visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나
장소 B501, Room Red, KI bldg. 5nd fl. 
일시 2015/08/04, 11PM 
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 일시 장소 연사 제목
142 2012/04/02, 4PM  E6, 1501  Yong Hee Jeong  A new route to ferroelectricity in magnetic spinels: a case of Co2MnO4
141 2013/03/11-06/10  E6, 1501  강명수교수(KAIST) 외  Physics Colloquium : 2013 Spring
140 2013/09/09-12/09  E6, 1501  박혁규교수(부산대) 외  Physics Colloquium : 2013 Fall
139 2014/03/10-06/09  E6, 1501  신용일교수(서울대)  Physics Colloquium : 2014 Spring file
138 2015/09/15-12/08  E6, 1501  박제근 교수(서울대 물리학과) 외12명  Physics Colloquium : 2014 Fall file
137 2015/03/09-06/08  E6, 1501  최현용교수(연세대) 외12명  Physics Colloquium : 2015 Spring file
136 2015/10/23-12/4 10:30 AM  E6, #1501  Prof. YongKeun Park & Prof. Tae-Young Yoon  How to write a good scientific paper[Open lecture series]
135 July 8(Mon), 14:00  E6, #1322  T. L. M. Guedes (Univ. of Konstanz)  Ultrabroadband squeezed pulses and their relation to relativity file
134 August. 16th (Fri), 14:00  E6 Room(#1323)  Jinxing Zhang  Multiferroic and Magnetoelectric Effects by Tailoring Interfacial Chemistry and Physics in Correlated Oxides file
133 August. 6th (TUE), 14:00  E6 Room(#1323)  Kanghyun Chu  Visualization of in-plane piezoresponse vector fields file
132 August. 1st (Thu), 14:00  E6 Room(#1323)  Hyeok Yoon  Low-density Superconductivity in SrTiO3 Probed by Planar Tunneling Spectroscopy file
131 May. 8th (Wed), 16:00  E6 Room(#1323)  Jieun Lee  Imaging valley dependent electron transport in 2D semiconductors file
130 Nov. 22th (Thur), 15:00  E6 Room(#1323)  Prof. Suprijadi Haryono  Experimental and Computational Study on Physical Properties based on Granular System file
129 2015/07/23,1:30PM  E4, B401  Prof. Gilles Lérondel (Univ. of Technology of Troyes)  Enhanced ZnO based UV photonics and related applications file
128 2015/12/17, 11:00AM  E4(KI Building), Matrix Hall (2nd fl.)  Dr. Jung-Hoon Park (Purdue University)  Wavefront engineering for in-vivo Deep brain imaging
127 2015/12/09, 11AM  E4(KI Building), Connect room (2nd fl.)  Arjun G. Yodh (University of Pennsylvania)  Functional Imaging & Monitoring of Brain & Breast with Diffuse Light
126 2015/03/13, 2PM  Connect Room, KI Bldg.    The 15th Innovative Workshop on Soft/Bio Materials file
125 October 15, 2020 (Thursday  CAPP Seminar Room #C303, Creation Hall (3F), KAIST Munji Campus  Prof. Gil-Ho Lee (POSTECH)  Graphene-based Josephson junction microwave bolometer file
124 Jun. 1(Wed) 10:30 AM  BK21 Conference Room (#1318, E6-2)  Dr. Noriaki Horiuchi, Editor, Nature Photonics  Welcome to Nature Photonics
» 2015/08/04, 11PM  B501, Room Red, KI bldg. 5nd fl.  Dr. Eric Jin Ser Lee(Univ. of Manitoba, Canada)  Propagation of ultrasound through two- and three-dimensional strongly scattering media