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.
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.
Ultrasonics. 2014 Mar;54(3):953-60. doi: 10.1016/j.ultras.2013.11.006. Epub 2013 Nov 27.
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.
在通过波导单元将超声波传输到测试结构的波导换能器中，最理想的情况是发送具有窄波束宽度的非弥散或少弥散超声波。然而，在产生非弥散或少弥散波与将窄波束波传输到测试结构之间存在未解决的冲突。在其他因素中，波导换能器中波导单元的厚度是决定这两个相互冲突标准的关键变量，但使用任何厚度的均匀厚度波导都不能同时满足这两个相互冲突的标准。在本研究中，我们提出了一种特殊设计的锥形波导单元，以同时满足这些要求。激励单元安装在锥形波导的薄区域的末端，仅产生最低的非弥散剪切横波。然后，生成的波通过波导单元的锥形区域传播，并到达波导的厚区域，模式转换到更高模式的程度可以忽略不计。如果使用锥形波导，则在波导的厚区域中幸存的最低模式将携带大部分传输功率，并最终传播到测试结构中。由于传播波的波束尺寸与接触波导区域的厚度成反比，因此锥形波导的厚接触区域确保了窄波束宽度。进行了数值和实验研究，以检查所提出的波导变细方法的有效性。
