Wireless Rotation Sensor Using Dual-Layered Twofold Spiral Resonator

Abstract

This letter presents an electrically small rotation sensor using dual-layered Fermat spiral-shaped resonators where one of the resonators acts as a rotator, while the other acts as a stator. The sensor has two key characteristics. First, it is designed to operate wirelessly and the resonators are excited by a dual-polarized patch antenna. Second, the structure of the sensor has a twofold symmetry that provides the cross-polarized field component in the radar cross-section response of the sensor and contributes to the robustness of the sensor against background interference. The angular displacement of the rotator causes the changes in the coupling between the two resonators, and thus, it can be measured in terms of resonant frequency shifts in the cross-polarized response of the sensor. To analyze the response of the sensor and quantify the angular displacement, a mathematical model is used to relate the coupling coefficient and spectral shifts of the resonant frequencies. The sensor is fabricated and experimentally characterized, and it is shown that for the angular dynamic range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0^{\circ }\text{--}90^{\circ }$</tex-math></inline-formula> , a comparatively high maximum bandwidth average sensitivity of 7.4 MHz/degree is obtained.