Capacitive Humidity Research Articles

Gelatin-Coated High-Sensitivity Microwave Sensor for Humidity-Sensing Applications.

In this paper, the humidity-sensing characteristics of gelatin were compared with those of poly(vinyl alcohol) (PVA) at L-band (1 ~ 2 GHz) microwave frequencies. A capacitive microwave sensor based on a defected ground structure with a modified interdigital capacitor (DGS-MIDC) in a microstrip transmission line operating at 1.5 GHz without any coating was used. Gelatin is a natural polymer based on protein sourced from animal collagen, whereas PVA is a high-sensitivity hydrophilic polymer that is widely used for humidity sensors and has a good film-forming property. Two DGS-MIDC-based microwave sensors coated with type A gelatin and PVA, respectively, with a thickness of 0.02 mm were fabricated. The percent relative frequency shift (PRFS) and percent relative magnitude shift (PRMS) based on the changes in the resonant frequency and magnitude level of the transmission coefficient for the microwave sensor were used to compare the humidity-sensing characteristics. The relative humidity (RH) was varied from 50% to 80% with a step of 10% at a fixed temperature of around 25 °C using a low-reflective temperature and humidity chamber manufactured with Styrofoam. The experiment's results show that the capacitive humidity sensitivity of the gelatin-coated microwave sensor in terms of the PRFS and PRMS was higher compared to that of the PVA-coated one. In particular, the sensitivity of the gelatin-coated microwave sensor at a low RH from 50% to 60% was much greater compared to that of the PVA-coated one. In addition, the relative permittivity of the fabricated microwave sensors coated with PVA and gelatin was extracted by using the measured PRFS and the equation was derived by curve-fitting the simulated results. The change in the extracted relative permittivity for the gelatin-coated microwave sensor was larger than that of the PVA-coated one for varying the RH.

Flexible capacitive humidity sensor based on potassium ion-doped PVA/CAB double-layer sensing film

Flexible capacitive humidity sensor based on potassium ion-doped PVA/CAB double-layer sensing film

Electric-field assisted spatioselective deposition of MIL-101(Cr)PEDOT to enhance electrical conductivity and humidity sensing performance

Precise deposition of metal–organic framework (MOF) materials is important for fabricating high-performing MOF-based devices. Electric-field assisted drop-casting of poly(3,4-ethylenedioxythiophene)-functionalized (PEDOT) MIL-101(Cr) nanoparticles onto interdigitated electrodes allowed their precise spatioselective deposition as percolating nanoparticle chains in the interelectrode gaps. The resulting aligned materials were investigated for resistive and capacitive humidity sensing and compared with unaligned samples prepared via regular drop-casting. The spatioselective deposition of MOFs resulted in up to over 500 times improved conductivity and approximately 6 times increased responsivity during resistive humidity sensing. The aligned samples also showed good capacitive humidity sensing performance, with up to 310 times capacitance gain at 10 versus 90 % relative humidity. In contrast, the resistive behavior of the unaligned samples rendered them unsuitable for capacitive sensing. This work demonstrates that applying an alternating potential during drop-casting is a simple yet effective method to control MOF deposition for greater efficiency, conductivity, and enhanced humidity sensing performance.

Low humidity hysteresis and fast response silicon based capacitive humidity sensor based on SiO2 supported GO film

Low humidity hysteresis and fast response are important parameters for evaluating sensor performances. However, it is difficult for a sensor to simultaneously obtain a low humidity hysteresis and fast response time. In this work, a low humidity hysteresis and fast response silicon based capacitive humidity sensor was fabricated based on a two-step deposition strategy using SiO2 and GO. The scanning electron microscope (SEM) was used to characterize the morphologies for the fabricated sensor, demonstrating the successful synthesis of sensitive films. The experimental results suggested that, compared with the pure GO and GO/SiO2 composite film sensors, the two-step deposition strategy fabricated layered SiO2 supported GO film humidity sensor exhibited the lowest humidity hysteresis and the fastest response speed. The humidity hysteresis and response/recovery time are 3.5 % and 3 s/2 s, respectively. The humidity sensing mechanism for the observed low humidity hysteresis and fast response was analyzed via morphologic structures and Young-Laplace equation. This work demonstrates that the morphological structures modulation is an important and effective method for improving sensor performance, providing a valuable reference for high performance sensor fabrication.

Design and Characterization of Printed Flexible Humidity Sensor

The development of humidity sensors is essential for applications in the environmental, agriculture, medical and semiconductor industries [1-2]. The basic mechanism of humidity sensors is explained by a Grotthuss chain reaction, which is usually simplified as a proton-hopping process [3]. This refers to a dynamic charge transfer process at a certain relative humidity (RH). The humidity sensors can be of different types such as capacitive type, resistive, colorimetric and surface acoustic wave [4-7]. Capacitive type sensors are linear, require less complex circuitry and can operate for a wide range of humidity [8]. A typical capacitive type humidity sensor uses hydrophilic films as sensing layers which are stable at higher humidity levels [9]. Polymers that are being used for the fabrication of capacitive type humidity sensors include poly (2-hydroxyethyl methacrylate) (pHEMA) [9], cellulose acetate butyrate (CAB) [10], polyimide [11] and polymethyl methacrylate (PMMA) [12]. In this work, a humidity sensor has been fabricated on glass and flexible substrates.The design of humidity sensor consists of printed pattern of a conductor such as silver and a spin coated dielectric such as polymer poly (2-hydroxyethyl methacrylate) (p-HEMA) and polyimide. The printing of conductor was done in an interdigitated pattern as shown in figure 1. The thickness of sensitive materials was controlled by varying the spin time from 10 to 30 seconds. A thick solution of sensitive materials was prepared by adding a 3 gm of polymer in 50 mL ethanol in the case of p-HEMA. Currently we are preparing one more set of samples using polyimide and we will present a comparison of two humidity sensors- one with p-HEMA and another with polyimide. A humidity sensor that employs interdigitated capacitors (IDC) printed with silver on a glass and flexible substrate was successfully fabricated using p-HEMA and polyimide at spin speed of 2000 rpm for 20 seconds. Our goal is to integrate the humidity sensor into a robotic arm to perform real-time object characterization in agricultural applications via comprehensive understanding of the operations of harvesting robots in various crop types and environmental conditions.

Structural, Optical and Humidity Sensing performance of Lanthanum doped CoCr2O4 nano-ceramics for Sensor Applications

In the present study, we have investigated the influence of Lanthanum doping concentration on the structural, microstructural, dielectric, and humidity sensing performance of rare earth Lanthanum cobalt chromite nanoparticles. These nanomaterials were synthesized by the solution combustion method using glucose and urea as fuels. Structural investigations revealed that the synthesized materials are single-phase, highly crystalline, and porous, with spherical agglomerated nanoparticles of crystallite size ranging from 13 nm to 17 nm. Particle size distribution and pore area distribution were plotted using imageJ software. Energy dispersive spectroscopy confirmed the accurate elemental composition of all samples, consistent with the calculated stoichiometry. Optical absorption studies showed a blue shift in the peak as the doping concentration increased, indicating a quantum confinement effect. Dielectric constant and electrical resistivity measurements ensured that the materials are electrically conducting, which is necessary for humidity sensing applications. Humidity sensing measurements demonstrated that the capacitive humidity sensitivity coefficient (SC) and resistive humidity sensitivity coefficient (SR) were highest for the La (0.05) sample. The XPS survey spectra and high-resolution core-level spectra provide a thorough understanding of the elemental composition, oxidation states, and electronic environments in La-doped cobalt chromite nanoparticles. This detailed analysis is critical for tailoring the material's properties for specific applications in catalysis, electronics, and magnetic devices.

Ultra-sensitive humidity sensing based on Coherent perfect absorber-lasing system

Abstract As a singularity in non-Hermitian physics, coherent perfect absorber-lasing (CPAL) point theoretically has an infinite quality factor and can detect small perturbations, so it has potential applications in ultra-sensitive sensors. However, in the radio frequency field, due to deviations in actual components, the system will deviate from the CPAL point and the performance will degrade significantly (the output coefficient amplitude is only 30 dB). At the same time, actual sensing research is also very lacking. Based on these, we demonstrate a CPAL-based sensor system that increases its output coefficient amplitude to 60dB. When using the lasing state as the sensing mode, it has a capacitance detection accuracy of 10 fF. Then a high-frequency capacitive humidity sensor based on polyaniline/graphene oxide/titanium dioxide film is designed. The heterojunction formed between these materials increases the number of active sites for adsorbing water molecules. With the ultra-high capacitance detection accuracy of the CPAL sensor system, it is finally able to distinguish a 1% relative humidity change at 20%RH (corresponding to a 20 fF capacitance change, or a 1.63 dB output coefficient change), showing potential sensing application prospects.

High-Sensitivity Fully Printed Flexible BaTiO3- Based Capacitive Humidity Sensor for In-Space Manufacturing by Electrohydrodynamic Inkjet Printing

High-Sensitivity Fully Printed Flexible BaTiO₃- Based Capacitive Humidity Sensor for In-Space Manufacturing by Electrohydrodynamic Inkjet Printing

Impact of Compositional Engineering on PTB7-Th:PC71BM Capacitive Humidity Sensor Performance

Impact of Compositional Engineering on PTB7-Th:PC71BM Capacitive Humidity Sensor Performance

Unveiling capacitive humidity characteristic of CdSe quantum dots synthesized by facile route

Improving the practical uses of a multifunctional humidity sensor requires developing an easy, economical, and environmentally friendly synthesis process. Unfortunately, most humidity sensors have a complicated fabrication process, which drives up their price and restricts their range of applications. In this present work, quantum dots have prevailed as a potential sensing material owing to their small size and large surface area. Herein, we reported the three different colored (green, yellow, and red) based cadmium selenide (CdSe) quantum dots (QDs) using a solution-processed method. Physical characterization of as synthesized CdSe QDs is confirmed using photoluminescence (PL), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible analysis, diffused light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR). TEM analysis of CdSe QDs revealed the average particle size of 6 nm. These CdSe QDs were further employed as capacitive humidity sensors. Among the investigated samples, Cd-1 (prepared by 225℃) exhibited the highest sensitivity 93.842 pF/% RH with a rapid response and recovery time of 10 s and 13 s, respectively at 20 Hz. The excellent sensitivity of the Cd-1 is accredited to its least particle size and wider energy band gap as compared to Cd-2 and Cd-3 (prepared by 235 and 245℃) samples. Overall, this work opens an avenue for high performance CdSe QDs based humidity sensors.

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

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

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.

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

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

A Micro Capacitive Humidity Sensor Based on Al-Mo Electrodes and Polyimide Film.

Quickly sensing humidity changes is required in some fields, such as in fuel cell vehicles. The micro humidity sensor used for the relative humidity (RH) measurement with fast response characteristics, and its numerical model and method are rare. This paper firstly presents a numerical model and method for a parallel plate capacitor and a numerical analysis of its dynamic characteristics. The fabrication of this sensor was carried out based on the numerical results, and, the main characteristics of its moisture-sensitive element are shown. This parallel plate capacitor is made using complementary metal-oxide semiconductor (CMOS)-compatible technology, with a P-type monocrystalline silicon wafer used as the substrate, a thin polyimide film (PI) between the upper grid electrode and the lower parallel plate electrode, and electrodes with a molybdenum-aluminum bilayer structure. The shape of the micro sensor is square with 3 mm on the side of the source field. The humidity sensor has a linearity of 0.9965, hysteresis at 7.408% RH, and a sensitivity of 0.4264 pF/%RH. The sensor displays an average adsorption time of 1 s and a minimum adsorption time of 850 ms when the relative humidity increases from 33.2% RH to 75.8% RH. The sensor demonstrates very good stability during a 240 h test in a 25 °C environment. The numerical model and method provided by this study are very useful for predicting the performance of a parallel plate capacitor.

A capacitive humidity sensor based on nanodiamond/silver nanoparticles (ND/Ag) nanocomposite with high stability and rapid response for respiratory monitoring

In this work, a high-performance capacitive humidity sensor based on nanodiamond/silver nanoparticles (ND/Ag) nanocomposite is proposed. The influence of silver nanoparticles with different content in nanodiamond is investigated, and the optimum ratio of 5 wt% Ag in the composite shows the maximum humidity sensing performance, which is three times than that of the pure nanodiamond based humidity sensor. Moreover, the proposed sensor exhibits a superior repeatability, ultrafast response time (<2 s) and recovery time (<1 s). More importantly, the sensor can maintain a good repeatability and rapid response speed when exposure to high humidity for a long time, demonstrating the excellent stability of the proposed sensor. Furthermore, complex impedance spectroscopy was applied to account for the underlying sensing mechanisms of the ND/Ag composite film humidity sensor. Finally, we design a circuit to realize non-contact breathing control by using the fabricated humidity sensor, which demonstrate that the fabricated humidity sensor could be applied to some auto-control systems by human-breath. This work demonstrated that ND/Ag composite film is an ideal candidate material for constructing high-performance humidity sensors for respiratory applications.

Humidity Diode Sensors Based on 1D Nanosized Silicon Structures

Introduction. Humidity measurement is essential in microelectronics, aerospace, biomedical, and food industries, as well as in households for climate control. Currently, various types of devices have been used as humidity sensors: capacitive, resistive, diode, gravimetric, optical structures, field-effect transistors and devices based on surface acoustic waves.Problem Statement. Today, there is a need to develop IC-compatible humidity sensors that have high sensitivityand low cost. To this end, silicon nanowires have been successfully used in resistive and capacitive humidity sensors. However, there is a lack of research on the nanowire effect on device parameters of diode-type humidity sensors.Purpose. To develop diode sensors based on silicon nanowires and to determine the effect of process parameters of synthesis and structural features of nanowires on the performance of humidity sensors.Materials and Methods. The process of sensor fabrication includes several steps: chemical cleaning of silicon wafer, synthesis of silicon nanowires using standard or modified metal-assisted chemical etching, phosphorus diffusion to create a p-n junction, front and back metallization. The surface morphology of the nanostructures has been studied by scanning electron microscopy. The humidity-sensitive characteristics have been studied with theuse of salt hygrostats.Results. It has been shown that the addition of one-dimensional silicon nanostructures to the diode-type sensor signifi cantly improves its characteristics. The rectification ratio increases from 161 to 1807, the response ups from 4.5 to 25, the sensitivity grows from 1.6 to 4.02 (%RH)–1, while the response time and recovery time are reduced from 85/90 to 25/30 s, the hysteresis value goes down from 75 to 16%, the signal deviation after cycling drops from 15to 3%, and the signal fluctuation during continuous device operation decreases from 17 to 15%.Conclusions. The results have shown that the use of a simple and cheap nanowire synthesis technology is effective to produce humidity sensors.

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.

Mems capacitive humidity sensors based on different structures for low humidity applications

Mems capacitive humidity sensors based on different structures for low humidity applications

DHT11 Sensor: A Comprehensive Study on Temperature and Humidity Sensor

The DHT11 sensor is a fundamental component in the realm of sensor technology, offering a simple yet effective solution for measuring temperature and humidity. This paper presentation aims to provide a comprehensive overview of the DHT11 sensor, highlighting its key attributes, operating principles, and practical applications. It is a compact and affordable sensor that utilizes a capacitive humidity sensor and a thermistor to accurately measure both temperature and humidity. Its digital output makes it easy to interface with microcontrollers and data acquisition systems, making it a popular choice for DIY enthusiasts, hobbyists, and professionals alike. Keywords: 1.Arduino IDE program software. 2.Development board ESP8266. 3.DHT 11

An Ultrafast Capacitive Humidity Sensor With Excellent Static and Dynamic Characteristics

An Ultrafast Capacitive Humidity Sensor With Excellent Static and Dynamic Characteristics