Humidity Sensor Research Articles

Carrageenan-modified MXene nanocomposite-based all-printed flexible humidity sensor for healthcare application

Transition metal carbides and carbonitrides (MXene) have emerged as promising nanomaterials for humidity-sensitive applications due to their abundant hydrophilic active sites and chemically reactive surfaces. However, designing MXene-based flexible humidity sensors with rapid response rates, high sensitivity, and structural stability remains a formidable challenge. Herein, we propose an all-printed humidity sensor fabricated on a paper-based substrate with copper electrodes and carrageenan-modified MXene composite materials. The all-printed humidity sensor prepared in this work exhibited outstanding potential in humidity sensing, showcasing high sensitivity (2073.5 %) and rapid response/recovery times (4.6/5.8 s). Meanwhile, the humidity sensor exhibits outstanding structural stability (with capacitance fluctuation maintained within 8.5 % after 500 bending cycles) and remarkable cyclic stability. Based on its excellent sensing performance and stability, the CAMX-2 sensor can effectively monitor skin humidity, fingertip contact levels, and humidity changes during various exercise modes. Therefore, this work offers a viable strategy for achieving reliable humidity monitoring, showcasing significant potential in the fields of sensing devices and healthcare.

Efficient Fabrication of CrFeO3‐Based Humidity Sensing Device with Fast Dynamics for Real‐Time Breath Monitoring and Contact‐Less Sensing

AbstractIn 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.

Effect of Au nanoparticles on mitigating the negative impacts of humidity on ZnO gas sensors to detect triethylamine at room temperature

The impact of humidity on the efficiency of gas sensors has become highlighted in the realm of gas detection. Due to the complex relationship between humidity and gas sensor performance, the development of gas sensors has recently focused on minimizing humidity-related interference. This research aims to address humidity-related challenges in zinc oxide (ZnO) gas sensors designed to detect triethylamine. The ZnO nanostructures (NSs) were synthesized using thermal decomposition methods at varying temperatures (380 °C, 480 °C, and 580 °C) and annealing times (3 h, 7 h, 12 h, and 21 h). X-ray diffraction (XRD) confirmed the formation of a wurtzite hexagonal close-packed structure in ZnO NSs. Scanning electron microscopy (SEM) images provided insights into the morphologies of ZnO NSs at different annealing temperatures, while energy dispersive spectroscopy (EDS) demonstrated the elemental distribution. Subsequently, gold (Au) nanoparticles were uniformly sputtered onto ZnO sensors with thickness variations (0.1 nm, 0.6 nm, 1 nm, 5 nm, and 10 nm). XPS was employed to analyse the elemental composition and oxygen vacancies of the synthesized sensing materials. The effectiveness of 0.6 nm-thick Au nanoparticles in mitigating humidity effects was observed in ZnO sensors synthesized at 380 °C. The results indicated that ZnO sensors coated with 0.6 nm-thick Au nanoparticles exhibited highly stable responses to ethanol and triethylamine at different humidity levels from 50 % to 90 %. Notably, these sensors demonstrated promising selectivity towards triethylamine (with a response of 17.57) compared to various gas targets at room temperature. The sensor exhibited rapid response and recovery times of 9.8 s and 4.4 s, respectively, toward triethylamine with excellent stability in variable humid environments. The sensor maintained a consistent response over 24 days, demonstrating good stability at high humidity.

Flexible Multimodal Sensors Enhanced by Electrospun Lead-Free Perovskite and PVDF-HFP Composite Form-Stable Mesh Membranes for In Situ Plant Monitoring.

The pH and humidity of the crop environment are essential indicators for monitoring crop growth status. This study reports a lead-free perovskite/polyvinylidene fluoride-hexafluoropropylene composite (LPPC) to enhance the stability and reliability of in situ plant pH and humidity monitoring. The mesh composite membrane of LPPC illustrates a hydrophobic contact angle of 101.982°, a tensile strain of 800%, and an opposing surface potential of less than -184.9 mV, which ensures fast response, high sensitivity, and stability of the sensor during long-term plant monitoring. The LPPC-coated pH electrode possesses a sensitivity of -63.90 mV/pH, which provides a fast response within 5 s and is inert to environmental temperature interference. The LPPC-coated humidity sensor obtains a sensitivity of -145.7 Ω/% RH, responds in 28 s, and works well under varying light conditions. The flexible multimodal sensor coated with an LPPC membrane completed real-time in situ monitoring of soilless strawberries for 17 consecutive days. Satisfactory consistency and accuracy performance are observed. The study provides a simple solution for developing reliable, flexible wearable multiparameter sensors for in situ monitoring of multiple parameters of crop environments.

A Highly Responsive Graphene Oxide Humidity Sensor Based on PVA Nanofibers.

Graphene oxide (GO) humidity sensors based on poly(vinyl alcohol) (PVA) nanofibers have been proposed. The PVA nanofiber layers of different densities were obtained by adjusting the electrospinning time. Then, GO films were deposited on PVA nanofibers by a spin-coating method. The electrical properties of GO films are improved due to the increased distribution of PVA nanofibers in the GO films. The humidity sensors exhibit good sensitivity under a high relative humidity range of 40-80%. The response of sensors has reached 98.44% at a humidity level of 80% RH. The GO/PVA sensors have good stability at various humidity levels for 1 week. Furthermore, the GO/PVA sensors were used for respiration monitoring under different statuses. These sensors have good application prospects in the respiratory detection and analysis of diseases.

β-enhanced humidity robust high performance triboelectric nanogenerator for energy harvesting and sensors

Limited output current and harsh environmental conditions are big challenges to harvesting electrical energy from triboelectric nanogenerators (TENG) in sensing applications. One contributing factor to this issue is matching the density of state between two layers of TENG for maximum charge transfer. To ensure a stable output performance, a superhydrophobic interface between the TENG's two layers has been achieved by applying a novel fluorescence enhanced hexamethyldisiloxane (HMDSO) dielectric barrier discharge (DBD) plasma. The plasma coating not only improve the hydrophobicity but also the interface contacts between the two layers of TENG and therefore a maximum charge transfer and ultra-high current density are obtained. The plasma treatment increases the surface roughness and introduces functional groups such as amino (-NH2), hydroxyl (-OH), and siloxane (-Si-O-Si) on the PMMA film, which increases the electron affinity difference between the two layers, increases humidity resistance. The modified TENG generates a maximum stable output voltage of 1400 V and a maximum current of 125 µA with a power density of 55 W/m2, which is significantly higher than those reported in previous studies. Therefore, the TENG has been used as a self-powered droplet detector with an ultra-fast response time of 1.8 ms and has the potential to be used as a self-powered humidity sensor.

GO/MoS2@PVA composite membrane-based optical fiber Mach-Zehnder interferometer for humidity sensing and its non-contact sensing application.

A humidity sensor based on an optical fiber Mach-Zehnder interferometer (MZI) coated with a GO/MoS2@PVA composite membrane was investigated for non-contact sensing. MoS2 was used as a nanospacer to enhance the humidity-sensitive properties of GO, and the adhesion and stability of the composite membrane on the fiber surface could be increased by PVA. The proposed sensor shows a maximum sensitivity of 0.26 dB/%RH with average response and recovery times of 1.62 and 1.11 s, respectively. In non-contact sensing applications, the sensor can effectively recognize a maximum distance of 10 mm for the proximity of a human finger with a distance variation interval of 3 mm. The proposed sensor is expected to be applied in non-contact distance detection and localization or as a non-contact human-computer interaction panel.

A Design and implementation of a sustainable microcontroller based solar power automatic water irrigation control and monitoring system

The major cause of the shortage of land reserve water owing to the lack of rainfall makes the proper operation of irrigation systems extremely important. A major concern for farmers these days is water scarcity. Pakistan is an important agricultural nation and major part of economy depend on agriculture. This study analyses the soil moisture monitoring and automatic plant watering system since it is really helpful in all kinds of weather. In this study a prototype is design and implement using Arduino-based automation sensors are employed for the control and observation of a solar powered smart irrigation system. An Arduino based remote irrigation system developed for the agricultural plantation, which is placed at a remote location and requires water, provides for plantation when the moisture of the earth drives under the set-point rate which turns on the pump on autopilot. An estimation was carried for solar power energy potential agriculture system condition using soil and humidity sensors. The measurements and mathematical formulation were observed to monitor effectivity of solar based power generation. This analysis is conducted for 20 Watt power panel integrated with 5-watt electrical drive with battery capacity 1200 m-Ah. A modified energy model was used to determine the agricultural load for a 5-watt dc motor. The results showed a cumulative analysis to implement this system inspired by smart sustainable clean renewable energy technologies which meet the farmer’s demands significantly increase the productivity of farming and reduce wastage of water and energy.

Prototype of Smart Grain Storage Based Internet of Things

Rice (Oryza sativa L.) is a crucial staple food, particularly in Indonesia, one of the largest rice-producing countries. Proper storage of rice grains is essential to maintain their quality and quantity. This research aims to develop a smart rice grain storage prototype based on the Internet of Things (IoT) that can monitor temperature, humidity, and light intensity in real-time. The method used is Design-Based Research (DBR), involving six stages: focus, understanding, definition, conception, creation, and testing. The prototype utilizes DHT22 sensors for temperature and humidity, LDR sensors for light intensity, and soil moisture sensors, all integrated with an ESP32 microcontroller. Data collected from the sensors are sent to a cloud-based platform for analysis and early warnings if storage conditions are unsuitable. The results indicate that the prototype effectively monitors storage conditions and provides accurate data. System testing shows that all components function according to specifications. This prototype helps maintain grain quality and reduce damage risk during storage. The use of IoT in grain storage enhances efficiency and reduces farmers' costs. Future research should focus on developing more advanced prototypes with automatic control features and mobile application integration.

Meshed, Flexible, and Self-Supported Humidity Sensors by Direct-Writing with Multifunctional Applications.

Flexibility endows humidity sensors with new applications in human health monitoring except for traditionally known environmental humidity detection in recent years. In this study, a flexible, mesh-structured, and self-supported humidity sensor was designed and manufactured by direct writing in a homemade two-dimensional stepping numerical control workstation. Bacterial cellulose with humidity sensitivity and good film-forming properties was applied as the self-supporting substrate, in which conductive activated carbon and water-absorptive magnesium chloride (MgCl2) were incorporated. The humidity sensing performance of the printed sensor was measured and optimized. Besides, the fundamental insight into the sensing mechanism of the printed humidity sensor was analyzed by a complex impedance spectrum. The multifunctional applications of the self-supported humidity sensor were demonstrated by human breathing detection, noncontact distance sensing, and speaking recognition. The simple self-supported structure combined with the meshed attribute of the flexible sensor showed large use potential in real-time monitoring of human respiration, voice detection, environmental humidity monitoring, and noncontact switches.

Reliability Assessment and Multi-Physics Simulation of Additively Printed Wearable Humidity Sensor with Super Capacitive Material for Astronaut in Extreme Condition

Abstract Additive technologies, such as aerosol jet printing, direct write printing are increasingly being used in the production of printed circuit boards because they eliminate the need for costly tooling, such as photomasks or etching containers. This is because additive methods allow for the direct deposition of printing materials onto a substrate. This versatility in a broad variety of applications allows engineers to create diverse applications, such as sensing devices with ECG sensors, pulse-oxygen sensors, galvanic skin response sensors, body temperature sensors, humidity sensors, and so on. Due to its potential for adaptability and integration, the development of additively printed humidity sensors has been the subject of several prior investigations. There are still issues with the reliability of current humidity sensor technology when flexing force is coupled with the humidity sensor. For the avoidance of stability issues, it is required to develop a better printing technique, process recipe, and sensing material encapsulation. In this research, the direct-write (D-write) printing approach with a nScrypt printer was employed to print the humidity sensor as a test vehicle in a laboratory setting. The sensor was characterized by analyzing the print recipe and its interaction with humidity in regards to resistance and humidity sensitivity. Additionally, the characterization of sensor accuracy, hysteresis, linearity, and stability in relation to temperature and humidity variation has been measured. Furthermore, a multi-physics simulation model was created in order to comprehend the electrochemical processes that occur when the humidity sensor is exposed to a very humid environment.

Investigation of the free-base Zr-porphyrin MOFs as relative humidity sensors for an indoor setting

Maintaining optimal relative humidity is paramount for human comfort. Therefore, the utilization of quartz crystal microbalance (QCM) as a relative humidity sensor platform holds significant promise due to its cost-effectiveness and high sensitivity. This study explores the efficacy of three free-base Zr porphyrin metal-organic frameworks (MOFs) - namely MOF-525, MOF-545, and NU-902 - as sensitive materials for QCM-based relative humidity sensors. Our extended experimental findings reveal that these materials exhibit notable sensitivity, particularly within relative humidity ranges of 40–100 %. However, we observe potential irreversible adsorption sites within the MOF-545 framework, hindering its ability to revert to its initial state after prolonged exposure. In light of this observation, we conduct periodic cycling experiments at relative humidity levels of 40–70 % to evaluate the measurement repeatability and feasibility of these sensors for indoor applications. Interestingly, the periodic cycling study demonstrates that MOF-545 shows promising repeatability, positioning it as a strong contender for indoor relative humidity sensing. In contrast, MOF-525 may necessitate extended desorption time, and NU-902 displays diminished sensitivity at low relative humidity levels. Nevertheless, a preliminary treatment of the MOF-545 QCM sensor may be necessary to address irreversible adsorption sites and uphold measurement repeatability, as only reversible adsorption sites are currently accessible. This study underscores the potential of MOF-based QCM sensors for effective relative humidity monitoring in indoor environments, thus facilitating improved comfort and environmental control.

High-sensitivity humidity sensor based on Poly(vinylidene fluoride)/Deep eutectic solvent composites

This study explores the incorporation of deep eutectic solvent (DES) into a poly (vinylidene fluoride) (PVDF) matrix to fabricate PVDF/DES composite thin films. Subsequently, electrodes were screen-printed onto the thin films to create PVDF/DES humidity sensors. The investigation delved into the crystalline structure of PVDF, the cross-sectional morphology and electrochemical property of PVDF/DES composite films, and the humidity sensing response of PVDF/DES humidity sensors. The study revealed that adding DES leads to the formation of porous composite films with electrical active phases and high electrical conductivity. The sensitivity of the PVDF/DES humidity sensor increases with the content of DES. This work provides a novel method for the fabrication of humidity sensors, holding significant potential in various applications such as respiratory monitoring.

Enhancing hygrothermal monitoring of wet construction with digital twins

The development of digital building twins in the Architecture, Engineering, Construction and Operation (AECO) sector requires the adoption of adequate monitoring strategies for building components. This article presents a proposal and validation of a digital twin-enabled hygrothermal monitoring procedure applied to lightweight concrete using an IoT Arduino-based prototype. This study conducted tests to measure moisture in three types of lightweight concrete for over a year. Temperature and relative humidity sensors were embedded in the lightweight concrete samples. The recorded data were compared to four in-situ surface moisture meters and gravimetric analysis. Although surface moisture meters have different reference scales, the qualitative assessment is similar. The embedded sensors preserved their performance levels during the entire testing period, even those exposed to relative humidity levels near 100 %. The continuous monitoring of temperature and relative humidity in non-structural construction elements, using low-cost sensors embedded during construction, is proven to be viable.

Implementation Of Temperature, Humidity And Ammonia Measuring Equipment And Adding Notifications To Sibebe (Case Study: Berkah Bersama)

Broiler chickens are a rapidly growing breed, and their growth is influenced by environmental conditions. The poultry house is one of the most crucial aspects of broiler chicken management, particularly the conditions inside the house, such as air temperature, humidity, and ammonia levels. Therefore, it is essential to regularly check the poultry house conditions. In this research, the author developed an embedded system capable of detecting temperature, humidity, and ammonia levels inside the poultry house. The system periodically sends temperature, humidity, and ammonia gas information to the Berkah Bersama information system, and this information is displayed in the form of graphs. Temperature, humidity, and ammonia gas information will be sent via email if the environmental conditions exceed or fall below the threshold. The embedded system was created using a microcontroller, temperature and humidity sensors (DHT11), and an ammonia level sensor (MQ-135). Arduino serves as the microcontroller, and NodeMCU ESP8266 is used as the communication tool to send poultry house environmental conditions to the Berkah Bersama information system (SIBEBE) and the manager via email. Testing was conducted in two stages: functionality and connectivity. Functionality testing demonstrated that the sensors can produce air temperature, humidity, andammonia level information by comparing them with conventional tools. Connectivity testing proved that the NodeMCU ESP8266 module can send monitoring data every day and under specific conditions.

Monoolein-Based Wireless Capacitive Sensor for Probing Skin Hydration.

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.

Synergistic energy harvesting and humidity sensing with single electrode triboelectric nanogenerator

Humidity sensors using triboelectric nanogenerators (TENGs) technology can provide continuous operation without the need for additional batteries. These sensors provide sustainable and self-powered humidity monitoring solutions, that can be utilized in various agriculture platforms and food processing industries. In this work, a sol-gel method is utilized to process the bismuth ferrite (abbreviated as BFO) materials and a simple mould pressing method to obtain freestanding Ethylene-vinyl acetate (abbreviated EVA)-BFO composites. These composites were characterized to shed light upon structural and microstructural properties. The single electrode mode operating TENG was fabricated having 2 cm × 2 cm active area at various wt.% of BFO onto EVA-based composites to compare the electrical response. The 5 wt.% BFO-EVA-based composites/FEP-based TENG generates a voltage and current of 45 V and 800 nA. Further, the TENG device was tested for long-term stability for 400 s, and charging of various capacitors having capacitance values such as 0.1 μF, 1 μF, 4.7 μF, and 10 μF along with 3 times charging/discharging cycles of 0.1 μF capacitor have been demonstrated. The humidity sensing mechanism elucidated which follows the conduction process based on the Grotthuss proton hopping mechanism. The TENG demonstrates a sensitivity of 0.53 V/RH% over the relative humidity range from 25 % to 85 %. The powering of the wristwatch confirms that fabricated TENG can be a reliable power source for future low-power electronics.

Charge generation by passive plant leaf motion at low wind speeds: design and collective behavior of plant-hybrid energy harvesters

Energy harvesting techniques can exploit even subtle passive motion like that of plant leaves in wind as a consequence of contact electrification of the leaf surface. The effect is strongly enhanced by artificial materials installed as ‘artificial leaves’ on the natural leaves creating a recurring mechanical contact and separation. However, this requires a controlled mechanical interaction between the biological and the artificial component during the complex wind motion. Here, we build and test four artificial leaf designs with varying flexibility and degrees of freedom across the blade operating on Nerium oleander plants. We evaluate the apparent contact area (up to 10 cm2 per leaf), the leaves’ motion, together with the generated voltage, current and charge in low wind speeds of up to 3.3 m s−1 and less. Single artificial leaves produced over 75 V and 1 µA current peaks. Softer artificial leaves increase the contact area accessible for energy conversion, but a balance between softer and stiffer elements in the artificial blade is optimal to increase the frequency of contact-separation motion (here up to 10 Hz) for energy conversion also below 3.3 m s−1. Moreover, we tested how multiple leaves operating collectively during continuous wind energy harvesting over several days achieve a root mean square power of ∼6 µW and are capable to transfer ∼80 µC every 30–40 min to power a wireless temperature and humidity sensor autonomously and recurrently. The results experimentally reveal design strategies for energy harvesters providing autonomous micro power sources in plant ecosystems for example for sensing in precision agriculture and remote environmental monitoring.

High-Performance Self-Cleaning Triboelectric Mini Humidity Sensor Enabled by Facet Engineered Titania Nanocrystals Adorned Nylon-6,6 Electrospun Nanofibers

High-Performance Self-Cleaning Triboelectric Mini Humidity Sensor Enabled by Facet Engineered Titania Nanocrystals Adorned Nylon-6,6 Electrospun Nanofibers

Sea urchin inspired ultrafast response low humidity sensor based on ionic liquid modified UiO-66 with advanced applications

Numerous applications require low humidity sensors that not only sensitive but also stable, small hysteresis, high resolution and fast response. However, most reported low humidity sensors cannot possess these properties at the same time. In this work, inspired by sea urchin, we developed an ionic liquid (IL) modified metal organic framework (UiO-66) based low humidity sensor. Owing to the synergistic effect of the hydrophilicity and ionic conductivity of IL and the steric hindrance effects of UiO-66, the optimized low humidity sensor simultaneously exhibits high response (47.5), small hysteresis (0.3 % RH), ultrafast response speed (0.2 s), high resolution (1 % RH), and excellent long-term stability (>120 days). In particular, the sensor has been proved to have potential applications in visual humidity detection and water source location. This work provides a preliminary design principle that will contribute to the preparation of high-performance low humidity sensing materials.