# Delamination Localization in Multilayered CFRP Panel Based on Reconstruction of Guided Wave Modes
## 1 Introduction  
Multilayered composite materials are extensively used in aerospace and other engineering fields because of their impressive material properties, such as high stiffness, low weight, and corrosive resistance. As a result, the implementation of these materials contributes to reducing aircraft weight, improving fuel economy, and decreasing flight operation costs [1; 2; 3; 4; 5]. Various failure mechanisms can affect composite structures during manufacturing due to design errors or overheating or during service due to static overload, shock, and fatigue. Common defects in composites are fiber failure, buckling, matrix cracking, and delamination [6; 7; 8; 9; 10]. If these defects are not detected in composite materials, they can lead to catastrophic structural failure. Fiber failure is relatively straightforward to detect when the composite structure experiences static and dynamic loads. Matrix damage takes different forms, such as voids or cracks within the fibers of the lamina or as a single intralaminar defect within a composite layer. Buckling is another form of failure, commonly appearing as a shear or compression failure. Delamination is a crucial failure mechanism and represents one of the significant vulnerabilities in multilayered composites. If these types of defects are not detected, delamination can propagate through the composite laminates. Delamination in composite structures can significantly compromise their stiffness, potentially leading to complete structural failure. Therefore, it is important to monitor multilayered composite structures to reduce maintenance costs. Guided wave structural health monitoring (GSHM) can be used to ensure the structural integrity of composites [11]. The following tasks can be achieved, such as damage detection, localization, and quantification [12; 13; 14; 15; 16]. Baseline-dependent SHM techniques require data from both defect-free and defective specimens. On the other hand, baseline-independent SHM techniques can detect damages by monitoring the structural response obtained from external forces [17; 18; 19; 20; 21]. The structural integrity and reliability of the system can be achieved by implementing an appropriate maintenance procedure. [PERSON] proposed a baseline-dependent SHM technique using a single transmitter and multiple sensors to monitor defects up to 4 m despite significant attenuation due to the honeycomb structure [22]. An in situ SHM technique by [PERSON], based on GW acoustic emission and wireless sensor network to monitor and localize impact damages [23]. The baseline independent active SHM technique using thin PZT sensors was presented by [PERSON] to monitor disbonds. However, operational conditions such as vibrations, loading conditions, and environmental conditions such as temperature and humidity can influence the signals [24; 25; 26; 27; 28; 29; 30; 31]. GW inspections have received significant attention in the non-destructive field due to their high sensitivity and their ability to travel a long distance. However, the interpretation of GW signals is complex, especially when dealing with unknown materials. Inspection of composite materials is challenging due to their anisotropic properties [32; 33; 34; 35; 36; 37]. Numerous research studies have shown that guided wave inspection is used to identify and assess impact damage, delamination, and other types of defects presented in multilayered composites. A GW inspection method was proposed by [PERSON] and [PERSON] to detect and measure the delamination caused by the low-velocity impact on multi-layered composite material [38]. [PERSON] presented a guided wave inspection method to determine delamination by analyzing the local response from the composite material using a single transmitter and receiver [39]. Several factors that influence the guided wave propagation in composites are the multilayered structure, anisotropic properties, specimen boundaries, mode dispersion, distortion, multiple overlapped modes, and mode conversion [40; 41; 42; 43; 44; 45].