Irreversible sensing of oxygen ingress

Absorption-based opto-chemical sensors for oxygen are presented that consist of leuco dyes (leuco indigo and leuco thioindigo) incorporated into two kinds of polymer matrices. An irreversible and visible color change (to red or blue) is caused by a chromogenic chemistry involving the oxidation of the (virtually colorless) leuco dyes by molecular oxygen. The moderately gas permeable copolymer poly(styrene-co-acrylonitrile) and a highly oxygen-permeable polyurethane hydrogel, respectively, are used in order to increase the effective dynamic range for visualizing and detecting oxygen. We describe the preparation and properties of four different types of such oxygen sensors that are obtained by dip-coating a gas impermeable foil made from poly(ethylene terephthalate) with a sensor layer composed of leuco dye and polymer.     

A CMOS optical detection system for point-of-use luminescent oxygen sensing

This work describes a stable and sensitive optical oxygen sensor based on a consumer CMOS image sensor array and polarization signal isolation. The consumer CMOS image sensor is inherently color discriminating, while the polarization is a wavelength-independent scheme for filtering excitation light. Combination of these two components generates a compact, multi-color detection system applicable to luminescence-based sensing. The optical system is applied to point-of-use oxygen sensing based on quenching of platinum octaethylporphine (PtOEP) luminophore. Sensitivity of the demonstrated portable oxygen sensor is comparable to that of benchtop spectroscopy-based systems. Taking advantage of the spatial resolution of the CMOS image sensor, an oxygen insensitive reference can be integrated to improve the reliability when powered by a battery. The low-cost and high sensitivity of the demonstrated optical sensing approach make it promising for point-of-use applications.     

New NIR dyes for ammonia sensing

Three series of new cyanine dyes were synthesised and the Vis–NIR spectra of the dyes were measured and interpreted by semi-empirical methods of quantum chemistry. As a basic building block for the synthesis, 4-(dimethylaminomethylene)-5-oxo-2-furfurylidenedimethyliminium perchlorate I was used. The dyes were prepared by condensing I with appropriate salts. The tests for sensitivity to ammonia have shown that the series of mono-substituted dyes III are reversibly sensitive to ammonia in ethanol solutions. The dyes exhibit a peak at 620–680 nm arising from the interaction with ammonia and, hence, these dyes are promising as chemical transducers for distributed fibre-optic ammonia sensors.     

Labeling sensing data for mobility modeling

In urban environments, sensory data can be used to create personalized models for predicting efficient routes and schedules on a daily basis; and also at the city level to manage and plan more efficient transport, and schedule maintenance and events. Raw sensory data is typically collected as time-stamped sequences of records, with additional activity annotations by a human, but in machine learning, predictive models view data as labeled instances, and depend upon reliable labels for learning. In real-world sensor applications, human annotations are inherently sparse and noisy. This paper presents a methodology for preprocessing sensory data for predictive modeling in particular with respect to creating reliable labeled instances. We analyze real-world scenarios and the specific problems they entail, and experiment with different approaches, showing that a relatively simple framework can ensure quality labeled data for supervised learning. We conclude the study with recommendations to practitioners and a discussion of future challenges.     

Low-cost colorimetric sensor for the quantitative detection of gaseous hydrogen sulfide

A simple, rapid and low-cost method for differentiating a wide range of concentrations of gaseous hydrogen sulfide (H₂S) is described. A large dynamic range (50 ppb to 50 ppm) was successfully classified at ambient temperature using a colorimetric sensor array comprised of chemoresponsive dyes coupled to a commercially available 8-bit flatbed scanner. Principle component analysis of the composite magnitude and kinetics of color change for the array of dye spots over the entire dynamic range resulted in 100% classification. This was achieved by including chemoresponsive dyes which reacted specifically with H₂S at different detection thresholds.     

HF molecules laser sensing in gaseous flows

The lidar monitoring are widely used for the gaseous molecules ultra low concentration levels in atmosphere and technological gaseous flows. It demands the detail studies of the atmospheric optics basics and computer simulation of the laser sensing possibility in such a molecules detection by the laser radiation with pulse energy up to 35 mJ at the wavelength of 532 nm. The lidar signal of the HF molecule versus the sensing distance have been a subject of the simulation studies of this signal molecules concentration dependence. It has been taken into account the Sun background radiation as the minimal lidar HF signal. The HF concentration versus distance dependences for this molecules ultra low concentration level in atmosphere simulation results show the HF molecules Raman and DAS lidar sensing efficiency for low concentration in the distance range from 1 to 1000 m by chosen laser wavelength and pulse energy in the daytime ranging regime. The text was submitted by the authors in English.     

Hollow microcapsules for sensing micro-scale flow motion in X-ray imaging method

For synchrotron X-ray micro-imaging of micro-scale biological flows in organisms, the development of a suitable flow-sensing tracer is essential for visualizing opaque flows quantitatively. In order to achieve this development in this study, the techniques employed in three different research fields were integrated namely, X-ray optics for enhancing X-ray concentration, fluid dynamics to satisfy the flow traceability and drug delivery system to fabricate bio-compatible microcapsules. On the front burner, we need a special sensor which can be well observed in X-ray micro-imaging and follow working fluid as well. As a result, bio-compatible micro-scale microcapsule sensors that perform the role of spherical micro lenses were developed. These novel microcapsules exhibit not only much improved contrast enhancement but also better performance as sensor tracers in micro-scale flows, compared to conventional solid particles.     

Increasing pattern recognition accuracy for chemical sensing by evolutionary based drift compensation

Artificial olfaction systems, which mimic human olfaction by using arrays of gas chemical sensors combined with pattern recognition methods, represent a potentially low-cost tool in many areas of industry such as perfumery, food and drink production, clinical diagnosis, health and safety, environmental monitoring and process control. However, successful applications of these systems are still largely limited to specialized laboratories. Sensor drift, i.e., the lack of a sensor’s stability over time, still limits real industrial setups. This paper presents and discusses an evolutionary based adaptive drift-correction method designed to work with state-of-the-art classification systems. The proposed approach exploits a cutting-edge evolutionary strategy to iteratively tweak the coefficients of a linear transformation which can transparently correct raw sensors’ measures thus mitigating the negative effects of the drift. The method learns the optimal correction strategy without the use of models or other hypotheses on the behavior of the physical chemical sensors.     

汽车空燃比控制用的TiO2 系厚膜氧传感器

本文介绍了掺五价金属氧化物(M_2O_5)对TiO_2氧敏材料电阻率的影响,测定了半导化后的TiO_2材料不同温度下的氧敏特性,并讨论了其敏感机理.     

Capability representation model for heterogeneous remote sensing sensors: Case study on soil moisture monitoring

Sensor capability information can be used as a basis for the integrated management of vast and heterogeneous remote sensing sensors in Global Earth Observation System of Systems environment. However, the existing representation of this information shows an inconsistent pattern, incomplete capability aspects, and casual expression forms, resulting in information silos among different systems. A sensor capability representation model (SCRM) is proposed in this study. Based on the Meta Object Facility architecture, a five-tuple hierarchical SCRM framework is formulated. Five specific representation element collections for typical remote sensing sensor types are developed to satisfy the requirements of detailed capability expression. The Open Geospatial Consortium Sensor Model Language is used as the expression form of the proposed SCRM. A prototype system is developed and a case study is conducted for a soil moisture monitoring application in Baoxie Town. The SCRM can also be extensively utilised for other environmental monitoring and modelling situations.     

Contact CMOS imaging of gaseous oxygen sensor array

We describe a compact luminescent gaseous oxygen (O₂) sensor microsystem based on the direct integration of sensor elements with a polymeric optical filter and placed on a low power complementary metal-oxide semiconductor (CMOS) imager integrated circuit (IC). The sensor operates on the measurement of excited-state emission intensity of O₂-sensitive luminophore molecules tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp)₃]²⁺) encapsulated within sol-gel derived xerogel thin films. The polymeric optical filter is made with polydimethylsiloxane (PDMS) that is mixed with a dye (Sudan-II). The PDMS membrane surface is molded to incorporate arrays of trapezoidal microstructures that serve to focus the optical sensor signals on to the imager pixels. The molded PDMS membrane is then attached with the PDMS color filter. The xerogel sensor arrays are contact printed on top of the PDMS trapezoidal lens-like microstructures. The CMOS imager uses a 32 × 32 (1024 elements) array of active pixel sensors and each pixel includes a high-gain phototransistor to convert the detected optical signals into electrical currents. Correlated double sampling circuit, pixel address, digital control and signal integration circuits are also implemented on-chip. The CMOS imager data is read out as a serial coded signal. The CMOS imager consumes a static power of 320 μW and an average dynamic power of 625 μW when operating at 100 Hz sampling frequency and 1.8 V DC. This CMOS sensor system provides a useful platform for the development of miniaturized optical chemical gas sensors.     

Sensor selection via compressed sensing

Sensor selection is an NP-hard problem involving the selection of S$S$ out of N$N$ sensors such that optimal (in some predefined sense) filtering performance is attained. We present a novel approach for sensor selection that utilizes a measure quantifying the incoherence of the vector space spanned by the sensors with respect to the system’s principal directions. This approach provides a formulation of a convex relaxation problem that can be efficiently modeled and solved using compressed sensing (CS) algorithms. One of the key requirements in the theory of CS is that of a sufficiently incoherent sensing matrix. Such matrices are normally neither encountered in the sensor selection problem nor in many other engineering and scientific problems, which, to some extent, limits the applicability of the theory. In this work, this requirement is alleviated via the concept of semi-random sensing, where the standard sensing matrix pertaining to the problem at hand is deliberately contaminated by noise. We provide relations between the noise intensity and the incoherence properties of the contaminated sensing matrix. The viability of this concept is demonstrated and analyzed in the context of the sensor selection problem.     

The use of pervasive sensing for behaviour profiling — a survey

With the maturity of sensing and pervasive computing techniques, extensive research is being carried out in using different sensing techniques for understanding human behaviour. An introduction to key modalities of pervasive sensing is presented. Behaviour modelling is then highlighted with a focus on probabilistic models. The survey discusses discriminative approaches as well as relevant work on behaviour pattern clustering and variability. The influence of interacting with people and objects in the environment is also discussed. Finally, challenges and new research opportunities are highlighted.     

Rapid nitroaromatic compounds sensing based on oligopyrene

Conjugated oligopyrene with high fluorescence quantum yield was synthesized by a simple one-step electropolymerization of pyrene in a mixed electrolyte of boron trifluoride diethyl etherate and diethyl ether, and thin film fluorescent sensors based on this material were fabricated through a spin-coating technique. These oligopyrene sensors showed rapid fluorescence quenching upon exposure in nitroaromatic compound vapors including trinitrotoluene, dinitrotoluene and nitrobenzene. In combination with theoretical investigation, it was concluded that the high performance of these sensors was due to the high fluorescence quantum yield, “molecular wire” effect, the large free energy change for electron transfer from the excited oligopyrene to the analytes, and the twist chain structures in the sensing films.     

Modification of the oxygen diffusivity in limiting current oxygen sensors

Effect of sacrificial carbon on microstructure of protective layer and sensing properties of limiting current oxygen sensors were studied. Graphite and carbon nanofiber with different concentrations were examined as sacrificial layer. Therefore, several YSZ-based electrochemical gas sensors were fabricated with dissimilarity in the diffusivity of the layer covering their measuring electrodes.Gas sensors were tested as potentiometric and amperometric devices under O₂-N₂ mixtures, and synthetic gases similar to the exhaust gas mixtures from combustion engines. Sensors with low diffusivity (low concentration of sacrificial material) exhibit more abrupt and O₂-sensitive potentiometric responses. Indeed, less O₂-linear amperometric responses and higher response times are their characteristics. Sensors with high diffusion in their layers (high concentration of sacrificial material) show a less abrupt step-drop potentiometric response but a more linear O₂ dependence for the amperometric response and, in general, lower response times.Results suggest that the configuration of the diffusive layer shall be controlled in terms of the expected performance of the sensor, as an amperometric or potentiometric device. The controlling parameters are discussed and given in this study.     

Functionalized graphene as an aqueous phase chemiresistor sensing material

Here we report on the successful detection of benzene, toluene, ethylbenzene, xylenes and cyclohexane dissolved in water at low ppm concentration levels using functionalized graphene in a microelectrode chemiresistor platform. The use of microelectrodes results in a small double layer capacitance that effectively impedes charge transfer through the solution and allows the resistance of the graphene film to be measured preferentially. Comparing the relative chemiresistor response between cyclohexane (a non-aromatic molecule) and aromatic compounds (e.g. toluene), we have deduced that the response mechanism is most likely due to film swelling and not doping through the direct interaction of the molecule with the graphene basal plane.     

Hydrogen sensors with double dipole layers using a Pd-mixture-Pd triple-layer sensing structure

This paper reports on new GaN sensors using a Pd-mixture-Pd triple-layer sensing structure to enhance their sensitivity to hydrogen at the tens of ppm level. The proposed hydrogen sensor biased with a constant voltage produced relatively high sensing responses of 4.84 × 10⁵% at 10,100 ppm and 8.7 × 10⁴% at 49.1 ppm H₂ in N₂. The corresponding barrier height variations are calculated to be 220 and 168 mV. When the sensor is biased by a constant current with maximum power consumption of 0.4 mW, a sensing voltage as an output signal showed a voltage shift of more than 17 V (the highest value ever reported) at 49.1 ppm H₂ in N₂. By comparison to Pd-deposited GaN sensors, the improvement in static-state performance is likely attributed to double dipole layers formed individually at the Pd–GaN interface and inside the mixture. Moreover, voltage transient response and current transient response to various hydrogen-containing gases were experimentally studied. The new finding is that the former response time is shorter than the latter one.     

Influence of pH on particle size and sensing response of chemically synthesized chromium oxide nanoparticles to alcohols

Nanoparticles of chromium oxide have been synthesized by following a co-precipitation route at various pH values of the precursor solution. Structural and morphological analysis were carried out by using XRD and TEM techniques which revealed that the size of nanoparticles synthesized at pH 9 was smaller as compared to those synthesized at other pH values. The thick films of synthesized samples were deposited on alumina substrate and their sensing response to methanol, ethanol and isopropanol was investigated at different operating temperatures. It was observed that all the sensors gave optimum response at 250 °C. It has been observed that sample prepared at pH 9, being a collection of smallest particles as compared to other samples, exhibited high sensing response to alcohol vapour. Sensor response of all the samples tested was significantly higher towards isopropanol vapour than towards methanol or ethanol.In the present study the effect of particle size on intergranular activation energy has been studied as well. It was found that smaller particles possess high activation energy and exhibit higher sensing response as compared to that of larger particles. This type of study may help in the selection of particle suitable for gas sensing.     

Ammonia sensing characteristics of a Pt/AlGaN/GaN Schottky diode

The interesting ammonia sensing current-voltage (I-V) characteristics of a Pt/AlGaN/GaN Schottky diode are firstly studied and demonstrated. It is found that the ammonia sensitivity is increased by increasing the temperature. Yet, the sensitivity is decreased when the temperature is higher than 423 K. Experimentally, the studied device exhibits a good sensitivity of 13.1 under exposing to a relatively low concentration ammonia gas of 35 ppm NH₃/air. In addition, the good sensing performance of the studied device is demonstrated over a wide operating temperature regime from 298 K to 473 K. A highest ammonia sensing response of 182.7 is found at 423 K while a 10,000 ppm NH₃/air gas is introduced.     

Towards the development of a portable device for the monitoring of gaseous toxic industrial chemicals based on a chemical sensor array

The ability of chemical sensor array (CSA) technology to identify multiple gaseous analytes and differentiate between various analyte concentrations has been documented. To date, CSA response was monitored using a flatbed scanner driven by a personal computer. While this system is suitable for use in a laboratory setting it is not suitable for use in the field for environmental monitoring. We describe herein progress made towards the development of a rapid, inexpensive, portable, battery-operated, handheld device based on CSA technology for the detection of toxic industrial compounds (TICs). This prototype successfully differentiates between four TICs at both permissible exposure limit (PEL) and immediately dangerous to life and health (IDLH) concentrations, and three interferent gases, in less than 2 min.