Humidity Sensor Research Articles

High-sensitivity QCM humidity sensor based on chitosan/carboxymethylated multiwalled carbon nanotubes composite for non-contact respiratory monitoring

Respiratory humidity is an important indicator that can reflect respiratory disorders and is easily accessible in daily life, thus attracting attention in non-contact home respiratory monitoring systems. In this work, a high-sensitivity quartz crystal microbalance (QCM) humidity sensor based on a chitosan/carboxymethylated multiwalled carbon nanotubes composite coating is developed with a response time of 36 s and a recovery time of 38 s. The humidity variations from 11 to 97 % can be detected while the wet hysteresis is 0.95 % RH. The sensor also exhibits good repeatability and stability. The physicochemical characterizations of the materials reveal the mechanism of the rapid humidity response, i.e., compared to the physically blended CS with MWCNT, the crosslinking CS-MWCNT formed the new intercalation by stronger hydrogen and amide bonding, which leads to the homogeneous coverage of CS on MWCNT, exposing more active sites and facilitating the binding rate of water molecules. Combined with respiration monitoring, the sensor is able to accurately monitor human respiration rate and depth in real time, effectively predicting and differentiating between different types of obstructive sleep apnea syndromes, providing a fast and reliable solution for daily health monitoring.

Microscale Humidity Sensor Based on Iron-Coated Elaters of Equisetum Spores.

Humidity sensors deeply influence human manufacturing production and daily life, while researchers generally focus on developing humidity sensors with higher stability, higher linearity, rapid response time, etc. Yet, few people discuss measuring humidity in the microenvironment by miniaturizing sensor size into a microscale, in which the existing humidity sensors are difficult to reach. Accordingly, this study proposes a methodology for measuring relative humidity in the microscale by utilizing the distinctive morphologies of Equisetum spores across a range of relative humidities between 50% and 90%. Equisetum spores are responsive to changes in ambient relative humidity and remain in their original activities even after iron sputtering, which aims to endow the sensor with magnetic properties. The test performed in this study demonstrated a response time of 3.3 s and a recovery time of 3.6 s. In the first application, we employed such microscale sensors to work in the channel of the microfluidic chip or the cell migration microchip, as an example of working in the microenvironment. COMSOL Multiphysics 6.2 software was also used to simulate the change in relative humidity in such microchannels. Secondly, such microscale sensors are combined with smartphone-based microscopy to measure the humidity of the skin. These microscale sensors pave the new way to sensing humidity in microenvironments.

High recovery speed optical humidity sensing enabled with GQD for non-contact finger distance detection

Finger distance perception plays a crucial role in enabling humanoid intelligent robotic systems to achieve smooth interaction with humans. Here, a rapidly response optical humidity sensor enabled with graphene quantum dots (GQD) for non-contact finger distance detection was proposed. The GQD was prepared through the functionalization of graphene oxide (GO) with hydrophilic groups. This modification enhances the responsiveness of GO to atmospheric humidity and promotes the deposition of conformal films of functional materials on the surfaces of optical fiber. Utilizing a light-driven coating method, the GQD was deposited onto a tilted fiber Bragg grating (TFBG) to fabricate humidity sensor. When water molecules were absorbed by GQD, the dielectric constant of GQD film was changed, causing an alteration in the intensities of the TFBG’s cladding modes. The proposed sensor shows a sensitivity of 0.032 dB/%RH with the equilibrium response and recovery time of 3.66 s and 0.92 s, respectively. The equilibrium recovery time is the fastest as far as we know. Furthermore, the sensor is capable of precisely identifying the action of a finger, such as approaching, remaining, and departing with a detection range of 0–10 mm.

Nanofluidic sensing inspired by the anomalous water dynamics in electrical angstrom-scale channels

Manipulation of confined water dynamics by voltage keeps great importance for diverse applications. However, limitations on the membrane functions, voltage-control range, and unclear dynamics need to be addressed. Herein, we report an anomalous electrically controlled gating phenomenon on cation-intercalated multi-layer Ti3C2 membranes and reveal the confined water dynamics. The water permeation rate was improved rapidly following the application and rise of voltage and finally reached a maximum rate at 0.9 V. The permeation rate starts to decrease from 0.9 V. Below 0.9 V, the electric field affects the charge and polarity of water molecules and then leads to ordered and denser rearrangement in the two-dimensional (2D) channel to accelerate the permeation rate. Above 0.9 V, with the assistance of metal cations, the surge in current induced aggregation of water molecules into clusters, thereby limiting the water mobility. Based on these findings, a high-performance humidity sensor was developed by simultaneously optimizing the response and recovery speeds through electric manipulation. This work provides flexible strategies in intelligent membrane design and nanofluidic sensing.

Bromine-defect induced high sensitivity of Cs4PbBr6 nanocrystals humidity sensor

Recently, all-inorganic halide perovskite materials have attracted much attention in the fields of humidity sensor due to their sensitive surface, tunable bandgap, high conductivity and excellent carrier mobility. However, their inherent instability and limited sensitivity restrict further application in electronic devices. Herein, we demonstrate a high-performance impedimetric humidity sensor based on an all-inorganic halide perovskite Cs4PbBr6 nanocrystals (NCs), which are obtained by anti-solvent method without long chain ligands. It is found that VBr∙ defects act as the active site to enhance the ability of adsorbing water molecules. The humidity sensor of Cs4PbBr6 NCs achieves high response value over 4 orders of magnitude at 11–98 % relative humidity, short response/recovery time (8 s/6 s), favorable repeatability, excellent selectivity and good long-term stability. Moreover, high humidity sensing performance enables the humidity sensor of Cs4PbBr6 NCs to possess great potentials in breath monitor and noncontact switch application.

Enhancing the Longevity and Structural Stability of Humidity Sensors: Iron Thin Films with Nitride Bonding Synthesized via Magnetic Field-Assisted Sparking Discharge.

Developing long-lasting humidity sensors is essential for sustainable advancements in nanotechnology. Prolonged exposure to high humidity can cause sensors to drift from their calibration points, leading to long-term accuracy issues. Our research aims to develop a fabrication method that produces stable sensors capable of withstanding the environmental challenges faced by humidity sensors. Traditional iron-based nanoparticles often require complex treatments, such as chemical modification or thermal annealing, to maintain their properties. This study introduces a novel, one-step synthesis method for iron-based thin films with exceptional stability. The synthesized films were thoroughly characterized using X-ray photoelectron spectroscopy (XPS) to evaluate their phase stability and nitride formation. The method proposed in this study employs an electrical sparking discharge process within a pure nitrogen atmosphere under a 0.2 T magnetic field, producing thin films composed of nanoparticles approximately 20 nm in size. The resulting films demonstrate superior performance in humidity sensing applications compared to conventional methods. This straightforward and efficient approach offers a promising path toward robust and sustainable humidity sensors.

Two Birds with One Stone: Impedance-Voltage Dual-Mode Low Humidity Sensor Based on LiBr-MOF-801 with High Response.

Dual-mode humidity sensors have received wide attention in recent years due to their great potential in multifunction applications. Herein, following a "two birds with one stone" strategy, a dual-mode and self-powered low humidity sensor based on LiBr-MOF-801 with high response and power generation is proposed. The optimized LiBr-MOF-801-based sensor exhibits impedance-voltage dual-mode sensitivity in the low humidity range of 0-23% relative humidity (RH) with high response (57.1 and 0.61V), small hysteresis (0.3% RH) and good long-term stability at room temperature (20°C). Moreover, an integrated humidity power generator is obtained by series connection of the self-powered humidity sensor within 15cm2, and the output voltage reaches 2.6V with an output power density of 110 nW cm-2, and can be used as energy, supplying power to commercial electronic equipment even in low humidity. This work provides a new sight for fabricating high-performance, dual-mode, and self-powered low-humidity sensors.

Customizable Colorimetric Sensor Array via a High-Throughput Robot for Mitigation of Humidity Interference in Gas Sensing.

One challenge for gas sensors is humidity interference, as dynamic humidity conditions can cause unpredictable fluctuations in the response signal to analytes, increasing quantitative detection errors. Here, we introduce a concept: Select humidity sensors from a pool to compensate for the humidity signal for each gas sensor. In contrast to traditional methods that extremely suppress the humidity response, the sensor pool allows for more accurate gas quantification across a broader range of application scenarios by supplying customized, high-dimensional humidity response data as extrinsic compensation. As a proof-of-concept, mitigation of humidity interference in colorimetric gas quantification was achieved in three steps. First, across a ten-dimensional variable space, an algorithm-driven high-throughput experimental robot discovered multiple local optimum regions where colorimetric humidity sensing formulations exhibited high evaluations on sensitivity, reversibility, response time, and color change extent for 10-90% relative humidity (RH) in room temperature (25 °C). Second, from the local optimum regions, 91 sensing formulations with diverse variables were selected to construct a parent colorimetric humidity sensor array as the sensor pool for humidity signal compensation. Third, the quasi-optimal sensor subarrays were identified as customized humidity signal compensation solutions for different gas sensing scenarios across an approximately full dynamic range of humidity (10-90% RH) using an ingenious combination optimization strategy, and two accurate quantitative detections were attained: one with a mean absolute percentage error (MAPE) reduction from 4.4 to 0.75% and the other from 5.48 to 1.37%. Moreover, the parent sensor array's excellent humidity selectivity was validated against 10 gases. This work demonstrates the feasibility and superiority of robot-assisted construction of a customizable parent colorimetric sensor array to mitigate humidity interference in gas quantification.

Thin Film of Poly-peri-naphthalene (PPN) Fabricated by Direct Laser Writing and Its Use for Humidity Sensing.

Inspired by the versatility of the direct laser writing carbonization (DLWc) technique as well as the metal-ion-assisted coordination polymer of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), in the present study, we present a DLWc-enabled approach for cost-effectively fabricating a poly-peri-naphthalene (PPN) thin film with the advantages of patternability, environmental benignity, and scalability. Optical and scanning electron microscopy, as well as ultraviolet-visible-near-infrared, Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies, were performed to confirm that the spray-coated thin film of the Mg-PTCDA coordination polymer can be in situ converted into a PPN thin film upon CO2 laser irradiation. The effects of the laser power and Mg2+ concentration on the structure and electrical properties of the laser-processed PPN thin films were investigated. Lastly, we demonstrated that the laser-processed PPN thin films can be used for humidity sensing with characteristics of a rapid response time and excellent hysteresis. It is expected that this new method for fabricating PPN thin films will lead to a wide range of applications of PPN in the fields of sensing, electronics, and energy storage.

Humidity sensors based on octaphenylcyclotetrasiloxane hypercrosslinked porous polymers for non-contact sensing and respiratory monitoring

Polyhedral oligomeric silsesquioxane (POSS) is renowned for its facile modification and excellent stability, rendering it a promising candidate for humidity-sensitive materials. Achieving humidity sensors based on POSS with broad response ranges and fast response times remains a considerable hurdle. In this investigation, four organic-inorganic hybrid porous polymers, denoted as HCP-X, were synthesized through Friedel-Crafts reaction utilizing octaphenylcyclotetrasiloxane (OPCTS). The incorporation of hydrophilic functional groups onto HCP-X polymers increases their specific surface area and enhances their adsorption capacity for water molecules, thereby accelerating the humidity sensor's response to humidity. The resulting humidity sensors derived from HCP-X demonstrated rapid response times ranging from 0.6 s to 7 s. Notably, the HCP-B-SO3 humidity sensor exhibited outstanding performance due to the synergistic effects of -OH and -SO3- groups, with a 6 orders of magnitude impedance change across the entire measured humidity range (11 % - 97 % RH), a rapid response time of 0.2 s, and excellent repeatability. It also showcased consistent long-term stability over a 30-day duration, maintaining its performance integrity at both 11 % and 97 % RH levels. The resulting humidity sensor was further utilized into non-contact switches and integrated into masks for health monitoring applications, underscoring its substantial potential in non-contact sensing and healthcare domains.

Directional Adaptive Triboelectric Nanogenerator with Wind-Wave Synergy.

To enhance the adaptability and synergy of the triboelectric nanogenerator (TENG) in a wave environment, this paper introduces a directional adaptive triboelectric nanogenerator (DA-TENG) with wind-water synergistic action for wave energy collection. An innovative design combining a wind vane on the top and fan-shaped blade electrodes internally allows the DA-TENG to adjust its swinging direction adaptively to align with the direction of wave motion. The internal multiple power generation units work in coordination, effectively addressing the issues of low efficiency associated with spherical TENGs in capturing multidirectional wave energy. The DA-TENG demonstrates superior performance under various wind speed conditions, showcasing its practical application potential. Experimental results show that the DA-TENG, equipped with a single tail wind vane and a 700 g mass block, can achieve an output voltage, current, and charge of 374.97 V, 84.77 μA, and 622.69 nC under a mild wind environment. Its peak power density reaches 7.51 W m-3, enabling successful data transmission for a wireless temperature and humidity sensor and powering 248 light-emitting diodes (LEDs). This research expands the possibilities of omnidirectional wave energy collection and the collaborative operation of multiple power generation units, offering an effective method for powering low-power maritime devices.

Design of Moringa Leaf Dryer Based on Programmable Logic Control Laboratory Scale

Moringa plants can be found in most tropical and subtropical climates. In some parts of Indonesia, the plant is called kelor or marungga. People need the tree as a source of protein, vitamins, minerals, and carbohydrates. The plant contains more than 90 nutrients, antioxidants, and 8 essential amino acids, called the ‘elixir tree’. The problem with this plant is that its leaves are easily damaged when picked. One way to avoid this is to perform a drying process. This Moringa dryer consists of an inner cabinet made of aluminum and an outer side made of zinc. The cabinet measures 40 cm long, 35 cm wide, and 35 cm high, has three shelves arranged horizontally, and each shelf can dry between 100 grams to 200 grams of moringa leaves simultaneously. In addition, it has a heater consisting of two 125-watt heaters and two upper and lower fans. In the first experiment, Moringa leaves were dried for 9 hours at 40°C, yielding 30g of dried leaves from 100g of fresh leaves. The second experiment lasted 6 hours at 50 °C, yielding 30 g of dried leaves from 100 g of fresh leaves. Finally, the leaves were dried for 3 hours at 60°C, yielding 30g of dried leaves from the initial 100g. These results also show a large weight loss at various temperatures and durations. After calculating the percentage of weight loss, it was found that the leaves lost 70% of their weight. Outseal PLC can automatically control the drying process according to the pre-programmed program. Temperature and humidity sensors maintain the nutritional quality and texture of the moringa leaves produced by controlling the dryer environment appropriately. This tool can be used easily by users without requiring high technical skills.

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.

Dual-Approach Calibration Unlocks Potential of Low-Power, Low-Cost Temperature and Humidity Sensors

Dual-Approach Calibration Unlocks Potential of Low-Power, Low-Cost Temperature and Humidity Sensors

Ultra-Flexible, Anti-Freezing, and Adhesive Collagen Fiber-Derived Conductive Organohydrogel E-Skin for Strain, Humidity, Temperature, and Bioelectric Sensing Applications

Ultra-Flexible, Anti-Freezing, and Adhesive Collagen Fiber-Derived Conductive Organohydrogel E-Skin for Strain, Humidity, Temperature, and Bioelectric Sensing Applications

Laser Fabrication of Humidity Sensors on Ethanol-Soaked Polyimide for Fully Contactless Respiratory Monitoring.

Humidity-sensor-based fully contactless respiratory monitoring can eliminate the discomfort and infection risks associated with any wearable device. However, challenges in the facile fabrication of highly sensitive humidity sensors continue to hinder their widespread application for fully contactless respiratory monitoring. In this study, we introduce a simple method to fabricate highly sensitive humidity sensors. Our method employs laser-induced graphene (LIG) on an ethanol-soaked polyimide (PI) film as the electrode of the humidity sensor. The ethanol-soaked PI between adjacent LIG electrodes functions as the sensing material, enabling ion-conductive humidity sensing. Compared to the LIG humidity sensors fabricated on untreated PI films, LIG humidity sensors fabricated on ethanol-soaked PI films exhibit superior performance with higher linearity (R2 = 0.9936), reduced hysteresis (ΔH = 5.1% RH), and increased sensitivity (0.65%/RH). Notably, the LIG humidity sensor fabricated on the ethanol-soaked PI film can detect a person's breathing from a distance of 30 cm, a capability not achieved by sensors fabricated on untreated PI films. Moreover, incorporating these LIG humidity sensors into an array further enhances both the detection distance and the sensitivity for respiratory monitoring. Experimental results demonstrate that the LIG humidity sensor array can be employed for fully contactless on-bed respiration monitoring and for continuous, fully contactless monitoring of the respiratory rate during treadmill exercise. These results highlight the great potential of our LIG humidity sensors for various practical applications in medicine and sports.

Determining cold strain in cold air: a comparison of two methods of partitional calorimetry to calculate heat storage and debt in cold air with mild hypothermia.

We compared two methods of partitional calorimetry to calculate heat storage and heat debt during cold air (0°C) exposure causing mild core cooling. Twelve participants performed a 5 min baseline in thermoneutral conditions (∼22.0°C, ∼50% relative humidity) followed by cold air exposure (∼0°C) until rectal temperature was reduced by ∆-0.5°C. Partitional calorimetry was used to calculate avenues of heat exchange (radiative, convective, and evaporative), heat storage, and heat debt continuously throughout cold exposure. We compared deriving these variables using prediction equations based on environmental and participant characteristics (PCALEquation Method) versus using measurement tools such as humidity sensors and heat flux discs (PCALHeat Flux Method). There were significant differences between methods (all p≤0.001) for determining heat exchange, heat storage, and heat debt. At ∆-0.5°C, PCALHeat Flux Method had greater levels of radiative and convective heat exchange (PCALHeat Flux Method: -143.0±16.8 W∙m2 vs PCALEquation Method: -123.0±12.9 W∙m2, p≤0.001), evaporative heat exchange (PCALHeat Flux Method: -9.0±1.7 W∙m2 vs PCALEquation Method: -4.1±0.0 W∙m2, p≤0.001), heat storage (PCALHeat Flux Method: -15.0±31.0 W∙m2 vs PCALEquation Method: +6.0±25.9 W∙m2, p=0.020), and heat debt (PCALHeat Flux Method: -692.0±315.0 kJ vs PCALEquation Method: -422.0±136.0 kJ, p≤0.001). Overall, this study found the largest discrepancies between the two methods were when the environmental conditions and skin temperature were in high flux, as well as when core temperature was reduced by ∆-0.5°C. The use of PCALHeat Flux Method may be more advantageous to use in the cold to provide a higher resolution measurement of cold strain.

A fully integrated electronic fabric-enabled multimodal flexible sensors for real-time wireless pressure-humidity-temperature monitoring

Real-time physiological information monitoring can predict and prevent disease, or improve treatment by early diagnosis. A comprehensive and continuous monitoring of human health requires highly integrated wearable and comfortable sensing devices. To address this need, we propose a low-cost electronic fabric-enabled multifunctional flexible sensing integration platform that includes a flexible pressure sensor for monitoring postural pressure, a humidity sensor for monitoring the humidity of the skin surface, and a flexible temperature sensor for visualizing the ambient temperature around the human body. Thanks to the unique rough surface texture, hierarchical structure, and robust electromechanical features of the MXene-modified nonwoven fabrics, the flexible pressure sensor can achieve a monitoring sensitivity of 1529.1 kPa−1 and a pressure range of 150 kPa, which meets the demand for human pressure detection. In addition, the unique porous structure of the fabric and the stacked multilayer structure of MXene enable the humidity sensor to exhibit extremely high monitoring sensitivity, even through clothing, and still be able to detect the humidity on the skin surface. Temperature sensors based on screen-printed thermochromic liquid crystals enable visual monitoring in the range of 0 °C–65 °C. Through further integration with flexible printed circuit board circuits, we demonstrate a proof-of-concept device that enables real-time monitoring of human physiological information such as physical pressure, humidity, and ambient temperature environment, suggesting that the device provides an excellent platform for the development of commercially viable wearable healthcare monitors.

SWINDU (Smart Farming dengan Wind Turbine) = Rancang Bangun Wind Turbine Sederhana berbasis ESP32 untuk Smart Farming Deteksi Kelembapan Tanah pada Sayuran Pokcoy

This research describes the design and implementation of a wind turbine system integrated with an ESP32 microcontroller to detect soil moisture in pakcoy vegetable plants. The main objective of this research is to create a sustainable solution that combines renewable energy with smart crop monitoring technology. The system uses a wind turbine as the main energy source that can generate electricity to operate the soil moisture sensor and DHT11 temperature sensor. The data obtained from these two sensors is used to measure and monitor the environmental conditions of pakcoy plants in real-time. The goal is to support the development of renewable energy, such as wind turbines, to address climate change and safeguard natural resources. Benefits include a reduction in the negative impacts of conventional energy and support for global efforts to address climate change. The methodology involves designing a wind turbine prototype, using temperature and humidity sensors, and integrating smart farming systems. The research also includes a research schedule. The results are expected to be an efficient prototype for generating electrical energy and a MitApp application for monitoring crop and wind energy data. This proposal is relevant to environmental and climate change issues and has the potential for a positive impact on sustainability and the environment.

Prototype smart integrated fire detection based on deep learning YOLO v8 and IoT (internet of things) to improve early fire detection

The high incidence of fires in Indonesia in 2018-2023 is 5,336 fire incidents have caused many deaths and enormous material losses. This system is designed to identify early signs of fire through object detection and sensor technology, which is integrated with the Blynk IoT platform for real-time sensor monitoring and Telegram for instant notifications to users. The waterfall prototype method was designed through observation, system design, program code creation, tool testing, and tool implementation. This research uses Deep Learning YOLOv8 technology and IoT using ESP 32 as a microcontroller. Based on the training datasets, it produces precision=0.95872; recall=0.91; mAP50=0.97; mAP50-95 =0.66. The system uses the integration of a multisensor KY-026 flame sensor, DHT 22 temperature and humidity sensor, and MQ-2 sensors can detect CO, LPG, and smoke gas. All these multisensors can be monitored on Blynk IoT and Telegrambot in real time.