# 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 |

308 | Apr. 27, 2017 (Thu) 4:00 pm | Seminar Room(#1323, E6-2) | Prof.Donghan Lee (Chungnam National Univ.) | 반도체 양자점을 이용한 단광자 광원 |

307 | 2017/03/06 - 05/29 | Seminar Room 1501 | 이종봉 박사 (POSTECH) 외 | Spring 2017: Physics Colloquium |

306 | 2017/03/21 - 06/08 | Seminar Room 1323 | 조길영 박사(KAIST) 외 | Spring 2017: Physics Seminar Serises |

305 | Thursday, December 14, 2017 at 3:00 pm | Seminar Room (C303), Creation Hall (3F), KAIST Munji Campus | Chunglee Kim (KASI) | Exploring the Universe via GWs in the era of multi-messenger astronomy |

304 | July 2. 2018 (Monday) 3:00 PM | Seminar Room (C303), Creation Hall (3F), KAIST Munji Campus | Dr. Peter Winter (Argonne National Laboratory) | High Precision Magnetic Field Measurement for the Muon g-2 Experiment |

303 | Jun. 14 (Tue) 4PM | Seminar Room (#2502, 2nd fl.) | Young-Sik Ra, Université Pierre et Marie Curie | Photonic quantum network based on multimode squeezed vacuums and single-photon subtraction |

302 | Nov. 1 (Tue.) 2:30 pm | Seminar Room #1323(E6-2) | Prof. Youngjoon Kwon, Yonsei Univ. | Search for dark sector particles in the B-factory experiments |

301 | 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 |

300 | 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 |

299 | 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 |

298 | 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 |

297 | 2015/06/03, 12PM | Room 101, E11 | Prof. Min-Kyo, Seo & Hansuek, Lee(KAIST) | The First Wednesday Multidisciplinary Forum |

296 | 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 |

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

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

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

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

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