{"70836":{"#nid":"70836","#data":{"type":"news","title":"New Generator Produces AC Current by Stretching Zinc Oxide Wires","body":[{"value":"\u003Cp\u003EResearchers have developed a new type of small-scale electric power generator able to produce alternating current through the cyclical stretching and releasing of zinc oxide wires encapsulated in a flexible plastic substrate with two ends bonded.  \u003C\/p\u003E\n\u003Cp\u003EThe new \u0027flexible charge pump\u0027 generator is the fourth generation of devices designed to produce electrical current by using the piezoelectric properties of zinc oxide structures to harvest mechanical energy from the environment.  Its development was reported November 9, 2008 in the advance online publication of the journal \u003Cem\u003ENature Nanotechnology\u003C\/em\u003E.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The flexible charge pump offers yet another option for converting mechanical energy into electrical energy,\u0022 said Zhong Lin Wang, Regent\u0027s professor in the School of Materials Science and Engineering and director of the Center for Nanostructure Characterization at the Georgia Institute of Technology.  \u0022This adds to our family of very small-scale generators able to power devices used in medical sensing, environmental monitoring, defense technology and personal electronics.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe new generator can produce an oscillating output voltage of up to 45 millivolts, converting nearly seven percent of the mechanical energy applied directly to the zinc oxide wires into electricity.  The research has been supported by the U.S. Department of Energy, the National Science Foundation, the Air Force Office of Scientific Research and the Emory-Georgia Tech Center for Cancer Nanotechnology Excellence.\n\u003C\/p\u003E\n\u003Cp\u003EEarlier nanowire nanogenerators and microfiber nanogenerators developed by Wang and his research team depended on intermittent contact between vertically-grown zinc oxide nanowires and an electrode, or the mechanical scrubbing of nanowire-covered fibers.  These devices were difficult to construct, and the mechanical contact required caused wear that limited how long they could operate.  And because zinc oxide is soluble in water, they had to be protected from moisture.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Our new flexible charge pump resolves several key issues with our previous generators,\u0022 Wang said.  \u0022The new design would be more robust, eliminating the problem of moisture infiltration and the wearing of the structures.  From a practical standpoint, this would be a major advantage.\u0022\n\u003C\/p\u003E\n\u003Cp\u003ETo boost the current produced, arrays of the flexible charge pumps could be constructed and connected in series.  Multiple layers of the generators could also be built up, forming modules that could then be embedded into clothing, flags, building decorations, shoes - or even implanted in the body to power blood pressure or other sensors.\n\u003C\/p\u003E\n\u003Cp\u003EWhen the modules are mechanically stretched and then released, because of the piezoelectric properties, the zinc oxide material generates a piezoelectric potential that alternately builds up and then is released.  A Schottky barrier controls the alternating flow of electrons, and the piezoelectric potential is the driving force of the charge pump.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The electrons flow in and out, just like AC current,\u0022 Wang explained.  \u0022The alternating flow of electrons is the power output process.\u0022  \n\u003C\/p\u003E\n\u003Cp\u003EConstructed with zinc oxide piezoelectric fine wires with diameters of three to five microns and lengths of 200 to 300 microns, the new generator no longer depends on nanometer-scale structures. The larger size was chosen for easier fabrication, but Wang said the principles could be scaled down to the nanometer scale. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022Nanoscale materials are not required for this to work,\u0022 he said.  \u0022Larger fibers work better and are easier to work with to fabricate devices.  But the same principle would apply at the nanometer scale.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe wires are grown using a physical vapor deposition method at approximately 600 degrees Celsius.  Using an optical microscope, the wires are then bonded onto a polyimide film and silver paste applied at both ends to serve as electrodes.  The wires and electrodes were then encased in polyimide to protect them from wear and environmental degradation.\n\u003C\/p\u003E\n\u003Cp\u003ETo measure the electric energy generated, the researchers subjected the substrate and attached zinc oxide wires to periodic mechanical bending created by a motor-driven mechanical arm.  The bending induced tensile strain which created a piezoelectric potential field along the laterally-packaged wires.  That, in turn, drove a flow of electrons into an external circuit, creating the alternating charge and discharge cycle - and corresponding current flow.  \n\u003C\/p\u003E\n\u003Cp\u003EIncreasing the strain rate increased the magnitude of the output electricity, both in voltage and current.  Wang believes the frequency of the current is limited only by the mechanical properties of the polyimide substrate.\n\u003C\/p\u003E\n\u003Cp\u003EThe researchers conducted a number of tests to verify that the current measured was produced by the generator - and not an external measurement artifact.  Using the same experimental setup, they stretched carbon fibers and Kevlar fibers coated with polycrystalline zinc oxide, and did not observe current flow.  The research team also developed two criteria and eight tests for ruling out experimental artifacts, Wang noted.\n\u003C\/p\u003E\n\u003Cp\u003EIn addition to Wang, the research team included Rusen Yang and Yong Qin from Georgia Tech and Liming Dai of the Department of Chemical and Materials Engineering at the University of Dayton.\n\u003C\/p\u003E\n\u003Cp\u003EFor the future, Wang sees the family of small-scale generators enabling development of a new class self-powered wireless sensing systems.  The devices could gather information, store it and transmit the data - all without an external power source.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Self-powered nanotechnology could be the basis for a new industry,\u0022 he said.  \u0022That\u0027s really the only way to build independent systems.\u0022\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) or Abby Vogel (404-385-3364); E-mail: (\u003Ca href=\u0022mailto:avogel@gatech.edu\u0022\u003Eavogel@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETechnical Contact\u003C\/strong\u003E: Zhong Lin Wang (404-894-8008); E-mail: (\u003Ca href=\u0022mailto:zhong.wang@mse.gatech.edu\u0022\u003Ezhong.wang@mse.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"Flexible charge pump offers another means of producing electricity"}],"field_summary":[{"value":"Researchers have developed a new type of small-scale electric power generator able to produce alternating current through the cyclical stretching and releasing of zinc oxide wires encapsulated in a flexible plastic substrate with two ends bonded.","format":"limited_html"}],"field_summary_sentence":[{"value":"A new small-scale generator produces current by stretching wires"}],"uid":"27303","created_gmt":"2008-11-09 01:00:00","changed_gmt":"2016-10-08 03:03:19","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2008-11-09T00:00:00-05:00","iso_date":"2008-11-09T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"70837":{"id":"70837","type":"image","title":"Zhong Lin Wang","body":null,"created":"1449177314","gmt_created":"2015-12-03 21:15:14","changed":"1475894623","gmt_changed":"2016-10-08 02:43:43"},"70838":{"id":"70838","type":"image","title":"Flexible Charge Pump","body":null,"created":"1449177314","gmt_created":"2015-12-03 21:15:14","changed":"1475894623","gmt_changed":"2016-10-08 02:43:43"},"70839":{"id":"70839","type":"image","title":"Flexible charge pump","body":null,"created":"1449177314","gmt_created":"2015-12-03 21:15:14","changed":"1475894623","gmt_changed":"2016-10-08 02:43:43"}},"media_ids":["70837","70838","70839"],"related_links":[{"url":"http:\/\/www.mse.gatech.edu\/","title":"Georgia Tech School of Materials Science and Engineering"},{"url":"http:\/\/www.mse.gatech.edu\/FacultyStaff\/MSE_Faculty_researchbios\/Wang\/wang.html","title":"Zhong Lin Wang"},{"url":"http:\/\/cncf.nanoscience.gatech.edu\/","title":"Center for Nanostructure Characterization"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"144","name":"Energy"},{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"3265","name":"charge"},{"id":"436","name":"electricity"},{"id":"6300","name":"generator"},{"id":"3520","name":"pump"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EJohn Toon\u003C\/strong\u003E\u003Cbr \/\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=jt7\u0022\u003EContact John Toon\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-894-6986\u003C\/strong\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}