Inductive Link: Basic Theoretical Model

In this chapter, we present the theoretical foundation of the inductive links (near-field), deducing analytical expressions to calculate the Power Transfer Efficiency (PTE) of the inductive link, g˙eta˙link, and the power delivered to the Receiver (Rx) Circuit, g˙pmn. We first analyze a 2-coil link in Sect. 2.1, presenting the inductive link circuit model in Sect. 2.1.2 and deducing expressions for g˙eta˙link and g˙pmn in Sects. 2.1.3 and 2.1.4, respectively. For the 2-coil link, the importance of coil quality factors and coupling coefficient is addressed in Sect. 2.1.5, while the influence of coil resonance in the link performance is studied in Sect. 2.1.6. The frequency splitting effect is addressed from different points of views, and its impact on the link performance is discussed in Sect. 2.1.7. Then, the use of additional resonant coils is addressed in Sect. 2.2. A 3-coil link is introduced in Sect. 2.2.1, and the analytical expressions are generalized to an N-coil link in Sect. 2.2.2. Finally, we compare the 2-, 3-, and 4-coil links in Sect. 2.3.