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ACu 3 Ti 4 O 12 (A = Sr, Ba) double perovskites are attractive dielectric materials, yet they have not been reported in the field of gas and humidity sensors. In this work, SrCu 3 Ti 4 O 12 (SCTO) and BaCu 3 Ti 4 O 12 (BCTO) powders were synthesized by a facile modified solid-phase sintering method with characteristic of abundant cation-oxygen dual-defects (oxygen vacancy, metal deficiencies of Cu+ and Ti3+). For the first time, SCTO and BCTO are explored as humidity sensing materials, while the SCTO sensor holds a response value of four orders of magnitude (S r = 2.8× 104), which is over a thousand times higher than that of BCTO (S r = 25). In addition, the SCTO sensor is featured in fast response (7 s), reliable linearity (R2 = 0.97), small hysteresis (ΔH max = 0.8%) and good repeatability in a wide relative humidity (RH) range (11%–97%). The boosted humidity sensing performance enables the SCTO sensor to possess great potential in human-body related moisture monitoring of breath and finger detection. Finally, the complex impedance analysis reveals different majority carriers of SCTO (H+) and BCTO (H 3 O+) under high RH range. The enhanced humidity sensing performance of SCTO can be attributed to the synergistic effects of richer dual-defects and larger ion potential. This work provides an excellent humidity sensing material of SCTO, and furthermore, gives new insights on defect sensitization strategy of perovskites for high-performance electronic sensory devices. [ABSTRACT FROM AUTHOR]

Fully‐printed humidity sensors based on BiFeO3/BiOCl heterojunctions fabricated using a two‐step process with serigraphic printing are reported. Most importantly, this unique sensor architecture provides a broader relative humidity sensing range compared to pristine BFO sensors due to a synergistic effect between dense networks of BiOCl nanosheets synthetized atop BFO powders. With surface‐to‐weight ratios reaching 7.75 m2 g−1, these heterostructures increase the sensitivity and operating range of BFO‐based humidity sensors. While previously reported BFO humidity sensors only detect relative humidities above 30%, The BFO/BiOCl heterojunctions can measure relative humidities as low as 15% due to their increased surface area. Optimal growth and packing of the BiOCl nanosheet/BFO powder heterostructure are achieved by tuning the loading of the BFO powder and simultaneously forming the BiOCl sheets by chemical etching and annealing of the BFO powder. Excellent performance of optimized sensors including tracking and monitoring different types of breathing are demonstrated while mounted on an oxygen mask. [ABSTRACT FROM AUTHOR]

The current investigation focuses on the development of capacitive humidity sensors utilizing an organic polymer blend of poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and [6,6]-phenyl-C71-butyric-acid methyl ester (PC71BM), which were successfully achieved. A cost-effective spin-coating technique was employed to produce surface-type sensors in the Al/PTB7-Th:PC71BM/Al horizontal geometry. The investigation focuses on the capacitive behavior of the devices under ambient conditions, specifically at room temperature. The devices are subjected to an alternating current operational bias of 1 V, while the relative humidity (RH) is varied within the range of 20–95%. The sensors are examined at frequencies of 100 Hz, 1 kHz, 10 kHz, and 100 kHz. Specifically, the sensors demonstrate improved sensitivity to changes in capacitance in relation to relative humidity when operating at a frequency of 100 Hz. In addition, an optimal volumetric ratio of 1.5:1 is selected for PTB7-Th to PC71BM. The optimized composite sensor demonstrates superior performance, exhibiting minimal hysteresis of 6.16% and significant sensitivity of 1.58 pF/% RH. In addition, response and recovery times of 2 s and 3 s, respectively, are obtained. The results of investigations demonstrate that the composite sensor exhibits significant improvements in sensing parameters compared to single-material sensors. As a result, the composite sensor has great potential for use in advanced sensor applications, especially in the education sector in underdeveloped countries. [ABSTRACT FROM AUTHOR]

Real‐time monitoring of respiration plays a very important role in human health assessment, especially in monitoring and analyzing respiration during exercise and sleep. However, traditional humidity sensors still have problems in flexibility, sensitivity, and durability, so there is an urgent need to develop humidity sensors with high sensitivity, stretchability, and environmental resistance as respiratory monitoring applications. Here, based on the double network hydrogel structure of polyvinyl alcohol and polyacrylamide, a highly sensitive, highly stretchable, and environmentally stable organic hydrogel humidity sensor has been manufactured by using the synergistic effect of lithium chloride and MXene. The hydrogel humidity sensor shows rapid response in the humidity range of 40–85% RH, and has a high sensitivity of −103.4%/% RH. In addition, it exhibits more than 3000% mechanical strain and excellent environmental resistance, which is attributed to the chemical cross‐linking in the hydrogel network and the synergistic effect of multiple hydroxyl groups in glycerol forming rich hydrogen bonds with water and polymer chains. The hydrogel humidity sensor is used for real‐time monitoring of breathing and sleep processes. This work provides a new strategy for preparing high‐performance, extensibility, and environmental stability hydrogel‐based sensors for respiratory monitoring. [ABSTRACT FROM AUTHOR]

A highly sensitive and repeatable humidity sensor that can measure relative humidity at room temperature (25 °C) was fabricated using activated carbon-ZnO (AC/ZnO) nanocomposites. The AC/ZnO nanocomposites with high oxygen vacancies were prepared by a facile one-pot synthesis method through carbonization of ZnCl 2 -impregnated biomass precursor. The sensor exhibited a better response (96 % at 0.5 V biasing), short response time (17.4 s), and recovery time (32.1 s). The same 96 % relative response at 0.5V biasing for all four consecutive cycles was observed without losing the response-recovery time, indicating excellent repeatability. On the other hand, biomass-derived single-phase activated carbon (AC) did not respond to humidity change at room temperature. The improved humidity sensing in AC/ZnO nanocomposites was ascribed to the synergistic effects of increased oxygen vacancies, increased active sites in the AC phase, and the formation of p–n heterojunction at the composite interface, substantiated with X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) studies. The sensing mechanism of AC/ZnO nanocomposite was discussed based on the enhanced reduction of H 2 O by adsorbed O 2 − at AC/ZnO heterojunction, leading to increasing sensor resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

2D transition metal borides (MBenes) with abundant surface terminals hold great promise in molecular sensing applications. However, MBenes from etching with fluorine‐containing reagents present inert ‐fluorine groups on the surface, which hinders their sensing capability. Herein, the multilayer fluorine‐free MoBTx MBene (where Tx represents O, OH, and Cl) with hydrophilic structure is prepared by a hydrothermal‐assisted hydrochloric acid etching strategy based on guidance from the first‐principle calculations. Significantly, the fluorine‐free MoBTx‐based humidity sensor is fabricated and demonstrates low resistance and excellent humidity performance, achieving a response of 90% to 98%RH and a high resolution of 1%RH at room temperature. By combining the experimental results with the first‐principles calculations, the interactions between MoBTx and H2O, including the adsorption and intercalation of H2O, are understood first in depth. Finally, the portable humidity early warning system for real‐time monitoring and early warning of infant enuresis and back sweating illustrates its potential for humidity sensing applications. This work not only provides guidance for preparation of fluorine‐free MBenes, but also contributes to advancing their exploration in sensing applications. [ABSTRACT FROM AUTHOR]

This study focused on utilizing cellulose nanocrystal (CNC)–polyvinyl alcohol (PVA) composite in optical sensor applications to detect high humidity conditions and determine water concentration in ethanol. We focused on the composite's effectiveness in moisture absorption to demonstrate visual color change. We demonstrated that the different molecular weights of PVA significantly affect CNC's chiral nematic structure and moisture absorption capability. PVA with molecular weight 88 k–97 k exhibited the disintegration of its chiral nematic structure at 30 wt%, whereas low molecular weight PVA (n~1750) showed no structural disintegration even at 100 wt% concentration when analyzed through UV-Vis spectroscopy. Further, the thermal crosslinking of the CNC-PVA composite showed no significant loss of moisture sensitivity for all molecular weights of the PVA. We observed that the addition of PVA to the sulfated CNC obtained from sulfuric acid hydrolysis did not facilitate moisture absorption significantly. A CNC-PVA sensor was developed which can detect high humidity with 2 h. of exposure time. 2,2,6,6-tetramethylpiperidin-1-piperidinyloxy oxidized CNC (TEMPO-CNC) having carboxylic functionality was also used to prepare the CNC-PVA composite films for comparing the effect of functional groups on moisture sensitivity. Finally, we demonstrated a facile method for utilizing the composite as an optical sensor to detect water concentration in ethanol efficiently; thus, it can be used in polar organic solvent dehydration applications. [ABSTRACT FROM AUTHOR]

The evolution of clothing towards functionalization and intelligence has led to increasing attention on wearable smart garments. In modern military combat systems, the smart sensing fabric plays crucial role in soldiers' combat attire. It possesses characteristics of perception, feedback, response, as well as the softness and wearability of textiles. This enables it to detect changes in the external environment and make corresponding adjustments to meet specific needs. In the military field, smart sensing fabrics can more comfortably and safely monitor soldiers health status while playing an important role in battlefield information perception, combat command, and other aspects. It can monitor soldiers' physiological states, environmental changes, and battlefield situations in a real-time manner, providing commanders with timely and accurate information support to enhance soldiers survivability and combat effectiveness. The smart sensing fabric integrates various types of sensors with fabric substrates to perceive and monitor various physical or environmental parameters, converting them into readable electrical signals. Featureing excellent flexibility, stretchability, and wearability, it is able to conform to various human body curves and irregular shapes, meeting the demands of different application scenarios, especially suitable for scenarios requiring flexible measurement of strain or pressure. This article systematically reviews the research progress in recent years on textile-based strain sensors, pressure sensors, temperature sensors and humidity sensors, and the application of smart sensing textiles in military equipment. It also analyzes issues such as data security, washability, stability, and reliability of data transmission. Therefore, the smart sensing fabric demonstrates tremendous development potential and diverse applications in the military equipment field, such as monitoring soldiers' physiological states, battlefield environments, and movement postures. As textile technology advances and intelligent technologies continue to evolve, smart sensing fabrics will achieve more innovations in materials, functions, and structures. They will not only become lighter, softer, and more comfortable but also integrate more sensors and intelligent components for more precise and comprehensive perception and monitoring. [ABSTRACT FROM AUTHOR]

Humidity sensors have gained tremendous attention due to their practical applications in the pharmaceutical industry, food processing, biomedical applications, microelectronics, and meteorology. Herein, a polymer-based multifunctional humidity sensor (PANI-Bi-ZnO) has been fabricated. This study describes a polymer-based capacitive-type humidity sensor that has excellent repeatability, negligible hysteresis (0.5% RH at 60% RH), quick response (8 s) and relaxation times (20 s), high stability (30 days), high sensitivity, and good linearity in a wide humidity detection range of 10–90% RH and has become increasingly significant for applications involving industrial control and environmental monitoring. Moreover, the fabricated sensor possesses a highly reliable/stable output performance that remains constant after multiple test cycles. The current work also provides a cost-effective method to fabricate high-performance humidity sensors. The designed humidity sensor would be an excellent choice for measuring a variety of applications in the field of humidity. [ABSTRACT FROM AUTHOR]

To effectively solve the problem that the measurement uncertainty evaluation result is not accurate and the calculation is complicated when the humidity measuring instrument is calibrated. The "Monte Carlo simulation method" (MCM) was proposed to evaluate the measurement uncertainty of humidity sensor calibration results. In this process, firstly, by analyzing the calibration process of humidity sensor, the measurement model that can accurately and completely reflect the actual measurement situation is constructed; then, design a performance testing method for the humidity generator to obtain parameter data that can truly reflect the performance of the current humidity generator; finally, taking the 55%RH calibration point as an example, by using the above measurement model and related parameters, single MCM method and adaptive MCM method were used to evaluate the measurement uncertainty of the humidity sensor calibration results. The evaluation results obtained are the same as: the best estimated value of humidity sensor measurement error ΔH = 0.01%RH, the standard uncertainty u(ΔH) = 0.14%RH, and the shortest coverage interval [ΔHlow, ΔHhigh] = [− 0.24%RH, 0.26%RH] when the coverage probability is 95%. Through this application experiment on the MCM method, it was found that compared to the GUM method, the MCM method can effectively improve the credibility of the measurement uncertainty results of the humidity sensor. Moreover, when the adaptive MCM method is applied to evaluate the measurement uncertainty of the humidity sensor, compared to the single MCM method, it can effectively reduce simulation times, reduce storage space resources, and improve evaluation efficiency. Prioritizing the adaptive MCM method in practical operation is recommended. [ABSTRACT FROM AUTHOR]

Humidity sensors are commonly utilized in a variety of fields. However, present humidity detection devices have many liabilities, such as narrow ranges, poor repeatability, and short lifespans. Therefore, it is essential to explore new humidity sensors with high sensitivity. Here, a new humidity sensor based on ZnO microspheres (MS) decorated with graphene (GR) is introduced. The sensing range of the ZnO MS/GR sensor has been measured to be 20–95% relative humidity (RH). The ZnO MS/GR sensor achieves a large change in resistance of over 4 orders of magnitude, which is 1–2 orders larger than ZnO or GR humidity sensors. The enhanced humidity-sensing performance of the ZnO MS/GR nanocomposite is attributed to the Grotthuss mechanism and the combined effect of the heterojunction at the ZnO/GR interface. This work demonstrates a new humidity sensor with high performance based on a ZnO MS/GR nanocomposite, which may impact future humidity-sensing fields. [ABSTRACT FROM AUTHOR]

This work designed and implemented of photonic crystal fiber Fabry–Perot interferometer based on (SPR) technology for sensing the humidity of the environment. The FPI was created by directly splicing a short length of PCF (4 cm) solid core on one side with traditional multimode fiber (MMF) and depositing a nano-film of gold with a thickness of 40 nm on the end of the PCF sensor. The PCF–SPR experiment was observed for different degrees of relative humidity. The location of the resonant wavelength peaks is seen to change to longer wavelengths (redshift) as (the RH) increases due to the transmission of maximum energy from the reflected power of the light guided via the fiber to the surface plasmons. The calculated sensitivity, signal-to-noise ratio, figures of merit, and resolution are approaching; the S is 1.25 nm/%RH, SNR is 0.0066, the resolution is 0.08, and the FOM is 0.00083 for photonic crystal fiber. [ABSTRACT FROM AUTHOR]

Abstract In this study, we investigated the humidity sensing properties of TiO2-based ceramics doped with tantalum pentoxide (Ta2O5) and indium tin oxide (ITO). Pure TiO2, 1%Ta-doped TiO2 (1%TTO), 1%ITO-doped TiO2 (1%ISTO), and 1%(Ta2O5 + ITO) co-doped TiO2 (1%ISTTO) ceramic samples were obtained by sintering at 1200 °C for 3 h. The rutile phase was observed in all samples. The lattice parameters of the single and co-doped samples were larger than those of pure TiO2, confirming the substitution of dopants. Porosity was observed in all ceramics. The mean grain sizes of all doped samples were significantly reduced compared to undoped TiO2. A homogeneous element dispersion was observed in the 1%TTO and 1%ISTTO ceramics, while segregation particles of related In-rich elements was observed in the 1%ISTO ceramic. Giant dielectric properties were not achieved in any samples due to the porosity. Nevertheless, excluding the undoped TiO2, the dielectric properties of all porous ceramics varied significantly with changes in humidity. The 1%ISTTO ceramic demonstrated superior humidity sensing properties, including a low maximum hysteresis error of 3.6% at 102 Hz. In contrast, the 1% TTO and 1% ISTO ceramics showed higher maximum hysteresis errors of 7.2% and 19.8%, respectively. Notably, the response and recovery times were 7.05 ± 0.18 and 2.48 ± 0.39 min, respectively, with good repeatability. This improvement is likely due to the synergistic effect of oxygen vacancies and $${\text{Ta}}_{{{\text{Ti}}}}^{ \cdot }$$ Ta Ti · defects on the surface, enhancing the humidity sensing properties of the 1% ISTTO ceramic, coupled with its optimal microstructure due to its lowest porosity and grain size.

This study focused on utilizing cellulose nanocrystal (CNC)–polyvinyl alcohol (PVA) composite in optical sensor applications to detect high humidity conditions and determine water concentration in ethanol. We focused on the composite’s effectiveness in moisture absorption to demonstrate visual color change. We demonstrated that the different molecular weights of PVA significantly affect CNC’s chiral nematic structure and moisture absorption capability. PVA with molecular weight 88 k–97 k exhibited the disintegration of its chiral nematic structure at 30 wt%, whereas low molecular weight PVA (n~1750) showed no structural disintegration even at 100 wt% concentration when analyzed through UV-Vis spectroscopy. Further, the thermal crosslinking of the CNC-PVA composite showed no significant loss of moisture sensitivity for all molecular weights of the PVA. We observed that the addition of PVA to the sulfated CNC obtained from sulfuric acid hydrolysis did not facilitate moisture absorption significantly. A CNC-PVA sensor was developed which can detect high humidity with 2 h. of exposure time. 2,2,6,6-tetramethylpiperidin-1-piperidinyloxy oxidized CNC (TEMPO-CNC) having carboxylic functionality was also used to prepare the CNC-PVA composite films for comparing the effect of functional groups on moisture sensitivity. Finally, we demonstrated a facile method for utilizing the composite as an optical sensor to detect water concentration in ethanol efficiently; thus, it can be used in polar organic solvent dehydration applications.

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.

Cellulose nanofibers (CNFs) are part of organic crystallization macromolecular compounds that can be found in bacteria's capsular polysaccharides and plant fibers. CNFs have a lot of potential as suitable matrices and advanced materials, and there have been a lot of studies done on them so far, both in terms of modifying them and inventing uses for them. In this paper, CNFs/reduced graphene oxide (GO) (rGO) nanocomposites were developed to create renewable, flexible, and cheap humidity sensors. The composite film's performance as a humidity sensor was evaluated by analyzing the variations in capacitance at different humidity levels. The synthesized composite film underwent characterization using various analytical techniques, including scanning electron microscopy (SEM), UV (ultraviolet)/Vis (visible) spectrophotometry, Fourier transform infrared spectroscopy (FTIR), and thermomechanical analysis (TMA). The sensing mechanism is elucidated based on hydrophilic functional groups within the composite material. It has been observed that 3 wt% rGO/CNF composite is the best suited for humidity sensing among all other samples. [ABSTRACT FROM AUTHOR]

In this study, we investigated the humidity sensing properties of TiO2-based ceramics doped with tantalum pentoxide (Ta2O5) and indium tin oxide (ITO). Pure TiO2, 1%Ta-doped TiO2 (1%TTO), 1%ITO-doped TiO2 (1%ISTO), and 1%(Ta2O5 + ITO) co-doped TiO2 (1%ISTTO) ceramic samples were obtained by sintering at 1200 °C for 3 h. The rutile phase was observed in all samples. The lattice parameters of the single and co-doped samples were larger than those of pure TiO2, confirming the substitution of dopants. Porosity was observed in all ceramics. The mean grain sizes of all doped samples were significantly reduced compared to undoped TiO2. A homogeneous element dispersion was observed in the 1%TTO and 1%ISTTO ceramics, while segregation particles of related In-rich elements was observed in the 1%ISTO ceramic. Giant dielectric properties were not achieved in any samples due to the porosity. Nevertheless, excluding the undoped TiO2, the dielectric properties of all porous ceramics varied significantly with changes in humidity. The 1%ISTTO ceramic demonstrated superior humidity sensing properties, including a low maximum hysteresis error of 3.6% at 102 Hz. In contrast, the 1% TTO and 1% ISTO ceramics showed higher maximum hysteresis errors of 7.2% and 19.8%, respectively. Notably, the response and recovery times were 7.05 ± 0.18 and 2.48 ± 0.39 min, respectively, with good repeatability. This improvement is likely due to the synergistic effect of oxygen vacancies and Ta Ti · defects on the surface, enhancing the humidity sensing properties of the 1% ISTTO ceramic, coupled with its optimal microstructure due to its lowest porosity and grain size. [ABSTRACT FROM AUTHOR]

Porous silicon (PSi) has received a lot of attention in nanotechnology research in recent years for its potential use as sensing layers in sensor application. However, there have been relatively limited studies concerning the effect of varying contact gaps and bias voltages on the humidity sensor based on PSi. In this work, the nanostructure PSi layer was synthesized via the anodization method and fabricated at different annealing temperatures of 250 ℃, 450 ℃, 650 ℃, and 850 ℃. Subsequently, the four samples were deposited with varying gold (Au) contact gaps of 3.5 mm, 4.5 mm, 7.5 mm, and 8.5 mm. The morphological and structural characteristics of the PSi layer were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The PSi-based humidity sensors with varied Au contact gaps were evaluated in a humidity chamber at 40–90% relative humidity (RH) levels with different bias voltages of 2 V, 5 V, and 10 V. The optimized fabricated PSi device was evaluated for its electrical behaviour using I-V measurement under various operating temperatures ranging from 25 °C to 100 °C. The findings showed that the enhanced PSi structure of the 450 °C annealed sensor produced the highest sensitivity performance of 18.4705 µA/%RH with stable output at a contact gap of 4.5 mm and a bias voltage of 10 V. The sensor exhibited a high surface area to volume ratio, which facilitated efficient interactions between surface active sites and water molecules, resulting in a highly sensitive humidity sensor. [ABSTRACT FROM AUTHOR]

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In this study, a simple and cost‐effective method is presented for developing a metal oxide‐based humidity sensor. CrFeO3 is synthesized without any precipitating agent and chosen as a model material to study the validity of humidity sensing properties. The surface morphology and structural analysis are provided using field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X‐ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) analysis. Elemental analysis is provided with the help of X‐ray photoelectron spectroscopy (XPS). Obtained results demonstrate the tunable response of order 860 and stability in a large range of humidity. Also, by controlling the porosity and film uniformity, a fast response time of 1.6 s and a recovery time of 2.6 s are achieved with very low hysteresis. Also, cole–cole plot and Fourier transform infrared spectroscopy (FTIR) spectra in the presence and absence of humidity provide detailed analysis of surface interaction with H2O molecules. In addition to this, the developed sensor demonstrates excellent response and reproducibility toward real‐time human respiration monitoring along with non‐contact sensing. This work enables the study of developed sensors in real‐time humidity monitoring for practical applications. [ABSTRACT FROM AUTHOR]

Indium hydroxide (In-(OH)3) nanoparticles were prepared with a size of ∼25-45 nm using the homogeneous precipitation method, and a humidity sensor was developed based on this material. The crystal phase and elements of In-(OH)3 were characterized and analyzed using X-ray diffraction and X-ray photoelectron spectroscopy. The morphology and specific surface area were determined using scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption (Brunauer-Emmett-Teller) measurements. Additionally, humidity sensing tests were conducted on In-(OH)3. Owing to the unique porous structure of In-(OH)3, the fabricated In-(OH)3 humidity sensor exhibited excellent humidity sensitivity characteristics, with a wide humidity detection range (11-95%), comparatively excellent response/recovery time (14 s/204 s), high response (430.6), good stability, and high resolution with a minimum detection limit of 1% relative humidity. The humidity response of the In-(OH)3 humidity sensor was tested at different temperatures, indicating its potential for use in diverse environments such as cold storage and bathrooms. Notably, the low manufacturing cost of this sensor further enhances its appeal for widespread applications. This work provides a promising humidity sensing material for the manufacture of high-performance humidity sensors. [ABSTRACT FROM AUTHOR]

Capacitive humidity sensors typically consist of interdigitated electrodes coated with a dielectric layer sensitive to varying relative humidity levels. Previous studies have investigated different polymeric materials that exhibit changes in conductivity in response to water vapor to design capacitive humidity sensors. However, lipid films like monoolein have not yet been integrated with humidity sensors, nor has the potential use of capacitive sensors for skin hydration measurements been fully explored. This study explores the application of monoolein-coated wireless capacitive sensors for assessing relative humidity and skin hydration, utilizing the sensitive dielectric properties of the monoolein–water system. This sensitivity hinges on the water absorption and release from the surrounding environment. Tested across various humidity levels and temperatures, these novel double functional sensors feature interdigitated electrodes covered with monoolein and show promising potential for wireless detection of skin hydration. The water uptake and rheological behavior of monoolein in response to humidity were evaluated using a quartz crystal microbalance with dissipation monitoring. The findings from these experiments suggest that the capacitance of the system is primarily influenced by the amount of water in the monoolein system, with the lyotropic or physical state of monoolein playing a secondary role. A proof-of-principle demonstration compared the sensor's performance under varying conditions to that of other commercially available skin hydration meters, affirming its effectiveness, reliability, and commercial viability. [ABSTRACT FROM AUTHOR]

A double layer membrane humidity sensor was designed with a synergistic effect of force and hygroscopic expansion, capitalizing on the high sensitivity demonstrated by MXene material. This sensitivity was achieved through the modulation of resistance change associated with layer spacing of MXene. The double layer structure of sensor was made by vacuum filtration, with an inner layer of MXene for conductivity and an outer layer of cellulose nanofibers (CNF) for moisture absorption, which is rooted in the MXene through the CNFs, similar to the biomimetic structure of hairs rooted in the skin. The synergistic effect of humidity sensitivity is achieved by trapping and dissociating water molecules through the CNF layer generating a change in MXene stress and disrupting the conductive pathway of MXene upon swelling. The CNF/MXene humidity sensor showed a resistance change rate of 117.93 % from 11 % RH to 98 % RH, accompanied by a response time of 319s and a recovery time of 132s. Stable sensing performance is maintained even after 5 times adsorption and desorption cycling, prolonged exposure (7 days) or bending and folding. CNF/MXene bilayer membrane also has good electrical heating performance, reaching about 80 °C at 7V and maintaining stable performance under 5 cycles of heating and 10 min of long heating, respectively. The CNF/MXene membrane humidity sensor can monitor human respiration monitoring, fingertip humidity, pipeline leakage and artifact dehumidification, and combined with the function of electric heating can realize the cycle of dehumidification and humidity monitoring, which has a wide range of application prospects in flexible equipment. [ABSTRACT FROM AUTHOR]

TiO2 is a typical semiconductor material, and it has attracted much attention in the field of humidity sensors. Doping is an efficient way to enhance the humidity response of TiO2. Eu-doped TiO2 material was investigated in both theoretical simulations and experiments. In a simulation based on density functional theory, a doped Eu atom can increase the performance of humidity sensors by producing more oxygen vacancies than undoped TiO2. In these experiments, Eu-doped TiO2 nanorods were prepared by hydrothermal synthesis, and the results also confirm the theoretical prediction. When the doping mole ratio is 5 mol%, the response of the humidity sensor reaches 23,997.0, the wet hysteresis is 2.3% and the response/recovery time is 3/13.1 s. This study not only improves the basis for preparation of high-performance TiO2 humidity sensors, but also fills the research gap on rare earth Eu-doped TiO2 as a humidity-sensitive material. [ABSTRACT FROM AUTHOR]

In this work, polypyrrole (PPy) is synthesized, characterized, and employed as an active sensing material for the fabrication of humidity sensors. An 80 nm thick layer of PPy is spin coated on the pre-patterned thermally deposited silver (Ag) electrodes spaced 50 µm apart to fabricate Ag/PPy/Ag surface-type sensor. Atomic force microscopy analysis revealed granular microstructure morphology in the thin films of PPy. Additionally, X-ray diffraction (XRD), ultraviolet–visible (UV-Vis) and Fourier transformed infrared (FTIR) spectra of PPy are analyzed to study its crystallinity, optical bandgap and bond dynamics to confirm the molecular composition of PPy. The fabricated Ag/PPy/Ag sensor is characterized by varying the humidity levels between a broad range [0–95% relative humidity (RH)] at different frequencies of 120 Hz and 1 kHz. The prepared sensor showed promising sensing features such as higher sensitivity 233 nF/%RH (at 120 Hz), 83 pF/%RH (at 1 kHz), quick response time (5.20 ± 0.2 s) and recovery times (6.43 ± 0.2 s), a wide working range of relative humidity (20–95%RH) and low hysteresis gap (1.57%) with outstanding recyclability. This study reveals the potential of PPy as the best candidate for humidity sensing applications. [ABSTRACT FROM AUTHOR]

Because of the sensitivity enhancement of the fiber Bragg grating (FBG) sensor is still matter of challenge, and it is very important in different field of study, this paper proposes a new approach to enhance the humidity and temperature sensitivities of FBG sensors based on Levenberg–Marquardt algorithm by utilizing artificial neural networks (ANNs). The ANN's usage yield a more precise model that considered uncertainties and nonlinearities in the response of the FBG sensor, leading to a significant humidity and temperature measurements with higher sensitivity and accuracy. Compared to traditional sensors, the presented FBG sensor based on ANNs reflects a significant enhancement in both humidity and temperature sensitivity. The current work also illustrates the ANNs potential as a tool to improve the performance of FBG fiber-optic sensors, which could be utilized to other kinds of fiber optic sensors, leading to better accuracy and sensitivity for a wide range of applications. According to sensitivity of humidity, the FBG sensor based on the ANNs exhibited a good enhancement estimated by 20.13 pm/%RH. The linearity performance of the current FBG sensor based on the ANNs approach referred a significant behavior under different surrounding factors and conditions of humidity with estimated R square value of 0.95328. Moreover, in terms of percentage errors for humidity sensitivity, the values were estimated to be 1%, 1.3%, 1%, 1%, and 1.2% for 30, 40, 55, 75, and 95%RH, respectively. According to sensitivity of temperature, the FBG sensor based on ANN method showed a significant improvement calculated to be 0.8625 pm/°C. Additionally, the linearity performance of the proposed approach refers to a good FBG sensor performance under wide range of applied temperatures with calculated R square value of 0.98199. Furthermore, in terms of percentage errors for temperature sensitivity, the values were estimated to be 1%, 1.1%, 1.2%, 1%, and 1.1% for 25, 35, 55, 75, and 95 °C, respectively. The contribution of the current work is to develop more reliable and advanced fiber optic based on FBG humidity and temperature sensors, which could have an essential influence on structure health monitoring systems and related applications. The current work impact is essential, because it proposes a promising solution for conventional FBG limitations in terms of humidity and temperature sensors, leading to more reliable and accurate measurements in different applications, for example, structural health monitoring systems, automation of building, and processing of food. [ABSTRACT FROM AUTHOR]

Real‐world applications of graphene require reliable routes for synthesizing large‐area graphene and methods to tune its structural and electrical properties. A viable and facile route is presented for synthesizing 3D porous graphene (3PG) on PI films with tunable patterns and locations via the photon‐pen writing technique and subsequent oxygen plasma treatment. The laser power and scan speed are optimized for 3PG synthesis. The electrical properties and surface hydrophilicity are controlled via surface customization of 3PG with optimal oxygen plasma treatment duration and laser inter‐spacing. The capability of humidity sensors based on surface‐customized 3PG with hydrophobic surface is demonstrated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

PANI is a nanostructure conductive polymer that has been widely researched by making nanofibers using electrospinning, by adding PVA as a non-conductive material. In this research, we have successfully synthesized PVA/PANI nanofiber using the electrospinning method and applied it as a humidity sensor. The oxidation polymerization method was conducted to produce polyaniline (PANI) powder. PVA was used as a non-conductive polymer to carry PANI. PANI is blended with 10 % PVA to produce nanofiber PVA/PANI. The results of the synthesis of PVA/PANI nanofibers using the electrospinning method have been characterized by FTIR and EDX to identify the functional groups and elements of PVA/PANI. The FTIR results confirmed that for the PVA nanofiber samples, the type of polyvinyl alcohol bond has been identified according to the reference. The EDX results show the elements C, O and N. The element nitrogen (N) is the characteristic element of polyaniline (C6H5(NH)2)n. The optical Microscope and Scanning Electron Microscope show that the electrospinning method has succeeded in synthesizing PVA/PANI nanofibers with a fiber size of around 0.313 mm. The porosity of PVA/PANI is around 55 %, which is related to the ability of PVA/PANI sensitivity to detect humidity. These results are demonstrated by measurements using a Four-Point Probe (FPP), with the humidity value varying from 64 - 80 %. The results show that variations of PANI powder content improve the sensitivity performance of PVA/PANI nanofibers. This method can optimize PVA/PANI nanofiber as a humidity sensor, increase conductivity flexibility, make it easier and enhance the PANI to use as an active sensor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The emergence of novel self-powered humidity sensors has attracted considerable attention in the fields of smart electronic devices and personal healthcare. Herein, self-powered humidity sensors have been fabricated using a moisture-driven energy generation (MEG) device based on asymmetric tubular graphitic carbon nitride (g-CN) films prepared on anodized aluminum (AAO) template. At a relative humidity (RH) of 96%, the MEG device can provide an open-circuit voltage of 0.47 V and a short-circuit current of 3.51 µA, with a maximum output power of 0.08 µW. With inherent self-powered ability and humidity response via current variation, an extraordinary response of 1.78 × 106% (41%–96% RH) can be gained from the MEG device. The possible power generation mechanism is that g-CN/AAO heterostructure can form ion gradient and diffusion under the action of moisture to convert chemical potential into electrical potential, evoking a connaturally sensitive response to humidity. Self-powered respiration monitoring device based on the sensor is designed to monitor human movement (sitting, warming up, and running) and sleep status (normal, snoring, and apnea), maintaining excellent stability during cumulative 12-h respiration monitoring. This self-powered humidity sensing technology has promising potential for extensive integration into smart electronic and round-the-clock health monitoring devices. [ABSTRACT FROM AUTHOR]

The proposed system is an advanced early warning system designed to mitigate disasters such as landslides and floods by providing crucial minutes of warning. It consists of a wireless sensor network deployed on the slopes of landslide and flood-prone mountainsides. The network utilizes a Node MCU topology, and for demonstration purposes, a two-node system is suggested. The nodes in this system are equipped with various sensors to gather essential data. They utilize a tipping rain sensor to measure precipitation and an accelerometer to detect potential landslides by monitoring module position changes. Additionally, there's a humidity sensor continuously monitoring surface temperature changes. These sensor nodes transmit their data to a central base station, which acts as a receiver. Both the public and the base station are equipped with Node MCU microcontrollers to facilitate communication. The base unit, positioned at a strategic location, such as the district collector's office, utilizes a long-range transmitter to communicate with the master unit. When the sensor nodes detect significant landslide or flood activity within a specific timeframe, indicating a potential flash flood, this critical information is transmitted to the master unit. The master unit responds by activating an alarm and promptly sending messages to relevant officials and the general public through Node MCU microcontrollers connected to it. This swift communication allows for timely evacuation and response measures to minimize the impact of the disasters. [ABSTRACT FROM AUTHOR]

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Abstract Fully‐printed humidity sensors based on BiFeO3/BiOCl heterojunctions fabricated using a two‐step process with serigraphic printing are reported. Most importantly, this unique sensor architecture provides a broader relative humidity sensing range compared to pristine BFO sensors due to a synergistic effect between dense networks of BiOCl nanosheets synthetized atop BFO powders. With surface‐to‐weight ratios reaching 7.75 m2 g−1, these heterostructures increase the sensitivity and operating range of BFO‐based humidity sensors. While previously reported BFO humidity sensors only detect relative humidities above 30%, The BFO/BiOCl heterojunctions can measure relative humidities as low as 15% due to their increased surface area. Optimal growth and packing of the BiOCl nanosheet/BFO powder heterostructure are achieved by tuning the loading of the BFO powder and simultaneously forming the BiOCl sheets by chemical etching and annealing of the BFO powder. Excellent performance of optimized sensors including tracking and monitoring different types of breathing are demonstrated while mounted on an oxygen mask.

Abstract 2D transition metal borides (MBenes) with abundant surface terminals hold great promise in molecular sensing applications. However, MBenes from etching with fluorine‐containing reagents present inert ‐fluorine groups on the surface, which hinders their sensing capability. Herein, the multilayer fluorine‐free MoBTx MBene (where Tx represents O, OH, and Cl) with hydrophilic structure is prepared by a hydrothermal‐assisted hydrochloric acid etching strategy based on guidance from the first‐principle calculations. Significantly, the fluorine‐free MoBTx‐based humidity sensor is fabricated and demonstrates low resistance and excellent humidity performance, achieving a response of 90% to 98%RH and a high resolution of 1%RH at room temperature. By combining the experimental results with the first‐principles calculations, the interactions between MoBTx and H2O, including the adsorption and intercalation of H2O, are understood first in depth. Finally, the portable humidity early warning system for real‐time monitoring and early warning of infant enuresis and back sweating illustrates its potential for humidity sensing applications. This work not only provides guidance for preparation of fluorine‐free MBenes, but also contributes to advancing their exploration in sensing applications.

Abstract The humidity has often been measured through a single point sensor. Where, the humidity could be varied at different locations as well as depending on environmental conditions. The present paper developed the dual point humidity measuring sensor by using a polymer optical fiber (POF) based on a single illuminating fiber. The sensor’s basic structure is to twist two fibers and bend them at a certain radius. However, the dual point sensor is developed through the cascading of twisted micro bend (TMB-1 and TMB-2). The twisting of fibers couples the light from one fiber to another fiber through the side coupling method. An increase in the humidity level leads to a change in the reflective index, which helps to get variation in coupled light intensity. To measure the humidity, the dual point sensors are placed into the control humidity chamber at two random positions. The power reading variation is significantly linear when the humidity level increases from 30 to 80%. The sensor has a fast response of about 1 s and a recovery time of about 4 s. Furthermore, the chemical coating is applied to improve the sensor’s sensitivity. Between 30 and 80% range of humidity, the both sensors of dual point TMB-1 and TMB-2 have appropriate sensitivity and detection limits, which is about 680.8 nW/% and 763.9 nW/% and 1.37% and 1.98%, respectively. To measure the humidity at variable positions, the present dual points humidity sensor is well-stable, easy, and straightforward, which uses a less expensive method.

Porous silicon nitride structures were fabricated for a humidity sensor. The porous silicon structures were fabricated by the metal-assisted chemical etching process, and the conformal silicon nitride thin film was deposited by the atomic layer deposition process. The optimized porous sensor with the 10 nm-thick silicon nitride thin film had a hydrophilic surface and compared to other sensors, had an excellent humidity sensing response. Especially, it showed a superior humidity sensing response at 1 kHz with fast response and recovery times of 13.3 s and 12.4 s, respectively, were observed. Based on the electrochemical impedance spectroscopy results, the equivalent circuits and humidity sensing mechanism were discussed. The chemical stability of the silicon nitride was characterized using Tafel analysis in alkaline electrolytes. Additionally, the sensor's humidity sensing capabilities were tested under cement-embedded conditions.

An all-optical fiber humidity sensor based on a Mach-Zehnder interferometer (MZI) covered with graphene oxide (GO) film is demonstrated. The MZI is formed by inserting a section of etched surface core fiber (SCF) between two standard single mode fibers (SMFs) with a lateral-offset. Such configuration of the interferometer allows a strong evanescent field between the water molecules and the GO layer and hence enhances the change in refractive index of GO nanostructures after water absorption, which significantly improves the humidity sensitivity. Experimental results showed that the fabricated sensor exhibited a super-high humidity sensitivity of 707.3pm/%RH in the RH range of 40–80% and a rapid response/recovery time (4.8/8.4 s). The high-performance of the proposed all fiber humidity sensor is potentially promising for industrial production, medical diagnoses, environmental and health monitoring.

The humidity has often been measured through a single point sensor. Where, the humidity could be varied at different locations as well as depending on environmental conditions. The present paper developed the dual point humidity measuring sensor by using a polymer optical fiber (POF) based on a single illuminating fiber. The sensor's basic structure is to twist two fibers and bend them at a certain radius. However, the dual point sensor is developed through the cascading of twisted micro bend (TMB-1 and TMB-2). The twisting of fibers couples the light from one fiber to another fiber through the side coupling method. An increase in the humidity level leads to a change in the reflective index, which helps to get variation in coupled light intensity. To measure the humidity, the dual point sensors are placed into the control humidity chamber at two random positions. The power reading variation is significantly linear when the humidity level increases from 30 to 80%. The sensor has a fast response of about 1 s and a recovery time of about 4 s. Furthermore, the chemical coating is applied to improve the sensor's sensitivity. Between 30 and 80% range of humidity, the both sensors of dual point TMB-1 and TMB-2 have appropriate sensitivity and detection limits, which is about 680.8 nW/% and 763.9 nW/% and 1.37% and 1.98%, respectively. To measure the humidity at variable positions, the present dual points humidity sensor is well-stable, easy, and straightforward, which uses a less expensive method. [ABSTRACT FROM AUTHOR]

One of the crucial factors in grain storage is appropriate moisture content, which plays a significant role in reducing storage losses and ensuring quality. However, currently available humidity sensors on the market fail to meet the demands of modern large-scale grain storage in China in terms of price, size, and ease of implementation. Therefore, this study aims to develop an economical, efficient, and easily deployable grain humidity sensor suitable for large-scale grain storage environments. Simultaneously, it constructs humidity calibration models applicable to three major grain crops: millet, rice, and wheat. Starting with the probe structure, this study analyzes the ideal probe structure for grain humidity sensors. Experimental validations are conducted using millet, rice, and wheat as experimental subjects to verify the accuracy of the sensor and humidity calibration models. The experimental results indicate that the optimal length of the probe under ideal conditions is 0.67 m. Humidity calibration models for millet, rice, and wheat are constructed using SVM models, with all three models achieving a correlation coefficient R2 greater than 0.9. The measured data and model-calculated data show a linear relationship, closely approximating y = x, with R2 values of all three fitted models above 0.9. In conclusion, this study provides reliable sensor technological support for humidity monitoring in large-scale grain storage and processing, with extensive applications in grain storage and grain safety management. [ABSTRACT FROM AUTHOR]

The lack of low-cost methods to synthesize large-area graphene-based materials is still an important factor that limits the practical application of graphene devices. Herein, we present a facile method for producing large-area graphene oxide-metal (GO–M) films, which are size controllable and transferable. The sensor constructed using the GO–M film exhibited humidity sensitivity while being unaffected by pressure. The relationship between the sensor's resistance and relative humidity followed an exponential trend. The GO–Mg sensor was the most sensitive among all the tested sensors. The facile synthesis of GO–M films will accelerate the widespread utilization of graphene-based materials. [ABSTRACT FROM AUTHOR]