Structural damage detection in noisy environments based on electromechanical impedance and Lamb Waves with piezoelectric diaphragms excited with high frequency signals

Structural health monitoring (SHM) systems have shown their high potential over the decades. With the development of technology, methods of implementing these systems through computational processing have been widely applied. The great value of these systems is in protecting the structures and people involved. Ideally, detect early-stage damage using high-frequency excitation signals. As these systems can be built using sensors that are attached to the structure, temperature and noise effects will inevitably be inserted in the signals read by their sensors, thus generating a false positive. The development and knowledge of sensors available on the market that can be used in SHM systems is of global interest, as they offer a cost reduction in the development of these systems as well as a wide choice for a given application, due to the extensive knowledge of sensors that can be used. Piezoelectric diaphragms are sound components widely used in everyday electronic devices and, in addition to their low cost, they have the advantage of being mass produced by several manufacturers in standardized sizes and readily available. Based on this information, the objective of this thesis is to present the results of the feasibility study of piezoelectric diaphragms as an alternative transducer for the Lamb wave technique, allowing to expand the research, as well as to accelerate the implementation of SHM systems with lower installation costs, these diaphragms are already widely used in the electromechanical (EMI) impedance technique. To assess the viability of these components using Lamb waves, basic analyzes by the finite element method (FEM) and experimental tests were carried out on aluminum plates and the results obtained with the diaphragms were compared with those obtained with conventional piezoelectric ceramics. After verifying the effectiveness of these components in generating and detecting damage using Lamb waves, the research continued by carrying out a comparative analysis of the effects of noise in the detection of structural damage using the EMI technique and Lamb waves with signals of excitation at high frequency. In addition, tests were carried out to compare the ability of each technique to detect, quantify and locate damage in the structure before the analysis with noise. The results showed that both techniques are effective in detecting structural damage in a noisy environment and quantifying and locating damage under ideal conditions. (AU)