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 ==========================================================================
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

========================================================================== Story Source: Materials provided by Shinshu_University. Note: Content
may be edited for style and length.


========================================================================== 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 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230530125407.htm

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