• 한국생산제조학회지
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• 제21권2호
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• pp.252-258
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• 2012

A study of terahertz waves was made for the nondestructive evaluation of FRP (Fiber reinforced plastics) composite materials. The terahertz systems were consisted of time domain spectroscopy (TDS) and continuous wave (CW). The composite materials investigated include both non-conducting polymeric composites and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was not able to detect a material with conductivity. The CFRP (Carbon fiber reinforced plastics) laminates were utilized for confirming the experimentation in the terahertz NDE. In carbon composites the penetration of terahertz waves is quite limited and the detection of flaws is strongly affected by the angle between the electric field direction of the terahertz waves and the intervening fiber directions. A refractive index (n) was defined as one of mechanical properties; so a method was obtained in order solve the "n" in the material with non-conductivity. The usefulness and limitations of terahertz radiation are investigated for the NDE of FRP composites.

• Journal of electromagnetic engineering and science
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• 제10권3호
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• pp.158-165
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• 2010

This study reviewed terahertz technologies of time domain spectroscopy, T-ray imaging, and high rate wireless data transfer. The main topics of the terahertz research area were investigation of materials and package modules for terahertz wave generation and detection, and setup of the terahertz system for time domain spectroscopy(TDS), T-ray imaging and sub-THz wireless communication. In addition to Poly-GaAs film as a photoconductive switching antenna material, a table-top scale for the THz-TDS/imaging system and terahertz continuous wave(CW) generation systems for sub-THz data transfer and narrow band T-ray imaging were designed. Dielectric properties of ferroelectric BSTO($Ba_xSr_{1-x}TiO_3$) films and chalcogenide glass systems were characterized with the THz-TDS system at the THz frequency range. Package modules for terahertz wave transmitter/receiver(Tx/Rx) photoconductive antenna were developed.

• 한국전자파학회논문지
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• 제21권4호
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• pp.340-351
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• 2010

전기적인 장치를 기반으로 한 테라헤르츠 송신기(Terahertz Transmitter: Tx)를 이용하여 0.34 THz의 전자기파를 발생시키는 소형 CW sub-THz 이미징 시스템을 제시하였다. Tx에 의해 발생된 0.34 THz의 전자기파는 테라 헤르츠 수신기(Terahertz Receiver: Rx)를 이용하여 샘플의 진폭(magnitude)과 위상(phase) 정보를 각각 측정하였다. 이 논문에서는 보다 좋은 이미지 해상도를 얻기 위하여 데이터 수집 시 이미지의 분해능(resolution)에 영향을 미치는 주사 스테이지(scanning stage)의 시간 지연과 스텝 거리를 변수로 두어 다양한 샘플들을 주사하여 그 결과를 측정, 비교하였다. 또한 플라스틱, 종이, 나무 등 다양한 샘플들의 이미징 측정을 통해 테라헤르츠 파의 응용 가능성을 확인하였다.

• 비파괴검사학회지
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• 제30권4호
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• pp.352-358
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• 2010

전기적인 장치를 기반으로 한 테라헤르츠 송신기(terahertz transmitter; Tx)를 이용하여 0.34 THz의 전자기파를 발생시키는 소형 CW sub-THz 이미징 시스템을 제시하였다. Tx에 의해 발생된 0.34 THz의 전자기파를 point by point 스캔방식으로 샘플에 투과시켰고, 여기서 얻어진 데이터는 테라헤르츠 수신기(terahertz receiver; Rx)를 이용하여 진폭(magnitude)과 위상(phase) 정보로 측정한 후 이를 영상화하였다. 이 논문에서는 보다 좋은 이미지 해상도를 얻기 위하여 데이터 수집 시 이미지의 분해능(resolution)에 영향을 미치는 주사 스테이지(scanning stage)의 시간지연과 스텝거리를 변수로 두어 다양한 샘플들을 주사하여 그 결과를 측정, 비교하였다. 또한 플라스틱, 종이, 나무 등 다양한 샘플들의 이미징 측정을 통해 테라헤르츠 파의 응용 가능성을 확인하였다.

• 한국생산제조학회지
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• 제21권1호
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• pp.102-108
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• 2012

A study of terahertz waves (T-ray) was made for the nondestructive evaluation of FRP (Fiber reinforced plastics) composite materials. The to-be-used systems were time domain spectroscopy (TDS) and continuous wave (CW). The composite materials investigated include both turbine blades of wind energy (non-conducting polymeric composites) and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was not able to detect a material with conductivity. This was demonstrated in CFRP (Carbon fiber reinforced plastics) laminates. Refractive index (n) was defined as one of mechanical properties; so a method was solved in order solve the "n" in the material with the cut parts of the turbine blades of wind energy. The defects and anomalies investigated by terahertz radiation were foreign material inclusions and simulated disband. Especially, it is found that the T-ray went through the turbine blade with greater thickness (about 90mm).

• 센서학회지
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• 제27권5호
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• pp.328-334
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• 2018

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.

• 한국전자파학회논문지
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• 제21권6호
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• pp.617-626
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• 2010

본 논문에서는 광혼합 방식으로 서브 밀리미터 및 테라헤츠 대역 연속파 신호를 발생시키는 기법 중 가장 널리 사용되는 광반송파가 억제된 양측 대역 발생 방식(Double Sideband-Suppressed Carrier: DSB-SC)을 이용하여 발생된 연속파(Continuous Wave: CW) 신호의 위상 잡음 개선을 위하여 광신호의 편광과 위상 제어 기법을 제안하고 실험적으로 증명하였다. 광신호의 편광 및 위상 제어 기법은 일반적인 DSB-SC 신호와 DSB-SC 신호에 포함된 광반송파와 동일한 파장과 위상차를 가지며, 광반송파의 편광 성분 중 하나의 편광 성분만을 갖도록 편광제어된 광신호를 결합하여 광혼합하는 방법이다. 실험 및 측정 결과, 서브 밀리미터파 대역 CW 신호의 크기는 1.5 dB 증가하였으며, 위상 잡음 특성은 약 3 dB@10 kHz offset frequency 개선됨을 확인하였다. 따라서 본 논문의 결과는 광신호의 위상 및 편광 성분 제어만으로 광반송파를 효과적으로 억제하여 서브 밀리미터 및 테라헤르츠 대역 CW 신호의 특성을 개선함으로써 광혼합 방법을 이용한 밀리미터파 및 테라헤르츠파 대역 CW 신호 발생기의 저가화를 위한 기본적인 데이터로서 활용 가치가 높다.

• 공학기술논문지
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• 제11권4호
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• pp.245-251
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• 2018

Terahertz waves (T-ray) was extensively studied for the NDE (nondestructive evaluation) of characterization of trailing edges for a use of turbines composed with composite materials. The used NDE system were consisted of both CW(Continuous wave) and TDS (Time domain spectroscopy). The FRP composites were utilized for two kinds of both trailing edges of wind energy (non-conducting polymeric composites) and carbon fiber composites with conducting properties. The signals of T-ray in the TDS (Time domain spectroscopy) mode resembles almost that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity unlike ultrasound. Also, a method was suggested to obtain the "n" in the materials, which is called the refractive index (n). The data of refractive index (n) could be solved for the trailing edges. The trailing edges were scanned for characterization and inspection. C-scan and B-scan images were obtained and best optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. Especially, it is found that the defect image of T-ray corresponded with defect locations for the trailing edges of wind mill.

• ETRI Journal
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• 제38권4호
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• pp.665-674
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• 2016

We designed and fabricated a semiconductor optical amplifier-integrated dual-mode laser (SOA-DML) as a compact and widely tunable continuous-wave terahertz (CW THz) beat source, and a pin-photodiode (pin-PD) integrated with a log-periodic planar antenna as a CW THz emitter. The SOA-DML chip consists of two distributed feedback lasers, a phase section for a tunable beat source, an amplifier, and a tapered spot-size converter for high output power and fiber-coupling efficiency. The SOA-DML module exhibits an output power of more than 15 dBm and clear four-wave mixing throughout the entire tuning range. Using integrated micro-heaters, we were able to tune the optical beat frequency from 380 GHz to 1,120 GHz. In addition, the effect of benzocyclobutene polymer in the antenna design of a pin-PD was considered. Furthermore, a dual active photodiode (PD) for high output power was designed, resulting in a 1.7-fold increase in efficiency compared with a single active PD at 220 GHz. Finally, herein we successfully show the feasibility of the CW THz system by demonstrating THz frequency-domain spectroscopy of an ${\alpha}$-lactose pellet using the modularized SOA-DML and a PD emitter.

• 전자통신동향분석
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• 제33권3호
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• pp.59-69
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• 2018

Terahertz (THz) imaging and spectroscopy have been developed as non-destructive testing methods for various industrial applications. However, they have not been widely adopted in real applications owing to a high system price and the large size of conventional THz time-domain spectroscopy systems, which are based on ultrashort optical pulse lasers. Recently, various types of compact THz emitters and detectors have become available. As a result, THz non-destructive test (NDT) systems have become viable solutions. Herein, we briefly review the recent advances in THz NDT techniques adopting continuous-wave THz systems, including our recent results of a THz-based waterproof test system and an electrical connection inspection system for car manufacturing.