Double-layer Sensor Research Articles

Annealing effect on the methane sensing performance of Pt–SnO2/ZnO double layer sensor

Low power consumption is a new emerged requirement for methane sensors long-term working in a gas supervisorycontrolsystem. Great challenges remain in development of heat free methane sensors based on metal oxide semiconductors (MOS). In this work, Pt-doped SnO2 (Pt-SnO2) grow on well aligned ZnO nanorod-array to form an inter-staggered double-layer structure on AZO glass by a two-step hydrothermal method, with the annealing temperature being systematically studied. The optimized processing parameters are 1 at% Pt doping content and 700 °C annealing temperature, offering the best sensing response of 3.36 to 800 ppm CH4 at room temperature. SnO2/ZnO without Pt doping shows linear I-V relationship, while the Pt-SnO2/ZnO shows a Schottky-like I-V curve with the Schottky barrier height decreases as increasing the CH4 concentration. The activation energy (ΔEa) for CH4 dissociation decreases with increasing the annealing temperature, and the ΔEa of the optimized Pt-SnO2/ZnO sample is only one-third of that in the SnO2/ZnO. In addition to the piezoelectric polarization electric field in ZnO, the build up Schottky-like barrier and the reduced activation energy via Pt doping and annealing are demonstrated to be efficient for enhancing the methane sensing performance at low operation temperature.

High FOM Refractive Index Sensor Based on Quasi-Bound States in the Continuum of Tri-Prism Metasurface

Due to the inevitable ohmic losses and radiation losses from metal materials and nanoparticles, the figure of merit (FOM) of plasmon sensors is usually very low. The all-medium material combined with bound states in the continuum (BIC) can effectively improve the FOM of sensors. In this article, a single-layer tri-prism metasurface sensor based on quasi-BIC (Q-BIC) was first proposed and simulated. Some meaningful results were obtained by adjusting and optimizing the structural parameters. By reducing duty ratio (DR) and dielectric column height, the sensor was sensitive to refractive index (RI) changes and had an excellent spectral performance. The results showed the sensitivity and full width at half maximum (FWHM) of the single-layer tri-prism sensors were 680.7 nm/RIU and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 10^{-{2}}$ </tex-math></inline-formula> nm, respectively, and the FOM could reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.36\times 10^{{4}}$ </tex-math></inline-formula> RIU−1. On this basis, we proposed a novel double-layer metasurface sensor model to improve the sensing performance and simulate it further. Because of the complete symmetry of the two-layer metasurfaces, the sensor had perfect phase matching condition. Under the same conditions, double-layer sensor had higher sensitivity and narrower FWHM in Q-BIC. The results showed the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> and FWHM of the sensor were 715.6 nm/RIU and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7\times 10^{-{5}}$ </tex-math></inline-formula> nm, respectively, and the FOM could reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{7}}$ </tex-math></inline-formula> RIU−1, detection limit (DL) could reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.89\times 10^{-{9}}$ </tex-math></inline-formula> RIU. FOM had been improved by three orders of magnitude than the single-layer sensor. It provided ideas for sensors with ultralow DLs in the future.

Electrohydrodynamic printed nanoparticle-based resistive temperature sensor

Temperature sensors based on the principle of a change of resistance are fabricated on polyethylene terephthalate (PET) substrates using a silver nanoparticles (AgNPs)-based ink using a bespoke drop-on-demand (DoD) electrohydrodynamic (EHD) printer. Two sensors consisting of either a single or double layer of silver were deposited using EHD printing and were found to exhibit an internal resistance of a few hundred ohms for the double-layer sensor compared to 1 kΩ for the single-layer sensor. The achieved pattern width was almost half the size of nozzle internal diameter (160 μm), and printed without treatment of substrate and nozzle. The sensors were characterized over a temperature range of 20 °C–110 °C. Both sensors showed a linear behavior with low hysteresis within the temperature ranges considered in this study and are found to recover the nominal resistance value with good reproducibility. The double-layer sensor showed high sensitivity with a temperature coefficient of resistance (TCR) of 3.4 × 10−3 , which is an order of magnitude larger than that observed for the single-layered sensor with a TCR of 8.41 × 10−4 . The sensors were also tested in a controlled humid environment and results are presented on the dependence of the internal resistance on the level of humidity. The proposed flexible printed sensors are promising for temperature monitoring systems and wearable technologies.

Automatic detection of microcracks on the surface of special steel wire based on remanence effect

ABSTRACT In this study, a remanence detection technology and double-layer sensor crack depth quantitative method for the on-line detection of microcracks on the surface of steel wire using remanence were developed. First, an instrument and a verification experiment were designed. Second, the magnetic signal of the prefabricated crack was analysed, and a defect recognition algorithm was designed. Finally, a detection instrument was applied in the industrial field. The results indicate that the practical application of remanence detection technology is feasible, the recognition algorithm is accurate and reliable, and a minimum crack depth of 0.078 mm can be detected. The magnetic anomaly amplitude difference of the double-layer sensor is positively correlated with the crack depth. The maximum error rate of the quantitative formula for the depth obtained by the fitting method is 10.95%. However, distinguishing the tilt direction of the crack from the shape of the notch remains a challenge for remanence detection technology.

Double-Layered NiO/SnO2 Sensor for Improved SO2 Gas Sensing with MEMS Microheater Device

Micro Electro mechanical systems (MEMS) sensor is fabricated for testing low concentration gas sensing of sulphur dioxide (SO2) with sensing layers of single layer tin oxide (SnO2) and double layered heterojunction structure of nickel oxide and tin oxide (NiO/SnO2). NiO and SnO2 structures are deposited with RF sputtering and the elemental composition were identified with structural properties such as X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive X-ray Analysis (EDX) analysis. Sensing results proved that NiO/SnO2 double layered sensor had better sensing characteristics than single layered SnO2 sensor due to the formation of p-n junctions. At 400 ppb of SO2 gas concentration, NiO/SnO2 sensor has maximum sensing response of 20% is recorded and at 2000 ppb, 30% sensing response is recoded. The optimal temperature of the sensor is 250 °C (∼63 mW). Selectivity of the sensor is tested with 5 different gases such as VOC, pyruvate, CO, NH3, SO2 and the sensor has high and better response with SO2 gas.

Fabrication and static calibration of double-layer thermal film sensor for fluid wall shear stress measurement

A double-layer flexible sensor array with an active thermal insulation method for fluid wall shear stress was fabricated in this study and evaluated experimentally. Static calibration of the sensor was studied in both wind and water tunnels and the experimental results reveal that the sensor’s static performance was improved by active thermal insulation. Compared to single-layer methods, the static sensitivity of the proposed double-layer sensor is increased by approximately 48% in a wind tunnel and 13% in a water tunnel. Additionally, consistent deviations in the static calibration coefficients of sensors with different basic parameters were clearly compensated in the wind tunnel. The calibration coefficient deviation of the sensors was reduced from 57% in single-layer mode to 5% in double-layer mode.

Determination of Nitroaromatics Using a Double-Layer of Gelatin Nanofibers and a Pyrene-Doped Polystyrene Membrane

ABSTRACTA double-layered sensor was prepared by an electrospinning method using pyrene, polystyrene, and gelatine to prepare a pyrene-polystyrene/gelatin/glass device for the determination of nitroaromatics. The pyrene- polystyrene top layer, which was an electronspun membrane from a mixture of the starting materials in 3:1 N, N-dimethylformaide:tetrahydrofuan, served as the sensing layer for detecting 2,4-dinitrotoluene. The bottom layer was the gelatin electrospun membrane that served as an intermediate between the top layer and the glass slide. The dinitrotoluene analyte was transferred into the sensing layer above and below due to the porosity of the gelatin layer. With a large number of hydroxyl and amino groups, the gelatin layer formed hydrogen bonds with the 2,4-dinitrotoluene molecules, which caused the enrichment of the analyte around the gelatin layer. Additionally, single-layer pyrene-polystyrene/glass sensor was also prepared for control measurements. The quenching efficiency of the pyrene-polystyrene/gelatin/glass sensor was 76.7% at equilibrium obtained within 6 minutes, while the monolayer sensor pyrene–polystyrene/glass device provided 65.8% quenching efficiency within 6 minutes. The gelatin layer played an important role in the superior performance of the double-layered sensor.

Gas-sensing behaviour of ZnO/diamond nanostructures.

Microstructured single- and double-layered sensor devices based on p-type hydrogen-terminated nanocrystalline diamond (NCD) films and/or n-type ZnO nanorods (NRs) have been obtained via a facile microwave-plasma-enhanced chemical vapour deposition process or a hydrothermal growth procedure. The morphology and crystal structure of the synthesized materials was analysed with scanning electron microscopy, X-ray diffraction measurements and Raman spectroscopy. The gas sensing properties of the sensors based on i) NCD films, ii) ZnO nanorods, and iii) hybrid ZnO NRs/NCD structures were evaluated with respect to oxidizing (i.e., NO2, CO2) and reducing (i.e., NH3) gases at 150 °C. The hybrid ZnO NRs/NCD sensor showed a remarkably enhanced NO2 response compared to the ZnO NRs sensor. Further, inspired by this special hybrid structure, the simulation of interaction between the gas molecules (NO2 and CO2) and hybrid ZnO NRs/NCD sensor was studied using DFT calculations.

Double-Layer Zeolite Nano-Blocks and Palladium-Based Nanocomposite Fiber Optic Sensors for Selective Hydrogen Sensing at Room Temperature

Double-layer fiber optic sensors have been fabricated and tested for hydrogen (H 2 ) gas at room temperature. The optical fiber was coated with a palladium/silica (Pd/SiO 2 ) sensing layer and a zeolite nano-blocks filter layer. The sensors demonstrated clear sensitivity to a broad range of H 2 concentrations. The selectivity study was focused on methane (CH 4 ) and carbon monoxide (CO). It was found that CH4 had no influence on the sensing response while the filter layer minimized the CO interference. The double-layer sensors are, thus, potentially useful for online monitoring of dissolved H2 in power transformers and other electrical grid assets which utilize insulation oils.

Design and construction of a new optical solid-state mercury(ii) sensor based on PVC membrane sensitized with colloidal carbon dots

A new Hg2+ ion solid-state double layer sensor impregnated with colloidal carbon dots and N′-(3-(4-(dimethylamino)phenyl)allylidene)isonicotinohydrazide (NDPAI, as a second layer) was inserted in plasticized polyvinyl chloride (PVC) as the first layer.

Selectivity Enhancement by Using Double-Layer MOX-Based Gas Sensors Prepared by Flame Spray Pyrolysis (FSP).

Here we present a novel concept for the selective recognition of different target gases with a multilayer semiconducting metal oxide (SMOX)-based sensor device. Direct current (DC) electrical resistance measurements were performed during exposure to CO and ethanol as single gases and mixtures of highly porous metal oxide double- and single-layer sensors obtained by flame spray pyrolysis. The results show that the calculated resistance ratios of the single- and double-layer sensors are a good indicator for the presence of specific gases in the atmosphere, and can constitute some building blocks for the development of chemical logic devices. Due to the inherent lack of selectivity of SMOX-based gas sensors, such devices could be especially relevant for domestic applications.

A novel double-layer electrospun nanofibrous membrane sensor for detecting nitroaromatic compounds

Conjugated polymer P, which was synthesized by introducing 9,9-diphenylfluorene and thiophene units into the backbone of poly(fluorenylene ethynylene), showed high sensitivity in detecting nitroaromatics. A double-layer sensor, named P-PS/GEL, was prepared by electrospinning technique using polymer P, polystyrene (PS), and gelatin (GEL). A nanofibrous membrane from the mixture of PS and P as the top layer (P-PS) served as the sensing layer for detecting nitroaromatics (NACs). A gelatin nanofibrous membrane as the bottom layer (GEL) served as porous scaffold for the top layer. Therefore, apart from transferring into the top layer directly from above, the NACs molecules could also approach the top sensing layer through the bottom porous layer. This double-layer conformation greatly improved the permeability of the P-PS layer. As a result, the double-layer sensor exhibited a greater quenching efficiency (Q f) of 75 % than that of the single-layer P-PS (55 %). Importantly, the sensor showed good reversibility of quenching process after being exposed to saturated DNT vapor for 6 cycles.

Response and stability improvement by fusing optimized micro-hotplatform and double layer bowl-like nano arrays

Sensors with single layer (SL) and double layer (DL) tin dioxide porous bowl-like nano arrays were prepared via two-dimensional (2D) colloidal crystal template method and their sensing response and stability towards ethanol were investigated. The Micro-HotPlatform (MHP), which was the substrate of the sensor, was carefully designed and fabricated to achieve low power consumption, well-controlled temperature distribution and high mechanical strength. It was found that with the help of DL bowl-like nano arrays (BNA) the response and stability of sensors with double layers were better than that of single layer. The DL sensors were sensitive to 20ppb ethanol and the low detection limit was predicted to be as low as 7ppb. Further experiments indicated that after seven days continuous work, the performance of the sensors became stable. Before stabilization, SL sensors went through about 80% decrease of response while DL sensors only about 40%. DL sensors showed better performance and were good candidates for future commercial applications.

Gigantically enhanced NO sensing properties of WO3/SnO2 double layer sensors with Pd decoration

Five micrometers thick SnO2 bottom layer and 8μm thick WO3 top layer were consecutively printed onto the Al2O3 substrate with Pt electrodes, and decoration with Pd nanoparticles was also applied to the WO3 top layer, thus sensors with the structure of Pt/SnO2/WO3(Pd) were fabricated. The NO sensing properties were characterized in the temperature range of 250 to 500°C. When exposed to 200ppm NO at 400°C, the sensor achieved a response of 38, and the response and recovery time were only 20s and 37.5s, respectively. The WO3 top layer with Pd decoration ensured a good response to NO gas, and the SnO2 bottom layer accelerated the electron transport, therefore, enhancing the response and recovery speed dramatically.

A Molecularly Imprinted Fluoral-P/Polyaniline Double Layer Sensor System for Selective Sensing of Formaldehyde

We demonstrate the capacity of a double layer thin-film system, composed of polyaniline and fluoral-p, to sensitively detect and selectively bind formaldehyde vapor using an interdigitated electrode assembly. The sensor response scales with the concentration of formaldehyde vapor and does not respond significantly to other potentially interfering molecules. This heightened response and selectivity result from imprinting the polyaniline layer with a molecular memory for ammonia. The chemistry of the double layer detection is discussed in terms of the Hantzsch reaction and the p-type semiconducting activity of polyaniline.

New generation of wearable goniometers for motion capture systems.

BackgroundMonitoring joint angles through wearable systems enables human posture and gesture to be reconstructed as a support for physical rehabilitation both in clinics and at the patient’s home. A new generation of wearable goniometers based on knitted piezoresistive fabric (KPF) technology is presented.MethodsKPF single-and double-layer devices were designed and characterized under stretching and bending to work as strain sensors and goniometers. The theoretical working principle and the derived electromechanical model, previously proved for carbon elastomer sensors, were generalized to KPF. The devices were used to correlate angles and piezoresistive fabric behaviour, to highlight the differences in terms of performance between the single layer and the double layer sensors. A fast calibration procedure is also proposed.ResultsThe proposed device was tested both in static and dynamic conditions in comparison with standard electrogoniometers and inertial measurement units respectively. KPF goniometer capabilities in angle detection were experimentally proved and a discussion of the device measurement errors of is provided. The paper concludes with an analysis of sensor accuracy and hysteresis reduction in particular configurations.ConclusionsDouble layer KPF goniometers showed a promising performance in terms of angle measurements both in quasi-static and dynamic working mode for velocities typical of human movement. A further approach consisting of a combination of multiple sensors to increase accuracy via sensor fusion technique has been presented.

A New Clustering Routing Algorithm for WSN Based on PSO

A wireless sensor network (WSN) consists of spatially distributed wireless sensor nodes. The node power constrains the development of WSN. Employing techniques of clustering can reduce energy consumption of wireless sensor nodes and prolong the network lifetime. Therefore, in the study a new clustering routing algorithm is presented. The clustering algorithm uses the double-layer sensor nodes to communicate. And in order to optimize power energy consumption for WSN node energy, PSO algorithm is employed to find cluster head in each layer. Simulation results show that the algorithm not only can equal power energy of node, but also can reduce consumption in the long distance data transmission.

High-Performance Humidity Sensors Based on Double-Layer ZnO-TiO2 Nanofibers via Electrospinning

ZnO and TiO2 nanofibers are synthesized via electrospinning methods and characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Humidity sensors with double-layer sensing films are fabricated by spinning the ZnO and TiO2 nanofibers on ceramic substrates sequentially. Compared with sensors loading only one type of nanofiber, the double-layer sensors exhibit much better sensing properties. The corresponding impedance changes more than four orders of magnitude within the whole humidity range from 11% to 95% relative humidity, and the response and recovery times are about 11 and 7s, respectively. Maximum hysteresis is around 1.5% RH, and excellent stability is also observed after 180 days. The humidity sensing mechanism is discussed in terms of the sensor structure. The experimental results provide a possible route for the design and fabrication of high performance humidity sensors based on one-dimensional nanomaterials.

Highly sensitive NH3 sensor using Pt catalyzed silica coating over WO3 thick films

Abstract Ammonia gas sensing properties of a single layer WO 3 thick film and a double layer sensor structure having a supported catalyst on it have been investigated. The single layer sensor exhibited low response to NH 3 . An enhancement in gas response was achieved by doping WO 3 with Pt, Pd or Au. Ammonia sensing properties of the WO 3 thick film was improved markedly by overcoating a platinum catalyzed silica-niobia layer onto the WO 3 film surface. Such a double layer structure not only increased the gas response, but decreased the response time also.

Effect of Oxidizing Agent of Polypyrrole Layer Prepared by Vapor Polymerization

The influence of oxidant on surface morphology and sensing property of polypyrrole (PPy) – poly (vinyl alcohol) (PVA) double layer sensors was investigated. PPy–PVA double layer sensors were prepared by vapor polymerization using FeCl3 as oxidizing agent and PVA as adhesive agent. The surface of PPy–PVA layer was observed on a scanning electron microscope (SEM). The surface morphology of sensor showed homogeneous layer and thickness of 1µm. And the sensing properties were investigated using a flow measuring system. The maximum sensitivity to methanol 1000ppm was proportional to increasing 12wt % FeCl3 concentration at 25°C. The response time was not affected by FeCl3 concentration, but the recovery time increased according to the amount of FeCl3. The best amount of FeCl3 was observed at 12wt%.