FIG. 2D shows a blown up view of one of the pairs of small loop transmission coils 22, where one small loop transmission coil 22a of the pair is smaller than the other small loop transmission coil 22b and the two small loop transmission coils 22a, 22b are connected to each other in parallel. It should be noted that the “pair” of small group loop transmission coils 22 is not limited to only two (2) small loop transmission coils, but it is possible that there are 3 or more small loop transmission coils 22 in a “pair” as used in this specification D1-1 and D2-1 are the inner and outer diameters, respectively, of the small loop transmission coil 22a, and D1-2 and D2-2 are the inner and outer diameters, respectively, of the small loop transmission coil 22b.
FIG. 3A illustrates the operations of obtaining inductance and capacitance values in order to have optimal coupling efficiency for wireless charging. Referring to FIGS. 3A, 3B and 3C, assuming there are two pairs of small loop transmission coils 22, for each pair of the small loop transmission coils 22, with a number of turns N, turn width W, spacing between turn S, inner diameter D1, outer diameter D2, inductance L and capacitance C, given that f=6.78 MHz, the inductance Lloop and capacitance Ctotal can be obtained by formulae (1) and (2). For a more detailed parameter determination, commercial simulation tools such as a high frequency structural simulator (HFSS) can be utilized.
