Introduction

Wireless power transmission (WPT) is defined as the transmission of electrical power from a power transmitter to one or more electrical loads, such as a network of wireless sensors or electronic devices, without the use of interconnecting cables or conductive wires. The wireless sensor networks hidden in bridges or buildings to track the effect of heavy loads and environmental changes on the structure strength [1–4], are an example of the importance of WPT. WPT is crucial for implanted biomedical devices in order to avoid performing surgical procedures to replace the battery [5]. WPT systems can be implemented by different power transmission techniques that employ time-varying magnetic, electric, or electromagnetic fields. In these systems, the power transmitter (resonator or antenna) is connected to a power source, which transfers the field energy across an intermediate space to one or more receivers, where it is converted back to an electrical current and then exploited [6].