July R&D Round UpJuly 1, 2011 By: Melanie Martella, Sensors
This month we've got a new magnetic alloy that could be used for energy harvesting, another nanowire-based chemical sensor, and a sensing skin that could be used to monitor the condition of concrete structures. Also, for those of you who are Canadian, Happy Canada Day!
A Magnetic Material for Energy Harvesting
As a piezoelectric material converts mechanical stress to a voltage, University of Minnesota researchers have found a magnetic alloy that converts heat into electricity. The multiferroic alloy, Ni45Co5Mn40Sn10 (and doesn't that just trip off the tongue) undergoes a reversible phase transformation when exposed to heat, at which point its magnetic properties change. The Eurekalert news article, "University of Minnesota engineering researchers discover source for generating 'green' electricity" includes a link to a video showing a sample of the material changing from nonmagnetic to strongly magnetic when it absorbs heat. Surround the material with a coil and when that nonmagnetic to magnetic behavior happens, electricity is produced in the coil. There's an awful lot of waste heat in our world crying out to be converted to useful energy, and although it's still very early days for this particular material as a new energy harvester, it's still a welcome addition to the energy harvesting toolbox.
A Nanowire-based Gas Sensor Those clever, clever people at NIST, working with other researchers from George Mason University and the University of Maryland have developed a highly sensitive gas sensor that uses a single gallium nitride nanowire and titanium doxide nanoclusters carefully selected to react with the target gas. The proof-of-concept device can detect the target gas over a range of concentrations—from 50 ppb up to 1% of the air in a room—and will work at room temperature, an improvement over existing thin-film gas sensors that must be heated to operate and that can suffer reliability issues as a result. As described in the news article, "Nanosized Sensors for Detecting Volatile Organic Compounds", the single-crystal gallium nitride nanowires are coated with titanium dioxide nanoclusters to detect benzene and related volatile organic compounds. Traditional gas sensors experience a current change in the metal oxide thin film as the target gas reacts with it. The new sensor, rather than using heat, uses ultraviolet light to promote the reaction between the titanium dioxide and the gas. The new sensor is tiny, robust (each nanowire is a defect-free single crystal and it's not like there are any moving parts), and requires very little power. The researchers plan to create an array of nanowire-based sensors, tuned to react with different gases, to allow them to analyze gas mixtures.
A Novel Sensing 'Skin'
A new approach to structural monitoring has been developed by civil engineers at MIT working with physicists at the University of Potsdam in Germany. Their idea? To use patches of 'sensing skin', applied to structures in locations where cracks are most likely to occur, to provide continual structural monitoring. The sensing skin they've developed is a soft stretchy thermoplastic elastomer mixed with titanium dioxide and painted with patches of black carbon. When the patch is stuck to a surface,and a crack occurs, the patch experiences a change in its capacitance. The titanium dioxide in the skin is sensitive to cracks while the patches of carbon black measure the change in the electrical charge of the skin. By sending a current into the patches once a day, and determining whether any patches have experienced capacitance changes and if so, which ones, allows those maintaining the structures to determine within a day whether there are new cracks and, if so, where the cracks are. Further details are available in the PhysOrg.com article, "'Sensing skin' could monitor the health of concrete infrastructure continually and inexpensively". Considering how many aging concrete structures litter our landscape, and how many of them we rely on not to fall down, wouldn't it be nice to have such rapid information about potential problems?
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