• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.135-137
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• 2002

In the favor of adjusting microwave signal, Hairpin type Filter, which delay microwave signal enough to several nanosecond, is a key component. One of the main advantage in using Hairpin type Filter is a conveniency for equipping with Delay Module, and because of having a wide bandwidth, Hairpin type Filter can be designed to satisfy the most applications. In this work, we attempted to estimate the delay time in a superconductive hairpin type filter A software to synthesize even and odd order equiripple hairpin type filter has been developed. This software arbitrarily locate its transfer zeros making symmetric of asymmetric amplitude response and equalizing group delay. Borland C++ compiler has been used. The program was designed to run under MS-DOS, Window 98, Window 2000. The program optimizes the position of the transfer function zeros in order to fulfill the group delay specification masks. We designed and fabricated a hairpin type HTS 2-pole microstrip bandpass filter to operate at 5.8Ghz. The fabrication method was pulsed laser deposition and YBCO films were deposited on sapphire substrates with a Ce$O_{2}$ thin layer as a buffer layer. We also developed a new style hairpin type filter by using interdigitide inner-pole. Compared to the same size regular hairpin type filters, our filters had a lower center frequency.

• Journal of the Optical Society of Korea
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• 제11권4호
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• pp.192-195
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• 2007

A high-conversion efficiency, nanosecond pulsed optical parametric generation and amplification with repetition rate of 20 kHz based on a periodically poled MgO-doped stoichiometric lithium tantalate was presented. Pumped by a Q-switched $Nd:YVO_4$ laser at 1064 nm with a pumping power of 4.8W, the generated output power was 1.6W for the signal and idler waves, achieving a slope efficiency of 50%. Using a seed source at signal wave the amplified signal output-pulse energy reached $65{\mu}J$. The obtained maximum gain was 72.4 dB.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.369-369
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• 2016

A nanostructure composite is a highly suitable substance for photoacoustic ultrasound generation. This allows an input laser beam (typically, nanosecond pulse duration) to be efficiently converted to an ultrasonic output with tens-of-MHz frequency. This type of energy converter has been demonstrated by using a carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite film that exhibit high optical absorption, rapid heat transition, and mechanical durability, all of which are necessary properties for high-amplitude ultrasound generation. In order to develop the CNT-PDMS composite film, a high-temperature chemical vapor deposition (HTCVD) method has been commonly used so far to grow CNT and then produce a CNT-PDMS composite structure. Here, instead of the complex HTCVD, we use a mixed solution of hydrophobic multi-walled CNT and dimethylformamid (DMF) and fabricate a solution-processed CNT-PDMS composite film over a spherically concave substrate, i.e. a focal energy converter. As the solution process can be applied over a large area, we could easily fabricate the focal transmitter that focuses the photoacoustic output at the moment of generation from the CNT-PDMS composite layer. With this method, we developed photoacoustic energy converters with a large diameter (>25 mm) and a long focal length (several cm). The lens performance was characterized in terms of output pressure amplitude for an incident pulsed laser energy and focal spot dimension in both lateral and axial. Due to the long focal length, we expect that the new lens can be applied for long-range ultrasonic treatment, e.g. biomedical therapy.

• 한국광학회지
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• 제33권1호
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• pp.1-10
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• 2022

본 연구에서는 고가의 일반 펄스 레이저 없이 비교적 근거리에서 강한 거리 분해능을 지니며, 원거리에서도 공간 분해능을 지닌 연속광원 레이저를 이용한 미세먼지 라이다를 제안한다. 일반적인 라이다 시스템은 짧은 펄스의 레이저를 사용하고, 특정 거리 사이의 time-of-flight (TOF) 왕복시간을 측정하여 거리 정보를 얻고 있으나, 본 연구에서는 상용 카메라와 연속광 레이저 빔을 조사하여 얻은 영상을 사용하여 공간 분해능을 얻는 새로운 에어로졸 라이다를 소개한다. 본 연구에서는 라이다 신호와 함께 얻은 레이저의 이미지를 사용하여 주어진 하나의 화소에 해당하는 산란 에어로졸까지의 거리와 그 화소에 기여하는 에어로졸의 범위를 계산하였다. 이러한 거리와 기여 범위를 사용하여 거리 분해능을 갖는 에어로졸의 소멸계수를 계산하였으며, 기존 에어로졸 라이더의 경우 400 m 이상에서만 에어로졸 소산계수를 얻을 수 있었지만 제안 된 방법과 주어진 카메라의 조건을 사용하면 수십 미터 이하까지 그 소산계수를 얻을 수 있음을 알 수 있었다.

• Imaging Science in Dentistry
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• 제51권2호
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• pp.107-115
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• 2021

Purpose: This study aimed to demonstrate the presence of dental caries through a photoacoustic imaging system with visible and near-infrared wavelengths, highlighting the differences between the 2 spectral regions. The depth at which carious tissue could be detected was also verified. Materials and Methods: Fifteen permanent molars were selected and classified as being sound or having incipient or advanced caries by visual inspection, radiography, and optical coherence tomography analysis prior to photoacoustic scanning. A photoacoustic imaging system operating with a nanosecond pulsed laser as the light excitation source at either 532 nm or 1064 nm and an acoustic transducer at 5 MHz was developed, characterized, and used. En-face and lateral(depth) photoacoustic signals were detected. Results: The results confirmed the potential of the photoacoustic method to detect caries. At both wavelengths, photoacoustic imaging effectively detected incipient and advanced caries. The reconstructed photoacoustic images confirmed that a higher intensity of the photoacoustic signal could be observed in regions with lesions, while sound surfaces showed much less photoacoustic signal. Photoacoustic signals at depths up to 4 mm at both 532 nm and 1064 nm were measured. Conclusion: The results presented here are promising and corroborate that photoacoustic imaging can be applied as a diagnostic tool in caries research. New studies should focus on developing a clinical model of photoacoustic imaging applications in dentistry, including soft tissues. The use of inexpensive light-emitting diodes together with a miniaturized detector will make photoacoustic imaging systems more flexible, user-friendly, and technologically viable.