Elastic guided waves constitute a promising approach for structural health monitoring (SHM) applications involving composite structures. Guided-wave SHM systems are composed of a network of ultrasonic sensors, which are permanently attached to a structural component. Besides monitoring, the supplementary capability of the network nodes to exchange information across this mechanical wave-guide itself, represents an innovative feature for future intelligent SHM systems. In this research, the wireless transmission of encoded data across a glass-fiber reinforced polymer (GFRP) plate is demonstrated. Digital communication is based on Lamb waves, which are excited and recorded by piezoceramic transducers. Two distinct processing schemes are explored, namely amplitude modulation (AM) as well as frequency-division multiplexing (FDM), which allows the simultaneous sending from different actuators. The experimental investigation on a transversely isotropic planar wave-guide is accompanied by finite-element (FE) analysis. We have achieved: (i) reliable recovery of sent data, despite the dispersive multi-modal nature of Lamb waves and their multipath propagation, (ii) perfect message reconstruction at bitrates up to approximately 100 kbps, (iii) possibility for parallel communication by means of FDM.
Reference: Kexel, C.; Maetz, T.; Mälzer, M. & Moll, J., Digital communication across orthotropic composite components using guided waves, Composite Structures, 2018 (accepted in October 2018), Link