Humidity Sensor Research Articles

Fabrication and Implementation of PVA Thin Film-based Relative Humidity Sensor

This paper presents the fabrication of polyvinyl alcohol (PVA)-based relative humidity sensors using copper interdigitated electrodes (IDEs). These sensors were fabricated by patterning copper IDEs onto FR4 fiberglass substrates and coating them with a thin film of PVA. By varying the number of IDE electrode pairs and the concentration of PVA, the sensors exhibited different resistance values, demonstrating an inverse relationship with the number of IDE electrodes and PVA concentration. Additionally, the thickness of the sensing layer, controlled by spin coating speed, affected the resistance of the sensors. The fabricated sensors achieved a humidity measurement range from 50% to 99% RH based on resistance changes. Furthermore, an interface circuit was designed to integrate the fabricated sensors with an ESP8266 microcontroller, achieving accurate measurements above 74% RH.

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.

Mitigating urban heat island and enhancing indoor thermal comfort using terrace garden

The United Nations advocates for sustainable urban planning and design, emphasizing green infrastructure initiatives to mitigate urban heat island effects and enhance the resilience and livability of cities globally. To address urban heat challenges, a study was conducted in Chennai, India, from April to June 2023. The study focused on assessing temperature dynamics on a building's terrace by comparing a well-maintained garden area with an exposed region. Temperature and humidity sensors were deployed in both the garden and exposed areas of the terrace, as well as within rooms beneath it, to monitor hourly temperature fluctuations. The findings indicate a significant reduction in internal room temperatures in areas with rooftop gardens, ranging from 4 to 11 °C, depending on the time of year and sun's position, compared to rooms with fully exposed roof configurations. Additionally, simulation studies were performed to validate these findings, suggesting that optimizing the distribution of soil beds and plant density across the roof could yield an additional temperature reduction of 3–4 °C, resulting in an overall difference of up to 14–15 °C. The study highlights the efficacy of rooftop gardens in providing cooling effects during daylight hours and maintaining temperature parity post-sunset. Through analysis of sensor data, the research elucidates the intricate relationship between green infrastructure and thermal comfort, offering insights for energy-efficient building design and resilient urban planning. The findings underscore the potential of rooftop gardens in fostering a more comfortable, energy-efficient, and sustainable urban living environment.

IoT Based Flood Monitoring and Alerting System

The primary objective of this project is to create a reliable system for ongoing water level monitoring in dams or Wadis, ensuring timely alerts are sent to nearby residents and the Royal Oman Police (ROP) when levels approach hazardous thresholds. Although preventing floods may not always be feasible, implementing an early detection and alert system through continuous monitoring can significantly reduce the impact on communities. This initiative introduces an Internet of Things (IoT)-enabled flood detection and warning system, utilizing a NodeMCU board, an ultrasonic sensor (HC-SR04), temperature and humidity sensors (DHT11), and the Blynk app. The system diligently tracks water levels, transmitting sensor data to the Blynk Server at regular intervals, allowing for global access and oversight. Should water levels exceed predetermined safe limits, an immediate notification is dispatched via email to designated contacts, warning individuals in the vicinity of the dam or Wadi and the ROP of the potential danger.

Microwave humidity sensor based on shorted split ring resonator with interdigital capacitance and α-Al2O3 nanoflakes/chitosan sensitive film for respiration monitoring

A microwave relative humidity (RH) sensor based on shorted split ring resonator with interdigital capacitance (SSRR-IDC) as a test platform and α-Al2O3 nanoflakes/chitosan (CS) composite as sensitive film is proposed for the detection of human respiration. The SSRR-IDC was designed by optimizing the finger spacing and width of the IDC. Electromagnetic simulation of the designed SSRR-IDC confirms a strong electric field distribution and high dielectric sensitivity in the IDC region. The porous α-Al2O3 nanoflakes/CS composite was coated onto the IDC region of the SSRR to obtain a microwave humidity sensor. Abundant hydrophilic groups and large specific surface area of the α-Al2O3 nanoflakes/CS contribute to the adsorption of water molecules. The proposed microwave humidity sensor shows excellent sensitivity in wide RH range, especially at high humidity condition. The working principle and the sensitivity enhancement mechanism of the proposed microwave sensor were explained by combining a circuit model analysis and the dielectric property and surface microstructure changes of the sensitive materials. Furthermore, the microwave sensor also demonstrates short response/recover time and outstanding repeatability, long-term stability, temperature stability, and selectivity. Additionally, the prepared microwave humidity sensor successfully records respiratory data from different volunteers. Changes in respiratory depth before and after drinking water of the volunteers can also be distinguished by this sensor.

Hyaluronic acid microresonators for memorable humidity sensing

Abstract Self-assembled hyaluronic acid (HA) microspheres are utilized for memorable optical humidity sensing. Because of the extremely high hygroscopic property of HA, the microsphere deforms in a highly humid atmosphere and the shape change is irreversible, thereby memorizing the history of the humidity change. The optically memorable humidity sensor can notify whether the humidity exceeds the upper limit of 50%.

Carbon nanotubes for optimizing response stability and speed of acrylate hybrid copolymers humidity sensor

AbstractCarbon nanotubes (CNTs) are one‐dimensional nanomaterials with a hollow structure, high specific surface area and excellent chemical conductivity, which show great potential for application in the field of humidity‐sensitive responsive materials and humidity sensors. In this paper, CNTs were composited with a hybrid copolymer (HAC) of octavinyl POSS/acrylate to prepare the hybrid copolymer composites HAC/CNTs and their humidity sensors, which demonstrated exceptional thermal stability and fast response speed. Among them, acrylic resin serves as a humidity‐sensitive material; POSS introduce a stable three‐dimensional cage skeleton structure to the material; and CNTs are used as conductive fillers, which further enhance the stability of the material, as well as improve the sensitivity and humidity‐sensitive response speed of the material. The experimental findings indicate that the HAC/8.0% CNTs composite material exhibits a remarkable sensitivity of 119.94 KΩ/%RH within the humidity range of 11%–95%RH. Compared with HAC, HAC/8.0% CNTs demonstrate a significant reduction in response/recovery time from 16.0 s/70.0 s to 0.8 s/80.0 s, representing a considerable improvement in response speed; the wet hysteresis is reduced from 0.88 %RH to 0.77 %RH; and the temperature change coefficient is reduced from 0.035 %RH/°C to 0.008 %RH/°C over the temperature range of 20–60°C, indicating superior stability against temperature variation. Meanwhile, the humidity response mechanism of HAC/CNTs was discussed by using complex impedance spectrum. The hybrid copolymer composites, HAC/CNTs, that were prepared in this study have tremendous potential in the development of advanced, high‐performance, and miniaturizable humidity sensing technologies.Highlights A hybrid copolymer composite humidity‐sensitive material HAC/CNTs is prepared. HAC/CNTs are compounds consisting of CNTs and POSS/acrylate hybrid copolymer. POSS improve the skeleton structural stability of acrylic resins. CNTs enhance the sensitivity and response speed of humidity sensor. The HAC/8.0% CNTs have higher response stability and faster response speed.

High-response humidity sensor based on silicon microbridge with edge-constrained sandwich sensing structure

Silicon microbridge structures have attracted the attention of researchers in humidity sensing area owing to their small size and ease of integration with the integrated circuit (IC). However, the preparation of silicon microbridge humidity sensors with high response are still a challenge. This paper proposed a silicon microbridge humidity sensor based on an edge-constrained sandwich sensing structure, in which a graphene oxide core layer with small area was covered on the surface of the silicon bridge by a larger area of Nafion film. Due to the constraint of the peripheral edge, the swelling deformations of this sandwich structure in the vertical direction were effectively magnified during humidity detection. Hence, the proposed humidity sensor exhibited a higher humidity sensitivity (109.97 µV/%RH) compared to the silicon microbridge sensors with general sandwich sensing structure or monolayer sensing film. Meanwhile, the novel sensor also demonstrated a small humidity hysteresis and good linearity in humidity range of 11.3–97.3%.

Incorporating MIL‐125 Metal‐Organic Framework for Flexible Triboelectric Nanogenerators and Self‐Powered Sensors for Robotic Grippers

AbstractTriboelectric nanogenerators (TENGs) are getting popular as biomechanical energy harvesters to power small electronic devices and as self‐powered sensors for pressure, motion, vibration, wind, waves, biomedical information, and chemical substance detections. In this study, the TENG is designed with biocompatible materials, and concentrations of its components have been optimized to generate higher power for application as an energy source and tactile sensor. The process involves using metal‐organic frameworks (MOFs), namely MIL‐125, with high charge‐inducing and charge‐trapping capabilities incorporated into the commercial Ecoflex matrix. Electrical characterization demonstrated that the sample with 0.25 wt% MIL‐125 (0.25%MOF/Ecoflex) is the optimal concentration in the matrix with an output of up to 305 V and 13 µA, respectively. Moreover, the proposed flexible TENG converts mechanical energy to electrical, with a maximum power density of 150 µW cm−2 (1.5 W m−2), which is more than twice superior to the pristine Ecoflex‐based counterparts. The TENG shows robust and stable performance without noticeable degradation during continuous 200,000 cyclic testing. Furthermore, 0.25%MOF/Ecoflex TENG can power small electronic devices such as calculators, humidity sensors, and cardiac pacemakers. A robotic gripper trained via machine learning to identify various objects is also successfully developed with a self‐powered 0.25%MOF/Ecoflex TENG sensor.

Design of a Humidity Sensor for a PPE Kit Using a Flexible Paper Substrate.

The present work reports the rapid sweat detection inside a PPE kit using a flexible humidity sensor based on hydrothermally synthesized ZnO (zinc oxide) nanoflowers (ZNFs). Physical characterization of ZNFs was done using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR), UV-visible, particle size analysis, Raman analysis, and X-ray photoelectron spectroscopy (XPS) analysis, and the hydrophilicity was investigated by using contact angle measurement. Fabrication of a flexible sensor was done by deposition on the paper substrate using the spin coating technique. It exhibited high sensitivity and low response and recovery times in the humidity range 10-95%RH. The sensor demonstrated the highest sensitivity of 296.70 nF/%RH within the humidity range 55-95%RH, and the rapid response and recovery times were also calculated and found as 5.10/1.70 s, respectively. The selectivity of the proposed sensor was also analyzed, and it is highly sensitive to humidity. The humidity sensing characteristics were theoretically witnessed in terms of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and electronic properties of sensing materials in ambient and humid conditions. These theoretical results are evidence of the interaction of ZnO with humidity. Overall, the present study provides a scope of architecture-enabled paper-based humidity sensors for the detection of sweat levels inside PPE kits for health workers.

Implementasi greenhouse untuk mendukung agropark di Desa Tanjung Pinang II Kecamatan Tanjung Batu Kabupaten Ogan Ilir

Tanjung Pinang II Village is one of the districts in Tanjung Batu, Ogan Ilir Regency, South Sumatra, which is currently developing its potential to become a tourist village through an agro-park. However, the process of transforming the village into a tourism and educational area for the community has not yet implemented technology. Therefore, in this community service, a smart greenhouse was developed and implemented in Tanjung Pinang II Village. The methods used in this community service included situational analysis, greenhouse construction, counseling and training, as well as evaluation, analysis, and conclusion. The constructed greenhouse is equipped with temperature and humidity sensors to measure the conditions inside the room. The greenhouse is built with a steel frame and uses UV plastic for its roof and walls. The results of the community service showed that the village residents and the community benefited from the greenhouse in the process of developing Tanjung Pinang II Village as an ecotourism area.

Research on the influence of solar radiation fuzzy adaptive system on the wet and hot environment in greenhouse

Chinese solar greenhouse (CSG) is an artificially constructed agricultural facility that provides a suitable environment for crop growth. However, the imbalanced temperature and humidity phenomenon occurring in greenhouse during summer greatly affects crop yield. This article proposes the application of solar radiation fuzzy adaptive system in greenhouse to address this issue. The design process includes hardware and algorithm design. The hardware part involves designing the travel distance of the curtain machine and the film winding machine, laying out the temperature and humidity sensors, and designing the control cabinet. The algorithm is optimized based on fuzzy control theory, data acquisition module consists of temperature and humidity sensors, executive components include the curtain machine and the film winding machine, and the data transmission, storage and feedback module consists of the control cabinet and the cloud-based database. These form an adaptive system, which will be subjected to a 10-day comparative experiment. The experimental results showed that in region 3, the peak value of temperature reduction in the third layer during the daytime was 26.2 °C, and the humidity increased by a maximum of 31.5 %. In region 2, the temperature increased by a maximum of 4.2 °C during the nighttime in the second layer, and the humidity decreased by 4.1 °C. Introduction of adaptive systems can play an important role in maintaining microclimate temperature and humidity in summer.

Environmental Monitoring and Control System of Green House with Microcontroller and GSM Using IoT Devices

This paper presents a comprehensive solution for monitoring and controlling greenhouse environments using microcontroller technology and GSM connectivity through IoT devices. The system integrates various sensors to collect real-time data on environmental parameters such as temperature, humidity, soil moisture, and light intensity within the greenhouse. A microcontroller unit processes the sensor data and executes control actions to optimize environmental conditions for plant growth. Through GSM connectivity, the system enables remote monitoring and control, allowing users to access greenhouse data and adjust settings from anywhere using a mobile device or computer. The proposed system offers efficient management of greenhouse conditions, leading to improved crop yield, reduced resource consumption, and enhanced sustainability in agriculture. Continuing from the abstract, the system architecture employs a microcontroller, such as Arduino or Raspberry Pi, as the central processing unit. The microcontroller interfaces with a variety of sensors including temperature sensors, humidity sensors, soil moisture sensors, and light sensors to continuously monitor the greenhouse environment. Data collected from these sensors are processed in real-time by the microcontroller to make informed decisions regarding environmental control parameters such as irrigation, ventilation, and lighting. Control actions are executed autonomously based on predefined thresholds and algorithms to maintain optimal growing conditions for the plants. The inclusion of GSM connectivity enables the system to communicate data and receive commands remotely. Users can access the greenhouse monitoring system through a web or mobile application, providing real-time updates on environmental conditions and allowing for remote control of the greenhouse parameters. Furthermore, the integration of IoT devices allows for scalability and flexibility in the system architecture, facilitating the addition of new sensors or control mechanisms as needed. Additionally, data analytics and machine learning techniques can be implemented to further optimize the system's performance and predictive capabilities. Overall, the proposed monitoring and control system offers a cost-effective, efficient, and sustainable solution for greenhouse management, with potential applications in commercial agriculture as well as small-scale or hobbyist setups

Relative humidity measurements of a thin-film humidity sensor in condensing conditions in the temperature range from −40 °C to 5 °C

In condensing conditions, metastable states such as supersaturation of water vapour and supercooling of liquid water are commonly observed in the free atmosphere. This study investigates the response of a polymeric thin-film humidity sensor under condensing conditions at various temperatures (−40 °C, −20 °C, −5 °C, and 5 °C) and different relative humidity (RH) levels. To ensure precise control of RH, a saturator-based humidity generator operating in a two-temperature mode is utilized. The condensing conditions are achieved in two ways: by increasing water vapour pressure (WVP) at a fixed temperature and by decreasing the temperature while maintaining a constant WVP. In general, when measuring RH under condensing conditions, the sensor indicates a temporary supersaturation state with an RH peak exceeding 100% before the onset of condensation. Subsequently, the RH value exhibits a delayed decrease when exposed to a non-condensing RH level. The experiments with a constant WVP demonstrate a lower likelihood of ice condensation compared to those with a constant temperature. This study demonstrates the measurement capability and behaviour of thin-film humidity sensors above 100% RH in the supersaturation states that are commonly observed in the free atmosphere at meteorologically-relevant temperatures.

Numerical and experimental investigation of an auxetic piezoelectric energy harvester with frequency self-tuning capability

To deal with the limited availability of long-lasting power sources for sensor nodes in industrial environments, a novel piezoelectric energy harvester with high efficiency and a wide working bandwidth was designed to harvest broadband and random vibrations from the ambient environment. The developed energy harvester adopts a doubly clamped piezoelectric beam with a peanut-shaped auxetic structure to improve the power output. It also incorporates a sliding proof mass for frequency self-tuning, enabling a wider working bandwidth. As the doubly clamped beam exhibits geometry nonlinearity under large vibration amplitudes, the power output of the energy harvester can be further enhanced in the frequency self-tuning process. Finite element simulations are conducted to evaluate the impact of the auxetic structure and the position of the proof mass on the performance of the energy harvester. Experiments are performed to examine the energy harvesting performance of the proposed energy harvester. Under an excitation acceleration of 0.3 g, the use of the sliding proof mass widens the working bandwidth of the auxetic energy harvester (AEH) by 9 Hz, with the maximum root mean square output power of AEH reaching 18.78 μW, which is much higher than that of the plain energy harvester (PEH) or the AEH with a fixed proof mass. The developed energy harvester can successfully power a wireless temperature and humidity sensor node based on the vibration produced by a centrifuge, which demonstrates the practical feasibility of the proposed energy harvester for industrial applications.

Preparation and properties study of high performance Eu2Sn2O7–SnO2 composites humidity sensor

In the work, a high-performance Eu2Sn2O7–SnO2 (ES-2) humidity sensors were prepared through a one-step hydrothermal method. Eu2Sn2O7 is a bimetallic material can increase the adsorption capacity to water molecules and promote electron transfer, thus improving the sensitivity of the sensor. The introduction of Eu2Sn2O7 promotes the increase of the content of oxygen vacancies in the ES-2 composite material, which promotes the accelerated decomposition of water molecules, and facilitates the formation of the chemisorbed layer to improve the sensitivity of the sensor and the response time. The increase in specific surface area of ES-2 provided more adsorption sites for H2O and also provided a good transport channel for water molecules to diffuse into the interior of the material. ES-2 humidity sensor exhibits high sensitivity (22,405 ± 363), small humidity hysteresis (1 ± 0.3 %), short response/recovery time (7/6 ± 0.5 s), good repeatability and stability (11%–95 % RH). This study not only promotes the development of SnO2-based humidity sensors, but provides new ideas for the preparation of high-performance humidity sensors.

Paper-based humidity sensor for wearable based on near-field electrohydrodynamic direct writing

Flexible humidity sensors have been widely used in wearable electronics, owing to their flexibility and compatibility with electronic device substrates. This study fabricated a flexible paper-based humidity sensor with a grid-like sensing film using the near-field electrohydrodynamic direct writing (NFEDW) method. A grid-like sensing layer with a dense network of carbon nanotubes/cellulose nanofiber (CNTs/CNF) was prepared, and induced by a voltage field applied during printing. The effects of the substrates and pattern width on the performance of the sensor were systematically investigated. The prepared sensor exhibited high sensitivity of 101 % at 95 % relative humidity (RH). An interlocking structure formed between the CNTs/CNF composite and the paper substrate, endowing the sensor with outstanding bending (minimum diameter of 5 mm) and folding (up to 100 times) durability. Furthermore, the prepared sensor exhibited rapid response performance (17 % within 10 s). This addresses the issue of long response time, which is typically associated with CNTs-based sensors, making these sensors more suitable to practical applications. The above-mentioned advantages enable the sensor to be used for respiration monitoring and even for vocal recognition. Finally, a real-time respiration monitoring platform was developed to demonstrate the sensor’s potential in wearable devices.

Highly sensitive humidity sensor based on composite film of partially reduced graphene oxide and bacterial cellulose

Breathing is an important physiological activity of human body, which not only reflects the state of human movement, but also is one of the important health indicators. Breathing can change the concentration of water molecules, so monitoring humidity has gradually become a hot topic in modern research. In this study, a humidity sensing composite film with high sensitivity and short response time was made by using the mixture of graphene oxide (GO) and bacterial cellulose (BC) with simple dry film-forming method. L-ascorbic acid was used as reducing agent to reduce GO and improve the conductivity of GO/BC composite film (BG). The influence of different BC contents and the different reduction degree on the resistance change rate of composite film was investigated in details. The maximum resistance change rate of partially reduced BG humidity sensitive composite film reached up to 94%, and the response and recovery time were 13 s and 47 s respectively. Furthermore, the sensor shows obvious resistance change in noncontact sensing test and different breathing states. This kind of humidity sensitive film with fast response and high sensitivity has great potential in human health monitoring and noncontact sensing, and is of great significance in promoting health detection and intelligent life.

Ultrafast and low-hysteresis humidity sensors based on mesoporous LaFe0.925Ti0.075O3 perovskite

Humidity sensors are omnipresent. Thus, significant efforts have been undertaken to advance their performance, for example, to have a fast detection time, negligible hysteresis, and excellent stability. Despite numerous active research endeavors, establishing a sensor that excels in all these key performances is still challenging. Here, we address this challenge by designing a capacitive-based humidity sensor employing porous LaFeO3 perovskite. Integrating Ti into the perovskite using a sol-gel method, i.e., LaFe0.925Ti0.075O3, results in a 400% increase in specific surface area achieved through pore formation, translating to a 2094% response parameter. Furthermore, due to the rapid equilibrium between adsorption and desorption processes, the sensor achieves ultrafast 4.4 s response time and 1.4 s recovery time, with <1% hysteresis and excellent stability over 28 days, when assessed at 300 K. Our work significantly advances current humidity sensor performance and, in a broader context, emphasizes the efficacy of porous (perovskite) materials for high performance gas detection.

VR digital twin of office space with computer vision-based estimation of room occupancy and power consumption

AbstractIn the past years, energy consumption has increased rapidly due to many factors, including the rise in technology adoption. This has many downfalls, from higher costs to CO$$_2$$ 2 emissions. Human activities in offices and houses represent a considerable amount of energy usage. A digital twin (DT) of an open-plan common space is created, serving the purpose of remote room occupancy monitoring and automatic detection of energy consumption. A virtual reality (VR) model is developed and integrated to temperature, humidity and imaging sensors. For maintaining privacy, images are processed in local computers to measure occupancy levels and live video feed were never transmitted. The same set of imaging sensors were also used in a bespoke computer vision module for energy consumption estimation. The human avatars were mapped with high correlation (R$$^{2}$$ 2 $$= 0.85$$ = 0.85 ) with actual positions on floor. Our energy consumption algorithm accuracy obtained true positive rate of $$91.58\%$$ 91.58 % and F1 score of $$81.96\%$$ 81.96 % . Finally, all this information is transmitted and visualized to the 3D digital twin for remote monitoring and simulation.