Design and Development for Capacitive Humidity Sensor Applications of Lead-Free Ca,Mg,Fe,Ti-Oxides-Based Electro-Ceramics with Improved Sensing Properties via Physisorption
"> Figure 1
<p>Flow chart for sensor fabrication with the morphology at different sintering temperature.</p> "> Figure 2
<p>Experimental setup for the measurement of the capacitive humidity response of the electro-ceramic based sensors.</p> "> Figure 3
<p>Pore size distribution (PSD) and relative cumulative frequency (RCF) of (<b>a</b>) unsintered and sintered at (<b>b</b>) 450 °C, (<b>c</b>) 650 °C, (<b>d</b>) 850 °C and (<b>e</b>) 1050 °C materials measuring from the electron micrographs using ImageJ.</p> "> Figure 4
<p>Density, open-porosity, water absorption and water contact angle (WCA) of (<b>a</b>) unsintered and sintered at (<b>b</b>) 450 °C; (<b>c</b>) 650 °C; (<b>d</b>) 850 °C and (<b>e</b>) 1050 °C ceramic samples.</p> "> Figure 5
<p>The response curves of the capacitance versus relative humidity (RH) at different frequencies of CMFTO electro-ceramic at 25 °C. Inset image represents the variation of capacitance with RH at 25 °C at different frequency in logarithmic scale (log(<span class="html-italic">C</span>) vs. % RH). Note: the capacitance increases monotonically with % RH at different frequencies, but increased rate is faster at 10<sup>2</sup> Hz.</p> "> Figure 6
<p>The variations of capacitance with frequency at different humidity condition (33%–95% RH) for CMFTO based humidity sensor at 25 °C. Inset image represents the variation of capacitance with frequency at different RH in logarithmic scale (log(<span class="html-italic">C</span>) vs. log(RH)). Note: The value of capacitance increases with increased % RH, but decreases with increased frequency. The decreased rate is faster in lower frequency (<10<sup>4</sup> Hz) and higher humidity range (>85% RH).</p> "> Figure 7
<p>The sensitivity (%S) response of CMFTO based capacitive sensor with % RH at different test frequencies at 25 °C. Note: the sensitivity increases monotonically with % RH at different frequencies, but the value of sensitivity is highest (~3000%) at 10<sup>2</sup> Hz. Hence, 10<sup>2</sup> Hz is considered as the most suitable frequency for the further analysis.</p> "> Figure 8
<p>Schematic representation of the humidity sensing mechanism of CMFTO electro-ceramic at different humidity environment. Note: the adsorption of water molecules on CMFTO nanoceramic is characterized by two processes. The first-layer water molecules (at lower humidity) are attached on the CMFTO electro-ceramic through two hydrogen bonds. As a result, the water molecules are not able to move freely and thus, the impedance value increases. In contrast, from the second layer (at higher humidity), water molecules are adsorbed only through one hydrogen bond. Hence, the water molecules are able to move freely and thus, the impedance value decreases. This insists to increase the capacitance value.</p> "> Figure 9
<p>The transformed response curves of logarithmic capacitance (logC) vs. RH of CMFTO electro-ceramic based capacitive sensor. Note: first linear transformation curve (red-line) is well fitted by logC = 0.0102RH − 10.8148 in the RH range from 33% to 75% and the second linear transformation curve (green-line) is well fitted by the formula logC = 0.0532RH − 14.0401 at the higher humidity range (>75% RH). Here, regression, R<sup>2</sup> represents a best fit of the curves to improve linearity.</p> "> Figure 10
<p>The hysteresis property of CMFTO electro-ceramic-based capacitive humidity sensor at 10<sup>2</sup> Hz under 25 °C. Note: the value of hysteresis is extremely low (~3.2%) compared to other conventional capacitive sensors. The low hysteresis value is mainly due to the fast adsorption and desorption rate of water particles on the surface of the CMFTO electro-ceramic.</p> "> Figure 11
<p>Response and recovery times of the CMFTO humidity sensors for humidity levels between 33% RH and 95% RH at 10<sup>2</sup> Hz. (<b>A</b>) Response time (14.5 s); (<b>B</b>) Recovery time (34.27 s).</p> "> Figure 12
<p>Stability analysis of CMFTO electro-ceramic-based humidity sensor measured at a test frequency 10<sup>2</sup> Hz at 25 °C. Note: The measurement was conducted repeatedly for 30 days at 2-day interval and very negligible changes are observed.</p> "> Figure 13
<p>Complex impedance plots and equivalent circuits of CMFTO based electro-ceramic under different humidity levels. (<b>A</b>) At lower humidity range (33%–75% RH), single semicircles are formed; the inset represents an equivalent circuit at lower RH; (<b>B</b>) At higher humidity condition (85%–95% RH), the radii of semicircle decrease and a straight line appears, and the straight lines become longer with increasing of humidity; the inset represents an equivalent circuit at higher RH. <span class="html-italic">R</span><sub>f</sub> and <span class="html-italic">C</span><sub>f</sub>: are the resistance and capacitance of CMFTO electro-ceramics, respectively; <span class="html-italic">Z</span><sub>i</sub>: interface impedance between CMFTO electro-ceramic surface and electrode.</p> ">
Abstract
:1. Introduction
2. Experimental Section
2.1. Preparation of the Sensing Nanomaterial
2.2. Fabrication of Humidity Sensor
2.3. Physical Characterizations
2.4. Humidity Sensor Measurements
3. Results and Discussion
3.1. Structural and Morphological Characterization
3.2. Humidity Sensing Measurements
4. Conclusions
Supplementary Materials
Supplementary File 1Acknowledgments
Author Contributions
Conflicts of Interest
References
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Steps | Parameters | Sample Details | |||
---|---|---|---|---|---|
450 °C | 650 °C | 850 °C | 1050 °C | ||
Step-I | Temperature (°C) | 450 | 250 | 350 | 350 |
Time (h) | 3.5 | 1 | 1 | 1 | |
Ramp rate (°C/min) | 5 | 5 | 5 | 5 | |
Step-II | Temperature (°C) | - | 650 | 550 | 550 |
Time (h) | - | 3.5 | 3.5 | 3.5 | |
Ramp rate (°C/min) | - | 10 | 10 | 10 | |
Step-III | Temperature (°C) | - | - | 850 | 1050 |
Time (h) | - | - | 1.3 | 1.3 | |
Ramp rate (°C/min) | - | - | 15 | 15 | |
Step-IV | Temperature (°C) | - | - | 750 | 750 |
Time (h) | - | - | 3 | 3 | |
Ramp rate (°C/min) | - | - | 20 | 20 |
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Tripathy, A.; Pramanik, S.; Manna, A.; Bhuyan, S.; Azrin Shah, N.F.; Radzi, Z.; Abu Osman, N.A. Design and Development for Capacitive Humidity Sensor Applications of Lead-Free Ca,Mg,Fe,Ti-Oxides-Based Electro-Ceramics with Improved Sensing Properties via Physisorption. Sensors 2016, 16, 1135. https://doi.org/10.3390/s16071135
Tripathy A, Pramanik S, Manna A, Bhuyan S, Azrin Shah NF, Radzi Z, Abu Osman NA. Design and Development for Capacitive Humidity Sensor Applications of Lead-Free Ca,Mg,Fe,Ti-Oxides-Based Electro-Ceramics with Improved Sensing Properties via Physisorption. Sensors. 2016; 16(7):1135. https://doi.org/10.3390/s16071135
Chicago/Turabian StyleTripathy, Ashis, Sumit Pramanik, Ayan Manna, Satyanarayan Bhuyan, Nabila Farhana Azrin Shah, Zamri Radzi, and Noor Azuan Abu Osman. 2016. "Design and Development for Capacitive Humidity Sensor Applications of Lead-Free Ca,Mg,Fe,Ti-Oxides-Based Electro-Ceramics with Improved Sensing Properties via Physisorption" Sensors 16, no. 7: 1135. https://doi.org/10.3390/s16071135