Researchers have developed a membrane that can be incorporated in an aircraft fuselage dramatically to reduce low-frequency cabin noise – like the noise of the engine.
“This design is promising for making structures that are strong, lightweight, and sound-proof,” says Yun Jing, an assistant professor of mechanical and aerospace engineering at North Carolina State University and senior author of a paper describing the work that was carried out in conjunction with MIT.
Aircraft designs incorporate light materials with a honeycomb-like structure into their wings and cabins. It’s the material that makes up the floor and ceiling of most airplane cabins. It is strong but not very good at blocking engine noise.
The new thin, lightweight membrane covers one side of the honeycomb structure, like the skin of a drum and when sound waves hit it, they bounce off rather than pass through.
“It’s particularly effective against low-frequency noise,” Jing says. “At low frequencies – sounds below 500 Hertz – the honeycomb panel with the membrane blocks 100 to 1,000 times more sound energy than the panel without a membrane.”
The membrane is made of rubber that is about 0.25 millimeters thick, and adds approximately 6% to the overall weight of the honeycomb panel.
“The membrane is relatively inexpensive to produce, and can be made of any material that does not impact the structural integrity of the honeycomb panel,” says Ni Sui, a PhD student in Jing’s lab and lead author of the paper. “It could make flying much more pleasant for passengers -particularly in helicopters.”