Terahertz imaging. NASA does not have exclusivity on commercializing extraterrestrial scientific research. Its sister agency in Europe, the European Space Agency coordinates multinational projects in space. Among the fruits of the ESA’s labors is included a new imaging system based on terahertz radiation. According to Peter de Maagt, ESA’s StarTiger project manager, “When we started last June, we set an ambitious goal: to build in four months the first compact submillimeter-wave imager with near real time image capturing using state-of-the-art micromachining technology. We reached this goal when the first terahertz images were taken in September.” The first version had a low 8 x 8 pixel resolution with a long acquisition time. Early attempts at constructing a camera operating in this range have arisen from waveguide-based technology, resulting in bulky solutions assembled from discrete elements. By pushing the development of a lithographically and micro-machined detector array with MEMs technology, the researchers were able to enhance their product into a 2-color, 16-pixel array the size of a postage stamp. “The StarTiger imager fits within a briefcase and is easily transportable. The core of the instruments is the size of a cigarette package,” says Maagt. “Next generation instruments will go for another magnitude smaller size, by using electronic scanning.” According to their website, the StarTiger program is a new R&D program whose “concept is to bring together a small group of highly motivated researchers, grant them full access to laboratory and production facilities, remove all administrative distractions, and let them work for an intense period of four to six months.” To put it into perspective, most radio waves stop at around 0.1 THz; the StarTiger project has created a sensor array that works with terahertz waves in the 0.2 to 0.3 THz range. Unlike heat or light waves, terahertz radiation passes through many solid objects, allowing images to be created of the physical and chemical characteristics of optically hidden objects. The technology was first investigated for the purpose of sensing atmospheric and ground phenomena from satellites; Pierre Brisson, head of ESA’s Technology Transfer Promotion Office (the European equivalent of NASA’s NCTN), says, “we have recognized the huge potential in nonspace applications, and in parallel to exploiting the use of terahertz waves and StarTiger technology in space, we have kicked off a commercialization study to identify the best way of transferring it to terrestrial systems.” The main advantage to using terahertz radiation for the purposes of imaging is that no radiation is emitted by the passive equipment; thus, it is possible to substitute this imaging for more aggressive X-ray techniques.
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High impact amorphization. Ballistics experts have puzzled over the loss of impact resistance in an extremely hard and lightweight ceramic material called boron carbide, sometimes used in protective armor. The material does an excellent job of blocking low-energy projectiles such as handgun bullets, but shatters too easily when struck by more powerful ammunition. Writing in the March 7 issue of the journal Science, researchers from The Johns Hopkins University and the U.S. Army Research Laboratory say they have discovered that higher-energy impacts cause tiny bands of boron carbide to change into a more fragile glassy form, which was determined by observing the atomic structure of boron carbide fragments retrieved from a military ballistic test facility. This high-impact pressure amorphization has previously been seen in minerals and semiconductors, but the researchers say they are the first to report such behavior in a ceramic as hard as boron carbide. The extremely high velocities and pressures associated with impact of a high-powered projectile appear to cause microscopic portions of the material’s crystalline lattice structure to collapse. “It’s like having a sturdy table and suddenly kicking the legs out from underneath it,” said Mingwei Chen, associate research scientist in the Department of Mechanical Engineering at Johns Hopkins and lead author of the Science article. Chen came up with a way to position ultra-thin edges of the fragments so that their atomic structure could be viewed through a high-resolution transmission electron microscope at Johns Hopkins. Localized areas that initially appeared to be cracks in the material were found to consist of the new glassy form of boron carbide. Under normal conditions, atoms in boron carbide form a crystal lattice. In the 2-nanometer glassy bands, however, the atoms were in a jumbled or disordered arrangement. “This discovery was very enlightening, because it tells us that under extremely high pressures the crystal structure collapses and forms these nano-scale amorphous bands,” said Kevin J. Hemker, a professor in the Department of Mechanical Engineering, co-director of the electron microscope lab, and senior author of the Science article. “Then the material fractures along these bands because the glassy material appears to be weaker than the crystalline boron carbide.” Having found why boron carbide abruptly loses its protective capabilities, the researchers hope they have opened a door toward development of a new form of the material that will do a better job of keeping soldiers and police officers safe. The observations also provide experimental evidence that extreme conditions in pressure, temperature and/or loading and quenching rates can lead to the creation of entirely new materials or structures with substantially altered physical and mechanical properties. 
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