Humidity Sensor Applications Research Articles

Regulating the microstructure and hydrophilicity of cellulose nanofibers using taurine and the application in humidity sensor and actuator

Exploring the interrelationships between microstructure, hydrophilicity, humidity response, and material stability through molecular structure design and low-cost preparation, and manufacturing sensing and driving materials with a perfect balance between structures and properties is crucial for biomimetic robots and intelligent devices. Herein, inspired by the capillary phenomenon, the cellulose nanofiber (CNF) was grafted by using taurine to form the “micro cilia” microstructure on its surface (CNF-TAU). By controlling the cilia density and symmetry, the hydrophilicity of the materials was adjusted, and the water was allowed to quickly separate from the inside of the materials, which led to improving the humidity sensitivity and stability of materials. Concretely, compared with CNF, the puncture load, tearing strength, and elongation at break of the CNF-TAU-1.0 were improved by 11.95 times, 2.16 times, and 15.6 %, respectively, and excellent tensile strength was presented. Moreover, the hydrophilicity of CNF-TAU was first weakened and then enhanced with TAU content increasing. At last, the CNF-TAU-1.0 (WCA 55.43°) was selected and blended with single-layer graphene oxide (GO) to prepare CNF-TAU/GO composite films by vacuum filtration. The results indicated that the composite film had excellent mechanical (room and high humidity), humidity responsiveness, and humidity gradient-driven properties. In detail, the CNF-TAU/GO-10 % composite film had the generated stable induced voltage (68.4 mV), the fast response/recovery time (0.3 s/0.9 s), the large max. bending angle (178.4°), and the drive cycle stability (1000 cycles). Moreover, the composite film could be applied to produce biomimetic soft robots, such as human fingers and butterfly-shaped robots.

Research on channel-exposed carbon-based FET humidity sensor

Abstract The ability to detect humidity is crucial for a variety of sectors, including industrial manufacturing, meteorological surveillance, and the preservation of materials, among others. Field effect transistor (FET) based sensor, renowned for its signal amplification effect, plays a pivotal role in detecting trace-level analytes with high sensitivity. Our work demonstrates the preparation of a humidity sensor based on carbon-based FET architecture, employing micro-nano processing techniques. In this work, semiconducting carbon nanotubes serve as the sensing material and channel at the same time. The outcomes indicate that the sensor exhibits a linear response ranging from 0% to 80% relative humidity (RH) and good repeatability. It also shows long-term stability in a 40-day test, proving potential applications in FET-type humidity sensors.

Outstanding dielectric permittivity and humidity sensitivity in (Y/Sb) co[sbnd]doped TiO2 ceramics with rapid response/recovery time

The synthesized (Y0.5Sb0.5)xTi1-xO2 (YSTO) ceramics (x=0.005 and 0.05) were investigated for their potential application in humidity sensors. The rutile phase of TiO2 for YSTO ceramics was confirmed. SEM images revealed dense microstructures, with relative densities and average grain sizes decreasing with doping concentrations. YSTO ceramics exhibited outstanding dielectric constants (ε′∼ 6.617.31×104) and low loss tangents (tanδ∼0.0190.067) at 25°C and 1 kHz. Capacitive humidity sensing properties demonstrated significant increases in capacitance with rising relative humidity (%RH) levels, with sensitivities of 165 and 386 pF/%RH. Hysteresis analysis showed narrow loops with low hysteresis error (γH∼1.4 and 2.0 %). Rapid response (∼9 s) and recovery (∼7 and 4 s) times, with stable repeatability, were observed. The presence of VO•• and SbTi• was confirmed, enhancing humidity sensing through chemical absorption reactions. This analysis underscores the potential of YSTO ceramics for humidity sensors, emphasizing the role of microstructural characteristics and induced defects in sensor performance, which is vital for the development of advanced sensing technology.

A high-sensitive capacitive humidity sensor based on chitosan-sodium chloride composite material

Chitosan, as a hydrophilic, renewable, biodegradable, and cost-effective natural polymer, holds great promise in humidity sensor applications. This study proposes a green high-performance capacitive humidity sensor based on chitosan (CS)-sodium chloride (NaCl) composites. The CS-NaCl films were fabricated through a simple drip coating method, and their surface morphology and structure were characterized using SEM, XRD, FTIR and XPS techniques. The pure chitosan humidity sensor demonstrates an impressive response of 1180.17 % with excellent linearity. The introduction of NaCl markedly boosted the sensor response, with CS-50 wt% NaCl composites exhibiting a 72-fold increase (86, 492.84 %) in capacitance response compared to pure CS films. The contact angle test demonstrated that the chitosan film exhibited good hydrophilicity, which was further enhanced by the addition of NaCl. XRD and FTIR characterization confirmed that NaCl altered the structural properties of chitosan, disrupted hydrogen bonds, and consequently increased the mobility of polarizing groups and the dielectric constant. A water adsorption model was developed to elucidate the humidity sensing mechanism of the CS-NaCl sensor. The CS-NaCl composite material presents advantages such as easy preparation, high sensitivity, eco-friendliness, and promising practical applications in humidity sensing.

Design, Synthesis, and Characterization of a Humidity Sensor Application Using Nano-Rod Shaped ZnWO4–TiO2 Porous Composite Electronic Material

Design, Synthesis, and Characterization of a Humidity Sensor Application Using Nano-Rod Shaped ZnWO4–TiO2 Porous Composite Electronic Material

Synthesis of Li doped MgFe2O4 nanoparticles for humidity sensor applications

Recently, there has been a greater emphasis on researching the potential use of ferrite nanoparticles as humidity-sensing materials. We report on the humidity-sensing properties of Mg1-yLiyFe2O4 (y = 0, 0.01, 0.03 and 0.05), which were synthesized using the solution combustion synthesis route. According to the XRD analysis, it was observed that both the unit cell volume and the crystallite size increased as the concentration of lithium-ion increased. The crystallite size was measured to be 17–22 nm, indicating the presence of nanomaterials. Moreover, the material exhibited a single phase with the Fd-3m space group, suggesting its structural integrity and uniformity. The FE-SEM images revealed that the porous nature of the material became more pronounced with higher concentrations of Li, indicating potential benefits for sensing applications. The synthesized powder demonstrated promising characteristics for use in humidity sensors. Specifically, it was noted that increasing the Li composition led to a notable increase in resistance, particularly significant for the Li = 0.05 concentration, which exhibited the highest average sensitivity. This suggests that Li doping at this concentration effectively enhances resistance, a crucial aspect for sensor functionality. The response and recovery times of thin film humidity sensors fabricated from these materials were determined to be 9 and 12 s, respectively. These times indicate rapid and efficient sensing capabilities, essential for real-time monitoring applications. Moreover, the newly discovered sensing material exhibited exceptional stability and reproducibility, further highlighting its potential for practical sensor applications. In summary, the synthesized materials show great promise for humidity sensor applications due to their enhanced sensitivity, rapid response and recovery times, as well as their stability and reproducibility. These findings open up avenues for the development of advanced sensing technologies with improved performance and reliability.

Advanced humidity sensing properties of CuO ceramics

This research explores the capacitive humidity sensing properties of CuO ceramic, selected for its simplicity as an oxide and ease of fabrication, in addition to its remarkable dielectric properties. The CuO sample was fabricated by sintering at 980 °C for 5 h. A microstructure with a relative density of 88.9% was obtained. X-ray diffraction confirmed the formation of a pure CuO phase. Broadband dielectric spectroscopy revealed that the observed giant dielectric properties at room temperature (RT) were attributed to extrinsic effects, including the internal barrier layer capacitor and sample-electrode contact effects. A key focus of this study was to examine the giant dielectric properties of CuO ceramic as a function of relative humidity (RH) at RT and frequencies of 102 and 103 Hz. It was observed that the capacitance of CuO continuously increased with rising RH levels, ranging from 30 to 95%. Notably, the maximum hysteresis errors were constrained to 2.3 and 3.3% at 102 and 103 Hz, respectively. Additionally, the CuO ceramic demonstrated very fast response and recovery times, approximately 2.8 and 0.95 min, respectively. The repeatability of the humidity response of the capacitance was also established. Overall, this research highlights the high potential of CuO as a giant dielectric material for application in humidity sensors.

Improved humidity sensing performances of boron doped ZnO nanostructured thin films depending on boron concentration

Abstract This study details the production and analysis of undoped zinc oxide (uZnO) and boron (B) doped zinc oxide nanostructured thin films, with a specific focus on assessing the influence of varying B doping concentrations on humidity sensing performance. The synthesis of undoped ZnO and B doped ZnO nanoparticles was carried out using sol–gel method. B doping concentrations within the ZnO lattice were adjusted to 1, 3, 4, 5, and 10 mol%. Subsequently, nanostructured thin films were obtained through the spin coating technique on glass substrates. X-ray diffraction analysis revealed a hexagonal wurtzite structure for all nanostructured thin films. Notably, a change in preferential orientation from the (002) plane to the (100) plane occurred when B doping concentration exceeded 5 mol%. Scanning electron microscopy showcased nano-sized grains and capillary nanopores on the surface of each thin film. Energy dispersive X-ray spectra confirmed the presence of zinc, oxygen, and boron elements in the nanostructured thin films. Humidity sensing performance was assessed through electrical resistance measurements in the range of 45%–90% relative humidity at room temperature. All fabricated sensors exhibited sensitivity to humidity. Remarkably, the sensor with a 5 mol% B doping concentration demonstrated the highest humidity sensitivity (438.44 times) and the fastest response (2.0 s) and recovery times (14.2 s). The study concluded that the optimal B doping concentration for designing a highly efficient humidity sensor was determined to be 5 mol%. Overall, the study underscores the potential of B doped ZnO nanostructures for humidity sensor applications, given their exceptional sensor performance.

Huge permittivity with decreasing dissipation factor and humidity sensing properties of CaCu2.9Mg0.1Ti4.2-xGexO12 ceramics

CaCu2.9Mg0.1Ti4.2-xGexO12 ceramics with x = 0, 0.1, and 0.2 were fabricated to study the electrical and dielectric properties, nonlinear current–voltage properties, humidity sensing properties. The main phase of CaCu3Ti4O12 (CCTO) was obtained in the sintered ceramics with dense microstructure and slight change in grain size. All sintered ceramics showed high dielectric permittivity (ε′ > 104) at frequencies below 105 Hz, while the loss tangent was reduced by a factor of 3 (from 0.034 to 0.010 at 1 kHz and 25 °C), as x increased from 0 to 0.1. The temperature dependence of ε′ was also reduced. Furthermore, the enhanced nonlinear coefficient (α = 4.8–5.9) and breakdown electric field (Eb = 227–755 V/cm) were achieved. The dielectric and nonlinear properties originated from the electrically heterogeneous microstructure, which was confirmed by impedance and admittance spectroscopies. Both the resistance and activation energy of the insulating internal barriers were higher than that of the semiconducting core grains. Furthermore, these two parameters of the doped samples were larger than that of the undoped sample (x = 0). It was found that a low frequency ε′ was strongly dependent in the relative humidity in the range of 11–95 %RH, which could be applied in a humidity sensor. Accordingly, the hysteresis error was also calculated to determine the possibility of application in humidity sensors.

Preparation of silver nanoparticles modified SnO2 humidity sensor for tobacco storage environment detection

In this paper, silver nanoparticles (AgNPs) modified SnO2 (Ag/SnO2) nanocomposite with excellent humidity performance was prepared by hydrothermal method. Experimental results demonstrate that AgNPs enhance the performance of the SnO2 humidity sensor, which is primarily attributed to increase the oxygen vacancies on the surface of the SnO2 through the incorporation of AgNPs. Density functional theory (DFT) demonstrated that more oxygen vacancies can enhance the chemical and physical adsorption energy of water molecules by SnO2, and decompose more water molecules into conductive H+ ions: simultaneously, the response/recovery times and hysteresis error of SnO2 are reduced. Compared to the SnO2 humidity sensor, Ag/SnO2 exhibits low humidity hysteresis (2.7%), relatively short response/recovery time (5/8 s) and high sensitivity (24292.3). Furthermore, the Ag/SnO2 humidity sensor employed in this study has successfully demonstrated its efficacy in detecting humidity levels within tobacco storage environments, which expands the potential applications of humidity sensors.

Structure, microstructure, and enhanced sensing behavior of nickle ferrite–cobalt chromate for humidity sensor applications

Structure, microstructure, and enhanced sensing behavior of nickle ferrite–cobalt chromate for humidity sensor applications

Polypyrrole: synthesis, characterization and its potential application for humidity sensor

Polypyrrole: synthesis, characterization and its potential application for humidity sensor

Facile green synthesis of Ni/NiO/MoO3 nanocomposite for Photocatalytic, chromium (VI) Reduction, electrochemical dopamine (DA) and humidity sensor applications

Many researchers concentrated their efforts on chemical method for the synthesis of metal oxide nanocomposite (NCs). This article focused on developing a rapid method to prepare Ni/NiO/MoO3 NCs using leaf powder of Butea monosperma as a novel green fuel. Synthesised NCs were characterised using XRD, FT-IR, UV–Visible, Photoluminescence spectroscopy, SEM- EDAX, and TEM analysis. XRD pattern prove the orthodromic structured MoO3 nanoparticles (NPs), rhombohedral structure of Ni/NiO NCs and observed the average crystallite size of 25 nm. The band gap of Ni/NiO/MoO3 NCs was found to be 2.9 eV and TEM analysis revealed irregularly shaped morphologies. Results of photocatalytic dye-degradation of methylene blue dye under various conditions proven the good photocatalytic activity. Additionally, Ni/NiO/MoO3 NCs shows 60 % toxic chromium (VI) reduction. Ni/NiO/MoO3 NCs were successfully employed for the electrochemical detection of dopamine, showcasing good sensing performance. It is also an ideal material for humidity sensor with sensitivity of 4.8 MΩ/%RH and limit of detection of 5 % RH. All the above results indicate the diverse application of the Ni/NiO/MoO3 NCs.

Observation of enhanced sensing response and recovery time of lutetium-doped zinc ferrite ceramics for humidity sensor application

Observation of enhanced sensing response and recovery time of lutetium-doped zinc ferrite ceramics for humidity sensor application

Fabrication of rare earth(R[dbnd]Ce,Gd, Ho and Sm) doped CoCr2-x RxO4 pigments for capacitive and resistive humidity sensor applications

Rare earth (Ce, Gd, Ho & Sm) doped CoCr2O4 green pigments with an extremely porous nature powder were produced using a quick and affordable chemical synthesis procedure called solution combustion. X-ray diffraction analyses revealed the phase composition and average crystallite size. SEM images of the samples that had been annealed at 600°C revealed the existence of cuboids and soft agglomerations. Using an LCR metre to analyse the dielectric properties of as-synthesised samples, it is discovered that the small crystallite size exhibits a higher dielectric constant. The results were impressive when permittivity and electrical resistivity fluctuated with frequency under humid circumstances. By varying the relative humidity from 0 to 100%, electrical measurements were performed to investigate the rare earth pigments' capabilities for sensing humidity. Sample electrical resistance decreases over the entire humidity range. At room temperature, the resistive responses were measured at various relative humidity (RH) levels ranging from 0% to 98% and at various frequencies ranging from 20 Hz to 20 MHz. The rare earth-doped green pigments used in the humidity sensor have a linear response, high sensitivity, and low hysteresis. In addition, the sensor has 35 and 240 s reaction and recovery times, respectively. Our research indicates that this material could be employed as a capacitive and resistive humidity sensor. The results of this work open the door for the use of rare earth doped cobalt chromate pigments in applications for humidity sensing.

Fabrication and Characterization of Humidity Sensors Based on PEDOT:PSS Doped with Gold and Silver Nanoparticles by Laser Ablation

This paper presents a simple, fast, and inexpensive method for the large-scale fabrication of polymer-based humidity sensors on glass substrates. The nanoparticles were synthesized using laser ablation, this is an environmentally friendly method for fabricating metal nanoparticles and provides a unique tool for nanofabrication. In this work, humidity sensing material, poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) along with different kinds of nanoparticles, Au and Ag, are employed to enhance the stability and sensitivity to humidity sensing. Based on the experimental results, the TEM images show the crystallinity of the nanoparticles, indicating alloying of the nanoparticles. Based on XRD, this result indicates that the amorphous structure of PEDOT:PSS is only slightly affected by mixing with nanoparticles. According to FE-SEM analysis, the formation of interconnected crystallites facilitates the charge transport mechanism in the polymer chains due to improved conduction paths. Has been Characterization of humidity sensors Using (LCR), study the effect of humidity on capacitance at different frequencies (100[Formula: see text]Hz, 1[Formula: see text]kHz, 10[Formula: see text]kHz, and 100[Formula: see text]kHz), and the response and recovery time characteristics. The results show excellent linear and active behavior of the capacitive humidity response. Ag, PEDOT, and Au NPs have a synergistic effect, exhibiting a more extended sensing range and better stability. This work shows a high-sensitivity and low-cost sensing material for different humidity sensor applications.

A flexible humidity sensor constructed by ordered-pore-array of slightly reduced graphene oxide with much enhanced sensing response

Reduced graphene oxide (rGO) flexible film humidity sensor has received increasing attention, but the low sensing response caused by lack of available hydrophilic functional groups is still a limitation. Herein, a slightly reduced graphene oxide (SrGO) ordered-pore-array, fabricated via a monolayer colloid crystal template method, was introduced as a resistive humidity sensor. It was obtained based on adsorption between the GO sheets and the template microspheres, in-situ slight reduction of the GO shells and the removal of template. The reduction way allows the functional groups of GO to be retained as much as possible, and the unique structures (e.g., spherical double surfaces and small through-holes on pore-walls) facilitate the substantial exposure of functional groups, the penetration of water molecules and the utilization of buried functional groups. The available functional groups are thereby efficiently increased, giving the sensor an unprecedented high sensing response, more than 2600 times the maximum response of existing rGO sensors. The sensor also demonstrated excellent practical characteristics, and by detecting a single exhale, it could be employed in quick and quantitative evaluation of human activities and health. This strategy paves a facile and promising route to improve the sensing response and application of graphene-based humidity sensors or gas sensors.

Role of holmium on the humidity sensing properties of the CoCr2O4 ceramics for possible applications in humidity sensors

Role of holmium on the humidity sensing properties of the CoCr2O4 ceramics for possible applications in humidity sensors

Enhanced humidity sensing stability of Dy3+-doped Mg-Rb ferrites for room temperature operatable humidity sensor applications

Enhanced humidity sensing stability of Dy3+-doped Mg-Rb ferrites for room temperature operatable humidity sensor applications

Wafer-Level, High-Performance, Flexible Sensors Based on Organic Nanoforests for Human-Machine Interactions.

High-performance flexible sensors are essential for real-time information analysis and constructing noncontact communication modules for emerging human-machine interactions. In these applications, batch fabrication of sensors that exhibit high performance at the wafer level is in high demand. Here, we present organic nanoforest-based humidity sensor (NFHS) arrays on a 6 in. flexible substrate prepared via a facile, cost-effective manufacturing approach. Such an NFHS achieves state-of-the-art overall performance: high sensitivity and fast recovery time; the best properties are at a small device footprint. The high sensitivity (8.84 pF/% RH) and fast response time (5 s) of the as-fabricated organic nanoforests are attributed to the abundant hydrophilic groups, the ultra-large surface area with a huge number of nanopores, and the vertically distributed structures beneficial to the transfer of molecules up and down. The NFHS also exhibits excellent long-term stability (90 days), superior mechanical flexibility, and good performance repeatability after bending. With these superiorities, the NFHS is further applied as a smart noncontact switch, and the NFHS array is used as the motion trajectory tracker. The wafer-level batch fabrication capability of our NFHS provides a potential strategy for developing practical applications of such humidity sensors.