ehrenberg says that such a lightweight device could also be mounted on satellites to image stars and other celestial bodies in space, “where you don’t want to bring up a hefty lens.” Cheng Sun, an assistant professor of mechanical engineering at Northwestern University, says the metamaterial design is a promising demonstration that may lead to stronger, faster telecommunications. “The low-loss design can be considered a significant step forward toward practical applications at microwave or radio-frequencies ranges,” Sun says. Beyond the lens’ applications, Ehrenberg says its fabrication is simple and easily replicated, allowing other scientists to investigate 3-D metamaterial designs. “You can really fully explore the space of metamaterials,” Ehrenberg says. “There’s a whole other dimension that now people will be able to look into.” (Comment on this)
5:00a	Driving drones can be a drag On its surface, operating a military drone looks a lot like playing a video game: Operators sit at workstations, manipulating joysticks to remotely adjust a drone’s pitch and elevation, while grainy images from the vehicle’s camera project onto a computer screen. An operator can issue a command to fire if an image reveals a hostile target, but such adrenaline-charged moments are few and far between. Instead, a drone operator — often a seasoned fighter pilot — spends most of his shift watching and waiting, as automated systems keep the vehicle running. Such shifts can last up to 12 hours, as is the case for operators of the MQ-1 Predator, a missile-loaded unmanned aerial vehicle (UAV) used by the U.S. Air Force for overseas surveillance and combat. “You might park a UAV over a house, waiting for someone to come in or come out, and that’s where the boredom comes in,” says Mary “Missy” Cummings, associate professor of aeronautics and astronautics and engineering systems at MIT. “It turns out it’s a much bigger problem in any system where a human is effectively babysitting the automation.” Cummings says such unstimulating work environments can impair performance, making it difficult for an operator to jump into action in the rare instances when human input is needed. She and researchers in MIT’s Humans and Automation Lab are investigating how people interact with automated systems, and are looking for ways to improve UAV operator performance. In a study to be published in the journal Interacting with Computers, Cummings’ team found that operators working with UAV simulations were less bored, and performed better, with a little distraction. While the study’s top performer spent the majority of time concentrating on the simulation, the participants with the next-highest scores performed almost as well, even though they were distracted nearly one-third of the time. The findings suggest that distractions may help avoid boredom, keeping people alert during otherwise-tedious downtimes. “We know that pilots aren’t always looking out the window, and we know that people don’t always pay attention in whatever they’re doing,” Cummings says. “The question is: Can you get people to pay attention enough, at the right time, to keep the system performing at a high degree?” Keeping boredom at bay The researchers set up an experiment in which participants interacted with a UAV simulation in four-hour shifts. During the simulation, subjects monitored the activity of four UAVs, and created “search tasks,” or areas in the terrain for UAVs to investigate. Once a UAV identified a target, participants labeled it as hostile or friendly, based on a color-coded system. For hostile targets, subjects issued a command for a UAV to fire, destroying a target, and earning points in the simulation. The researchers videotaped each participant throughout the experiment, noting when an operator was engaged with the system, and when he or she was distracted and facing away from the computer screen. The person with the highest score overall was the one who paid the most attention to the simulation. “She’s the person we’d like to clone for a boring, low-workload environment,” Cummings says — but such a work ethic may not be the norm among most operators. Cummings and her colleagues found that the next-best performers — who scored almost as high — were distracted 30 percent of the time, either checking their cellphones, reading a book, or getting up to snack. The team also found that while the simulation only required human input 5 percent of the time, most people “made themselves busy” in the simulation for 11 percent of the time — an indication that participants wanted more to do, to keep from getting bored. Cummings says creating busywork or distractions once in a while may, in fact, be good for productivity, keeping an operator engaged when he or she may otherwise lose focus. Personality complex Cummings says personality may also be a consideration in hiring UAV operators. In the same experiment, she asked participants to fill out a personality survey that ranked them in five categories: extroversion, agreeableness, conscientiousness, neuroticism and openness to experience. The group found among the top performers, conscientiousness was a common personality trait. Cummings says conscientious people may work well in low-taskload environments such as UAV operation — although she says they may also hesitate when the time comes to fire a weapon. “You could have a Catch-22,” Cummings says. “If you’re high on conscientiousness, you might be good to watch a nuclear reactor, but whether these same people  would be effective in such military settings is unclear.” “It’s an aphorism that ‘war is long periods of boredom punctuated by moments of sheer terror,’” says Lawrence Spinetta, a lieutenant colonel in the U.S. Air Force and a former Predator squadron commander. “That's true in spades for unmanned aircraft combat operations.” Spinetta says the success of UAV missions depends on keeping operators alert — a challenging task when missions can run for months at a time without a day of rest. “A mission may be to watch a suspected location where a terrorist is hiding for days, weeks, or even months,” Spinetta says. “Attention to detail is required for success. That can go out the window when boredom sets in. Thus analyzing ways to overcome, address and analyze boredom, which is the thrust of this paper, is critical to mission effectiveness.” Cummings’ group is continuing to run experiments to tease out conditions that may improve performance and discourage boredom: For example, periodic alerts may redirect an operator’s attention. The group is also looking into shift duration, and the optimal period for operator productivity. “We need people who can monitor these systems and intervene, but that might not be very often,” Cummings says. “This will be a much bigger problem in five to 10 years because we’re going to have so much more automation in our world.” EVENT: As part of the MIT News at Noon program, Mary “Missy” Cummings will speak about this research at the MIT Museum on Friday, Nov. 16, from 12:10 to 12:50 p.m. Learn more (Comment on this)

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