The electromechanical impedance (EMI) technique is considered to be one of the most promising methods for developing structural health monitoring (SHM) systems. This technique is simple to implement and uses small and inexpensive piezoelectric sensors. However, practical problems have hindered its application to real-world structures, and temperature effects have been cited in the literature as critical problems. In this paper, we present an experimental study of the effect of temperature on the electrical impedance of the piezoelectric sensors used in the EMI technique. We used 5H PZT (lead zirconate titanate) ceramic sensors, which are commonly used in the EMI technique. The experimental results showed that the temperature effects were strongly frequency-dependent, which may motivate future research in the SHM field.

In this paper, we experimentally analyze the sensitivity of piezoelectric transducers for damage detection in structural health monitoring (SHM) systems based on the electromechanical impedance (EMI) method, which has been reported as one of the most promising methods for non-destructive detection of damage. The sensitivity of the transducers for damage detection was assessed by comparing the electrical impedance signatures in an appropriate frequency range and using damage indices. Two damage indices commonly used in the literature were used in this study: the root mean square deviation (RMSD), which is based on the Euclidean norm, and the correlation coefficient deviation metric (CCDM), which is based on the correlation coefficient. Three types of transducers were evaluated: conventional 5H PZT (lead zirconate titanate) piezoceramics; macro fiber composite (MFC) devices, which have been widely used in recent years due to its high flexibility; and piezoelectric diaphragms, which are commonly known as "buzzers" and have a very low cost. Tests were carried out on aluminum beams and the electrical impedance signatures of the transducers were acquired in a frequency range of 0-550 kHz using a measurement systems based on a personal computer (PC) and a data acquisition (DAQ) device.Structural damage was induced by adding mass (small nuts) in the aluminum beams. The addition of mass changes the mechanical impedance simulating damage, such as crack or corrosion. This procedure has the advantage of not causing permanent damage in the specimens. Thus, the sensitivities of the transducers to detect damage were compared using the damage indices, as previously mentioned. The experimental results conclusively demonstrate that the transducers have different sensitivities for detection of structural damage. In addition, each transducer has an appropriate frequency range for damage detection, which provides high sensitivity. Therefore, the results presented in this paper allow selecting appropriately the piezoelectric transducer according to the application and the suitable frequency range in impedance-based SHM systems.