Flexible Printed RFID Tag Antennas for Scalable and Sustainable IoT: Design Physics, Manufacturing Technologies, and System-Level Validation.

Flexible printed passive Ultra-High Frequency Radio Frequency Identification (UHF RFID) tag antennas couple electromagnetic design to conductor formation, substrate properties, chip attachment, and the mounting environment. This critical narrative review examines how those dependencies affect manufacturing choices and the strength of device-level evidence. Screen printing, inkjet printing, aerosol jet printing, flexography, and gravure are compared using reported process conditions and explicit gaps in reporting. Passive UHF tags containing an integrated circuit form the principal scope; High-Frequency/Near Field Communication (HF/NFC), chipless, and higher-frequency examples supply supporting process evidence. Given the difficulty of establishing a universal range limit across varying Equivalent Isotropically Radiated Power (EIRP) levels, chip sensitivities, polarizations, and mounting environments, this synthesis carefully categorizes performance metrics into directly measured distances, threshold-based estimates, and simulation-based predictions. Within-study comparisons show that reducing conductor consumption can sacrifice activation margin, while substrate morphology and chip bonding can limit performance even when nominal conductivity is high. Complete-tag scalability requires reproducible inter-connections, post-processing, and durability evidence in addition to successful printing. Environmental conclusions are separated into quantitative life-cycle results and indicators such as lower material use or biodegradability. The resulting framework identifies which design choices are supported by controlled comparisons, and which still require repeated device measurements, application validation, and environmental inventories matched to equivalent service.