Design and implementation of a digital smart layer for ultrasonic-guided wave-based structural health monitoring

Ultrasonic-guided wave (UGW) is an important technology for realizing structural health monitoring (SHM), and the piezoelectric transducer (PZT) is a commonly used actuator and sensor. The PZT layer is fabricated using a flexible printed circuit (FPC), and the interface of the PZTs is connected to the host of the monitoring system via cables. The flexible PZT layer (FPL) is easy to install, highly reliable, and widely used in industrial sites. However, as the distance between the host and the FPL gradually increases, the problem of guided wave (GW) signal attenuation caused by cables cannot be ignored. In addition, the use of shielded cables has the problem of heavy quality and high cost, and the use of unshielded cables has the problem of signal interference. Therefore, this paper proposes a digital smart layer (DSL) composed of a flexible signal acquisition system and a PZT array. The DSL acquires excitation and GW signals acquisition and performs PZT diagnostics. It connects to the host via a fixed six-wire cable and uses digital signals for communication. Multiple DSLs can be interconnected to form a network and perform damage detection simultaneously, improving the monitoring area and damage detection efficiency of the system. An experimental system was constructed on an aluminum plate to verify the functionality of the DSL. The results prove that the DSL solves the problems of signal attenuation and interference susceptibility of GW signal in long-distance cable transmission and realizes the diagnosis of PZT faults such as debonding and breakage. This paper provides a highly reliable and practical means of monitoring the condition of equipment structures such as airplanes, trains, and bridges.