MSGID: 1:317/3 64af7e18   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Bound states in the continuum is possible in the acoustoelastic coupling   
      
      
     Date:   
         July 12, 2023   
     Source:   
         Pohang University of Science & Technology (POSTECH)   
     Summary:   
         Professor Junsuk Rho's research team at POSTECH reveals a physical   
         phenomenon for vibration focusing and energy storage   
      
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   Let's imagine a hypothetical scenario where two individuals are gripping   
   a rope, each holding one end. Person A proceeds to shake the rope in   
   an up-and- down motion, thus generating a propagating wave that travels   
   towards person B.   
      
   Now, if person C, positioned between person A and B, engages in a   
   comparable frequency of waving motion as that of the rope's wave,   
   could the wave be redirected back to person A rather than reaching   
   person B? Initially, this situation appears implausible, as person   
   C does not physically interact with the rope held by person A and B,   
   seemingly defying the possibility of achieving a 100% wave reflection   
   similar to that observed in a perfect mirror.   
      
   Nonetheless, this phenomenon finds explanation within the domain of   
   physics and is known as the "bound state in the continuum (BIC)."   
   The study of BIC has encompassed diverse disciplines including quantum   
   mechanics, optics, semi-conductors, and nano-optics. Utilizing this   
   phenomenon facilitates the confinement of light particles, or photons,   
   preventing their forward propagation. Moreover, BIC holds promise for   
   the development of highly sensitive sensors. Previous research into BIC   
   has predominantly focused on microscale and nanoscale contexts while   
   investigations using visible structures to explain this phenomenon have   
   been absent.   
      
   Recently, a research team led by Professor Junsuk Rho from the Department   
   of Mechanical Engineering and the Department of Chemical Engineering   
   and PhD candidates Dongwoo Lee, Jeonghoon Park, and Seokwoo Kim from   
   the Department of Mechanical Engineering at Pohang University of Science   
   and Technology (POSTECH) successfully demonstrated bound states in the   
   continuum through the utilization of an acoustoelastic coupling structure   
   for the first time. The research findings have been published in Extreme   
   Mechanics Letters, one of the world's most influential journals in the   
   field of mechanics.   
      
   The research team designed an experiment setup aimed at verifying   
   the existence of the BIC phenomenon through the interplay of sound and   
   elasticity. Commencing with the fabrication of an elastic bar resembling   
   a stick, the team proceeded to induce vibrations in the elastic bar by   
   means of a shaker. Subsequently, air injection at a predetermined location   
   on the elastic bar engendered coupling between sound and elasticity.   
      
   In the experiment, when the frequency of the elastic progressive wave   
   aligned closely with the resonance frequency generated within the   
   acoustic cavity, a strong interaction manifested, resulting in the   
   complete reflection of the progressive elastic wave. In essence, the   
   elastic wave reverted back along the direction it came from, becoming   
   indefinitely confined within a certain space, similar to the behavior   
   observed when encountering a mirror, despite having ample room for forward   
   propagation. While many studies have explored the utilization of bound   
   states in the continuum, this research represents the first instance   
   of unveiling the BIC phenomenon through the combination of elasticity   
   and sound.   
      
   Professor Junsuk Rho emphasized the potential implications of the   
   findings, "This study illustrates that applications of acoustoelastic   
   coupling can be expanded to vibration focusing and energy storage." He   
   added, "The findings from this research hold promise for diverse   
   applications including the development of filters capable of selectively   
   isolating specific frequencies or the advancement of energy harvesting   
   methodologies that convert kinetic energy into electric energy."   
   The study was conducted with the support from the Ministry of Science   
   and ICT and the National Research Foundation of Korea.   
      
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   Materials provided by Pohang_University_of_Science_&_Technology_(POSTECH).   
      
   Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Dongwoo Lee, Jeonghoon Park, Seokwoo Kim, Jungho Mun, Jaekyung Kim,   
         Xianji Piao, Namkyoo Park, Junsuk Rho. Elastic bound states in the   
         continuum by acoustoelastic interaction. Extreme Mechanics Letters,   
         2023; 61: 101965 DOI: 10.1016/j.eml.2023.101965   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230712011607.htm   
      
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