Inkjet Printing of Epidermal RFID Antennas by Self-Sintering Conductive Ink

Abstract

The recently introduced inkjet printing technology with ambient sintering is here investigated for the fabrication of epidermal antennas suitable for radio-frequency identification (RFID) and sensing. The attractive feature of this manufacturing process is the possibility to use low-cost printers without any high-temperature curing. In spite of the estimated maximum achievable conductivity of the ink ( $\sigma _{\text {UHF}}=1\times 10^{5}$ S/m) in the UHF-RFID band that is two orders of magnitude lower than that of the bulk copper, a threefold printing process provides the same on-skin radiating performance as manufacturing technologies using bulk conductors. Experiments demonstrate that the epidermal antennas printed on the PET substrate are insensitive to moderate mechanical stress, like the natural bending occurring over the human body, and to the possible exposure to body fluids (e.g., sweat). Moreover, the electromagnetic response remains stable over the time when the printed layouts are coated with biocompatible membranes.