Chipless-RFID Sensors for Motion Control Applications

This paper presents a sensor for the measurement of linear motion, including displacement, velocity and acceleration. For that purpose, a linear chain of metallic inclusions printed or etched at periodic positions on a dielectric substrate is considered. The measurement of displacements and velocities is based on the detection of the inclusions through microwaves when the linear chain of inclusions is in relative motion to the (static) reader, a transmission line based structure fed by a pair of harmonic signals. The inclusions are detected through their effect on the amplitude of the injected signals at the output port of the reader line (giving rise to pulses in the envelope function of the AM modulated signals). As compared to other previous linear displacement and velocity sensors based on a similar approach, in the proposed system the linear chain of inclusions is equipped with an identification (ID) code, where the binary state associated to each inclusion is given by its size. Thus, these electromagnetic encoders are useful for the determination of the chain position by reading a certain (predefined) number of bits, rather than from the cumulative number of pulses (the usual approach). A prototype device is presented in order to validate the approach.