Humidity Sensor Applications Research Articles

Properties of ZnO with Oxygen Vacancies and Its Application in Humidity Sensor

Properties of ZnO with Oxygen Vacancies and Its Application in Humidity Sensor

Fabrication of quartz crystal microbalance humidity sensors based on super-hydrophilic cellulose nanocrystals

Natural cellulose nanocrystals (CNCs) possess outstanding properties, such as biodegradability, hydrophilicity, large specific surface areas, and are low in cost. A highly stable and sensitive humidity sensor based on a quartz crystal microbalance (QCM) was prepared using CNCs as the sensing film. To investigate the impact of CNCs loading on the sensor performance, a series of humidity-sensitive performance tests, including linearity, response and recovery times, repeatability, hysteresis characteristics, selectivity, and long-term stability tests, was conducted. The experimental results indicated that the humidity sensor with CNCs loading of 2 μg (QCM-2) exhibited excellent logarithmic linearity, high sensitivity (32.35 Hz/% relative humidity (RH)), excellent reversible behavior, and long-term stability at a RH of 11–84%. The contact angle of QCM-2 was 12.5°, revealing its suitable hydrophilicity. Thus, we demonstrate that CNCs are great prospects for potential application in humidity sensors with high performance and low cost.

A reversible and fast-responsive humidity sensor based on a lead-free Cs2TeCl6 double perovskite

Owing to their high conductivity and carrier mobility, the outstanding achievements of lead halide perovskites have been demonstrated in humidity sensor applications.

Humidity sensor based on poly(lactic acid)/PANI-ZnO composite electrospun fibers.

The electrospinning technique has been successfully used to prepared micro-fibers of the poly(lactic acid)/polyaniline–zinc oxide (PLA/PANI–ZnO) composite. The polyaniline–zinc oxide (PANI–ZnO) nanocomposites are synthesized by hydrothermal and in situ polymerization methods. X-ray diffraction techniques are used to study the structural properties of the PLA/PANI–ZnO composite fibers and the PANI–ZnO nanocomposite. The average crystallite size of the PANI–ZnO nanocomposite is found to be 36 nm. The morphology and diameter of the composite fibers are analyzed by scanning electron microscopy (SEM). The average fiber diameter of the pure poly(lactic acid) (PLA) fiber is around 2.5 μm and that of the PLA/PANI–ZnO composite fiber is around 1.4 μm. Differential scanning calorimetry (DSC) provides the thermal properties of the PLA/PANI–ZnO composite fibers. The melting temperature (Tm) for the pure PLA is observed at 149.3 °C, and it is shifted to 153.0 °C for the PLA/PANI–ZnO composite fibers. The enhanced thermal properties of the composite fibers are due to the interaction between the polymer and the nanoparticles. The water contact angle measurements probe the surface hydrophilicity of the PLA/PANI–ZnO composite fibers. The role of the PANI–ZnO nanocomposite on the sensing behavior of PLA fibers has also been investigated. The humidity sensing properties of the composite fiber based sensor are studied in the relative humidity (RH) range of 20–90% RH. The experimental results show that the composite fiber exhibited good response (85 s) and recovery (120 s) times. These results indicate that the one-dimensional (1D) fiber structure enhances the humidity sensing properties.

A review on Ti3C2Tx-based nanomaterials: synthesis and applications in gas and humidity sensors

Ti3C2Tx, which is a novel two-dimensional (2D) material, has received enormous interest in the field of sensor technology due to its large surface area, excellent electrical conductivity, and abundant active surface sites. In recent years, several Ti3C2Tx-based gases and humidity sensors have been developed and reported. In this review, we focus on the latest applications of Ti3C2Tx-based nanomaterials in gas and humidity sensors. First, the synthesis of Ti3C2Tx from the dangerous fluorine-containing etching process to the safe fluorine-free preparation method was discussed, and the structures of the Ti3C2Tx controlled by different delamination methods were also outlined. Subsequently, the functionalization of pristine Ti3C2Tx and composite strategies for enhancing its gas and humidity sensing performance were reviewed. In addition, the gas and humidity sensing mechanisms of sensors based on Ti3C2Tx were also summarized. Finally, the challenges and opportunities for the use of Ti3C2Tx gas and humidity sensors were discussed to provide guidance on the promising potential of Ti3C2Tx in this field.

The effect of Adding (ZrC) Nanoparticles to (PVP-PVA) Blend on their Optical properties for Humidity Sensor Application

The optical properties for adding (ZrC) nanoparticles to (PVP-PVA) were studied. The Poly(vinyl alcohol) and poly(vinyl pyrrolidone) were blended and films were obtained by the casting method. Zirconium carbide nanoparticles (ZrC) were added with different weight percentages (4 wt.%, 8 wt.%, 12 wt.% and 16 wt.%) to the (PVP-PVA) blend. The wavelength range used to measure the optical properties is (220-820) nm. Analyzing the results it is found that the absorbance (A) decrease by increasing the (ZrC) nanoparticles concentrations, while the coefficient of absorption (α), coefficient of extinction (k), index of refraction and the constants of real and imaginary (∈ 1, and ∈ 2) increased by increasing the concentration of (ZrC) nanoparticles. The gap of energy (Eg ) of (PVP-PVA) blend increases with the increasing of (ZrC) nanoparticles weight percentages.

Effect of cerium on structural, microstructural, magnetic and humidity sensing properties of Mn–Bi ferrites

In this report novel material Cerium doped Mn–Biferrite nanoparticles were synthesized by adopting a modified solution combustion route. X-ray diffraction patterns confirm the spinel cubic structure with single phase having space group Fd3m. The crystallite size decreases with increase in Ce3+ concentration. The scanning electron microscopy (SEM) micrographs show that the particles are agglomerated. The humidity sensing properties were investigated through resistance measurements, sensing response, recovery time, hysteresis and stability studies measurements. As per investigation the resistance decreases with increase in relative humidity from 11% to 97%. The sensing response values increases with increase in Ce3+ concentration. The response and recovery time study reveals the sample have quick response and recovery time. The magnetic hysteresis curves revealed that synthesized samples exhibits ferrimagnetic nature, the saturation magnetization and remanent magnetization decreases with the increase in Ce3+ concentration. Hence synthesized materials are good candidate for humidity sensor applications.

Research Progress of Graphene-Based Flexible Humidity Sensor.

Graphene is a new type of carbon material with a flexible, two-dimensional structure. Due to the excellent stability of its lattice structure and its mechanical flexibility, graphene-based materials can be applied in flexible humidity sensors. At present, the application of graphene-based flexible humidity sensors in the fields of medical care and environmental monitoring is attracting widespread attention. In this review, the basic properties of graphene oxide (GO) and reduced graphene oxide (rGO) as moisture-sensitive materials and methods for their preparation were introduced. Moreover, three methods for improving the performance of moisture-sensitive materials were discussed. The working principle of different types of graphene-based humidity sensors were introduced. The progress in the research on graphene-based flexible humidity sensors in four respects: Human respiration, skin moisture, human sweat, and environmental humidity were discussed. Finally, the future research, following the development trends and challenges, to develop the potential of integrated, graphene-based flexible humidity sensors were discussed.

Flexible humidity sensors for wireless monitoring based on electrospun sulfonated polyether ether ketone (SPEEK) nanofibres

The development of flexible and high-performance humidity sensors for continuous wireless monitoring is receiving increasing attention. In this work, electrospun sulfonated polyether ether ketone (SPEEK) nanofibres with different sulfonation degrees were prepared and directly deposited onto flexible substrates for humidity sensor applications. On a logarithmic scale, both resistance (Rdc) and capacitance (Cs) of the SPEEK nanofibre-based sensors showed linear responses to changes between 30 and 80 % in relative humidity (RH). Our devices showed higher sensitivities (up to LogRdc(Ω)/RH(%) = -0.06952 and LogCs(F)/RH(%) = 0.07078) and improved linearity (over 0.980) than humidity sensors using continuous SPEEK films. The humidity sensors exhibited fast sensing responses (75 s), mechanical flexibility and durability. These beneficial properties can be attributed to the fibrous structure of electrospun SPEEK. The potential of SPEEK fibre-based humidity sensor was further demonstrated by monitoring real-time humidity levels using a printed near-field communication (NFC)-enabled circuit for wireless sensing.

Enhanced humidity sensing and magnetic properties of bismuth doped copper ferrites for humidity sensor applications

In present investigation, the CuFe(2-x)BixO4 (where, x = 0.00, 0.01, 0.02, 0.03) nanoparticles synthesized by solution combustion technique using mixture of fuels as glucose and carbamide. The refined XRD (X-ray diffraction) patterns of the samples confirms the spinel cubic structure having space group Fd3m. The average crystallite size was found to be in nanometer. The lattice parameter, volume, strain and hopping lengths were estimated. TEM (Transmission Electron Microscopy) micrographs confirm the particles are agglomeration. SAED (Selected Area Electron Diffraction) pattern reveals the polycrystalline nature of the material. The magnetic nature of spinel ferrite can be explained by Neel’s two sub-lattice model. In the present work, the observed decrease in magnetization can be ascribed to occupancy and migration of cations at/from B sites by the substitution of Bi3+ ions. The magnetic parameters such as saturation magnetization, remanent magnetization (Mr), coercivity field (Hc), remanence (S), uniaxial anisotropy (Ku) and cubic anisotropy (Kc) were estimated. The resistance and humidity sensing responses increases with increase of the Bi3+ concentration. The hysteresis curves reveal the desorption process is somewhat slower than the adsorption process. The sensing response time 73 s was recorded when sample was moved from 11% RH to 97% RH and the recovery time 36 s was recorded when sample was moved from 97% RH to 11% RH. The humidity sample shows exceptionally stable response at relative humidity 99% RH and 33% RH.

Fabrication of leaf shaped SnO2 nanoparticles via sol–gel route and its application for the optoelectronic humidity sensor

In this report, synthesis of nanostructured SnO2via sol–gel technique and its application for the detection of humidity level has been studied. Scanning electron microscopy (SEM) micrographs showed the formation of uniform leaf like structured SnO2 nanoparticles. The average crystalline size is discovered as 9 nm calculated by Debye Scherrer’s formula using X-ray diffraction (XRD) which shows tetragonal crystal structure. The crystallite size is further confirmed by transmission electron microscopy (TEM). The optical band gap is estimated as 3.63 eV by UV–Visible absorption spectra. The prepared SnO2 based thin film with leaf like structure enhances the feasibility for the detection of humidity, especially in the high range of 65–90 %RH. The prepared SnO2 samples shows good sensitivity towards the relative humidity. It shows 1.8nW/% RH in the humidity range 65–90% RH at 25 °C.

Synthesis of In Situ Photoinduced Halloysite-Polypyrrole@Silver Nanocomposite for the Potential Application in Humidity Sensors.

Halloysite-polypyrrole-silver nanocomposite has been prepared via in situ photopolymerizations of pyrrole in the presence of silanized halloysite and silver nitrate as a photoinitiator. The halloysite nanoclay (HNT) was modified using the hydrogen donor silane coupling agent (DMA) in order to provide anchoring sites for the polypyrrole/silver composite (PPy@Ag). The mass loadings for both PPy and Ag have been estimated to be 21 and 26 wt%, respectively. The anchored Ag particles were found in the metallic state. The resulting PPy@Ag-modified silanized HNT has been evaluated for the potential application for impedance humidity sensors. HNT-DMA-PPy@Ag nanocomposite with different weight % of PPy@Ag (0.25 wt%, 0.5 wt%, and 1 wt%) was deposited on the pre-patterned interdigital Indium Tin Oxide (ITO) electrodes by spin coating technique. The addition of Ag nanoparticles within the nanocomposite enhances the hydrophilicity of the sensing film, which improves the sensitivity of the humidity sensors. The HNT-DMA-PPy@Ag (0.5 wt%) nanocomposite-based impedance sensors showed good sensitivity and lowered hysteresis as compared to the other ratios of the composite. The maximum calculated hysteresis loss of the HNT-DMA-PPy@Ag (0.5 wt%)-based humidity sensor is around 4.5% at 80% RH (relative humidity), and the minimum hysteresis loss estimated to be 0.05% at 20% RH levels. The response and recovery time of HNT-DMA-PPy@Ag (0.5 wt%) nanocomposite-based impedance sensors were found to be 30 and 35 s, respectively. The interesting humidity-dependent impedance properties of this novel composite make it promising in humidity sensing.

Thermally reduced graphene oxide showing n- to p-type electrical response inversion with water adsorption

Graphene oxide (GO) is regarded as one of the potential candidates for gas and humidity sensor applications owing to its excellent water adsorption capabilities. However, there is a lack of understanding the response of GO to humidity. Some authors believe the water adsorption leads to p-type response while other think it to be n-type. The present work demonstrates the mechanism of water adsorption and n- to p-type response inversion of GO to humidity. The GO suspension was synthesised by modified Hummers’ method and then drop-casted onto the substrates having already patterned gold interdigital electrodes (IDE). The sensors can detect wide humidity range (5–95 %RH) with a low voltage 0.1 V leading to low power consumption <10−5 W. It is also found that rGO samples annealed at temperature below 150 °C show n-type (e.g. Rair/RRH ~ 1.29 × 105 for rGO-40) while the samples annealed above this temperature demonstrate p-type humidity response (e.g. RRH/Rair ~ 40 for rGO-150). The static test response time is 8 s, while recovery time is 13 s with excellent long-term stability and RH accuracy value (±4% RH). Further characterization are performed to elucidate the physio-chemical model of the sensing mechanism as well as n- to p-type conductivity inversion under humidity.

Paper-Based Sensors for Gas, Humidity, and Strain Detections: A Review.

Paper, as a flexible, low-cost, lightweight, tailorable, environmental-friendly, degradable, and renewable material, is emerging in electronic devices. Especially, many kinds of paper-based (PB) sensors have been reported for wearable applications in recent years. Among them, the PB gas, humidity, and strain sensors are widely studied for monitoring gas, humidity, and strain from the human body and the environment. However, gas, humidity, and strain often coexist and interact, and the paper itself is hydrophilic and flexible, resulting in that it is still challenging to develop high-performance PB sensors specialized for gas, humidity, and strain detections. Therefore, it is necessary to summarize and discuss them systematically. In this review, we focus on summarizing the state-of-art studies of the PB gas, humidity, and strain sensors. Specifically, the fabrications (electrodes and sensing materials) and applications of PB gas, humidity, and strain sensors are summarized and discussed. The current challenges and the potential trends of PB sensors for gas, humidity, and strain detections are also outlined. This review not only can help readers to understand the development status of the PB gas, humidity, and strain sensors but also is helpful for readers to find out and solve the problems in this field through comparative reading.

Rapid response humidity sensor based on DC magnetron sputtered Mn1.2Co1.5Ni0.3O4 thin film

This paper reported a Mn1.2Co1.5Ni0.3O4 thin film humidity sensor prepared according to the DC magnetron sputtering method. Scanning electron microscopy (SEM) was conducted to determine the morphology and microstructure of the film. The crystal structure and composition of the thin film were characterized by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS), respectively. The impedance of the film changed by three orders of magnitude within the relative humidity (RH) range of 11% to 95% RH. Moreover, the response time and recovery time were shortened to 0.3 s and 3 s, respectively, as the deposition power decreased. The above results indicated that, the as-prepared Mn1.2Co1.5Ni0.3O4 thin film was an excellent candidate for humidity sensor applications.

Diamine decorated graphene oxide film on quartz crystal microbalance for humidity-sensing analysis

Graphene oxide (GO) materials using various synthetic processes and amination were deposited on quartz crystal microbalance (QCM) device for humidity sensor application. Characteristics of various GO materials including surface morphology and functional groups were investigated by SEM images equipped with EDX, Fourier transform infrared spectra (FTIR) and Raman spectra. Hydrophilic property was identified by contact angle measurement. Mechanism of humidity-sensing performance are were adopted to analyze the moisture sensitivity of GO loaded QCM sensors ranging from 23% to 92% relative humidity. In this study, GO produced by strong reductant (NaNO3) and temperature control combined with amination process could generate much intercalate functional groups and high hydrophilic property. High adsorption of water molecules in graphene oxide produce large interlayer expansion of GO layers, resulting in crystal motional resistance increase, energy loss and broaden peak pattern. In humidity-sensing property, amine GO exhibits quick humidity response/recovery (10 s/11 s) sensitivity and high Q-factor, thus amination of GO film can be a candidate for future humidity sensor material.

Graphene oxide-polyvinyl alcohol film in micro cavity for optical comb filter generation

An optical comb filter which is usually based on low pass characteristics is an excellent component for removing unwanted noise from high frequency spectra in data transmissions and signal processing. A simple interferometric based micro-cavity is proposed to generate an optical comb filter. Graphene oxide (GO)-polyvinyl alcohol (PVA) film was fabricated through a modified Hummer's method from graphite flakes. A micro cavity with a Fabry-Perot interferometer is supplied with an amplified spontaneous emission (ASE) through a single mode optical coupler. The comb filter started to form as the distance was set to over 100 μm owing to the interference effect in the micro cavity as the Fabry-Perot interferometer configuration was used to vary the distance from the fibre tip. The free spectral range, extinction ratio, quality factor, and finesse of the generated comb were recorded from 100 μm up to 400 μm, with the 400 μm distance exhibiting a more stable and efficient comb. The micro cavities parameters were compared with those with no GOPVA and both outputs were recorded. At 400 μm, GO-PVA film generated the most stable optical comb filter of free spectral range, extinction ratio, quality factor, and finesse of 1.94 nm, 11.74 dB, 997.54, and 1.24, respectively. With the advantage of the hydrophilic nature of GO, the device can be implemented in humidity sensor applications.

Analyzing the effect of the Front-end circuit for the FBAR sensor

The FBAR sensor can be affected severely by its front-end circuit, especially the phase noise; however, it has rarely been discussed up to now. Herein, we analyze the influence of phase noise in the front-end circuit on an FBAR humidity sensor. A frequency shift detecting system was designed combined with the theoretical calculation and Advanced Design System (ADS) simulation. The available range of frequency shift is seriously influenced by phase noise particularly for its lower limit, improved from 380 kHz to 200 kHz during the reduction of phase noise from − 107.92 dBc/Hz@1 MHz to − 135.97 dBc/Hz@1 MHz. Simultaneously, the display range for the FBAR humidity sensor system increases by 23% thanks to the reduction of it by − 28 dBc/Hz@1 MHz. Summarily, the phase noise optimization in the front-end circuit can effectively improve the display range of sensor systems, which is not limited to the application of FBAR humidity sensors.

Testing and Characterization of Different Papers as Substrate Material for Printed Electronics and Application in Humidity Sensor

Testing and Characterization of Different Papers as Substrate Material for Printed Electronics and Application in Humidity Sensor

Humidity sensor applications based on mesopores LaCoO3

Humidity sensor plays a pivotal role in determining the quality of products and the precision of instruments. In order to measure and control humidity, LaCoO3 mesopores sensor was prepared by a modified citrate technique. The sample was characterized by X-ray diffraction, Field emission scanning electron microscopy, High resolution transmission electron micrographs, Energy dispersive X-ray spectroscopy and Brunauer–Emmet–Teller. LaCoO3 exhibits rhombohedral distorted perovskite crystal structure with R3c space group. The humidity-sensing properties were investigated in a wide range of working humidity (11–97% RH) and frequency (100 Hz–100 kHz). The obtained results confirm that the optimum measuring frequency is 1 kHz. A great advantage of LaCoO3 is its porosity, which is essential for a humidity sensor. These pores serve as humidity adsorption sites. Another advantage is its high resistivity, which is reduced by approximately eight times its normal magnitude with increasing the surrounding humidity. The average crystallite size and surface area of the sample are 12.88 nm and 154.125 m2/g respectively. According to VSM results, the hysteresis loop of the sample indicates its paramagnetic nature. Furthermore, the ferroelectric hysteresis loop, that was observed at room temperature, implies the antiferroelectric nature of LaCoO3 nanoparticles. The obtained data confirms that the LaCoO3 sample is very sensitive to humidity and can be commercially used as a humidity sensing element.