Before the news covered by this post it is necessary to take a step back, or rather two. The first: last May, the researchers of the US Naval Research Laboratory in Washington revealed that a special method can create extremely efficient acoustic metamaterials.
What are acoustic metamaterials? They are advanced materials that block the passage of sound waves only with their shape. There is no need for anything else, no expensive methods or electronic devices. The question is: do they also block the passage of air? The answer is no. In March 2019, for example, researchers from Boston University, Xin Zhang e Reza Ghaffarivardavagh, presented in a paper an acoustic metamaterial capable of effectively eliminating sounds while maintaining the flow of air. Good, but thick panels like heavy walls were needed.
This new method makes it possible to use acoustic metamaterials almost anywhere. Especially in situations where thick, heavy walls cannot be used (think jet exhausts). We're talking about planes where pilots have to put earplugs on if they don't want to lose their hearing.
Now Zhang and Ghaffarivardavagh have perfected the method by inventing acoustic materials that could allow a jet engine's airflow to pass, but block the sound. Silent jets like the rustle of leaves.
How Super Quiet Acoustic Metamaterials Were Obtained
In the very first tests, the researchers used the 3d printing to materialize an open plastic structure and tested it with a loudspeaker. A triumph: loudspeaker on maximum and no noise. Perfectly successful experiment and scientists in seventh heaven. Take a look, or rather have a look at this video. Basically the "MUTE" button in real life.
We've seen this kind of results in our computer modeling for months, but it's one thing to see the sound pressure levels modeled on a computer, and it's quite another to hear the impact for yourself.Jacob Nikolajczyk, co-author of the study and former university researcher in Zhang's lab
Further testing by the team indicated that these metamaterials they can block 94% of the noise from anything. From airplanes to buildings, a quieter era is looming on the horizon. Peace for the ears (but who knows if it is a good military point).
The study is published in Physical Review B.