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
251 2019-12-13 13:30  #1323, E6-2  Biophysics Mini-symposium at KAIST file
250 2019-12-18 16:00  #1323, E6-2  Road to Higher Tc Superconductivity file
249 2019-12-27 15:00  #5318, E6-2  The superconducting order parameter puzzle of Sr2RuO4 file
248 2019-12-27 15:00  E6-2,#5318  The superconducting order parameter puzzle of Sr2RuO4 file
247 2020-01-17 16:00  #1323, E6-2  Symmetry Breaking and Topology in Superfluid 3He file
246 2020-02-12 13:00  E6-2, #5318  From inflation to new weak-scale file
245 2020-02-13 16:30  E6-6, #119  Enhanced Light-Matter Interactions in Graphene with Noble Metal Plasmonic Structures file
244 2020-02-20 16:00  #1323, E6-2  Unconventional superconductivity in the locally non-centrosymmetric heavy-fermion CeRh2As2 file
243 2020-07-02 16:00  Zoom Video Conference Seminar  An irreversible qubit-photon coupling for the detection of itinerant microwave photons file
242 2020-08-17 20:00  Zoom webinar  Using magnetic tunnel junctions to compute like the brain file
241 2020-08-25 20:00  Zoom webinar  KAIST Global Forum for Spin and Beyond (Second Forum) file
240 2020-09-11 14:00  zoom  SRC Seminar file
239 2020-09-14 17:30  Zoom webinar  KAIST Global Forum for Spin and Beyond (Third Forum) file
238 2020-09-22 09:30  Zoom webinar  Physics and applications of soliton microcombs(Quantum- & Nano-Photonics) file
237 2020-09-24 09:00  Zoom Video  (CAPP/IBS)Searching for Dark Matter with a Superconducting Qubit , Cryogenic Microwave Circuit Development at the NSTU file
236 2020-09-28 17:30  Zoom webinar  KAIST Global Forum for Spin and Beyond(Fourth Forum) file
235 2020-10-09 09:00  https://kaist.zoom.us/j/85161896513?pwd=U3pwWFFZaWVRamxDZUR5REhNeVk0UT09  Quantum Many-Body Simulation file
234 2020-10-15 16:00  CAPP Seminar Room #C303, Creation Hall (3F), KAIST Munji Campus  Graphene-based Josephson junction microwave bolometer file
233 2020-10-15 16:00  (https://kaist.zoom.us/j/93997220310)  Towards resource-efficient and fault-tolerant quantum computation with nonclassical light
232 2020-10-15 17:00  https://bit.ly/3ndIiJn  Time crystals, quasicrystals, and time crystal dynamics in the superfluid universe file