Browsing by Subject "Nested split ring resonators"

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Open Access
Design and implementation of a wireless passive sensing system for structural health monitoring
(2016-06) Özbey, Burak
Structural health monitoring (SHM) aims to ensure detection and prevention of damage in structures and protection of human life via observation of certain damage indicators. In SHM, one of the most important damage indicators is the strain forming on the steel reinforcing bars (rebars) embedded inside concrete. This strain can slowly develop over time, or can suddenly occur due to an overload such as an earthquake. In this dissertation, a novel wireless passive sensing system is presented for detecting and measuring the level of strain and relative displacement in structures. The sensing system comprises a nested split-ring resonator (NSRR) probe along with a transceiver antenna. These two elements form an electromagnetically coupled system that yields very high sensitivity and resolution of displacement and strain sensing accompanied with a wide dynamic range of measurement. Using this wireless system, it is possible to track strain/displacement in both the elastic (reversible-linear) and plastic (irreversiblenonlinear) deformation regions of steel rebars. In the dissertation, the results of the following experiments are presented: Characterization experiments carried out on a translation stage in laboratory environment, tensile test experiments where a rebar is loaded with a pulling force until fracture, and simply supported beam experiments where a beam undergoes loading, which leads to tensile strains on rebars at the bottom of the beam. Especially, the simply supported beam experiments constitute a decisive step toward a real-life application of the proposed sensing system. The sensing system is shown to acquire accurate data until the end of the measurements in which the wired devices such as strain gages break down and fail to capture. Furthermore, the eects of the complex electromagnetic medium formed by the rebars and the concrete on sensing are investigated. In addition, a multi-point sensing capability via multiple probes and single antenna is proposed and experimentally demonstrated, which can be used in 2-D surface strain mapping with further improvements. Finally, an equivalent circuit model is given for the NSRR structure, the results of which are compared to and found to be in good agreement with full-wave simulations and measurements. This study shows that the designed sensing system has the potential to be an alternative for both microstrain-level SHM and large displacement measurements, which can be useful for post-earthquake damage assessment.
Open Access
Wireless meta-structured RF probes for vibration sensing
(2023-07) Kılıç, Tuğba
Vibration signals are widely used for different monitoring purposes in numerous areas of applications. Sensing vibration and examining its properties play a critically important role essential to damage monitoring especially in the fields of construction and machinery. Detection of possible damages to these structures/machines requires cost-effective and easy-to-use solutions both to protect human health and/or reduce the cost of potential damage to the structures/machines. In this thesis, to offer an efficient and reliable solution for monitoring the health and integrity of various structures and machinery, we proposed and developed a new class of meta-structure based vibration probes that offer high-resolution and real-time wireless monitoring capabilities in vibration sensing. Operating in the radio frequency (RF) domain, this sensor concept relies on the near-field coupling of two nested split ring resonators (NSRRs), each of which is free to move toward each other. In response to the mechanical vibration occurring on a surface to which one of the NSRRs is attached, the amplitude of the electromagnetic wave read out only in vertical direction with respect to the NSRR probe from the coupled-NSRR pair by a transceiver antenna monotonously changes, making the sensing system capable of detecting mechanical vibrations over a wide RF range. The most important advantage of the proposed sensing architecture is that the resonant frequency read-out is very strongly dependent on the spacing between the coupled-NSRR probes, which makes wireless vibration detection at low amplitudes possible. The experimental findings show that this system can wirelessly measure vibration amplitudes as low as 50 µm. Equally important, this opportunely enables a high level of vibration resolution of (differentiation of two close vibration amplitudes separated by) 38.4 µm with an average error rate of only 1.2%. The sensing system exhibits a sensitivity level of 866 kHz/mm. The wireless and passive nature of the proposed system, together with the cost-effectiveness of our NSRR probes, make it highly promising for real-life applications including remote structural health monitoring, deformation detection, and vibration wave monitoring.