FDTD analysis of Reconfigurable Intelligent Surfaces for 5G applications in presence of the human body

Everywhere in the environment, electromagnetic fields can be produced by either natural or man-made sources and are absolutely invisible to the human eye. Since more and more artificial sources have been produced as a result of rising electricity demand, ever-improving technology, and changes in social behavior, electromagnetic field exposure has been constantly rising. Both at home and at work, everyone is exposed to a complex mixture of weak electric and magnetic fields due to the production and transmission of energy, home and office appliances, industrial machinery, telecommunications, and broadcasting. The primary biological impact of electromagnetic and radiofrequency radiation is heating. This fact is used in microwave ovens to warm meals. People are typically exposed to radiofrequency fields at levels that are substantially lower than what is required to cause considerable heating. The fundamental element of current rules is the heating impact of radio waves. Researchers are also looking into the idea that prolonged exposure could have effects below the threshold for body heating. Although low level, prolonged exposure to radiofrequency or power frequency fields has not yet been linked to any known harmful health effects, researchers are still actively investigating this topic. Metasurfaces are next-generation engineered devices that are still almost completely unknown but have almost unlimited potential. In fact, these devices were initially created for the purpose of redirecting a more precise signal to those areas that are difficult to reach due to a particularly adverse environment full of obstacles. In fact, the metasurfaces are capable, through a precise configuration of the elements that constitute it, of focusing the electromagnetic signal at a precise point in space, this then ensures an improved operation of the devices that constitute the environment, but is not enough, a future possibility of use could be to exploit the metasurface to limit electromagnetic exposure by human tissues. This could be possible due to the fact that a possible smart reconfigurable metasurface would be able to track and geolocate the devices that are in contact with humans in the everyday life and thus be able to focus the signal received from the source much more precisely on the device so as not only to make it work more efficiently but also to precisely reduce the electromagnetic exposure of tissues. The purpose of this study is to develop through the numerical analysis method FDTD implemented in C programming language a metasurface model composed of varactor diodes at different capacitances, which can be configured manually, and to evaluate the electric field distributions on it as a result of the 'incidence of a plane wave, also the reflection of the signal passing through the metasurface at a generic point in space is evaluated. Then the metasurface will be placed in an environment with a biological tissue, a device, a PEC barrier, and a dipole antenna. The purpose is to carry out a series of simulations to demonstrate that the presence of the metasurface is capable of causing a lower absorption of the reflected signal by tissues