Multichannel Electromechanical Impedance Structural Diagnostics in Plate Specimens

Structural health monitoring has become increasingly important in order to save costs and improve the safety of structures. One of the methods of monitoring the health of structures is the use of thin piezoelectric wafer active sensors to measure the electromechanical impedance of the integrated structure/sensor system. These wafers have proved to be efficient in structural diagnostics as they serve as both actuator and sensor for the structures they are attached to. In this contribution, a multichannel unit, which is an arrangement of single miniaturized electro-mechanical impedance units, is utilized to measure the electromechanical impedance of a complex plate structure. The multi-channel unit was validated by measuring the impedance signature of a cantilevered beam and comparing the results with those obtained using a desktop impedance analyzer, the HP4192A. A numerical modelling of 2D structures was performed using finite element analysis on COMSOL multiphysics software. This was validated by comparing the electromechanical impedance data obtained from the numerical modelling with analytical and experimental data. The specimen was numerically modelled for each sensor bonded to its surface and the results were analyzed. Furthermore, all the sensors on the specimen were simultaneously excited within the same frequency band and the electromechanical impedance data from each sensor was compared with those from same sensor when only one sensor was excited. The results were analyzed and discussed. A numerical modelling of the specimen with all the sensors simultaneously excited was also carried out and the results were compared with experimental data. The multi-channel unit was also used for damage detection in plate specimens. Structural damage was introduced in the specimen and the electromechanical impedance signatures of the damaged specimen was measured. The result was analyzed and compared with results obtained from the pristine specimen in the same frequency band. The data from each sensor was analyzed and discussed. The efficiency of piezoelectric sensors for detecting damages in structures was highlighted and the effect of sensor location on the accuracy of detecting damages in structures was presented. This suggests optimum sensor location for damage detection in structures. Finally, the multichannel unit was used to measure damage detection in the specimen at different frequencies when excited simultaneously by all sensors. The electromechanical impedance data obtained was analyzed and compared with data from the pristine specimen and in the single frequency band. The ability of piezoelectric sensor to detect damages in simultaneously varying frequency bands was explored. Recommendations for the application of the multichannel electro-mechanical impedance approach in structural health monitoring were given.