A Structural-Aware Frequency Division Multiplexing Technique for Acoustic Data Communication in SHM Applications

The technological advancements in the sensor design and fabrication process brought about a new generation of smart sensor nodes to be used for Structural Health Monitoring (SHM) purposes, which are concurrently capable of data sensing and processing in situ. This is the case of GWs-based monitoring applications, where the capability of the state-of-the-art transducers to generate custom signals inspired new potentials for acoustic data communications without the need for external cabling. Thus, information about the structural integrity might be transferred between sensor nodes permanently attached to the structure and exchanged across the monitored mechanical waveguide as a numerical damage indicator. Here, a combination of square-wave excitation sequences and frequency-division multiplexing (FDM) is explored for simultaneous communication with multiple nodes. In detail, the problem of selecting the most appropriate carrier frequencies is specifically tackled, by proposing two different strategies for structural aware SHM data communication systems. A Multiple-in Multiple-out (MIMO) miniaturized smart sensor network, consisting of low-power and low-cost sensor nodes, was deployed to prove the effectiveness of the advanced solutions. Transducers were positioned in a spatially distributed and permanently installed network. Cable-free exchange of encoded information across a square metallic plate as well as on a stiffened carbon-fiber reinforced plastics (CFRP) panel is achieved.