Ssshhhh...Noise Free Environment

Engineers of Washington, USA, recently are turning to innovative approach to hush aircraft noise and reduce environmental problems for communities near airports.

In this approach, tiny parallel tubes in porous media such as metasl or ceramics create a honeycomb-like structure that traps sound regardless of frequency. Instead of resonating, sound waves plunge into channels and dissipate through a process called viscous shear.

Viscous shear involves the interaction of a solid with a gas or other fluid. In this case, a gas - sound waves composed of compressed air. This contacts a solid, the porous medium, and is weakened by the resulting friction.

Creating such low-density structures presents an interesting challenge. It requires a material that's light, strong enough to enable the walls between the tubes to be very thin, and yet robust enough to function reliably amid the high-temperature, aggressive environments inside aircraft engines.