The electro-mechanical impedance technique has been extensively studied in recent decades as a non-destructive method for detecting structural damage in structural health monitoring applications using low-cost piezoelectric transducers. Although many studies have reported the effectiveness of this detection method, numerous practical problems, such as the effects of noise and vibration, need to be addressed to enable this method's effective use in real applications. Therefore, this article presents an experimental analysis of noise and vibration effects on structural damage detection in impedance-based structural health monitoring systems. The experiments were performed on an aluminum bar using two piezoelectric diaphragms, where one diaphragm was used to measure the electrical impedance signatures and the other diaphragm was used as an actuator to generate noise and controlled vibration. The effects of noise and vibration on impedance signatures were evaluated by computing the coherence function and basic damage indices. The results indicate that vibration and noise significantly affect the threshold of the lowest detectable damage, which can be compensated by increasing the excitation signal of the piezoelectric transducer.

Piezoelectric transducers are widely used in many nondestructive methods for damage detection in structural health monitoring applications. Among the various methods for detecting damage, the electromechanical impedance technique is known for using thin and small piezoelectric ceramics operating simultaneously as actuators and sensors. The basic method of installing these piezoelectric ceramics in the host structure is using a high-stiffness adhesive such as epoxy or cyanoacrylate glue. However, some studies have proposed alternative methods of transducer mounting, therein aiming to reuse the transducer or allowing for the monitoring of structures under adverse conditions under which the direct installation of the sensor would not be possible. Thus, the objective of this study is to analyze and compare the performance of three main mounting methods for metal structures for applications based on the electromechanical impedance technique: magnetic mounting, metal-wire-based mounting, and conventional mounting using adhesives. Tests were conducted on aluminum beams, and the performances of the three transducer mounting methods were compared using basic damage indices and the pencil-lead-break test. The experimental results indicate that the mounting method has a significant effect on the frequency response and sensitivity for damage detection.

Abstract:The use of low-cost transducers such as piezoelectric diaphragms in structural health monitoring (SHM) applications based on the electromechanical impedance (EMI) method has grown in recent years. Although many studies report the feasibility of such transducers for impedance-based damage detection, the experiments are typically performed on small structures. Therefore, the objective of this work is to perform an experimental analysis of the feasibility of the piezoelectric diaphragms for the detection of damage in large structures. Several tests were carried out on a large aluminum plate in which a diaphragm was attached. The electrical impedance signatures of the transducer were collected and a basic damage index was calculated in order to verify the feasibility of quantifying the size of the damage at different distances from the transducer. The experimental results indicate that the piezoelectric diaphragms have a good sensitivity to provide a damage size classification in large structures. In addition, the sensitivity to damage detection and classification decrease as the distance between the transducer and the damage increases. Therefore, the results reported in this study indicate that low-cost piezoelectric diaphragms are feasible for impedance-based SHM applications in large structures.

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