Browsing by Subject "Structural health monitoring"

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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.
Embargo
Process development for microfabrication of phase reversal CMUT devices for structural health monitoring and development of dynamic characterization processes for MEMS applications
(2024-08) Küçük, Merve Mintaş
If appropriately designed, Capacitive Micromachined Ultrasonic Transducers (CMUTs) offer advantageous properties such as low cost, small size, low impedance, and environmental friendliness, over piezoelectric transducers. These advantageous properties of CMUTs enable the CMUT devices to be employed in a large area of applications, such as medical applications and non-destructive testing (NDT) applications. CMUT devices and technologies that are heavily developed for medical applications also shed light on the development of CMUT devices to be used in Structural Health Monitoring (SHM) applications for civil infrastructures. Continuous monitoring of the signals produced by the sudden changes happening within civil infrastructures such as bridges or railways may give crucial information about the health of these structures. The rapid release of localized strain energy, which generates Acoustic Emission (AE) waves, is an important indicator of the state of the health of a structure. Detecting AE wave signals may give significant clues about damage formation such as impact, crack initiation, or crack growth. Because AE waves are scattered among a broad range of frequencies, sensing of such AE waves should also be done in broadband, and sensors are preferred to be highly sensitive among such band. For real-life applicable developments, it should be also considered that the environment of the real-life application may be very noisy due to many unrelated reasons, which makes employment of the CMUTs developed in a tightly controlled laboratory environment unpractical for the real-life applications. The noise may often be induced by the noise interferences that are produced by a variety of events that are not needed to be detected. To prevent misjudgments, it is important to differentiate between noise interferences and relevant AE signals, as the presence of significant noise can hinder the detectability of AE waves associated with structural damage. In this process development for CMUT prototype microfabrication study, we collaborated with a group of researchers who have introduced a new approach to designing broadband CMUTs, as well as a unique type of CMUT combination that uses phase-reversal (PR) of generated electrical current for detecting a wide range of mechanical vibration wave frequencies and reducing unwanted noise. By considering the simplest combination of two CMUT cells, the theoretical study, supported by FEM simulations, demonstrated that reversing the electrical current phase of one cell can create low-frequency and high-frequency stopbands for noise rejection, which is applicable for CMUTs operating in air damping. The primary objective of this thesis study is to develop microfabrication processes to microfabricate PR-CMUT devices to bridge the gap between theoretical design and real-world application of PR-CMUT devices. These PR-CMUT arrays that are designed for wafer-scale batch-compatible manufacturability have a flat passband in the 200-250 kHz and 200-300 kHz frequency ranges and two improved stopbands on both sides of the relevant frequency ranges. The photolithography masks, compatible material selections, and microfabrication process flows (integration processes) required for the microfabrication of these PR-CMUT devices were designed considering the capabilities of our cleanroom facility. Microfabrication of the devices was tried multiple times, and in line with the problems encountered in these processes, the microfabrication process flows were updated and the PR-CMUT devices were tried to be produced in multiple iterations. Unit processes, and multiple integration processes were developed and completed. Possible solutions to be implemented in the future microfabrication studies were determined. Additionally, dynamic characterization of individual circular geometry CMUT membranes were explored using a ZYGO Optical Profilometer. With this measurement tool (ZYGO), it is possible to measure CMUT device membrane displacements precisely when the membrane of the CMUT device is moving (vibrating) dynamically. Results obtained from ZYGO Optical Profilometer tool were compared with the impedance analyzer results. It was shown that the resonance frequency of a circular membrane CMUT device can be observed with the ZYGO Optical Profilometer. Furthermore, based on the conclusions from the studies in this thesis, future studies are suggested for further development towards realization and characterization of these PR-CMUT MEMS (MicroElectroMechanical System) devices.
Open Access
RF displacement and strain sensing system for wireless structural health monitoring
(IEEE, 2015) Özbey, Burak; Kurç, O.; Demir, Hilmi Volkan; Ertürk, Vakur B.; Altıntaş, Ayhan
Structural health monitoring (SHM) is a technology with worldwide interest that is vital to ensure the reliability of any structure while also protecting the safety of human life. Over the years, a lot of research has been conducted on this topic, proposing SHM methods that may be instrumental in understanding the condition of critical parts of a structure. These methods generally rely on wired and/or active technologies, which are not preferable since the wires disallow telemetric measurements and mean increased weight and space, while the active technologies require electric power in order to operate. Two of the most important damage indices of a building structure such as a reinforcing bar (rebar) are the strain and displacement forming either with time or a sudden impact like an earthquake.
Open Access
A wireless passive sensing system for displacement/strain measurement in reinforced concrete members
(MDPI AG, 2016) Ozbey B.; Erturk V.B.; Demir H.V.; Altintas, A.; Kurc O.
In this study, we show a wireless passive sensing system embedded in a reinforced concrete member successfully being employed for the measurement of relative displacement and strain in a simply supported beam experiment. The system utilizes electromagnetic coupling between the transceiver antenna located outside the beam, and the sensing probes placed on the reinforcing bar (rebar) surface inside the beam. The probes were designed in the form of a nested split-ring resonator, a metamaterial-based structure chosen for its compact size and high sensitivity/resolution, which is at µm/microstrains level. Experiments were performed in both the elastic and plastic deformation cases of steel rebars, and the sensing system was demonstrated to acquire telemetric data in both cases. The wireless measurement results from multiple probes are compared with the data obtained from the strain gages, and an excellent agreement is observed. A discrete time measurement where the system records data at different force levels is also shown. Practical issues regarding the placement of the sensors and accurate recording of data are discussed. The proposed sensing technology is demonstrated to be a good candidate for wireless structural health monitoring (SHM) of reinforced concrete members by its high sensitivity and wide dynamic range. © 2016 by the authors; licensee MDPI, Basel, Switzerland.