Boeing's Phantom Works is planning tests of a soundproofing "wallpaper" that uses compressed air to suppress low-frequency noise made by aircraft engines, rockets and propellors.

Potential applications for the fluidic material, which is being developed with Rockville, Maryland-based Defense Research Technologies, include wall trim in airliners and military aircraft to reduce cabin noise, rocket-noise protection for satellites, and detection prevention for sound-emitting military equipment.

The 6mm (0.25in) thick wallpaper comprises a honeycomb of air chambers linked by millions of tiny holes. Compressed air flows through the honeycomb and into the space (cabin or other compartment) to be acoustically insulated. When sound waves strike the wallpaper's surface, the air already in the system is forced through the holes and chambers.

The delay induced by the air having to negotiate this extensive network allows the wallpaper to "hold its breath", according to Boeing Phantom Works technical fellow Anders Andersson. The air is then released as normal into the external environment, no longer transmitting the original sound wave.

Andersson says the "signal sensing, actuating and processing is performed in the fluidic domain", and that no ancillary electronic or mechanical control is required. The compressed air could be generated by aircraft engines or air conditioning.

Boeing says the wallpaper "promises to be inexpensive and very lightweight compared to many other sound-treatment measures". Andersson predicts good performance in insulating against noise frequencies up to 1,200Hz, and, if the 3mm size of the chambers within the paper can be halved, frequencies up to 4,800Hz could be blocked, he says.

Source: Flight International