Acoustic emission analysis techniques for wireless sensor networks used for structural health monitoring

Continuous structural health monitoring provides data from inside a structure and will help engineers to better understand the structural performance and to predict the durability and remaining life time of civil engineering structures. Failure of steel tendons and concrete cracking are important aspects of structural health and maintenance that could be determined by acoustic emission analysis techniques. Wired systems for acoustic emission analysis are still used to monitor structures today, but their installation is relatively expensive, vulnerable and time consuming. In this paper, acoustic emission techniques are presented that could be implemented into competitive wireless sensor networks. The acoustic emission analysis based on onset detection of the acoustic wave is one of the most common techniques for the localization of acoustic events. However, the onset detection requires high accuracy in time synchronization as well as high sampling rates of 100 kHz or even more. Both, high sampling rates and the high time accuracy require a lot of power. However, if wireless sensors will be used, power efficiency is very important. For that reason the array beamforming technique is presented in this paper. Array beamforming for acoustic emissions means that the direction of the approaching elastic wave is determined with an array of sensors. The theoretical background of this technique as well as first results obtained from tests with test specimens are shown and discussed in this paper.