Polycaprolactone-Based Zinc Ink for High Conductivity Transient Printed Electronics and Antennas

Distributed sensors and electronics can be used in agriculture to optimize crop management and improve environmental outcomes. Electronic devices in these outdoor spaces require medium to long range (>1m) wireless communication of data over several weeks or months, which in turn requires high conductivity (1 × 10^(5) Sm^(−1)) antennas. Printed bioinert or ecoresorbable conductors, comprising carbon, magnesium, or zinc fillers, typically exhibit conductivity on the order of 10–1000 Sm6(−1) and lifetimes from a few hours to a few days. A print-based fabrication process for chemically treated zinc traces, which achieves conductivity of up to 6 × 10^(5) Sm^(−1) is reported here. The ink formulation uses a non-water-soluble soil biodegradable polycaprolactone binder. The ink and printing processes reported here led to stable conductive traces that are used in ultra high frequency radio frequency identification (UHF-RFID) folded dipole antennas operating at 915 MHz. The conductivity of the printed traces is maintained for over 70 days in ambient environments when traces are protected by a biodegradable beeswax encapsulation layer.