High-sensitivity Humidity Sensor Research Articles

High-sensitivity humidity sensor based on multimode fiber coating black phosphorus quantum dot-polyvinyl alcohol

High-sensitivity humidity sensor based on multimode fiber coating black phosphorus quantum dot-polyvinyl alcohol

High-sensitivity humidity sensor based on Mach-Zehnder Interferometer in seven-core fiber

High-sensitivity humidity sensor based on Mach-Zehnder Interferometer in seven-core fiber

Miniature fiber optic SPR high sensitivity humidity sensor based on coated polyvinyl alcohol film

For the measurement of relative humidity, this study employed Surface Plasmon Resonance (SPR) technology, a sensor with a micro-conical fiber structure (sensing length is only 375 μm) was combined with Polyvinyl Alcohol (PVA) to create a humidity sensor that is highly sensitive, compact, dense, and exhibits good linearity. The humidity sensor is based on a gold film (thickness of about 40 nm) on the surface of the miniature fiber optic structure, and by applying PVA coating, the SPR humidity sensor shows resonance peaks in the transmission spectrum in ambient air, and as the number of layers of PVA coating (thickness) is added, the resonance peaks’ positions are red-shifted. The experimental findings demonstrated that this SPR humidity sensor’s sensitivity was 0.162 nm/%RH at an initial resonance wavelength of about 550 nm (one layer) and about 1.542 nm/%RH at an initial resonance wavelength of 656 nm (five layers) in the range of 46 %RH to 93 %RH. The wavelength and the relative humidity had a good linear connection. Temperature tests revealed the sensor has a −0.152 nm/°C temperature sensitivity between 20 °C and 50 °C and has a high linearity (0.999). Therefore, the sensor has potential applications in humidity measurement.

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.

High sensitivity humidity sensor based on the U-shaped tapered no-core fiber coated with MXene.

Ti3C2Tx MXene is an emerging two-dimensional material that has good potential in relative humidity (RH) measurement because of its unique layer structure, strong hydrophilic nature, and large specific surface area. Here, a high-performance RH sensor integrating Ti3C2TX MXene nanosheets and U-shaped tapered no-core fiber (UTNCF) is proposed. The sensing principle is based on mode interference. The change of ambient RH leads to the change of the refractive index (RI) of Ti3C2Tx MXene, which eventually leads to the shift of the transmission spectrum of the sensing probe. The average sensitivity is 1.11 nm/%RH in the RH range of 45% to 80%, and the response time is 25 ms. The proposed micro-nano fiber RH sensor has the advantages of high sensitivity, fast response, good repeatability, and stability. In addition, the proposed sensor has a broad application prospect in human respiratory monitoring, industrial and agricultural production, and environmental monitoring.

Nanoarchitectonics of high-sensitivity humidity sensors based on graphene oxide films for respiratory monitoring

Respiration monitoring is important for assessing human health, but most sensors have complex structures and processes. In this paper, the response of graphene oxide (GO) sensors with bottom- and top-connected structure to humidity is investigated for respiratory monitoring. The sensors of the bottom-connected structure increase the current by 132.97 % and 2077.55 % compared to those of the top-connected structure at GO concentrations of 25 mg/ml and 50 mg/ml, respectively. Both types of sensors can achieve corresponding responses to humidity (40 %–80 % relative humidity (RH)). The bottom-connected sensors, however, exhibit better performances with the responsivity of 96.25 % at 80 % RH and the sensitivity of 131.33 %/RH. In real-time monitoring for humidity, the bottom-connected sensors have good repeatability. The sensors can distinguish different breathing modes and detect the respiration rate/depth of the target. This provides an important method for the development of simple and fast humidity sensors.

Graphene-based multifunctional humidity sensors with an ultrahigh current response.

Prospective composites, based on graphene (G) and hexagonal boron nitride (h-BN) nanoparticles, synthesized using a plasma jet and conducting polymer PEDOT:PSS, were used to create and study a set of sensors in the current study. The composites used were G:PEDOT:PSS (GPP) and G:h-BN:PEDOT:PSS (GBNPP). The PEDOT:PSS content in the composites was 10-3 wt%, and the ratio of G : h-BN was 1 : 1 in GBNPP. The development of these new highly conductive graphene-based composites makes it possible to create an active sensor layer with an ultra-low thickness of several nanometers. The ultra-high sensitivity of the current response, S, was ((2.0-3.3) × 106)% for GPP and GBNPP (2-3 printing layers) for a humidity range of 20-80%. The sensor response in the form of current pulses associated with human breathing has a range of ∼2-3 orders of magnitude. Two different processes are assumed to determine the form of the current pulse: the first is a fast process with a rise time of less than 1-4 seconds; the second is a relatively slow process with a front time of several tens of seconds. When touching with a finger (useful, for instance, for a flexible touchpad), a current response was observed as pulses of ∼2-3 orders of magnitude. We hypothesize that skin sweat is likely to play a critical role in the sensory response. Thus, this work presents an effective approach to creating a highly sensitive humidity sensor based on composite 2D materials. Moreover, the ultra-high sensitivity of the studied sensors is accompanied by their low cost and ease of manufacturing by 2D-printing.

High-sensitivity humidity and temperature sensor by cascading a polyimide coated long period fiber grating and a polydimethylsiloxane wrapped Mach-Zehnder interferometer.

Two different structures, long period fiber grating (LPFG) and a Mach-Zehnder interferometer (MZI), were cascaded to fabricate a sensor for sensing humidity and temperature simultaneously. Due to the humidity sensitive characteristic of polyimide (PI) and the temperature sensitive characteristic of polydimethylsiloxane (PDMS), the LPFG was coated with PI and the MZI was wrapped in PDMS to improve the humidity and temperature sensitivities, respectively. Humidity and temperature experiments and the stability and repeatability of the proposed sensors were performed. The sensor shows humidity and temperature sensitivities of ∼164 pm/%RH and 183 pm/°C in the humidity and temperature increasing experiments, respectively. Combining increasing, decreasing, and repeatable experiments of temperature and humidity, the proposed sensor shows stable performance in humidity sensitivity of ∼159 pm/%RH and temperature sensitivity of ∼175 pm/°C, with good linearity of ∼0.994. The structure of the proposed sensor has the advantages of low implementation cost, easy fabrication, and good stability.

High sensitive humidity sensor based on PEDOT:PSS/CMC-Na coated polyester fabric with directional moisture transport performance

Flexible humidity sensors with excellent flexibility and sensitivity have been widely used in various fields such as human and plant health monitoring and management, non-contact human-machine interaction, smart e-textiles, and industrial and agricultural production. However, many sensors are limited their application due to the problems of unbreathable and poor wear comfort. Herein, a highly sensitive humidity sensor based on flexible polyester fabric with directional moisture transport is proposed. The facile method of coating is conducted by the preparation of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and sodium carboxymethylcellulose (CMC-Na) paste with adjustable content and applied to the polyester fabric. The difference of hydrophilicity between the two sides of the fabric caused by the coating helps to directional moisture transport, thus giving rapid sensitivity, while using PEDOT: PSS can obtain the changes of electrical conductivity coming from the humidity. and the addition of CMC-Na not only helps the coating, but also provides hydrophilic groups, which is conducive to humidity sensing and directional moisture transport. The combination of this moisture-sensitive coating and directional moisture transport gives the sensor a fast humidity response time of 0.35 s, a wide humidity detection range (0‐100%(0–100% RH) and sensitivity of 4.15. Furthermore, the sensor can maintain the humidity response time in milliseconds even after being subjected to water washing and friction, indicating its excellent durability and stability.

Preparation of Reduced Graphene Oxide Sheets with Large Surface Area and Porous Structure for High-Sensitivity Humidity Sensor

Humidity sensors provide environmental conditions suitable for several applications. However, they suffer from a limited reliable range originating from the low electrical conductivity and low water-sensitive sites of humidity-sensing materials. In this study, we developed high-sensitivity humidity sensors based on holey-reduced graphene oxide (HRGO) with a large surface area (274.5 m2/g) and an abundant pore structure. HRGO was prepared via the H2O2-etching-reaction-assisted hydrothermal processing of graphene oxide sheets. The resulting humidity sensor exhibited high sensitivity (−0.04317 log Z/%RH, R2 = 0.9717), a fast response time (<3 s), and long-term stability over 28 days. The impedance responses of the humidity sensor were almost similar between the mechanically standard and bent states. Furthermore, electrochemical impedance spectroscopy was performed to understand the humidity-sensing mechanism of the HRGO materials.

High-sensitive humidity sensor based on MoS2/graphene oxide quantum dot nanocomposite

In this work, a high sensitivity humidity sensor based on Molybdenum disulfide/graphene oxide quantum dot (MoS2/GOQD) composite film was proposed. The humidity sensitive thin film of MoS2/GOQD was deposited on Au interdigitated microelectrodes via a facile drop-coating technique. The sensing characteristics of the MoS2/GOQD composite film sensor were investigated against various relative humidity (RH) at room temperature. The experimental results indicated that MoS2/GOQD composite film sensor possessed a high sensitivity of 369 pF/%RH, which is about twenty times larger than that of pure MoS2 based humidity sensor. Moreover, the sensor exhibited a good repeatability, rapid response/recovery speed, low hysteresis, and good long-term stability. Furthermore, the underlying humidity sensitivity enhancement mechanism of the fabricated sensor was analyzed and discussed in detail. This research demonstrates that the MoS2/GOQD composite film is a promising sensitive material for fabricating a high sensitivity humidity sensor.

Correction to: High-sensitivity fiber-optic humidity sensor based on microfiber overlaid with niobium disulfide

Correction to: High-sensitivity fiber-optic humidity sensor based on microfiber overlaid with niobium disulfide

Aerosol-Printed MoS2 Ink as a High Sensitivity Humidity Sensor.

Molybdenum disulfide (MoS2) is attractive for use in next-generation nanoelectronic devices and exhibits great potential for humidity sensing applications. Herein, MoS2 ink was successfully prepared via a simple exfoliation method by sonication. The structural and surface morphology of a deposited ink film was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). The aerosol-printed MoS2 ink sensor has high sensitivity, with a conductivity increase by 6 orders of magnitude upon relative humidity increase from 10 to 95% at room temperature. The sensor also has fast response/recovery times and excellent repeatability. Possible mechanisms for the water-induced conductivity increase are discussed. An analytical model that encompasses two ionic conduction regimes, with a percolation transition to an insulating state below a low humidity threshold, describes the sensor response successfully. In conclusion, our work provides a low-cost and straightforward strategy for fabricating a high-performance humidity sensor and fundamental insights into the sensing mechanism.

A high-sensitivity, fast-response and high-stability humidity sensor of curly flake Ti3C2Tx MXene prepared by electrolytic intercalation of NaOH solution

A high-sensitivity humidity sensor based on curly flake Ti3C2Tx MXene obtained by rapid NaOH electrolytic intercalation.

Porous Nanostructured Gadolinium Aluminate for High-Sensitivity Humidity Sensors.

This paper presents the synthesis of gadolinium aluminate (GdAlO3), an oxide compound with a perovskite structure, for applications as a capacitive and/or resistive humidity sensor. Gadolinium aluminate was synthesized by the sol-gel self-combustion method. This method allowed us to obtain a highly porous structure in which open pores prevail, a structure favorable to humidity sensors. Most of the materials studied as capacitive/resistive humidity sensors have significant sensitivities only with respect to one of these types of sensors. In the case of the studied gadolinium aluminate with p-type electric conductivity, the relative humidity of the air has a significant influence on both capacitive and resistive types of electric humidity sensors. The capacity increases about 10,000 times, and the resistance decreases about 8000 times as the relative humidity increases from 0 to 98%. The investigated gadolinium aluminate can be used successfully to obtain high-sensitivity capacitive and/or resistive humidity sensors.

Supercontraction of spider dragline silk for humidity sensing.

The spider dragline silk (SDS) has a supercontraction characteristic, which may cause the axial length of the SDS to shrink up to 50% when the SDS is wet or the relative humidity is higher than 58% RH. In this manuscript, we employ the supercontraction characteristic of the SDS to measure relative humidity. We connect two sections of a single-mode fiber (SMF) and a section of multimode fiber (MMF) with a sandwich structure to fabricate a single-mode-multimode-single-mode (SMS) interferometer. Then we fix the SDS on two SMFs to configure a bow-shaped sensing unit. The increase of environmental humidity will cause the supercontraction of the SDS, which will cause the change of the SDS length. The excellent mechanical properties of the SDS will generate a strong pulling force and change the bending of the arch, whose interference spectrum will shift correspondingly. In this way, we may perform relative humidity sensing. In the relative humidity range of 58% RH to 100% RH, the average sensitivity is as high as 6.213 nm/% RH, higher than most fiber-based humidity sensors. Compared with the traditional sensing structure with humidity-sensitive materials, the proposed sensor improves the sensitivity with environmental friendliness. The results suggest that the SDS can be used for high-sensitivity humidity sensors, and its degradability and biocompatibility also have a vast development space in biochemical sensors.

High-sensitivity humidity sensor based on natural hydroxyapatite

In the present work, we study the ability of materials based on hydroxyapatite to be developed as a sensing materials toward relative humidity. Natural (NHAp) and synthetic (SHAp) hydroxyapatites are used as sensitive layers on interdigitated copper electrodes. The morphological structure and composition of HAp are characterized by X-ray diffraction analysis (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy EDS. The capacitive and impedance responses of the humidity sensors are analyzed at frequencies ranging from 0.1 kHz to 1 MHz at different humidity values varying from 16 to 87%. Other properties and characteristics of moisture detection are studied for both sensors such as sensitivity, hysteresis, response and recovery times and conduction mechanisms. The results showed that the best performance of all our manufactured sensors is obtained for the NHAp sensor. This sensitivity is around 17900pF/%RH, whereas the response and recovery times are approximately 8 s and 11 s, respectively, the hysteresis value was very low. The obtained results proved that the natural hydroxyapatite is a good candidate and suitable for moisture sensing application.

Flexible Noncontact Sensing for Human–Machine Interaction

From typical electrical appliances to thriving intelligent robots, the exchange of information between humans and machines has mainly relied on the contact sensor medium. However, this kind of contact interaction can cause severe problems, such as inevitable mechanical wear and cross-infection of bacteria or viruses between the users, especially during the COVID-19 pandemic. Therefore, revolutionary noncontact human-machine interaction (HMI) is highly desired in remote online detection and noncontact control systems. In this study, a flexible high-sensitivity humidity sensor and array are presented, fabricated by anchoring multilayer graphene (MG) into electrospun polyamide (PA) 66. The sensor works in noncontact mode for asthma detection, via monitoring the respiration rate in real time, and remote alarm systems and provides touchless interfaces in medicine delivery for bedridden patients. The physical structure of the large specific surface area and the chemical structure of the abundant water-absorbing functional groups of the PA66 nanofiber networks contribute to the high performance synergistically. This work can lead to a new era of noncontact HMI without the risk of contagiousness and provide a general and effective strategy for the development of smart electronics that require noncontact interaction.

Highly sensitive and rapid responding humidity sensors based on silver catalyzed Ag2S-TiO2 quantum dots prepared by SILAR.

We developed a resistive humidity sensor based on a heterojunction of silver sulfide (Ag2S) quantum dots (QDs) and TiO2 because of its specificity to water vapor adsorption and its insensitivity to environmental gases. The QDs were grown on a mesoporous TiO2 layer using the successive ionic layer adsorption and reaction (SILAR) method. The boundary condition between TiO2 and Ag2S provides a tunable energy gap by adjusting the number of SILAR cycles. Besides, the large surface-to-volume ratio of QDs provides a strong water vapor adsorption ability and electron transfer. Nano-silver precipitated during the SILAR process provides free electrons and lowers the Fermi level to between n-type TiO2 and p-type Ag2S. The resistance response increased significantly to 4600 and the reaction equilibrium time decreased greatly to 7 seconds due to the presence of nano-silver. Finally, the Ag2S QDs possess a best sensing range of 13–90%. To sum up, Ag2S QDs are high sensitivity and selectivity humidity sensors.

High sensitive and fast response humidity sensor based on polymer composite nanofibers for breath monitoring and non-contact sensing

A rapid and stable polymeric humidity sensor is demonstrated using electrospun sulfonated poly (ether ether ketone)/polyvinyl butyral (SPEEK/PVB) composite nanofiber and applied in breath monitoring and non-contact sensing for the first time. First, SPEEK was fabricated into thin film sensor by drip casting and nanofiber sensor by electrospinning, respectively. By comparing the humidity sensing characteristics of the two sensors, it is found that the hysteresis and response/recovery time of the nanofiber humidity sensor have been significantly improved. To further improve its sensing performance, we incorporated different contents of polyvinyl butyral (PVB) to the electrospinning solution to prepare SPEEK/PVB composite nanofiber humidity sensors. The morphology and diameter of nanofibers with different PVB contents were observed by Scanning Electron Microscope. The composite nanofiber humidity sensor exhibited high sensitivity, wide working range of relative humidity, small hysteresis (2.68 %), fast response time (<1 s), rapid recovery time (5 s) and stable sensing performance when the ratio of SPEEK to PVB is 1:3. In addition, the breath monitoring and non-contact sensing performance of SPEEK/PVB = 1:3 composite nanofiber humidity sensor was also studied. This work indicates that electrospun SPEEK/PVB nanofibers have good application prospects as humidity sensors for real-time humidity monitoring and non-contact sensing devices.