MSGID: 1:317/3 6476cd81   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Source-shifting metastructures composed of only one resin for location   
   camouflaging    
    Novel numerical optimization methodology paves the way for acoustic   
   camouflaging in the form of sound source-shifters    
      
     Date:   
         May 30, 2023   
     Source:   
         Shinshu University   
     Summary:   
         Acoustic source-shifters make observers mis-perceive the   
         location of sound by reproducing a sound emanating from   
         a location different from the actual location of a sound   
         source. Researchers have now developed a design approach to produce   
         high-performance source-shifters using a common polymer for location   
         camouflage. Utilizing inverse design based on topology optimization,   
         this development could pave the way for advanced augmented reality   
         and holography technology.   
      
      
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   FULL STORY   
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   The field of transformation optics has flourished over the past decade,   
   allowing scientists to design metamaterial-based structures that   
   shape and guide the flow of light. One of the most dazzling inventions   
   potentially unlocked by transformation optics is the invisibility cloak   
   -- a theoretical fabric that bends incoming light away from the wearer,   
   rendering them invisible. Interestingly, such illusions are not restricted   
   to the manipulations of light alone.   
      
   Many of the techniques used in transformation optics have been applied   
   to sound waves, giving rise to the parallel field of transformation   
   acoustics. In fact, researchers have already made substantial progress by   
   developing the "acoustic cloak," the analog of the invisibility cloak for   
   sounds. While research on acoustic illusion has focused on the concept   
   of masking the presence of an object, not much progress has been made   
   on the problem of location camouflaging.   
      
   The concept of an acoustic source-shifter utilizes a structure   
   that makes the location of the sound source appear different from   
   its actual location. Such devices capable of "acoustic location   
   camouflaging" could find applications in advanced holography and virtual   
   reality. Unfortunately, the nature of location camouflaging has been   
   scarcely studied, and the development of accessible materials and surfaces   
   that would provide a decent performance has proven challenging.   
      
   Against this backdrop, Professor Garuda Fujii, affiliated with the   
   Institute of Engineering and Energy Landscape Architectonics Brain   
   Bank (ELab2) at Shinshu University, Japan, has now made progress in   
   developing high-performance source- shifters. In a recent study published   
   in theJournal of Sound and Vibration online on May 5, 2023, Prof. Fujii   
   presented an innovative approach to designing source-shifter structures   
   out of acrylonitrile butadiene styrene (ABS), an elastic polymer commonly   
   used in 3D printing.   
      
   Prof. Fujii's approach is centered around a core concept: inverse design   
   based on topology optimization. The numerical approach builds on the   
   reproduction of pressure fields (sound) emitted by a virtual source, i.e.,   
   the source that nearby listeners would mistakenly perceive as real. Next,   
   the pressure fields emitted by the actual source are manipulated to   
   camouflage the location and make it sound as if coming from a different   
   location in space. This can be achieved with the optimum design of a   
   metastructure that, by the virtue of its geometry and elastic properties,   
   minimizes the difference between the pressure fields emitted from the   
   actual and virtual sources.   
      
   Utilizing this approach, Prof. Fujii implemented an iterative algorithm   
   to numerically determine the optimal design of ABS resin source-shifters   
   according to various design criteria. His models and simulations had to   
   account for the acoustic-elastic interactions between fluids (air) and   
   solid elastic structures, as well as the actual limitations of modern   
   manufacturing technology.   
      
   The simulation results revealed that the optimized structures could   
   reduce the difference between the emitted pressure fields of the masked   
   source and those of a bare source at the virtual location to as low   
   as 0.6%. "The optimal structure configurations obtained via topology   
   optimization exhibited good performances at camouflaging the actual   
   source location despite the simple composition of ABS that did not   
   comprise complex acoustic metamaterials", remarks Prof. Fujii.   
      
   To shed more light on the underlying camouflaging mechanisms, Prof. Fujii   
   analyzed the importance of the distance between the virtual and actual   
   sources.   
      
   He found that a greater distance did not necessarily degrade the source-   
   shifter's performance. He also investigated the effect of changing the   
   frequency of the emitted sound on the performance as the source-shifters   
   had been optimized for only one target frequency. Finally, he explored   
   whether a source-shifter could be topologically optimized to operate at   
   multiple sound frequencies.   
      
   While his approach requires further fine-tuning, the findings of this   
   study will surely help advance illusion acoustics. He concludes,   
   "The proposed optimization method for designing high-performance   
   source-shifters will help in the development of acoustic location   
   camouflage and the advancement of holography technology."   
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Physics # Acoustics # Energy_Technology # Optics   
             o Computers_&_Math   
                   # Software # Computer_Modeling # Virtual_Reality #   
                   Video_Games   
       * RELATED_TERMS   
             o Acoustics o Sound_effect o Speed_of_sound o Speech_recognition   
             o Virtual_reality o User_interface_design o Periodic_table   
             o Circuit_design   
      
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   Story Source: Materials provided by Shinshu_University. Note: Content   
   may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Garuda Fujii. Camouflaging the location of a sound source via   
      topology-   
         optimized source-shifter. Journal of Sound and Vibration, 2023;   
         559: 117768 DOI: 10.1016/j.jsv.2023.117768   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230530125407.htm   
      
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