Revisiting Antenna Topology for Wearable RFID Tags on Lossy Dielectric Substrates

This study critically revisits the suitability of microstrip patch antennas for wearable RFID tags on thin, low-cost, lossy dielectric substrates, such as those of common garments, within the context of energy harvesting for wireless body area networks. Through full-wave analysis and equivalent circuit modeling, we demonstrate that the patch resonating behavior is not only determined by the substrate thickness and permittivity, but it is also strongly influenced by its dielectric conductivity. This behavior, observed in lossy substrates, suggests the selection of materials with higher permittivity, as they not only facilitate antenna miniaturization but also enhance radiation performance, contrary to the results typically associated with lossless or low-loss substrates. To further address these limitations of patch antennas, we propose a comparative analysis of two wearable rectennas on denim textile, operating at 2.4 GHz ISM band, using a patch antenna and a shielded meandered dipole as the receiving antennas. The results highlight the advantages of the latter topology in terms of conversion efficiency, and thus in terms of output DC power, besides adaptability for wearable RFID solutions.