Continuous Sensor Research Articles

Assessing Detection Efficiencies for Continuous Methane Emission Monitoring Systems at Oil and Gas Production Sites

Continuous monitoring systems, consisting of multiple fixed sensors, are increasingly being deployed at oil and gas production sites to detect methane emissions. While these monitoring systems operate continuously, their efficiency in detecting emissions will depend on meteorological conditions, sensor detection limits, the number of sensors deployed, and sensor placement strategies. This work demonstrates an approach to assess the effectiveness of continuous sensor networks in detecting infinite-duration and fixed-duration emission events. The case studies examine a single idealized source and a group of nine different sources at varying heights and locations on a single pad. Using site-specific meteorological data and dispersion modeling, the emission detection performance is characterized. For these case studies, infinite-duration emission events are detected within 1 h to multiple days, depending on the number of sensors deployed. The percentage of fixed-duration emission events that are detected ranged from less than 10% to more than 90%, depending on the number of sources, emission release height, emission event duration, and the number of sensors deployed. While these results are specific to these case studies, the analysis framework described in this work can be broadly applied in the evaluation of continuous emission monitoring network designs.

Heat flux measurement using 3D-printed continuous wire polymer composite sensors

Fused filament fabrication (FFF) 3D printing was used to fabricate continuous wire polymer composite (CWPC) heat flux sensors; the integrated wires acted as resistive sensing elements. Sensor configurations consisting of polylactic acid (PLA) with copper wire (Cu), PLA with nickel (Ni) wire, and thermoplastic polyurethane (TPU) with Cu wire were investigated. For each composition, samples with different numbers of layers were 3D printed to investigate the effect of sensor thickness on performance. Element spacing, polymer conductivity, and wire temperature coefficient of resistances were quantified. Performance testing of the 3D-printed CWPC as a heat flux sensor showed promising results for all compositions and demonstrated their ability to be used as heat flux sensors for low temperature and low heat flux applications. Measurement errors were less than 17% for all configurations and less than 10% for 2-layer samples at the higher heat fluxes. A case study demonstrated the use of a 3D-printed flexible CWPC heat flux sensor to estimate heat loss from an insulated system with good accuracy. This sensor fabrication approach can potentially be employed in a wide range of applications because it allows for custom geometries and can use different types of polymers and sensing elements.

Glucose Metabolism and Stress Hyperglycemia in Critically Ill Children.

Abnormalities in glucose metabolism and stress hyperglycemia (SH) are commonly seen in critically ill children. While SH may represent an adaptive stress response as a source of fuel for the body during the "fight or flight response" of critical illness, several studies have observed the association of SH with worse outcomes in different disease states. In addition to alterations in glucose metabolism and acquired insulin resistance from inflammation and organ dysfunction, specific intensive care unit (ICU) interventions can also affect glucose homeostasis and SH during critical illness. Common ICU interventions can mediate the development of SH in critical illness. The strategy of tight glucose control combined with intensive insulin therapy (TGC-IIT) has been well studied to improve outcomes in both adult and pediatric critical illness. Though early single-center studies of TGC-IIT observed benefits with better outcomes albeit with greater incidence of hypoglycemia, subsequent larger multicenter studies in both children and adults have not conclusively demonstrated benefits and have even observed harm. Several possible reasons for these contrasting results include differences in patient populations, glycemic control targets, and glucose control protocols including nutrition support, and variability in achieving these targets, measurement methods, and expertise in protocol implementation. Future studies may need to individualize management of SH in critically ill children with improved monitoring of indices of glycemia utilizing continuous sensors and closed-loop insulin administration.

A Continuous Tilt Sensor Based on UWFBG Technology for Landslide Real-Time Monitoring

Displacement monitoring is the key work of landslide disaster early warning. Distributed and real-time displacement monitoring can provide a more accurate and timely reference for landslide instability evaluation. However, existing technologies have deficiencies in combining distributed and real-time capabilities. Given this, a novel continuous ultra-weak fiber Bragg grating (UWFBG)-based tilt sensor is proposed. First, the tensile test is designed and carried out to investigate the strain transfer mechanism of the UWFBG cable. Then, calibration experiments are used to verify the monitoring performance of the sensors. Finally, the UWFBG tilt sensors are applied in the Majiagou landslide, a typical reservoir landslide located in Three Gorges Reservoir Area (TGRA). The results show that the sliding surface of the landslide is located at 33 m, and the maximum displacement value is 8.1 mm during the monitoring period. When the landslide is in a stable deformation state, the dynamic range of displacement is 1.4 mm. The UWFBG tilt sensors with distributed and real-time monitoring characteristics can achieve accurate landslide displacement measurement and provide outlets for early warning.

NIR Luminescent Oxygen-Sensing Nanoparticles for Continuous Glucose and Lactate Monitoring.

A highly sensitive, biocompatible, and scalable phosphorescent oxygen sensor formulation is designed and evaluated for use in continuous metabolite sensors for biological systems. Ethyl cellulose (EC) and polystyrene (PS) nanoparticles (NPs) stabilized with Pluronic F68 (PF 68), Polydimethylsiloxane-b-polyethyleneglycol methyl ether (PDMS-PEG), sodium dodecylsulfate (SDS), and cetyltimethylammonium bromide (CTAB) were prepared and studied. The resulting NPs with eight different surfactant−polymer matrix combinations were evaluated for physical properties, oxygen sensitivity, effect of changes in dispersion matrix, and cytotoxicity. The EC NPs exhibited a narrower size distribution and 40% higher sensitivity than PS, with Stern−Volmer constants (Ksv) 0.041−0.052 µM−1 for EC, compared to 0.029−0.034 µM−1 for PS. Notably, ethyl cellulose NPs protected with PF68 were selected as the preferred formulation, as they were not cytotoxic towards 3T3 fibroblasts and exhibited a wide phosphorescence lifetime response of >211.1 µs over 258−0 µM and ~100 µs over 2.58−0 µM oxygen, with a limit of detection (LoD) of oxygen in aqueous phase of 0.0016 µM. The EC-PF68 NPs were then efficiently encapsulated in alginate microparticles along with glucose oxidase (GOx) and catalase (CAT) to form phosphorescent nanoparticles-in-microparticle (NIMs) glucose sensing microdomains. The fabricated glucose sensors showed a sensitivity of 0.40 µs dL mg−1 with a dynamic phosphorescence lifetime range of 46.6−197.1 µs over 0−150 mg dL−1 glucose, with a glucose LoD of 18.3 mg dL−1 and maximum distinguishable concentration of 111.1 mg dL−1. Similarly, lactate sensors were prepared with NIMs microdomains containing lactate oxidase (LOx) and found to have a detection range of 0−14 mg dL−1 with LoD of 1.8 mg dL−1 and maximum concentration of 13.7 mg dL−1 with lactate sensitivity of 10.7 µs dL mg−1. Owing to its versatility, the proposed NIMs-based design can be extended to a wide range of metabolites and different oxygen-sensing dyes with different excitation wavelengths based on specific application.

A Double-Needle Gold-Silver Electrodes Continuous Glucose Monitoring Device

ObjectivesDiabetes is a serious, long-term disease and the use of continuous glucose monitoring sensors can reduce reliance on other painful invasive blood testing methods such as the finger blood glucose test. According to our work, a low-cost continuous glucose sensor has been developed based on electrochemical measurement techniques. MaterialsThe sensor is based on a two needles system; a gold and a silver electrode are integrated into a circular shaped electronic printed circuit board (PCB). The sensing part is based on biological electrochemical measurements. Glucose oxidase (Gox) was used as the active sensing element and ferrocene (Fc) as a mediator. Simple and low-cost coating methods were used; these methods are self-assembled monolayers and deep coating. This will reduce the final cost of the sensor as no expensive technique was used. The electrical subsystem contains a low-noise and low-power trans-impedance front-end as well as a single-chip low-power Bluetooth microcontroller with a 12-bit Analog-to-Digital Converter (ADC). ResultsThe sensor was tested in various concentrations of glucose. As a result of initial in vitro experiments, detailed analytical performance metrics are presented. The device has consistently shown a sensitivity of 3.059 mV/(mg/dl) reading with a linear range of 0-400 mg/dl. ConclusionThe proposed study shows promising results for glucose detection. Thus, this type of sensor can be used for different analyzes targeting biological applications after further investigations and analysis.

High-Frequency Bromide Sensor Performance during Denitrifying Bioreactor Tracer Testing

Abstract. High-frequency bromide (Br-) sensors could resolve challenges during denitrifying bioreactor tracer tests. Deployment of a Br- sensor during a tracer test resulted in both under- and over-reported concentrations. Collecting high-resolution Br- concentrations generally did not add value to calculated tracer metrics. However, high-frequency Br- sensors were overall considered a convenient tool, in part, due to ease of deployment. Bromide (Br-) tracer tests are an important environmental monitoring method for assessing internal hydraulics in denitrifying woodchip bioreactors. The objective was to assess performance of relatively new high-frequency Br- sensing technology to help resolve challenges associated with sampling uncertainty and failure during bioreactor tracer tests. A Seametrics TempHion™ Bromide Logger was used to: (1) continuously log Br- concentrations at least every 30 s during three tracer tests in the field and (2) determine Br- concentrations in sample bottles post-hoc following eight tracer tests (sampling frequency in the field: every 2 to 300 min). Both were compared to lab-analyzed Br- concentrations. The sensor underreported Br- concentrations at two real-time tracer tests and overreported during one test, but this mainly impacted the tracer metric of percent recovery. While Br- sensor deployment during a tracer test is the ideal use of this convenient tool, use of the sensor post-hoc in collected bottles matched the lab-analyzed concentrations more closely based on the Root Mean Square Errors and the Mean Absolute Errors. The sensor’s ability to collect large amounts of high-resolution concentrations did not necessarily add value because most tracer metrics were interpolated with reasonable accuracy from the discrete lab-analyzed samples. The relatively continuous nature of the sensed concentrations, however, along with ease of deployment were important sensor benefits. Keywords: Conservative tracer test, Continuous sensor, Double peak, Subsurface drainage, Woodchip bioreactor.

Robust Nonlinear Self-Triggered Control Policy for a Novel Fully Actuated UAVs

This paper proposes a self-triggered control policy for a general kind of nonlinear system, ensuring robust performance under various perturbations and alleviating communication burden simultaneously. A novel fully actuated multirotors applied this method shows great robustness to perturbations and is able of tracking six dimensional decoupled trajectories without continuous background sensor monitoring. Rigorous input-to-state stability analysis is deduced and numerical simulations confirm the validity of the policy.

Temperature Monitoring in the Refractory Lining of a Continuous Casting Tundish Using Distributed Optical Fiber Sensors

This article explores the prospects of using spatially distributed optical fiber temperature sensors based on Rayleigh optical frequency domain reflectometry (OFDR) technology in the continuous casting of molten steel. The measurement capability of the optical fiber sensors in a simulated steelmaking environment was demonstrated using a mock refractory-lined tundish, which was fabricated in-house. Single-mode optical fibers, contained in protective stainless-steel tubing, were embedded in the refractory lining of the mock tundish. The instrumented tundish was preheated up to a temperature of 960 °C (recorded at the surface of the working lining) before the molten steel pour. A low-alloy steel (AISI 4140 grade) was melted in a 200 lb (90.7 kg) coreless induction furnace and was poured into the instrumented preheated tundish. The embedded optical fiber sensors were used to measure the temperature distribution in the castable lining during the preheating process of the tundish and during its contact with molten steel. Temperatures were metered with a spatial resolution of 0.65 mm along the embedded optical fibers. The measurements were recorded with an update rate of 1 Hz. The maximum temperature recorded by the optical fiber sensors in the castable lining after the steel pour was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$591^{\circ }\text{C}$ </tex-math></inline-formula> . The spatially continuous optical fiber sensors provided useful information on thermal gradients in the castable lining. Real-time monitoring of spatially distributed thermal profiles in the refractory lining can improve superheat control, reduce energy losses, detect refractory wear, and improve the quality of the cast.

Multiplexed and continuous microfluidic sensors using dynamic complex droplets.

Emissive complex droplets with reconfigurable morphology and dynamic optical properties offer exciting opportunities as chemical sensors due to their stimuli-responsive characteristics. In this work, we demonstrated a real-time optical sensing platform that combines poly(dimethylsiloxane) (PDMS) microfluidics and complex droplets as sensing materials. We utilized a mechanism, called directional emission, to transduce changes in interfacial tension into optical signals. We discuss the fabrication and integration of PDMS microfluidics with complex emulsions to facilitate continuous measurement of fluorescent emission and, ultimately, the interfacial tensions. Furthermore, by varying the interfacial functionalization and fluorescent dye with characteristic wavelength, we generate multiple formulations of droplets and obtain differential responses to stimuli that alter interfacial tensions (i.e., composition of surfactants, pH). Our results illustrate a proof-of-concept multiplexed and continuous sensing platform with potential applications in miniaturized, on-site environmental monitoring and biosensing.

Liquid Metal-Based Flexible Sensor for Perception of Force Magnitude, Location, and Contacting Orientation

Flexible sensors have the advantage to enable intelligent systems to interact with the environment with high safety and versatility. Liquid metal is a useful element for flexible sensors due to its stretchable, reconfigurable, and healing characteristics. However, it is difficult to decode the stimuli position using uniform liquid metal because of its homogeneity and fluidity. Current sensing systems for the perception of force magnitude and contact location mostly rely on sensing arrays and massive crossover electrodes. In this paper, we proposed a novel method for simultaneously sensing the force magnitude and contact location without crossover electrodes. In the new design, we encapsulate the liquid metal electrodes with varying cross-sections in two silicon layers that function as protective skin and govern the geometry of liquid metals. When a force is applied to the flexible sensor, the change of resistance is dependent on both location and stimuli magnitude. Three liquid metal channels with different gradient resistance are embedded in the prototypes with parallel distributions. Combining the signals collected from the three channels, we can simultaneously measure the force magnitude, stimuli location, and contacting orientation. The overall force resolution is sub-Newton in the range from 0.5 N to 20 N. The position can also be determined with a 100% success rate for the segmented sensor and a position resolution of 2 mm for the continuous sensor. The error for contact orientation measurement is 4.58° when the orientation ranges from 45° to 135°. The proposed multifunctional sensing device with high accuracy and wide sensing range has significant potential for developing interactive interfaces for human-machine interactions and industrial applications.

Selective Antibody-Free Sensing Membranes for Picogram Tetracycline Detection.

As an antibody-free sensing membrane for the detection of the antibiotic tetracycline (TC), a liquid PVC membrane doped with the ion-pair tetracycline/θ-shaped anion [3,3'-Co(1,2-C2B9H11)2]- ([o-COSAN]-) was formulated and deposited on a SWCNT modified gold microelectrode. The chosen transduction technique was electrochemical impedance spectroscopy (EIS). The PVC membrane was composed of: the tetracycline/[o-COSAN]- ion-pair, a plasticizer. A detection limit of 0.3 pg/L was obtained with this membrane, using bis(2-ethylhexyl) sebacate as a plasticizer. The sensitivity of detection of tetracycline was five times higher than that of oxytetracycline and of terramycin, and 22 times higher than that of demeclocycline. A shelf-life of the prepared sensor was more than six months and was used for detection in spiked honey samples. These results open the way to having continuous monitoring sensors with a high detection capacity, are easy to clean, avoid the use of antibodies, and produce a direct measurement.

Graph-Based Feature Weight Optimisation and Classification of Continuous Seismic Sensor Array Recordings

Slope instabilities caused by heavy rainfall, man-made activity or earthquakes can be characterised by seismic events. To minimise mortality and infrastructure damage, a good understanding of seismic signal properties characterising slope failures is therefore crucial to classify seismic events recorded from continuous recordings effectively. However, there are limited contributions towards understanding the importance of feature selection for the classification of seismic signals from continuous noisy recordings from multiple channels/sensors. This paper first proposes a novel multi-channel event-detection scheme based on Neyman-Pearson lemma and Multi-channel Coherency Migration (MCM) on the stacked signal across multi-channels. Furthermore, this paper adapts graph-based feature weight optimisation as feature selection, exploiting the signal's physical characteristics, to improve signal classification. Specifically, we alternatively optimise the feature weight and classification label with graph smoothness and semidefinite programming (SDP). Experimental results show that with expert interpretation, compared with the conventional short-time average/long-time average (STA/LTA) detection approach, our detection method identified 614 more seismic events in five days. Furthermore, feature selection, especially via graph-based feature weight optimisation, provides more focused feature sets with less than half of the original number of features, at the same time enhancing the classification performance; for example, with feature selection, the Graph Laplacian Regularisation classifier (GLR) raised the rockfall and slide quake sensitivities to 92% and 88% from 89% and 85%, respectively.

Simulation of high-frequency dissolved oxygen dynamics in a shallow estuary, the Corsica River, Chesapeake Bay

Understanding shallow water biogeochemical dynamics is a challenge in coastal regions, due to the presence of highly variable land-water interface fluxes, tight coupling with sediment processes, tidal dynamics, and diurnal variability in biogeochemical processes. While the deployment of continuous monitoring devices has improved our understanding of high-frequency (12 - 24 hours) variability and spatial heterogeneity in shallow regions, mechanistic modeling of these dynamics has lagged behind conceptual and empirical models. The inherent complexity of shallow water systems is represented in the Corsica River estuary, a small basin within the Chesapeake Bay ecosystem, where abundant monitoring data have been collected from long-term monitoring stations, continuous monitoring sensors, synoptic sensor surveys, and measurements of sediment-water fluxes. A state-of-the-art modeling system, the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), was applied to the Corsica domain with a high-resolution grid and nutrient loads from the most recent version of the Chesapeake Bay watershed model. The Corsica SCHISM model reproduced observed high-frequency variability in dissolved oxygen, as well as seasonal variability in chlorophyll-a and sediment-water fluxes. Time-series signal analyses using Empirical Model Decomposition and spectral analysis revealed that the diurnal and M2 tide frequencies are the dominant high-frequency modes and physical transport contributes a larger share to dissolved oxygen budgets than biogeochemical processes on an hourly time scale. Heterogeneity and patchiness in dissolved oxygen resulting from phytoplankton distributions and geometry-driven eddies amplify the physical transport effect, and on longer time scales oxygen is controlled more by photosynthesis and respiration. Our simulation demonstrates that interactions among physical and biological dynamics generate complex high-frequency variability in water quality and non-linear reposes to nutrient loading and environmental forcing in shallow water systems.

Development of RF-Photonic System for Automatic Targets’ Nonlinear Rotational/Flapping/Gliding Signatures Imaging Applications

Nowadays, developing the radio frequency (RF)-photonic sensors suitable for several Defence and civil applications is emerging due to its various unique advantages. In today’s scientific world, the involvement of low radar cross-section (RCS) airspace targets, such as unman aerial vehicles, drones, mini-helicopters, ornithopters, bionic birds, etc., is more for the purpose of airspace traffic management/guidance, materials delivery, legal/illegal surveillance and Defence/offense applications. The detection and recognition of such targets using the conventional RF sensors (which process only the main Doppler) is almost impossible. Therefore, extracting the distinctive micro-Doppler (m-D) signatures of these low-RCS targets and using them to image/differentiate/recognize their postures become significant which is the main contribution in this paper. A C-band continuous wave RF-photonic sensor is developed and different low-RCS targets: 2/3 blades rotating propeller system (drones), cone like structure (warhead) and a bionic-bird (spy-bird); are operated in front of it. The different nonlinear postures, of these targets, covered in our experimental measurements are m-D extraction of a slowly moving propeller system, detection of back-and-forth movements of a rotational propeller system, discerning the moving and static rotational propeller systems, simultaneous extraction of m-D signatures of a rotational and moving targets and recognition of flapping/gliding motions of bionic-bird. The analysis and recognition of all these postures using the experimentally generated m-D signatures are described.

Online Change Point Detection in Application With Transition-Aware Activity Recognition

Transition-aware activity recognition is an inherent component of online health monitoring and ambient assisted living. An explosion of technology breakthroughs in wireless sensor networks, wearable computing, and mobile computing has facilitated this. However, real time, dynamic activity recognition is still challenging in practice. As reported in the existing literature, machine learning techniques are successfully used on the presegmented data to deliver transition-aware activity recognition systems. However, these strategies are frequently ineffective when used in a near-real-time context. This article presents an online change point detection (OCPD) strategy to segment the continuous multivariate time-series smartphone sensor data and its application in a transition-aware activity recognition framework. The proposed OCPD strategy is based on the hypothesis-and-verification principle. After the online data stream segmentation using the proposed OCPD strategy, feature engineering is performed to retain the essential features. Then, synthetic minority oversampling technique (SMOTE) is applied to balance the dataset. Finally, practical experiments are carried out to verify the suggested frameworks’ efficiency and reliability. The results reveal that the proposed OCPD strategy with ensemble classifier achieves a greater recognition rate (F-Measure: 99.80%) compared to methods stated in the literature.

Comparing the Rise in Glucose Concentration in Blood, Aqueous and Interstitial Fluid During a Glucose Tolerance Test.

The purpose of the study was to determine if aqueous glucose levels rise in a comparable time frame to interstitial fluid and could therefore be suitable for a continuous glucose monitoring (CGM) site. An intravenous glucose tolerance test was performed on five New Zealand white rabbits. Aqueous humor from the posterior and anterior chamber of the eye and venous blood were sampled for glucose concentration measurement. Glucose concentrations in the interstitial fluids were monitored using a CGM system. A compartment model was created to map the glucose response curves in each compartment. The delay in rising glucose concentrations between blood and interstitial fluid and aqueous humor in the posterior chamber and anterior chamber of the eye were analyzed. The results showed a statistically similar time lag and rate of change in glucose concentrations between blood and interstitial fluids or aqueous humor in either the posterior or anterior chamber. The results of this study add further support to the aqueous humor being used as an alternative CGM site. The study provides the basis for developing an intraocular continuous glucose sensor that can overcome limitations of current CGM systems.

Construction of continuously enhanced fluorescent sensor for detection of glutathione in normal and cancer cells

In this paper, water-soluble cysteamine (CA)-capping CdSe quantum dots (CA-CdSe) could be used as a continuous fluorescent sensor. The CA-CdSe QDs can respond to Ag+ with a detection limit of 54.1 nM. Interestingly, CA-CdSe quantum dots combined with Ag+ to generate a new nano-fluorescence sensor-Ag+ modified CA-CdSe QDs (Ag+@CA-CdSe). Ag+@CA-CdSe can detect glutathione (GSH) with good sensitivity and anti-interference performance. The detection limit of Ag+@CA-CdSe fluorescenct sensor for GSH is as low as 0.74 μM. In addition, the novel nano-fluorescent sensor Ag+@CA-CdSe exhibited good cell permeability and was successfully applied to detect exogenous and endogenous GSH concentrations in cells. It could distinguish cancerous and normal cells by in vitro cell fluorescence imaging.

A guideline for spatio‐temporal consistency in water quality modelling in rural areas

A guideline for spatio‐temporal consistency in water quality modelling in rural areas

Artificial Intelligence Based Dam Concrete Seepage Prediction Using Wireless Sensor Network

Leakage checking is a fundamental errand in the gamble the executives of substantial dams. Dams assume a fundamental part in reaping energy and using the energy for zap and water system purposes. Aside from that dam safeguard against flooding by gathering and holding waters when they arrive at a specific level. When gathered, a dam may be intended to deliver the water once again into the stream at a controlled speed or redirect the water somewhere else for different purposes. Because of unexpected circumstances blunder of dams would prompt devastating harms, which is exceptionally obvious on account of 2018 Kerala floods, where 35 of its 54 dams were let open without earlier alerts and early activity plans prompting loss of lives, property harms and so on Thus, the issue referenced above is corrected by continuous sensors, for example, temperature, water level, and precipitation and water pressure. These qualities are likewise shown through LCD