In the last decades, a huge effort has been dedicated to the development of vibration-based techniques for damage detection. In this article, an algorithm based on the wavelet packet transform and the Karhunen-Loéve transform is analysed to perform a pattern recognition application for the structural health monitoring purpose. In this article, the wavelet packet transform is used to decompose the signals coming from an accelerometer on a vibrating composite beam. The configuration of the beam has been changed and the wavelet packet transform was tested as a feature extraction tool. Then the Karhunen-Loéve transform was applied to the data to classify the different patterns and to test its capability of pattern recognition.

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The evolution of the smart structure technology on one side and the recent innovations in ICT have generated a new functionality in structural engineering: wireless structural sensing (WSS). This concept refers to the idea of measuring the structural response of a mechanical component and transmitting in remote the data to a control centre. WSS can be viewed as an extension of the features of a smart structure that includes now not only a sensing capability but also the possibility of transmitting signals, in the presence of a transceiver. In the paper, the characteristics of this technology and the potential outcomes in terms of products and services are illustrated. The constituent elements of the system are also described and the evolution of structural design for such structural systems is highlighted in terms of the driving design parameters. Some basic demonstrators produced by the research group of the authors are also illustrated as practical implementation of the WSS technology.

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