Structural health monitoring using acoustic emission array techniques

The inspection of building structures is currently made by visual inspection or by wired sensor techniques, which are relatively expensive, vulnerable to damage, and time consuming to install. In contrast, wireless sensor networks are easy to deploy and flexible in application so that the network can adjust to the individual structure. Different sensing techniques can be used with such a network, but acoustic emission techniques have been rarely utilized. With the use of acoustic emission (AE) techniques it is possible to detect internal structural damage from cracks propagating during the routine use of a structure. Most of the existing AE data analysis techniques are not appropriate for the requirements of a wireless network, especially power consumption. Sensors with low price are required for AE systems to be accepted. To fully utilize the power of the acoustic emission technique on large, extended structures, recording and analysis techniques need more powerful algorithms to handle and reduce the immense amount of data generated. These new algorithms are de\eloped using, a new concept called Acoustic Emission Array Processing. As a first step, beam forming and source discrimination techniques were tested as well as a method based on a modified velocity spectral (VESPA) process. Hardware questions are also addressed, e.g., the network combines multi-hop data transmission techniques with efficient data pre-processing in the nodes. Using these techniques, AE monitoring of large structures in civil engineering becomes very efficient including the sensing of temperature, moisture, strain and other data continuously.