Last time, while looking for some ideas for my noise-cancelling speaker project, I read an article on EPFL’s website (Swiss Federal Institute of Technology in Lausanne) about plasma-made speakers able to reduce noise.
On paper, it’s an already well-known yet unused concept, but in practice, it’s a true invention that could be a game-changer in some fields. Indeed, Sergeev S., Fleury R., and Lissek H., the three researchers behind this project, are using what they describe as a “plasmacoustic metalayer.”
Now, before diving into the project, we could ask ourselves an obvious question: what’s the deal with classic speakers? Well, here’s the answer given in the article: “The problem with using the conventional loudspeaker as a sound absorber is that its membrane limits the frequency range of operation. For sound absorption, the membrane behaves mechanically, vibrating to cancel out the sound waves in the air. The fact that the membrane is relatively heavy, i.e., the inertia of the membrane, limits its ability to interact efficiently with fast-changing sounds or at high frequencies.”
From this perspective, it is not really shocking that they used plasma. Indeed, if the membrane is heavy and if that’s the real problem, then why wouldn’t they use just air, right? The way it works is not really that hard because making plasma is something that we already know how to deal with: first, they ionize the thin layer of air between the electrodes, which is called the plasmacoustic metalayer. Then these air particles can respond to external electric fields on command, which means that they can interact with sound vibrations in the air. They are basically being accelerated and then stopped many times depending on the voltage that is applied; this creates compression in the air, which is more commonly called sound. One funny thing about this is that it also produces a little bit of wind :).
It makes the speaker able to have a large range from low to very high frequencies that is very easily dimmable because it is versatile.
Moreover, they have shown amazing performance of 100% noise cancellation with this active technology: “100% of the incoming sound intensity is absorbed by the metalayer, and nothing is reflected back.” Finally, you can hear in the video how the sound is really well directed and there’s little propagation around the speaker… This is, to me, the best part of all because it means we can direct what we want to hear AND what we don’t want. Picture this: a speaker on maximum volume in your living room with your family, but you are the only one hearing it.
Not gonna lie, I might try to replicate this at home because I believe it could be used in my noise-cancelling project in order to have perfectly straight destructive sound waves.
Credits:
https://actu.epfl.ch/news/actively-reducing-noise-by-ionizing-air-2/
https://www.youtube.com/watch?v=-7Eemh63NcA