Influence on an electrically small UHF RFID split ring resonator antenna by biocompatible conformal thin and thick film coatings

The integration of low-cost electronic components into medical plastic parts for sensory data acquisition will be an essential feature of innovative medical products in the future. The realization of these wireless communicating Smart Biomedical Devices requires sufficient bioprotection by appropriate encapsulation of the toxic electronic components. These, however, influence wireless communication. The aim of the study was to investigate the influence of thin-walled conformal coated polymer lacquers on an electrically small antenna (ESA) of the type split ring resonator (SRR). The antenna was developed in order to derive integration strategies of UHF RFID antenna structures into medical products. To predict the signal transmission behavior of the antenna, eight different lacquers were used, which were tested for biocompatibility in previous studies. All coating materials examined showed a detuning of up to 50 Hz and an increase of the input reflection attenuation S11 of up to 50 % at layer heights of approximately 30–200 µm and relative permittivities up to εr = 5 with complete coating on the top and bottom layer of the PCB. The results allow conclusions to be drawn about the relationship between dry film thickness, dielectric properties, and the influence on the radiation and transmission behavior of the ESA. Concrete recommendations for integration strategies in Smart Biomedical Devices could be identified based on the results.