Response Time Of Sensor Research Articles

Ppb-Level Self-Calibrating Ozone Detection Using a T-Type Multipass Enhanced Photoacoustic Sensor with a 9.46 μm Quantum Cascade Laser.

A sensitive, real-time, and accurate ozone (O3) sensor system is developed based on the combination of multipass enhanced photoacoustic (MPPA) and direct multipass absorption spectroscopy with a mid-infrared quantum cascade laser (QCL). The QCL with an emission wavelength of 9.46 μm was used to probe the O3 absorption lines without interference from the absorption of water and carbon dioxide in the flowing mixtures. The MPPA sensor was constructed with a T-type cell composed of a vertical cylinder and a horizontal cavity which were designed as an acoustic resonator and for multipass absorption enhancement, respectively. By periodically on-off switching the modulation of the laser wavelength, rapidly switched measurements of direct absorption and PA spectra can be achieved for real-time and accurate calibrations of the second harmonic (2f) PA signals with the direct absorbance spectra of O3. Moreover, a detection limit of O3 of 6 ppb at an average time of 300 s was achieved, and a short sensor response time of 16 s was also obtained in the flow mixtures with a flow rate of 50 sccm. This work provides a reliable method for O3 detection with capabilities of parts-per-billion-level sensitivity and on-site real-time concentration calibration, thus holding promise for in situ ozone monitoring under various environments.

BiOI: Self‐Powered Humidity Sensor and Breath Monitor

AbstractThe self‐powered, adaptable, quick, and precise humidity sensors are required to measure humidity in the microenvironment. Here, a simple one‐step wet chemical method is presented to prepare stacked layered bismuth oxyiodide (BiOI) nanoplates. The remarkable response and self‐powered behavior of BiOI nanoplates‐based humidity sensors are demonstrated for the first time. The humidity sensing characteristics of BiOI are examined within the range of 30–80% relative humidity (RH) at an operating temperature of 323 K. The highest sensitivity level of 39 kΩ per %RH is determined for a relative humidity of 75.5%. A successful attempt is made to use this sensor as a human breathing process monitor. The sensor response times at room temperature in this test are 3.04(9) s at 0 V and 3.31(7) s at 20 V, whereas the recovery times are estimated to be 6.57(6) s at 0 V and 6.42(4) s at 20 V. Future advancements in sensing devices utilizing BiOI hold the potential to yield highly responsive, ultrafast sensors with simplified device geometries, and self‐powered.

Pyridinium surfactants can modulate the UV response of methyl green dye‐doped polymeric films for sensor development

AbstractConcerns about ultraviolet radiation (UV‐R) are increasing due to climate change. The effects of UV‐R on living organisms depend on exposure duration and intensity, making it crucial to monitor UV‐R levels. In this study, we investigated the role of surfactants as photosensitizing or stabilizing agents in a colorimetric sensor based on a polymeric film doped with methyl green dye. The films were synthesized using the casting technique from a filmogenic solution containing either carboxylated polyvinyl alcohol (P1) or hydroxylated polyvinyl alcohol (P2). We evaluated the impact of surfactant structure (dodecylpyridinium chloride, C12; hexadecylpyridinium chloride, C16; or sodium dodecyl sulfate, SDS) and concentration on the colorimetric response of the films to UV‐R. Color changes were monitored using the CIELab system. The results showed that, under UV‐R exposure for up to 5 h, films without surfactants did not lose their blue hue (negative b* parameter in CIELab). While SDS stabilized the dye in the polymeric matrix, films containing pyridinium surfactants (C12 or C16) changed color from blue to pale yellow (positive b* parameter in CIELab). The color change, which was modulated by surfactant concentration, was attributed to radical reactions involving the pyridinium surfactants, influenced by their hydrophobicity and the polymer structure. These results represent a significant advancement in colorimetric sensors for UV‐R, as they allow for the modulation of the sensor's response time through surfactant concentration in the polymeric film.

Home-based Waste Monitoring System using Internet of Things with Fuzzy Logic Method

The accumulation of waste in certain locations, especially in residential areas, due to the continuous accumulation of waste can cause environmental disturbances such as disease and unpleasant odors. This system is designed to find out whether the trash bin is full or not by applying fuzzy logic, if the status of the trash bin can be cleaned, it will be handled immediately so that the waste does not accumulate and disturb people around. This system can find out when the last time the waste was taken and the location of the trash bin as a prototype which can later be applied to areas with a wider range by cleaning service officers in Mamuju City. This system uses the HC-SR04 sensor to detect the distance of the waste to the sensor and uses the Load Cell sensor to detect the weight of the waste. Several tests were carried out, first by measuring the accuracy of each sensor used, the HC-SR04 sensor accuracy was obtained at 96.68% with an error of 3.32%. While the accuracy of the load cell sensor is 90.68% with an error of 9.32%. The second test calculates the sensor response time and Blynk notification response since the sensor detects waste, the average HC-SR04 sensor detection response is around 0.83 seconds. For the response time of incoming notifications when there is movement in the HC-SR04 sensor area has an average of 2.65 seconds. While the Load Cell sensor response time is only around 0.53 seconds. For Blynk notification response time since the Load Cell sensor detects it has an average of 2.51 seconds. The third test calculates the response time of the two sensors (HC-SR04 and Load Cell) and the Blynk notification response since the two sensors detected the waste, the average response time of the two sensors finished detecting only around 0.91 seconds. For the response time of the trash bin status condition, if there is movement in the area of the two sensors, the condition of the trash bin will change and display the status of Normal, Needs Cleaning and Highly Needs Cleaning with an average response time of 1.18 seconds. The system successfully sends notifications according to the fuzzy rules and expected to speed up the waste handling process

A Review of Semiconductor Metal Oxides for Hydrogen Sulfide and Methane Gas Detection

This review contains comprehensive study of semiconductor metal oxide films gas sensors. SMO are smaller in size, simple fabrication technique, sensitivity and selectivity is good. Review study paper offers understanding about the dopants impurity made the deviations in the SMO materials used to fabrication of gas sensor. Reviews study shows SnO₂-WO₃, ZnO, Au composites good for H2S and methane (CH4) gases it has sensitivity in the range 75 % to 90% at operating temperature between 200 0C to 350 0C. Composites of ZnO-Au, SnO₂, TiO₂ shows decent sensitivity in the range between 72 % to 95% at operating temperature between 200 0C to 350 0C towards H2S and methane (CH4) gases. Pure and composite of different SMO films prepared using Sol-Gel, Sputtering, CVD and Screen printing method result shows Screen printing technique is most preferred and it shows increase in sensitivity at lower operating temperature. This review provides summary of the advance and performance of pure and composites of ZnO and SnO2 based films sensors for H₂S and CH₄ detection, focusing on key parameters such as response time, operating temperature, sensitivity and fabrication technologies. It provides detail analysis of the pure and composite of SnO2 &ZnO towards H₂S and CH₄ and shows future perspective towards increase in sensitivity, lower operating temperature, response time and stability of gas sensor.

Investigating the impact of crystal face on SnO2/GO-A humidity sensor via adsorption kinetics and DFT calculations

Ranging from monitoring indoor air quality to controlling processes in the food, pharmaceutical, and electronics industries, humidity-sensitive sensors play a pivotal role in various industrial and environmental applications. The crystallographic orientation of their surfaces is one of the key factors influencing the performance of metal oxide-based humidity sensors. However, the study of different crystal faces of metal oxides is rarely discussed, such as surface energy, charge distribution and reactivity, which can significantly affect their water absorption behavior and thus affect the sensitivity and response time of the humidity sensor. Hence, the present study introduces a meticulously designed SnO2/GO-A sensor that not only validates the successful fabrication of SnO2/GO-A sensor featuring optimized crystal alignment but also delves into the intricate water absorption mechanisms operative across various SnO2 crystal faces. The First-principles results show that (110) face of SnO2 is more sensitive to the water molecule than others. Consequently, due to the (110) crystal surface growth with annealing process, the SnO2/GO-A sensor demonstrates significant performance enhancements, especially in response speed, recovery time, linearity, and repeatability. In particular, the SnO2/GO-A sensor exhibiting faster response and recovery times of 20s and 18s, respectively, which is higher than SnO2 and SnO2/GO sensor. This advantage makes SnO2/GO-A sensor a potential candidate for humidity sensing applications.

Preliminary mechanistic insights into the detection of ethanol vapour using MnO2 NRs-CNPs-poly-4-(vinylpyridine) based solid-state sensor operating at room temperature.

Semiconductor metal oxide gas sensors are widely used to detect ethanol vapours, commonly used in industrial productions, road safety detection, and solvent production; however, they operate at extremely high temperatures. In this work, we present manganese dioxide nanorods (MnO2 NRs) prepared via hydrothermal synthetic route, carbon soot (CNPs) prepared via pyrolysis of lighthouse candle, and poly-4-vinylpyridine (P4VP) composite for the detection of ethanol vapour at room temperature. MnO2, CNPs, P4VP, and MnO2 NRs-CNPs-P4VP composite were characterised using scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Five sensors were prepared, namely, sensor 1 (MnO2 -NRs), sensor 2 (CNPs), sensor 3 (CNPs-P4VP composite of a mass ratio of 1:3), sensor 4 (MnO2 NRs-CNPs-P4VP composite of a mass ratio 1:1:3), and sensor 5 (MnO2 NRs-CNPs-P4VP composite of a mass ratio 2:1:3). All the five sensors were used detect to 2-propanol, acetone, ethanol, methanol, and mesitylene vapours at room temperature, but among all the tested sensors, sensor 4 was highly sensitive to ethanol vapour and less sensitive to 2-propanol, methanol, acetone, and mesitylene vapours. The response and recovery time of sensor 4 towards ethanol vapour at 20.4ppm were 82seconds and 74seconds, respectively. The limit of detection on ethanol vapour using sensor 4 was 789ppb. During detection, the ethanol vapour undergoes total deep oxidation on the surface of sensor 4.

A step towards non-invasive diagnosis of diabetes mellitus using in situ synthesized MOF-MXene hybrid material with extended gate field-effect transistor integration.

The increasing demand for non-invasive and non-enzymatic glucose sensors is driven by the objective of eliminating the need for blood pricks from the body and enabling enzyme-free detection of glucose for diagnosing diabetes mellitus. To address this need, we synthesized Ni MOF-MXene (NiBDC-MXene) hybrid material through a one-pot synthesis method, which acts as a catalyst to detect salivary glucose using an extended gate field effect transistor (EGFET) method. The resulting sensor exhibits good selectivity towards glucose over common interfering molecules such as sucrose, fructose, maltose, uric acid, and ascorbic acid under physiological conditions in saliva. The fabricated electrode demonstrated high sensitivity of 531.78 μA mM-1 cm-2 with a detection range of 10 μM to 1100 μM, a sensor response time of less than 5 s, and a limit of detection (LOD) of 0.29 μM. The real saliva sample measurements under postabsorptive and postprandial conditions highlight the electrode's effectiveness in detecting salivary glucose. In addition to EGFET measurements, scanning Kelvin probe (SKP) measurements were performed to understand the mechanism of charge transfer between the glucose and NiBDC-MXene/CP electrode. Overall, the EGFET results demonstrate the capability of the sensor to detect salivary glucose in hypoglycemia, normal, and hyperglycemia ranges.

Innovative IoT-Based Automatic Gate System with RFID and Electro-Magnetic Lock for Secure Access

In this study, we developed an innovative IoT-based automatic gate system aimed at enhancing security and providing flexible access control. The system incorporates an ESP32 microcontroller with integrated Wi-Fi, enabling seamless remote access via mobile devices. It also features RFID technology for reliable physical access control when an internet connection is unavailable. To ensure user safety, an HC SR-04 ultrasonic sensor is implemented to detect obstacles during gate movement, preventing potential accidents. The security of the system is further reinforced by a dual-layer mechanism utilizing an electromagnetic lock (Emlock), which activates upon gate closure to prevent unauthorized access and deactivates when the gate opens. Experimental results indicate that the system effectively addresses the shortcomings of conventional gate control methods, delivering improved security, convenience, and safety for users. Performance tests confirm the reliable operation of both RFID and mobile control functions, with minimal delays observed in sensor response times. This comprehensive solution is well-suited for residential and commercial properties, offering a modern approach to automatic gate security.

Ammonia and ethanol detection via an electronic nose utilizing a bionic chamber and a sparrow search algorithm-optimized backpropagation neural network.

Ammonia is widely acknowledged to be a stressor and one of the most detrimental gases in animal enclosures. In livestock- and poultry-breeding facilities, a precise, rapid, and affordable method for detecting ammonia concentrations is essential. We design and develop an electronic nose system containing a bionic chamber that imitates the nasal-cavity structure of humans and canines. The sensors are positioned based on fluid simulation results. Response data for ammonia and ethanol gases and the response/ recovery times of an ammonia sensor under three concentrations are collected using the electronic nose system. Response data are classified and regressed using a sparrow search algorithm (SSA)-optimized backpropagation neural network (BPNN). The results show that the sensor has a relative mean deviation of 1.45%. The ammonia sensor's output voltage is 1.3-2.05 V when the ammonia concentration ranges from 15 to 300 ppm. The ethanol gas sensor's output voltage is 1.89-3.15 V when the ethanol gas concentration ranges from 8 to 200 ppm. The average response time of the ammonia sensor in the chamber is 13 s slower than that of the sensor directly exposed to the gas being measured, while the average recovery time is 19 s faster. In tests comparing the performance of the SSA-BPNN, support vector machine (SVM), and random forest (RF) models, the SSA-BPNN achieves a 99.1% classification accuracy, better than the SVM and RF models. It also outperforms the other models at regression prediction, with smaller absolute, mean absolute, and root mean square errors. Its coefficient of determination (R2) is greater than 0.99, surpassing those of the SVM and RF models. The theoretical and experimental results both indicate that the proposed electronic nose system containing a bionic chamber, when used with the SSA-BPNN, offers a promising approach for detecting ammonia in livestock- and poultry-breeding facilities.

Detection of ammonia in aquaculture wastewater using mango leaf extract-immobilized paper sensors and smartphone colorimetric analysis

This study uses smartphones to introduce a simple, sustainable, eco-friendly colorimetric method for rapid ammonia detection in aquaculture wastewater. The device comprises a paper sensor immobilized with a natural indicator and a sample container. An acidic extract from mango leaf was prepared under optimal conditions: water with a pH of 5.0, a mango leaf powder to solvent ratio of 1:20, and extraction at 80 °C for 10 min. This extract was used to prepare paper sensors by immersing pre-cut Whatman filter papers (No. 1) into the solution. A 20 mL clear glass bottle with a black screw cap served as the sample container. The bottle was filled with an ammonium solution and NaOH. Heating this mixture released ammonia gas. A paper sensor was placed on top of the bottle, which changed color when exposed to the gas. A smartphone, positioned 8 cm above, captured images of the sensor after the color change. These images were then analyzed to determine the ammonia concentration in the samples. The optimal conditions for ammonia detection were determined to be a 10:5 ratio of ammonium to 0.50 M NaOH, a temperature of 60 °C, a 10 min sensor response time, and 1 g of sprayed water on the sensor surface. Under these conditions, the LOD was 0.50 mg L−1, with an LDR of 1.70–10.00 mg L−1. The sensor remained stable for up to 45 days. This method has proven to be highly effective in testing aquaculture wastewater samples, achieving recovery rates of 91 % to 101 %.

Coarse-Grained Molecular Dynamics Simulations on Aggregation and Dispersion Mechanisms of Organically Modified CeO2 Nanoparticles for Electrochemical Sensor Applications

CeO2 nanoparticle with a size between 1 nm and 100 nm has gained many attentions due to its attractive properties such as biocompatibility, good superficial electrical diffusivity, high conductivity, chemical and thermal stability, and significant oxygen transfer ability. CeO2 nanoparticle has been widely employed to develop electrochemical sensors and biosensors because it increases response time, sensitivity, and stability of sensors [1]. For mass production of CeO2 nanoparticles, CeO2 nanoparticles are often handled in organic solvents [2]. To maintain the unique physical properties of CeO2 nanoparticles, it is important to disperse nanoparticles in organic solvents. Especially, CeO2 nanoparticles have low affinity for organic solvents, and they easily aggregate in the organic solvents. Therefore, CeO2 nanoparticles are usually coated with the organic ligands to prevent aggregation and to improve their dispersibility. It is well known that the dispersibility of organically modified CeO2 nanoparticles strongly depends on the solvents, and however the effects of the organic solvents on the aggregation and dispersion of organically modified CeO2 nanoparticles have not been well established.Therefore, in the present study, we employed a coarse-grained molecular dynamics method for clarifying the aggregation and dispersion mechanism of organically modified CeO2 nanoparticles. We employed our in-house molecular dynamics simulation code “Laich” [3]. Here, decanoic acid ligands are used for organic modification of CeO2 nanoparticles. Figure 1 shows the model of the present simulations. Hexane, tetradecane, cyclohexane, and benzene are used for the organic solvents. After the molecular dynamics simulations, we performed cluster analysis for the final structures (Figure 2). In figure 2, blue is nanoparticle, cyan is not bundled, and other colors are bundled. This figure indicates that ligands are bundled on the large surface and are not bundled on the corner surface of all the models. Table 1 shows the number of bundled parts in the hexane, tetradecane, cyclohexane, and benzene solvents. This table also shows the experimental dispersibility in each solvent [4]. It indicates that the number of non-bundled part corresponds to the experimental dispersibility. It means that the ligands tend to swell in the solvent to disperse organically modified CeO2 nanoparticles. Furthermore, to investigate the solvent penetration in the ligands, the density profile of solvents was calculated and the calculated average relative density of the solvents in the ligands is shown in table 2. Table 2 indicates that the average relative density of the solvents corresponds to the experimental dispersibility. This result suggests that the solvent penetration into the ligands contribute to ligand swelling. Further analysis will be presented in the conference.[1] Y. W. Hartiti, S. N. Topkaya, S. Gaffar, H. H. Bahti, and A. E. Cetin, RSC Adv., 11 (2021) 16216-16235.[2] X. Hao, C. Chen, M. Saito, D. Yin, K. Inoue, S. Takami, T. Adschiri, and Y. Ikuhara, Small, 14 (2018) 1801093.[3] S. Uehara, Y. Wang, Y. Ootani, N. Ozawa, and M. Kubo, Macromolecules, 55 (2022) 1946-1956.[4] R. J. G. B. Campello, D. Moulovi, and J. Sander, Advances in Knowledge Discovery and Data Mining (2013) 160-172. Figure 1

FIPEX: Sensor Kinetics of Thin-Film Solid Electrolyte Atomic Oxygen Sensors for Space Applications

Atomic oxygen (AOX) quantification in the upper atmosphere of the Earth is of fundamental interest for the understanding of weather and climate development. Solid electrolyte sensors are suitable instruments for this task since they qualify as payload on all common spaceflight systems due to their small size and low power consumption. The High Enthalpy Flow Diagnostics Group (HEFDiG) at the Institute of Space Systems (IRS) (University of Stuttgart, Germany) has been developing solid electrolyte sensors (FIPEX) for applications aboard sounding rockets in the past 12 years.FIPEX sensors employ YSZ (yttria stabilized zirconia) as solid electrolyte. Together with platinum or gold electrodes they form an electrochemical cell that is operated in an amperometric mode of operation. At elevated temperatures and with a voltage applied between the electrodes this setup forces a migration of oxygen anions through the electrolyte. The corresponding electrical current is measured in an outer circuit and is a function of the AOX flux onto the surface of the sensor.On sounding rockets, the measurement of atomic oxygen is particularly difficult because of the rocket’s high vertical speed yielding strong gradients in AOX number densities along the trajectory. Therefore, our research focuses on the measurement of sensor response times and their reduction. Initially, FIPEX sensors were manufactured with screen printed electrodes that are robust yet comparably thick. Surface diffusion of adsorbed oxygen atoms at the cathode was identified as the rate limiting step in this configuration. In order to reduce the diffusion length, the screen printed electrodes were replaced by porous thin-film electrodes leading to significantly improved response times.This contribution focuses on the analysis of the sensor kinetics governing the behavior of the new thin-film FIPEX sensors. We demonstrate how porosity of the initially dense anode is triggered by high polarization. From this, we provide evidence that an increased porosity at the anode is sufficient to improve the response time of a FIPEX sensor. This is different from the conclusions drawn from the analysis of sensors with thicker screen printed electrodes. An experimental configuration to determine sensor step responses to sufficiently fast changes in oxygen particle flux is presented. Above that, we discuss cyclic voltammetry observations to develop a deeper understanding of the underlying kinetic processes.In conclusion, the transient behavior of thin-film sensors is shown to be dictated by kinetic steps different from what was found for screen printed sensors. Impacts on the suitability and further application of FIPEX sensors in space are presented.Fig. 1: a) Functional layers of a FIPEX sensor. b) Photography of a FIPEX sensor with thin film electrodes. Figure 1

Enhancing Uncrewed Aerial Vehicle Techniques for Monitoring Greenhouse Gas Plumes at Point Sources

The urgency of the global climate crisis necessitates advanced monitoring of greenhouse gases, with an emphasis on capturing their spatial and temporal variability. This study explores techniques to enhance plume detection and concentration measurements using uncrewed aerial vehicles (UAVs) for monitoring at point sources, specifically at an incineration stack. Through preliminary site investigations, our approach employed strategically designed flight paths and an autopilot system to optimize flight operations within the constraints of limited flight time due to battery capacity. We combined a UAV-mounted anemometer with a plume rise model to localize the plume center at a distance of 30 m from the stack center and evaluated its performance by comparing the model-based estimations at different altitudes and angular directions with the observation results. The comparison demonstrated that the results obtained by localizing the plume center using a plume rise model and a UAV-mounted anemometer aligned well with observations based on CO2 concentration analysis. The comparative analysis showed a RMSE of 8.44 m and a MAE of 7.26 m for altitude, and a RMSE of 32.31∘ and a MAE of 25.78∘ for angular direction. Furthermore, we assessed the effectiveness of hovering UAV flights, in which a UAV remains stationary at a fixed point in the air, compared to non-hovering flights in capturing pollutant concentration. While both methods performed similarly in detecting the plume center, non-hovering flights underestimated the CO2 concentration due to insufficient time for measurement despite a sensor response time of less than three seconds. Overall, our proposed hybrid monitoring strategy integrates non-hovering and hovering flights, enhancing both plume detection efficiency and concentration measurement accuracy at point sources.

Facile synthesis of cerium doped Co-Mn-FeO nano ferrites as highly sensitive and fast response humidity sensors at room temperature

Herein, this work presents the facile synthesis of Cerium (Ce3+) doped Cobalt-manganese-iron oxide ferrite as an effective humidity sensor operated at ambient temperature. This work reports, one step solution combustion technique to synthesize Co0.5Mn0.5Fe2−xCexO4 (x = 0.0, 0.050 and 0.1) ferrites. The structural and morphological features of the synthesized Co0.5Mn0.5Fe2−xCexO4 ferrites NPs were investigated through scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet visible (UV–visible) spectroscopy. The XRD results indicates the creation of single phase in pure Co0.5Mn0.5Fe2−xCexO4 ferrite that remains unchanged by the mechanism of Ce3+inclusion. The humidity sensing mechanism was systematically investigated using adsorption–desorption isotherms. Highest humidity sensing response was achieved for Co0.5Mn0.5Fe2−xCexO4 (x = 0.1) ferrite of the order of 98 % in comparison to the pure Co0.5Mn0.5Fe2−xCexO4 (x = 0) which is about 41 %. The sensors response and recovery times for the Co0.5Mn0.5Fe2−xCexO4 (x = 0.1) was recorded to be 36 s and 63 s respectively and the sensors long term stability was examined for a duration of 90 days. The results of the present investigation offer new dimensions to fabricate high performance, room temperature operable humidity sensors for next generation sensors applications.

Fabrication of hydrogen gas sensor using sputtered palladium-copper composite on tapered optical fiber

Abstract In this study, we fabricated a hydrogen (H2) gas sensor based on tapered optical fiber using sputtering method. Also, as the first attempt, we explored how palladium (Pd) and palladium-copper (Pd-Cu) coatings, deposited using the sputtering method (RF and DC), affect tapered optical fibers as H2 gas sensors (ranging from 1 to 8% H2). It investigates changes in sensor output power, response and recovery times, and the influence of fiber tapering angle on output power. The investigation reveals that two main factors, including permeability and elasto-optic effect significantly impact the results. At H2 concentrations of 1 to 3%, permeability predominantly affects Pd sensors, yielding better output power changes and sensitivity than Pd-Cu tapered optical fiber sensors. Conversely, at higher H2 concentrations (4 to 8%), the dominant factors appear to be permeability as well as elasto-optic effect. These characteristics have a greater influence in the Pd-Cu layer at higher H2 concentration, resulting in smoother slope in response to H2. Due to higher permeability, Pd sensors reach saturation faster, while Pd-Cu sensors exhibit more linear changes with increasing H2 levels and do not saturate like Pd sensors very fast. Moreover, the study shows that a larger tapering angle can enhance the output power of Pd-Cu tapered optical fiber sensors.

Graphene-based chemiresistive hydrogen sensor for room temperature operation

Taking advantage of ultraviolet (UV) irradiation to clean the surface and tuning the charge carriers of graphene, n-doped graphene shows excellent hydrogen sensing capabilities. With assistance of a 265 nm UV light irradiation, the response time of sensor reaches 3 s to 5 ppm hydrogen. And after being relented in ambient condition for a year, it still maintains nearly identical performance. Furthermore, by adding PMMA layer as molecular sieve, the sensor can effectively shield against humidity changes, exhibiting high selectivity towards hydrogen. When the relative humidity varies within the range in 20–70 %, the sensor basically maintains similar response performance. This work streamlines the preparation process of hydrogen sensors and introducing exceptional selectivity with the help of a molecular sieve, facilitating the practical application of hydrogen sensors.

High-Temperature Sensing with Iron-Ceramic Enhanced Fiber Bragg Grating Sensors: Encapsulation Strategies and Concentration Dependencies

This research article primarily aims to enable type-I FBG(fiber Bragg grating) for high-temperature sensing and to explore the influence of varying concentrations of iron fillings in the ceramic on the sensor's sensitivity and response time. A set of six identical probes were fabricated, each with a different iron filling concentration ranging from 0% to 50%. Increasing the iron filling concentration from 0% to 50% enhanced the temperature sensitivity of the probe from 14.08±0.24 pm/°C to 14.67±0.17 pm/°C. To evaluate the response time, the probes were subjected to an abrupt heating process from 27 °C to 700 °C, and the duration was measured. The response time improved from 270 seconds to 180 seconds, representing a 33.33% improvement, as the iron filling concentration increased from 0% to 50%. Beyond a 40% concentration, both the temperature sensitivity and response time reached saturation. The lifetime of the optimized probe with a 40% iron filling concentration is estimated to be 4.46 years. During repeated exposures to high temperatures, no permanent drift in its Bragg wavelength was observed, and its repeatability during a heating-cooling cycle exhibited hysteresis of less than 1%. Received: 23 April 2024 | Revised: 30 June 2024 | Accepted: 18 October 2024 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The data that support the findings of this study are available within the manuscript. Author Contribution Statement Raja Yasir Mehmood Khan: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Writing - original draft, Visualization. Rahim Ullah: Conceptualization, Validation, Resources, Data curation, Writing - original draft. Muhammad Faisal: Conceptualization, Validation, Resources, Data curation, Writing - review & editing, Visualization, Supervision, Project administration.

Single walled carbon nanotubes/ZnO nanowires heterostructure array for NO2 gas sensing at low ppm levels

A layer-by-layer ZnO nanowire (NW)-Single Walled Carbon Nanotube (CNT) hybrid gas sensor has been proposed for effective detection of NO2 gas under a low exposure limit of 5 ppm. The fabricated hybrid sensor displayed good sensor response (S %), good selectivity and fast response time towards the target gas. S % value of 36.4 % under 5 ppm NO2 level at 250 °C and good selectivity response towards different interfering gases like SO2, CO and H2 have been observed. Meanwhile, fast response time values of 44.08 s (response) and 62.11 s (recovery) were observed at 300 °C under 5 ppm NO2 level. The sensor baseline resistance of the hybrid heterostructure (HS) was also found to be lower when compared to that of a bare ZnO NW sensor. In addition, the presence of Single Walled CNT in the HS was also shown to reduce the operational temperature of the sensor. Temperature played a significant role by controlling the adsorption and desorption kinetics of gas molecules on the surface. Moreover, the formation of p-n interface between Single Walled CNT (p-type) and ZnO NW (n-type) might have modulated the potential charge barrier on interacting with the adsorbed gases which inturn might have impacted the response of the hybrid sensor. In addition, the large surface areas offered by both NWs and nanotubes might have improved the gas adsorption capability thereby enhancing the overall hybrid sensor’s response.

Surface acoustic wave platform integrated with ultraviolet activated rGO-SnS2 nanocomposites to achieve ppb-level dimethyl methylphosphonate detection at room-temperature

Dimethyl methylphosphonate (DMMP) is commonly used as an alternative for demonstrating to detect sarin, which is one of the most toxic but odorless chemical nerve agents. Among various types of DMMP sensors, those utilizing surface acoustic wave (SAW) technology provide notable advantages such as wireless/passive monitoring, digital output, and a compact, portable design. However, key challenges for SAW-based DMMP sensors operated at room temperature lies in simultaneous enhancement of sensitivities and reduction of detection limits. In this study, we developed a binary material strategy by combining reduced graphene oxide (rGO) and tin disulfide (SnS2) with (100)-facets orientation as sensing layers of SAW device for DMMP detection utilized at room temperature. Ultraviolet (UV) light was applied to activate the sensitive film and reduce the sensor's response time. The developed SAW DMMP sensor demonstrated a superior sensitivity (−1298.82 Hz/ppm), a low detection limit of 50 ppb, and a hysteresis below 1.5%, along with fast response/recovery time (39.2 s/28.4 s), excellent selectivity, long-term stability and repeatability. The formation of shrub-like rGO-SnS2 heterojunctions with abundant surface defects and large specific surface areas, high-energy (100) crystalline surfaces of SnS2, and photogenerated carriers generated by UV irradiation were pinpointed as the crucial sensing mechanisms. These factors collectively enhanced adsorption and reaction dynamics of DMMP molecules.