visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나
날짜 2015-08-04 11:00 
연사  
장소 B501, Room Red, KI bldg. 5nd fl. 

Propagation of ultrasound through two- and three-dimensional strongly scattering media

2015/08/04(TUE), 11PM, B501(Room Red, KI bldg. 5nd fl.)
Dr. Eric Jin Ser Lee,  Department of Physics and Astronomy, Univ. of Manitoba, Canada

 

 

During my Ph. D study at the University of Manitoba, I have investigated the propagation of ultrasound through two- and three-dimensional strongly scattering media, with either random or ordered internal structures, through experiments and finite element simulations.  All media investigated have strong scattering resonances, leading to novel transport behaviour. 

 

The two-dimensional samples consist of nylon rods immersed in water.  Nylon fishing lines under tension are used as two-dimensional scatterers.  Note that since the rods are parallel and of uniform diameter, there is negligible scattering of waves out of the plane perpendicular to the rods, so that the system appears two-dimensional from the wave point of view for propagation in this plane.  When nylon rods are surrounded by water, they exhibit strong scattering resonances.  In such an environment, the nylon scattering resonance can couple with the propagating mode through water to create a bandgap.  This is a called hybridization gap.  When the nylon rods are arranged in a triangular lattice to form two-dimensional phononic crystals, very unusual dispersion properties are observed when the lattice constant is adjusted so that Bragg and hybridization gaps overlap in frequency.  This behaviour is attributed to the competition between two co-existing propagating modes, leading to a new method for tuning bandgap properties and adjusting the transmission by orders of magnitude. 

 

The three-dimensional media were fabricated by brazing aluminum beads together to form a disordered porous solid network with either vacuum in the pores.  This system is of particular interest because it has been shown to exhibit Anderson localization of ultrasound.  With such system, the density of states (DOS) was investigated.  It is the number of vibrational states per unit frequency range per unit volume.  The DOS is a fundamental property of any system and can influence not only wave transport but also the possibility of forming localized states.  The DOS was measured by directly counting the modes in the frequency domain.  At intermediate frequencies, the DOS was found to be approximately independent of frequency, while at higher frequencies, the frequency dependence was consistent with traditional DOS models.  Furthermore, the level statistics, which describe the distribution of the separations between neighbour modes in frequency, of the modes was investigated to determine the conditions under which level repulsion occurs.  As the sample becomes larger to have more modes, the modes start to overlap and repel each other so that level repulsion effects become important.  Consequently, the level statistics were observed to become closer to GOE predictions as the sample size increased.  For the last, as there is a transition from diffusive to localized regime around the lower bandgap edge, a transition from GOE to Poisson distribution is observed.

 

Contact: Prof. YongKeun Park, Physics Dept., (yk.park@kaist.ac.kr)

 

 

번호 날짜 연사 제목
공지 2025-02-24 16:00    2025년 봄학기 콜로키움 안내
공지 2025-02-27 16:00    2025년 봄 물리학과 특별세미나 (광학/응집물리 분야)
374 2019-07-08 14:00    Ultrabroadband squeezed pulses and their relation to relativity file
373 2019-07-10 16:00    Public Lectures file
372 2019-07-16 16:00    2019 Physics Distinguished Lecture file
371 2019-07-21 12:00    Challenges and Opportunities in Theoretical Particle Physics 2019 file
370 2019-07-25 16:00    Band topology of twisted bilayer graphene file
369 2019-07-30 16:00    Dirac fermions and flat bands in correlated kagome metals file
368 2019-07-31 16:00    Features of ballistic superconducting graphene file
367 2019-08-01 14:00    Low-density Superconductivity in SrTiO3 Probed by Planar Tunneling Spectroscopy file
366 2019-08-06 16:00    Visualization of in-plane piezoresponse vector fields file
365 2019-08-14 16:00    Quantum Optics, at the heart of quantum metrology and quantum information file
364 2019-08-16 14:00    Multiferroic and Magnetoelectric Effects by Tailoring Interfacial Chemistry and Physics in Correlated Oxides file
363 2019-08-19 10:00    Tutorials on Multimode Quantum Optics in the Continuous Variable Regime file
362 2019-08-22 16:00    Physics and Applications in Nanoelectronics and Nonomechanics file
361 2019-08-27 16:00    Critical current properties of Fe-based superconductors file
360 2019-09-02 16:00    Fall 2019: Physics Colloquium file
359 2019-09-10 15:00    Two-Stage Kondo Effect file
358 2019-09-10 15:00    (2+1) D Duality Web from 3D Euclidean Lattice file
357 2019-09-18 16:00    Exploring Synthetic Quantum Matter in Superconducting Circuits file
356 2019-09-18 16:00    Fall 2019: Physics Seminar Serises file
355 2019-09-26 16:00    Entanglement Swapping with Autonomous Polarization-Entangled Photon-Pairs from Warm Atomic Ensemble file