Application of broadside-coupled split ring resonator (BC-SRR) loaded transmission lines to the design of rotary encoders for space applications

The accurate measurement of angular displacement and velocity is necessary in many space applications (e.g. in reaction wheels or pointing mechanisms). This paper reports a novel microwave rotary sensor that is contactless, low cost, and robust in space environments. The stator part is a coplanar waveguide loaded with a pair of split ring resonators, whereas the rotor is a periodic circular array of split ring resonators. The stator and the rotor are arranged face-to-face, and the splits of the stator and rotor rings are on opposite sides, giving rise to a broadside-coupled split ring resonator (BC-SRR). Its resonance frequency depends on the relative position between the stator and rotor rings, which determines their coupling. The key point of the reported approach is the fact that the period can be made as small as the printing technology allows for, making quasi-instantaneous measurements possible. By feeding the structure with a fixed harmonic signal, tuned in the vicinity of the BC-SRR resonance frequency, the angular velocity can be accurately determined.