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
186 2023-05-15 16:00  CAPP Seminar Room C303, Creation Hall, KAIST Munji Campus  Role of dark Higgs boson in DM physics and cosmology file
185 2016-05-16 16:00  #1323(E6-2, 1st Fl.)  Tuning microwave cavities with biased nonlinear dielectrics for axion searches
184 2023-05-17 16:30  Zoom  Detecting Hidden Photon Dark Matter via the Excitation of Qubits file
183 2016-05-19 16:00  #1323(E6-2, 1st fl.)  Nonlinear/quantum optical effect in silicon nano-photonics
182 2016-05-19 15:00  May 19, 2016 (Thur.) 3PM,  The CERN Resonant WISP Search: Development, Results and Lesson-Learned
181 2019-05-02 16:00  #1323, E6-2  Anomalous optical properties of halide perovskites file
180 2019-05-21 16:00  #5318, E6-2  Classification of flat bands according to the band-crossing singularity of Bloch wave functions file
179 2023-05-22 13:00  E6-6 119  Design & Development of Electrochemical Biosensors for the Detection of T2DM Biomarkers
178 2019-05-24 16:00  #1323, E6-2  Infrared spectroscopy study on metal-insulator transitions in layered perovskite iridates file
177 2016-05-24 16:00  E6-2. #1323(1st fl.)  Electronic and magnetic properties of 2D transition-metal thiophosphates and tunability of magnetic order with carrier density
176 2022-05-27 11:00  Online seminar  Current Status and Future Plans of ADMX file
175 2018-05-29 16:00  #1323, E6-2  Investigation on metal nanostructure/semiconductor junction and its applications file
174 2023-05-03 16:00  E6-2, #2502  Probing microscopic origins of axions by the chiral magnetic effect
173 2019-05-30 16:00  #1323, E6-2  Tuning the excitonic properties of semiconductors with light-matter interactions file
172 2019-05-31 11:00  #1323, E6-2  Cavity QED with Spin Qubits file
171 2016-05-31 16:00  #1323(E6-2, 1st fl.)  Understanding 3D tokamak physics towards advanced control of toroidal plasma
170 2018-05-31 16:00  #1323, E6-2  Dynamic control of optical properties with gated-graphene metamaterials file
169 2023-05-31 16:00  E6-2, #2502  [High-Energy Theory Seminar] Resurgence and complex Chern-Simons theory
168 2019-05-08 16:00  E6 Room(#1323)  Imaging valley dependent electron transport in 2D semiconductors file
167 2019-05-09 16:00  #1323, E6-2  Quantum Optical Sensing Using Single Photons And Single Photon Emission from Single Emitters file