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 air flow. Good, but thick panels like heavy walls were needed.
This new method allows acoustic metamaterials to be used practically anywhere. Especially in situations where thick, heavy walls cannot be used (think jet exhaust). We're talking about planes in which pilots have to wear earplugs if they don't want to lose their hearing.
Now Zhang and Ghaffarivardavagh have refined the method by inventing acoustic materials that could allow a jet engine's airflow to pass through, but block the sound. Silent jets like the rustle of leaves. To the point that to hear them, I have to invent new noises by myself.
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 speaker. A triumph: speaker at maximum and no noise. Perfectly successful experiment and scientists over the moon. Take a look, or rather a listen to this video. Basically the “MUTE” button in real life.
We've been seeing these kinds of results in our computer modeling for months, but it's one thing to see sound pressure levels modeled on a computer, and another to feel the impact for yourselfJacob 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 construction, a quieter era is on the horizon. Peace of mind (but who knows if it's a good thing on a military level).
The study is published in Physical Review B.