Single-layer Sensor Research Articles

Effects of Geometry and Supporting Silicone Layers on the Performance of Conductive Composite High-Deflection Strain Gauges

Piezoresistive sensors composed of nickel nanostrands, nickel-coated carbon fibers, and silicone can be used to measure large physical deflections but exhibit viscoelastic properties and creep, leading to a complex and nonlinear electrical response that is difficult to interpret. This study considers the impact of modifying the geometry and architecture of the sensors on their mechanical and electrical performance. Varying the sensor thickness leads to potentially significant differences in conductive fiber alignment, while adding external layers of pure silicone provides elastic support for the sensors, potentially reducing their extreme viscoelastic nature. The impact of such modifications on both mechanical and electrical behavior was assessed by analyzing strain to failure, the magnitude of hysteresis with cycling, the repeatability of the electro-mechanical response, the strain level at which resistance begins to monotonically decrease, and the drift in electrical response with cycling. The results indicate that thicker single-layer sensors have less electrical drift. Sensors with a multilayered architecture exhibit several improvements in behavior, such as increasing the range of the monotonic region by approximately 52%. These improvements become more significant as the thickness of the pure silicone layers increases.

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.

Sub-nT Resolution of Single Layer Sensor Based on the AMR Effect in La2/3Sr1/3MnO3 Thin Films

Single-layer magnetoresistive sensors were designed in a Wheatstone bridge configuration using La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/3</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ferromagnetic oxide thin film. Uniaxial anisotropy was induced by performing epitaxial deposition of the films on top of vicinal SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrate. X-ray scan confirms the high crystalline quality of the films and the magnetic anisotropy was checked by magneto-optical Kerr effect measurements. Thanks to the anisotropic magnetoresistive effect and the very low noise measured in the devices, sub-nT resolution was achieved above 100 Hz at 310 K.

Single-layer wire-mesh sensor to simultaneously measure the size and rise velocity of micro-to-millimeter sized bubbles in a gas-liquid two-phase flow

In this work, we propose a conductivity-based single-layer wire-mesh sensor (WMS) system to simultaneously measure the planar bubble distribution, equivalent diameter, and rise velocity of micro-to-millimeter sized bubbles in a gas-liquid two-phase flow. Compared with the conventionally available WMS system, the proposed system is capable of simultaneously measuring the bubble size and velocity using a single-layer sensor by establishing the correlation between the effective time taken for the bubble to pass through the sensor wires and its rise velocity, which is validated for micro-to-millimeter sized bubbles. Using this correlation, we have improved the recursive bubble identification method to develop a nonlinear model for bubble size, making it possible to selectively measure and distinguish between the bubbles in micro-to-millimeter scales (previous sensors were validated for large bubbles only). To accomplish this, we also investigated the differences in the dynamics of bubble-wire contact in detail. In a vertical upward bubbly flow, the present sensor was employed for a wide range of bubble sizes (200μm to 3.5 mm on average) and liquid velocity of 0−0.5 m/s; the measured data were in good agreement with those measured with a high-speed shadowgraphy. Finally, we discuss some issues of the proposed system, which requires a further attention.

3D electromagnetic tomography using a single layer sensor array

Electromagnetic tomography (EMT) is a non-invasive technique to gain the induced voltages and to reconstruct the distribution of electromagnetic properties. A volume imaging using a single layer sensor array, namely, Single Layer 3D-EMT, has been developed in this paper. To solve the forward problem, three kinds of sensor arrays are established with different number of coils,—8, 12 and 16, to conduct simulations. Four typical conductivity distributions are used to verify the 3D-EMT imaging with single layer sensor array. The calculation of sensitivity maps in 3D views is presented, and the sensitivity maps of different layers, from z = 0 to z = 20, are analyzed. The conjugate gradient iterative method has been adopted in image reconstruction. It can be seen from the simulation results that the 3D reconstructed images using a single layer sensor array can display the distribution of the measured objects in position, shape, and size. By calculating the relative error, the quality of the reconstructed images is evaluated andthe result shows that the 12-coil sensor array has the best image quality among three sensor arrays. In addition, the single layer 3D experimental system has been established to evaluate the effectiveness of 3D imaging using a single layer sensor array. In order to save the hardware resources, the paper presents the author's research work about the possibility of Single Layer 3D-EMT imaging in simulations and experiments. This can also provide a guide to explore the potential application with electromagnetic testing technique.

Comparison between one layer and bilayer surface plasmon resonance optical fiber chemical sensor

Surface Plasmon Resonance (SPR) - based plastic optical fiber has been provided as a sensor to estimate the refractive index and then the concentration of specific chemical samples. Two configurations were suggested for the design. The first was through using a single layer of gold with a thickness of about 40nm deposited on a 10mm portion in the middle of plastic optical fiber. In the second configuration, a bilayer is deposited on the fiber. This bilayer consisted of a gold layer with a thickness of about 30 nm and an aluminum layer with a thickness of about 30 nm. Both of these configurations are utilized as chemical sensors. The resonance wavelength for the bilayer-based sensor was higher than that of the single-layer sensor for all studied chemical samples. The highest resonance wavelength was for the salt-water solution with a concentration of 30%. For the salt-water solution with a concentration of 30%, the resonance wavelength with the bilayer-based sensor was 568nm while it was 540nm with the single-layer sensor.

Designing sandwich-type single-layer graphene decorated by copper nanoparticles for enhanced sensing properties

It has already been theoretically shown that sandwich-type structures prepared by stacking metal nanoparticles in two graphene layers would have exceptional optical and electrical properties for practical applications. These sandwich structures designed by band gap engineering could lead to materials capable of being developed to meet industrial demands. In order to confirm this theoretical approach, copper nanoparticle (CuNP) islands decorated in sandwich-type single-layer graphene (SLG) have been designed and used as a non-enzymatic sensor platform for the first time. Firstly, SLG has been synthesized on copper foil using a chemical vapor deposition technique and transferred onto a fluorine-doped tin oxide surface. Next, CuNPs on this SLG have been prepared using an inert-gas condensation method based on DC magnetron sputtering. A sensor platform based on the sandwich-type hetero-structure (SLG/CuNP/SLG) has been constructed by transferring another single layer of graphene onto the prepared CuNP-decorated graphene layer. In this way, a unique sandwich structure has been obtained for further applications by stacking nanoparticles with high stability, controlled size and regular particle distribution between impurity-free, large-area single layers of graphene. The sensor properties of this sandwich structure to the saccharides have been compared with those of the single-layer sensor platform (CuNP/SLG). In accordance with the theoretical studies in the literature, it has been found that the sandwich structure greatly improves sensor properties such as limit of detection, stability and response time. More importantly, it was determined that the sandwich structure acts as a shielding layer, protecting nanoparticles from electrochemical/optical and other environmental conditions.

Enhanced NO2 gas sensing of a single-layer MoS2 by photogating and piezo-phototronic effects

NO2 sensors with ultrahigh sensitivity are demanded for future electronic sensing systems. However, traditional sensors are considerably limited by the relative low sensitivity, high cost and complicated process. Here, we report a simply and reliable flexible NO2 sensor based on single-layer MoS2. The flexible sensor exhibits high sensitivity to NO2 gas due to ultra-large specific surface area and the nature of two-dimensional (2D) semiconductor. When the NO2 is 400 ppb (parts per billion), compared with the dark and strain-free conditions, the sensitivity of the single-layer sensor is enhanced to 671% with a 625 nm red light-emitting diode (LED) illumination of 4 mW/cm2 power under 0.67% tensile strain. More important, the response time is dramatically reduced to ∼16 s and it only needs ∼65 s to complete 90% recovery. A theoretical model is proposed to discuss the microscopic mechanisms. We find that the remarkable sensing characteristics are the result of coupling among piezoelectricity, photoelectricity and adsorption-desorption induced charges transfer in the single-layer MoS2 Schottky junction based device. Our work opens up the way to further enhancements in the sensitivity of gas sensor based on single-layer MoS2 by introducing photogating and piezo-phototronic effects in mesoscopic systems.

Prospects of using rare-earth hexaborides in thermoelectric single-photon detectors

The results of the numerical simulation of heat propagation processes occurring after the absorption of single photons with energies of 1 eV–1 keV in a three-layer sensor of a thermoelectric detector are analyzed. Different configurations of the sensor with a tungsten absorber, a thermoelectric layer of cerium hexaboride, and a tungsten heat sink are considered. It is shown that sensors for detecting photons of a specific spectral range with the required energy resolution and counting rate can be developed by varying the geometric sizes of the sensor layers. It is concluded that a three-layer sensor has a number of advantages in comparison with a single-layer sensor and has characteristics allowing consideration of the thermoelectric detector as a realistic alternative to superconducting single-photon detectors.

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.

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.

Experimental Comparison of Fiber-Optic Surface Plasmon Resonance Sensors with Multi Metal Layers and Single Silver or Gold Layer

Fiber-optic surface plasmon resonance sensors with multi metal layers (Ti/Ag/Au) and single silver or gold layer are presented. In comparison with widely used single-layer sensors, the multi-layer sensor shows a wider refractive index measurement range (in a range of 1.3344 to 1.4111 RIU) and a better resolution in the high refractive index region (refractive index over 1.3697 RIU). In addition, the sensitivity of multi-layer sensor is between those of sensors with silver and gold layers, the chemical stability, and the film adhesion capability of multi-layer sensor are much better than those of silver layer sensor.

Gas sensors for CO2 detection based on RGO–PEI films at room temperature

In this paper, polyethyleneimine (PEI) and reduced graphene oxide (RGO) were selected as sensing materials for carbon dioxide detection. Two kinds of sensors with different sensitive film structures, i.e., RGO–PEI composite film and RGO–PEI bi-layer film were fabricated by airbrushing the sensitive films on interdigitated electrodes. Response performances of both sensors at room temperature were investigated. Results showed that sensors with bi-layer film exhibited smaller baseline drift and more stable sensing characteristics than the counterparts with composite film. Furthermore, bi-layer film sensors with different quantity of PEI solution deposited were studied. Performances of long-time stability, repeatability, low concentration of detection for carbon dioxide, and measurements of response time and recovery time were investigated. It was found that appropriate weight ratio of RGO and PEI was critical for sensing response. In addition, the sensor with bi-layer film exhibited a better repeatability but had longer response time and recovery time than RGO single-layer sensor, and both of them could detect as low as 20 parts per million carbon dioxide gas. Sensing responses of the prepared sensors to carbon dioxide under dry air or nitrogen were compared. The relevant sensing mechanisms were studied as well.

An adaptive sensor sleeping solution based on sleeping multipath routing and duty-cycled MAC protocols

Various applications of wireless sensor networks require multihop data transmission over error-prone wireless links, hence multipath routing can be used to meet the application's reliability requirement. On the other hand, wireless sensors are usually battery powered, and thus it is very important to save energy in order to prolong the network lifetime. In this article, we propose (1) Sleeping Multipath Routing, which can trade off reliability and network lifetime by dynamically activating an optimal number of paths to support the application's reliability requirement and putting the rest of the sensors to sleep, and (2) an adaptive sensor sleeping solution, which includes Sleeping Multipath Routing, a duty-cycled MAC protocol, and cross-layer coordination to further prolong the network lifetime by putting sensors to sleep at both the routing and the MAC layers. Our proposed Sleeping Multipath Routing and adaptive sensor sleeping solution can be implemented on any multipath routing protocol that discovers multiple disjoint paths between two nodes, and any duty-cycled MAC protocol that has fixed cycle length. We show an example of implementing our adaptive sensor sleeping solution using Directed Diffusion and S-MAC. Simulation results show that our proposed adaptive sensor sleeping solution outperforms single-layer sensor sleeping with a longer network lifetime with required reliability support. Moreover, our proposed adaptive sensor sleeping solution can significantly prolong the network lifetime when the application's reliability requirement varies over time, or when the number of alive nodes in the network changes over time.

Enhancement of Methanol Gas Sensitivity of Cu Intermediate ITO Film Gas Sensors

Sn doped (ITO) and ITO/Cu/ITO (ICI) multilayer films were prepared on glass substrates with a reactive radio frequency (RF) magnetron sputter without intentional substrate heating, and then the influence of the Cu interlayer on the methanol gas sensitivity of the ICI films were considered. Although both ITO and ICI film sensors had the same thickness of 100 nm, the ICI sensors had a sandwich structure of ITO 50 nm/Cu 5 nm/ITO 45 nm. The ICI films showed a ten times higher carrier density than that of the pure ITO films. However, the Cu interlayer may also have caused the decrement of carrier mobility because the interfaces between the ITO and Cu interlayer acted as a barrier to carrier movement. Although the ICI films had two times a lower mobility than that of the pure ITO films, the ICI films had a higher conductivity of due to a higher carrier density. The changes in the sensitivity of the film sensors caused by methanol gas ranging from 50 to 500 ppm were measured at room temperature. The ICI sensors showed a higher gas sensitivity than that of the ITO single layer sensors. Finally, it can be concluded that the ICI film sensors have the potential to be used as improved methanol gas sensors.

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.

Sensing of CH4, CO and ethanol with in situ nanoparticle aerosol-fabricated multilayer sensors

Abstract A new nanoparticle aerosol method was used to synthesize and directly deposit multilayers of metal oxides on sensor substrates. Flame spray pyrolysis (FSP) was used to fabricate Pd/SnO2 and undoped SnO2 sensors with Pd/Al2O3 filter layers on top. These sensing layers were studied for their gas sensing properties and catalytic conversion for CH4, CO and ethanol. The filter effect of the Pd/Al2O3 layer was compared to single layer sensors and was found to be temperature- and gas-dependent. Sensors with improved behaviour with regard to sensor signal and selectivity have been achieved.

Time-Resolved pH/pO2 Mapping with Luminescent Hybrid Sensors

A method for simultaneous and referenced 2D mapping of pH and pO2 is described. The experimental setup combines a fast gateable CCD camera as detector, a LED as excitation light source and a single-layer sensor membrane as optical transducer. The planar optode comprises a lipophilic fluorescein derivative (lifetime approximately 5 ns) and platinum(II) mesotetrakis(pentafluorophenyl)porphyrin (approximately 70 micros in the absence of a quencher) immobilized in a hydrogel matrix. Depending on the fluorescent pH indicator, a pH transition in the physiological range (pH 6-pH 8) or in the near-basic region (pH 7-pH 9) can be achieved. The measuring scheme involves the time-resolved acquisition of images in three windows during a series of square-shaped excitation pulses. A method allowing the calculation of both parameters from these three images is presented. The pH/pO2 hybrid sensor incorporating the pH indicator 2',7'-dihexyl-5(6)-N-octadecyl-carboxamidofluorescein was characterized in detail. The pH and pO2 were determined with a maximum deviation of 0.03 pH unit and 6.5 hPa pO2, respectively, within the range of pH 7.6-pH 8.7 and 0-200 hPa pO2 in test measurements. The ionic strength (IS) cross-sensitivity was found to be relatively small (pH/IS < 3.5 x 10(-4) mM(-1) and pO2/IS <-0.053 hPa mM(-1) at a transition from 0.5 to 0.1 M IS). Whereas a strong temperature effect on the sensor signal was observed (DeltapH/DeltaT = 0.011-0.034 K-1 and DeltapO2/DeltaT = 1.85-7.17 hPa K-1 in the range from 277 to 308 K). Examples of pH/pO2 images obtained in natural marine sediment are presented.

Gas sensing properties of semiconductor heterolayer sensors fabricated by slide-off transfer printing

H 2 and NO x sensing properties of semiconductor heterolayer sensors fabricated by a slide-off transfer printing method on alumina substrates equipped with electrodes have been investigated at 200–600°C. A TiO 2 single layer sensor exhibited high resistance in air and low sensitivity to H 2 at every temperature. Stacking of an M-SnO 2 layer (M: noble metals, loading amount: 0.5 wt.%) over the TiO 2 layer led to a decrease in sensor resistance and to an increase in the sensitivity. In contrast, stacking of an M-SnO 2 layer over an In 2O 3 layer was less effective for improving the sensitivity. The difference in the stacking effect between TiO 2- and In 2O 3-based is considered to arise from a change in the electrical conduction path induced by fabrication of the upper layer, based on the resistance level of each sensing and stacked layer. In the case of M-SnO 2/TiO 2 heterolayer sensors, it was suggested that the conduction path changed from the bottom of the TiO 2 layer to that of an M-SnO 2 layer plus the specific TiO 2 region just above the electrode and that the specific region dominated the sensor resistance and hence the H 2 sensing performance. The sensitivity enhancement is considered to arise from the diffusion control of gaseous O 2 by the M-SnO 2 upper layer. Among the metal oxides tested, WO 3 exhibited the highest sensitivity to both NO 2 and NO, but the NO sensitivity was about a tenth of the NO 2 sensitivity. Stacking of a SiO 2 layer on the WO 3 layer decreased the NO 2 sensitivity, while the NO sensitivity remained almost unchanged. In this case, therefore, the SiO 2 layer was suggested to act as a diffusion control layer for NO 2. These results suggest that the slide-off transfer printing is quite useful for processing of semiconductor heterolayer sensors.