• Journal of Korean Society for Atmospheric Environment
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• v.27 no.6
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• pp.663-671
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• 2011

Although a scooter is a convenient transportation means for a short distance traveling with a light package in the congested urban center, it might be one of the significant sources of air pollutants to which many people can easily be exposed during its passing-by. In this paper, we measured concentrations of gases and particles emitted from a scooter at roadside with no other traffic. To understand the characteristics of scooter emissions with respect to driving speed (idling, 30 km/h) at the roadside, total particle number concentration, particle size distribution, average surface area of particles deposited in the alveolar region, and concentrations of black carbon, CO, and $NO_x$ were measured. The concentrations of the particle number, surface area of deposited particles, CO, and $NO_x$ were highly fluctuated in the scooter's idling condition. The trends of particle number concentration, CO, and $NO_x$ generation were similar to one another. When the scooter started to move, all of $NO_x$, CO and particle number concentrations increased and after it passed by at the speed of 30 km/h, the concentration peaks of the particles and gases appeared at the same time. Unimodal size distribution with ~70 and ~93 nm mode diameters was observed for the idling and cruising condition, respectively. From this work, we found that emission from a passing vehicle could be characterized using a roadside monitoring technique.

• Korean Journal of Materials Research
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• v.33 no.5
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• pp.195-204
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• 2023

Micro-electronic gas sensor devices were developed for the detection of carbon monoxide (CO), nitrogen oxides (NO_x), ammonia (NH₃), and formaldehyde (HCHO), as well as binary mixed-gas systems. Four gas sensing materials for different target gases, Pd-SnO₂ for CO, In₂O₃ for NO_x, Ru-WO₃ for NH₃, and SnO₂-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were then fabricated using a micro sensor platform. The gas sensing behavior and sensor response to the gas mixture were examined for six mixed gas systems using the experimental data in MEMS gas sensor arrays in sole gases and their mixtures. The gas sensing behavior with the mixed gas system suggests that specific adsorption and selective activation of the adsorption sites might occur in gas mixtures, and allow selectivity for the adsorption of a particular gas. The careful pattern recognition of sensing data obtained by the sensor array made it possible to distinguish a gas species from a gas mixture and to measure its concentration.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.601-604
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• 1998

NOX detecting gas sensors using TiO2 doped tungsten oxide semiconductor were prepared and their electrical and sensing characteristics have been investigated. In normal air condition, the sensors of WO3, TiO2 doped WO3 show grain boundary heights of 0.34 eV, 0.25 eV, respectively. The grain boundary barrier energy variation was increased by doping TiO2 into large variation of resistance to NOX gases. And doping the TiO2 4 wt.%, the particle size of WO3 polycrystal films showed higher sensitivity and better sorption characteristics to NOX gas than the pure WO3 films material in air at operating temperature of $350^{\circ}C.$ The TiO2 doped WO3 semiconductor gas sensor shows nano-sized particle size and good sensitivity to sub-ppm concentration of NOX.

• Journal of Sensor Science and Technology
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• v.31 no.6
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• pp.455-460
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• 2022

Brush-like ZnO hierarchical nanostructures decorated with MgxZn1-xO (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were fabricated and examined for application to a gas sensor. They were synthesized using vapor phase growth (VPG) on indium tin oxide (ITO) substrates. To generate electronic accumulation at ZnO surface, MgZnO nanoparticles were prepared by sol-gel method, and the ratio of Mg and Zn was adjusted to optimize the device for NO₂ gas detection. As the electrons in the accumulation layer generated by the heterojunction reacted faster and more frequently with the gas, the sensitivity and speed improved. When tested as sensing materials for gas sensors at 100 ppm NO₂ at 300℃, these MgZnO decorated ZnO nanostructures exhibited an improvement from 165 to 514 times compared to pristine ZnO. The response and recovery time of the MgZnO decorated ZnO samples were shorter than those of the pristine ZnO. Various analyzing techniques, including field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) were employed to confirm the growth morphology, atomic composition, and crystalline information of the samples, respectively.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.299-303
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• 2013

In this study, a micro gas sensor for $NO_x$ was fabricated using a microelectromechanical system (MEMS) technology and sol-gel process. The membrane and micro heater of the sensor platform were fabricated by a standard MEMS and CMOS technology with minor changes. The sensing electrode and micro heater were designed to have a co-planar structure with a Pt thin film layer. The size of the gas sensor device was about $2mm{\times}2mm$. Indium oxide as a sensing material for the $NO_x$ gas was synthesized by a sol-gel process. The particle size of synthesized $In_2O_3$ was identified as about 50 nm by field emission scanning electron microscopy (FE-SEM). The maximum gas sensitivity of indium oxide, as measured in terms of the relative resistance ($R_s=R_{gas}/R_{air}$), occurred at $300^{\circ}C$ with a value of 8.0 at 1 ppm $NO_2$ gas. The response and recovery times were within 60 seconds and 2 min, respectively. The sensing properties of the $NO_2$ gas showed good linear behavior with an increase of gas concentration. This study confirms that a MEMS-based gas sensor is a potential candidate as an automobile gas sensor with many advantages: small dimension, high sensitivity, short response time and low power consumption.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.5
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• pp.515-523
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• 2015

In this paper, we fabricated and evaluated the gas sensor for the detection of CO gas and $NO_X$ gas among the vehicle exhaust emission gasses. The $SnO_2$ (tin dioxide) layer is used as the detection material, and the thin-film type and the nano-fiber type layers are deposited with various thicknesses using sputtering method and electro spinning method, respectively. The experiments are performed in the chamber where the gas concentration is controlled with mass flow controller. The fabricated devices are applied to the CO and $NO_X$ gas, where the device with the thinner $SnO_2$ layer shows better sensitivity. The nano-fiber has the larger surface area, and the shorter response time and recovery time are obtained. From the experimental results, both types of gas sensors successfully detect CO and $NO_X$ gases, which can be applied to measure those gases from the vehicle emissions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.499-502
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• 2008

In this work, Ga-doped ZnO (GZO) thin films for gas sensor application were deposited on low temperature co-fired ceramics (LTCC) substrates, by RF magnetron sputtering method. The LTCC substrate is one of promising materials for this application since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.). The LTCC substrates with thickness of $400\;{\mu}m$ were fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The structural properties of the fabricated GZO thin film with thickness of 50 nm is analyzed by X-ray diffraction method (XRD) and field emission scanning electron microscope (FESEM). The film shows good adhesion to the substrate. The GZO gas sensors are tested by gas measurement system and show fast response and recovery characteristics to $NO_x$ gas that is 27.2 and 27.9 sec, recpectively.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.104-109
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• 2005

This paper describes the effect of the split injection on combustion and emission characteristics in a common rail diesel engine at various operating conditions. The combustion pressures and exhaust emissions such as $NO_x$ and soot were measured at various split injection timings. The experimental apparatus of this study is composed of 4 cylinder engine installed with piezoelectric pressure sensor, EC dynamometer, and exhaust gas analyzer for the measurement of $NO_x$, CO, HC and soot emissions. Results show that the split injection has a great effect on reducing the rapid premixed combustion and $NO_x$ emissions.

• Journal of Sensor Science and Technology
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• v.7 no.2
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• pp.103-110
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• 1998

Pyroelectric infrared detectors based on La-modified $PbTiO_{3}$ (PLT) thin films have been fabricated by RF magnetron sputtering and rnicrornachining technology. The detectors form $Pb_{l-x}La_{x}Ti_{1-x/4}O_{3}$ (x=0.05) thin film ferroelectric capacitors epitaxially grown by RF magnetron sputtering on Pt/MgO (100) substrate. The sputtered PLT thin film exhibits highly c-axis oriented crystal structure that no poling treatment for sensing applications is required. This is an essential factor to increase the yield for realization of an infrared image sensor. Micromachining technology is used to lower the thermal mass of the detector by giving maximum sensor efficiency. Polymide is coated on top of the sensing elements to support the fragile structure and the backside of the MgO substrate is selectively etched to reduce the heat loss. The sensing element exhibited a very high detectivity D* of $8.5{\times}10^{8}cm{\cdot}\sqrt{Hz}/W$ at room temperature and it is about 100 times higher than the case of micromachining technology is not used. A sensing system that detects the position as well as the existence of a human body is realized using the array sensor.

• Journal of Sensor Science and Technology
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• v.14 no.4
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• pp.244-249
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• 2005

In this study, radiation sensor tips are fabricated for remote sensing of X or gamma ray with inorganic scintillators and plastic optical fiber. The visible range of light from the inorganic scintillator that is generated by radiation source is guided by the plastic optical fiber and is measured by optical detector and power-meter. Two kinds of sensor tips are designed and fabricated such as film type and powder type. Many kinds of inorganic scintillators are used to fabricate both sensor tips, and the different wavelength of emitting lights from them are measured to determine the optimal inorganic scintillator which has maximum light output. As a radiation source X-ray generator and Ir-192 are selected to test a performance of sensor tip. It is expected that the fiber-optic radiation sensor is widely used in nuclear industry and medical applications due to its special characteristics such as good flexibility, easy in processing, long lengths and no interference to electro magnetic field.