Near Field Regulation Method of Electric Field Coupling and Magnetic Field Coupling

This study elucidates the energy transmission mechanism and Poynting vector distribution in wireless power transfer systems, explores coil inductance and capacitance effects, and experimentally verifies the regulation of energy transmission through theoretical calculations, while highlighting the importance of electric field coupling in high-frequency environments and the dual role of magnetic and electric field couplings in energy transfer, culminating in a frequency-based control method to optimize the system’s performance and efficiency.

DOI link：10.1109/CEFC55061.2022.9940689

The transmission of Poynting vector in wireless power transmission system is one of the essential laws of energy exchange in space. This paper gives its energy transmission mechanism in space and the distribution law of Poynting vector. At the same time, the coil inductance effect and capacitance effect in the actual work process are explored. The proportional coefficient of system energy transmission is given through theoretical calculation, and the regulation of energy proportion is realized through the key factors in the regulation coefficient，and It is verified by experiments.

The distribution of active power density in the Poynting vector for a dual-capacitor wireless power transfer system in the spatial domain:

1. The active power density in the spatial domain mainly originates from the power source above and propagates along the transmission line, ultimately concentrating near the load.
2. As the Poynting vector passes through the capacitors, the active power density bifurcates into two parts and flows along the surface of the capacitor plates through the gaps between them. Subsequently, these two parts converge at the lower end of the transmission line.
3. only reactive power exchange occurs within the capacitor plates, while the net sum of the active power density vectors is zero.

Furthermore, it is crucial to acknowledge the significance of electric field coupling energy, particularly in high-frequency operational environments. For a dual-coil wireless power transfer system wound in a high-frequency configuration, the two planar coils can be considered equivalent “capacitor plates.” Consequently, the energy transmitted within the system encompasses both magnetic fields coupling energy and electric field coupling energy. The spatial energy flow patterns can be summarized as follows:

1. Magnetic field coupling energy predominantly transfers in the region between the coils, exhibiting a symmetrical star-shaped distribution pattern.
2. The magnitude of the active power density in the Poynting vector increases as the cross-sectional distance from either side of the coils decreases. When the cross-section is positioned at the midpoint between the coils, the active power density in the Poynting vector reaches its minimum value.
3. Electric field coupling energy emanates from the power source towards the load end, primarily conveyed through the transmission line. Along the outer side of the “capacitor plates,” the energy bifurcates into two parts. It propagates through the gaps between the plates toward the connected transmission line on the opposite side. Finally, the transmitted energy converges and supplies the load.

In the high-frequency operating environment of a wireless energy transfer system, two forms of energy transfer exist magnetic field coupling and electric field coupling. Experimental data reveals that the proportion of electric field coupling energy increases from 0.2% to 8% as the frequency range extends from 100kHz to 600kHz. These findings signify a substantial improvement in the system’s resistance to misalignment and transmission efficiency. This study primarily investigates a single coupler incorporating hybrid coupling transmission and proportional control. The frequency-based control method is proposed through meticulous electromagnetic field calculations to manage the magnetic and electric fields in the wireless energy transfer system. The research objectives mentioned above have been accomplished.