Electronic Products - June 2007 - 26
OUTLOOK Fig.2. The prototype direct-current nanogenerator (left) uses an array of flexible zinc-oxide nanowires (right) that generate current when vibrated. Though the process must still be fine-tuned, the structures have thus far remained stable at temperatures to 800°C, which would allow them to be recycled and re-used in catalytic reactions according to Wang. Researchers are able to control the size such that only 4.5% the nanocrystals produced are larger or smaller than the target size—the smallest units produced to date are 20 nm in diameter— but want to find a way to make the nanocrystals even smaller while preserving the shape. Wang notes, “If we can reduce the size through better control of processing conditions, we will have a catalytic system that would allow production of hydrogen with greater efficiency.” The previous month, Wang’s group demonstrated a prototype nanometer-scale generator that produces continuous dc power by harvesting mechanical energy from such environmental sources as ultrasonic waves or me- chanical vibration, or even blood flow. Based on arrays of vertically-aligned zinc oxide nanowires that move inside a novel “zig-zag” plate electrode, the nanogenerators could power nanoscale devices without batteries or other external power sources. The nanogenerators take advantage of the unique coupled piezoelectric and semiconducting properties of zinc oxide nanostructures, which produce small electrical charges when flexed (see Fig. 2). Fabrication begins with growing an array of nanowires approximately 0.5 μm apart on gallium arsenide, sapphire, or a flexible polymer substrate. A layer of zinc oxide is grown on top of substrate to collect the current. The researchers then fabricate silicon “zig-zag” electrodes, which contain thousands of nanometer-scale tips made conductive by a platinum coating, which is placed on top of the array but leaves just enough space so that nanowires are free to flex within the gap. When moved by mechanical energy, the nanowires periodically contact the tips, transferring their electrical charges to produce nA-range current. Researchers expect that with optimizations the device could produce as much as 4 W/cm3. For more information on both developments, call Zhong Lin Wang at 404-894-8008 or e-mail at zhong. wang@mse.gatech.edu. Richard Comerford This year, IMS visits Hawaii eld from June 3 to 8 in Honolulu, Hawaii, the International Microwave Symposium (IMS) 2007 is the centerpiece of Microwave Week 2007, which also includes the Radio-Frequency Integrated Circuit Symposium (www. rfic2007.org) and the Automatic RadioFrequency Techniques Group Conference (www.arftg.org). The conference expects to draw over 10,000 participants and will include about 400 exhibiting companies RFMD’s LNAs from around the world. Attendees will hear presentations outlining the latest advances in the industry and see innovative new products. Here is a sampling of some of the products to be exhibited. H Ideal for the wireless infrastructure and WiMax markets, the family of GaAs pHEMT LNAs from RFMD (Greensboro, NC) operates from 700 to 3,800 MHz in a QFN package. Features include a noise figure of 0.7 dB, an intercept point of 36.0 dB, and a single supply voltage of 3.0 to 6.0 V. Mimix Broadband (Houston, TX) will demo the XM1001-QH image reject mixer that operates over 10.0 to 34.0 GHz. Suited for millimeterwave point-to-point radio, LMDS, satellite communications, and VSAT applications, this device features 6.0-dB conversion loss and an image rejection of 20.0 dB across the band. The part is availSemiconductors able in a low-cost 4 x 4-mm QFN National Instruments (Austin, TX) will show 11 Mimix Broadband’s XM1001QH image reject mixer package that is RoHS compliant. PXI RF switches, which include 4 x 1, terminated 4 Tyco Electronics (Lowell, MA) x 1, dual 4 x 1 and 8 x 1 multiplexers as well as quad will announce the M/A-COM MAPRST1030SPDT and dual-terminated SPDT general-purpose 1KS, a 1,000-W-peak Class C bipolar tranconfigurations. The six 2.5-GHz 75-Ω modules sistor designed for 1,030-MHz pulsed aviare suited for high-frequency video applicaonics applications. The transistor is ideally tions, such as set-top box testing. The other five suited to operate in IFF/TACAN (tactical air 2.7-GHz 50-Ω modules are ideal for expanding navigation system) or similar short pulse the channel count of RF generators, such as the NI formats and features a minimum gain of 8.0 PXI-5671 2.7 GHz vector signal generator, or RF dB with 45% minimum collector efficiency analyzers such as the NI PXI-5661 2.7 GHz vector Tyco Electronics 1,000-W peak bipolar transistor on a 50-Vdc supply. The part is housed in a signal analyzer. ELECTRONIC PRODUCTS http://electronicproducts.com JUNE 2007 26
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