Authors: M. Dragoman, M. Aldrigo, A. Dinescu, D. Vasilache, S. Iordanescu, and D. Dragoman.

Title: Nanomaterials and Devices for Harvesting Ambient Electromagnetic Waves

Abstract: In this review, we consider energy harvesting from ambient electromagnetic (EM) waves, since this method, together with energy harvesting from heat, are the most promising approaches for renewable energy production after photovoltaic DC power production via solar cells. Furthermore, solar cells are not referred to here, since there are already a large number of reviews dedicated to these devices, which are widespread in daily life. Although solar cells have been commercialized for some time, the research for more efficient harvesting solutions is growing every year, supported by the discovery of new materials, such as perovskites; among the reviews on the latter type of solar cells, see [1]. At the end of 2020, solar cells provided about 1 TW of electrical energy around the globe [2]. The radiofrequency (RF) energy harvesting (RF-EH) challenge originates from the unprecedented development of wireless high-frequency communications, such as 5G and 6G networks, able to generate an ambient EM energy available at any time and in a large band, spreading from the microwave spectrum up to sub-terahertz frequencies. This EM energy can be used on demand by equipment such as smartphones, tablets, laptops, and receivers at various frequencies, but a large part of it is not used and, hence, is lost. Harvesting the fraction of EM energy that is unexploited allows the self-powering of low-consumption electronic devices, e.g., those connected within Internet of things (IoT) architectures. The power supply mechanism associated with RF-EH techniques is based on a rectenna, i.e., an antenna loaded with an (un)biased diode [3,4,5]. Figure 1 shows the schematic of a generic rectenna, in which the antenna provides the RF input to a rectifying diode, whose DC output voltage VDC is the voltage drop on the load capacitor. A DC block capacitance and a RF choke inductance are (ideally) necessary at the input and output, respectively, of the diode to let only the DC component of the received RF signal pass. Furthermore, the diode should work in the unbiased state; however, in some circumstances (e.g., when the power at the input of the diode is too low to allow the device working in forward conduction), a small DC bias voltage could be necessary to force the rectifier to operate in its nonlinear region (this bias could be provided by EH sources other than the RF ones). Depending on the requested DC power, these rectennas can be arranged in arrays with various configurations involving one or more diodes. Many new materials are involved in the gathering of this ambient EM energy, such as two-dimensional (2D) materials (e.g., graphene and MoS2) [6,7], oxides [8], and nanoscale ferroelectrics (e.g., HfO2-based ferroelectrics) [9].

Published in: Nanomaterials 13, no. 3: 595

Date/Place: 2023

DOI: https://doi.org/10.3390/nano13030595