UHF RFID Analog Sensor System Using Power-Independent Antenna Optimization

Ultrahigh frequency radio-frequency identification (UHF RFID) tags are extensively utilized for their cost-effective provision of rudimentary sensing capabilities. However, the existing UHF RFID analog systems face efficiency challenges in multitag scenarios due to the need for individual radiated power adjustments for each tag to accommodate varying chip impedances. This letter introduces a novel sensing consistency coefficient and power transfer efficiency to ensure a point-to-point mapping between antenna-sensitive factors and auto-tuned values, independent of spatial factors across supported received power levels. By optimizing the dimensions of the RFID antenna layout based on chip impedance values at these power levels, we achieve a power-independent consistent mapping model that does not compromise communication performance. Furthermore, we propose an infusion monitoring system that employs a flexible, passive UHF RFID tag placed exterior to the drip chamber. This system triggers an early warning indicator for low liquid levels within the drip chamber by measuring auto-tuned values, prompting nursing staff to take follow-up actions. Experimental results demonstrate consistent mapping relationships between antenna-sensitive factors and auto-tuned values under diverse spatial conditions. This study not only enhances the time efficiency of the read/write device in multitag environments but also paves the way for new applications of UHF RFID in medical monitoring and similar fields.