Scalable Fabrication of Highly Flexible Porous Polymer-Based Capacitive Humidity Sensor Using Convergence Fiber Drawing

In this study, we fabricated a highly flexible fiber-based capacitive humidity sensor using a scalable convergence fiber drawing approach. The sensor’s sensing layer is made of porous polyetherimide (PEI) with its porosity produced in situ during fiber drawing, whereas its electrodes are made of copper wires. The porosity induces capillary condensation starting at a low relative humidity (RH) level (here, 70%), resulting in a significant increase in the response of the sensor at RH levels ranging from 70% to 80%. The proposed humidity sensor shows a good sensitivity of 0.39 pF/% RH in the range of 70%–80% RH, a maximum hysteresis of 9.08% RH at 70% RH, a small temperature dependence, and a good stability over a 48 h period. This work demonstrates the first fiber-based humidity sensor fabricated using convergence fiber drawing.

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Compliant and Low-Cost Humidity Sensors Using Nano-Porous Polymer Membranes

Microelectromechanical Systems ◽

10.1115/imece2004-59557 ◽

2004 ◽

Author(s):

Bozhi Yang ◽

Burak Aksak ◽

Shan Liu ◽

Qiao Lin ◽

Metin Sitti

Keyword(s):

Relative Humidity ◽

Room Temperature ◽

Capillary Condensation ◽

Low Cost ◽

Polymer Membranes ◽

High Sensitivity ◽

Porous Polymer ◽

Humidity Sensors ◽

Water Leakage Detection

This paper proposes non-fragile compliant humidity sensors that can be fabricated inexpensively on various types of nano-porous polymer membranes such as polycarbonate, cellulose acetate, and nylon membranes. The sensor contains a pair of interdigitated electrodes deposited on the nano-porous polymer membranes. The resistance and/or capacitance between these electrodes vary at different humidity levels with a very high sensitivity due to the water adsorption (capillary condensation) inside the nano-pores. The proposed sensors are low-cost in both material and fabrication. Due to its compliance, the sensors can be suitable for certain applications such as in-situ water leakage detection on roofs, where people can walk on top of them. Testing results demonstrated that the sensor changes resistance within large range of humidity values. For most sensors, the resistance changes from 0.1 GΩ to 2000 GΩ when the relative humidity changes from 39% to 100% at room temperature. It takes about 4–8 minutes for the resistance to reach steady state when the sensor was taken from 100% to 39% relative humidity at the room temperature.

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Analysis of Capillary Condensation of Vapor in Multi-Wall Carbon Nanotubes

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.483.694 ◽

2011 ◽

Vol 483 ◽

pp. 694-698

Author(s):

Wei Wang ◽

Xin Wang ◽

Tuo Li ◽

Wei Ping Chen

Keyword(s):

Carbon Nanotubes ◽

Relative Humidity ◽

Humidity Sensor ◽

Quartz Crystal ◽

Capillary Condensation ◽

Equivalent Model ◽

Sensing Element ◽

Multi Wall Carbon Nanotubes ◽

As Adsorption ◽

Humidity Environment

Multi-wall Carbon Nanotubes (MWNTs) is the new hotspot material as the active sensing element, but there is no certain theory on the phenomenon of the vapor's capillary condensation in MWNTs for the present. This paper presents a new theory that the capillary condensation of vapor in MWNTs mostly occur in the internal hollow tube, according to the calculation of equivalent model of MWNTs. A kind of carbon nanotubes (CNTs) humidity sensor based on quartz crystal microbalance was fabricated, CNTs employed as adsorption materials. The sensor was put in 11% and 97% relative humidity environment in experimental, and the value of MH2O/MCNT was calculated. The theory in this paper is proved by the comparison between the experimental and the analysis results.

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Influence of Dimension and Temperature on Capacitive Humidity Sensor

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.562-565.178 ◽

2013 ◽

Vol 562-565 ◽

pp. 178-181

Author(s):

Hui Jin Yu ◽

Jiao Ling ◽

Hua Qin Shen ◽

Wu Zhou ◽

Bei Peng

Keyword(s):

Dielectric Constant ◽

Relative Humidity ◽

Empirical Data ◽

Humidity Sensor ◽

Temperature Influence ◽

Influence Of Temperature ◽

Influence Of Temperature On ◽

Semi Empirical ◽

The Relationship ◽

Capacitive Humidity Sensor

The influence of dimension and temperature on a MEMS-based capacitive humidity sensor is researched in this paper. Looyenga’s equation and Dubinin’s semi-empirical data are used to describe the change of dielectric constant of sensing film when absorbing or desorbing water. For these equations and data, a picture of the relationship between dielectric constant and temperature, relative humidity is presented. In the basis of this theory, a simulation is finished, a curve showing good linearity and presenting the relationship between capacitance and relative humidity is obtained. A graph showing the influence of temperature on capacitance at different %RH is given, which considers the change of dielectric constant of Looyenga’s equation and Dubinin’s semi-empirical data only. the result shows that the capacitance decreases with the increasing of temperature. Influence of sensing layer thickness on sensitivity is presented. It shows that when the thickness of sensing layer is about 0.6 micron, the model of humidity sensor has the highest sensitivity.

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