crease of all the singular values indicates also that the energy on the receiving antenna is higher when using the EPD. This is not a trivial result. EPD requires electronically controlled scattering elements that cause losses in the scattering process. The EPD design is a delicate balance between increasing the number of elements to extend the set of radiated fields and the ability to concentrate the energy toward the receiver and the use of a smaller number of elements to reduce losses avoiding the use of expensive amplifiers. Furthermore, the response of the scattering elements (including the electronic switches) changes with the frequency, making it difficult to select the best scattering response of a broadband EPD. Despite the difficulties mentioned above, there has recently been a renewed interest in controlling the propagation environment by means of reconfigurable scattering devices. Indeed, one of the main novelties in 6G is the introduction of electromagnetic signal processing directly at the Deep Physical Layer level. One of the most promising solutions is represented by the Reconfigurable Intelligent Surfaces (RIS) [5]. The main application of RISs consists in extending the cell size in millimeter or THz communication beyond the line of sight The RISs are designed to obtain a reflection of the incident wave in the desired direction by means of an appropriate phase variation on their surface obtained from electronically controlled scattering elements. 2 Information Flows at the DPL Level The implementation of RIS in communication systems is a great challenge from both a theoretical and a technological point of view. Although the basic structure is similar to that of reflectarrays [79], whose design methods are now well established, their use in non-military systems, where cost is the determining factor for the success or failure, requires new economical, reliable, and large-band technological solutions. 2.6 Conclusions The communication systems of the next generation will face the enormous chal- lenge