Capacitive Humidity Research Articles

IOT BASED SOUND AND AIR POLLUTION MEASURING TEMPERATURE AND HUMIDITY MONITORING SYSTEM

Now a day in metropolitan cities air and sound pollution becomes serious issues, because of high decibels and toxic gases present within the environment which directly effect on human health and thus needs a special attention. Therefore, it's now become necessary to regulate the pollution (air and noise) to ensure healthy livelihood and better future. In this paper, an efficient implementation for Internet of Things is employed for monitoring atmospheric conditions of environment like air pollution and noise pollution. And also we monitor The Temperature and Humidity. Using MQ7 sensor for sensing Carbon Monoxide (CO) and MQ135 gas Sensor for detecting wide range of gases, including NH3, NOx, alcohol, benzene, smoke and CO2.constantly transmit this data. Also, system keeps measuring sound level using MIC sensor and reports it. DHT11 sensor consists of a capacitive Humidity sensing element and Thermistor for sensing Temperature. Soil moisture is the amount of water in the soil. Soil moisture monitoring system that helps the govt authorities to understand the data about dry soil areas within the agricultural lands within a village, town or maybe a state so that the required precautionary steps will be taken to create such lands fertile.

Design of Experiments and Optimization of Laser-Induced Graphene.

Realization of graphene-based sensors and electronic devices remains challenging, in part due to integration challenges with current fabrication and manufacturing processes. Thus, scalable methods for in situ fabrication of high-quality graphene-like materials are essential. Low-cost CO2 laser engravers can be used for site-selective conversion of polyimide under ambient conditions to create 3-D, rotationally disordered, few-layer, porous, graphene-like electrodes. However, the influences of non-linear parameter terms and interactions between key parameters on the graphitization process present challenges for rapid, resource-efficient optimization. An iterative optimization strategy was developed to identify promising regions in parameter space for two key parameters, laser power and scan speed, with the goal of optimizing electrode performance while maximizing scan speed and hence fabrication throughput. The strategy employed iterations of Design of Experiments Response Surface (DoE-RS) methods combined with choices of readily measurable parameters to minimize measurement resources and time. The initial DoE-RS experiment set employed visual response parameters, while subsequent iterations used sheet resistance as the optimization parameter. The final model clearly demonstrates that laser graphitization through raster scanning is a highly non-linear process requiring polynomial terms in scan speed and laser power up to fifth order. Two regions of interest in parameter space were identified using this strategy: Region 1 represents the global minimum for sheet resistance for this laser (∼16 Ω/sq), found at a low scan speed (70 mm/s) and a low average power (2.1 W) . Region 2 is a local minimum for sheet resistance (36 Ω/sq), found at higher values for scan speed (340 mm/s) and average power (3.4 W), allowing ∼5-fold reduction in write time. Importantly, these minima do not correspond to constant ratios of average laser power to scan speed. This highlights the benefits of DoE-RS methods in rapid identification of optimum parameter combinations that would be difficult to discover using traditional one-factor-at-a-time optimization. Verification data from Raman spectroscopy showed sharp 2D peaks with mean full-width-at-half-maximum intensity values <80 cm–1 for both regions, consistent with high-quality 3D graphene-like carbon. Graphene-based electrodes fabricated using the parameters from the respective regions yielded similar performance when employed as capacitive humidity sensors with hygroscopic dielectric layers. Devices fabricated using Region 1 parameters (16 Ω/sq) yielded capacitance responses of 0.78 ± 0.04 pF at 0% relative humidity (RH), increasing to 31 ± 7 pF at 85.1% RH. Region 2 devices (36 Ω/sq) showed comparable responses (0.88 ± 0.04 pF at 0% RH, 28 ± 5 pF at 85.1% RH).

Ingestible, Biofriendly, and Flexible Flour-Based Humidity Sensors with a Wide Sensing Range

Ecofriendly and biofriendly materials are highly appealing in electronic devices with the booming development of the Internet of Things. Humidity sensors perform an indispensable role in various fields such as monitoring industry processes and living systems. In this contribution, for the first time, edible and abundant material-flour has been introduced to the sensing layers for humidity detection. The ionic conductive K2CO3 and hygroscopic glycerol (Gly) with biosafety were introduced to the sensing layer to promote a humidity sensing capability and long-time stability. The ingestible Gly-K2CO3 flour-based humidity sensor using PLA as substrates displays an excellent sensing performance and wide humidity detecting range. Good linearity between capacitance and relative humidity (RH) has been achieved for the RH range from 6% to 94%. According to a wireless monitoring system, even at 250 kHz, the sensor can still monitor the nuance of the humidity difference between 40% and 43% and exhibited an ultrafast response time (0.3 s) and recovery time (0.7 s). Furthermore, the consistent and stable sensing performance after long-time measurements for 100 days and bending tests for 500 cycles also demonstrated a long-time humidity detecting stability and mechanical flexibility for the Gly-K2CO3 flour-based humidity sensor. Humidity sensing mechanisms were thoroughly investigated through SEM-EDX, FTIR, XPS, and complex impedance spectroscopies. The enhanced sensing performance, wide humidity detecting range, and long-time stability are attributed to the ionic conductivity from K2CO3 and the hydrogen-bond interaction between H2O and enormous hydrophilic groups, such as hydroxyl and amino groups in the flour-based networks and binary solvent.

Fully inkjet-printed BaTiO3 capacitive humidity sensor: Microstructural engineering of the humidity sensing layer using bimodal ink

Humidity sensors are often used in industries where humidity levels must be monitored due to their possible effects on the manufacturing processes and products. These sensors must possess high sensitivity that can detect changes in the environment's humidity level. This paper presents a novel technique to improve the sensing performance of humidity sensors by varying the microstructure of the BaTiO3 humidity sensing layers by optimizing the mixing ratios of the bimodal inks deposited by the inkjet printing technique. By varying the mixing ratio of bimodal inks, the surface area, pore size, and packing density of the humidity sensing layers were modulated because of the incorporation of smaller particles into larger particles. The optimal sensor was produced by a 70:30 mixing ratio due to its higher surface area, which allowed a higher area for water adsorption and therefore improved the humidity sensitivity. Microstructural analyses, such as Focused-Ion-Beam Field-Emission Scanning Electron Microscope (FIB FE-SEM), image analysis, and Brunauer–Emmett–Teller (BET) were performed to examine the microstructural differences of the sensors. The fully inkjet-printed BaTiO3 capacitive sensors, which had the optimal mixing ratio, exhibited a high sensitivity of 5.75 × 105 pF/%RH, which exceeded that of most reported humidity sensors, good repeatability, a linearity of 0.989, an acceptable response and recovery time of 41 s and 34 s, respectively, low hysteresis, and good stability over a long period of time. The fabricated BaTiO3-based capacitive humidity sensor exhibited an outstanding performance that can be utilized toward various applications.

Enhanced sensitivity of zinc phthalocyanine-based microporous humidity sensors by varying size of electrode gaps

The use of organic materials has become an increasingly important issue in sensing devices in recent times. Phthalocyanine is among the most promising materials in this undertaking. Zinc phthalocyanine (ZnPc) based microporous device was fabricated and its capacitance was utilized as the sensing mechanism for a humidity sensor. The effect of the electrode gap of the device on the electrical properties was investigated along with the correlation between the device’s performances and the morphology of the sensing film. Using the solution-processed spin coating method, the capacitive type humidity sensor devices have been fabricated in a planar geometry of Al/ZnPc/Al with the presence of a microporous template. The size of electrode gaps measured with a surface profiler was 53.00 ± 0.06 μm, 119.00 ± 0.03 μm and 286.00 ± 0.01 μm. The surface morphology was characterized by using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). Analysis of the experimental results showed that the device with the shortest electrode gap (53.00 μm) produced the best sensitivity of 1.03 ± 0.04 pF/%RH than that of the longer gaps. Additionally, hysteresis as well as response and recovery performances have also been investigated.

A high-and-rapid-response capacitive humidity sensor of nanoporous anodic alumina by one-step anodizing commercial 1050 aluminum alloy and its enhancement mechanism

Anodic aluminum oxide (AAO) is a well-known nanoporous material and a template for nanotechnology application. The AAO based humidity sensor is traditionally fabricated using low-temperature (0–10 °C) two-step anodization in oxalic acid at 40 V from the expensive high-purity aluminum of small-area as well with low response and low intensity. Here, one-step anodizing commercial large-area low-purity aluminum 1050 alloy was realized for high-performance humidity sensor by hybrid-pulse anodization in 0.3 M oxalic acid at 20 V at 25 °C that merits low cost, short fabrication time and high-and-rapid capacitive response. The performance enhancement is attributed to the increased total pore area adsorption ratio and the electrode area of AAO with lower thickness to make much more water vapor molecules adsorb onto the wall surface of pores for sensing with high capacitance, response and short response-recovery time. The low-thickness pores make water molecules adsorb onto and desorb from the pores surface more quickly because of shorter diffusion path. Also, a small-area sample of traditional 40 V AAO is used as a reference for comparison. A shorter anodization time of 55 min is also fabricated for understanding the thickness effect on the response-recovery time. The large-area AAO humidity sensor of 16 cm2 at 20 V exhibits high response (above 5000 %, 3.5 times the traditional reference) and quick response-recovery time (9 s). The high-and-rapid-response enhancement mechanism of AAO capacitive humidity sensor is established.

Enhanced sensitivity of humidity sensor using Nafion/graphene oxide quantum dot nanocomposite

In this paper, a capacitance humidity sensor which was fabricated by interdigital electrodes (IDEs) coated with Nafion/graphene oxide quantum dot (GOQD) thin film was reported. The sensor could convert concentration change of moisture into capacitance change of the IDEs. The morphological and nanostructure of the prepared Nafion/GOQD nanocomposite were characterized by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), confirming that the Nafion/GOQD nanocomposite was successfully prepared. Test result showed that the proposed sensor exhibited higher sensitivity of 1025.99 pF/%RH (nearly double) and better linearity, compared with pure Nafion sensor, which could be ascribed to formation of a subordinate-assembly of 0D GOQD in the Nafion film. Furthermore, the humidity sensor exhibited excellent repeatability, fast response and recovery, and little hysteresis. It could offer a potential method to monitor the respiration. Lastly, the humidity sensing mechanism was studied through complex impedance spectra (CIS).

Fluid dynamics analysis and experimental study for solar radiation error correction of sounding humidity sensor.

In order to correct the solar radiation error of relative humidity, the mainstream capacitive sounding humidity sensor HC103M2 is selected and investigated by simulation analysis and experimental verification. First, the basic theories for solar radiation error and sensor error itself are elaborated, and simulational and experimental platforms are introduced. The computational fluid dynamics (CFD) method is utilized to theoretically investigate the dry error of the humidity sensor caused by solar radiation heating, which is related to radiation intensity, altitude, and solar elevation angle as well as reflectivity, thickness, and shape of the shield. Then, in order to verify the accuracy of the simulation, an experimental platform including a humidity sensor and two temperature sensors to measure the solar radiation heating is built to analyze the relative error of humidity obtained by the CFD simulation and experiment. It is found that their maximum deviation is 3.30% and the average error is 1.94%, which indicates that the calculation using the CFD method is accurate and feasible. In order to easily and operationally predict the solar radiation heating of the humidity sensor, a back propagation (BP) neural network fusion algorithm based on three inputs of radiation intensity, air pressure, and solar elevation angle is proposed. Compared with the solar radiation heating obtained by CFD simulation, the maximum absolute error is about 0.2K, and the relative error of humidity is about ±1.30%. Finally, a case of vertical humidity profile correction considering the temperature-sensitive error of HC103M2 is analyzed. The response time of sensor measurement and the airflow into the shield are discussed as well. The corrected results after taking solar radiation heating into account are more similar to those measured by RS92 and cryogenic frost point hygrometer (CFH). This result shows that the prediction model is accurate, which may be applied to correct the dry error and further improve the accuracy of humidity measurement.

Ultrafast-response/recovery capacitive humidity sensor based on arc-shaped hollow structure with nanocone arrays for human physiological signals monitoring

Abstract Flexible humidity sensors have attracted substantial attention due to the promising application in medical health monitoring. Up to now, the realization of such devices with ultrafast response/recovery and controllable morphology via a facile and cost-effective approach still remains a severe challenge. Herein, a high-performance flexible capacitive humidity sensor by creating the arc-shaped hollow structure with the poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] nanocone arrays is developed. Particularly, a facile method based on combining the hot-pressing method and the anodized aluminum oxide template transfer method is proposed to realize the large-scale preparation of the nanostructure arrays with controllable morphology. Benefiting from the open arc-shaped hollow structure and the large-area P(VDF-TrFE) nanocone arrays, the proposed humidity sensor shows several conspicuous features, such as ultrafast response/recovery time (3.693/3.430 s), long-term stability (25 days), excellent bending stability (10,000 cycles), unaffected capacitance response to humidity in a certain temperature range (20−50℃) and high selectivity toward water vapor. The above salient superiorities enable the proposed humidity sensor to be successfully utilized in extraction of a variety of physiological signals including breathing detection, skin noncontact sensing, and real-time monitoring of diaper wetting process and skin humidity, which reveals great potential value in prevention and diagnosis of many diseases.

Quaternary Oxidized Carbon Nanohorns—Based Nanohybrid as Sensing Coating for Room Temperature Resistive Humidity Monitoring

We report the relative humidity (RH) sensing response of a resistive sensor, employing sensing layers, based on a quaternary organic–inorganic hybrid nanocomposite comprising oxidized carbon nanohorns (CNHox), graphene oxide (GO), tin dioxide, and polyvinylpyrrolidone (PVP), at 1/1/1/1 and 0.75/0.75/1/1/1 mass ratios. The sensing structure comprises a silicon substrate, a SiO2 layer, and interdigitated transducer (IDT) electrodes. The sensing film was deposited via the drop-casting method on the sensing structure. The morphology and the composition of the sensing layers were investigated through Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and RAMAN spectroscopy. The organic–inorganic quaternary hybrid-based thin film’s resistance increased when the sensors were exposed to relative humidity ranging from 0 to 100%. The manufactured devices show a room temperature response comparable to that of a commercial capacitive humidity sensor and characterized by excellent linearity, rapid response and recovery times, and good sensitivity. While the sensor with CNHox/GO/SnO2/PVP at 0.75/0.75/1/1 as the sensing layer has the best performance in terms of linearity and recovery time, the structures employing the CNHox/GO/SnO2/PVP at 1/1/1/1 (mass ratio) have a better performance in terms of relative sensitivity. We explained each constituent of the quaternary hybrid nanocomposites’ sensing role based on their chemical and physical properties, and mutual interactions. Different alternative mechanisms were taken into consideration and discussed. Based on the sensing results, we presume that the effect of the p-type semiconductor behavior of CNHox and GO, correlated with swelling of PVP, dominates and leads to the overall increasing resistance of the sensing layer. The hard–soft acid–base (HSAB) principle also supports this mechanism.

Armalcolite Nanocomposite: A New Paradigm for Flexible Capacitive Humidity Sensor

In this paper, a unique Armalcolite-PDMS-based flexible capacitive humidity sensor is designed by using spin coating technique, which uses interdigitated gold (Au) electrode and ultrathin ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 80~\mu \text{m}$ </tex-math></inline-formula> ) flexible polyimide substrate. The structural and morphological properties of the Armalcolite nanocomposite are characterized by X-ray diffraction (XRD) and SEM. The electrical characterization of the Armalcolite-PDMS-based flexible capacitive humidity sensor is performed at 25 °C, followed by relative humidity ranging from 33% to 95% and frequency varying 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Hz to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Hz. The experimental investigation reveals a fast response time (8.53 s) and recovery time (11.25 s). The developed sensor exhibits a reversible response with ultra-low hysteresis of 0.92%. The sensor response is recorded for 30 days to confirm its long-term stability. The sensing mechanism is studied using impedance plots obtained at different humidity environments. The excellent sensing performance of the developed sensor could be beneficial for the researchers working in the area of flexible humidity sensors.

Experimental Study of Parylene Based Capacitive Humidity Sensor for Integrated Thermal Comfort Sensing Application

In this letter, we report the temperature effect and noise characterization of the Parylene-based capacitive humidity sensor which can be used for integrated CMOS compatible thermal comfort sensing. The sensor is comprised of a pair of interdigitated Pt electrodes deposited on a silicon substrate and a parylene hygroscopic layer coated on the electrodes using room temperature chemical vapor deposition process. The sensor was characterized at different relative humidity (RH) values and working temperatures in a testing setup. The capacitance of the sensor increases with the RH due to the absorption of water molecules on the surface of the sensing film. The capacitance of the sensor also increases with temperature, which is due to the stronger thermal movement of the molecules that helps increase the polarization at increased temperature levels. Besides, a readout circuit was done on a printed circuit board using capacitance to voltage converter for the sensor. The sensor achieved a maximum sensitivity of 76.2 mV/%RH and response and recovery times of about 31.5 and 29.2 s, respectively. Besides, the sensor shows a noise level of 1.399 mV rms within 25 Hz bandwidth in the output voltage response. The experimental results also indicated a resolution of about 0.072-2% within the ASHRAE standard approved RH range (25-95%) for the fabricated sensor.

Capacitive Humidity Sensor Based on Carbon Black/Polyimide Composites.

A novel capacitive humidity sensor based on carbon black/polyimide composites is presented in this paper. The details of the fabrication, sensor characteristics, and effect of the carbon black additive are described. It was confirmed that the polyimide composite filled with a tiny amount of carbon black was suitable for a humidity sensing dielectric. The humidity sensors with three different dielectrics, which were pure polyimide, 0.01 wt% carbon black/polyimide, and 0.05 wt% carbon black/polyimide, were fabricated by a micro-electro-mechanical-system (MEMS) process. As the amount of the carbon black additive increased, the sensitivity of the humidity sensor increased. The humidity sensor with 0.05 wt% of carbon black had a much higher sensitivity of 15.21% (20–80% RH, 0.2535%/% RH) than that of the sensor with pure polyimide, which was 9.73% (0.1622%/% RH). The addition of carbon black also led to an enhancement in the hysteresis and response speed. The hysteresis of the humidity sensor decreased from 2.17 to 1.80% when increasing the amount of the carbon black additive. The response speed of the humidity sensor with 0.05 wt% of carbon black was measured to be ~10% faster than that of the sensor with pure polyimide. The long-term stability of the humidity sensors was demonstrated as well.

Capacitive humidity sensing performance of naphthalene diimide derivatives at ambient temperature

We report for the first-time the development of capacitive type humidity sensors employing naphthalene diimide derivatives (NDI) as sensing layer. Three different naphthalene diimide derivatives bearing imide side chains of different hydrophilicity were designed, synthesised and characterised. X-ray diffraction and thermogravimetric analyses gave useful information about structural and thermal behaviour of the newly developed materials, indicating their crystallinity and stability. Atomic force microscopy analysis revealed a variety of morphologies in thin films as a result of the structural properties of the NDIs. Devices bearing NDI layers were fabricated on ceramic substrates with gold interdigitated electrodes spaced 200 µm apart. Humidity sensing performance, as a change in capacitance, was studied upon exposure to a wide range of relative humidity levels (0–95%) at ambient temperature. Importantly, an increase in the capacitance of the sensors was recorded with an increase in relative humidity. The developed sensors exhibited high sensitivity, good long-term stability, excellent reproducibility, and low hysteresis. The sensor performance was also tested against different operating frequencies (250 Hz–2 kHz) to improve linearity, illustrating directions for optimised performance. These results confirm that sensors based on NDIs possess better sensing performance to other types of reported capacitive humidity sensors.

A capacitive humidity sensor based on all-protein embedded with gold nanoparticles @ carbon composite for human respiration detection

Wool and silk fiber are the most extensive resources of protein fibers and have been used in the textile field for many years. The extracted biocompatible proteins are more and more widely used in flexible devices, sensors, tissue engineering, etc. Here, a fully biomaterial based flexible humidity sensor has been successfully fabricated for the first time. Interdigital electrodes of humidity sensor are printed on a transparent sensor substrate made of silk protein by inkjet printing. The humidity sensitive material is gold nanoparticles hosted nitrogen doped carbon (AuNPs@NC), which is fabricated by in situ dispersion of gold nanoparticles in a wool keratin assisted porous carbon precursor. The best treatment condition of the sensitive materials is obtained by comparing the sensitivity of humidity response. Moreover, the as-prepared biocompatible flexible sensor was successfully used to detect human respiration.

New Electronic Interface Circuits for Humidity Measurement Based on the Current Processing Technique

Abstract The paper describes a new electronic conditioning circuit based on the current-processing technique for accurate and reliable humidity measurement, without post-processing requirements. Pseudobrookite nanocrystalline (Fe2TiO5) thick film was used as capacitive humidity transducer in the proposed design. The interface integrated circuit was realized in TSMC 0.18 μm CMOS technology, but commercial devices were used for practical realization. The sensing principle of the sensor was obtained by converting the information on environment humidity into a frequency variable square-wave electric current signal. The proposed solution features high linearity, insensitivity to temperature, as well as low power consumption. The sensor has a linear function with relative humidity in the range of Relative Humidity (RH) 30-90 %, error below 1.5 %, and sensitivity 8.3 x 1014 Hz/F evaluated over the full range of changes. A fast recovery without the need of any refreshing methods was observed with a change in RH. The total power dissipation of readout circuitry was 1 mW.

Fully self-powered instantaneous wireless humidity sensing system based on triboelectric nanogenerator

Self-powered wireless sensor systems are highly sought for the forthcoming Internet of Things era. However, most of the technologies take the route of energy harvesting, storage, and power regulation to power wireless sensor systems, which has a limited operation duration due to the low energy utilization efficiency of the multiple energy conversions involved. Here, we propose a triboelectric nanogenerator (TENG) based fully self-powered, instantaneous wireless sensor system which yet does not contain electronic devices and chips, but the passive components only. By integrating a capacitive sensor and an inductor coil with TENG, the pulse voltage output of the TENG is converted into a sinusoidal signal containing the sensing information with a resonant frequency and is transmitted to the receiver in distance wirelessly and continuously. A precise analytical model is developed for the capacitive sensor system with general implication; the oscillating signal generated by the model shows excellent agreement with experimental results. A capacitive humidity sensor is then utilized for sensing demonstration, showing that the maximum transmission distance of the sensor system is 50 and 90 cm for a 1 cm diameter magnetic-core coil pair and 20 cm diameter air-core coil pair, respectively. The wireless humidity sensor exhibits a sensitivity of 1.26 kHz/%RH, fast response speed, and excellent linearity, demonstrating its great application potential of the self-powered technology.

A Dual-Slope-Based Capacitance-to-Time Signal Conditioning Circuit for Leaky Capacitive Sensors

A robust signal conditioning circuit for capacitive sensors, based on the dual-slope and phase-sensitive-detection technique, is presented in this article. The circuit is designed to measure the capacitance of the leaky capacitive sensors. The phase-sensitive-detection technique mitigates the effect of the shunting conductance. In addition, the circuit is designed in such a way that the error due to the parasitic/stray capacitance on the measurement of the sensor capacitance is negligible. Furthermore, an autotuning frequency-independent quadrature phase-shifter circuit is designed for an accurate 90° phase generation. A prototype of the circuit is built and tested. The experimental results show that the designed circuit can measure the sensor capacitance in the range from 65 to 528 pF with accuracy within ±1%. The robustness of the proposed circuit is tested against the variation in the amplitude and frequency of input sinusoidal excitation signal. The results confirm that the proposed circuit is well suited for sensors, such as capacitive humidity sensors, water level detection sensors, and fingerprint sensors.

Interlaboratory comparison of relative humidity standards among Latin American National Metrology Institutes (SIM.T-S10)

Main textThis report presents the results of a comparison in the context of an international collaboration that gives confidence in the relative humidity measurements carried out by several Latin-American institutes within the Mutual Recognition Arrangement (MRA) of the International Committee on Weights and Measures (CIPM). This interlaboratory comparison of humidity standards, the first one in Latin-America and one of the few of this type in the world, was organized in two rounds and carried out by the following National Metrology Institutes: INMETRO (Brazil), IBMETRO (Bolivia), INEN (Ecuador), INM (Colombia), CENAMEP AIP (Panama), ENAER (Chile), INTI (Argentina), LATU (Uruguay) and INTN (Paraguay). The interlaboratory comparison was performed in the scope of relative humidity in the range from 30 %rh to 90 %rh at temperatures of 20 °C and 40 °C. In this comparison, INMETRO was the reference laboratory, and acted as coordinator together with IBMETRO. Two thermohygrometers with capacitive humidity sensors were used as transfer standards, which were calibrated three times by the reference laboratory during the course of the interlaboratory comparison. A technical protocol prepared by INMETRO and IBMETRO circulated among the participants for comments. To sum up, the participants used their own calibration procedures for calibrating the transfer standards together with some instructions given in the technical protocol. Besides, the participants had to submit with the measurement results the respective uncertainties estimated according to their internal procedures and the Guide to the Expression of Uncertainty in Measurement (GUM). The performance of each participating laboratory was evaluated by comparing its measurements results with those of the reference laboratory by means of the normalized error, according to ISO/IEC 17043:2010, and by the degree of equivalence.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Performance of the highly sensitive humidity sensor constructed with nanofibrillated cellulose/graphene oxide/polydimethylsiloxane aerogel via freeze drying.

A kind of capacitive humidity sensor with high sensitivity constructed with nanofibrillated cellulose (NFC), graphene oxide (GO) and polydimethylsiloxane (PDMS) is presented in this work, via a simple ultrasonic dispersion and freeze drying technology. The NFC and GO with a strong adsorption for water molecules were used as a substrate for the promotion of capacitive response of the humidity sensor. Moreover, anhydrous ethanol was added to inhibit the generation of big cracks in the humidity sensor in the freeze drying process, so as to obtain a regular network porous structure, then providing a great deal of conduction channels and active sites for molecular water. Also, the addition of PDMS can effectively enhance the flexibility and stability of its porous structure. The results confirmed that the humidity sensor with 30 wt% GO showed an excellent humidity sensitivity (6576.41 pF/% RH), remarkable reproducibility, low humidity hysteresis characteristic in 11–97% relative humidity (RH) at 25 °C, and short response/recovery times (57 s/2 s). In addition, the presented sensor exhibited small relative deviation of the measured relative humidity value compared with the commercial hygrometer. The realization of the high sensitivity can be attributed to the theories about interaction of the hydrophilic group, proton transfer of water molecules and the three-dimensional network transport structure model. Therefore, the NFC/GO/PDMS humidity sensor finally realizes stable, reproducible and fast humidity sensing via an eco-friendly process, exhibiting promising potential for wide practical application.