Phased array imaging for damage localization using multi-narrowband Lamb waves

In the conventional phased array imaging methods based on only single narrowband Lamb waves, as the scattering behavior between Lamb waves and defects is closely related to the wavelength and the defect size, the information within only a single narrowband is limited. Besides, limited by the size of elements in phased arrays, the ratio of the element spacing to the wavelength may not be able to reach a small enough value, as a result, grating lobes in some directions and high sidelobes will inevitably appear. Aimed at utilizing Lamb wave information contained in multiple frequency bands so as to improve the image quality of Lamb wave phased array imaging, a multi-narrowband fusion method is proposed. The information of multi-narrowband Lamb waves with different carrier frequencies is fused using the geometric mean. Because the positions of grating lobes and the sidelobes are related to the carrier frequency once the sensor array is fixed, the mainlobe is retained and grating lobes as well as sidelobes can be suppressed after the fusion of multiple narrowband signals with different carrier frequencies. So imaging results with fewer artifacts are achieved compared with that generated using only single narrowband signals. The results of damage localization on an aluminum plate with two defects verify the effectiveness of the proposed method. •A damage imaging method using multi-narrowband Lamb waves is proposed.•Grating lobes and sidelobes are suppressed while mainlobes are retained.•Imaging results with fewer artifacts are achieved.