Exploiting Self-Tunable RFID Chips for Wireless Sensing of Permittivity to Enable Passive Low-Cost Food-Quality Monitoring Systems

Self-tunable RFID chips allow for dynamic adjustment of their susceptance to improve the conjugate complex matching with the tag antenna even when working conditions vary over time. By exploiting this feature, the chip can wirelessly provide digital information related to the varied boundary condition. In this work, a fully-passive sensor based on a self-tunable Axzon Magnus-S3 chip has been designed and tested to sense the variations in the dielectric constant of a substrate. To achieve this, a planar interdigitated capacitor was fabricated, characterized, and connected to a tag antenna that was designed to ensure a robust communication link during the chip susceptance excursions. The experimental results demonstrate the feasibility and effectiveness of the proposed approach, showing significant potential for a wide range of applications in the food industry and beyond.