Combination of frequency shift and impedance-based method for robust temperature sensing using piezoceramic devices for shm

The influence of temperature is a major problem in Structural Health Monitoring diagnosis using guided waves. In this article, two methods for temperature compensation are used to evaluate the temperature of a structure monitored by Piezoceramic Transducers (PZT). The first one consists in a linear regression of the static capacity of the PZT (computed with the electromechanical impedance) with the temperature. It allows one to determine temperature of a PZT from any impedance measurement. The second method is based on the Modes Frequency Shift (MFS) of the frequency response function (FRF) calculated in a pitch-catch mode with an exponential sweep signal. A linear regression between the MFS and the temperature is settled for most modes and allow the estimation of temperature between two PZT. Experiments on a composite plate monitored by 5 PZT patches showed that a $\pm$2{\textdegree}C degree variation can easily be identified with both methods. Combined together, those two methods could replace actual temperature sensors and bring an efficient improvement for temperature compensation in applications where the temperature variation is heterogeneous on a structure.