Fabrication of a hydrogel-based microstrip patch antenna by laser-induced graphitization

Hydrogels have attracted attention as highly biocompatible supporting materials for wearable devices. An antenna is a key component for wireless transmission of information collected by the devices worn on the human body. Furthermore, integrating antennas into the devices eliminates the need for external wiring, which could obstruct the movement of the human body. In this study, we demonstrated the fabrication of planar conductive structures by laser-induced graphitization of tannic acid-containing alginate hydrogels and the fabrication of microstrip patch antennas (MPAs) using the fabricated structures. In a single laser scan onto the hydrogels, cracks were formed in the fabricated structures. For the fabrication of continuous planar structures, we used a method leveraging the water absorption property of hydrogels. By the method, in which an aqueous solution of tannic acid was added to the structures, followed by rescanning the laser beam to convert tannic acid to graphitic carbon, the number of cracks decreased. Additionally, it is confirmed that the fabricated structures can be applied to the radiation patches of hydrogel-based MPAs. A decrease in the resonant frequency of the fabricated MPAs corresponding to the decrease in the number of cracks is observed.