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
113 2020-10-09 09:00  https://kaist.zoom.us/j/85161896513?pwd=U3pwWFFZaWVRamxDZUR5REhNeVk0UT09  Quantum Many-Body Simulation file
112 2020-10-16 14:30  https://kaist.zoom.us/j/89198078609  Nanoscale magnetic resonance detection towards nano MRI file
111 2020-10-16 16:00  https://kaist.zoom.us/j/89198078609  Hidden room-temperature ferroelectricity in CaTiO3 revealed by a metastable octahedral rotation pattern file
110 2017-04-06 16:00  IBS CAPP seminar room, Creation Hall (3F), KAIST Munji Campus  For whom the Belle tolls
109 2017-07-10 16:00  Jul. 10th (Mon), 4pm  “Intertwined Orders in a Heavy-fermion metal” file
108 2015-10-14 18:00  KAIST Munji Campus Supex Hall  인터스텔라 영화 속의 물리 file
107 2016-04-04 09:30  KAIST Natural Science Building (E6-2), RM #4314  Radio frequency engineering
106 2016-08-04 14:30  KAIST Natural Science Building (E6-5), EDU 3.0 Room(1st fl.)  Relational Logic (with applications to Quantum Mechanics, String Theory, Cosmology, Neutrino Oscillations, Statistical Mechanics)
105 2024-09-26 14:00  KAIST, Physics Bldg. (E6-2) / (Rm. 3441)  Quantum spin nematic phase in a square-lattice iridate
104 2022-01-18 14:00  KI bldg. 5th fl. Room B501 & Zoom  Data-driven interrogation of biological dynamics: from subcellular interactions to neuronal networks in vivo file
103 2022-08-09 14:00  KI building (E4), Lecture Room Red (B501)  Quantum biology in fluorescent protein: a new model system to study quantum effects in biology file
102 2023-02-20 17:00  KI building (E4), Lecture Room Red (B501)  (Optics Seminar) Neural Holography for Next generation Virtual and Augmented Reality Displays file
101 2024-07-23 16:00  KI Building(E4) Matrix Hall(2F)  Spin Conversion Research Towards Novel Spintronic Functionalities file
100 2014-05-28 17:00  KI Building, Matrix Hall  부품소재산업이 미래다
99 2016-04-18 15:30  KI빌딩(E4), 강의실 B501 (5F)  First Principles Approaches for Intermolecular Interactions: From Gas-Phase Dimers to Liquid Water and Molecular Crystal Polymorphism file
98 2017-01-09 16:00  Lecture Hall, College of Natural Sciences [#1501,E6-2]  Topological Defects and Phase Transitions" file
97 2016-05-19 15:00  May 19, 2016 (Thur.) 3PM,  The CERN Resonant WISP Search: Development, Results and Lesson-Learned
96 2016-09-05 16:00  Natual Scien Bldg.(E6)m #1501  Physics Colloquium : 2016 Fall file
95 2022-05-19 15:00  online  (광학분야 특별세미나)Development of a multimodal optical system for improved disease diagnosis
94 2022-03-31 16:00  online  (광학분야 특별세미나)Ultrafast time-resolved spectroscopy in topological materials