Sensor Elements Research Articles

Features of gas environment influence on the electrical properties of nano- and microcrystals ZnO

Nanocrystalline powder based on ZnO:Mn is used to create sensitive elements of gas sensors. It is shown that the nanocrystalline material has a structure similar, from an energy point of view, to the structure of micro-sized ZnO:Ag ceramics, which contains intercrystalline potential barriers formed by chemisorbed oxygen.Adsorbed water can have a significant effect on the electrical conductivity of sensors at operating temperatures below T = 100oC. When evacuated, flammable gases such as propane or butane influence electrical conductivity opposite to what is observed in a normal air atmosphere containing oxygen.

De-Striping and De-Smiling of Aerial Hyperspectral Image for Water Color Analysis

Hyperspectral imagery is typically acquired in push-broom mechanism, which is prone to image artifacts such as striping and smile for the sensor array whose sensor elements are not perfectly calibrated. The best practice would be to calibrate the sensor elements before the flight, but post-correction is required when images are already acquired without calibration. While there are some studies that addressed those striping and smile effects for hyperspectral images acquired from satellite or aircraft platforms, few studies were done for hyperspectral images that are focusing water color analysis, where the radiance level is approximately only a tenth of terrestrial scenes. This study proposes a correction method specialized for water scenes that also may contain terrestrial objects together, and analyzes the results using real drone-borne hyperspectral imagery taken for an island area in Korea. The result revealed that the variation in columnar mean before the de-striping, which ranges 5-15%, reduced to under 2% after the correction, also exhibiting successful removal of striping in visual inspection. The smile effect that ranges approximately 1-2 mW/m2/nm/sr, which accounts for 30% of radiance from water area, also reduced to under 0.1 mW/m2/nm/sr after the smile correction.

Fiber-Optic Hydraulic Sensor Based on an End-Face Fabry–Perot Interferometer with an Open Cavity

The paper describes the design and manufacturing process of a fiber optic microphone based on a macro cavity at the end face of an optical fiber. The study explores the step-by-step fabrication of a droplet-shaped macro cavity on the optical fiber’s end surface, derived from the formation of a quasi-periodic array of micro-cavities due to the fuse effect. Immersing the end face of an optical fiber with a macro cavity in liquid leads to the formation of a closed area of gas where interfacial surfaces act as Fabry–Perot mirrors. The study demonstrates that the macro cavity can act as a standard foundational element for diverse fiber optic sensors, using the droplet-shaped end-face cavity as a primary sensor element. An evaluation of the macro cavity interferometer’s sensitivity to length alterations is presented, highlighting its substantial promise for use in precise fiber optic measurements. However, potential limitations and further research directions include investigating the influence of external factors on microphone sensitivity and long-term stability. This approach not only significantly contributes to optical measurement techniques but also underscores the necessity for the continued exploration of the parameters influencing device performance.

Gas-Sensitive Material for Semiconductor Hydrogen Sulfide Sensor

In this work, the synthesis of porous silica gas-sensitive materials for semiconductor sensors of hydrogen sulfide is presented. As a result of studying the activity and selectivity of individual and binary oxides in the oxidation of combustible gases, the composition of the catalyst (10CuO + 90WO3) for the gas-sensitive element of the H2S sensor was selected. The selected catalysts ensure high semiconductor sensor (SCS) selectivity in a wide range of temperatures and H2S concentrations. The optimal ratio of the initial components for the synthesis of silica gas-sensitive materials for a semiconductor hydrogen sulfide sensor has been selected. It has been established that the period of maturation of the film-forming solution based on tetraethoxysilane (TEOS) is 6.5 hours, the period that ensures the production of gas-sensitive films is 18.5 days, and the aging period is 3.5 days. It was found that an increase in the process temperature from 20 to 40°C with a slight change in the viscosity of the solution leads to a sharp reduction in the stability time of the solution from 18.5 to 7.5 days.

Surface-Engineered Nanomaterials for Optical Array Based Sensing.

Array based sensing governed by optical methods provides fast and economic way for detection of wide variety of analytes where the ideality of detection processes depends on the sensor element's versatile mode of interaction with multiple analytes in an unbiased manner. This can be achieved by either the receptor unit having multiple recognition moiety, or their surface property should possess tuning ability upon fabrication called surface engineering. Nanomaterials have a high surface to volume ratio, making them viable candidates for molecule recognition through surface adsorption phenomena, which makes it ideal to meet the above requirements. Most crucially, by engineering a nanomaterial's surface, one may produce cross-reactive responses for a variety of analytes while focusing solely on a single nanomaterial. Depending on the nature of receptor elements, in the last decade the array-based sensing has been considering as multimodal detection platform which operates through various pathway including single channel, multichannel, binding and indicator displacement assay, sequential ON-OFF sensing, enzyme amplified and nanozyme based sensing etc. In this review we will deliver the working principle for Array-based sensing by using various nanomaterials like nanoparticles, nanosheets, nanodots and self-assembled nanomaterials and their surface functionality for suitable molecular recognition.

Tin Oxide Modification of Indium Oxide Gas Sensitive Layers to Increase Efficiency of Gas Sensors

Monitoring of air pollutions is one of actual trends in the development of industrial and domestic instrumentation. There are sets of tasks for improving gas analytical instruments because of increasing demand for control of a concentration of explosive and toxic gases on a level with maximum allowable concentration. The aim of the paper was to investigate the methods of formation and elemental composition of indium oxide films modified with tin oxide on the surface of gas sensor elements as one of the promising compounds for improving the detection efficiency of explosive and toxic gases in the environment. The processes of formation of gas-sensitive films deposited on the surface of nichrome alloy information electrodes were studied in this article. Substrates of anodic aluminum oxide with area of 10 × 10 mm2 and a thickness of 45 ± 0,5 μm were chosen for research. Two layers on the surface of the samples were formed. The first layer was formed from NiCr alloy (Ni – 80 %, Cr – 20 %) with a thickness of ≈ 0.3 μm by ion-plasma sputtering. The second layer was based on indium oxide with addition of tin oxide with thicknesses from ≈ 0.3 μm to ≈ 1.0 µm and coated with sol-gel technology. Five samples of gas-sensitive films were formed with different methods of deposition and heat treatment. Scanning electron microscopy was used for study of films’ morphology and elemental compositions of samples. The most perfect continuous semiconductor films were obtained by multilayer applying of a sol-gel paste. When semiconductor films were processed at annealing temperatures of 700 °C and higher in vacuum so there was observed cracking of semiconductor films up to a layer of NiCr alloy. The developed surface of gas-sensitive films allows to reach high sensitivity and affectivity of semiconductor sensors for control of air gas composition.

A LA-BTC MOF as a sensor element of an electronic nose for selective adsorption of biomarkers of diseases: Molecular dynamics simulations of adsorption

The advanced non-invasive diagnostic method is an analysis of exhaled volatile organic compounds (VOCs), which are regarded as biomarkers of various diseases. A gravimetric-type electronic nose (e-nose) has shown great promise in exhaled VOC-pattern identification, and its efficiency is determined by the adsorption capacity of the sensing materials towards a specific VOC. The present study employed molecular dynamics (MD) calculations with the OPLS all-atom force field to investigate the adsorption of an isolated molecule of volatile fatty acids, acetone, ethanol, methanol, acetic aldehyde, neopentane, and ethane in a unit cell of the lanthanum-based metal-organic framework (La-BTC MOF), which was proposed as a potential sensing material for the gravimetric-type e-nose. The adsorption potential determined as a change in the potential energy, ΔEp, of the total simulation system upon the penetration of a single molecule into a unit pore of La-BTC MOF was calculated for all the targeted VOCs and water to be 1.56–10.78 kJ·mol−1, following the order: ethane < neopentane < acetic aldehyde < ethanol < methanol < water < acetone < butanoic acid < caproic acid. Therefore, the biomarkers with ΔEp > ΔEp(water) ∼ 7.3 kJ/mol can be captured from the exhaled breath. According to the MD calculations, an oxygen-containing biomarker molecule in the adsorbed state was oriented by its oxygen atom towards the La3+ cation, so that the O---La3+ distance of 0.28–0.32 nm was the shortest among those for other constituent atoms. Thus, the strong electrostatic interactions between the oxygen atoms of the adsorbate molecules and the La3+ cation of the adsorbent were most responsible for the capture of the oxygen-containing biomarkers by the La-BTC MOF. The competing adsorption effect between water and oxygen-containing biomarker molecules was examined in dependence on the water content and the way the water molecules were introduced into the simulation system.

Screening of broad-spectrum aptamer and development of electrochemical aptasensor for simultaneous detection of penicillin antibiotics in milk

Penicillin antibiotics (PENs) play an important role in killing pathogenic bacteria. However, the residues of various penicillin antibiotics in milk gradually accumulate in the human body with the increase of milk intake, which causes direct harm to the human body. Aptamers can be used as recognition element of sensors. It is great significance to use broad-spectrum aptamers for simultaneous detection of PENs. In this study, we reported the screening and identification of DNA aptamers for PENs. The aptamers were screened by graphene oxide-systematic evolution of ligands by exponential enrichment (GO-SELEX). The broad-spectrum aptamers with high affinity and specificity were successfully obtained after 13 rounds of screening. The affinity and specificity of candidate aptamers were analyzed by a GO fluorescence competition method. Further sequence analysis revealed that a truncated 47 nt aptamer (P-11-1) had a higher affinity than the original 79 nt aptamer. The truncated aptamer P-11-1 was used as a recognition element, and an electrochemical aptasensor was prepared using gold nanoparticles (AuNPs) combined with ferroferric oxide-multi walled carbon nanotube (Fe3O4-MWCNTs) complex. The results showed that the developed aptasensor achieved the simultaneous detection of PENs in milk samples across a concentration range of 2 nM–10,000 nM, achieving a limit of detection of 0.667 nM. This methodology provided a simple and sensitive new thinking for antibiotic multi-residue detection.

Review and Analysis of the Characteristics of IoT Sensors

Internet of things (IoT) is the concept of data transmission network between physical objects ("things"), equipped with built-in tools and technologies for interaction with each other or with the environment. The work is devoted to the inspection and analysis of sensors, how the IoT systems are associated with environmental objects. IOT uses a wide class of measurement tools, from elementary sensors (eg, temperature, pressure, light), consumption metering devices (such as intellectual meters) to complex integrated measuring systems. The parameters of 30 types of sensors for IoT are given, 2 of them of the type of temperature and humidity sensors, 2 type of pressure sensors, 13 sensors that measure the flow and amount of gas or liquid, 2 type of accelerometers, 10 approach and movement sensors and 1 noise sensor. Among them are 4 sensors for wireless sensory networks (WSM), a single-time medical sensor for internal blood pressure measurement, calorimetric, vortex and electromagnetic flow sensors and gas or fluid, accelerometer, and memes of memes, and e-memometers, and electromagnetic measurement motion, a device of measuring noise level in the range of sound vibrations. For some sensors, there are no metrological characteristics at all, at best there is only a range of measurements and resolution. The resolution ranges from 8 bits to 16 bits with a signal sampling rate from 0.5 Hz to 48 kHz. There is even a LDC1612 digital induction chip with 28 bits. WSM sensors are designed to work with DigiMesh, LoraWan and Arduino, Raspberry. Many sensors use outdated RS 232, RS 432, I2C. Keywords: internet of things, network, review, analysis, sensors, objects, metrology.

Development of fluorescence sensor and paper chips based on EDTA etched-CdTe@CdS QDs for the selective and sensitive detection of Cd(II) in rice samples

EDTA-etched CdTe@CdS QDs were used as the specific recognition element and signal probe of a fluorescence sensor or paper chip for the highly sensitive detection of Cd(II) with an electronic eye device as readout. The results showed that the CdTe@CdS QDs were successfully synthesized with a typical core–shell structure. Under the optimum conditions, the EDTA-etched CdTe@CdS QDs sensor achieved the sensitive detection of Cd(II) with a detection limit of 0.092 μM and a concentration range of 0.44–6.67 μM. The paper chips based on the EDTA-etched CdTe@CdS QDs sensor had a visual cut-off value of 0.44 μM with a short detection time (<15 min). The proposed method also exhibited excellent stability, high specificity, and good recovery for Cd(II) in real rice samples. These results suggested that the EDTA-etched CdTe@CdS QDs provide a promising platform for on-site and visual detection of Cd(II) in rice samples.

Error analysis of the compact microphone array for sound source localization

Smart sensing is used to provide specific information by using physical quantities measured by multiple sensors or multi-modal sensor modules. Nowadays, the smart sensor is configured as a compact system using very small transducers implemented by MEMS technology. Accordingly, the multi-modal sensing device is getting miniaturized. A microphone array can be classified as a smart sensing device that estimates the sound field information. However, it is difficult to implement a compact system because the measurable frequency range is limited by the spacing between adjacent microphones. Also, the calibration is difficult due to the irregularly shaped sensor element; therefore, the traceability is not yet established. In this study, sound source localization algorithms are applied for implementing the compact microphone array. The inherent error due to the sensor position tolerance, magnitude difference, and phase mismatch is analyzed. Because the coherent noise increases uncertainty in the actual test environment, the estimation error depending on the critical distance is analyzed. Finally, a compact webcam-based multi-modal sensor is implemented and the localization test result is reviewed.

Optical wavefront phase-tilt measurement using Si-photonic waveguide grating couplers.

Silicon photonic wavefront phase-tilt sensors for wavefront monitoring using surface coupling grating arrays are demonstrated. The first design employs the intrinsic angle dependence of the grating coupling efficiency to determine local wavefront tilt, with a measured sensitivity of 7 dB/°. The second design connects four gratings in an interferometric waveguide circuit to determine incident wavefront phase variation across the sensor area. In this device, one fringe spacing corresponds to 2° wavefront tilt change. These sensor elements sample a wavefront incident on the chip surface without the use of bulk optic elements, fiber arrays, or imaging arrays. Both sensor elements are less than 60 µm across and are potential unit cell sensor elements for large arrays that monitor wavefront shape across an image or pupil plane in adaptive optics systems for free-space optical communications, astronomy, and beam pointing applications.

Oligohexamethylene Guanidine Derivative as a Means to Prevent Biological Fouling of a Polymer-Based Composite Optical Oxygen Sensor.

The use of biocidal agents is a common practice for protection against biofouling in biomass-rich environments. In this paper, oligohexamethyleneguanidine (OHMG) polymer, known for its biocidal properties, was further modified with para-aminosalicylic acid (PAS) to enhance its properties against microorganisms coated with a lipid membrane. The structure of the product was confirmed by 1H NMR, 13C NMR, and FTIR spectroscopy. The values of the minimum inhibitory concentration (MIC) against Mycobacterium smegmatis ATCC 607 and Pseudomonas chlororaphis 449 were found to be 1.40 and 1.05 μg/mL, respectively. The synthesized substance was used as an additive to the polymer matrix of the composite optical oxygen sensor material. A series of samples with different contents of OHMG-PAS was prepared using a co-dissolution method implying the fabrication of a coating from a solution containing both polymers. It turned out that the mutual influence of the components significantly affects the distribution of the indicator in the matrix, surface morphology, and contact angle. The optimal polymer content turned out to be wt.3%, at which point the water contact angle reaches almost 122°, and the fouling rate decreases by almost five times, which is confirmed by both the respiratory MTT assay and confocal microscopy with staining. This opens up prospects for creating stable and biofouling-resistant sensor elements for use in air tanks or seawater.

SERS substrates based on polymer-protected self-assembled plasmonic films with gold nanoparticles as enhancing element of a microfluidic sensor

We report a self-assembled plasmonic film of 20 nm gold nanoparticles with a protective polymer matrix enabling detection of SERS signals in flow-through microfluidic chips, various environments and pH ranging from 3 to 9, and with a temperature applicability limit of ∼150 °C. Proposed SERS substrate as a sensing platform has demonstrated the retention of its enhancement characteristics with transfer from stationary spectroscopy to microfluidic systems, as well as the ability to be reused and quickly respond to changes in the analyte. The detection limit of such a system based on a model analyte (pseudoisocyanine) in an isopropanol solution was determined as 10−12 M. Our SERS-based sensor have demonstrated clear visibility for real analytes, such as solutions containing various amino acids with different side chains, even at a concentration as low as 10−5 M.

The Use of Polyurethane Composites with Sensing Polymers as New Coating Materials for Surface Acoustic Wave-Based Chemical Sensors—Part I: Analysis of the Coating Results, Sensing Responses and Adhesion of the Coating Layers of Polyurethane–Polybutylmethacrylate Composites

The sensing layers for surface acoustic wave-based (SAW) sensors are the main factor in defining the selectivity and reproducibility of the responses of the sensor systems. Among the materials used as sensing layers for SAW sensors, polymers present a wide range of advantages, from availability to a large choice of chemical-sensing environments. However, depending on the physical–chemical properties of the polymer, issues about the chemical and mechanical stability of the sensing layer have been reported that can compromise the application of sensor systems in the long-term. The sensor properties are defined basically by the properties of the coating material and the quality of the coating process. The strategy used to improve the properties of polymeric coating layers for SAW technology involved the use of polyurethane (PU) in combination with a second polymer that is responsible for the sensing properties of the resulting layer; this is obtained by a reproducible and robust coating procedure. In this first part of our research, we used polymer composites of different compositions of polybutylmetacrylate (PBMA) as the sensing polymer with polyurethane. The analysis of the coating (ultrasonic parameters), the relative sensor responses and the adhesion results for the PU–PBMA composites were determined. The ultrasonic analysis and the relative sensor responses showed very reproducible and precise results, indicating the reproducibility and robustness of the coating process. Accurate correlations between the results of the ultrasonic parameters due to the coating and the relative sensor responses for the organic analytes analyzed were obtained, showing a precise quantitative relationship between the results and the constitution of the composite coating materials. The composites show practically no significant sensor responses to water. The PU–PBMA composites substantially enhanced adhesion to the surface of the piezoelectric sensor element in comparison to the coating with pure PBMA, without loss of its sensing properties. Other PU–polymer composites will be presented in the future, as well as an analysis of the selectivity for the organic analytes for these types of coating materials.

A study on MMG sensor using piezoelectric polymer nanofibers by electrospinning

AbstractIn the fields of medical and sports science, it is required to evaluate muscle activity qualitatively and quantitatively. Currently, mechanomyogram (MMG) that can reflect the mechanical activity of muscle fibers is attracting attention. The purpose of this study is to develop a sensor that can measure MMG during exercise. In this study, a small and flexible MMG sensor using P(VDF/TrFE), which is a piezoelectric polymer material, spun into nanofibers by the electrospinning method has been fabricated and evaluated. By the fabricated electrospinning equipment and the obtained fabrication conditions of the nanofibers MMG sensor has been fabricated by using piezoelectric polymer fibers. By using nanofiber nonwoven fabric for the sensor element, the flexible sensor has been realized. In a sound wave reception experiment assuming MMG measurement, the P(VDF/TrFE) nonwoven fabric element showed that the element detected the sound pressure. Additionally, MMG during isometric contraction and pedaling motion has been measured using the fabricated sensor. The results show that the proposed sensor is effective for measuring MMG during exercise.

First field measurements of optical turbulence near the ground with a newly developed fine-wire thermometer

First results of optical turbulence field measurements collected with a newly developed fine-wire temperature sensing system are presented and discussed. The centerpiece of the sensing system is an array of fine-wire platinum resistance thermometers. The active fine wire in each sensor element has a diameter of 0.64 μm and a length between 0.5 and 1 mm. The sampling rate is 44.1 kHz, and the noise level is 1 mK for a bandwidth of 10 kHz. Data were recorded while the car onto which the sensors were mounted was traveling at a speed of about 40 mph, or 18 m s . Estimates of the temperature structure function are compared against the classical Obukhov-Corrsin theory, which predicts power-law asymptotes with in the viscous-diffusive range and in the inertial-convective range. For the pair of separations cm and cm, we observed . The frequency spectrum follows the theoretically predicted power law in the inertial-convective subrange. The ‘Hill bump’ in the transition regime between the inertial-convective and viscous-diffusive subranges is visible.

Sensor Systems for Extremely Harsh Environments

Sensors are key elements for capturing environmental properties and are today indispensable in the industry for monitoring and control of industrial processes. Many applications are demanding for highly integrated intelligent sensors to meet the requirements on safety, clean and energy efficient operation or to gain process information in the context of industry 4.0. While in many everyday objects highly integrated sensor systems are already state of the art, the situation in an industrial environment is clearly different. Frequently the use of sensor systems is impossible, due to the fact that the extreme ambient conditions of industrial processes like high operating temperatures or strong mechanical loads do not allow a reliable operation of sensitive electronic components. Eight Fraunhofer Institutes have bundled their competencies and have run the Fraunhofer Lighthouse Project ‘eHarsh’ to overcome this situation. The project goal was to realize sensor systems for extremely harsh environments, whereby sensor systems are not only pure sensor elements, rather containing one or multiple sensor elements and integrated readout electronics. Various technologies which are necessary for the realization of such sensor systems have been identified, developed and finally bundled in a technology platform. These technologies are e. g. MEMS and ceramic based sensors, SOI-CMOS based integrated electronics, board assembly and laser based joining technologies. All these developments have been accompanied by comprehensive tests, material characterization and reliability simulations. Based on the platform a pressure sensor for turbine applications has been realized to prove the performance of the eHarsh technology platform.

Optimal design of bi-planar heater with magnetic field self-suppression configuration based on multi-objective optimization

As a crucial component, the vapor cell serves as the fundamental sensing element in various atomic sensors, and electric heating is typically required to enhance the density of alkali metal atoms. Due to the presence of driving current, electric heating can unavoidably introduce interfering magnetic fields, which affect the performance of atomic sensors. To suppress this magnetic field interference, the electric heater trace configuration must be designed to achieve the magnetic field self-suppression effect. However, previous studies have solely focused on the optimization design of a single-sided heater, which leads to the spatial magnetic field gradient and limited improvement of the self-suppression effect. Therefore, this study proposes an optimization design method for the bi-planar heater, and uses the combination optimization of two heater pieces with spatial symmetrical distribution. Using the multi-objective optimization algorithm, the structure parameters and current directions of the heater are optimized to achieve superior magnetic field suppression and reduce the vapor cell magnetic field gradient. Both finite element simulation and experimental results demonstrate that the proposed bi-planar heating configuration generates an average magnetic field of 0.06 nT/mA in the central region of the vapor cell, which is more than three times less than the previous single-sided optimal configuration and more than five times less than the bi-planar symmetrical use of the single-sided optimal configuration. The proposed approach is expected to enhance the performance of atomic magnetometers and other atomic sensors that are sensitive to magnetic fields.

On the low-temperature isotropic point in Rb2SO4 crystals

In this work, Rb2SO4 single crystals of good optical quality were synthesized and the spectral (300–700 nm) and temperature (300–77 K) dependencies of birefringence were experimentally investigated. It was found that with a temperature decreasing, at a temperature of T = 85 K and a light wavelength of λ = 500 nm, the birefringence value in the Y direction is zero (Δny = nz – nх = 0), which testifies to the existence of a new isotropic point. The influence of uniaxial compression on changes in Δny (Т, λ) was studied, and their significant sensitivity was revealed. The temperature-baric and spectral-baric changes of the isotropic point position were analyzed, based on which the temperature-spectral-baric diagram of the isotropic state of the crystal was constructed, which will be of practical importance for the use of crystal as an active element in a crystal-optical temperature sensor for a low-temperature region. Based on the Δny (Т, λ, σ) dependencies, the combined piezo-optic coefficients of the crystal were estimated, and it was assumed that not only thermal but also mechanical deformation of the optical indicatrix takes place in the vicinity of the isotropic point.