Airplanes are often synonymous with noise. A new membrane that can be incorporated in to aircraft could change that notion by drastically reducing the low-frequency noise that dominates planes and helicopters.
“This design is promising for making structures that are strong, lightweight, and sound-proof,” said Yun Jing, a North Carolina (NC) State University assistant professor of mechanical and aerospace engineering.
Honeycomb-like structure
Most airplanes boast a lightweight, honeycomb-like structure in their cabins and wings. It may pass unnoticed by passengers, but the material actually makes up the bulk of a plane’s floor and ceiling. The sandwiched honeycomb structure gives the cabin strength while maintaining a light weight, which is important for fuel efficiency.
However, the structure also has a disadvantage: it is incapable of blocking low-frequency noise, such as an aircraft’s engine. Adding insulation materials would potentially limit noise levels, but it would also add weight and reduce the aircraft’s fuel efficiency.
New technology developed by NC State researchers could solve this problem. Their thin, lightweight membrane behaves similar to drum skin; It would cover one side of the honeycomb structure and block soundwaves by bouncing them off as opposed to letting them in.
Blocks 100 to 1,000 times more sound
“It’s particularly effective against low-frequency noise,” Jing explained. “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 consists of rubber approximately 0.25 millimeters thick, which makes the honeycomb structure six percent heavier. It would not significantly impact an aircraft’s weight.
“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,” said Ph.D. student Ni Sui. “It could make flying much more pleasant for passengers –particularly in helicopters.”