MSGID: 1:317/3 64781f28   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Actively reducing noise by ionizing air    
      
     Date:   
         May 31, 2023   
     Source:   
         Ecole Polytechnique Fe'de'rale de Lausanne   
     Summary:   
         Scientists show that a thin layer of plasma, created by ionizing   
         air, could be promising as an active sound absorber, with   
         applications in noise control and room acoustics.   
      
      
         Facebook Twitter Pinterest LinkedIN Email   
      
   ==========================================================================   
   FULL STORY   
   ==========================================================================   
   Did you know that wires can be used to ionize air to make a   
   loudspeaker? Simply put, it's possible to generate sound by creating an   
   electric field in a set of parallel wires, aka a plasma transducer, strong   
   enough to ionize the air particles. The charged ions are then accelerated   
   along the magnetic field lines, pushing the residual non-ionized air in   
   a way to produce sound.   
      
   If a loudspeaker can generate sound, it can also absorb it.   
      
   While this plasma loudspeaker concept is not new, EPFL scientists went   
   ahead and built a demonstration of the plasma transducer, with the aim to   
   study noise reduction. They came up with a new concept, what they call   
   the active "plasmacoustic metalayer" that can be controlled to cancel   
   out noise. Their results are published in Nature Communications.   
      
   The scientists were intrigued by the idea of using plasma to reduce noise,   
   since it gets rid of one of the most important aspects of conventional   
   loudspeakers: the membrane. Loudspeakers equipped with membranes, like   
   the ones in your car or at home, are some of the most studied solution   
   for active noise reduction. It's active because the membrane can be   
   controlled to cancel out different sounds, as opposed to a wall that   
   does the job passively.   
      
   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.   
      
   "We wanted to reduce the effect of the membrane as much as possible, since   
   it's heavy. But what can be as light as air? The air itself,"explains   
   Stanislav Sergeev, postdoc at EPFL's Acoustic Group and first author. "We   
   first ionize the thin layer of air between the electrodes that we call a   
   plasmacoustic metalayer. The same air particles, now electrically charged,   
   can instantaneously respond to external electrical field commands and   
   effectively interact with sound vibrations in the air around the device   
   to cancel them out."  Sergeev continues, "As expected, the communication   
   between the electrical control system of the plasma and the acoustic   
   environment is much faster than with a membrane."  Not only is the   
   plasma efficient at high frequencies, but it is also versatile since it   
   can be tuned to work at low frequencies as well. Indeed, the scientists   
   show that the dynamics of thin layers of air plasma can be controlled   
   to interact with sound over deep-subwavelength distances, to actively   
   respond to noise and cancel it out over a broad bandwidth. The fact that   
   their device is active is key, since passive noise reduction technologies   
   are limited in the band of frequencies that can be controlled.   
      
   The plasma absorber is also more compact that most conventional solutions.   
      
   Exploiting the unique physics of plasmacoustic metalayers, the scientists   
   experimentally demonstrate perfect sound absorption: "100% of the   
   incoming sound intensity is absorbed by the metalayer and nothing is   
   reflected back," says EPFL's Acoustic Group's senior scientist Herve'   
   Lissek. They also show tunable acoustic reflection from several Hz to   
   the kHz range, with transparent plasma layers of thicknesses down to   
   only a thousandth of a given wavelength, much smaller than conventional   
   noise reduction solutions.   
      
   To give an idea of how much more compact the plasma absorber is, consider   
   a low, audible sound frequency of 20 Hz, where the sonic wavelength is   
   17m meters long. The plasma layer would only need to be 17 mm thick to   
   absorb the noise, whereas most conventional noise reduction solutions,   
   like absorbing walls, would need to be at least 4 m thick which often   
   limits its feasibility.   
      
   "The most fantastic aspect in this concept is that, unlike conventional   
   sound absorbers relying on porous bulk materials or resonant structures,   
   our concept is somehow ethereal. We have unveiled a completely new   
   mechanism of sound absorption, that can be made as thin and light as   
   possible, opening new frontiers in terms of noise control where space   
   and weight matter, especially at low frequencies" says Herve' Lissek.   
      
   EPFL has partnered with Sonexos SA, a Swiss-based audio technology   
   company, to develop cutting-edge active sound absorbers that use the   
   plasmacoustic metalayer concept. Together, they aim to provide novel and   
   efficient solutions for reducing noise in a wide range of applications,   
   including the automotive, consumer, commercial, and industrial sectors.   
      
   "This strategic collaboration leverages EPFL's expertise in material   
   science and acoustics, as well as Sonexos' proven track record in   
   delivering high- performance audio solutions," explains Mark Donaldson,   
   CEO and Founder of Sonexos.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Acoustics # Physics # Aerospace # Chemistry # Aviation #   
                   Fuel_Cells # Energy_and_Resources # Transportation_Science   
       * RELATED_TERMS   
             o Acoustics o Speed_of_sound o Sound_effect o Altimeter o   
             Hafnium o Geologic_fault o Soap_bubble o Air_conditioning   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Ecole_Polytechnique_Fe'de'rale_de_Lausanne. Original written by Hillary   
   Sanctuary. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Stanislav Sergeev, Romain Fleury, Herve' Lissek. Ultrabroadband   
      sound   
         control with deep-subwavelength plasmacoustic metalayers. Nature   
         Communications, 2023; 14 (1) DOI: 10.1038/s41467-023-38522-5   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230531102009.htm   
      
   --- up 1 year, 13 weeks, 2 days, 10 hours, 50 minutes   
    * Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)   
   SEEN-BY: 15/0 106/201 114/705 123/120 153/7715 218/700 226/30 227/114   
   SEEN-BY: 229/110 112 113 307 317 400 426 428 470 664 700 291/111 292/854   
   SEEN-BY: 298/25 305/3 317/3 320/219 396/45   
   PATH: 317/3 229/426