1 Damage imaging in plates by evaluating local entropy in 1 guided wavefield data 2 3 Erfan Basiri 1 , Reza P. R. Hasanzadeh 1 ∗ and Mathias Kersemans 2 4 1 Department of Electrical Engineering, University of Guilan, Rasht, Iran 5 2 Mechanics of Materials and Structures, Ghent University, Ghent, Belgium 6 7 8 Abstract— This paper presents a new algorithm called broadband entropy-based two-stage damage imaging 9 (BE2DI) for the detection and imaging of defects in multi-layer plates. The method differentiates defects from 10 either local scattering phenomena of propagating Lamb waves or locally increased vibrational activity for 11 stimulated global plate resonances by exploiting the higher vibrational activity of full-field broadband vibration 12 signals at defective regions and the distinct spatial behavior of defects and artifacts. Using these features, first, a 13 candidate damage map is constructed by means of iterative thresholding based on descriptive statistics of 14 broadband data. After-wards, an adaptive regional damage index based on local entropy is introduced, which 15 utilizes operational deflection shapes to process previously identified candidate regions and subsequently reveal 16 both shallow and deep defects. BE2DI can be seen as an automated local defect resonance identification 17 approach in the case of shallow defects. Multiple plates having various defect types with different sizes and 18 depths are investigated. Broadband chirp signals are used to excite the plates using low-power piezoelectric 19 actuators, and vibrational data is registered by 3D scanning laser Doppler vibrometry. The obtained results 20 quantitatively and qualitatively demonstrate that the proposed method can effectively detect different kinds of 21 damage, regardless of being shallow or deep. 22 Keywords: Multi-layer plates, Non-destructive testing, Operational deflection shape, Local entropy, 23 Guided waves, Laser Doppler vibrometry 24 Abbreviations: Nondestructive testing (NDT), Scanning laser Doppler vibrometer (SLDV), Local defect resonance (LDR), Operational deflection shape (ODS), Carbon fiber reinforced polymers (CFRP), Piezoelectric transducer (PZT), Defect-to-background ratio (DBR), Root mean square (RMS), True positive (TP), False positive (FP), Preliminary candidate damage map (PCDM), Candidate damage map (CDM), Adaptive regional damage index (AR-DI), Adaptive damage index (A-DI), Broadband entropy-based two-stage damage imaging (BE2DI) ∗ Corresponding author: hasanzadehpak@guilan.ac.ir CLEAN REVISED VERSION