Development of a distance-independent wireless passive RF resonator sensor and a new telemetric measurement technique for wireless strain monitoring

We proposed and developed a novel wireless passive RF resonator scheme that enables telemetric strain sensing avoiding the need for calibration at different interrogation distances. The specific architecture of the proposed structure allows for strong inductive coupling and, thus, a higher wireless signal-to-noise ratio. Here, in operation, the frequency scan of the sensor impedance was used to measure simultaneously both the impedance amplitude and resonance frequency. Using this wireless sensor, we further introduced a new telemetric monitoring modality that employs full electrical characteristics of the system to achieve correct strain extraction at any interrogation distance. In principle, any deformation of the sensor structure results in the resonance frequency shift to track strain. However, changing of the interrogation distance also varies the inductive coupling between the sensor and its pick-up antenna at the interrogation distance. Therefore, at varying interrogation distances, it is not possible to attribute an individual resonance frequency value solely to an individual strain level, consequently resulting in discrepancies in the strain extraction if the interrogation distance is not kept fixed or distance-specific calibration is not used. In this work, we showed that by using both the proposed passive sensor structure and wireless measurement technique, strain can be successfully extracted independent of the interrogation distance for the first time. The experimental results indicate high sensitivity and linearity for the proposed system. These findings may open up new possibilities in applications with varying interrogation distance for mobile wireless sensing.