## 3 SHM Using Guided Ultrasonic Waves in Laminated Composites
### Recent Advancements in Ultrasonic Guided Waves for SHM of Composites
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Technique** & **Principle** & **Advantages** & **Challenges** & **Applications** \\ \hline \multirow{4}{*}{TFM} & Utilizes every element of a transducer array to generate a focused image at each pixel & Provides high-resolution imaging and accurate defect localization & Demands extensive computational resources and significant hardware support & Inspection of aerospace components, detection of micro-cracks [107] \\ \cline{2-5}  & Utilizes elastic waves that propagate through thin plates in various modes & Offers wide area coverage and high sensitivity to surface defects & Complexity of modes, signal attenuation in composite materials & Detection of cracks in aircraft panels, monitoring of delamination [81, 108] \\ \hline \multirow{4}{*}{GWT} & Employs multiple transducers to reconstruct an image of the internal structure & Detects hidden flaws with high spatial resolution & Requires a dense sensor network and is susceptible to noise interference & Used for damage detection in pipelines and monitoring wind turbine blades [109] \\ \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires expensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \hline \multirow{4}{*}{Nonlinear Ultrasonic Technique} & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and radiilites early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires expensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \hline \multirow{4}{*}{Nonlinear Ultrasonic Technique} & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires expensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \hline \multirow{4}{*}{Nonlinear Ultrasonic Technique} & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \hline \multirow{4}{*}{Nonlinear Ultrasonic Technique} & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and involves calibration complexity & Used in fatigue damage analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5}  & Utilizes multiple elements in an array to steer, focus, and scan ultrasonic beams & Enables fast scanning and adjustable focus for depth profiling & Complex interpretation of data and requires extensive equipment & Suitable for the inspection of complex geometries and real-time monitoring [71] \\ \cline{1-1} \cline{2-5}  & Measures the nonlinear behavior of materials subjected to ultrasonic waves & Sensitive to microstructural changes and facilitates early damage detection & Influenced by environmental factors and analysis and analysis and early detection of material degradation [102] \\ \cline{1-1} \cline{2-5