Piezoelectric Transducer Self-diagnosis Based On Electrical Admittance Measurements

Structural health monitoring (SHM) techniques based on the use of active-sensing piezoelectric materials have received considerable attention in the structural community. However, the structures in question are usually subjected to various external loading and environmental condition changes that may adversely affect the brittle PZT sensors. Any damage in the sensor could be mistaken as damage in the structure depending on its effect to the signal.This paper proposes a piezoelectric sensor/actuator self-diagnostic procedure based on the principle of piezoelectric impedance technology to ensure the effective operation of the structural health monitoring (SHM) system. The premise of this procedure is to track the changes in the capacitive value of piezoelectric materials resulting from the degradation of the mechanical/electrical properties and its attachment to a host structure, which is manifested in the imaginary part of the measured electrical admittances. In detail, the research work of this thesis mainly consists of the following five parts:1. The piezoelectric sensor self-diagnostic procedure based on the piezoelectric impedance technology is analyzed, and the formula of the PZT's admittance is deduced. It is confirmed that sensor failure causing a downward (sensor breakage) and an upward (debonding between PZT transducers and the host) shift in the slope of the susceptance.2. Finite element model of the cantilever bonded with PZT is simulated by ANSYS software, and the harmonic response analysis of the good and damaged PZT is studied. The result shows that: by monitoring the the susceptance, one can quantitatively assess the breakage of the PZT and the integrity of its attachment to a host structure. The result is consistent with the theory.3. Experiment on the aluminum beam and design a simple detection circuit to take the imaginary part of the admittances. The result is consistent with the theory and simulation.4. The sensor diagnostics method is also susceptible to temperature.Take a lot of experiments on the beam to generate a temperature compensation which can separate temperature changes from sensor degradation.5. Design a self-diagnostic system base on ATmega16 and AD5933.Successfully use the system to identify the damage of the PZT.