Theoretical And Experimental Research On Mechanical Model Of Piezoelectric Ceramics Sensors

A variety of large and complex engineering structures have been developing and structural health monitoring (SHM) technology has been becoming an academic research focus with the economic developing in China. Over the last decades, some smart materials which are typically represented by piezoelectric ceramics material (such as Lead Zirconate Titanate, PZT) have predominant properties of dual-function of sensing and actuating. The sensor made by use of the sensing function of the PZT has been widely used in the field of structural damage detection and health monitoring. The sensor has advantages of fast response, good linearity, low energy-consumption, low cost and easy manufacturing. However, it is difficult to precisely take theoretical analysis in practical application, especially in health monitoring of concrete structures, due to complex boundary conditions of PZT patch and the complicated stress situation. At present, it is believed that the pressure applied on the surface of the PZT patch has linear relationship with the output voltage of the signal, which is not considering the impact of the layer thickness and has the deference with actual situation.The purpose of the research is to establish a mechanical model for the PZT sensor, and take a parameter analysis and experimental validation based on the above background. Taking the PZT crystal, the pasted-type and the embedded-type sensors as the main research subjects, respectively, the paper presents a method to set up the mechanical model by use of the piezoelectric equation and the vibration equation. Based on the proposed mechanical model, the parameters such as the actuating signal, layer thickness, PZT area, boundary condition et al are theoretically and numerically developed by selecting the appropriate actuating way to theoretically make the signal analysis. The paper has carried out the theoretical analysis and the experimental validation in several aspects as following:Firstly, based on the piezoelectric constitutive equations, the paper establishes the simplified mechanical models for the sensor by using the lumped mass method, sets up the theoretical expression of the piezoelectric effect for the PZT sensor, and solves the stiffness of the PZT patch.Secondly, based on the proposed the expression of the electric charge of the piezoelectric effect, the mechanical models for both the pasted-type and the embedded-type PZT sensors are simplified respectively and the multi-parameter expression is established by considering the damping of the layer thickness and the energy dissipation of the cable and devices which is equivalently changed into system damping.Then, the established sensing model is numerically analyzed under a harmonic loading and the influence of the parameters is further clarified.Finally, the experiments for the pasted-type and embedded-type PZT sensors with deferent thickness under a harmonic loading are conducted to validate the proposed models. The experimental results are compared with the numerical ones with the same parameters and they match well.The proposed mechanical model may lay a basic foundation for damage detection and health monitoring of concrete structures.