## 3 Transfer and Harvesting Energy Metamaterials
### Energy Harvesting Devices in Big Cities  
The term Internet of Things is more and more common. IoT is rapidly evolving in big cities, as more devices are able to communicate with each other. This has led to the creation of smart cities, where everything is connected and can be controlled and monitored remotely [60; 61]. This not only improves the efficiency and sustainability of these systems, but it also enables new services and applications. The evolution of IoT is happening quickly due to advances of technology, such as the miniaturization of sensors and the increasing availability of radiation (5G). The demand of smart city solutions is growing as cities become more populous and face challenges related to a few United Union goals [62]. \"Microwave\" refers to a range of electromagnetic waves with frequencies between 300 MHz and 300 GHz. In the context of communication technology, microwave is often used to refer the band of frequencies between 1 GHZ and 100 GHz [63], which is used for various types of communication: wireless [64], satellite [65], or local wireless areas (WLANs) [66]. In cites, they have a wide range of application: wireless communication (such as phone networks and wireless internet) are used to transmit and to receive signals for voice and data communication, TV and radio broadcasting, radars, remote sensing (satellite imagery), industrial heating [67], or medical applications (cancer treatments and diagnostic techniques) [68]. All of the above are common, and their use is increasingly similar to IoT. While harvesting energy from microwaves in a city, this could potentially interrupt or weaken microwave signals. This is because harvesting devices would capture some of the energy from microwave signals, which could reduce their strength. Let us not forget that, in general, the strength of signals used for communication is relatively high, so this should require a large number of energy harvesting devices to have a significant impact on the signals. Additionally, energy harvesting devices designed properly will not interfere with the signals, and they will work alongside them. Creating energy harvesting devices to capture microwaves in a city requires proper design and optimization to minimize the impact of the surrounding environment. While it is possible to capture energy and apply it to power sensors where in need, this is only a small portion of the microwave energy, so this will not weaken the signal. On the other hand, one can also apply the filtering technique to ensure that the energy harvesting device only captures specific frequency while avoiding other frequencies (from communication). In terms of making an economic circuit and capturing lost signals, microwaves in the use of energy harvesting processes are typically highly directional, which meansthat they are focused in a specific direction in order to reach their intended destination. This minimizes the amount of lost signals. However, some can be lost due to reflection, scattering, or atmospheric conditions. Some signals are not captured by receivers, which represents a bigger problem in big cities. Devices, which could be able to capture and store energy from environment, can be a sustainable alternative to traditional methods of energy transfer. Moreover, in sustainability, one of the main advantages of energy harvesting is reducing the need for large-scale power transmissions and distribution systems that can be costly and have significant environmental impact. When it comes to metamaterials and their impact on the environment, it is important to consider more things: the entire life cycle of the materials, from extraction of raw materials to production, as well as the time of living, use, and disposal. In terms of carbon footprint, typically the production of structures and products has significant impact on the environment. Most of this is related to the usage of energy, as well as the pollution that comes with it. In this case, what is important to also consider is the usage of raw materials and the place where they come from.