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Aims This study investigated the association of persistent organic pollutants (POPs), an emerging new risk factor for type 2 diabetes and the metabolic syndrome, with the presence of opposite phenotypes of glucose and lipid metabolism among normal-weight Koreans of similar body composition. Methods Fifty subjects, randomly selected from an ongoing community-based cohort study, from two opposite phenotype groups — metabolically unhealthy normal weight (MUHNW) and metabolically healthy normal weight (MHNW) — were matched for waist circumference, visceral fat mass and demographic variables, then compared for serum concentrations of POPs. Results Most POPs (10 out of 13 compounds) were present in higher serum concentrations in the MUHNW than in the MHNW. In particular, serum concentrations of all compounds of the organochlorine pesticide class were 2.2 to 4.7 times higher in cases than in controls. Compared with the lowest tertile of summary measures of POPs, Odds ratios (95% confidence interval) for the second and third tertiles were 7.4 (1.9–29.4) and 10.4 (2.6–41.2), respectively. Adjusting for possible confounders did not change the results. Conclusion Taken altogether, these findings from the present and previous studies suggest that increased serum POP concentrations may play an important role in the development of unhealthy metabolic phenotypes in lean people.

BACKGROUND In an era of increasing concerns about drug resistance, there are limited data on treatment outcomes and recurrence rates after standard short-course anti-tuberculosis treatment in patients with culture-negative tuberculous pleural effusion (TPE). OBJECTIVE To compare treatment outcomes and recurrence rates between a standard anti-tuberculosis regimen with negative culture and unavailable drug susceptibility testing (DST) data, and a tailored anti-tuberculosis regimen based on individual DST data. DESIGN We analysed the data of all patients with TPE from the TB registry database at Kyungpook National University Hospital, South Korea, during 2008-2012. The study population was divided into two groups according to regimen. RESULTS Standard and tailored anti-tuberculosis regimens were administered to respectively 124 and 146 patients with TPE. Drug resistance was detected in 10% of patients with TPE, about a quarter of whom were multidrug-resistant. The treatment completion rate was not significantly different between the two groups (91% vs. 93%). During a median 20-month follow-up, the recurrence rate was also similar in both groups (1% vs.1%). CONCLUSIONS Despite limited statistical power, these preliminary results support the hypothesis that immunocompetent patients with culture-negative TPE can be appropriately managed with a standard short-course anti-tuberculosis regimen, even in this era of increasing concerns about drug resistance.

Controlled synthesis of ZnO nanorods (ZNRDs), nanotubes (ZNTs) and nanorings (ZNRs) has been carried out by a two-step sonochemical/chemical process at room temperature without any catalyst, template or seed layer. The crystallinity, structure and morphology of ZNRDs, ZNRs and ZNTs were examined by X-ray diffraction (XRD) analysis, scanning electron micrographs (SEM), high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED). The as-prepared ZnO nanostructures were single crystalline with hexagonal cross-section and uniform size. The effect of precursor concentration on the growth and that of the etching duration on the hollow formation were analyzed, and the obtained results revealed that the precursor concentration and etching time play an important role in determining final morphologies of the samples. By tuning the etching time, the precise size control of ZNTs and ZNRs was achieved. Possible formation mechanisms of these nanostructures are proposed based on the experimental results.

Whether a person is feeling sleepy or reasonably awake is important safety information in many areas, such as humans operating in traffic or in heavy industry. The changes of body signals have been mostly researched by looking at electroencephalogram(EEG) signals but more and more other medical signals are being examined. In our study, an electrocardiogram(ECG) signal is measured at a sampling rate of 100 Hz and used to try to distinguish the possible differences in signal between the two states: awake and drowsy. Practical tests are conducted using a wireless sensor node connected to a wearable ECG sensor, and an ECG signal is transmitted wirelessly to a base station connected to a server PC. Through the QRS complex in the ECG analysis it is possible to obtain much information that is helpful for diagnosing different types of cardiovascular disease. A program is made with MATLAB for digital signal filtering and graphing as well as recognizing the parts of the QRS complex within the signal. Drowsiness detection is performed by evaluating the R peaks, R-R interval, interval between R and S peaks and the duration of the QRS complex..

A SnO 2 -based recoverable thick-film gas sensor was developed in this study for the detection of dichloromethane (DCM) of ppb level at 350 °C. The response of the SnO 2 sensor decreased gradually during multiple cycles of detection and recovery, while the response of the SnO 2 -based sensor, promoted simultaneously with Mo and Ni, was maintained during multiple cycles without deactivation. In particular, the Mo3·Ni3(I) sensor, which was prepared by the physical mixing of 3 wt% MoO 3 and Ni/SnO 2 (Ni3(I)) prepared by impregnation of SnO 2 with 3 wt% NiO, showed a very high sensor response of about 50% in the detection of DCM of 0.5 ppm at 350 °C, unlike the SnO 2 sensor which showed a sensor response of about 1.2%. This result was due to the effects of textural property of the pure material and the promoter. The MoO 3 promoter played an important role in the improvement of the recovery ability of sensor, and the NiO promoter played an important role in the enhancement of the response level of the sensor. In addition, the response of the Mo3·Ni3(I) sensor increased almost linearly in the concentration range between 0.1 ppm and 0.5 ppm. Moreover, the sensor showed the response of 30% even at a very low concentration of DCM of 0.1 ppm (100 ppb).

A recoverable SnO 2 -based gas sensor, promoted simultaneously with three components such as Mo, Sb, and Ni (Mo5Sb1·Ni(I)), was developed in this study for the detection of DMMP. The Mo5Sb1·Ni(I) sensor showed not only excellent sensor response in the detection of a very low concentration of DMMP (ppb level) in a flow system, but also complete recovery. In particular, the Mo5Sb1·Ni 2 (I) sensor developed in this study showed a high sensor response of about 70% in the detection of 0.5 ppm DMMP at 350 °C, and the sensor response was maintained during multiple cycles of detection and recovery. Moreover, the sensor showed the sensor response of 42% in the detection of even very low concentrations of DMMP of 0.1 ppm. These results were due to the effects of promoters such as Mo, Sb, and Ni. Mo and Sb promoters play an important role in the improvement of the recovery ability of sensor, and Ni promoter plays an important catalytic role in the enhancement of the response level of sensors.

There have been continued effects to develop various types of chemical sensors according to the demands in many application fields such as safety, pollution, environment, medical engineering and food industries etc. In this review, the author intended to cover the general aspects of chemical sensors, including the history of the development, the classification, the sensing properties, and the types and application examples. And the future outlook of the chemical sensor technology, focusing on the advanced materials, high technology fusion, miniaturized intelligent system and ubiquitous sensor networks etc., has been described.

Low power bridge type micro gas sensors were fabricated by micro machining technology with TMAH (Tetra Methyl Ammonium Hydroxide) solution. The sensing devices with different heater materials such as metal and poly-silicon were obtained using CMOS (Complementary Metal Oxide Semiconductor) compatible process. The tellurium films as a sensing layer were deposited on the micro machined substrate using shadow silicon mask. The low power micro gas sensors showed high sensitivity to NO with high speed. The pure tellurium film used micro gas sensor showed good sensitivity than transition metal (Pt, Ti) used tellurium film.

In this paper, the gas responses of tungsten oxide films prepared by anodic reaction was discussed. Sensing electrodes and heating electrodes were patterned by photolithography method on quartz substrate. Porous tungsten oxide was fabricated in electrolyte solutions of 5 % HF (HF

NASICON sensors compare properties with manufacture method in order to improve sensitivity and stability the sensing behaviors. Oxidation mixing method and Sol-gel method were compare analyze to characteristic in which each other sintered to and NASICON gas sensors were fabricate. Oxidation mixing method showed better sensing properties at sintered result to NASICON electrolyte analyze with manufacture methods.

The characteristic of tellurium thin films was studied for detecting nitrogen dioxide gas at room temperature. The film was deposited on substrate by using thermal evaporator. The subsequent process was heat treatment by several conditions. (temperature, flowed gases) Surface and grain boundary was investigated using SEM. The results showed that resistance of the tellurium film decreases reversibly in the presence of nitrogen dioxide. The sensitivity of this device depends on the gas concentration and detect lower concentrations less than 10 ppm.

This study provides the electrical model of combustible catalytic gas sensor. Physical characteristics such as thermal behavior, resistance change were included in this model. The finite element method analysis for sensor device structure showed that the thermal behavior of sensor is expressed in a simple electrical equivalent circuit that consists of a resistor, a capacitor and a current source. This thermal equivalent circuit interfaces with real electrical circuit using two parts. One is `power to heat` converter. The other is temperature dependent variable resistor. These parts realized with the analog behavior devices of the SPICE library. The gas response tendency was represented from the mass transferring limitation theory and the combustion theory. In this model, Gas concentration that is expressed in voltage at the model, is converted to heat and is flowed to the thermal equivalent circuit. This model is tested in several circuit simulations. The resistance change of device, the delay time due to thermal capacity, the gas responses output voltage that are calculated from SPICE simulations correspond well to real results from measuring in electrical circuits. Also good simulation result can be produced in the more complicated circuit that includes amplifier, bios circiut, buffer part.

Semiconductor thick film gas sensors based on tin oxide are fabricated and their gas response characteristics are examined for four simulant gases of chemical warfare agent (CWA)s. The sensing materials are prepared in three different sets such as impregnation, physical mixing (ball-milling) and co-precipitation method. Surface morphology, particle size, and specific surface area of fabricated sensing films are performed by the SEM, XRD and BET, respectively. Response characteristics are examined for test gases with temperature in the range 200–400 °C, with different gas concentrations. Test gases are dimethyl methyl phosphonate (DMMP), dipropylene glycol methyl ether (DPGME), acetonitrile, and dichloromethane which are used simulant gases of chemical warfare agents. These sensors showed sensitivities higher than 50% in 500 ppb of test gases and also good repetition behaviour. Four sensing materials are selected with good sensitivity and stability and are fabricated as a sensor array. And then, principal component analysis (PCA) is adapted to classify objective gas among the four simulant gases. The thick film array sensor shows high sensitivity to CWA gases and four CWA gases are classified by using a sensor array composed of four sensing devices through PCA.

A semiconductor gas sensor based on SnO 2 was studied using chemical agent simulants such as acetonitrile, DMMP, DPGME and dichloromethane at a low concentration range from 0.02 to 0.8 ppm at 350 °C. The sensing behavior of SnO 2 -based gas sensors that included sensitivity, response, recovery and reproducibility were investigated by using a flow measuring system. In the case of acetonitrile and dichloromethane, the sensor prepared from a precipitated small SnO 2 particle (15 nm) was more sensitive than that prepared from the commercial SnO 2 (40 nm). The addition of NiO or Nb 2 O 5 promoters also increased the sensitivity of the commercial SnO 2 sensor. The experimental results could be explained by the effects of particle size, pore size and promoters. The recovery of the SnO 2 -based sensors seemed to be possible for acetonitrile and DPGME. In the cases of DMMP and dichloromethane, the complete recovery of SnO 2 -based sensors was not possible because of poisoning.

We fabricated a CuO–SnO 2 composite thin film for hydrogen sulfide (H 2 S) gas sensing. The CuO–SnO 2 sensing film was prepared by simple process steps. Firstly a metallic Cu/Sn double layer was deposited by thermal evaporation and then the double layer was oxidized in O 2 ambient furnace to obtain CuO–SnO 2 composite thin film. The sensing properties of the film to H 2 S gas were measured at the operating temperature of 200 °C. The film showed more than 90% of relative resistance change to H 2 S gas of 1 ppm at the operating temperature and had a good selectivity to H 2 S gas.

Recently, many researchers have been attempted to reduce the power consumption in the sensor system and to increase the sensitivity for toxic gases. Most metal oxide sensing films are deposited on an alumina substrate which is easy process but needs high power consumption. Moreover, thin film sensor deposited on the Si substrate shows low sensitivity. Accordingly, this study investigated the fabrication of thick film gas sensors based on tin oxide on a Si substrate. Two heater shapes using a micro electro mechanical system (MEMS) are designed and simulated, and their gas response characteristics to test gases were examined. The sensing materials are SnO2 mixed with Al2O3, and test gases are CH2Cl2, CH3CN as simulant chemical warfare agents. Consequently, high sensitivity is acquired by using a thick sensing film and low power consumption is achieved by using MEMS technology.

Many metal oxide gas sensors have been developed for improving stability during last several decades. In this paper, we proposed the hot-wire type micro-gas sensor with single electrode for improving sensitivity and stability. This type sensor has only a single electrode by forming a sensing material onto Pt heater so the resistance of the single electrode is very low for parallel values of Pt heater resistor and sensing materials of mixed oxide semiconductor. Mixed oxide (Sn–In)O + Pt with various composition Sn–In = 1:1, 2:1, 5:1 and 10:1 for sensing materials were prepared. The fabricated sensor showed high sensitivity for NOx at low gas concentration and good selectivity for CO and HC gases.

Silicon bridge type micro-gas sensor array was fabricated for detecting hydrogen sulfide (H 2 S) and ethanol (C 2 H 5 OH) gases simultaneously. Anisotropic wet etching of silicon in 25 wt.% KOH solution at 80 °C and silicon reactive ion etching (RIE) were applied to achieve the bridge type sensor for low power consumption. The fabricated device size and active region are 2 mm× 2 mm and 85 μm× 75 μm, respectively. SnO 2 –CuO and SnO 2 –Pt thin films were deposited on bridge type micro-heater in a simple way. The sensing characteristics of the packaged micro-sensor to target gases were also investigated.

The polyaniline (PANi) micro gas sensor was developed for medical application using the silicon process in order to detect ammonia odor of stomach inside. Fabricated sensor can be applied to medical purpose if it can detect the variation of ammonia concentration that is generated by Helicobacter pylori (H. pylori) living in stomach. Today, there are many ammonia sensors for various applications. However, no suitable clinical sensor exists. We started to study for fabrication of a suitable sensor. It is possible for PANi microsensor to use clinical application because it has a good sensitivity at room temperature and is harmless to human. For this sensor operated inside stomach, the bulk micromachining and silicon process were used to reduce sensor size. The mechanical well was made of SU-8 photoresistor in order to improve the adhesion of PANi film. The sensor will be introduced to medical filed for competitive power of medical indicators.

A micro gas sensor array, consisting of four porous tin oxide thin films added with noble metal catalysts on a micro-hotplate, was designed and fabricated. The micro-hotplate was designed to obtain a uniform thermal distribution along with a low-power consumption and fast thermal response. The sensing properties of the sensors toward certain combustible gases, i.e., propane, butane, LPG, and carbon monoxide, were evaluated. A multilayer neural network was then used to classify the gas species. The results demonstrated that the proposed micro sensor array, plus multilayer neural network employing a backpropagation learning algorithm, was very effective in recognizing specific kinds and concentration levels of combustible gas below their respective threshold limit values.

After the 9∙11 terrorism and America-Iraq war, apprehension of mass destruction weapons such as bio-chemical agents calls for much more sensitive sensors which can detect toxic gases. In this study, semiconductor gas sensors based on tin oxide were examined to detect chemical agent simulants: dimethyl-methyl-phosponate (DMMP), di(propylene glycol) methyl ether (DPGME), acetonitrile, and dichloromethane. DMMP((CH3O)3), DPGME(C7H16O3), acetonitrile(CH3CN), and dichloromethane(CH2Cl2) gases are the simulants of nerve agent-sarin, vesicant agent-HN(N(CH2CH2Cl)3), blood agent-AC(HCN), and choking agent-CG(COCl2) gases, repectively. The SnO2 powder was prepared by a coprecipitation method from the mixture of tin chloride and zinc acetate dihydrate. Zinc oxide was doped into SnO2 from 1 wt% to 4 wt% to improve its reliability and sensitivity. To fabricate a thick film, powders were made into paste with organic binder of ethyl cellulose and screen-printed on the alumina substrate. The phase development and morphology of ZnO-doped SnO2 film were investigated by XRD (X-ray diffraction analysis), BET (surface and pore size analyzer), and SEM (scanning electron microscope). The gas sensing characteristics for target gases were examined with a flow-type measurement system. The concentrations of simulants were controlled from 500 ppb to 1500 ppb, and working temperatures were regulated from 250 to 400 .

Thick films of LaCoO 3 perovskite and metal oxides (In, Bi and Pd) impregnated in LaCoO 3 have been used as sensor materials for sensing temperature and carbon monoxide gas. LaCoO 3 has shown good characteristics of a thermal sensor up to 500 °C. The thermal sensitivity is decreased considerably by the impregnation of metal oxides and it has shown very low with PdO and Bi 2 O 3 . The sensor response for CO is quite good with a good recovery for the partial pressures from 10 to 40 ppm at 200 and 250 °C. LaCoO 3 has exhibited good response in spite of low sensitivity and better recovery even at 200 °C for 10 ppm partial pressure of CO. Higher partial pressures have given higher sensor responses. Probable mechanisms have been proposed in the light of present investigation and the earlier work.

Polypyrrole (PPy)–poly(vinyl alcohol) (PVA) composite and pure polypyrrole methanol sensors were prepared by an in situ vapor state polymerization method and their chemical structures were identified by a FT-Raman spectroscopy. The various electrical sensing behaviors of both types of sensors were systematically investigated by a flow measuring system including mass flow controller (MFC) and bubbling bottle. The incorporation of PVA into the polymer film caused a higher sensitivity than that of pure PPy sensor, while the response and recovery time and long-term stability were worse. The effect of thickness of sensing film was also investigated, and it was found that the thinner film showed higher sensitivity, which indicated that the resistance involved in sensing behavior comes from bulk resistance of sensor rather than surface resistance.

N-type semi-conducting oxides such as , ZnO, and have been known for the detecting materials of inflammable or toxic gases. Of those materials, -based sensors are well known as high sensitive materials to detect toxic gases. And the sensitivity is improved if catalysts are added. Detecting toxic gases, especially DMMP (di-methyl-methyl-phosphonate) and DPGME (Dipropylene glycol methyl ether), was performed by a mixture of Tin oxide () and Zirconia (). The films consist of each three different mass% of Zr (from 1 mass% to 5 mass%), and they were tested by XRD, SEM, TEM, BET. Nano-structure, pore and particle size was controlled to verify the sensor`s sensing mechanism. The sensors was evaluated at five different degrees (from to ) and three different concentrations (from 500 ppb to 1500 ppb). The sensors had good sensitivity of both simulants, and high selectivity of DMMP.

Many works to improve the stability and sensitivity of metal-oxide based gas sensors have been carried out during last several decades. As one of stability problems, we can present an example that the resistance alters to some extent when the devices are exposed to the normal air, which becomes an obstacle to its practical use. In this paper, we proposed a new type of micro gas sensor with single electrode for improving stability and sensitivity. Generally, metal-oxide gas sensors have two electrodes for heating and sensing. But this new type sensor has only a single electrode by depositing a sensing metal-oxide material onto the heating electrode. Owing to this structure, the sensor output signal in ambient condition could be very stable unlikely to metal-oxide gas sensor. As a result of CO gas sensing characteristics, this sensor shows 80 mV voltage output for 1000 ppm and linearity for ranges (0–250 ppm) of gas concentrations. The deviation of sensor resistance is about 1% for 3 months and a little influence for humidity upto 90% RH.

Pt/Na+ ion conductive ceramic thin film/Pt/carbonate (Na2CO3:BaCO3=1:1.7 mol) system CO2 micro gas sensor was fabricated and the sensing properties were investigated. The Na+ ion conductive thin film was prepared by RF magnetron sputtering method. The thin film micro carbon dioxide sensor was prepared by using silicon process combined with MEMS technology. A NASICON thin film (2000–2500 A) as main layer of the device was formed on N/O/N film using magnetron sputtering system. In order to simplify the device process, both the heater and lower electrode were formed on the same plane. And carbonate thin film as a sensing layer was formed on the upper electrode by sputtering sodium–barium carbonate target (Na2CO3:BaCO3=1:1.7 molar ratio). The area of the sensing layer was 0.55 mm ×0.4 mm and that of total device was 3.2 mm ×4.5 mm. The study of NASICON thin film conductivity was carried out using AC impedance spectroscopy. The properties of NASICON thin film for various temperatures were investigated. The NASICON thin film showed a higher ionic conductivity (0.43 S/cm) compared to that of bulk NASICON material. The Nernst’s slope of 57 mV per decade for CO2 concentrations from 1000 to 10,000 ppm was obtained at operating temperature of 400 °C. The power consumption of the fabricated sensor was about 52 mW at 400 °C. As results, it is supposed that the fabricated sensor could be applied for monitoring CO2 gas in environment.

Thick films of having perovskite structure impregnated with indium and bismuth oxides have been used as sensing material for acetonitrile () gas. The sensor response for is quite good with an excellent recovery for partial pressure from 3 ppm to 20 ppm between 200 and . alone has exhibited low response, but after impregnation of and have given increased sensitivity even with 3 ppm partial pressure of at . It is assumed that is undergoing oxidation reaction on surface of the film.

Thin film gas sensor based on tin oxide was fabricated and its characteristics were examined. Target gas is acetonitrile () that is simulant gas of blood agent gas. Sensing materials are , /Pt, and (Sn/Pt)oxidation with thickness from to . Sensor was consisted of sensing electrode with interdigit (IDT) type in front side and a heater in back side. Its dimension was . Fabricated sensor was measured as flow type and monitored real time using PC. The optimal sensing material for was {Sn()/Pt()}oxidation and its sensitivity and operating temperature were 30%, in 3 ppm.

Nitrogen oxides (NOx) and carbon monoxide (CO) are among the most dangerous chemical species to human health present in the atmosphere. Acute CO toxicity leading to unconsciousness, respiratory failure or death can occur after 1 hr of exposure when ambient CO levels reach 1000 ppm, whilst increase of NOx emissions can contribute to acid deposition, pollution of groundwater, eutrophication of surface waters, and tropospheric ozone and ecosystem damage. In this work, pure SnO2 sensors for CO and NOx were prepared by spin coating solutions derived from a washed Gel-precipitate followed by a calcining step. SnO2 sensors of nanometer grain size prepared by this process showed good sensitivity to CO and NOx gases. The increase of calcining temperature not only affected grain size and surface morphology, but also caused a decrease in sensitivity of the SnO2 sensors.

Optical fiber sensors have been used to detect small amounts of chemical species. In this work, a new thin polymer-clad fiber sensor is developed. Polyaniline is chemically synthesized and thin clad layers of the polymer are easily deposited on optical fiber by dip-coating technique. The optical property of polyaniline as a sensing material is analyzed by UV-Vis-NIR. The light source is stabilized He-Ne laser at 635 nm wavelength with 1 mW power. The light power transmitted through the optical fiber is measured with a spectrophotometer. By selecting a fixed incident angle, variation of transmitted light intensity through the optical fiber can be detected as gas molecules absorbed in the polyaniline clad layer. Among the various gases, the fabricated optical fiber sensor shows good sensitivity to gas. The optical fiber sensors was shown more improved properties than polymer based sensors which measure conductivity changes.

In this paper, we propose neural network-based fault diagnosis method to diagnose of sensor in the gas monitoring system. In the proposed method, using thermal modulation of operating temperature of sensor, the signal patterns are extracted from the voltage of load resistance. Also, ART2 neural network is used for fault isolation. The performance and effectiveness of the proposed ART2 neural network based fault diagnosis method are shown by simulation results using real data obtained from the gas monitoring system.

The polypyrrole (Ppy) incorporated with DBSA and APS was synthesized by chemical polymerization at 0 °C under atmospheric conditions. Ppy films were prepared by the dip coating method on the alumina substrate with interdigitated electrodes in order to employ the gas sensor. The electrical properties of the sensors, such as sensitivity, response and recovery time, reproducibility and long-term stability were investigated in the flow systems after various pretreatments. The electrical properties of the sensors depended on the pretreatment conditions. Soaking pretreatment resulted in a quick response and recovery time of the sensor and maintained electrical properties of the sensor for 3 months. Initial resistance of the sensor decreased with thermal treatment and this improved the stability of the sensor.

Three types of metal oxide gas sensors were adopted to detect the degree of breath odor. Various sorts of information are included in the odor. Each sensor has different sensitivities to gaseous chemical substances and the sensitivities also differ according to human behaviors, for example taking a meal, teeth brushing and drinking something. There is also a possibility that the sensor can detect degrees of daily fatigue. Sensor sensitivities were low for the expiration of the elderly when the subject drank green tea. In this study, it is thought that the odor system can be incorporated into a healing robot. The robot can communicate with the elderly using several words and also by connecting to the Internet. As for the results, the robot can identify basic human behaviors and recognize the living conditions of the resident. Moreover, it can also execute a kind of information retrieval through the Internet. Therefore, it has healing capabilities for the aged, and can also receive and transmit information.

The thick type sensor having Pt/Na super ionic conductor(NASICON) Pt/Na 2 SO 4 /Pt catalyst system for SO 2 gas sensing was fabricated by screen printing method. The phases of NASICON with the variation of sintering temperature (1050°C, 1150°C, 1250 °C ) and sintering time (1.5hr, 2.5hr, 3.5hr) were investigated by XRD. The variation of electromotive force of the sensor with SO 2 concentration and operation temperature were also investigated. The major phase of NASICON film sintered at 1150°C for 3.5hr was sodium zirconium silicon phosphate (Na 3 Zr 2 Si 2 PO 12 ). The Nernest's slope of NASICON sensor for SO 2 gas with the variation of concentration from 10 to 100 ppm was 176.12 mV/decade at the operating temperature of 500°C. The increase of oxygen partial pressure was not affected to the variation of Nernst's slope.

A gas recognition system was fabricated using a conducting polymer (polypyrrole and polyaniline) sensor array that can recognize and analyze various kinds and quantities of volatile organic compounds (VOCs), such as ethanol, toluene, benzene, and chloroform. The sensors also exhibited different sensitivity curves to VOCs according to the different additive amounts and kinds of conducting polymer (polypyrrole or polyaniline) and electrode. Polypyrrole and polyaniline film sensors made by chemical polymerization were employed to detect the VOCs. The multi-dimensional sensor signals obtained from the sensor array were then analyzed using the principal component analysis (PCA) technique and a radial basis function network (RBFN). By implementing the sensing signals from the sensor array along with a multi-layer neural network using an Radial-Basis Function learning algorithm, the sensor array was successful in accurately classifying the gas species and also identifying the concentration of each VOC in a real-time process.

A three electrode type sensor was fabricated. This sensor consists of two parts. One is a tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) film. It was fabricated by the metal thermal oxidation method. This produces a large surface area and low resistivity. So, this film has two functions, a gas sensitive film and an effective heater. The other part is a platinum resistor line covered with oxidized aluminum film. This part is located in the backside of the sensor. It plays three roles. The first is a load resistor for a measuring system. Secondly, it also acts as a heater. Most of the consumed power in the sensor is used as the thermal energy of gas sensing. The last role is catalytic combustible gas sensing in high gas concentrations. In this paper, the fabrication method of gas sensitive ITO film is researched. A complex sensor structure is fabricated. It acts as a hot wire semiconductor sensor at low gas concentration and a combustible catalytic sensor at high concentration.

A micro-gas sensor array with the four porous tin oxide thin films with noble metal catalysts on a micro-hotplate, dangling in air by Pt bonding wires and controlling the thickness by chemical mechanical process (CMP) has been fabricated. The sensing properties of sensors to some combustible gases, i.e. propane, butane, LPG, and carbon monoxide (CO), were evaluated. And we employed a principal component analysis (PCA) and a multi-layer neural network for classification of the gas species. The simulation and experimental results showed that the multi-layer neural network employing back-propagation learning algorithm with the micro-sensor array is very effective in identifying the kinds and some concentration levels of the combustible gases within the range of threshold limit values (TLVs).

The tin dioxide (SnO2) films were been prepared by oxidization of tin black film which was deposited by thermal evaporation. This method can be used for a simple and economical fabrication of a SnO2 gas sensor. These films also have an ultra-porous structure and a grain size in the nanometer. The reduction of particle size to nanometers leads to a dramatic improvement in sensitivity. The particle size and structural properties of SnO2 film were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Through the addition of Pt sol as a catalyst, the SnO2/Pt films acquired an appropriate resistance and stable reaction, though sensitivity decreased. The gas sensing characteristics were also investigated using iso-C4H10, CH4, C3H8, and CO gases.

In this work, a new optical gas sensor using thin polymer layers was developed. The polymer sensing layers were synthesized by chemical polymerization using the distilled aniline. The optical property of a polymer as a sensing material was analyzed using UV-Vis-NIR. These layers were prepared using centrifugal force. The polymer layer was uniformly deposited on inner glass pillar. The light source was red-light emitting diode (LED) with a 655 nm wavelength. The light power transmitted through the guide cell was measured with a photodiode. Variation of the light power transmitted was detected when the gas was absorbed into the polymer layer. The transmitted light intensity decreased because gas molecules were absorbed into the polymer layer. This optical sensor showed a good sensitivity to NH 3 gas.