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테라헤르츠 파를 이용한 복합재 에폭시 접착 조인트의 흡습에 따른 접착력 및 특성 평가
오경환(Gyung?hwan Oh),김덕중(Dug-joong Kim),박동운(Dong?woon Park),김학성(Hak?Sung Kim) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
The application of epoxy adhesive joints in structural components fabricated by fiber-reinforced composites has increased significantly in recent years. However, the degradation of adhesively bonded joints through the effects of moisture is one of the major concerns affecting their wide implementation in composites. Therefore, non-destructive evaluate (NDE) method is necessary to detect the degradation of the adhesive. In this study, the pulse type terahertz time domain spectroscopy (THz-TDS) system was devised and used for evaluating the moisture absorption effects in epoxy adhesive-bonded glass fiber reinforced composite single lap joints. Tensile shear test was performed to estimate the degradtion of adhesive strength on sigle lap joints depending on moisture absorption time. Also, the complex refractive index was measured by THz-TDS system to correlate with degradation of adhesive strength. From these results, the degradation of adhesive strength on composite single lap joints depending on moisture absorption was evaluated by change of complex refractive, non-contact measured by THz-TDS system. In conclusion, it is expected that THz-NDE technique can be widely used to evaluate the reliability of composite structures.
비파괴검사를 위한 연속형 테라헤르츠 파 기반의 영상화 기술
오경환 ( Gyung-hwan Oh ),김학성 ( Hak-sung Kim ) 한국센서학회 2018 센서학회지 Vol.27 No.5
The paper reviews an improved continuous-wave (CW) terahertz (THz) imaging system developed for nondestructive inspection, such as CW-THz quasi-time-domain spectroscopy (QTDS) and interferometry. First, a comparison between CW and pulsed THz imaging systems is reported. The CW-THz imaging system is a simple, fast, compact, and relatively low-cost system. However, it only provides intensity data, without depth and frequency- or time-domain information. The pulsed THz imaging system yields a broader range of information, but it is expensive because of the femtosecond laser. Recently, to overcome the drawbacks of CW-THz imaging systems, many studies have been conducted, including a study on the QTDS system. In this system, an optical delay line is added to the optical arm leading to the detector. Another system studied is a CW-THz interferometric imaging system, which combines the CW-THz imaging system and far-infrared interferometer system. These systems commonly obtain depth information despite the CW-THz system. Reportedly, these systems can be successfully applied to fields where pulsed THz is used. Lastly, the applicability of these systems for nondestructive inspection was confirmed.
펄스형 테라헤르츠파의 시간응답 특성을 통한 굴절률 및 두께 측정 알고리즘 개발
박동운(Dong-Woon Park),오경환(Gyung-hwan Oh),김덕중(Dug-Joong-Kim),김학성(Hak-Sung Kim) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In this work, the pulse type therahertz time domain spectroscopy (THz–TDS) system was used for measuring the refractive index and thickness of EMC mold non-desructively. Based on terahertz time domain signals of transmission and normal mode, a theoretical model was developed to measure the refractive index of EMC Mold without measuring the thickness of EMC mold. In order to reduce the error that may occur when measuring therahertz signal, interpolation was applied to calculate the time delay. The refractive index of EMC Mold was measured using THZ-TDS system. At the same time, the thickenss of EMC Mold was calculated and compared to actual thickness which was measured through SEM.
테라헤르츠파를 이용한 실리콘 웨이퍼의 도핑 정도와 물리적 특성 측정에 관한 연구
박성현(Sung Hyeon Park),오경환(Gyung Hwan Oh),김학성(Hak Sung Kim) 한국비파괴검사학회 2017 한국비파괴검사학회지 Vol.37 No.1
본 논문에서는 테라헤르츠파 시간분광영상시스템을 이용하여 도핑된 실리콘 웨이퍼의 물리적 특성을 측정하는 것에 관한 연구를 진행하였다. 투과모드와 30°의 입사각을 가진 반사모드를 이용하여 측정하였으며 실리콘 웨이퍼의 도핑 정도는 N-type과 P-type 모두에서 10<SUP>14</SUP>에서 10<SUP>18</SUP>까지 다양하게 준비하였다. 그 결과, 도핑 정도와 테라헤르츠파와의 상관관계를 찾았으며 이를 이용하면 모든 경우에 대한 도핑된 실리콘 웨이퍼의 도핑 정도를 확인할 수 있다. 또한, 각 도핑된 실리콘 웨이퍼의 도핑된 두께, 굴절률, 유전율을 테라헤르츠 시간영역 파형분석을 통하여 계산할 수 있었다. 따라서, 테라헤르츠 시간분광영상화 기술은 도핑된 실리콘 웨이퍼의 굴절률과 유전율과 같은 물리적 특성뿐만 아니라 도핑 정도를 측정할 수 있는 유용한 기술이 될 것으로 기대된다. In this study, a terahertz time domain spectroscopy (THz-TDS) imaging technique was used to measure doping concentration and physical properties (such as refractive index and permittivity) of the doped silicon (Si) wafers. The transmission and reflection modes with an incidence angle of 30° were employed to determine the physical properties of the doped Si wafers. The doping concentrations of the prepared Si wafers were varied from 10<SUP>14</SUP> to 10<SUP>18</SUP> in both N-type and P-type cases. Finally, the correlation between the doping concentration and the power of the THz wave was determined by measuring the powers of the transmitted and reflected THz waves of the doped Si wafers. Additionally, the doped thickness, the refractive index, and permittivity of each doped Si wafer were calculated using the THz time domain waveform. The results indicate that the THz-TDS imaging technique is potentially a promising technique to measure the doping concentration as well as other optical properties (such as the refractive index and permittivity) of the doped Si wafer.