A group of acoustic engineers at Boston University has created an interesting metamaterial that can make jet engines quiet or absorb up to 94% of the noise in air flows from many other sources of acoustic noise. This could be noise from air conditioners or heat guns. The noise from the rotating blades of drones or sounds from a busy highway and much more.
The most interesting thing is that there is nothing complicated in making a promising muffler. To experiment with muting the sound from a speaker, for example, engineers printed a sound-absorbing nozzle on a regular 3D printer. The nozzle is a ring with a spiral edging along the edge. The muffler can be of any shape. For a sound-absorbing wall along a highway, for example, it can be a hexagon, the wall of which can be easily and reliably laid on a concrete mortar.
The main feature of the development is that air passes through it freely, but the sound is sent back to the source. If such mufflers are placed below the drone's blades, they will not interfere with the creation of lift, while the noise from the rotating propellers will be directed in the opposite direction from the ears of observers. In the laboratory, the pilot plant showed high efficiency in noise absorption. This allowed us to assume that the discovery has unlimited prospects in all spheres of human activity and life.
A report on the discovery was published in the January 2019 issue of Physical Review. Reza Ghaffarivardawag (pictured in the center), Stefan Anderson (left), Xin Zang (above center) and Jacob Nikolaychuk (right) took part in the creation of the development.
Source: 3dnews.ru
