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분산 반사경 기반 패브리-페로 필터를 이용한 비분산적외선 CO<sub>2</sub> 센서의 감지 특성
도남곤 ( Nam Gon Do ),이준엽 ( Junyeop Lee ),정동건 ( Dong Geon Jung ),공성호 ( Seong Ho Kong ),정대웅 ( Daewoong Jung ) 한국센서학회 2021 센서학회지 Vol.30 No.6
Non-dispersive infrared (NDIR) gas sensors typically use an optical filter that transmits a discriminating 4.26 μm wavelength band to measure carbon dioxide (CO2), as CO2 absorbs 4.26 μm infrared. The filter performance depends on the transmittance and full width at half maximum (FWHM). This paper presents the fabrication, sensitivity, and selectivity characteristics of a distributed Bragg reflector (DBR)-based Fabry-Perot filter with a simple structure for CO2 detection. Each Ge and SiO2 films were prepared using the RF magnetron sputtering technique. The transmittance characteristics were measured using Fourier-transform infrared spectroscopy (FT-IR). The fabricated filter had a peak transmittance of 59.1% at 4.26 μm and a FWHM of 158 nm. In addition, sensitivity and selectivity experiments were conducted by mounting the sapphire substrate and the fabricated filter on an NDIR CO2 sensor measurement system. When measuring the sensitivity, the concentration of CO2 was observed in the range of 0-10000 ppm, and the selectivity was measured for environmental gases of 1000 ppm. The fabricated filter showed lower sensitivity to CO2 but showed higher selectivity with other gases.
이산화탄소 감지를 위한 4.26 μm 필터용 poly-Si/SiO<sub>2</sub> 다층 박막 기반의 패브리 페로-필터
도남곤 ( Nam Gon Do ),이준엽 ( Junyeop Lee ),정동건 ( Dong Geon Jung ),공성호 ( Seong Ho Kong ),정대웅 ( Daewoong Jung ) 한국센서학회 2021 센서학회지 Vol.30 No.1
In this study, the relationship between the transmitted light intensity and full-width-at-half-maximum (FWHM) of a Fabry-Perot filter was investigated. The measured refractive indices and absorption coefficients of the fabricated thin films were applied to the Fabry-Perot filter via simulations using optical software. Although considerable research has been conducted on Fabry-Perot filters, this study focused on the usefulness of 4.26-μm infrared filtering in carbon dioxide detection. Optical analysis was performed considering the effects of the thickness, refractive indices, and number of thin films in a distributed Bragg reflector. Ultimately, a clear trade-off relationship was observed wherein the transmitted light intensity decreased as the number of multilayers increased; however, the FWHM was observed to be narrower.
비분산적외선 CO<sub>2</sub> 센서를 위한 DBR기반의 패브리 페로-필터 설계 및 성능 연구
도남곤 ( Nam Gon Do ),이준엽 ( Junyeop Lee ),정동건 ( Dong Geon Jung ),공성호 ( Seong Ho Kong ),정대웅 ( Daewoong Jung ) 한국센서학회 2021 센서학회지 Vol.30 No.4
A highly sensitive and selective non-dispersive infrared (NDIR) carbon dioxide gas sensor requires achieving high transmittance and narrow full width at half maximum (FWHM), which depends on the interface of the optical filter for precise measurement of carbon dioxide concentration. This paper presents the design, simulation, and fabrication of a Fabry-Perot filter based on a distributed Bragg reflector (DBR) for a low-cost NDIR carbon dioxide sensor. The Fabry-Perot filter consists of upper and lower DBR pairs, which comprise multilayered stacks of alternating high- and low-index thin films, and a cavity layer for the resonance of incident light. As the number of DBR pairs inside the reflector increases, the FWHM of the transmitted light becomes narrower, but the transmittance of light decreases substantially. Therefore, it is essential to analyze the relationship between the FWHM and transmittance according to the number of DBR pairs. The DBR is made of silicon and silicon dioxide by RF magnetron sputtering on a glass wafer. After the optimal conditions based on simulation results were realized, the DBR exhibited a light transmittance of 38.5% at 4.26 μm and an FWHM of 158 nm. The improved results substantiate the advantages of the low-cost and minimized process compared to expensive commercial filters.
황화수소(H<sub>2</sub>S) 감지를 위한 아세트산 납이 침염된 폴리에스터(PET) 섬유 기반의 변색성 센서
이준엽 ( Junyeop Lee ),도남곤 ( Nam Gon Do ),정동혁 ( Dong Hyuk Jeong ),정동건 ( Dong Geon Jung ),안희경 ( Hee Kyung An ),공성호 ( Seong Ho Kong ),정대웅 ( Daewoong Jung ) 한국센서학회 2020 센서학회지 Vol.29 No.5
In this study, the colorimetric sensor, polyester (PET) fabric dyed with lead (II) acetate (Pb(C<sub>2</sub>H<sub>3</sub>O<sub>2</sub>)<sub>2</sub>), was fabricated and characterized for the detection of the hydrogen sulfide (H<sub>2</sub>S). The surface morphology of the fabric was determined using scanning electron microscope and energy-dispersive X-ray spectroscopy. The optical properties of the fabric were evaluated by measuring the variation in the blue value of an RGB sensor. The fabric showed a significant color change, high linearity (R<sup>2</sup>: 0.98256), and fast response time (< 1.0 s) when exposed to H<sub>2</sub>S. This is because the sensor is highly porous and permeable to the gas. The fabric can not only be used as a hydrogen sulfide sensor but also be used to detect and prevent H<sub>2</sub>S influx using sticky tape on pipelines.
광 도파관이 외부로 노출된 구조를 가지는 비분산적외선 이산화탄소 센서
정동건 ( Dong Geon Jung ),이준엽 ( Junyeop Lee ),도남곤 ( Nam Gon Do ),정대웅 ( Daewoong Jung ) 한국센서학회 2021 센서학회지 Vol.30 No.6
In this study, a Non-Dispersive Infrared (NDIR) Carbon Dioxide (CO<sub>2</sub>) sensor with an externally exposed optical cavity is proposed for improving sensitivity. NDIR CO<sub>2</sub> sensors with high performance must use a lamp-type infrared (IR) source with a strong IR intensity. However, a lamp-type IR source generates high thermal energy that induces thermal noise, interfering with the accuracy of the CO<sub>2</sub> concentration measure. To solve this problem, the optical cavity of the NDIR CO<sub>2</sub> sensor is exposed to quickly dissipate heat. As a result, the proposed NDIR CO<sub>2</sub> sensor has a shorter warm-up time and a higher sensitivity compared to the conventional NDIR CO<sub>2</sub> sensor.