Development of a selective gas sensor utilizing a perm-selective zeolite membrane

Reported here is a novel sensor that utilizes a zeolite film to selectively limit gas exposure of the sensing surface. A unique amperometric sensor design based on a non-porous mixed conducting sensing electrode enables the formation of a continuous zeolite film covering the entire sensor surface. The sensor was tested in a variety of oxygen containing gases. The sensor without a zeolite film responded strongly to both oxygen and carbon dioxide at a bias of 1.8 V. In contrast, the sensor coated with a zeolite film showed a discernable, but diminished response to oxygen, and a more marked drop in response to CO₂ indicating that the diffusion of oxygen through the zeolite film is preferential to that of CO₂. The response of the zeolite coated sensor to a mixture of oxygen and carbon dioxide gases is attributed primarily to the oxygen content. Expanding this concept using a variety of different zeolite structures covering an array of sensors, complete analyses of complex gaseous mixtures could be performed in a very small device.     

Sensitivity analysis for PCA-based chiller sensor fault detection

This paper presents an algebraic solution of erroneous sensor's undetectable boundary to evaluate the sensitivity of chiller sensor fault detection based on principal component analysis. Q-statistic of PCA is normally applied as a collective statistical index to detect sensor fault by comparing its value with the threshold. However, Q-statistic has no specific physical meaning and cannot evaluate the sensitivity of the provided method for sensor fault detection. We analyzed the definition of Q-statistic and derived the numerical value of the minimum range not to detect sensor fault. Bias sensor fault of a fielded screw chiller was studied for each sensor in PCA model by introducing different severity levels. Results showed that each sensor has different fault detection sensitivity using the same PCA model. The undetectable boundary can be a criterion used to evaluate the detection sensitivity of PCA-based method easily.     

Indium oxide thin film based ammonia gas and ethanol vapour sensor

A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temperature. The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included in this paper.     

Transition metal oxides covered Pd film for optical H2 gas detection

We have developed a simple fiber optic Fabry-Perot interferometer (FPI) sensor that is used to detection and measure concentration of hydrogen gas in the air. The operating principle of the sensor is discussed in this paper, and it was noticed that the wavelength positions of the FPI reflectance peaks change with the concentration of hydrogen gas. The sensor has been successfully used to monitor concentration of H₂ in the air below Lower Explosion Limit (LEL). The sensor utilizes a layered sensing structure. This structure includes gasochromic titanium dioxide (TiO₂) and nickel oxide (NiO_x) sensing film. The optical H₂ gas sensor has a very short response time and a fast regeneration time at room temperature.     

PVA-coated miniaturized flexible fiber optic sensor for acetone detection: a prospective study for non-invasive diabetes diagnosis

Diabetes is a complex metabolic disorder that leads to various health complications. Present conventional diagnostic methods of puncturing a finger cause pain, discomfort and measurement procedures often lead to irregular testing. Therefore, there is a need for a simple, painless, and portable technique, which can diagnose diabetes non-invasively and in real-time. Acetone vapor in human exhaled breath is a natural biomarker correlated with some metabolic diseases, like diabetes. Thus in this work, Fabry–Perot Interferometer-based polyvinyl alcohol-coated sensor platform for acetone vapor detection non-invasively at room temperature has been proposed and investigated for the prospective study of diabetic detection. The developed sensor platform of approx. 61 μm cavity length was employed for acetone sensing from 0 to 80 µL/L concentration. The evaluation parameters of the developed sensor like sensitivity, the limit of detection, response and recovery time for the acetone vapor detection at room temperature were observed in the order of 43.9 pm/(µL/L), 0.45 µL/L, 60 s and 10 s, respectively. The cross-sensitivity of the sensor was checked with methanol and ethanol. The experimentally observed sensitivity response (swelling) was found in agreement with the theoretically calculated miscibility values obtained from the Hansen solubility parameter model. The thermal stability of the developed sensor was also studied and found linear between the temperature ranges of 25–75 °C. The proposed sensor is simple, miniaturized, flexible, cost-effective, and highly sensitive for low acetone vapor concentration detection at room temperature. Therefore, this sensor maybe explore for diagnosis of diabetes non-invasively via acetone detection from the exhaled breath.

     

Rapid-Response Hybrid-Type Surface-Temperature Sensor

A hybrid-type surface-temperature sensor that combines the advantages of contact and non-contact sensing methods has been developed and that offers a way to overcome the weak points of both methods. The hybrid-type surface-temperature sensor is composed of two main components: a metal film that makes contact with the object and an optical sensor that is used to detect the radiance of the rear surface of the metal film. Temperature measurement using this thermometer is possible with an uncertainty of 0.5 K after compensating for systematic errors in the temperature range from 900 to 1,000 K. The response time of our previous hybrid-type sensor is, however, as long as several tens of seconds because the measurement must be carried out under thermally steady-state conditions. In order to overcome this problem, a newly devised rapid-response hybrid-type surface-temperature sensor was developed and that can measure the temperature of an object within 1 s by utilizing its transient heat transfer response. Currently, the temperature of a silicon wafer can be measured with an uncertainty of 1.0 K in the temperature range from 900 to 1,000 K. This sensor is expected to provide a useful means to calibrate in situ temperature measurements in various processes, especially in the semiconductor industry. This article introduces the basic concept and presents experimental results and discussions.     

Monitoring of resin flow in the resin transfer molding (RTM) process using point-voltage sensors

Multiple point-voltage sensors were used to monitor the mold filling stage of the resin transfer molding (RTM) process. Both lineal- and point-voltage sensors are electrical circuits in which the two poles of the sensor are closed when liquid thermoset resin arrives at the sensor location in the mold cavity. The electrical conductance of the liquid resin causes an increase in the output voltage, V_sens of the circuit. Although the gradually varying in situ data of a lineal sensor is more informative than a point-voltage sensor, lineal-voltage sensors might mislead the user if the resin covers the wires at multiple sections, or if the resin covers the wires starting from an unexpected section. Two kinds of sensors were developed: a set of similar, wrapped and compact lineal-voltage sensors acting as point-voltage sensors; and a point-voltage sensor with voltage amplification. Without this amplification, the increase in V_sens might be difficult to detect if the resin system has a low electrical conductivity and there is noise in the DAQ system. The accuracy and reliability of the new sensor system was verified by comparing the in situ sensor data with the visually recorded resin flow.     

Edible pH sensor based on immobilized red cabbage anthocyanins into bacterial cellulose membrane for intelligent food packaging

An edible pH sensor has been developed based on anthocyanins of red cabbage (Brassica oleraceae var capitata L.) (ARC) immobilized on a bacterial cellulose (BC) membrane. The polivinyl alcohol (PVA) (1%) was added into the membrane to reduce swelling and water solubility. The edible pH sensor exhibited a various distinctive colors from red to purple, blue-gray, and then to yellow in the pH range (pH 1–14), with good linearity between pH 1–6, and pH 8–12, with a sensor response time of 4 min and reproducibility of <1% (RSD). The sensor showed obvious color turning as a pH response and excellent color stability after 17 and 22 days in room and chiller conditions, respectively. In application, the pH sensor was demonstrated by the detection of several beverage pH. Although as freshness sensor, milk freshness was monitored by a distinctive color turning from blue-gray to pinkish-gray after 8 h storage at room temperature. The edible pH sensor can distinguish fresh milk from spoilage, making it suitable to be used in an intelligent packaging system as a freshness sensor.     

Development of a micro thermal sensor for real-time monitoring of lubricating oil concentration

We report development of a micro thermal sensor and sensing techniques for monitoring the oil concentration in a refrigeration system. The sensor acquires the thermal response of the mixture to ac heating and then the concentration can be determined using one of the two different methods. In the first method, the thermal conductivity of the mixture is obtained using the three-omega method and the concentration is determined using the correlation between the mixture concentration and thermal conductivity. In the alternative fast-detection method, the concentration is determined by directly calibrating the sensor output signal to the mixture concentration. The performance of the sensor was tested using the R410A/polyvinyl ether (PVE) oil mixture. The uncertainty of the oil concentration measurement was estimated to be 5.8-7.3 wt.%, depending on the sensing scheme. Especially, the simple structure of the sensor makes the technique cost effective and adequate for miniaturization, i.e., for installation in a limited space.     

Humidity sensor structures with thin film porous alumina for on-chip integration

Our aim was to produce a cheap, reliable, low-power and CMOS-MEMS process compatible relative humidity (RH) capacitive sensor that can be incorporated into a state-of-the art wireless sensor network. Porous alumina, produced by electrochemical oxidation of aluminum thin film under anodic bias (AAO, Anodic Aluminum Oxide) was used for the purpose of the sensing layer. We prepared two different capacitive sensor structures on silicon substrate using semiconductor processing steps and anodic oxidation in addition. The first sensor has an ultra-thin, vapor-permeable palladium upper electrode, while in the second case, an electroplated gold-grid is used for the same purpose. The highest achieved average sensitivity is approx. 15 pF/RH%, which is much higher than the values found in product catalogues of discrete, off-the-shelf capacitive humidity sensors (0.2-0.5 pF/RH%).     

Highly sensitive protein sensor based on thermally-reduced graphene oxide field-effect transistor

We report the fabrication of a highly sensitive field-effect transistor (FET) biosensor using thermally-reduced graphene oxide (TRGO) sheets functionalized with gold nanoparticle (NP)-antibody conjugates. Probe antibody was labeled on the surface of TRGO sheets through Au NPs and electrical detection of protein binding (Immunoglobulin G/IgG and anti-Immunoglobulin G/anti-IgG) was accomplished by FET and direct current (dc) measurements. The protein binding events induced significant changes in the resistance of the TRGO sheet, which is referred to as the sensor response. The dependence of the sensor response on the TRGO base resistance in the sensor and the antibody areal density on the TRGO sheet was systematically studied, from which a correlation of the sensor response with sensor parameters was found: the sensor response was more significant with larger TRGO base resistance and higher antibody areal density. The detection limit of the novel biosensor was around the 0.2 ng/mL level, which is among the best of reported carbon nanomaterial-based protein sensors and can be further optimized by tuning the sensor structure.      

Response kinetics of a fiber-optic gas sensor using Pt/WO3 thin film to hydrogen

Response kinetics of a fiber-optic hydrogen gas sensor in air- and inert-atmosphere were characterized. The sensor is mainly based on the evanescent field interaction in hydrogen sensitive cladding which is used Platinum-supported tungsten trioxide (Pt/WO₃). When the sensor was exposed to 1 vol.% H₂/air and H₂/N₂ gas, the changes in optical power propagating through the fiber were about 30% and 50%, respectively. The detection limit was about 0.1 vol.% in air-atmosphere. The humidity dependence of the response kinetics was also evaluated. While the response speed in N₂-atmosphere was accelerated, the speed in air-atmosphere was suppressed by the humidity.     

Au@BSA prepared under alkaline conditions as an electrochemical non-enzymatic glucose sensor interface

Au@BSA was prepared at pH 8, pH 9, pH 10, pH 11, pH 11.4, and pH 12 as the working electrode of the non-enzymatic glucose sensor by biological template method. The six kinds of gold-cluster film working electrodes sintered by Au@BSA show golden color, especially the golden films corresponding to pH 8 and pH 12 are obvious. The gold-cluster films at pH 8, pH 9, pH 10, and pH 11 showed mono-layer gold nanoparticles, while the gold-cluster film at pH 11.4 showed porous structure. The gold-cluster film prepared at pH 12 presents a multi-layer 3D structure composed of a large number of gold nanoparticles. The linear detection range of the non-enzymatic glucose sensor prepared at pH 8 is the widest among the six sensors, and its sensitivity is also better than the other four sensors except the sensor prepared at pH 12. The sensor with the gold-cluster film-modified working electrode prepared at pH 12 show the highest sensitivity (330.002 μA mM^?1 cm^?2), because multi-layer 3D structure can bring more electric catalytic active site for this sensor. The electrochemical impedance spectroscopy showed that the specific surface area of the sensor prepared at pH 12 was much larger than that of the other five sensors. We provide a pH cycling method for once shaping preparation that can be extended to other metal films or metal-oxide films electrochemical interfaces. The Au@BSA non-enzymatic glucose sensor prepared in this paper is stable and can resist the toxicity of excessive chloride ions without losing activity.

     

Microhotplate Temperature Sensor Calibration and BIST

In this paper we describe a novel long-term microhotplate temperature sensor calibration technique suitable for Built-In Self Test (BIST). The microhotplate thermal resistance (thermal efficiency) and the thermal voltage from an integrated platinum-rhodium thermocouple were calibrated against a freshly calibrated four-wire polysilicon microhotplate-heater temperature sensor (heater) that is not stable over long periods of time when exposed to higher temperatures. To stress the microhotplate, its temperature was raised to around 400 °C and held there for days. The heater was then recalibrated as a temperature sensor, and microhotplate temperature measurements were made based on the fresh calibration of the heater, the first calibration of the heater, the microhotplate thermal resistance, and the thermocouple voltage. This procedure was repeated 10 times over a period of 80 days. The results show that the heater calibration drifted substantially during the period of the test while the microhotplate thermal resistance and the thermocouple-voltage remained stable to within about plus or minus 1 °C over the same period. Therefore, the combination of a microhotplate heater-temperature sensor and either the microhotplate thermal resistance or an integrated thin film platinum-rhodium thermocouple can be used to provide a stable, calibrated, microhotplate-temperature sensor, and the combination of the three sensor is suitable for implementing BIST functionality. Alternatively, if a stable microhotplate-heater temperature sensor is available, such as a properly annealed platinum heater-temperature sensor, then the thermal resistance of the microhotplate and the electrical resistance of the platinum heater will be sufficient to implement BIST. It is also shown that aluminum- and polysilicon-based temperature sensors, which are not stable enough for measuring high microhotplate temperatures (>220 °C) without impractically frequent recalibration, can be used to measure the silicon substrate temperature if never exposed to temperatures above about 220 °C.     

Microcontact imprinted surface plasmon resonance sensor for myoglobin detection

In this study, we prepared surface plasmon resonance (SPR) sensor using the molecular imprinting technique for myoglobin detection in human serum. For this purpose, we synthesized myoglobin imprinted poly(hydroxyethyl methacrylate-N-methacryloyl-l-tryptophan methyl ester) [poly(HEMA-MATrp)] nanofilm on the surface of SPR sensor. We also synthesized non-imprinted poly(HEMA-MATrp) nanofilm without myoglobin for the control experiments. The SPR sensor was characterized with contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, and ellipsometry. We investigated the effectiveness of the sensor using the SPR system. We evaluated the ability of SPR sensor to sense myoglobin with myoglobin solutions (pH 7.4, phosphate buffer) in different concentration range and in the serum taken from a patient with acute myocardial infarction. We found that the Langmuir adsorption model was the most suitable for the sensor system. The detection limit was 87.6 ng/mL. In order to show the selectivity of the SPR sensor, we investigated the competitive detection of myoglobin, lysozyme, cytochrome c and bovine serum albumin. The results showed that the SPR sensor has high selectivity and sensitivity for myoglobin.     

Analysis and validation of thermal and packaging effects of a piezoresistive pressure sensor

Abstract

In this study, a packaged silicon base piezoresistive pressure sensor with thermal stress buffer is designed, fabricated, and studied. A finite element method (FEM) is adopted for designing and optimizing the sensor performance. Thermal and pressure loading on the sensor is applied to make a comparison between experimental and simulation results. Furthermore, a method that transforms simulation stress data into output voltage is proposed in this study, and the results indicate that the experimental result coincides with the simulation data. In order to achieve better sensor performance, a parametric analysis is performed to evaluate the system sensitivity, as well as thermal and packaging effects of the pressure sensor. The design parameters of the pressure sensor include membrane size, sensor chip size, glass thickness, adhesive layer thickness, PCB thickness/material, etc. The findings show that proper selection of the sensor structure and material not only enhances the sensor sensitivity but also reduces the thermal effects as well as the packaging influence.     

Flexible single walled nanotube based chemical sensor for 2,4-dinitrotoluene sensing

In this work, we have attempted to fabricate flexible single walled carbon nanotube based sensor for detection of 2,4-dinitrotoluene (DNT) an explosive chemical. For analyte sensing study, the flexible sensor is fabricated by vacuum filtration method. These fabricated gas sensors are characterised by SEM and Raman spectroscopy. The sensor response is investigated toward the explosive chemicals which have NO₂ group in their molecular structure. The fabricated sensor is able to detect the traces of DNT at room temperature. The sensor gives 0.28–0.32% repeatable response to 0.22 ppm of DNT. The response of sensor increases with increase in the vapour concentration of the DNT vapours.     

A Novel On‐Package Sticker Sensor Based on Methyl Red for Real‐Time Monitoring of Broiler Chicken Cut Freshness

A novel sticker sensor has been fabricated based on methyl red, and tests have been conducted to detect the freshness of broiler chicken cuts. Methyl red was immobilized onto a bacterial cellulose membrane via absorption method. The methyl red/cellulose membrane as a freshness sensor worked based on pH increase as the basic spoilage volatile amines produced gradually in the package headspace, and subsequently, the colour of the sensor will change from red to yellow for spoilage indication, which is easily visible to the naked eye. The results show that the sticker sensor could be used to determine the degree of chicken cut freshness, as the relationship between the colour change of methyl red as a sensor response and the chicken cut freshness follows a similar trend. Therefore, the spoilage of the chicken cut could be detected visually. A sticker sensor indicates the chicken cut freshness by its colour change in real time. Thus, the sticker sensor can be used as an effective tool for monitoring the microbial quality of packaged fresh poultry meat. Finally, the methyl red/cellulose membrane was successfully used as a sticker sensor for the real‐time monitoring of chicken cut freshness in ambient and chiller conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Entwicklung des dynamischen Abschreckens in Hochdruck‐Gasabschreckanlagen

Development of dynamic quenching in high pressure gas quenching cells A new quenching sensor was developed for measuring the quenching conditions in high‐pressure gas quenching cells. This QC³‐Sensor (Quench Control in Cold Chambers) measures the cooling curve in a pre‐heated sensor‐head. The sensor can be used for process‐monitoring, process‐control and process‐steering. This quenching sensor was successfully tested for the precise initiation of “dynamic quenching”. The newly developed dynamic quenching consists of a gas‐quench with varying quenching intensity. It was shown on simple rings and on gear wheels made of the steel grade 16MnCr5 that the dynamic quenching has the potential to reduce heat treatment distortions. Especially the spread of the geometry‐changes can be reduced significantly, if the quenching intensity is lowered during quenching.     

电涡流传感器最佳工作区间确定方法研究

电涡流传感器因非接触测量、抗干扰力强等优点在生产中得到了广泛地应用,但其精度很难到达几个微米。根据精度分析理论,采用误差修正技术,提出“最小区间数”与“最大区间段”的工作区间优选原则,确定电涡流传感器的最佳工作区间,以提高传感器测量精度。应用该方法对商业电涡流传感器进行了精度标定,结果显示,将原有的电涡流传感器±10μm误差提升至最佳工作区间的±4μm精度。