## 6 Conclusions  
This study extensively reviewed the latest advancements in ultrasonic detection techniques for parameter assessment and damage diagnosis in composite materials. It investigated the effects of multiple damage types on these materials. Selecting ultrasonic testing techniques requires the consideration of specific damage characteristics. Ultrasonic testing technology provides a dependable, non-destructive method for structural health monitoring with a wide application range in damage identification in composite materials. This technology is valued for its simplicity, efficacy, affordability, and high detection accuracy in identifying various types of damage and the properties of composite materials. Despite ultrasonic techniques showing great promise for assessing and detecting damage in composite materials, there are considerable challenges in identifying damage within complex geometric structures under diverse conditions. Additionally, although ultrasonic techniques are robust and reliable for damage detection in composites, challenges in accurately assessing intricate geometries and fluctuating environmental conditions persist. Issues such as signal distortion and sensor durability continue to restrict the full potential of this technology. Nevertheless, advancements in signal processing, AI integration, and materials science are leading to more precise, cost-effective, and user-friendly SHM systems. Future research focused on addressing these obstacles will be essential in promoting the  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Challenge** & **Description** & **Possible Solution** \\ \hline Mode Complexity & The presence of multiple modes in guided waves can complicate signal interpretation. & Development of sophisticated signal processing algorithms to separate and identify modes \\ \hline Signal Attenuation & Composite materials significantly attenuate guided waves, particularly over extended distances. & Use of adaptive signal amplification, new sensor materials for increased sensitivity \\ \hline Environmental Variability & Temperature, humidity, and other environmental factors influence wave propagation and sensor performance. & Development of temperature-compensated sensors, application of machine learning for adaptive calibration \\ \hline Complex Geometries & Laminated composites often feature complex geometries that challenge uniform wave propagation. & Utilization of 3D numerical models for simulating complex structures, advanced transducer arrays \\ \hline Signal Noise Interference & Noise from manufacturing defects or the surrounding environment can disrupt damage detection. & Implementation of noise filtering algorithms, AI-based denoising techniques \\ \hline Limited Real-Time Monitoring & Many existing SHM systems cannot perform continuous real-time monitoring of structures. & Integration of wireless sensor networks and smart materials for self-sensing capabilities \\ \hline \hline \end{tabular}
\end{table}
Table 5: Challenges and possible solutions in UGW for SHM in composites.  
widespread application of ultrasonic techniques, contributing to safer and more dependable structures across various industries.  
Conceptualization, M.T.; Methodology, M.T. and S.K.; Resources, M.T. and M.U.E.; Writing--original draft preparation, M.T. and M.U.E.; writing--review and editing, M.T., M.M.A., S.K. and H.S.K.; Visualization, M.T. and J.J.; Supervision, H.S.K.; Funding Acquisition, H.S.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (RS-2024-00405691).  
Not applicable.  
The authors declare no conflict of interest.