Miniaturization limits of ceramic UHF RFID tags.

Radiofrequency identification (RFID) empowers numerous modern applications, enabling efficient accurate tracking and management of products, assets, and individuals in retail, logistics, and access control. Considering those and other perspective applications, there is a need to reduce the overall footprint of a passive tag while maintaining its reading range on at least a meter scale. Employing dielectric resonant antennas as a core of RFID tag design presents an appealing strategy, as it facilitates size minimization while counterbalancing this reduction by increasing the refractive index. Here we investigate the fundamental and practical constraints of this type of miniaturization, primarily focusing on the bandwidth limitations and temperature stabilities associated with high-index ceramic elements. Specifically, tags with relative dielectric permittivities ranging from 100 to 1250 were explored, demonstrating that a permittivity of 500 is optimal for footprint miniaturization and temperature monitoring, with a sensitivity of 3 MHz/°C. In contrast, a permittivity of 100 is ideal for thermostable tags. Further size reduction using permittivities above 500 decreases the communication channel bandwidth below the thresholds required by standard UHF RFID protocols, which thus serves as a practical limitation for further footprint reduction. RFID tags with cubic millimeter-scale footprints, capable of being accessed from distances well over a meter, and ideally integrated with sensor functionalities, have the potential to revolutionize the Internet of Small Things where compact and resource-limited items can become active participants in a global network.