Search Results (95)

This study investigates plant stress assessment by integrating advanced sensor technologies and Artificial Intelligence (AI). Multi-sensor data—including electrical impedance spectroscopy, temperature, and humidity—were used to capture plant physiological responses under environmental stress conditions. The key task addressed was the prediction of stress-related parameters using machine learning. A novel boosting-based ensemble method, AdapTree, combining AdaBoost and decision trees, was proposed to improve predictive accuracy and model interpretability. Experimental evaluation across multiple regression metrics demonstrated that AdapTree outperformed baseline models, achieving an R² score of 0.993 for impedance magnitude prediction and 0.999 for both relative humidity (RH) and temperature, along with low root mean squared error (134.565 for impedance, 0.006966 for RH, and 0.0050099 for temperature) and mean absolute error values (22.789 for impedance; 1.51 × ${10}^{-5}$ for RH and 2.51 × ${10}^{-5}$ for temperature). These findings validate the reliability and effectiveness of the proposed AI-driven framework in accurately interpreting sensor data for plant stress detection. The approach offers a scalable, data-driven solution to enhance precision agriculture and agricultural sustainability. Furthermore, this method can be extended to monitor additional stress markers or applied across diverse plant species and field conditions, supporting future developments in intelligent crop monitoring systems. Full article

Resistivity-type humidity sensors, which detect changes in electrical resistance in response to variations in environmental humidity, have garnered significant interest due to their widespread application in industry, agriculture, and daily life. These sensors rely on diverse materials for fabrication, but their increasing variety has contributed to the accumulation of electronic waste. As a biodegradable polymer, cellulose offers unique advantages, including a naturally hydrophilic structure and a large specific surface area. These properties enable cellulose to reduce e-waste generation while facilitating the efficient adsorption of water molecules. However, despite these benefits, humidity sensors based solely on cellulose often suffer from poor sensitivity due to its limited hydrophilicity and non-adjustable structure. To overcome these limitations, the development of composite materials emerges as a promising solution for enhancing the performance of cellulose-based humidity sensors. Combining the complementary properties of cellulose and TiO₂, this work presents the development of a cellulose/TiO₂ composite humidity sensor through a sustainable approach. The resulting composite material exhibits significantly improved sensitivity compared with a sensor fabricated purely from cellulose. To achieve this, TiO₂ nanoparticles were incorporated into cellulose extracted from potato peels, and the composite film was fabricated using the casting method. The sensor’s performance was evaluated by analyzing the dependence of its complex impedance, measured over a frequency range between 2 kHz and 10 MHz, while varying relative humidity (RH). Full article

Traditional humidity sensors frequently face challenges, especially in environments with fluctuating temperatures, which can compromise their efficiency, stability, and reliability. Therefore, there is an urgent demand to fabricate low-cost and high-performance temperature-independent humidity sensors. In this work, for the first time, highly stable and reliable temperature-independent humidity sensors have been proposed based on a PEO/PVA polymer composite. Four sensors were fabricated containing weight ratios of PEO/PVA as 50:50%, 40:60%, 60:40%, and 70:30%, respectively. All of the fabricated sensors were electrically characterized at three different temperatures, 30 °C, 35 °C, and 40 °C, to investigate the impedance response. The proposed sensor based on a PEO/PVA (40:60%) composite presents a remarkable and optimized temperature-independent performance in the range of 0–60%RH. Apart from this, the response and recovery time (9 s/16 s) of the temperature-independent humidity sensor based on PEO/PVA (40:60%) were investigated. Finally, the sensor showed long-term stability for 90 days, ensuring the reliability of the proposed device. These remarkable performances of the proposed sensor based on PEO/PVA with a weight ratio of (40:60)% can open a new gateway for low-range temperature-independent humidity sensors for various real-time applications. Full article

Accurate relative humidity (RH) measurement is critical in many applications, from process control and material preservation to ensuring human comfort and well-being. This study presents high-performance humidity sensors based on titanium oxide nanoparticles/graphene oxide (TiO₂/GO) composites, which demonstrate excellent sensing capabilities compared to pure GO-based sensors. The multilayer structure of the TiO₂/GO composites enables the enhanced adsorption of water molecules and improved dynamic properties while providing dual-mode sensing capability through both resistive and capacitive measurements. Sensors with different TiO₂/GO ratios were systematically investigated to optimize performance over different humidity ranges. The TiO₂/GO sensor achieved remarkable sensitivity (8.66 × 10⁴ Ω/%RH), a fast response time (0.61 s), and fast recovery (0.87 s) with minimal hysteresis (4.09%). In particular, the sensors demonstrated excellent mechanical stability, maintaining reliable performance under bending conditions, together with excellent cyclic stability and long-term durability. Temperature dependence studies showed consistent performance under controlled temperature conditions, with the potential for temperature-compensated measurements. These results highlight TiO₂/GO nanocomposites as promising candidates for next-generation humidity sensing applications, offering enhanced sensitivity, mechanical flexibility, and operational stability. The dual-mode sensing capability combined with mechanical durability opens up new possibilities for flexible and wearable humidity-sensing devices. Full article

This study investigates the humidity-sensing properties of two semiconductor metal oxide (SMO)-reduced graphene oxide (RGO) nanocomposites: TiO₂/RGO and α-Fe₂O₃/RGO, at room temperature. Both nanocomposites are synthesized via hydrothermal methods and coated onto printed circuit board (PCB) interdigital electrodes to construct humidity sensors. The surface morphology and crystallographic structure of the materials are characterized using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The sensors are tested across a humidity range of 11%RH to 97%RH, and the impedance is measured over a frequency range of 1 Hz to 1 MHz. The results show that both TiO₂/RGO and α-Fe₂O₃/RGO exhibit favorable humidity-sensing performance at room temperature. The sensitivity and humidity hysteresis of TiO₂/RGO are 12.2 MΩ/%RH and 3.811%RH, respectively, while those of α-Fe₂O₃/RGO are 0.826 MΩ/%RH and 8.229%RH. The response and recovery times of TiO₂/RGO are 72 s and 99 s, respectively, while those of α-Fe₂O₃/RGO are 48 s and 54 s. Both sensors demonstrate good repeatability and stability. These findings suggest that SMO/RGO nanocomposites are promising materials for the development of low-cost, high-sensitivity, and stable humidity sensors. Full article

Owing to its extensive use and intrinsic toxicity, NH₃ detection is very crucial. Moisture can cause significant interference in the performance of sensors, and detecting NH₃ in high humidity is still a challenge. In this work, a humidity-activated NH₃ sensor was prepared by urocanic acid (URA) modifying poly (ethylene glycol) diacrylate (PEGDA) via a thiol-ene click cross-linking reaction. The optimized sensor achieved a response of 70% to 50 ppm NH₃ at 80% RH, with a response time of 105.6 s and a recovery time of 346.8 s. The sensor was improved for response and recovery speed. In addition, the prepared sensor showed excellent selectivity to NH₃ in high-humidity environments, making it suitable for use in some areas with high humidity all the year round or in high-humidity areas such as the detection of respiratory gas. A detailed investigation of the humidity-activated NH₃-sensing mechanism was conducted using complex impedance plot (CIP) measurements. Full article

Highly sensitive resistometric sensors were applied for the real-time corrosion monitoring of carbon steel protected with a polyolefin coating with and without an inhibitor under static and dynamic atmospheric and immersion conditions. The results were compared with conventional electrochemical impedance spectroscopy (EIS) data. An increase in the coating thickness from 20 µm to 50 µm and an addition of 1wt.% tannic acid significantly improved the coating corrosion stability. Based on the real-time corrosion data, the drying stage of atmospheric exposure in a chloride-rich environment was found to be the most critical. The highest corrosion rate was detected at 50% relative humidity when the electrolyte corrosiveness in coating defects reached the maximum. Resistometric sensors have the potential to become an interesting alternative for evaluating coating performance and degradation mechanisms in both laboratory and industrial applications. Full article

In the post-pandemic era, human demand for a healthy lifestyle and a smart society has surged, leading to vibrant growth in the field of flexible electronic sensor technology for health monitoring. Flexible polymer humidity sensors are not only capable of the real-time monitoring of human respiration and skin moisture information but also serve as a non-contact human–machine interaction method. In addition, the development of moist-electric generation technology is expected to break free from the traditional reliance of flexible electronic devices on power equipment, which is of significant importance for the miniaturization, reliability, and environmentally friendly development of flexible devices. Currently, flexible polymer humidity sensors are playing a significant role in the field of wearable electronic devices and thus have attracted considerable attention. This review begins by introducing the structural types and working principles of various humidity sensors, including the types of capacitive, impedance/resistive, frequency-based, fiber optic, and voltage-based sensors. It mainly focuses on the latest research advancements in flexible polymer humidity sensors, particularly in the modification of humidity-sensitive materials, sensor fabrication, and hygrosensitivity mechanisms. Studies on material composites including different types of polymers, polymers combined with porous nanostructured materials, polymers combined with metal oxides, and two-dimensional materials are reviewed, along with a comparative summary of the fabrication and performance mechanisms of related devices. This paper concludes with a discussion on the current challenges and opportunities faced by flexible polymer humidity sensors, providing new research perspectives for their future development. Full article

Flexible humidity sensors (FHSs) with fast response times and durability to high-humidity environments are highly desirable for practical applications. Herein, an FHS based on crosslinked sodium alginate (SA) and MXene was fabricated, which exhibited high sensitivity (impedance varied from 10⁷ to 10⁵ Ω between 10% and 90% RH), good selectivity, prompt response times (response/recover time of 4 s/11 s), high sensing linearity (R² = 0.992) on a semi-logarithmic scale, relatively small hysteresis (~5% RH), good repeatability, and good resistance to highly humid environments (negligible changes in sensing properties after being placed in 98% RH over 24 h). It is proposed that the formation of the crosslinking structure of SA and the introduction of MXene with good conductivity and a high specific surface area contributed to the high performance of the composite FHS. Moreover, the FHS could promptly differentiate the respiration status, recognize speech, and measure fingertip movement, indicating potential in breath monitoring and non-contact human–machine interactions. This work provides guidance for developing advanced flexible sensors with a wide application scope in wearable electronics. Full article

Impedance Spectroscopy (IS) is a general term for the technique referring to small-signal measurements of the linear electrical response of a domain of interest. This method is based on the analysis of the system’s electrical response to yield helpful information about its domain-dependent physicochemical properties (generally, the analysis is carried out in the frequency domain). Nowadays, there are many areas of application where IS can be used to evaluate or enhance the development of emerging products and processes. As a contribution to this field of research, this paper presents relevant theoretical–practical aspects of the interpretation and analysis of the electrical behavior of materials based on IS and IS modelling. The work starts by historically introducing IS and then goes through different domains of application of the technique, such as Materials Science and correlated areas. Afterwards, an introduction to IS usage for constructing equivalent electrical circuits is presented, aiming at modelling the materials’ electrical behavior, followed by examples from the literature that use the two possible circuit development approaches, the series and the parallel association of circuit elements. Lastly, the authors present a case study of their most recent efforts of a circuit model development of relative humidity (RH) sensors based on heterogeneous mixed metal oxide (MMO) nanostructures, used to understand and identify existing contributions to the overall electrical response of the sensors to moisture; in their case, the electrical response of the MMO sensors was modelled with a high level of superposition between the experimental and fitted data, using a parallel combination of circuit elements, which is an unconventional one. Full article

This work demonstrates a completely wet-chemical procedure for the fabrication of a functional impedimetric humidity-sensing device on a titania (TiO₂) surface. Optically transparent anatase TiO₂ thin films were deposited on a glass substrate via dip-coating from a titanium tetraisopropoxide (TTIP)–acetylacetonate (AA)-based sol and surface-functionalized with a nickel oxide (NiO_x) layer by ultraviolet (UV) photodeposition. Photodeposition was employed to form the interdigitated electrode pattern on the TiO₂ surface as well through activation with a silver catalyst to promote electroless copper deposition. The relative humidity (RH) response of the pristine TiO₂- and NiO_x/TiO₂-functionalized sensors was studied by impedance (Z) measurements in the 15%–90% RH range. It was found that while NiO_x functionalization significantly dampens the RH–Z functional dependence, it improves its overall linearity and may successfully be employed for the purposeful design of titania-based sensing devices. Full article

Mullite substrates with two different porosities were 3D printed, and tested as humidity sensors. To evaluate the effects of porosity on humidity sensitivity, the samples were sintered at 1400 °C (Sensor 1) and 1450 °C (Sensor 2). The sensors were tested in a range from 0% to 85% relative humidity (RH) at room temperature. When exposed to water vapor at room temperature, the impedance value dropped down from 155 MΩ under dry air to 480 kΩ under 85 RH% for Sensor 1 and from 115 MΩ under dry air to 410 kΩ for Sensor 2. In addition, response time and recovery time were below 2 min, whatever the firing temperature, when RH changed from 0% to 74%. Finally, tests carried out involving ammonia, methane, carbon dioxide and nitrogenous oxide, as well as ethanol and acetone, showed no interference. Full article

In this work, pure phase and carbon/ZnSn(OH)₆ samples were synthesized by a hydrothermal method. The composite sample’s structure, morphology, and functional groups were investigated by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. Subsequently, ZnSn(OH)₆ samples were modified with different carbon contents, and their humidity-sensing properties were investigated. The introduction of carbon increased the specific surface area of pure ZnSn(OH)₆ samples, thus significantly improving the sensors’ humidity sensing response. The C10-ZnSn(OH)₆ sensor exhibited a high response, up to three orders of magnitude, a humidity hysteresisof 13.5%, a fast response time of 3.2 s, and a recovery time of 24.4 s. The humidity sensor’s possible humidity sensing mechanism was also analyzed using the AC complex impedance puissance method with a simulated equivalent circuit. These results revealed that ZnSn(OH)₆ can effectively detect ambient humidity and that the introduction of carbon significantly improves its humidity-sensing performance. The study provides an effective strategy for understanding and designing ZnSn(OH)₆-based humidity sensors. Full article

This paper reports a high-performance humidity sensor made using a novel cellulose nanofiber (CNF)–silver nanoparticle (AgNP) sensing material. The interdigital electrode pattern was printed via reverse-offset printing using Ag nano-ink, and the sensing layer on the printed interdigitated electrode (IDE) was formed by depositing the CNF-AgNP composite via inkjet printing. The structure and morphology of the CNF-AgNP layer are characterized using ultraviolet–visible spectroscopy, an X-ray diffractometer, field emission scanning electron microscopy, energy-dispersive X-ray analysis, and transmission electron microscopy. The humidity-sensing performance of the prepared sensors is evaluated by measuring the impedance changes under the relative humidity variation between 10 and 90% relative humidity. The CNF-AgNP sensor exhibited very sensitive and fast humidity-sensing responses compared to the CNF sensor. The electrode distance effect and the response and recovery times are investigated. The enhanced humidity-sensing performance is reflected in the increased conductivity of the Ag nanoparticles and the adsorption of free water molecules associated with the porous characteristics of the CNF layer. The CNF-AgNP composite enables the development of highly sensitive, fast-responding, reproducible, flexible, and inexpensive humidity sensors. Full article

This paper presents the development of a miniaturized sensor device for selective detection of pathogens, specifically Influenza A Influenza virus, as an enveloped virus is relatively vulnerable to damaging environmental impacts. In consideration of environmental factors such as humidity and temperature, this particular pathogen proves to be an ideal choice for our study. It falls into the category of pathogens that pose greater challenges due to their susceptibility. An impedance biosensor was integrated into an existing platform and effectively separated and detected high concentrations of airborne pathogens. Bio-functionalized hydrogel-based detectors were utilized to analyze virus-containing particles. The sensor device demonstrated high sensitivity and specificity when exposed to varying concentrations of Influenza A virus ranging from 0.5 to 50 $\mathsf{\mu }$g/mL. The sensitivity of the device for a 0.5 $\mathsf{\mu }$g/mL analyte concentration was measured to be 695 $\mathsf{\Omega }·$ mL/$\mathsf{\mu }$g. Integration of this pathogen detector into a compact-design air quality monitoring device could foster the advancement of personal exposure monitoring applications. The proposed sensor device offers a promising approach for real-time pathogen detection in complex environmental settings. Full article