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대구경 선집속 초음파 탐촉자를 이용한 실리콘 판재의 결정방향 측정
오재원(Jaewon Oh),정인영(Inyoung Jung),한규범(Kyubeom Han),김동현(Donghyun Kim),김영환(Young H. Kim) 한국비파괴검사학회 2017 한국비파괴검사학회지 Vol.37 No.3
램파(Lamb wave)는 주파수, 파의 두께, 입사각에 따라 다양한 모드가 존재한다. 본 연구에서는 이방성 재료인 (100), (110), (111) 실리콘 판재에서 초음파의 진행방향에 따른 전파 특성에 대하여 연구하였다. 대구경 선집속 탐촉자를 이용하여 초음파를 판재에 입사시킴과 동시에 판재 내에서 발생하는 램파의 파형을 얻었다. 램파는 분산성이 있어서 수신된 파형에는 다양한 주파수의 파가 섞여있다. 이들을 분리하기 위해서 일련의 신호처리를 하였다. 탐촉자와 시험편 사이의 거리를 변화시키면서 얻은 V(t,z) 를 FFT(fast Fourier transform)하여 V(f,z)를 얻고, 특정한 주파수에서 V(z)를 얻었다. 초음파 현미경과 마찬가지로 V(z) 로부터 위상속도를 얻었으며, 시험편을 돌리며 이 과정을 반복하면 진행방향에 따른 위상속도의 변화를 얻을 수 있었다. 진행방향에 따른 파수 및 위상속도를 얻었으며, 이는 결정구조와 잘 일치하였다. 결론적으로 본 연구에 사용된 방법이 판재의 이방성을 평가할 때에 유용할 것으로 판단된다. Lamb waves have numerous modes depending on the frequency of the waves, the thickness of the plate and the incident angle. In this experiment, the wave propagation in (100), (110) and (111) single-crystal silicon wafers were investigated. Lamb waves were generated using a line-focused ultrasonic transducer with a large aperture in the wafers, and these waves were detected using the same transducer. The frequency and phase velocity were determined from the incident angle at which a specific mode of Lamb waves were generated. However there are numerous incident angles with the transducer used in this experiment, received signal contains various waves of different frequencies. The V(z) curve for a specific frequency was obtained from V(f, z) which is the FFT (fast Fourier transform) of V(t, z). The phase velocity can be obtained from the V(z) curves by using a method similar to that used in acoustic microscopy. Finally, the phase velocity can be determined as a function of the propagation direction by rotating the silicon wafers. The angular dependences of the wavenumber and Lamb wave phase velocity were obtained, and they show good agreement with the crystalline orientation of the silicon wafers. In conclusion, a line-focused ultrasonic transducer with a large aperture is an epoch tool for evaluating anisotropic plates.
Improved semantic segmentation network using normal vector guidance for LiDAR point clouds
Kim Minsung,Oh Inyoung,Yun Dongho,Ko Kwanghee 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.6
As Light Detection and Ranging (LiDAR) sensors become increasingly prevalent in the field of autonomous driving, the need for accurate semantic segmentation of three-dimensional points grows accordingly. To address this challenge, we propose a novel network model that enhances segmentation performance by utilizing normal vector information. Firstly, we present a method to improve the accuracy of normal estimation by using the intensity and reflection angles of the light emitted from the LiDAR sensor. Secondly, we introduce a novel local feature aggregation module that integrates normal vector information into the network to improve the performance of local feature extraction. The normal information is closely related to the local structure of the shape of an object, which helps the network to associate unique features with corresponding objects. We propose four different structures for local feature aggregation, evaluate them, and choose the one that shows the best performance. Experiments using the SemanticKITTI dataset demonstrate that the proposed architecture outperforms both the baseline models, RandLA-Net, and other existing methods, achieving mean intersection over union of 57.9%. Furthermore, it shows highly competitive performance compared with RandLA-Net for small and dynamic objects in a real road environment. For example, it yielded 95.2% for cars, 47.4% for bicycles, 41.0% for motorcycles, 57.4% for bicycles, and 53.2% for pedestrians.
Fabrication of replica cliché with fine pattern using reverse offset printing process
Shin, Yejin,Kim, Inyoung,Oh, Dongho,Lee, Taik-Min Elsevier 2018 THIN SOLID FILMS - Vol.647 No.-
<P><B>Abstract</B></P> <P>Among the printing processes for printed electronic devices, the gravure offset and reverse offset methods have drawn attention for their fine pattern printing potential. These printing methods use a cliché, which has a decisive effect on the precision and quality of the final product. In this research, a precise cliché replica method is proposed. It consists of copper (Cu) sputtering, precise reverse offset printing with a 5-μm pattern width, nickel‑cobalt (Ni-Co) electroplating, rinsing, etching, and diamond-like carbon (DLC) coating. Cu is deposited on glass by sputtering to a thickness of 3μm. Ni-Co is electroplated to a thickness of 300nm only on the copper and not on the printed pattern. After removing the printed pattern during the rinsing process, Cu is etched through the revealed part resulting from the rinsing process. For the last step of the process, DLC coating is conducted to protect the surface. We finally compare the fabricated replica cliché with the original and print out precise patterns using the replica cliché.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The reverse offset printing method was adapted to replicate the fine pattern cliché. </LI> <LI> Silver nano ink pattern was dried but not sintered by controlling plasma treatment. </LI> <LI> The printed pattern with a line width of 4.8μm can be obtained using replica cliché. </LI> </UL> </P>