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Febry-Perot 간섭계를 이용한 강유전 P(VDF-TrFE) 폴리머 열광학 특성평가
송현철,김진상,윤석진,정대용,Song, Hyun-Cheol,Kim, Jin-Sang,Yoon, Seok-Jin,Jeong, Dae-Yong 한국재료학회 2009 한국재료학회지 Vol.19 No.4
Phase transition in ferroelectric polymer is very interesting behavior and has been widely studied for real device applications, such as actuators and sensors. Through the phase transition, there is structural change resulting in the change of electrical and optical properties. In this study, we fabricated the Febry-Perot interferometer with the thin film of ferroelectric P(VDF-TrFE) 50/50 mol% copolymer, and thermo-optical properties were investigated. The effective thermo-optical coefficient of P(VDF-TrFE) was obtained as $2.3{\sim}3.8{\times}10^{-4}/K$ in the ferroelectric temperature region ($45^{\circ}C{\sim}65^{\circ}C$) and $6.0{\times}10^{-4}/K$ in the phase transition temperature region ($65^{\circ}C{\sim}85^{\circ}C$), which is a larger than optical silica-fiber and PMMA. The resonance transmission peak of P(VDF-TrFE) with the variation of temperature showed hysteretic variation and the phase transition temperature of the polymer in heating condition was higher than in the cooling condition. The elimination of the hysteretic phase transition of P(VDF-TrFE) is necessary for practical applications of optical devices.
주파수 조정에 따른 에너지 하베스팅용 압전 캔틸레버의 특성
김형찬,송현철,정대용,김현재,윤석진,주병권,Kim, Hyung-Chan,Song, Hyun-Cheol,Jeong, Dae-Yong,Kim, Hyun-Jai,Yoon, Seok-Jin,Ju, Byeong-Kwon 한국재료학회 2007 한국재료학회지 Vol.17 No.12
Piezoelectric energy harvesting from our surrounding vibration has been studied for driving the wireless sensor node. To change the vibration energy into the electric-energy efficiently, the natural frequency of cantilever needs to be adjusted to that of a vibration source. When adding 6.80g mass on the end of the fabricated cantilever, a natural frequency shifts from 136 Hz into 49.5 Hz. In addition, electro-mechanical coupling factor increased from 10.20% to 11.90% and resulted in the 1.18 times increase of maximum output power.
한국어판 일상 생활 스트레스 척도(K-DSI)의 표준화 연구
조숙행,이현수,송현철,김승현,서광윤,신동균,고승덕,Joe, Sook-Haeng,Lee, Hyeon-Soo,Song, Hyun-Cheol,Kim, Seung-Hyun,Sub, Kwang-Yun,Sin, Dong-Kyun,Ko, Seung-Duk 한국정신신체의학회 2000 정신신체의학 Vol.8 No.1
연구목적 : 본 연구에서는 일상 생활에서 흔히 경험하는 사소한 스트레스 요인들을 측정하는데 민감한 척도인 일상생활 스트레스 명가 척도의 한국어판(K-DSI)올 표준화함으로써 정상인에서의 규준표를 제시하고자 하였다. 방법 : 19세 이상의 정상인 524명을 대상으로 한국어판 일상생활 스트레스 평가 척도의 58개 문항을 일주일 동안 연속적으로 매일 작성하도록 하였다. 마지막날에 상태-특성 불안 척도(STAI)와 Beck 우울척도(BDI), 사회 재적용 평가 척도(SRRS)를 작성하도록 하였다. 인구학적 변인에 따라 K-DSI의 사건, 영향, 영향/사건 비율 점수를 비교 분석하였으며(ANOVA or t-test). 변량 분석의 사후 검증 방법으로 Scheffe's test를 사용하였다. 내적 일치도를 통해 신뢰도를 검증하고. BDI, STAI, SRRS 점수와의 상관 분석을 통해 수렴 타당도를 검증하였다. K-DSI 점수들의 백분율 분포에 근거하여 규준표를 작성하였다. 결과 : K-DSI 점수는 남성에 비해 여성에서, 나이가 젊을수록 학력이 높을수록 높았으며, 5개의 하부 요인 범주 중 인지적 스트레스 요인들이 가장 많은 것으로 나타났다. K-DSI의 내적 일치도는 Chrombach $\alpha$값이 .99로 높게 나타났으며, BDI, STAI, SRRS 점수와 K-DSI의 일일 및 주간 사건, 영향 접수는 유의한 상관관계를 보여주었다. 백분율 분포에서 75%에 해당되는 사건 접수는 17점, 영향 접수는 57점, 영향/사건 비율은 3.48~3.49점이었으며, 1주일 사건 접수는 118~124점이고, 1주일 영향 점수는 368~389점, 영향/사건 비율은 3.47~3.48점이었다. 또한 95%에 해당하는 사건 점수는 57점, 영향 점수는 151~161점, 영향/사건 비율은 4.72~4.86점이었으며, 1주일 사건 점수는 405점이고, 1주일 영향 접수는 1038~1122점, 영향/사건 비율은 4.46~4.56점이었다. 결론 : DSI의 신뢰도와 타당도가 만족스러운 수준을 보였고 인구학적 특성에 따라 흥미로운 결과가 나타남으로써 임상적 유용성이 검증되었다. 무엇보다도 규준을 스트레스 경험의 평가에 대한 객관적인 비교기준이 될 수 있는 규준자료를 제시하였다는데 큰 의의가 있다고 할 수 있다. Objectives : This study was to provide normative data of Korean version of DSI(K-DSI), a sensitive measure of relatively minor stressors that could be administered daily. Methods : K-DSI was administered in 524 adults, age of 19 or over, daily for 1 week. On the seventh day, Becks Depression Inventory(BDI), State-Trait Anxiety Inventory(STAI), and Social Readjustment Rating Scale(SRRS) were also given to test the convergent validity. Analyses(ANOVA or t-test) were conducted to examine the potential effects of demographic variables on K-DSI score. Internal consistency for reliability and Pearson's corelation coefficient with BDI, STAI, SRRS for convergent validity were computed. Percentile scores were calculated for daily and weekly K-DSI Event, Impact and I/E Ratio scores. Results : K-DSI scores in women were higher than those in men. According to age and educational level, the younger and the higher educational level the normative groups were, the higher were K-DSI scores. Among the 5 categories of the inventory, the category of cognitive stressors was highest. Internal consistency of K-DSI(Cronbach's $\alpha$) was .99. Daily and Weekly events and impacts scores were significantly correlated with the scores of State-Trait Anxiety Inventory, Social Readjustment Rating Scale, and Beck Depression Inventory. 75 percentile scores of the daily/weekly Events, Impacts, and I/E ratio were 17/118 - 124, 57/368 - 389 and 3.48 - 3.49/3.47 - 3.48 respectively. And 95 percentile scores of daily/weekly Events, Impacts, and I/E ratio were 57/151- 161, 405/1038 - 1122, and 4.72 - 4.86/4.46 - 4.56 respectively. Conclusion : Reliability and validity of K-DSI were tested satisfactorily. Authors presented the normative data of K-DSI for Koreans. K-DSI could be a useful measure in clinical settings or researches to assess the minor stressors frequently experienced in everyday life.
허성훈(Sunghoon Hur),김현수(Hyun Soo Kim),송현철(Hyun-Cheol Song) 한국세라믹학회 2021 세라미스트 Vol.24 No.3
Wireless energy transfer (WET) is the transmission of electric power without any physical connections such as wires. Currently, inductive coupling mediated by electromagnetic (EM) waves is the most common method of WET and is widely used to charge portable devices such as smartphones, Bluetooth earphones, electric shavers, and visual prostheses. However, its application is still limited due to a number of issues including low efficiency, short charging distance, heating problem, and limited choice of transmission medium. Due to these issues, EM-based WET cannot be applied to implantable medical devices, marine cable operation sensors, and electronic devices with electromagnetic interference shielding. Recently, as an alternative to EMbased WET, acoustic energy transfer mediated by sound waves becomes more attractive. Ultrasound offers advantages for transmission in dense media such as liquids or solids and is regardless of electromagnetic shielding. In this review, we investigate recent progress in acoustic power transfer technology in terms of acoustic energy conversion mechanism and provide the future research direction of acoustic power transfer technology.
이동규(Dong-Gyu Lee),이연정(Yeon-Jeong Yee),송현철(Hyun-Cheol Song) 한국세라믹학회 2019 세라미스트 Vol.22 No.1
Recent advances in low-power sensors and transmitters are driving the search for standalone power sources that utilize unused ambient energy. These energy harvesters can alleviate the issues related to the installation and maintenance of sensors. Particularly piezoelectric energy harvesters, with the ability to convert ambient mechanical energy into useful electricity, have received significant attention due to their high energy density, low cost and operational stability over wide temperature and pressure conditions. In order to maximize the generated electrical power, the natural frequency of the piezoelectric energy harvester should be matched with the dominant frequency of ambient vibrations. However, piezoelectric energy harvesters typically exhibit a narrow bandwidth, thus, it becomes difficult to operate near resonance under broadband ambient vibration conditions. Therefore, the resonating of energy harvesters is critical to generate maximum output power under ambient vibration conditions. For this, energy harvesters should have broadband natural frequency or actively tunable natural frequency with ambient vibrations. Here, we review the most plausible broadband energy harvesting techniques of the multi-resonance, nonlinearity, and self-resonance tuning. The operation mechanisms and recent representative studies of each technique are introduced and the advantages and disadvantages of each method are discussed. In addition, we look into the future research direction for the broadband energy harvester.