An ultra-sensitive piezoresistive polymer nano-composite microcantilever platform for humidity and soil moisture detection

Simultaneous monitoring of soil moisture at different soil levels or near plant roots and relative humidity are crucial for optimizing the crop yield. In the present paper, we demonstrate a novel, compact and inexpensive polymer nano-composite piezoresistive microcantilever sensor platform for the measurement of relative humidity (% RH) and soil moisture. A piezoresistive microcantilever is realized using SU-8 and carbon black based nano-composite. Its surface is further modified by Poly-aniline (PANI) nanofibers as a sensing layer. The surface functionalization is confirmed by FTIR, SEM and contact angle measurements. The sensor exhibited a maximum response of 28 mV toward 93% RH with sensitivity of 64 μV/0.1% RH. Sensitivity values of 43.6, 275 and 78.6 μV/0.1% change in the moisture content for bentonite soil, white clay and sand, respectively, are achieved. Such high sensitivity values coupled with the low cost can be utilized further for the realization of rugged, portable and handheld devices with wireless networking facility.