Evaluation of SHM with the electromechanical impedance method using a high voltage excitation signal in high frequencies

Structural health monitoring (SHM) has originally been used for static structures. With the development of high-speed data acquisition technology, SHM systems can monitor structures in seconds. Advanced SHM systems for use in dynamic environments require operation in the microsecond timescale. One promising approach is the electromechanical impedance (EMI) technique. The EMI method monitors the impedance of a structure, and damage is indicated by changes in the impedance. Standard impedance measuring hardware are not practical for microsecond detection due to their slow sampling speeds. Faster impedance measuring techniques have been developed and allow for customizable excitation signals. Researchers have also considered taking measurements at higher frequencies to decrease the measurement time. Past works indicate sensitivity to damage is limited above 600 kHz. The goal of this study is to evaluate the sensitivity of the EMI method to damage with a high voltage excitation signal. It was hypothesized that increasing the voltage would increase damage sensitivity at higher frequencies. In this study, the amplitude of the excitation signal was increased using a high frequency voltage amplifier. A PZT disk bonded to a cantilevered aluminum beam was used as the test structure. Damage was created by decreasing the length of the beam. Finite element (FE) simulation was also employed to achieve a better understanding of the experiment. From the results of the experiment and FE model, using a higher excitation voltage has proven not to increase the sensitivity level of the EMI method. Higher voltages do improve the precision of the measurement by increasing the signal to noise ratio.