A Novel Sol–Gel Thin-Film Constant Phase Sensor for High Humidity Measurement in the Range of 50%–100% RH

This paper proposes a new type constant phase sensor (CPS) for solving the problem of high humidity measurement. It is based on change in phase angle of the CPS with variation of humidity. The CPS is having interdigitated electrode sandwiched between two identical thin films of
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-Al
₂
O
₃
fabricated by sol–gel dipcoating method. In the presence of relative humidity, the device shows a fairly constant phase behavior over wide signal frequency and its fractional exponent reduces to nearly 0.7 value at 90% RH from the initial value of 1 at dry humidity. Results show that the CPS is effective in measuring humidity in the range of 50%–100% RH at the signal frequency of 1–5 MHz. Finally, the device has been interfaced with a simple fractional-order differentiator circuit to measure the phase angle change with change in relative humidity.