Baseline-free Imaging Method based on New PZT Sensor Arrangements

The Lamb wave-based structural damage detection technique is widely viewed as one of the most encouraging tools for structural health monitoring. However, the propagation of Lamb waves is complicated. Damage-scattering components in the sensing signals may easily be mixed with the waves that come from the source and those reflected from boundaries. Traditionally, damage scattering signals are obtained by comparing test data with a baseline data. However, such a process is affected easily by environmental and operational variability. Major emphases of the research in this article are on developing a baseline-free damage diagnosis technique based on time reversal theory. First, the propagation of the Lamb wave and its time reversal process are discussed. Second, time window functions and improved piezoelectric actuators/sensors array arrangement are developed to separate the scattered signals from the sensing signals. A time reversal imaging method is also adopted to detect and show the damages. This method makes all the scattered signals focus at the corresponding sources so that damages can be revealed. The validity of the proposed method is demonstrated through experiment in which a quasi-isotropic composite plate with PZT array is successfully monitored without relying on any past baseline data.