visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나
날짜 2015-08-04 11:00 
일시 2015/08/04, 11PM 
장소 B501, Room Red, KI bldg. 5nd fl. 
연사 Dr. Eric Jin Ser Lee(Univ. of Manitoba, Canada) 

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 장소 제목
공지 2022-10-24 16:00  E6 #1501(공동강의실)  Physics Colloquim(Fall 2022)
공지 2022-09-21 10:30  E6-1 #1501  [Update 세미나 영상] Distinguished Lecture 'The Magic of Moiré Quantum Matter' Prof. Pablo Jarillo-Herrero(Department of Physics, MIT)
공지 2022-10-28 11:00  E6-2 #1323  [Update 세미나영상] (응집물리 세미나) Machine-Learning-Guided Prediction models and Materials discovery for high Tc cuprates
공지 2022-10-07 11:00  E6-2 #1323  [Update 세미나 영상] (응집물리 세미나) Competing orders in a vanadium-based kagome metal monolayer
공지 2022-09-23 11:00  E6-2 #1323  [Update 세미나 영상] (응집물리 세미나) Steady Floquet-Andreev states in graphene Josephson junctions
공지 2022-09-22 11:00  E6-1 #1323  2022 가을학기 응집물리 및 광학 세미나 전체 일정
158 2015-10-23 10:30  E6, #1501  How to write a good scientific paper[Open lecture series]
157 2019-07-08 14:00  E6, #1322  Ultrabroadband squeezed pulses and their relation to relativity file
156 2022-05-25 14:00  E6 Room(#2501)  Atomic-level insights into ferroelectric switching and preferred orientation of ultrathin hafnia file
155 2019-08-16 14:00  E6 Room(#1323)  Multiferroic and Magnetoelectric Effects by Tailoring Interfacial Chemistry and Physics in Correlated Oxides file
154 2019-08-06 16:00  E6 Room(#1323)  Visualization of in-plane piezoresponse vector fields file
153 2019-08-01 14:00  E6 Room(#1323)  Low-density Superconductivity in SrTiO3 Probed by Planar Tunneling Spectroscopy file
152 2019-05-08 16:00  E6 Room(#1323)  Imaging valley dependent electron transport in 2D semiconductors file
151 2018-11-22 15:00  E6 Room(#1323)  Experimental and Computational Study on Physical Properties based on Granular System file
150 2022-06-23 11:00  E6 Room(#1322)  JILA’s search for the electron’s Electric Dipole Moment (eEDM) to probe physics beyond the standard model file
149 2022-05-26 16:00  E6 1323  (광학분야 특별세미나)Topological photonic devices
148 2022-05-10 16:00  E6 1323  (광학분야 특별세미나)Testing quantum thermodynamics using quantum optics
147 2022-04-28 16:00  E6 1323  (광학분야 특별세미나)Adiabaticity and symmetry in optical waveguide design
146 2022-04-14 16:00  E6 1323  (광학분야 특별세미나)Holographic tomography of dielectric tensors at optical frequency
145 2022-10-04 16:00  E6 #2501  Distinguishing 6d (1, 0) SCFTs
144 2022-03-29 10:00  E6 #1501/zoom, E6 #2502/zoom  Non-reciprocal phase transitions file
143 2022-03-31 10:00  E6 #1501/zoom  Weiss fields for Quantum Spin Dynamics file
142 2022-01-25 15:00  E6 #1501/online  Emulating twisted double bilayer graphene with a multiorbital optical lattice file
141 2022-08-01 10:00  E6 #1501 & Zoom  [Update 세미나 영상] James Webb Space Telescope & OTE Commissioning
140 2022-07-14 15:00  E6 #1501 & Zoom  Pure two-dimensional quantum electron liquid and its phase transition