Inductively coupled capacitive soil moisture sensors printed on a biodegradable substrate: Characterization and long-term testing

• Wireless LC soil moisture sensors are fully printed on a biodegradable substrate • Sensors can be wirelessly interrogated at distances up to 10 cm in dry soil • Sensors respond to changes in soil moisture fast enough for agricultural monitoring • Sensors have a lifetime larger than 113 days in soil with varying moisture content Precision agriculture systems enabled by small, biodegradable, passive, wireless soil sensors will allow for more judicious use of limited resources while increasing crop yield. Here, a capacitive soil moisture sensor is integrated with an inductive loop antenna to enable wireless sensing through loose inductive coupling. To minimize sensor costs, the sensor is manufactured by screen printing a conductive ink onto a biodegradable paper-based substrate. The sensor is interrogated wirelessly using a vector network analyzer, and has an interrogation range up to 10 cm in air and dry soil. Five sensors were buried at varying depths alongside a plant and a commercial soil sensor. The sensor’s ability to respond to changes in soil moisture at depths up to 5 cm is demonstrated. The sensors’ ability to respond to changes in soil moisture over long periods of time (i.e. up to 113 days) is demonstrated. All sensors remained functional through the end of the testing period, illustrating their suitability for use in agricultural settings over an entire growing season.