Research On Wireless Power Transfer System Based On Metamaterial Enhancement

Wireless power transfer provides a richer power supply scenario for devices such as mobile devices,smart appliances,implantable medical devices and industrial sensors.Conventional wireless power transfer technology utilizes near-field magnetic coupling between coils to transmit electrical energy,which is difficult to meet the urgent requirements of increasing transmission distance and transmission efficiency.Metamaterials have designable properties such as negative magnetic permeability.Putting it in a suitable position of the wireless power transfer system can significantly enhance the magnetic coupling of the system and improve the energy transmission capability,thereby promoting the wide application of the wireless power transfer technology.Considering factors of human safety,the international mainstream wireless charging standard focuses on operating frequencies below 10 MHz,and many application scenarios limit the size of charging devices to within 10 cm.This means that the size of the metamaterial used for wireless power transfer must be less than one percent of the electromagnetic wavelength,that is,the metamaterial reaches the deep sub-wavelength scale.At the same time,the metamaterial slab also needs to overcome the problem of blocking the free space between the coils when applied,that is,the placement of metamaterial slabs need to be optimized.Therefore,this paper studies the metamaterial unit design and metamaterial location optimization that restricts the use of metamaterial-enhanced wireless power transfer applications.In this paper,an equivalent circuit model of the double-layer spiral metamaterial unit is established.A square spiral cell structure with built-in via and external capacitor is proposed,which fully utilizes the equivalent inductance and capacitance of the spiral and effectively reduces the operating frequency of the metamaterial.The simulation model was established based on the S-parameter inversion method to extract the equivalent magnetic permeability of the metamaterial unit.The deep sub-wavelength negative permeability metamaterial working at 6.78 MHz was designed.The ratio of electromagnetic wave wavelength to cell size is about 1000 and has been experimentally verified.In this paper,an equivalent circuit model of the dual-resonance coil wireless power transfer system is established to analyze the key factors affecting performance of the system.The system is simplified into a double dipole system to analyze the effect of the metamaterial on the mutual inductance between the coils.The finite element analysis was used to study the enhancement effect of metamaterials on the transmission performance of wireless power transfer systems.The differences between isotropic and anisotropic metamaterials were compared.And the effects of metamaterial slab of center-placed and side-placed were researched.The enhancement of the magnetic coupling path between the coils by the anisotropic side-placed metamaterial slabs was found.The experimental results show that in the case of a transmission distance of 21 cm,the center-placed metamaterial slab has a 167% enhancement to the system transmission coefficient |S21|,and the side-placed metamaterial slab provides about 200% enhancement.The improved square spiral unit structure proposed in this paper has the advantages of compact structure and low operating frequency.The side-placed metamaterial slab enhances the transmission performance of the wireless power transfer system while maintaining the free space between the coils,enriching the application scenario of metamaterials.The experimentally validated simulation model provides theoretical support for metamaterial design and wireless energy transfer system analysis.