A Comb-Type Capacitive 2-FAL Sensor for Transformer Oil With Improved Sensitivity

A molecularly imprinted polymer (MIP)-based 2-furfuraldehyde (2-FAL, C<sub>5</sub>H<sub>4</sub>O<sub>2</sub>) capacitive sensor with improved sensitivity has been presented. The electrode is shaped into a novel comb structure to increase the fringe field capacitance which is responsible for sensing 2-FAL. The MIP solution sensitive to 2-FAL molecules is prepared using polydimethylsiloxane (PDMS) and is coated on the printed circuit board (PCB) comb electrode. When the sensor is dipped in the transformer oil, the 2-FAL molecules are adsorbed on the template cavity of the MIP. The adsorbed layer of 2-FAL is responsible for the change in capacitance of the sensor. The sensor is tested for six oil samples containing the 2-FAL concentration (0–20-ppm range) and shows a mean sensitivity (<inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>) of 0.184 pF/ppm with a standard deviation (<inline-formula> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula>) 0.022 pF at 1 kHz. The sensor shows a linear result with the coefficient of correlation (<inline-formula> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula>) 0.998, and a maximum nonlinearity is 0.37% at 1 kHz in the 0–20-ppm range. The average repeatability of the sensor is ±0.12% over two weeks. Furthermore, the sensor is connected to a suitably designed electronic circuit based on the instrumentation amplifier for obtaining an electrical signal. The circuit gives an output voltage of 0.35 V/ppm at 1 kHz.

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