The irritating drone of an aircraft engine could be banished from the cabin forever with a new invention which reduces low-frequency sounds. Scientists at North Carolina State University and the Massachusetts Institute of Technology have discovered that insulating the fuselage with a thin membrane can cancel out much of the noise.
Most aircrafts have a honeycomb like structure in their wings which makes them strong and light for fuel efficiency. But these honeycomb structure are very bad at blocking low-frequency noise, such as the roar of a jet engine. Adding insulation materials to limit the noise would add significant weight to the aircraft, making it use more fuel. So engineers developed a thin, light weight membrane that covers one side of the honeycomb structure, like the skin of a drum. When soundwaves hit the membrane, they bounce off rather than passing through.
Professor Yun Jin, who lead the research, said: "This design is promising for making structures that are strong, lightweight, and sound-proof. "It's particularly effective against low-frequency noise. 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 millimetres thick and adds just six percent to the overall weight of the honeycomb panel. Co-author Ni Sui said: "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." The research is published in the science journal Applied Physics Letters.