Distance sensing using spiral resonators

A chipless RFID distance sensor is introduced. The sensor is based on a spiral resonator (SR) label printed on a dielectric substrate that is attached to the object to be sensed. The resonant structure is working at around 860 MHz, which is far from probing loop's self-resonant frequency. The change in the distance is tracked by observing the change in the sensor's behavior at resonance, in particular the change in the peak magnitude of the input impedance which is modulated by the distance between the spiral resonator tag and the probing loop. Preliminary data obtained from numerical simulations show that the proposed sensor is able to provide real-time remote sensing of the distance up to 20 mm with high resolution.