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)
574 2025-01-08 16:00  Dr. SangEun Han  Quantum impurity model for two-stage multipolar ordering and Fermi surface reconstruction
573 2024-12-17 15:00  Isaac H. Kim  Learning state preparation circuit for quantum phases of matter (Isaac H. Kim, UC Davis)
572 2024-12-06 16:00  Vladimir Y. Chernyak  Bright Squeezed Light (BSL) Spectroscopy with Interferometry from First Principles
571 2024-11-30 10:30  Joon Young Park  Towards probing topological phases in Corbino-geometry Josephson junctions on a topological insulator surface
570 2024-11-21 16:00  Prof. Ulrich Höfer  Time-resolved photoemission: From bandstructure to orbital movies file
569 2024-11-21 11:00  Daniel L. Jafferis  3d Gravity and Tensor Model file
568 2024-11-18 10:30    Manipulation of antiferromagnetic magnon polarization in synthetic antiferromagnets
567 2024-11-13 12:00    [11/13(수) 물리학과 세미나 안내] Separability as a window to mixed-state quantum phases and phase transitions / Tarun Grover (UC San Diego, Associate Professor)
566 2024-10-31 13:00    Mini-workshop on first-principles DFT methods and applications
565 2024-10-30 14:30    [Seminar Invitation] Mario Cuoco (CNR-SPIN, c/o University of Salerno, Fisciano, Italy) / 2024.10.30. 14:30 / E6-2, #3441
564 2024-10-21 13:00    [Physics Seminar] “Non-Hermitian Point-Gap Topology in Junction Systems” file
563 2024-10-17 16:00    Photonic Methods for Quantum Levitodynamics Beyond the Rayleigh Regime
562 2024-10-14 11:00    [RSVP, Oct 14th Mon] Ambassador of Hungary to Republic of Korea Special Lecture file
561 2024-10-02 12:00    Data-driven discovery of neural computations through brain-wide and cell-type-specific dynamical systems file
560 2024-09-26 14:00    Quantum spin nematic phase in a square-lattice iridate
559 2024-09-03 12:00    2024 가을학기 물리학과 특별세미나 전체 일정 (응집물리 및 광학분야) file
558 2024-09-02 16:00    2024학년도 가을학기 물리학과 콜로키움(Physics Colloquium) file
557 2024-08-22 16:00    [CAPP seminar] Development of a 12-20 GHz CO Intensity Mapping Receiver for Capturing the Star-formation History in the Early Universe file
556 2024-08-16 11:00    Cathodoluminescence for nanophotonics: Applications to plasmonic bandgap materials and perovskite semiconductors file
555 2024-08-14 11:00    Pair Density Waves and Supercurrent Diode Effect in Altermagnets