Optimal Sub-band Beamforming with Frequency Masking for SHM

Some classical structural health monitoring methods based on the vibration response of the structure use global parameters to detect damage. Because global parameters such as mode shapes and frequencies have a very low sensitivity to damage, they are poor indicators of structural changes. A different approach involves the use of the wavelet packet transform combined with a spatial filtering beamforming technique. While the wavelet packet decomposition provides a level-by-level decomposition of the signal in different sub-bands, the beamforming spatial filter bank provides spatial resolution. By using this approach, it is possible to localize damage in space and frequency. The damage is located using two realizations of a finite element model for a beam, the first simulating the structure in pristine conditions and the second simulating the structure with damage. The damage can be observed using a normalized energy difference approach and it is localized in frequency and space. This paper will discuss the optimization of the beamforming beampattern and a possible frequency masking to enhance the detection of the damage.