Fabrication and Characterization of Cellulose-Based Materials for Biodegradable Soil Moisture Sensors

Internet of things (IoT) systems for precision agriculture enabled by biodegradable sensors have the potential to lead to more efficient use of water and fertilizers. Here, a capacitive moisture sensor designed to operate in the 902–928 MHz frequency band is screen-printed on a fully biodegradable paper substrate with a surface that is improved via the infiltration of cellulose nanofibrils (CNFs). Sensor trace quality on the CNF composite substrate is comparable to traces printed on polyimide and superior to traces printed on conventional cardstock. Furthermore, the moisture response of the substrate is shown to be enhanced via the CNF infiltration. Small feature sizes achievable through screen-printing on the CNF composite enable their use in RF passive wireless sensing systems. The fabricated sensors are shown to have a self-resonance well above the operating frequency band.