This study is aimed to explore efficiency problems of using PZT patches in active vibration control of beams. The PZT patches are surface-bonded as actuators and strain gages are used as sensors. Distributed moment forcing mode is adopted to derive the control authority of actuators. Uniform beam model is applied when the mass and stiffness of PZT patches are ignored. Stepped beam model is then derived to describe the beam-actuator structure when the effect of patches is taken into consideration. Modal expansion method is used to determine the efficiency index of PZT patches in each mode. It is found that the structural modification caused by attaching PZT patches may degrade the control efficiency. It is also found that the optimal positions from stepped beam model are similar to those from the uniform beam model. The ratio of control efficiency from the stepped beam model to that from the uniform beam model is associated with stiffness of host structure and actuators. Base on this finding, the optimal thickness of PZT patches can be obtained. Because the factor is a constant when the structure is determined, we propose a modified model to estimate the control efficiency. This modified model, while taking advantage of simplicity of the uniform beam model, yet accounts for the effect of the inertia and stiffness the PZT patch. Experiments on vibration control of beams were conducted to verify our efficiency estimate.
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