Humidity Sensitivity Research Articles

Highly sensitive screen-printed soil moisture sensor array as green solutions for sustainable precision agriculture

Monitoring soil moisture in real-time is an important parameter that helps farmers decide to enhance agriculture productivity and reduce resource wastage for better production and plant growth. In this work, we presented an easy-to-use and highly sensitive screen-printed flexible soil moisture sensor array to monitor soil moisture remotely for precision agriculture. The proposed sensor is based on a unique interdigitated electrode (IDE)-based capacitive structure with conductive carbon ink printed on a flexible polyethylene terephthalate (PET) substrate using the screen printing technique. Before soil moisture monitoring, the sensor is tested for humidity monitoring in an environmental chamber. A response of ∼144–1760 pF for 20–100%RH with 10%RH variation is observed for a single sensor, while an array configuration ranges from ∼127–1802 pF. The sensor response is observed for a temperature range from 20 to 50 ‘C. The sensor's sensitivity for relative humidity sensing is 19.123%pF/RH, and the response and recovery time are ∼3.3 s and ∼4.2 s. Further, the sensor is tested for soil moisture sensing, as moisture content is gradually added to the completely dry soil. A highly sensitive response for soil moisture content (MC) with a ∼40.7%pF/MC sensitivity is obtained. The sensor data is transmitted wirelessly using a Bluetooth module. The sensor is supported by a wooden stick, which illustrates the capabilities of biodegradability, the sensor is cost-effective and provides a real-time measurement for soil moisture. The sensors have the potential to provide maintenance-free monitoring, facilitating precise control of irrigation practices in precision agriculture. With their affordability and ability to operate on a large scale, the sensor offers promising opportunities for enhancing irrigation systems.

Effect of Combination of Expansive Agent and Fiber on Freeze-Thaw Resistance of High-Strength Concrete at Dry Environment

This study employed a rapid freezing method to investigate the impact of individual additions of expansion agent, steel fibers, and High Elasticity Module Polyethylene Fiber (HEMPF), as well as their combinations, on the freeze-thaw resistance of High-Strength Concrete (HSC). The findings reveal that the non-air-entrained HSC of C80 exhibits excellent freeze-thaw resistance. However, this resistance is sensitive to the curing environment’s humidity. The expansion agent has a negative impact on the freeze-thaw resistance of HSC, while steel fibers and HEMPF fibers have positive effects. Combining HSC with an expansion agent and high elasticity modulus fibers ensures not only high freeze-thaw resistance but also a total alteration of humidity sensitivity, leading to an extended freeze-thaw life of HSC under dry curing conditions.

Highly selective and sensitive humidity sensor using reduced graphene oxide based iron oxide nanocomposites

For the humidity sensing, rGO/Fe2O3 nanocomposites were synthesized via an ultrasonic-assisted method, utilizing Hummers' and co-precipitation techniques for rGO and Fe2O3 synthesis. XRD analysis confirmed the formation of rGO and rhombohedral Fe2O3 NPs, while SEM revealed varied (rough sheet-like and dense compact) morphologies. UV–VIS spectra indicated characteristic absorption peaks for rGO, Fe2O3 NPs, and their NCs. In addition, FTIR spectra validated graphene oxide reduction and Fe2O3 NPs/NCs formation. Humidity sensing was assessed across 40–80 % RH at varying frequencies (100 Hz-10 kHz), with 100 Hz identified as the optimal frequency due to water molecule polarization limitations at higher frequencies. The rGO/Fe2O3 (70/30) NC exhibited a rapid response recovery time (5 s/10 s) and high sensitivity (2715.541 %), attributed to additional active sites provided by Fe2O3, enhancing water molecule adsorption and sensor sensitivity. The sensors demonstrated long-term stability and repeatability, showcasing promising potential for humidity sensing applications.

Surface charge manipulation for improved humidity sensing of TEMPO-oxidized cellulose nanofibrils

Cellulose-based humidity sensors have attracted great research interest due to their hydrophilicity, biodegradability, and low cost. However, they still suffer from relatively low humidity sensitivity. Due to the presence of negatively charged carboxylate groups, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibril (CNF) exhibits enhanced hydrophilicity and ion conductivity, which is considered a promising candidate for humidity sensing. In this work, we developed a facile strategy to improve the humidity sensitivity of CNF films by regulating their surface charge density. With the increase in surface charge density, both water uptake and charge carrier densities of the CNF films can be improved, enabling a humidity sensitivity of up to 44.5 % (%RH)−1, higher than that of most polymer-based humidity sensors reported in the literature. Meanwhile, the sensor also showed good linearity (R2 = 0.998) over the 15–75 % RH at 1 kHz. With these features, the CNF film was further demonstrated for applications in noncontact sensing, such as human respiration, moisture on fingertips, and water leakage, indicating the great potential of CNF film in humidity monitoring.

High linear sensitivity humidity and temperature sensing based on chiral long-period fiber grating

High linear sensitivity humidity and temperature sensing based on chiral long-period fiber grating

The ammonia modified ZIF-8@SnO2 core-shell nanosheets for improved the sensitivity and selectivity of NO2

For NO2, a gas that is widely used and harmful, domestic and foreign researchers have done a lot of work to develop a sensor with low detection limit and low humidity sensitivity to achieve efficient detection of NO2. In this work, first of all, dense and uniform SnO2 nanosheets were grown in situ on the surface of Al2O3 ceramic tube by hydrothermal method. Then, the ZIF-8@SnO2 porous composite gas-sensitive material was constructed by solvent thermal method. With the advantages of the ZIF-8 porous screening framework, the permeation of different gases can be selectively controlled, and the adsorption efficiency of NO2 gas can be enhanced through the modification of ammonia to improve the selectivity of NO2. The results show that the response of the Modified-ZIF-8@SnO2 sensor is significantly enhanced, and the selectivity is greatly improved at low operating temperature. At 140 °C, the response of Modified-ZIF-8@SnO2 to 50 ppm NO2 gas is as high as 61, which is about 18.4 times higher than that of SnO2 nanosheets and about 16.3 times higher than that of ZIF-8@SnO2. Meanwhile, the anti-interference ability of the Modified-ZIF-8@SnO2 sensor to humidity has been improved. This work provides a new idea for improving the selectivity and humidity insensitivity of gas sensors.

Sensitive humidity sensor based on moisture-driven energy generation

Sensitive humidity sensor based on moisture-driven energy generation

The Impact of Rotation on Tropical Climate, the Hydrologic Cycle, and Climate Sensitivity

AbstractThis work explores the impact of rotation on tropical convection and climate. As our starting point, we use the RCEMIP experiments as control simulations and run additional simulations with rotation. Compared to radiative convective equilibrium (RCE) experiments, rotating RCE (RRCE) experiments have a more stable and humid atmosphere with higher precipitation rates. The intensity of the overturning circulation decreases, water vapor is cycled through the troposphere at a slower rate, the subsidence fraction decreases, and the climate sensitivity increases. Several of these changes can be attributed to an increased flux of latent and sensible heat that results from an increase of near‐surface wind speed with rotation shortly after model initialization. The increased climate sensitivity results from changes of both the longwave cloud radiative effect and the longwave clear‐sky radiative fluxes. This work demonstrates the sensitivity of atmospheric humidity and surface fluxes of moisture and temperature to rotation.

Flexible Chitosan-Based Capacitive Humidity Sensors for Respiratory Monitoring.

As one of the most important human health indicators, respiratory status is an important basis for the diagnosis of many diseases. However, the high cost of respiratory monitoring makes its use uncommon. This study introduces a low-cost, wearable, flexible humidity sensor for respiratory monitoring. Solution-processed chitosan (CS) placed on a polyethylene terephthalate substrate was used as the sensing layer. An Arduino circuit board was used to read humidity-sensitive voltage changes. The CS-based sensor demonstrated capacitive humidity sensitivity, whereby the capacitance instantly increased from 10-2 to 30 nF when the environmental humidity changed from 43% to 97%. The capacitance logarithm sensitivity and response voltage change was 35.9 pF/%RH and 0.8 V in the RH range from 56% to 97%. And the voltage variation between inhalation and exhalation was ~0.5 V during normal breathing. A rapid response time of ~0.7 s and a recovery time of ~2 s were achieved during respiration testing. Breathing modes (i.e., normal breathing, rest breathing, deep breathing, and fast breathing) and tonal changes during speech could be clearly distinguished. Therefore, such sensors provide a means for economical and convenient wearable respiratory monitoring, and they have the potential to be used for daily health examinations and professional medical diagnoses.

A highly sensitive flexible humidity sensor based on a wafer-level composite material of carbon-quantum-dots@nanofiber clusters

A novel composite material composed of carbon-quantum-dots@nanofiber clusters (CQDs@NFCs) is successfully developed in wafer level, taking it as a sensitive material, a flexible humidity sensor is also developed. Since the composite material is superhydrophilic and contains a super large number of nanopores of different sizes, capillary condensation is able to take place within the composite material at different relative humidity (RH) conditions. Taking advantage of the chemi-physisorption and the capillary condensation, such a sensing material helps to significantly improve sensitivity of the flexible sensor, especially at low RH conditions. Compared with the device adopting only nanofibers as the sensing material, this novel sensor offers a 4.3-time increament in sensitivity within a humidity range of 7%−59% RH, while maintains high sensitivity in the entire humidity range. This heightened sensitivity is crucial for monitoring low-level humidity with high accuracy, making the sensor highly promising for various applications.

Large-area, size-controlled and transferable graphene oxide-metal films for humidity sensor

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.

Fully Printed Cellulose Nanofiber-Ag Nanoparticle Composite for High-Performance Humidity Sensor.

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.

A Tunable Interferometer for High Sensitivity and Resolution Humidity Sensing

A Tunable Interferometer for High Sensitivity and Resolution Humidity Sensing

Enhancing humidity sensitivity properties through RE (Er, La, and Sm) dopants in TiO2 nanofiber composites

Enhancing humidity sensitivity properties through RE (Er, La, and Sm) dopants in TiO2 nanofiber composites

Ultra-sensitive relative humidity sensor formed by two parallel Fabry-Perot interferometers and Vernier effect

In this paper, a relative humidity (RH) Vernier sensor based on gelatin diaphragm is proposed, in which the gelatin diaphragm is coated on the end surface of the quartz capillary by the dot-dip method, so that the prepared diaphragm is only 3 μm thick. The sensing cavity FPI1 is an air-cavity made of single-mode-fiber (SMF), quartz capillary (QC) and gelatin diaphragm. Gelatin diaphragm is an excellent humidity sensitive material, therefore FPI1 has high sensitivity to humidity. The reference cavity FPI2 is also an air-cavity spliced in the order of SMF-QC-SMF. When FPI1 and FPI2 have similar free spectral range, they form a Vernier effect in parallel, achieving maximum humidity sensitivity. The experimental results show that in the range of 1300 nm to 1650 nm, the envelope formed by two parallel FPIs is particularly regular and has a free spectral range of 95.2 nm. By tracking the variation of the envelope dip with humidity, the sensor obtained a highly fitting polynomial relationship in the range of 57 %RH − 84 %RH. However, in the range of 75 %RH − 84 %RH, the sensor achieved an excellent linear fitting relationship, with a linearity of up to 0.9997 and a sensitivity of up to 27.9726 nm/%RH. This is the most sensitive gelatin Vernier humidity sensor ever reported. And the crosstalk of temperature of the Vernier humidity sensor is only 0.0186 %RH/℃. The sensor is easy to manufacture, ultra-high sensitivity, small temperature crosstalk, good performance and low cost, and has good reversibility and stability. It is a competitive humidity candidate sensor.

Interconnected SnO2 nanoflakes decorated WO3 composites as wearable and ultrafast sensors for real-time wireless sleep quality tracking and breath disorder detection

Monitoring human breath is critical for determining human well-being. Most reported humidity sensors are unsuitable for breath monitoring because of their long response and recovery time, poor stability, and high operating temperature. To address these challenges, robust tungsten oxide (WO3) and tin oxide (SnO2) composite sensors were fabricated, and their humidity-sensing properties were investigated. The SnO2/WO3 composites were optimized by altering the SnO2 fraction to achieve high humidity sensitivity. The SnO2/WO3 composite exhibited superior sensing performance (88) than pristine WO3 and SnO2 under 97 % relative humidity. The sensor demonstrated good linearity while altering humidity from 15 % to 97 %, with an R2 = 0.9729. The sensor's rapid response (0.6 s) and recovery (0.6 s) time allow for breath rate monitoring and breath disorder detection. The wearable sensor demonstrated multifunctional human breath detections such as varied breath rates (5–60 breaths per minute), nose blocking for separate nostrils, wireless sleep quality tracking for more than 7 h continuously, and sleep apnea-hypopnea detection via a smartphone. The capabilities of the humidity sensor allow for robust application in sleep quality, sleep apnea, and hypopnea detection.

Fast repeatable measurement of hydrogen concentration based on a reflective fiber hybrid interferometer probe with vernier effect

A hydrogen (H2) sensor based on hybrid Fabry-Perot interference (FPI) and Michelson interference (MI) with Vernier effect is demonstrated. The optical probe is manufactured by fusing a multimode fiber (MMF) and a double-side hole fiber (DSHF) between a single-mode fiber (SMF) and a hollow core fiber (HCF) filled with polydimethylsiloxane (PDMS) at the end to form a cascaded FP and MI, which can generate a vernier envelope. by fusing a multimode fiber (MMF) and a double-side hole fiber (DSHF) between a single-mode fiber (SMF) and a hollow core fiber (HCF) filled with PDMS at the end. To accomplish H2 sensing, palladium-tungstic oxide (Pd-WO3) powder is attached to the exterior surface of PDMS, which will cause an exothermic redox reaction with H2. The released heat will lead to the volume expansion of PDMS with remarkable thermal response characteristics, and finally cause the movement of the vernier-like spectral envelope with the variation of H2 concentration. The sensitivity of the proposed sensor is 2.2 nm/% in the range of 0 %–1% through the H2 measurement experiment. For H2 with a concentration of 1 %, it has the response time of 28 s and shows good reversibility in the cyclic experiment. In addition, the sensitivity of temperature and relative humidity (RH) is 0.21 nm/°C and 0.0014 nm/%RH, respectively. The proposed sensor adopts a reflective probe, which is compact in structure and small in volume, and shows fast response and excellent repeatability. It has great advantages in H2 measurement in narrow spaces and long distances.

Gamma radiation impact on dielectrics and RH sensitivity of nylon–carbon–GNP–epoxy composites

AbstractComposites of carbon–graphene nanoplatelets (GNP) epoxy with nylon‐66 interleaving were fabricated and investigated to understand the impact of γ‐irradiation on their dielectrics and relative humidity (RH) sensitivity by capacitance and water absorption measurements. The moisture sensitivity was investigated by measuring memory effect (hysteresis) and response time of the capacitance. Composites were γ‐irradiated at doses of 1000 and 3000 kGy and studied by the same set of measurements. X‐ray diffraction analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to understand the impact of γ‐irradiation on the morphology and surface roughness of the composites. Results of these measurements suggest that 3000‐kGy dose γ‐irradiation produces good chain scission and cross‐linking, resulting in reduced water absorption and a 360% increase in capacitance values. The sensitivity of capacitance for 3000‐kGy γ‐irradiated composite was found to be highest at 40 pF/%RH, and hysteresis was 1.8% RH and not observed in non‐irradiated composites. Based on these observations, it seems that 3000‐kGy γ‐irradiated composite could be a potential candidate for moisture content diagnostics during condition monitoring of the carbon–epoxy structures in several industrial applications and needs to be further investigated.Highlights Composites of carbon–GNP epoxy with nylon‐66 interleaving were γ‐irradiated. 3000‐kGy dose γ‐irradiated composites exhibit 360% increase in capacitance. Sensitivity and hysteresis were higher than those of 1000‐kGy and non‐irradiated samples. Good chain scission and cross‐linking resulted in reduced water absorption.

Preparation and performance study of humidity sensor based on defect-controlled TiO2/CdS heterostructure

In this paper, a high-performance impedance humidity sensor based on defect control TiO2/CdS heterostructure was synthesized by hydrothermal method, and the influence of surface vacancy defects on sensing performance was analyzed by first principles based on density functional theory (DFT). Calculation results show that a large number of surface oxygen and sulfur vacancies appear on the surface of TiO2 and CdS, resulting in a great enhancement of the physical/chemical adsorption energy of TiO2 and CdS on water molecules, which is conducive to TiO2/CdS to capture more water molecules and improving the humidity sensitivity performance of the sensor. Experiments show that the regulation of surface vacancy defects of composite materials can effectively improves responsivity, linearity and hysteresis of TiO2/CdS humidity sensor. Compared with TiO2 and CdS, the TiO2/CdS humidity sensor exhibits high sensitivity (63459), fast response/recovery time (7/5 s), low hysteresis (∼3.5 %), good repeatability and long-term stability in a range of 11–95 % RH. This study not only provides an idea for designing defective TiO2/CdS high-performance humidity sensors, but proposes a new understanding for exploring the underlying mechanism of sensor performance.

Ni-doped Co3O4 the influence of different exposed crystal facets and doping amount on the humidity sensitivity: Experiment and theory

Water vapor causes the baseline resistance, response, recovery time, and long-term stability of the metal oxide semiconductor (MOS) gas sensors to change in different humidity. Combining first-principle and experimental can provide an in-depth understanding of the sensing mechanism from the atomic and molecular scales. In this work, we examined the humidity sensitivity of different concentrations of Ni-doped Co3O4 in detail. Co48O64 (110) and Co48O64(111) were constructed by HR-TEM and doped with single, double, and treble Ni atoms on both surfaces. We calculated the adsorption of water and n-butanol molecule on these eight surfaces. The results show that Ni doping improves the moisture resistance properties of Co48O64 (110) and Co48O64(111), and the sensing properties of C3H9OH adsorbed on Ni2Co46O64 (110) and Ni2Co46O64(111) are higher than single and treble Ni atoms doping. To investigate the humidity sensitivity further, we synthesized nanorods Co3O4 with and without Ni doping. The experimental results showed that the humidity sensitivity of Ni-Co3O4 was significantly lower than that of Co3O4. The decrease in the response value for the C3H9OH may be attributed to the change in the concentration of the Ni doping or the difference in the primarily exposed crystal facet.