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.

Piezoelectric diaphragms are low-cost acoustic components commonly used in a wide variety of electronic devices, where the typical function is to generate an audible alarm. However, scientific study concerning the use of these components in advanced applications has increased in recent years because of their low cost and widespread availability in several standard sizes. Based on a growing interest in these components, we propose a basic equivalent electromechanical circuit considering a 1-D vibration assumption of piezoelectric diaphragms for structural health monitoring applications based on the electromechanical impedance (EMI) technique, which was used in this paper to assess the sensitivity of piezoelectric diaphragms to structural damage. The proposed circuit is a three-port type and is suitable for small metal structures. The sensitivities of three diaphragms of different sizes to structural damage were assessed using the proposed equivalent circuit and compared with the sensitivity of a conventional transducer commonly used in the EMI method. In addition, tests were performed on aluminum bars to experimentally validate the equivalent circuit, and the theoretical and experimental results correspond well.

Structural health monitoring (SHM) systems are scientifically and economically relevant as methods of detecting structural damage to various types of structures, thus increasing safety and reducing maintenance costs. Among the various principles of damage detection, the electromechanical impedance (EMI) method is based on the electrical impedance measurement of piezoelectric transducers attached to the monitored structure. Here, the accuracy and precision of the measurement system are fundamental for the correct diagnosis of the structure. Therefore, this paper performs a comparative analysis of two impedance measurement techniques for damage detection that are typically used in commercial impedance analyzers and other alternative measurement systems: 1) transient-state measurements using a sweep excitation signal and 2) steady-state measurements using a pure sinusoidal signal for each excitation frequency. Tests were performed with resistive and capacitive loads with known values and a piezoelectric transducer fixed to an aluminum bar representing a monitored structure. The two techniques were compared based on the accuracy, precision, and time required for the measurements. The results highlight the important features of each technique that should be considered for the development of impedance-based SHM systems and the correct diagnosis of monitored structures.

Structural health monitoring (SHM) based on the electromechanical impedance (EMI) has been pointed out as a promising method for detecting structural damage. However, practical problems such as the effects of temperature variation on the electrical impedance signatures of piezoelectric transducers have made it difficult to effectively apply this method of detecting damage in real structures. Therefore, in order to contribute to the effective application of the EMI method in real structures, this study presents a new feature extraction approach insensitive to temperature variations. The proposed method is based on the Akaike statistical criterion algorithm, which extracts the number of significant resonance peaks from the electrical impedance signatures. Tests were performed on an aluminium bar with different damage sizes and under different temperatures. The experimental results indicate that the proposed method is capable of detecting and quantifying structural damage in environments under temperature variation.

Piezoelectric transducers are used in many applications due to electromechanical coupling, which allows mechanical and electrical quantities to be related. This principle is used in the development of structural damage detection techniques such as electromechanical impedance (EMI) commonly used in structural health monitoring (SHM), where structural health is monitored by measuring and analyzing the electrical impedance of a transducer. As a piezoelectric transducer is a primarily capacitive device, its reactance becomes small at high frequencies, reducing sensitivity to structural damage and increasing the excitation current required from the measuring system. Therefore, this paper proposes the use of a negative capacitance (NC) interface with the transducer to improve sensitivity to structural damage and reduce the excitation current. The improvement obtained with the NC interface is theoretically analyzed using an electromechanical model and experimentally validated with tests on an aluminum structure. The results conclusively indicate a significant improvement in the sensitivity to structural damage and a reduction in excitation current, which are critical for detecting incipient damage and developing onboard monitoring systems where the output current drive is usually low.