title: Waveguide tapering for beam-width control in a waveguide transducer.
abstract: In a waveguide transducer that transmits an ultrasonic wave through a waveguide unit to a test structure, it is most preferred to send a non-dispersive ultrasonic wave of a narrow beam width. However, there is an unresolved conflict between the generation of the non- or less-dispersive wave and the transmission of a narrow-beam wave into a test structure. Among others, the thickness of the waveguide unit in a waveguide transducer is the key variable determining these two conflicting criteria, but the use of a uniformly-thick waveguide of any thickness cannot fulfill the two conflicting criteria simultaneously. In this study, we propose a specially-engineered tapered waveguide unit for the simultaneous satisfaction. An excitation unit is installed at the end of the thin region of the tapered waveguide and generates only the lowest non-dispersive shear-horizontal wave. Then the generated wave propagates through the tapered region of the waveguide unit and reaches the thick region of the waveguide with insignificant mode conversion to higher modes. If the tapered waveguide is used, the surviving lowest mode in the thick region of the waveguide is shown to carry most of the transmitted power and is finally propagated into a test structure. Because the beam size of the propagated wave and the thickness of the contacting waveguide region are inversely related, the thick contacting region of the tapered waveguide ensures narrow beam width. Numerical and experimental investigations were performed to check the effectiveness of the proposed waveguide-tapering approach.
authors: Division of WCU Multiscale Mechanical Design, School of Mechanical and Aerospace Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea.
authors: Young Eui
authors: YE
authors: Kwon
authors: Advanced Mechanical R&D Group, Mobile R&D Office, Mobile Communication Business, Samsung Electronics, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 443-732, Republic of Korea.
authors: Hyun Joong
authors: HJ
authors: Jeon
authors: Fast Reactor Technology Demonstration Division, Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353, Republic of Korea.
authors: Hoe Woong
authors: HW
authors: Kim
authors: Division of WCU Multiscale Mechanical Design, School of Mechanical and Aerospace Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea. Electronic address: yykim@snu.ac.kr.
authors: Yoon Young
authors: YY
authors: Kim
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D019220:High-Energy Shock Waves; D008962:Models, Theoretical; D012542:Scattering, Radiation; D014159:Transducers; D014463:Ultrasonography / Q000295:instrumentation*
keywords: Narrow beam; Shear-horizontal; Tapered waveguide; Waveguide transducer