• Journal of ILASS-Korea
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• v.9 no.4
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• pp.67-76
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• 2004

Diode laser absorption sensors are advantageous because they may provide fast, sensitive, absolute, and selective measurements of species concentration. These systems are very attractive for practical applications owing to its compactness, reasonable cost, robustness, and ease of use. In addition, diode lasers we fiber-optic compatible and thus enable simultaneous measurements of multiple species along a line-of-sight. Recent advances of room-temperature, near-IR and visible diode laser sources for telecommunication, optical data storage applications make it possible to be applied for combustion diagnostics based on diode laser absorption spectroscopy. Therefore, combined with fiber-optics and high sensitive detection strategies, compact and portable sensor systems are now appearing for variety of applications. The objectives of this research are to develop new gas sensing system and to verify feasibility of this system. Wavelength modulation spectroscopy has been demonstrated in these experiments and has a bright prospect to this diode laser system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.594-597
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• 2023

We have proposed and demonstrated a fiber optic RH (relative humidity) sensor based on fiber Bragg grating covered with a polyimide film. As the polyimide film absolves the moisture in the air, its volume expands. As a result, the grating period of the FBG (fiber Bragg grating) covered with a polyimide film becomes wide and the Bragg wavelength is shifted. The sensor is implemented by fixing a 30 ㎛ thickness polyimide film on the surface of an optical fiber grating using an adhesive, and the characteristics of the device according to humidity are analyzed. The fabricated FBG RH sensor showed a high sensitivity of 0.0186 nm/RH% and a wide measurement range from 30% to 90%. The influence of environmental temperature on the characteristics of the RH sensor was also measured and analyzed. The feasibility of commercialization is presented.

• Design & Manufacturing
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• v.17 no.3
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• pp.28-33
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• 2023

The conventional FRP (Fiber Reinforced Plastic) manufacturing process used thermoset resins for ease of molding but faced the issue of non-recyclability. To address these shortcomings, a new process utilizing thermal plastic resin was developed. However, due to the high viscosity of thermal plastic resin, problems such as fiber deformation and a reduced fiber volume fraction occurred during the high-temperature, high-pressure process. In this study, to overcome the limitations of the conventional process, fiber-reinforced composite materials were manufactured through in-situ polymerization using PLA (Poly L-Lactide) resin in the VA-RTM (Vacuum Assistance Resin Transfer Molding) process. The fiber volume of the produced specimens was calculated, and resin impregnation and porosity were confirmed through optical microscopy. Additionally, molecular weight analysis using GPC (Gel Permission Chromatography) demonstrated improvements over the conventional process and emphasized the essential requirement of temperature control.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10a
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• pp.77-78
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• 2003

The surface evenness and texture of textile products are closely related with the irregularity of yarn thickness which has an important role to influence the quality and the process efficiency. For measuring yam thickness the capacitive method is known to dominate the market, delivering results that are in a close relation with the mechanical properties of yarn, while the optical method offers information that seems related rather with the apparent quality of yarn. If a thin light beam is applied for the optoelectrical measurement, it is very possible that this method can provide us with important information which is not obtainable from the capacitive type measurement. This paper reports the results of a study about the yarn thickness and its variation on the basis of a new measurement system using a laser slit beam. Analysis of the new system confirms that we can extract new information on the yarn irregularity ranging into much short wavelengths. Even the visual shade created by the yam doubling and twisting can be measured and represented well. Depending on the yam types, the thickness measurements show their own characteristics.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1100-1109
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• 2006

In this study, two different technologies which can measure temperature simultaneously at many points are introduced. One is to use a thermal sensor cable that is comprised of addressable thermal sensors connected in parallel within a single cable. The other is to use an optic fiber with Distributed Temperature Sensing (DTS) system. The difference between two technologies can be summarized as follows. A thermal sensor cable has a concept of 'point sensing' that can measure temperature at accurate position of a thermal sensor. So the accuracy and resolution of temperature measurement are up to the ability of the thermal sensor. Whereas optic fiber sensor has a concept of 'distributed sensing' because temperature is measured by ratio of Stokes and anti-Stokes component intensities of Raman backscatter that is generated when laser pulse travels along an optic fiber. It's resolution is determined by measuring distance, measuring time and spatial resolution. The purpose of this study is that application targets of two temperature measurement techniques are checked in technical and economical phases by examining the strength and weakness of them. Considering the functions and characteristics of two techniques, the thermal sensor cable will be suitable to apply to the assessment of groundwater flow, geothermal distribution and grouting efficiency within 300m distance. It is expected that the optic fiber sensor can be widely utilized at various fields (for example: pipe line inspection, tunnel fire detection, power line monitoring etc.) which need an information of temperature distribution over relatively long distance.

• Journal of Adhesion and Interface
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• v.4 no.1
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• pp.18-27
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• 2003

Interfacial properties and microfailure degradation mechanisms of the oxygen-plasma treated biodegradable poly(p-dioxanone) (PPDO) fiber/poly(L-lactide) (PLLA)composites were investigated for the orthopedic applications as implant materials using micromechanical technique and surface wettability measurement. PPDO fiber reinforced PLLA composite can provide good mechanical performance for long hydrolysis time. The degree of degradation for PPDO fiber and PLLA matrix was measured by thermal analysis and optical observation. IFSS and work of adhesion, $W_a$ between PPDO fiber and PLLA matrix showed the maximum at the plasma treatment time, at 60 seconds. Work of adhesion was lineally proportional to the IFSS. PPDO fiber showed ductile microfailure modes at We initial state, whereas brittle microfailure modes appeared with elapsing hydrolysis time. Interfacial properties and microfailure degradation mechanisms can be important factors to control bioabsorbable composites performance because IFSS changes with hydrolytic degradation.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.333-339
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• 1997

We fabricated a sensor head which consists of spliced different-diameter fiber gratings for discrimination between strain and temperature. Because the fibers were drawn from the same preform, their temperature characteristics were the same but not for strain sensitivities which are inversely proportional to fibers cross-sectional areas. In measurement range of 0-1500$\mu$strain and 20-10$0^{\circ}C$, we could obtain, by using the matrix calculation, the unknown physical quantities within 10% of calculation error compared with the micrometer and thermocouple values. To improve the strain measurement accuracy, we suggest a new, novel method which deploys an unbalanced fiber Mach-Zehnder interferometer. This new signal processing technique converts the strain information to interference signal amplitude variation, temperature-independently. we obtained measurement accuracy nearly 80 times better than that obtainable with the conventional optical spectrum analyzer usage.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.9
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• pp.721-728
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• 1991

In this paper, a magneto-optic modulator has been designed by using single crystal BSO and polycrystal ZnSe as Faraday cells. And practical core-type optical current sensors using pure iron and permalloy have been prepared and experimented. In order to obtain efficient magnetic field detection, LED(NEC OD08358, 0.87 $\mu$m) was used as optical source, PIN-PD(OD-8454)as optical receiver and multi-mode optical fiber (100/140$\mu$m) as transmission line. The characteristics matrix of the optical element was calculated by Stokes parameter, and optic modulation characteristics equations were derived by Muller matrix. Electromagnetic analysis program (FLUX 2D, micro VAX 3600) by finite element method was used to find the magnetic flux density around the core. The measuring error of the output voltage to input current has been masured below 5% in the range of 50A to 1000A. As the temperature was changed from -20$^{\circ}C$ to 60$^{\circ}C$, the maximum measurement error of the optical output has been found to be 0.5% at 60$^{\circ}C$. These experimental results show good temperature and linearity characteristics. The SNR of the overall system was 47dB in case of 600A (250.2 Oe) conductor current and the system has good noise immunity.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1509-1513
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• 2009

The research of applying reinforced retaining wall due to support the land pressure that given from train's load has been accomplished actively in domestic area. After the retaining wall has been installed, the collapse or partial destruction that generated by effect of train's vibration and repetitive load of train may be induced. Accordingly in the period of using this, the sufficient durability should be guaranteed and years of durability are one hundred and as these are longer than road structure's, the technique that introduced to wall and monitor the long-term strain is necessary. In this paper, the optical fibre is induced vertically to the reinforced retaining wall and after the subsistence of optical fibre is confirmed, the early strain that applied to optical fibre after insertion is monitored. Before and after the concrete placing, damage feasibility of optical fibre is measured by using OTDR(Optical Time Domain Reflectometer) and after concrete is cultivated, the early strain induced to optical fibre is measured by application of BOCDA (Brillouin Correlation Domain Analysis) system.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.3
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• pp.400-407
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• 1987

Thin film filter type 4-channel wavelength division multiplexing(WDM) device was designed and fabricated for the application in optical subscriber loop system. It has multi-mode fiber pigtails and four wavelength division consisting of 0.81, 0.89, 1.2 and 1.3 um. The evaluated performances are 1-2d B of insertion loss(connector loss excluded)and 30-35d B of crosstalk attenuation for all channels. The performance of the fabricated device was tested in the wideband optical transmission experiment, where the SNR degradation due to the crosstalk of the device was found to be within a measurement error.