{"70931":{"#nid":"70931","#data":{"type":"news","title":"Micro Honeycomb Materials Enable New Approach to Sound Reduction","body":[{"value":"\u003Cp\u003ENoise from commercial and military jet aircraft causes environmental problems for communities near airports, obliging airplanes to follow often complex noise-abatement procedures on takeoff and landing. It can also make aircraft interiors excessively loud.\n\u003C\/p\u003E\n\u003Cp\u003ETo address this situation, engineers at the Georgia Tech Research Institute (GTRI) are turning to innovative materials that make possible a new approach to the physics of noise reduction.  They have found that honeycomb-like structures composed of many tiny tubes or channels can reduce sound more effectively than conventional methods.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This approach dissipates acoustic waves by essentially wearing them out,\u0022 said Jason Nadler, a GTRI research engineer.  \u0022It\u0027s a phenomenological shift, fundamentally different from traditional techniques that absorb sound using a more frequency-dependent resonance.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe two-year project is sponsored by EADS North America, the U.S. operating entity of EADS.\n\u003C\/p\u003E\n\u003Cp\u003EMost sound-deadening materials - such as foams or other cellular materials comprising many small cavities - exploit the fact that acoustic waves resonate through the air on various frequencies, Nadler explains.  \n\u003C\/p\u003E\n\u003Cp\u003EJust as air blowing into a bottle produces resonance at a particular tone, an acoustic wave hitting a cellular surface will resonate in certain-size cavities, thereby dissipating its energy. An automobile muffler, for example, uses a resonance-dependent technique to reduce exhaust noise.\n\u003C\/p\u003E\n\u003Cp\u003EThe drawback with these traditional noise-reduction approaches is that they only work with some frequencies - those that can find cavities or other structures in which to resonate. \n\u003C\/p\u003E\n\u003Cp\u003ENadler\u0027s research involves broadband acoustic absorption, a method of reducing sound that doesn\u0027t depend on frequencies or resonance.  In this approach, tiny parallel tubes in porous media such as metal or ceramics create a honeycomb-like structure that traps sound regardless of frequency.  Instead of resonating, sound waves plunge into the channels and dissipate through a process called viscous shear. \n\u003C\/p\u003E\n\u003Cp\u003EViscous shear involves the interaction of a solid with a gas or other fluid.   In this case, a gas - sound waves composed of compressed air - contacts a solid, the porous medium, and is weakened by the resulting friction.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022It\u0027s the equivalent of propelling a little metal sphere down a rubber hose when the sphere is just a hair bigger than the rubber hose,\u0022 Nadler explained.  \u0022Eventually the friction and the compressive stresses of contact with the tube would stop the sphere.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThis technique, Nadler adds, is derived from classical mechanical principles governing how porous media interact with gases - such as the air through which sound waves move.  Noise abatement using micro-scale honeycomb structures represents a new application of these principles.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022You need to have the hole big enough to let the sound waves in, but you also need enough surface area inside to shear against the wave,\u0022 he said.   \u0022The result is acoustic waves don\u0027t resonate; they just dissipate.\u0022 \n\u003C\/p\u003E\n\u003Cp\u003EIn researching this approach, Nadler constructed an early prototype from off-the-shelf capillary tubes, which readily formed a low-density, honeycomb-like structure.  Further research showed that the ideal material for broadband acoustic absorption would require micron-scale diameter tubes and a much lower structural density. \n\u003C\/p\u003E\n\u003Cp\u003ECreating such low-density structures presents an interesting challenge, Nadler says.  It requires a material that\u0027s light, strong enough to enable the walls between the tubes to be very thin, and yet robust enough to function reliably amid the high-temperature, aggressive environments inside aircraft engines.  \n\u003C\/p\u003E\n\u003Cp\u003EAmong the likely candidates are superalloys, materials that employ unusual blends of metals to achieve desired qualities such as extreme strength, tolerance of high temperatures and corrosion resistance.\n\u003C\/p\u003E\n\u003Cp\u003ENadler has developed what could be the world\u0027s first superalloy micro honeycomb using a nickel-base superalloy. At around 30 percent density, the material is very light - a clear advantage for airborne applications - and also very strong and heat resistant.\n\u003C\/p\u003E\n\u003Cp\u003EHe estimates this new approach could attenuate aircraft engine noise by up to 30 percent.  Micro-honeycomb material could also provide another means to protect the aircraft in critical areas prone to impact from birds or other foreign objects by dissipating the energy of the collision.\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); Kirk Englehardt (404-407-7280); E-mail: (\u003Ca href=\u0022mailto:kirk.englehardt@gtri.gatech.edu\u0022\u003Ekirk.englehardt@gtri.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: Jason Nadler (404-407-6104); E-mail (\u003Ca href=\u0022mailto:jason.nadler@gtri.gatech.edu\u0022\u003Ejason.nadler@gtri.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: Rick Robinson\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"Innovation could help quiet military and commercial aircraft"}],"field_summary":[{"value":"Researchers at the Georgia Tech Research Institute (GTRI) are developing innovative honeycomb structures that could make possible a new approach to noise reduction in aircraft.","format":"limited_html"}],"field_summary_sentence":[{"value":"A new approach to sound control could help quiet jet aircraft"}],"uid":"27303","created_gmt":"2008-09-29 00:00:00","changed_gmt":"2016-10-08 03:03:19","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2008-09-29T00:00:00-04:00","iso_date":"2008-09-29T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"70932":{"id":"70932","type":"image","title":"Jason Nadler","body":null,"created":"1449177328","gmt_created":"2015-12-03 21:15:28","changed":"1475894625","gmt_changed":"2016-10-08 02:43:45"},"70933":{"id":"70933","type":"image","title":"Jason Nadler","body":null,"created":"1449177328","gmt_created":"2015-12-03 21:15:28","changed":"1475894625","gmt_changed":"2016-10-08 02:43:45"},"70934":{"id":"70934","type":"image","title":"Noise reduction material","body":null,"created":"1449177328","gmt_created":"2015-12-03 21:15:28","changed":"1475894625","gmt_changed":"2016-10-08 02:43:45"}},"media_ids":["70932","70933","70934"],"related_links":[{"url":"http:\/\/www.gtri.gatech.edu\/","title":"Georgia Tech Research Institute"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"136","name":"Aerospace"},{"id":"145","name":"Engineering"},{"id":"147","name":"Military Technology"},{"id":"135","name":"Research"}],"keywords":[{"id":"1833","name":"aircraft"},{"id":"7185","name":"honeycomb"},{"id":"1692","name":"materials"},{"id":"1522","name":"noise"}],"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":""}}}