Research on the Electromagnetic Energy Flow and Coupling Characteristics of Wireless Power Transfer Systems Based on Poynting’s Theorem

This study addresses the challenges in modeling and understanding electromagnetic energy transformation in wireless power transfer systems, proposing a reduced-order model based on Poynting’s theorem to explore energy coupling in the near-field, emphasizing the synergistic role of inductive and capacitive coupling for system performance, and providing theoretical and experimental insights for the design of high-density electromagnetic coupling devices, with the aim of enhancing wireless power transfer capabilities over large air gaps and in various applications.

• Wireless power transfer is a multidisciplinary research field grounded in electromagnetic theory. However, accurately describing the electromagnetic energy transformation process in the coupled space of a wireless power transmission system poses challenges due to the complexity of mathematical methods used and the lack of reasonable models to characterize spatial energy flow distribution. In this study, we establish a model for electromagnetic energy flow in wireless power transfer under sinusoidal excitation, based on Poynting’s theorem. By analyzing the common characteristics of electromagnetic energy flow in basic electrical components, we develop a reduced-order mathematical model. This model helps qualitatively explore the nature of energy coupling in the transmission space and differentiate wireless power transfer from other electromagnetic technologies. We discuss the coexistence of inductive and capacitive coupling in wireless power transfer, highlighting the importance of enhancing near-field electromagnetic coupling for overall system performance. From the perspective of energy flow mechanism, we present the working mode of wireless power transfer in the electromagnetic near-field region. Additionally, we construct an experimental platform to verify the effectiveness of inductive and capacitive coupling methods.
• This study is aimed at clarifying the research boundaries of near-field electromagnetic-based wireless power transfer technology. By analyzing the electromagnetic energy flow characteristics of common electrical components and the wireless power transfer system using the Poynting vector, the coexistence of inductive and capacitive coupling effects within the system is discussed. The Poynting theorem is utilized to describe the electromagnetic energy exchange process within the coupling space of the wireless power transfer system, where the electromagnetic field coupling in the near field is crucial for energy exchange.
• The coexistence of inductive and capacitive coupling effects can potentially expand the capacity of the energy transmission channel of the wireless power transfer system, offering value for the synergistic transmission of both types of coupling energy. This work provides significant reference for the theoretical research of wireless power transfer technology based on near-field electromagnetic fields and offers insights for the design of high power density electromagnetic coupling devices.
• A notable characteristic of the wireless power transfer system’s operation is the non-contact conduction of electromagnetic power. The Poynting vector analysis of common electrical components and the wireless power transfer system reveals that individual resistive, inductive, or capacitive components only store electrical energy and consume their own energy. For the wireless power transfer system operating in the electromagnetic near field, the electromagnetic field coupling in the near space is key to its functionality. The system’s energy coupling methods include capacitive coupling dominated by the electric field and inductive coupling dominated by the magnetic field, with the coexistence of both types of coupling effects.
• Through the analysis of electromagnetic energy flow, the relationship between wireless power transfer technology and other electromagnetic energy conversion technologies (transformer systems, capacitor series circuits) is clarified, highlighting the distinct technical features and working modes of wireless power transfer technology. Due to the presence of a large air gap, wireless power transfer systems cannot guide the electromagnetic field through high-permeability magnetic materials like transformers or through high-performance dielectric materials like capacitors. To achieve high power and high-efficiency wireless power transfer over large air gaps, it is necessary to enhance the strength of inductive and capacitive coupling.
• Dual experiments were designed to verify the coexistence of the two types of coupling effects and to analyze their frequency characteristics, clarifying the relationship between the two types of electromagnetic energy and the system’s operating frequency. Although the magnitude of the two types of electromagnetic energy and their ratio is relatively low, in certain scenarios such as underwater environments and biomedical applications, the capacitive coupling effect, due to the dielectric constant, will be significant and must be considered. In conventional engineering scenarios, it is also possible to separate factors that enhance these two types of coupling effects to strengthen the capacitive coupling effect and achieve synergistic transmission of both types of coupling energy.