A simple PZT transducer design for electromechanical impedance (EMI)-based multi-sensing interrogation

A simple sensor design to achieve different electromechanical impedance (EMI) characteristics is required for the serial/parallel multi-sensing interrogation. Aiming at the shortcomings of traditional trial-and-error method for collocating serial/parallel PZT transducer with different EMI characteristics, this paper proposes a simple but effective method to design and fabricate PZT transducers with distinguished EMI characteristics by bonding PZT patch on permanent magnet disks with different thickness. The thickness of the magnetic disk could change the impedance resonant frequency of the transducer almost linearly, which greatly simplifies the transducer design to ensure each one has distinguished peak frequency. The EMI responses of proposed smart modulation transducer (SMT) under different thickness of magnetic disk were obtained by finite element method (FEM) simulations, as well as by experiments. The simulation outcomes are in good agreement with experimental results. And it is concluded that the EMI resonant peak frequency of SMT increases linearly due to the increase of magnet thickness, which ensures each SMT has very different EMI characteristics. Both experiments and simulations have confirmed that the proposed method is effective. To obtain the insight of the performance of the SMT to structural damage detection using multi-sensing EMI method, the four fabricated SMTs with different thickness of magnetic disk were series-connected for multi-bolt loosening monitoring. Results validate that the response signatures with distinguished EMI characteristics can be obtained, and both the severity and location of bolt looseness can be identified via the modified MAPD (mean absolute percentage deviation) damage index. The proposed PZT design method has great guiding role for optimizing the design of sensors for EMI-based multi-sensing interrogation, promoting the practical application of EMI technology in metal structure health monitoring.