November R&D Round UpNovember 7, 2008 By: Melanie Martella, Sensors
This month: Taking cues from fish to improve an unmanned submarine's ability to sense water flow, an antireflective coating that boosts the efficiency of solar panels, and a new approach for electronic noses.
Smoother Sailing with Hairy Subs
In another example of taking tips from nature to solve engineering problems, researchers Michael McConney and Vladimir Tsukruk at the Georgia Institute of Technology have created sensors similar to those used by fish in their lateral lines. The lateral line is a sense organ on the fish's skin that detects the flow of water around the fish. In fish, the lateral line uses microscopic hairs capped with mucous—these are deflected by moving water and provide feedback to the fish. The artificial hairs developed by McConney and Tsukruk are 550 µm-long polymer fibers tipped with a hydrogel. These are mounted on a piezoelectric material that produces a voltage signal when the fibers are deflected by the water flow. All told, the resulting sensors can detect water flows as low as 2.5 µm/s (without the gel, the sensor can only detect water flows above 100 µm/s). Ultimately, these sensors may help unmanned submarines to move more efficiently through the water. For more detail, read "Hairy subs could feel their way through turbulence", courtesy of New Scientist.
Solar Power Gets a Boost
One of the current problems with solar panels is their inefficiency-a typical solar cell only absorbs about two thirds of the sunlight that falls on it. However, researchers at Rensselaer Polytechnic Institute, led by Shawn-Yu Lin, have developed a new anti-reflective coating can boost that absorption rate to 96.21%. The nanoengineered coating also works for light incident at any angle, which is not the case for existing solar panels. Typical antireflective coatings are designed to transmit light of a particular wavelength. According to the Science Daily article, "Solar Power Game-changer: 'Near Perfect' Absorption Of Sunlight, From All Angles," "Lin's new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to "bend" the flow of sunlight to an angle that augments the coating's antireflective properties. This means that each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it." Not only does this promise more efficient solar panels, but (as the article notes) it means that solar arrays will no longer need to move to maintain an optimum angle with the sun.
A Smarter Sniffer
NIST researchers Baranidharan Raman, Joshua Hertz, Kurt Benkstein, and Steve Semancik have developed a new approach to making electronic noses. By combining a pattern recognition module with a sensitive chemical detector, they have created an electronic nose that can still recognize molecular features of a smell that it's never been trained to recognize. The device uses 16 microheater platforms topped with oxide films. The microheaters are tiny machined structures combining a heater, a metal thermometer/heat distribution plate, and electrical contacts, with insulating layers between them. Gases adsorb into the sensing films deposited on to the structures. These adsorbed gases cause a change in the electrical conductance in the sensing film so that, by manipulating the temperature, the device can be used to create "fingerprints" for different gases. I quote from the NIST Tech Beat article, "Sniffing Out a Better Chemical Sensor" because I love their description: "Precise control of the individual heating elements allows the scientists to treat each of them as a collection of "virtual" sensors at 350 temperature increments between 150°C–500°C, increasing the number of sensors to about 5,600. The combination of the sensing films and the ability to vary the temperature gives the device the analytical equivalent of a snoot full of sensory neurons."
The researchers copied the approach used in animals to identify smells—the first step in odor recognition is quick and dirty, and each further step refines the information. The researchers note that by using this "divide and conquer" approach, they don't have to expose the electronic nose to every chemical compound it'll come into contact with to have the nose recognize and classify them.
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