HUMIDITY SENSOR PDF
𝗣𝗗𝗙 | Humidity is one of the most commonly measured physical quantities and is of great importance in a wide variety. This paper reviews the transduction. Numerous sorts of humidity sensors fabricated and developed for industrial Keywords: humidity sensors; capacitive/resistive sensor; relative. Humidity Overview. Humidity Sensors can be found in many products, ranging from smart home assistants to wireless base stations. The function of these.
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DHT11 Temperature & Humidity Sensor features a temperature & humidity sensor complex with a calibrated digital signal output. By using the exclusive. The MTH02 is a MCU based temperature and relative humidity sensor module, comprising one wire interface for direct temperature and humidity read out. The. Resistive humidity sensor, Model: HR 1. HR is a new kind of humidity- sensitive resistor made from organic macromolecule materials, it can be used in.
Introduction The use of paper as flexible substrate material for printed electronics has been increasing when compared to polymer-based substrates. This is due to its attractive characteristics, such as being a widely available substrate and a low-cost material. Its flexibility allows a wide range of different applications, and the biodegradability is very important when thinking about environmentally-friendly processes and applications. Nevertheless, this paper presents challenges that polymer-based substrates do not present; for example, the porosity or surface roughness of the substrate material, which are crucial parameters when printing conductive lines.
However, with polymer-based substrates, one of the crucial parameters is the glass transition temperature Tg , due to the use of temperature during the fabrication process [ 1 ].
Inkjet-printing enables cost-efficient mass manufacturing of electrodes and other functional materials on large and flexible substrates, such as plastic [ 2 ], paper [ 3 ], and fabrics [ 4 ], with a broad area of applications and huge business potential. First, inkjet-printing enables 3D-printed structures, changing the whole system of producing electronic devices, including the design and manufacturing phases, material selection, and device structure and architecture.
Second, printed electronics offer better economics to electronics manufacturing. Traditional electronics are cheap only on the mass production scale, in contrast to digital printing, and especially inkjet-printing, which offers flexible and cheap production for tailored small-volume products e. Nevertheless, there are some decisive production parameters that affect conductivity and mechanical properties, such as surface structure of the substrate material, cross-section of the printed layer, and curing parameters like sintering time and temperature [ 5 ].
This will influence and limit parameters such as nominal capacitance of the sensor or huge variation in capacitance changes with relative humidity, as well as response time, due to the sensing layer uniformity. Sintering can be simply explained as a process that welds together small metal particles.
It occurs by applying heat to the material below the melting point in such a way that the small metal particles diffuse through the microstructure, coalescing and forming a conductive track, while the organic material is burned off [ 6 ]. The most common and simple sintering technique is thermal sintering [ 7 ]. When thinking about roll-to-roll R2R mass manufacturing, this is a disadvantage, as it is time consuming. Alternative sintering methods can then be used, significantly reducing the sintering time.
Specifically, IR-sintering has easy operation, usually only requiring a set of lamps, and is compatible with R2R mass manufacturing. The sintering time is significantly reduced due to localized heating, tailored according to the substrate, such as Tg, thermal stability, and conductivity. In a relative humidity capacitive sensor, the dielectric material of a capacitor is allowed to diffuse and absorb water vapour so that it equilibrates with the external environment.
Usually, continuous and reversible humidity sensing is based on the exposure of thermoset polymers to different relative humidity conditions, followed by reversible dielectric permittivity change [ 16 ]. Ideally, thermoset polymer-based capacitive RH sensors detect changes in relative humidity as a change in sensor capacitance with fast response, high linearity, low hysteresis, and excellent long-term stability. Different electrodes configuration can be used for the printed capacitive humidity sensors.
The interdigitated electrodes IDE configuration is easy to fabricate, but can also detect relative humidity changes in the substrate film and therefore has a slow response time, whereas the well-known parallel-plate configuration detects only relative humidity changes in the thin polymer layer and has a faster response time.
The measurements can be performed without muffle furnace for 3 h at K and stored for analyses. The measured effec- isopropoxide, as above, after 1 h aging period; and tive dielectric constant gives a clear idea about the the desired amount of Ni hydroxide gel, which was nature of the bulk response showing whether it arises prepared as follows. A calculated amount of nickel from the solid phase or from interfaces.
Hydrolysis [i. A gel was formed corresponding to a different frequency] lead to a after the later solution neutralizes the nitrate solution. In this case, the second The final pH value of the gel was adjusted to 9.
Hence, the bonate solution. For all the mixing ratios, the total bulk electrical conductivity is obtained. The relaxation volume of hydrolyzed nickel nitrate solutions gels frequency of the material is found at the apex of the was made the same.
Nyquist semicircle. The bulk capacitance of the ma- Gel mixing was affected by the addition of the terial, also called the geometric capacitance , can corresponding nickel hydroxide gel to the alumina be calculated and hence the bulk dielectric constant gel and mixing was aided by magnetic stirring at can be determined. The days, dried, and calcined at K for 3 h as done humidity sensitivity of electrical conductivity and for the pure alumina.
Techniques 2. Prior to the measurements, Pure alumina was prepared by calcination of a all samples were outgassed for 2 h at K to 0. Assessment of mi- oration to make good electrical contacts of 8. External sur- holder constructed from Teflon. This measuring cell face area SExt surface area due to nitrogen adsorption was then inserted into the humidity chamber.
Water on mesopore and macropore surfaces, i. The accuracy corresponding SBET value, i. Impedance spectra were collected using an No.
Data were collected from 10 employs the conventional Gouy method. MHz to 0. The spectra obtained were analyzed Electrical measurements of the test materials are for resistance and capacitance equivalent circuit ele- performed on pellets prepared by the same procedure ments vs.
Relative Humidity Sensor ICs
RH by a commercial software package. A uniaxial force of 4 tons has been applied for a few minutes using a hydraulic press to form the 3. Results and discussion resulting nanostructured powder into pellets of 1.
The pellets faces Structural information of the prepared materials were coated with thin gold films using thermal evap- can be realized by inspection of Fig. In fact, X-ray analysis is No. However, a slight peak No. The increase of the d-spacing may be explained in terms of partial formation of the XRD patterns measured for the test materials. Textural character- According to the applied preparation method , istics including SBET surface area, micropore area Smic, short fibrous boehmite should be formed upon drying external surface area SExt along with the average of the alumina gel and upon calcinations thermally particle size for the test composite materials are stabilized transitional aluminas are formed, which displayed in Table 1.
These data indicate that NiO preserve high surface area due to the fibrous nature loaded materials shows slightly higher surface area of the precursor. Clearly, the pure alumina sample No. Sample No. However, sample No. These results indi- similar XRD patterns of little improved crystallinity. However, the de- did not considerably interrupt the structural evolution crease of specific surface area on going from the Fig. The magnetic susceptibility of the No.
The drawback of this method is the presence of spinel NiAl2O4 that might occur when high concen- trations of NiO on Al2O3 are heated at high temper- atures, which is not considerably the case for our samples. However, the error introduced in the size determination is found to be insignificant for NiAl2O4 content below 5 wt. The NiO particle size is estimated using the above equation to be 15 and 13 nm for samples No. Humidity sensing properties of the samples are shown in Fig.
RH at K for all specimens. The points in the figure represent the experimental data and the lines are drawn to guide the eye. All currents are normalized to a sample thickness of 1 mm. It should be noted that in general, for composites measured as functions of RH. In The dependence of the bulk electric conductivity the present series of samples, the conductance change obtained from the IS measurements on NiO content was found to cover the range of 10 10 to 10 3 is shown in Fig.
Accord- V 1. The be- change was found to cover the range of 10 8 to havior can be understood in view of the morpholog- 10 4 V 1. The relative conductivity of the samples pedance spectra of a pressed powder of sample No. In each spectrum, the frequency This order is exactly reversed for the SBET decreases from left to right. Two arcs are obtained, values, which were in the order No. Therefore, the observed nearly perfect semicircular, centered on the real axis, order of the materials conductivity may be explained at high frequency.
The low frequency arc was as: when higher surface area is available for adsorp- ascribed to the electrode polarization arc on the basis tion at a given humidity percentage e.
The high frequency bulk arc shrinks signifi- This was because, as long as more exposed free cantly as RH is increased. Similar results are from adsorption surface is present, water chemisorp- obtained for other samples with lower NiO content. This will decrease both resistor and capacitor in parallel. For all samples, the dissociation rate of physisorbed water and the the bulk impedance arcs are depressed below the real production of protons responsible for the electrical axis in Nyquist plots ZWvs.
In addition, due to the increase of NiO composition and RH. Capacitances for all samples ratio the textural data Table 1 indicates the removal for the whole RH range remain between 40 and 60 of microporosity and the shift of average pore pF whereas conductivities depend on sample com- diameter toward more reactive mesopore size f 5 position and strongly on RH.
Resistances typically nm for No.
Again, ing or decreasing RH, respectively. Thus, it is of interest to examine the test time to reach equilibrium.
Digital Humidity Sensor SHT3x (RH/T)
The sample is subsequent- materials response and recovery time. Two samples ly exposed to a vapor stream.
However, as a recovery characteristics for this sample at low RH matter of fact, most sensors exhibit some degree of levels. The sample was dried at K for 30 min as hysteresis, whereby the conductance path differs to was done before and then exposed to air stream of some extent.
This can be as- min when RH is increased, whereas the time re- cribed to the difficulty of evaporating water from the quired to move between the same points when RH is fine pore network as well as the thick pellets shape decreased, t 1V, is more than twice as large as t1. For of our samples. Moreover, capillary forces, which are the second sample, No.
Response and recovery characteristics of a No.
Electrical conductivity r and resistivity q are Upon exposing a dry ceramic oxide to humid envi- calculated as functions of RH from both DC and ronment, a layer of water vapor molecules is first IS data. It is evident that r changes ions on its surface. Charge transport occurs firstly by exponentially as a function of RH with different a hopping mechanism between hydroxyl groups of slopes in low and high RH regions.
It is noticed protons coming from the hydroxyl dissociation. With also that the DC conductivity is lower than that increasing humidity levels, water molecules are obtained from IS data for the same RH. It has been physically adsorbed on the top of the chemisorbed reported before  that the presence of hydroxyl hydroxyl layers, which increase the number of pro- ions on the oxide surface promotes the dissociate tons available for electrical conduction.
This explains hydroxyl and provides protons as charge carriers.
It giving rise to electrical conductivity. The change of should be mentioned that partial formation of the electrical conductivity has been shown by vari- NiAl2O4 phase, which may occur, has not been ous investigators to be almost exponential with RH considered in the above discussion. From Fig. The effective dielectric constant was conductivity at certain RH increases with increasing found to be close to Realistic values for our NiO content in our specimens.
The lines in Fig. Electrical conductivity and resistivity of No. Humidity sensing characteristics in the Acknowledgements case of ceramic systems have been ascribed to absorp- tion of water molecules on their surface [32,36].
It can This work was supported by Grant No. References 4. Conclusion  H. Gleiter, Prog. Siegel, MRS Bull. Siegel, Annu. Electrical conductance for sol — gel derived high  R. Siegel, Processing of metals and alloys, in: R. Electrical conductance increases as a function of RH  H. Gleiter, Nanostruct. Siegel, in: F. Fujita Ed. The increase of NiO content was found to  C. Brinker, G. Scherer, Sol — Gel Science, Academic increase the electrical conductances in humid air.
Humidity Sensor – Types and Working Principle
Press, Boston, From the texture point of view and within the inves-  K. Khalil, A. Elsamahy, M. Elanany, J. Colloid Inter- tigated group of materials, the removal of micropo- face Sci. Gusmano, G. Montesperelli, B. Morten, M. Prudenziati, A.
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Pumo, E.Biju, M. Featured Humidity Sensor Products. Prudenziati, A. The ink-jetted structures were printed onto the substrates without any pre-treatment. Humidity Sensors are very important devices that help in measuring the environmental humidity. Brinker, G.
Although they achieved better results when the paper was passivated, the sensor showed a very long response time to the humidity changes, independently of the parylene coating. IDT humidity sensors feature industry-leading specifications, helping to solve product design challenges and giving customers a competitive advantage.
Electrical conductance increases as a function of RH  H. Dias et al.