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RISS 인기검색어
- 검색키워드
- 저자 : Mijin Kim (검색결과 13 건)
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Fabrication and Analysis of Flexible Magnetic Sensor
In this thesis, we have fabricated flexible magnetic sensors using PDMS and Parylene C polymers for substrate instead of Si/SiO2, as Si/SiO2 being a hard substrate, cannot with-stand external stress. Here, we have also analyzed the performance of flexible magnetic sensors depending on the tensile stress due to the curvature of polymer substrates and in addition, we have analyzed mechanical and thermal properties such as stress, bending, reversibility to bending, and stability to temperature. The flexible magnetic sensor was fabricated as PHR (Planar Hall Magnetoresistance) sensor which has advantage of higher signal-to-noise ratio, low offset voltage, almost zero hysteresis signal and good linearity. Also, the magnetization behavior of sensors based on external magnetic field and human body temperature variation have been studied here and the magnetic properties of the magnetoresistive sensors were also analyzed. When the sensor was deposited directly on the PDMS, many cracks were formed during the sputtering process due to the difference between the thermal expansion coefficient of the metal film and the PDMS substrate, and hence the sensor signal did not appear in bend-ing state. We prevented the crack formation by inserting a parylene C layer in the interface between the metal film and the PDMS substrate. However, many cracks were still observed in the above mentioned type of sensor at a certain bending curvature because of tensile stress. Thus, the sensor film located on the top where the maximum stress is concentrated was inserted in the middle of the parylene C layers to relieve the stress. As a result, the sensor located in the middle of the parylene C layers exhibited stable output voltage and sensitivity depending on bending, and it also had reversibility after bending and stability for human body temperature variation. 본 논문은 외부 응력을 견딜 수 없는 Si / SiO2 기판 대신에 PDMS와 Parylene C 중합체를 사용하여 유연한 자기 센서를 제작하여, 기판의 곡률에 의한 인장 변형의 효과에 의한 유연자기센서의 성능을 분석하고, 다양한 온도와 외부 자기장을 기반으로 한 센서의 자화 거동을 분석하고 자기 저항 센서의 자기적 성질도 분석하였다. 우선 베이스 용액과 에이전트 용액을 10:1로 섞어 80℃에서 3시간 이상 굳힌 기판 PDMS기판 위에 DC 마그네트론 스퍼터링 기법을 이용하여 평면 홀 자기센서(PHR Sensor)를 이중층으로 증착한 뒤 VSM, SEM 및 Curvature에 따른 MR 측정을 해보았지만, Curvature가 0.042918이상의 Convex나 Concave bending을 견디지 못했다. 이는 30nm 이상의 금속박막을 PDMS 기판에 증착하는 경우 자성 박막 물질들의 영스모듈러스와 PDMS의 영스모듈러스가 2~3 order 정도 차이가 나고, 열팽창계수 또한 차이가 많이 나서 자성박막물질 증착 시 인장스트레스가 계속 가해지면서 많은 crack들과 wrinkle들이 형성이 되는 것이다. 따라서 이를 완화시켜줄 물질인 파릴렌을 사용하여PDMS위에 파괴점이 가장 높은 두께인 1μm를 증착하여 기판 (Parylene C- deposited PDMS 기판)으로 이용하였다. 이 기판도 마찬가지로 convex bending (tensile stress) curvature가 0.150588 이상일 경우에 신호가 나오지 않았고, concave bending (compressive stress) curvature가 0.074844만 되어도 신호가 나오지 않았다. 그래서 자성 센서 박막 층 위에 아래의 기판 재료와 같은 Parylene C를 1μm정도 쌓아 encapsulation을 시켜주어 측정한 결과 convex bending 및 concave bending 모두 최대 cur-vature가 0.174807이었고, curvature에 대해 한계점을 가지지 않았다. 또한 bending에 따른 센서의 민감도 및 온도에 따른 MR측정 결과 다른 기판들에 비해서 안정성을 보여주었으며, bend-ing 한 후 다시 flat하게 놓고 MR측정한 결과 한번도 bending을 하지 않았을 경우와 동일한 신호양상을 보여주었다.
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김미진 Graduate School, Yonsei University 2015 국내박사
Two algorithms to retrieve aerosol optical properties (AOPs) over Asia were developed in this study. Continuous monitoring of aerosol amount and transport over the region plays significant role in improving the prediction of air quality change as well as in understanding radiative effect of aerosol. From the reason, a single channel algorithm using visible measurement of a Meteorological Imager (MI) onboard a geostationary orbit satellite, Communication, Ocean, and Meteorological Satellite (COMS), was developed to retrieve aerosol optical depth (AOD) over Asia. The single channel algorithm is based on widely used look-up table (LUT) approach for inversion, and clear sky composite method for surface reflectance estimation. Since the algorithm has limitation in detecting aerosol optical type, the seasonally dependent aerosol model was adopted to calculate the LUTs. The aerosol models consists of refractive indices and volume size distribution with integrated from long-term measurements of Aerosol Robotic Network (AERONET) sun-photometer. For quantitative validation of the algorithm, the AOD from the single channel algorithm was compared with the result of the AERONET direct measurement. The comparison showed good agreement especially in spring. However, accuracy of the algorithm has fundamental limitation in the aerosol type selection as mentioned. Thus, the uncertainty induced by aerosol model assumption was analyzed, and improved by modifying inversion dataset. Furthermore, an effect of existence of background aerosol was corrected to improve the accuracy of surface reflectance estimation. Similarly as other retrieval uncertainties, inversion error in the LUT approach and instrument calibration error was analyzed in quantitative manner. Besides, critical reflectance method was introduced to overcome the limitation in aerosol type selection. In spite of the advantage of the continuous monitoring of AOD change, lack of information about scattering property results in increaseing uncertainty in understanding radiative effects of aerosol over Asia. From the reason, a multi-channel algorithm utilizing near ultra-violet (UV) measurements was developed to retrieve AOD and single scattering albedo (SSA). The algorithm used the optimal estimation (OE) method to reduce the retrieval uncertainty induced by assumption of aerosol loading height. The algorithm retrieved a priori states of retrieval values by using two channel LUT approach, and the a priori states were applied to find optimized solution to minimize difference between measured and simulated spectrum. The algorithm was developed for the planned Geostationary Environment Monitoring Spectrometer (GEMS) measurement to be launched in 2018, but was tested by using the measurement of Ozone Monitoring Instrument (OMI). An advantage of the UV-Vis algorithm lies in the self-sufficiency in a priori state. However, the large sensitivity to the a priori value in the retrieval of aerosol loading height is one of limitation of the algorithm. This study focused on the improvement of the satellite measurement of aerosol information over Asia, and presents the two aerosol retrieval algorithms developed by using UV-Vis and visible measurement. After the launch of GEMS, continuous monitoring of AOPs from multi-geostationary measurements is expected to be realized. The results can contribute to estimate its effects on regional climate change, and also can be applied to improve the air quality forecast via data assimilation system.
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Design and application of a new multi-pass system using a concept of optical loop
김미진 Graduate School, Yonsei University 2012 국내석사
It has been scientifically and medically demonstrated that nanoparticles have diversified harmful impacts on human body. Accordingly, Technologies based on many different principles have been developed to measure particles quantitatively and accurately. Among them, optical diagnostics such as LII (Laser Induced Incandescence) and LIF (Laser Induced Fluorescence) have been actively studied. One of their advantages is that they enable the in-situ and real-time measurements. In particular, laser extinction method (LEM) has the additional advantages: simplicity of the system and applicability of low power light source. Moreover, by applying LEM, particle measurement becomes possible in thinner environment because LEM has relatively high detecting sensitivity among laser-based measurement methods. The multi-pass cell is a system which can strengthen those advantages of LEM. Existing multi-pass cells consist of plane or convex mirrors and extend the optical path length by aligning the mirrors. With those systems, beam alignment is quite difficult. Besides, in case of measuring highly adhesive particles inside the cell, such optics as windows and mirrors would encounter contamination problems. Unfortunately, most of the harmful particles including particulate matter emission from diesel engine are viscous. In this study, the optical-loop type multi-pass system is newly developed. With the optical loop type multipass cell, window contamination can be easily prevented and beam alignment is also relatively simple. In this study, a new algorithm was developed by applying the concept of the control loop feedback mechanism to the optical path. Then, the algorithm was validated by experiments. Finally, the validated optical-loop type multi-pass system was applied to the nanoparticles measurement. The logic of control loop feedback mechanism is as in the following. Firstly, the input signal is changed by certain functions while passing through the system. Then, the changed signal becomes a feedback signal influencing the subsequent events so affects to the output signal. The calculated results from ideal optical loop algorithm suggest the optical loop type multipass cell improve detecting sensitivity of LEM at least twice compared to the single-pass cell. However, within actual experimental system, scattering and absorption coefficient of the optical component itself should have negative effects on the overall efficiency of the system. Considering it, correction factors were added to the algorithm, making the realistic optical loop algorithm. The main optical components used for the hardware implementation of optical loop algorithm were a beam splitter and mirrors. A beam splitter played a role in separating the attenuated signal for a certain proportion, rt/r. The calculated results show that the degree improvement in detecting sensitivity varies with the rt/r of the beam splitter. According to the calculation, the optimal value of rt/r is in 0.4 to 0.5. Prior to application to actual particle measurement, preliminary experiments were conducted in order to confirm the effectiveness of the system. The detecting sensitivity of optical-loop type multi-pass system was observed while rt/r varied by 0.5, and 1(single pass). Moreover, Experimental and calculated values were compared with different extinction factors within the multi-pass cell. The error between two values was 3.5 or below. As a final step, the validated optical-loop type multi-pass cell was applied to measure nanoparticles. The particles used in this experiment were generated by using Jing's soot generator Model 5202. These particles are products of the propane-air combustion and are self-adhesive. The particles from soot generator were sampled and dispersed interior the LEM cell. The volume fraction of particles inside LEM cell could be estimated by extrapolating from the detected signal intensity with optical-loop algorithm. According to the results, optical loop type multipass system enhances the detecting sensitivity of LEM up to 2.25 times while S/N ratio remained in order of 10^2.
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A two-hit stress, a combination of stresses in early life and adulthood, increases vulnerability for mental illness and then triggers the onset of depression. Previous studies reported that n-3 polyunsaturated fatty acids (PUFAs) have antidepressantlike effects on depression in rats with acute or chronic stress. The purpose of the present study was to investigate the hypothesis that supplementation of n-3 PUFAs had antidepressant-like effects in adult male pups with two-hit stress through a brain-derived neurotrophic factor (BDNF)-serotonergic mechanism. Male pups were fed a modified AIN-93G diet with 0% or 1% n-3 PUFAs relative to total energy intake during the pre-weaning, post-weaning, or lifetime period. In addition, male pups were allocated to daily 3-h maternal separation (MS) in early life, and chronic mild stress (CMS) including seven different stressors in adulthood. CMS and two-hit stress significantly increased depressive behaviors in forced swimming test and sucrose preference test, and decreased hippocampal expressions of cAMP response element binding protein (CREB), phosphorylated CREB (pCREB), BDNF, serotonin 1A receptor (5-HT1AR) compared to non-stress and CMS alone, respectively. Moreover, two-hit stress had more severe depressive effects than CMS alone. Regardless of stress type, supplementation of n-3 PUFAs improved depressive behaviors and increased hippocampal expressions of CREB, pCREB, BDNF, 5-HT1AR. Furthermore, pre-weaning or post-weaning supplementation of n-3 PUFAs had similar antidepressant-like effects compared to control diet during lifetime. In addition, lifetime supplementation of n-3 PUFAs had the greatest antidepressant-like effects. The present study suggested that n-3 PUFA supplementation had antidepressant-like effects on depression induced by a two-hit stress through BDNF-serotonergic mechanism in adult male pups.
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