## 7 Conclusions  
RISs have recently gained significant attention in wireless communication and beyond, due to their ability to manipulate and control electromagnetic waves. This review covered a broad range of topics related to RIS, including their operation principles, simulation techniques, fabrication methods, experimental implementations, and potential applications. Regarding operation principles, it was discussed how RISs can reflect, absorb, and re-transmit electromagnetic waves to achieve desired signal propagation characteristics. Simulation tools and techniques were also presented, including analytical, numerical, and experimental methods. It was noted that the choice of simulation technique depends on the problem's complexity and the desired accuracy level. Several fabrication techniques were described, including planar and non-planar approaches. Planar techniques are less expensive and easier to fabricate, while non-planar techniques allow for more complex and flexible designs. The review also presented a range of potential applications for RISs, including wireless communication, sensing and imaging, energy harvesting, security and defense, IoT, automotive and transportation, medical and healthcare, agriculture and environment, and smart homes and buildings. It was noted that RISs have the potential to improve the performance and efficiency of these systems significantly. However, several challenges currently exist in developing and implementing RIS technology, including cost, scalability, and integration with existing systems. To address these challenges, potential solutions were discussed, such as developing low-cost fabrication techniques, integrating RISs with existing wireless infrastructure, and using machine learning algorithms to optimize RISs' performance. Overall, this review highlights the potential of RIS technology in a wide range of applications and the need for continued research to overcome current challenges and fully realize their potential. RISs have the potential to revolutionize a wide range of technologies due to their ability to manipulate and control electromagnetic waves. Some potential applications of RISs include improving wireless communication systems, enhancing imaging and sensing systems, improving the efficiency of energy harvesting systems, improving security and defense systems, and enhancing the performance of IoT networks. Additionally, RISs can improve the performance of 5G wireless networks (as well as those beyond 5G), improve the safety and efficiency of automotive and transportation systems, enhance medical imaging and sensing technologies, improve the efficiency and sustainability of agriculture and environmental monitoring systems, and enhance the performance and energy efficiency of smart home and building systems. However, there are also several challenges to overcome, such as efficient and cost-effective fabrication techniques, optimization of RIS designs for specific applications, and integration with existing technologies. Potential solutions include developing new fabrication techniques, using artificial intelligence to optimize RIS designs, and collaborating with experts in other fields to exploit the potential of RISs fully. Overall,the impact of RISs on future technologies could be significant, enabling a wide range of previously impossible or impractical applications. RISs have emerged as a promising technology for various communication, sensing, energy, security, and IoT applications. However, several challenges need to be addressed to fully realize the potential of RISs, such as fabrication complexity, control complexity, and scalability. To overcome these challenges, future RIS research should focus on developing more efficient and cost-effective fabrication techniques, advanced control algorithms for real-time operation, and scalable solutions for large-scale deployment.