###### Abstract  
Wireless Charging (WC) is a promising technology that has recently attracted the research community and several companies. WC has a myriad of advantages and diverse applications especially in the emerging Internet of Things (IoT) and Wireless Sensor Networks (WSNs), where energy harvesting and conservation are very crucial to prolonging network lifetime. Several companies have launched WC products and solutions and made them available to the end-users. This paper provides experimental and practical insights about this technology utilizing off-the-shelf (commercially available) products provided by Powercast Inc. (Pittsburgh, PA, USA); a pioneering company that has made their wireless charging kits and solutions available to the research and academic communities. In addition, a theoretical study of this technology is presented, where a close match between the theoretical and practical results is demonstrated. This will in turn assist the learners and technology adopters to better understand the technology and adopt it in various application scenarios. Furthermore, the paper presents the potential of using WC in unsupervised clustered WSN, where the Cluster Head (CH) node is proposed to be a mobile Unmanned Ground Vehicle (UGV) equipped with a wireless charging station. The UGV position is chosen to be in the centroid of the cluster in order to ensure that wireless charging takes place in the context of the cluster nodes efficiently. radio frequency; wireless charging; energy harvesting; wireless power transfer +
Footnote †: journal: Accepted: 16 March 2021  
further processing and decision-making. Clustering can be done in several ways, however, Unsupervised Machine Learning (UML) algorithms are widely used in clustering the SNs within the Area of Interests (AoI) because they are less complex and provide better efficiency. _K_-means and its extended algorithms [7] are well-known UML algorithms that are widely used to cluster the nodes into \(K\) predefined non-overlapping clusters. Once the clusters are identified, several mechanisms that are reported in the open literature can be used to select the CH node. In this work, we propose to use Unmanned Ground Vehicles (UGVs) as CHs. These UGVs equipped with a wireless charger and powerful battery are sent to each cluster to charge the SNs. Furthermore, the UGVs have microcontrollers and communication modules, and are hence capable of simultaneously charging the nodes and receiving the sensed data that are transmitted by the SNs. WSNs are expected to have a long lifetime without human intervention for energy replenishment especially in an operating environment, where human intervention may not be possible such as in furnaces, high roofed factories, and hazardous chemical plants. Furthermore, WSN constitutes of large number of sensor nodes implying high operational cost and hence, human intervention is unattractive. Consequently, technologies that can assist in energy replenishment of the on-board batteries of the SNs, which in turn can extend the lifetime of WSNs have to be developed. Recently, developing such technologies have received wide spread attention among the research community. In this context, Wireless Charging (WC) is seen as a promising solution to replenish the batteries of sensor nodes. WC is a new and emerging technology that aims at charging the battery operated devices by utilizing the wireless signal, where the energy is transferred to the SNs via air in the form of electromagnetic waves. Radio Frequency (RF)-based Wireless Charging (RF-WC) uses the RF signal to achieve this goal in which the radio waves are sent from a DC-RF supply to a load connected to an energy-harvesting receiver. RF-WC offers several advantages especially for embedded systems and devices such as sensors, actuators, and portable devices. It can also be used to charge many IoT devices like smart meters, weather stations, wearable sensors and devices, WSNs [8; 9], and smart agents used for remote monitoring and sensing [10].