Planar Spiral Resonators for remote tracking of displacement

This paper presents a wireless displacement sensor based on a planar spiral resonator (SR) interrogated by a microstrip probing loop. The working principle is based on the relationship between the mutual coupling between the two RF components and the input impedance at the loop terminals. The distance estimation is obtained by monitoring the magnitude of the real part of the loop input impedance, at the operating frequency (about 860 MHz), which is a function of the tag-loop distance (d
tag
). The proposed design benefits of simplicity, robustness, single-frequency interrogation, high scalability potential, and accurate high-resolution measurements in the operating range.