Equivalent Circuit of Piezoelectric Diaphragms for Impedance-Based Structural Health Monitoring Applications

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.