Humidity response of a capacitive sensor based on auxeticity of carbon nanotube-paper composites

Abstract

Auxetic materials showing a negative Poisson’s ratio can offer unusual sensing capabilities due to drastic percolation changes. This study presents the capacitive response of wet-fractured carbon nanotube paper composites in exposure to humidity. A strained composite strip is fractured to produce numerous cantilevers consisting of cellulose fibers coated with carbon nanotubes. During stretching, the thin composite buckles in the out-of-plane direction, which causes auxetic behavior to generate the radially structured electrodes. The crossbar junctions forming among the fractured electrodes significantly increase capacitance and its response to humidity as a function of sensor widths. The molecular junctions switch electric characteristics between predominantly resistive- and capacitive elements. The resulting capacitive response is characterized for humidity sensing without the need for an additional absorption medium. The normalized capacitance change (ΔC/C) exhibits a sensitivity of 0.225 within the range of 40~80 % relative humidity. The novel auxetic behavior of a water-printed paper-based nanocomposite paves the way for inexpensive humidity and sweat sensors.

Capacitive Humidity Sensor with a Rapid Response Time on a GO-Doped P(VDF-TrFE)/LiCl Composite for Noncontact Sensing Applications

“…Therefore, the selection of sensing material is most significant. Several kinds of materials have been used to manufacture humidity sensors, such as ceramic [10], metal oxide [11], nanotubes [12], polymers [13], and carbon materials [14]. However, the complicated synthesis process, limited detecting range, and high cost of sensing materials are still challenging to overcome.…”