Recharging Zero Energy Devices: Multi-Frequency RF Energy Harvesting Perspective

Telecom and electronics have grown more multi-disciplinary than autonomous in the wake of Industry 5.0. As a result, it is expected that every facet of human life will contribute to the realization of a fully interconnected world through the Internet of Things (IoT) technology. The IoT system comprises vast low-power devices deployed for multi-purpose functionalities both in stationary and mobility applications. IoT devices present high versatility and complexity as they must be miniaturized, energy-efficient, scalable, and interoperable while providing seamless connectivity. However, the continuous operation of IoT devices is limited by the lifetime of the power supply. Moreover, IoT devices are randomly deployed on land, space, and marine systems so as to achieve visibility in remote areas. As such, the sustainable empowering of IoT devices has received enormous interest within the research community. In this context, radio frequency (RF) energy harvesting (EH) is viewed as a prominent solution to revitalize the energy of participating IoT devices wire-lessly. To achieve the desired multifunctionality in IoT devices, multi-frequency antennas are utilized. This implies that the RF-EH circuitry must meet multi-frequency operation requirements. Given this context, the techniques for multi-frequency RF -EH systems are reviewed and discussed in this article, including the most recent developments in antennas, impedance matching networks (IMNs), and rectifiers. Performance enhancement and numerous RF input harvesting capabilities are discussed. The pros and cons of various circuit architecture combinations are outlined and compared to ascertain the existing research gaps and directions for future works.