• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.83-87
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• 2015

This study was focused on developing an optical sensor that monitors ultraviolet (UV) light. Recently, we proposed and demonstrated a novel, highly sensitive UV sensor based on a fiber Bragg grating (FBG). To ensure that the incident UV light is focused on the FBG surface, the sensor was coated with an azobenzene polymer material that acts as a UV-induced stretchable functional material, in combination with a cylindrical focal lens. In this study we have improved the sensitivity of the sensor by employing a cylindrical focal mirror as a curved reflector, to refocus the UV light passing through the FBG. We considered the performance of several different types of reflectors and chose the optimal radius of curvature for the reflector. Compared to the UV sensor without an auxiliary device, the sensitivity of the FBG sensor with a focal lens and a curved reflector was 15 times as high.

• Polymer(Korea)
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• v.28 no.5
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• pp.361-366
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• 2004

The poling characteristics of PVDF (poly(vinylidene fluoride)) film was investigated by measuring the electric voltage generated by the external load for the distributed tactile sensor applications. The poling conditions for the PVDF films were controlled by changing temperature and electric field, and the resulting crystal structure of the $\beta$-phase crystal was confirmed by FT-IR, DSC, and XRD experiments. The $\beta$-phase crystal was increased with the poling temperature and poling voltage, and subsequently the permittivity of the Poled PVDF films was increased. Finally, the prototype tactile sensor was tested by a 8 $\times$ 8 may circuit exhibiting high voltage signal for the highly poled PVDF films.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.4 s.247
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• pp.364-372
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• 2006

In this paper, we present a finger tip tactile sensor which can detect contact normal force as well as slip. The sensor is made up of two different materials, such as polyvinylidene fluoride (PVDF) known as piezoelectric polymer, and pressure variable resistor ink. In order to detect slip on the surface of the object, two PVDF strips are arranged along the normal direction in the robot finger tip and the thumb tip. The surface electrode of the PVDF strip is fabricated using silk-screening technique with silver paste. Also a thin flexible force sensor is fabricated in the form of a matrix using pressure variable resistor ink in order to sense the static force. The developed tactile sensor is physically flexible and it can be deformed three-dimensionally to any shape so that it can be placed on anywhere on the curved surface. In addition, a tactile sensing system is developed, which includes miniaturized charge amplifier to amplify the small signal from the sensor, and the fast signal processing unit. The sensor system is evaluated experimentally and its effectiveness is validated.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.101-108
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• 2003

Polymeric positive temperature coefficient(PTC) composites have been prepared by incorporating carbon black(CB) into high density polyethylene(HDPE), polyphenylene sulfide(PPS) and polybutylene terephthalate(PBT) matrices. A PTC effect was observed in the composite, caused by the large thermal expansion due to He consecutive melting of HDPE, PPS and PBT crystallites. This theory is based upon the premise that the PTC phenomenon is due to a critical separation distance between carbon particles in the polymer matrix at the higher temperature. The influence of PTC characteristics of the PPS/CB composite can be explained by DSC result. HDPE, one of prepared composition, exhibit the higher performance PTC behavior that decreaseing of negative temperature coefficient(NTC) effect and improved reproducibility by chemically crosslinking. Also, PBT/CB and PPS/CB composites exhibit the higher PTC peack temperature than HDPE/CB PTC composite, individually $200^{\circ}C$ and $230^{\circ}C$. These PTC composite put to good use in a number of safety application, such as self$.$controlled heater, over-current protectors, auto resettable switch, high temperature proctection sensor, etc.

• Journal of Sensor Science and Technology
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• v.32 no.5
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• pp.280-284
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• 2023

In this study, a prototype micro-scale photomask and microfluidic channel mold were fabricated using the thermal shrinkage of the polymer. A polystyrene (PS) sheet was used as the heat-shrink polymer, and the patterns of the photomask and microchannel are interdigitated electrodes. Patterns were formed on the PS sheets using a commercial laser printer. The contraction ratio of the PS sheet was approximately 60% at a temperature of 150 ℃, and the transmittance was reduced by approximately 0% at a wavelength of 365 nm. The microfluidic channel had a round shape. The proposed technique is simple, facile, and inexpensive for fabricating a micro-scale photomask and microfluidic channel mold and does not involve the use of any harmful materials. Thus, this technique is well-suited for fabricating diverse micro-scale patterns and channels for prototype devices, including sensors.

• Journal of Sensor Science and Technology
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• v.21 no.5
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• pp.345-351
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• 2012

Biomimetic terpene sensors which have high sensitivity and stability have been fabricated using moleculary imprinted polymer (MIP) technology. Since it is impossible to make a resistive type sensor due to the high resistance of MIP, we improved the sensor by adding conductive polymers. We investigated the sensitivity of resistive type sensors with nano particles depending on the amount of conductive polymers. The MIP membrane contained the methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross linker, which formed specific cavities originated by the target terpene molecules. The mixture of MIP and the conductive polymer was coated on the patterns of interdigit electrodes on the alumina substrate. The fabricated sensors showed their highest specific sensitivities exposed to 500 ppm target gases : limonene 0.055 at 40% of amount of conductive polymers and geraniol $5.84{\times}10^{-4}$ at 20% of amount of conductive polymers. In conclusion, we found that the terpene sensors are affected by the target molecules, functional monomers and the conductive polymers.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.155-156
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• 2013

• Journal of Sensor Science and Technology
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• v.11 no.6
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• pp.335-341
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• 2002

In this paper, we investigated a novel UV sensor using evanescent field coupling between the side polished fiber and photo-functional polymer waveguide. It was found that resonant wavelength shifts occur due to variation in the refractive index of polymer planar waveguide for its photo-functional properties on exposed UV. Spiroxazine (photochromic dye) was used as the planar waveguide. The resonant wavelength responses were exhibited at 1.44 nm/mW, 1.64 nm/mW, and 1.78 nm/mW when UV irradiations were exposed for 20 seconds, 30 seconds, and 40 seconds, respectively. The recovery time of sensor was independent of UV exposure power and 90% recovery time was 100 seconds.

• Journal of Sensor Science and Technology
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• v.14 no.6
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• pp.395-401
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• 2005

A highly stable quartz crystal microbalance (QCM) that showed a stability of frequencies and exhibited a very low noise level has been developed. The long-term drift was <0.05 Hz/h over a period of 10 h, and the short-term rms (root mean square) noise was <0.015 Hz. Our QCM sensor was used as a humidity sensor employing a poly(methyl methacrylate) (PMMA) polymer film as a hygroscopic layer, which showed good characteristics in the relative humidity (RH) range of $2{\sim}90%$ RH. Comparing the characteristics of the QCM sensor with those of other types of humidity sensors employing PMMA film as a hygroscopic layer, and with other QCM sensors employing other hygroscopic layers is represented.

• Journal of Sensor Science and Technology
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• v.20 no.6
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• pp.375-381
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• 2011

Ionic polymer-metal composite(IPMC) consists of an ion conductive membrane plated by metallic electrodes on both surfaces. When it bends, a voltage is generated between two electrodes. Since IPMC is flexible and thin, it can be easily mounted on the various surfaces of a body. The present study investigates a sensor system using IPMC to effectively detect the bending angles applied on IPMC sensor. The paper evaluates several R and C circuit models that describe the physical composition of IPMC and selects the best model for the detection of angles. The circuit models implemented with a charge model describe the relationship between input bending angles and output voltages. The identification of R and C values was performed by minimizing the error between the real output voltages and the simulated output voltages from the circuit models of IPMC sensor. Then the output signal of a sensor was fed into the inverse model of the identified model to reproduce the bending angles. In order to support the validation of the model, the output voltages from an arbitrary bending motion were also applied to the selected inverse model, which successfully reproduced the arbitrary bending motion.