"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 × 105 Sm−1) antennas. Printed bioinert or ecoresorbable
conductors, comprising carbon, magnesium, or zinc fillers, typically exhibit
conductivity on the order of 10–1000 Sm−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 × 105 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.