## 3 Transfer and Harvesting Energy Metamaterials
### Application of Energy Harvesting Metamaterials  
In this paper, we propose an application of an energy harvesting device with the use of metamaterials to capture and store microwaves for sensor power (look Figure 2). It should contain metamaterial structure, antenna, rectifying circuit, power management, as well as a storage, control, and monitoring system. The main component of the energy harvesting wireless sensor is a metamaterial component. [PERSON] et al. [75] presented design and experimental implementation of a power harvesting metamaterial. He demonstrated that the maximum harvested power occurs for a resistive load close to 70 \(\Omega\) in both simulation and experiment. He also highlighted that it can be suitable for use in devices integrated with metamaterials. The rectenna is a device that combines a microwave antenna and a rectifier circuit to convert energy into DC electrical energy [76]. It can be designed to be omnidirectional, meaning it can absorb energy from microwaves coming from any direction [77]. An energy harvesting circuit should be responsible for converting the microwave energy absorbed by the rectenna into usable DC electrical energy. The circuit can include components, such as diodes, capacitors, and voltage regulators, to ensure a stable output voltage. In addition to the proposed system, there can be sensors detecting the presence of microwaves, thereby triggering the energy harvesting process. They can be designed to activate the rectenna and the energy harvesting circuit when they detect the specific frequency range of microwaves that the metamaterial absorber is designed to absorb. In another way, they can also be considered tunable metamaterial absorbers [78; 79; 80; 81; 82]. The device can be designed to be small and lightweight, making it suitable for use in discussed applications, where energy is needed, but it may be difficult or impractical to run wires or replace batteries. As shown in Figure 1. The metamaterial absorber is placed on top of the rectenna, with the conductive elements of the absorber facing downward towards the rectenna's antenna elements. This arrangement would allow the absorber to interact with the incoming microwaves and absorb their energy, which would then be collected by the rectenna's antenna and passed on to the rectifier circuit. The additional sensor is placed in proximity to the metamaterial absorber and rectenna. When the sensor detects the presence of microwaves within this frequency range, it activates the rectenna and energy harvesting circuit to begin collecting and converting the microwave energy into electrical energy. The  
Figure 2: (**1**) microwave radiation sensor; (**2**) metamaterial structure; (**3**) rectenna; (**4**) electronic circuit. energy harvesting circuit is integrated into the same device as the metamaterial absorber, rectenna, and sensor, and it should be designed to provide a stable output voltage to power various electronic devices. We want to highlight two recommended areas for applying such a system. For application on offshore wind farms, it can be a very desired technology in terms of separately placed wind turbines. Offshore wind farms need to be highly automated with good communication and real-time monitoring. The sensors used on offshore wind farms are typically powered by a combination of on-board batteries and external power sources. Some sensors, such as anemometers and meteorological sensors, are powered by batteries. Other sensors, such as LIDAR, require a more consistent and reliable power source. They are usually powered by an offshore substation. Anemometers and meteorological sensors typically require very low power inputs, even in the range of few mA. For vibration sensors, the power requirements can vary, depending on the size and complexity of the sensor, but they are typically in the range from few mA to a few amperes. Especially, these sensors with low power input are well suited to apply energy harvesting devices with metamaterials to them.