Fabrication and Characterization of Soil Moisture Sensors on a Biodegradable, Cellulose-Based Substrate

Internet of things (IoT) systems for precision agriculture offer the opportunity for more efficient use of water and fertilizers. Here, capacitive moisture sensors are screen-printed on a fully biodegradable paper substrate infiltrated with cellulose nanofibrils (CNFs). Screen-printed trace quality on the CNF-composite substrate is comparable to traces printed on polyimide and superior to traces printed on conventional cardstock. CNF-composite sensors absorb moisture and are shown to respond to changes in relative humidity (RH) in air. Sensors measured in loamy sand, similar to soil found in midwestern agricultural fields, are shown to respond to changes in soil moisture. The sensors demonstrate fast response times in both air and soil, making them ideal for use in agricultural applications. Small feature sizes achievable through screen-printing on the CNF-composite enable their direct use in 902–928 MHz chipless passive wireless sensing systems, as the fabricated sensors are shown to have a self-resonance well above the operating frequency band.