The Research Of Piezoelectric Impedance Technology Applying To The Dynamic Signal Excitation Beam

At the moment, with the researches on the damage detection by the piezoelectric impedance technology more and more, many research achievements are resulted in, which provide certain technical support and guidance for the structural damage identification. At the same time, the loading researches on the study object, from scholars at home and abroad, used mostly static signals, such as tension, torque. Moreover, piezoelectric element is stuck on the measured structure. Based on the integrated study of piezoelectric impedance technology application, a series of formulas derivation were carried out in theory. A piezoelectric impedance sensor was designed and manufactured. Combining with a variety of data processing methods, the research on the impedance technology applying to loading dynamic signal beam was discussed. The research contents and results could be summed up as follows.Firstly, the appearance and development information of the piezoelectric materials was summarized. The piezoelectric impedance theory of the piezoelectric coupled systems was introduced. And the theoretical analysis was made. The piezoelectric coupled electric admittance (electric impedance) formula was derived. The relationship between the piezoelectric coupling impedance and mechanical impedance was expounded.Secondly, the theoretically admittance formula under PZT free vibration was derived. What's more, the PZT resonance conditions were got. The defects in the process of pasting piezoelectric element were summarized. Then the piezoelectric impedance sensor was come up with and designed. Its feasibility was validated theoretically and experimentally. At last, its physical dimension was optimized to be involved in the beam damage detecting experiments (crack depth, crack number).By comparing with the patch type, the conclusion that the law of the sensor type is consistent with patch type was drawn, and the effect is remarkable.Thirdly, the theory of mechanical impedance and piezoelectric coupling impedance was analyzed and studied. The formulas of beam piezoelectric coupling impedance and mechanical impedance were derived. It was concluded that the resonant frequency of the piezoelectric coupling beam impedance analysis is completely consistent with mechanical impedance beam resonance frequencies, which explained the piezoelectric coupling impedance can reflect the aluminium beam mechanical impedance. The aluminium beam resonance frequency value was determined by the determination the resonant frequency value of the piezoelectric coupling beam. And of the experiment instrument, device, colloid and patch way, the points of experiment for attention were made detailed description.Fourthly, the experimental research of dynamic signal beams was done by applying piezoelectric impedance technology. The experiment scheme was determined. The experimental device was set up. The experiment was divided into three frequency areas:resonance region, low frequency non-resonant area, high frequency non-resonant area. Furthermore, the incentive signal frequency in or out of sweep frequency range was discussed. The methods of processing experimental data were also summarized. The influence index was defined, and it is found that RMSD method and COV method are good for data processing. By contrast, COV method is more precise.