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Composite acoustic attenuation and vibration damping materials

The Naval Aerospace Medical Research Laboratory (NAMRL) partnered with ElastoCall Services to develop and patent a new composite technology that provides a lightweight, inexpensive means of stopping low-frequency (below 125 Hz) noise such as that from roads, motors and generators, stereo bass, and aircraft. The technology works by improving the low-frequency sound-blocking characteristics of a variety of materials such as epoxies, resins, silicon gels, polyurethane foams, plastics, and silicon- and carbon-based rubbers with which it is combined. Applications of this technology are particularly important in reducing noise in marine vessels, homes that may be located near an airport or industrial plant, aircraft cockpits, and aircraft carrier flight decks. The technology has equally important application for the Joint Strike Fighter (JSF) rotary wing environment, where low-frequency, high-energy noise is a significant problem. Existing sound-absorptive materials are generally good barriers for acoustical noise above 500 Hz, but poor at lower frequencies. The new technology takes advantage of the fact that acoustical energy (noise) is inefficiently transferred between media differing in characteristic acoustical impedances, thus significantly increasing their sound-damping capability. The sound-absorptive materials dampen low-frequency sound while adding only marginally to the weight characteristics of the base material. Unlike the vast majority of sound-attenuating materials, doubling the thickness or weight of the product doubles its sound-attenuating properties. Another advantage is that components can be manufactured in a variety of ways, including casting, spraying, extrusion, and molding processes. In 1995, the original patented technology was transferred via a Cooperative Research and Development Agreement (CRADA) from NAMRL to Moldex Rubber Company, which subsequently applied for a nonexclusive license and developed the technology for the automotive industry. In 2000, ElastoCall Services, Inc. was also granted a nonexclusive license to the original patent and entered into a CRADA with NAMRL. It was under this CRADA that the matrix material was combined with a second layer of a decoupling material that serves to effectively isolate the matrix material and reduce its tendency to vibrate. For this invention, a second patent was issued and an exclusive license to ElastoCall resulted in 2007. ElastoCall incorporated the composite technology into its marine product line and, with NAMRL, has made large surface area sheets of the material, which has a well-defined potential in the marketplace for use under carpet mats, in headliners for cars, and for sound barriers for highways. Structural materials that dampen sound and vibration have an enormous application in the manufacturing of anything using an advanced composite. Products being sold using this technology will broadly benefit military and civilian areas, including automotive, marine, industrial, and aircraft markets.
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Southeast