In modern airliners, much of the structural paneling used in the cabin and wings has a honeycomb-like structure. Although this helps keep the weight down while maintaining strength, it does a poor job at blocking noise within the aircraft. That's why researchers from North Carolina State University and MIT have developed a membrane that helps the panels to do so.
The membrane is made from rubber that's just a quarter of a millimeter thick, and that's adhered to one side of a piece of the honeycomb paneling. Once in place, it acts sort of like the skin on a drum, causing incoming sound waves to bounce back off of it instead proceeding through into the cabin.
It's particularly good at blocking low-frequency sounds, such as those made by aircraft engines. In lab tests, a panel covered with the membrane reportedly blocked 100 to 1,000 times more sound energy than one without.
It does increase the weight of the panel by about six percent, although that's still significantly less than the amount that would be added if a more traditional sound-damping insulation was used.
According to the researchers, the membrane is relatively inexpensive to produce, and could be made from any material that doesn't adversely affect the structural integrity of the panel.
A paper on the research was recently published in the journal Applied Physics Letters.
Source: North Carolina State University
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