• 한국세라믹학회지
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• 제54권4호
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• pp.303-307
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• 2017

Pure $In_2O_3$, 0.5 and 1.0 wt% Mg doped $In_2O_3$ hollow spheres were synthesized by ultrasonic spray pyrolysis of a solution containing In-, Mg-nitrate and sucrose and their gas sensing characteristics to 5 ppm $C_2H_5OH$, p-xylene, toluene, and HCHO were measured at 250, 300 and $350^{\circ}C$. Although the addition of Mg decreases the specific surface area and the volume of meso-pores, the gas response (resistance ratio) of the 0.5 wt% Mg doped $In_2O_3$ hollow spheres to 5 ppm $C_2H_5OH$ at $350^{\circ}C$ (69.4) was significantly higher than that of the pure $In_2O_3$ hollow spheres (24.4). In addition, the Mg doped $In_2O_3$ hollow spheres showed the highest selectivity to $C_2H_5OH$. This was attributed to the dehydrogenation of $C_2H_5OH$ assisted by basic MgO into reactive $CH_3CHO$ and $H_2$.

• 센서학회지
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• 제29권3호
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• pp.156-161
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• 2020

In this study, hierarchical mesoporous CuO spheres, ZnO flowers, and heterojunction CuO/ZnO nanostructures were fabricated via a facile hydrothermal method. The as-prepared materials were characterized in detail using various analytical methods such as powder X-ray diffraction, micro Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy. The obtained results are consistent with each other. The H₂S-sensing characteristics of the sensors fabricated based on the CuO spheres, ZnO flowers, and CuO/ZnO heterojunction were investigated at different temperatures and gas concentrations. The sensor based on ZnO flowers showed a maximum response of ~141 at 225 ℃. The sensor based on CuO spheres exhibited a maximum response of 218 at 175 ℃, whereas the sensor based on the CuO/ZnO nano-heterostructure composite showed a maximum response of 344 at 150 ℃. The detection limit (DL) of the sensor based on the CuO/ZnO heterojunction was ~120 ppb at 150 ℃. The CuO/ZnO sensor showed the maximum response to H₂S compared with other interfering gases such as ethanol, methanol, and CO, indicating its high selectivity.

• 센서학회지
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• 제21권3호
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• pp.223-228
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• 2012

In this study, a fiber-optic pH sensor based on a pH sol-gel film is fabricated. The sol-gel film is made by co-polymerizing tetramethoxysilane, trimethoxymethylsilane, ethanol and distilled water. As a pH indicator, a neutral red is immobilized in a thin porous film formed by the sol-gel process. The pH change in a sensing probe gives rise to a change in the color of the pH sol-gel film, and the absorbance of reflected light through the pH sol-gel film is also changed. By using a spectrometer, therefore, the spectra of reflected lights in the sensing probe with different pH values are measured. Also, the relationships between the pH values and the absorbance are analyzed on the basis of the color variations of the pH sol-gel films. In repeated experiments, the fiber-optic pH sensor shows that it has reversibility, a high reproducibility and a wide absorbance change in a pH range from pH 5 to 9. Also, we confirmed that the fabricated pH sol-gel film exhibits a fast response time, little or no pH indicator leaching and a dynamic range of 2.04 dB from pH 5 to 9. Based on the results of this study, a fiber-optic pH sensor can be developed for the pH monitoring in the harsh environments.

• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2229-2237
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• 2012

The two chelates based on calix[4]arene and thiacalix[4]arene have been synthesized and used as neutral ionophores for preparing PVC based membrane sensor selective to $Ho^{3+}$ ion. The addition of potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and various plasticizers, viz., NDPE, o-NPOE, DOP, TEP and DOS have been found to improve significantly the performance of the sensors. The best performance was obtained with the sensor no. 6 having membrane of $L_2$ with composition (w/w) ionophore (2%): KTpClPB (4%): PVC (37%): NDPE (57%). This sensor exhibits Nernatian response with slope $21.10{\pm}0.3mV/decade$ of activity in the concentration range $3.0{\times}10^{-8}-1.0{\times}10^{-2}M\;Ho^{3+}\;ion$, with a detection limit of $1.0{\times}10^{-8}M$. The proposed sensor performs satisfactorily over a wide pH range of 2.8-10, with a fast response time (5 s). The sensor was also found to work successfully in partially non-aqueous media up to 25% (v/v) content of methanol, ethanol and acetonitrile, and can be used for a period of 4 months without any significant drift in potential. The electrode was also used for the determination of $Ho^{3+}$ ions in synthetic mixtures of different ions and the determination of the arsenate ion in different water samples.

• 센서학회지
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• 제20권6호
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• pp.368-374
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• 2011

A microfluidic device for real-time monitoring of residual free chlorine and pH in water based on optical absorption is proposed. The device consists of a serpentine micromixer for mixing samples with a reagent, and a photodiode and light emitting diode(LED) for the detection of light absorbance at specific wavelengths, determined for specific reagent combinations. Spectral analyses of the samples mixed with N, N'-diethyl-p-phenylenediamine(DPD) reagent for chlorine determination and bromothymol blue(BTB) for pH measurement are performed, and the wavelengths providing the most useful linear changes in absorbance with chlorine concentration and pH are determined and used to select the combination of LED and photodiode wavelengths for each analyte. In tests using standard solutions, the device is shown to give highly reproducible results, demonstrating the feasibility of the device for the inexpensive and continuous monitoring of water quality parameters with very low reagent consumption.

• 센서학회지
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• 제25권1호
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• pp.51-56
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• 2016

This study evaluates the performance of an optical sensor and measurement system (CMA-24) which can analyze the fluctuation of dissolved oxygen and pH simultaneously. In the optical sensor system, the fluorescent materials, Rudpp and HPTS which are sensitive to dissolved oxygen and pH, respectively, are coated on the bottom of a 24-well -plate by the sol-gel technology. The detection times of the emission light of the oxygen sensor were $4,186{\pm}13.90{\mu}s$ and $4,452{\pm}36.68{\mu}s$ for the dissolved oxygen of 17% $O_2$ and 7.6% $O_2$, respectively. On the other hand, the detection times of the pH sensor were $6,699.43{\pm}14.64{\mu}s$, $6,722.24{\pm}6.21{\mu}s$, and $6,748.52{\pm}2.63{\mu}s$ using pH 6, 7, and 8, respectively. When we determined cellular respiration levels of C2C12 myocytes with CMA-24, $O_2$/pH measurement system, the ratio of the uncoupled to coupled OCR (oxygen consumption rate) was 1.41. The results mean that this CMA-24 system shows almost the same sensitiveness as the commercial system.

• 센서학회지
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• 제8권2호
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• pp.108-114
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• 1999

표면 탄성파 가스센서는 소자의 크기가 작고, 값이 싸며, 가스에 대한 감도가 매우 높고 소자의 신뢰도가 높은 장점을 갖고 있다. 본 연구에서는, $LiTaO_3$ 단결정 압전기판 위에 이중지연선을 갖는 표면 탄성파 $NO_2$ 가스센서를 설계 및 제작하였다. 제조된 IDT의 커패시턴스는 79.3MHz의 주파수에서 326.34pF였다. 임피던스 매칭이 된 IDT의 반사손실은 79.3MHz의 주파수에서 최대인 -16.74dB로 나타났다. SAW 발진기를 성하여 고주파증폭기의 이득을 적절히 조정함으로써 안정된 발진이 이루어짐을 확인하였다. SAW 발진기의 $NO_2$ 가스에 대한 발진주파수의 변이는 28Hz/ppm으로 나타났다.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2005년도 추계학술대회 논문집
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• pp.186-189
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• 2005

An embedded monitoring and control system which can be controlled and monitored with web, was implemented in this paper. The principal data which should be controlled are the present temperature and pH of a fish farm. The input signals are from temperature sensors and pH sensors. The input data are digital which are A/D converted every constant time, and the results are stored to the database. The converted data are displayed on a large electric signboard at the fish-farm. This system was designed that supervisors can control the system and watch the real situation of the fish-farm at remote places.

• 센서학회지
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• 제20권4호
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• pp.260-265
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• 2011

The silicon vertical hall devices are fabricated using a modified bipolar process. It consists of the thin p-layer at Si-$SiO_2$, interface and n-epi layer without $n^+$buried layer to improve the sensitivity and influence of interface effects. Experimental samples are a sensor type I with and type H without p+isolation dam adjacent to the center current electrode. The experimental results for both type show a more high current-related sensitivity than the former's vertical hall devices. The sensitivity of type H and type I are about 150 V/AT and 340 V/AT, respectively. This sensor's behavior can be explained by the similar J-FET model.

• Transactions on Electrical and Electronic Materials
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• 제10권4호
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• pp.135-139
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• 2009

$H_2S$ micro-gas sensors have been developed employing $SnO_2$:CuO composite thin films. The films were prepared by e-beam evaporation of Sn and Cu metals on silicon substrates, followed by oxidation at high temperatures. Results of various studies, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that $SnO_2$ and CuO are mutually non-reactive. The CuO grains, which in turn reside in the inter-granular regions of $SnO_2$, inhibit grain growth of $SnO_2$ as well as forming a network of p-n junctions. The film showed more than a 90% relative resistance change when exposed to $H_2S$ gas at 1 ppm in air at an operating temperature of $350^{\circ}C$ and had a short response time of 8 sec.