# Propagation of ultrasound through two- and three-dimensional strongly scattering media

2015.07.27 12:59

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)

## 댓글 *0*

번호 | 일시 | 장소 | 연사 | 제목 |
---|---|---|---|---|

공지 | 2019/09/18 - 12/5 | Seminar Room #1323 | Prof. David Schuster and etc. | Fall 2019: Physics Seminar Serises |

공지 | 2019/09/02 - 12/09 | Seminar Room 1501 | 이호성 박사 (한국표준과학연구원) and etc. | Fall 2019: Physics Colloquium |

280 | July 13, 2018 at 14:00 | Room 5318, KAIST Natural Sciences Lecture Hall(E6). | Prof. Ian Lewis (The University of Kansas, Department of Physics & Astronomy) | Loop Induced Single Top Partner Production and Decay at the LHC |

279 | July 27, 2018 at 15:00 | Room 5318, KAIST Natural Sciences Lecture Hall(E6). | Dr. Hyejung Kim(Technische University Dresden) | Muon g-2 in the 2HDM and MSSM: comprehensive numerical analysis and absolute maxima |

278 | July 26, 2018 at 14:00 | Room 5318, KAIST Natural Sciences Lecture Hall(E6). | Manki Kim (Department of Physics, Cornell University) | Inflation in String Theory and Backreaction |

277 | Thursday, July 12, 2018 at 17:00 | Room 5318, KAIST Natural Sciences Lecture Hall(E6) | Dr. Jae Hyeok Yoo (University of California, Santa Barbara, Department of Physics) | The MilliQan Experiment: Search for Milli-Charged Particles at the LHC |

276 | 2015/06/03, 12PM | Room 101, E11 | Prof. Min-Kyo, Seo & Hansuek, Lee(KAIST) | The First Wednesday Multidisciplinary Forum |

275 | April 5th 2017, 12:00 ~ 13:00 | Room 101, Creative Learning Bldg.(E11) | Prof. Wonho Choe(Dept. of Physics),Prof. Young-chul GHIM(Dept. of Nuclear & Quantum Engineering) | 2017년 4월 첫수 융합포럼 개최 안내(물리학과 & 원자력 및 양자공학과 공동 개최)/The First Wednesday Multidisciplinary Forum in April 2017 organized by Dept. of Physics & Dept. of Nuclear & Quantum Engineering |

274 | January 23, 2019 | Rm. C303, Creation Hall (3F), Munji Campus | Mikko Mottonen | Ultrasensitive Microwave Bolometer: Opportunity for Axion Detectors |

273 | Feb. 25 - Jun 3 | Rm. 1501 (E6) | Spring 2019: Physics Colloquium | |

272 | - | RM. 1323, E6-2 | Spring 2019: Physics Seminar Serises | |

271 | August. 14th (Wed.), 4:00PM, | Rm. 1323, E6 | Prof. Nicolas Treps | Quantum Optics, at the heart of quantum metrology and quantum information |

270 | August 27 (Tue.), 4:00PM | Rm. 1323, E6 | Hiroshi Eisaki | Critical current properties of Fe-based superconductors |

269 | 2019. 7. 16(화) | Rm. 1323 (E6-2) | Prof. Sidney Nagel | 2019 Physics Distinguished Lecture |

268 | 8/19 (Mon), 10:00~11:30, 8/22 (Thur), 10:00~11:30 | Rm. 1322, E6-2 | Nicolas Treps | Tutorials on Multimode Quantum Optics in the Continuous Variable Regime |

267 | 3 PM, 12 Jun (Wed), 2019 | Rm# 1323, E6-2 | Dr. Minyoung You | The relation between free and interacting fermionic SPT phases |

266 | 2016/09/05-12/12 4PM | Natual Scien Bldg.(E6)m #1501 | Yeong Kwan Kim 외 | Physics Colloquium : 2016 Fall |

265 | May 19, 2016 (Thur.) 3PM | May 19, 2016 (Thur.) 3PM, | Dr. Michael Betz, CERN | The CERN Resonant WISP Search: Development, Results and Lesson-Learned |

264 | 2017.1.9(Mon), 4PM | Lecture Hall, College of Natural Sciences [#1501,E6-2] | Prof. John Michael Kosterlitz, Brown University | Topological Defects and Phase Transitions" |

263 | 4월 18일(월), 15:30~ | KI빌딩(E4), 강의실 B501 (5F) | Prof. Robert A. DiStasio Jr. (Cornell University) | First Principles Approaches for Intermolecular Interactions: From Gas-Phase Dimers to Liquid Water and Molecular Crystal Polymorphism |

262 | 2014/05/28, PM5 | KI Building, Matrix Hall | 이웅범 대표이사(LG이노텍) | 부품소재산업이 미래다 |