Electromagnetic Rotary Encoders Based on Split Ring Resonators (SRR) Loaded Microstrip Lines

This paper presents electromagnetic rotary encoders (used for angular velocity sensing) implemented in microstrip technology for the first time. The stator is a SRR-loaded microstrip line in bandpass configuration fed by a harmonic (single tone) signal. The rotor is a disc of dielectric material with a circular chain of SRRs, identical to the one of the stator, etched at the edge. By positioning the stator and the rotor with the SRR of the stator at short distance and face-to-face to the rotor chain, rotor motion modulates the amplitude of the feeding (carrier) signal at the output port of the line. This is due to the electromagnetic coupling between the SRR of the line and the SRRs of the chain, which in turn modulates the transmission coefficient of the line (stator) at the frequency of the carrier signal. Consequently, the envelope of the output (AM modulated) signal, which can be obtained by means of an envelope detector, exhibits pulses, and from the time distance between adjacent pulses, the angular velocity can be inferred. The main advantages of the proposed system, as compared to previous rotary encoders based on coplanar waveguide (CPW) technology, are backside isolation, necessary in certain applications, and, most important, major robustness against variations in the stator-to-rotor distance (air gap), caused by misalignments, rotor precession or rotor vibration.