Powering the Very Tiny
Nanoscale devices present a megascale bear of a problem when it comes to energy sources, especially when these devices are intended for implantation in the body.
 Stephanie vL Henkel |
Georgia Tech researcher Zhong Lin Wang (photo), who also holds positions at Peking University and the National Center for Nanoscience and Technology of China, and graduate student Jinhui Song are working on nanogenerators that produce current mechanically by bending and releasing zinc oxide nanowires, which are both piezoelectric and semiconducting. Interconnected arrays of millions of such wires could produce enough current to run nanoscale devices. Brought to fruition, this technology could resolve the dual issues of power supply bulk and toxicity.
Wang and Song grew arrays of zinc oxide nanowires and deflected individual wires using an atomic-force microscope (AFM) tip. This created a charge separation, positive on the stretched side and negative on the other. The charges were preserved because a Schottky barrier was formed between the AFM tip and the wire. Coupling between the semiconducting and piezoelectric properties resulted in the charging and discharging process when the tip scanned across the nanowire. When the tip lost contact with the wire, the strain was released and the wire vibrated through many cycles, but the researchers measured a current only at the instant of release. Similar tests on structures that were neither piezoelectric nor semiconducting indicated that the observed effect was truly a piezoelectric-induced discharge process.
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Wang estimates that as much as 30% of the mechanical input can be converted to electrical energy for a single cycle of vibration. This would argue for harvesting the energy produced by the body and using it to power implanted medical devices. (http://tinyurl.com/q2k4e)
SHORT TAKES
Look to the Birds
Oxford University zoologists Graham Taylor and Adrian Thomas have outfitted an eagle with four miniature high-speed spy cameras and other instruments in a 15 g pack to learn more about its aviational secrets. An inertial measurement unit recorded details of the bird's aerobatics and transmitted the data to a receiver on the ground. The collected data indicated that when the bird banks, it turns its head and its body follows. Also of interest was the way the bird changed shape during sudden braking and other free-flight maneuvers. The research could have important implications for aircraft design. http:// tinyurl.com/m27sy
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Is Your Engine Weary?
Scientists at the University of Manchester, U.K., are developing a new type of wireless sensor to remotely monitor mechanical parts and systems and allow predictions of breakdowns in advance of failure. Aimed at the machinery and transport markets, the sensors will fit inside gearboxes, motors, diesel engines, wheel bearings, and door mechanisms where troubles can arise. The MEMS sensor will monitor parameters such as vibration, temperature, and pressure. It could also be placed inside other machinery to measure concentrations of metallic elements created through wear and tear so that the expected lifetime of the part could be calculated. http:// tinyurl.com/gzee4
Keep Your Secrets Secret
NIST researchers including Xaio Tang (photo) have generated raw code for "unbreakable" encryption at a rate >4 million bps over 1 km of optical fiber. The work is described as a step toward using conventional high-speed networks such as broadband Internet and LANs to transmit ultrasecure video for surveillance and other sensitive applications. The quantum key distribution system uses single photons in different orientations to produce a continuous binary code. The rules of quantum mechanics ensure the detection of anyone intercepting the key, thus providing a highly secure key exchange. http:// tinyurl.com/l3zuq
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