Impedance-based damage detection and identification---Enhancements using circuitry effects

The basic idea of impedance-based damage detection is that, through multi-field coupling, the electrical impedance of an impedance sensor can be directly related to the mechanical impedance of the structure to which the sensor is attached. Therefore, damage effect can be reflected in the change of the sensor impedance curves before and after damage occurrence. As the impedance information can be extracted in high frequency range for many transducer materials, such method is sensitive to small-sized damage. Moreover, it can be used to identify both the location and severity of damage once the explicit relation between the impedance measurements and a high-fidelity model is established. ^ The first part of this dissertation is dedicated to improving the piezoelectric impedance-based sensing. First, an inverse sensitivity-based method, based on the spectral element method that is particularly suitable for high-frequency analysis, is developed for damage identification. Then, a new piezoelectric impedance sensor design with the integration of a tunable inductive circuitry is proposed. It is shown that this inductive circuitry can amplify remarkably both the impedance measurement and the anomaly amplification, thereby improving the detection sensitivity and robustness. It is also shown that further enhancement can be accomplished by integrating a negative capacitance element. ^ The second part of this dissertation discusses extending the circuitry integration concept to magnetic transducer. Since direct contact is not needed for magnetic transducer-based impedance sensing, this approach can be applied to structures with complex geometry and also can facilitate movable sensor design. One straightforward way of increasing the generally low magneto-mechanical coupling is to increase the number of turns of wire in the electrical coil of the sensor, which, however, increases the inherent inductance and parasitic resistance. Inspired by the piezoelectric circuitry integration concept, a tunable capacitive circuitry is integrated into the magnetic sensor to improve the detection sensitivity. Based on a newly established analytical model of the magneto-mechanically integrated system, comprehensive case studies are performed to elucidate the parametric influences. ^ Throughout this dissertation, numerical/analytical results are correlated to experimental results. Guidelines for the optimal design, tuning, and placement of the sensors are analyzed systematically.