Wireless metamaterial-inspired rotation sensors

Abstract

Recently steel construction structures have been attracting increasingly more attention due to the speed and ease of their construction. However, to detect potential damages in these structures, long-term and cost-effective health monitoring solutions are required. A rotation-based bending movement, which typically occurs in the load carrying elements of these structures (such as beams), is an example of the aforementioned potential damage. In this thesis, for measuring small bending rotations (10−4 ~ 10−5 radians) in the structures made of materials such as steel, a novel wireless rotation sensing system with a high level of sensitivity and resolution is proposed and demonstrated. This system consists of two elements: an interrogating antenna and an inter-digital double-layer sensor. The proposed sensing system operates based on the principle of near-field coupling between the antenna and the sensor. Briefly, by rotating one layer with respect to the other, the electromagnetic coupling between the layers changes and the resonance frequency is consequently shifted. This frequency shift can be recorded by tracking the resonance dips in the S11 response of the antenna. In the thesis work, various experiments were systematically performed to characterize the sensing system. A high rotation resolution of 20 µ-radians, an excellent sensitivity level of 28 MHz/degree, and a large dynamic range extending over 40◦ were measured. Furthermore, the validity of measurement results was verified by using full-wave electromagnetics simulator and applying digital image correlation (DIC) method for 2D measurements.