Soft and Ffexible wireless epidermal plaster made by laser-induced graphene

This letter introduces an epidermal antenna made of laser-induced graphene (LIG) that is designed for hosting sensors within the ultra-high frequency (UHF)-RFID band (860-960 MHz). The upper bound performance is identified through numerical simulations and it is just 4 dB lower than a copper counterpart. Comparative assessments reveal that a significantly wider trace width is necessary to mitigate the intrinsic power loss of LIG. Furthermore, this letter offers the first experimental demonstration of a LIG-based wireless flexible plaster, integrating a temperature-oriented radio frequency identification (RFID) IC encapsulated between skin-friendly elastomers. To address impedance matching challenges, a small coupled aluminum loop is employed to interface with the RFID IC. The device underwent testing on volunteers across different body parts with varying curvatures. Results indicate an averaged realized gain of -19 dBi, enabling a potential biophysical parameter collection from distances of up to 35 cm using a 3.2 W Effective Isotropic Radiated Power. This performance could support diverse applications in home care and sportswear. However, a notable efficiency degradation (5 dB) persists due to the interconnection of the antenna to the microchip transponder, presenting an ongoing challenge for optimization.