## 5 RIS Applications  
RISs have a wide range of potential applications due to their ability to manipulate and control electromagnetic waves. One of the most promising areas for RIS application is wireless communication. RISs can be used to improve wireless communication systems by increasing signal quality, coverage area, and data rate. By creating a virtual environment with multiple signal paths, RISs can improve the performance of a wireless network in indoor environments where signal strength and quality can be compromised [2; 55]. Another potential application of RISs is in sensing and imaging. An RIS can be designed and fabricated to act as a lens or a mirror that can focus or reflect electromagnetic waves, enhancing the resolution and accuracy of imaging and sensing systems. RISs can also be used to improve the signal-to-noise ratio and reduce imaging artifacts in synthetic aperture radar (SAR), computerized tomography (CT), and magnetic resonance imaging (MRI) systems. In those applications, RISs act as lenses or mirrors that can focus or reflect electromagnetic waves, leading to higher resolution and accuracy [56]. RISs can also be used to improve the efficiency of energy harvesting systems by optimizing the absorption and reflection of electromagnetic waves. By absorbing specific frequencies of electromagnetic waves, such as solar radiation or radio waves, RISs can convert them into usable energy, making energy harvesting systems more efficient [57]. Another potential application of RISs is in security and defense. RISs can be designed to selectively block or reflect specific frequencies of electromagnetic waves, such as radar waves or thermal radiation. By doing so, RISs can create invisible barriers or cloaking devices, making objects or areas invisible or undetectable and improving security and defense systems [58; 59]. Finally, RISs can be used to improve the performance, energy efficiency, and coverage area of Internet of Things (IoT) networks. By creating virtual environments with multiple signal paths, RISs can increase IoT devices' reliability and data rate and reduce energy consumption, improving their performance and coverage area [60; 61]. RISs have the potential to revolutionize many industries and fields due to their ability to control and manipulate electromagnetic waves. In addition to the applications discussed earlier, several other potential RIS applications are worth exploring. One such application is in 5G wireless networks, as well as those beyond 5G [3]. RISs can be strategically placed to enhance signal coverage, reduce interference, and increase the network's capacity, leading to improved performance and faster data transfer rates [62]. RISs can also be used in the automotive and transportation industry to improve safety and efficiency [63]. By selectively blocking or reflecting specific frequencies of electromagnetic waves, such as radar waves, RISs can improve the accuracy of collision avoidance systems and reduce accidents [64]. Agriculture and environmental monitoring systems can also benefit from RIS technology [65]. By optimizing the absorption and reflection of specific frequencies of electromagnetic waves, such as sunlight and radio waves, RISs can increase solar panels' efficiency and improve environmental sensors' accuracy [66]. With continuous technological advancement and the increasing demand for more efficient and reliable systems, there is great potential for future RIS applications [67]. One potential future application of RISs is in the field of space exploration. RISs can enhance spacecrafts' communication and navigation systems by improving signal quality and reducing interference [68]. RISs can also shield spacecraft from radiation and other harmful electromagnetic waves, improving space missions' safety and efficiency [69]. Another potential future application of RISs is in the field of robotics. RISs can be used to improve the sensing and control systems of robots by enhancing the resolution and accuracy of imaging and sensing technologies [60].