Takehiro Imura - Wireless Power Transfer: Using Magnetic and Electric Resonance Coupling Techniques

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This technology only recently came to light, making good use of the resonance phenomenon based on coupling through a magnetic field, that is, electromagnetic induction. On the other hand, various other methods of wireless power transfer have been studied in addition to magnetic resonance coupling. In this chapter, we describe the basic setup of wireless power transfer.

There are several available methods for wireless power transfer, and one common feature that all these methods share is the wireless power transmission using high-frequency alternating current (AC). Broadly speaking, there are two types of wireless power transfer: coupling and radiative. The coupling type is further categorized into the magnetic field and electric field types, whereas the radiative type is categorized into microwave (electromagnetic wave) and laser (optical) types. Hence, wireless power transfer can be typically classified into four types. However, because there has been relatively little research on lasers, it is often categorized into only three types.

Figure illustrates the corresponding diagrams. First, we refer to the power-transmitting side as the primary side and the power-receiving side as the secondary side. Thus, the coupling type can be categorized into magnetic field coupling (electromagnetic induction) and electric field coupling (displacement current) depending on whether the coupling is via a magnetic field H or an electric field E. The coupling type is further categorized into a total of four types based on the resonance phenomenon.

Fig. 1.2

Types of wireless power transfer

Fig. 1.3

Types of couplings

Fig. 1.4

Diagrams of magnetic field coupling, magnetic resonance coupling, electric field coupling, and electric resonance coupling

The magnetic field coupling type generally uses electromagnetic induction. The electric field coupling type uses an electric field instead of a magnetic field. Furthermore, introducing a resonant capacitor during electromagnetic induction will cause the capacitor to resonate with the coil, making the resonant frequency on the power-transmitting side the same as that on the power-receiving side. This enables the achievement of high efficiency and high power, as well as a large air gap. In other words, the skillful use of the resonance phenomenon is referred to as magnetic resonance coupling. Similarly, while the electric field coupling type generally uses electric field coupling, the introduction of a resonant coil, such that it resonates with a capacitor (coupler) and skillfully uses the resonance phenomenon, is referred to as electric resonance coupling.