We have proposed and analyzed an equivalent circuit for a magnetically coupled wireless power transmission (WPT) system between two loop resonators by considering its coupling coefficient and radiation-related parameters. A complete formulation is provided for all the necessary circuit parameters. The mechanism of radiation loss is sufficiently explained. The circuit and electromagnetic (EM) simulation results have been shown to be in good agreement. Based on the proposed circuit formulation, a specific load impedance for maximum WPT efficiency was found to exist. The proposed modeling of the WPT in terms of circuit characterizations provides sufficient insight into the problems associated with WPT.
Ⅰ. IntroductionWe live in a world of wireless communication. A huge amount of information is wirelessly communicated between mobile terminals. Now, the increasing requirement for the wireless transfer of electric power is making wireless power transmission (WPT) technology increasingly important. Based on the analysis, they successfully lit a 60 W bulb at a distance of 7 feet (more than 2 meters) by using helical coils of high Q. The efficiency was reported to be 60 % at 9.9 MHz. Most of the papers related to WPT focus on the power transmission efficiency. The mechanism of radiation loss and the coupling coefficient have rarely been explained in detail. The radiation loss is surely the most crucial limiting factor in WPT and it warrants an in-depth analysis.In this paper, in order to investigate the mechanism of WPT in a more detail, we focus on the analysis of a WPT system using an equivalent circuit. Based on the equivalent circuit, key parameters-such as WPT efficiency and the radiation loss rate are properly defined and derived.Furthemore, a method for extracting both from electromagnetic (EM) simulations or measurements is proposed. Finally, the proposed modeling for WPT is validated by comparing the circuit and the EM simulations.
Ⅱ. Analysis of an Equivalent Circuit for WPT using Two LoopsCommonly, WPT using magnetic coupling is realized using two resonant loops facing each other. One loop is connected to an AC power source and the other loop is connected to the load. Power is wirelessly transmitted from one loop to the other as a result of magnetic coupling between the two resonant structures with the same resonant frequency. Fig. 1 shows the equivalent circuit for a magnetically coupled WPT that considers radiation effects. V1 is the voltage source for the WPT system. R1 and R2 are the conductor loss resistances, R r1 and R r2 are the resistances accounting for radiation loss, and RL is the load resistance.L 1 and L 2 are the inductances, and C 1 and C 2 are the capacitances, for the first and second loops, respectively. M is the mutual inductance between the two loops. I1 and I 2 are the currents flowing on each loop.Using KVL's, we obtain
We design and analyze the cloaking circuit using 2D transmission line structure to make up for the weakness of the established cloaking circuit using only lumped inductor and capacitor elements. The 2D transmission line structure enables one to conveniently design the cloaking circuit with available element values. All the necessary analysis and synthesis(design) formulas have been derived. A cloaking circuit for a cylindrical scatterer in free space has been designed based on the provided design formulas and its effects have been investigated using the circuit simulator ADS. The effect of the cloaking medium for this specific case has been observed to be about 10.5 dB.Key words : Metamaterial, 2D Cloaking, Transmission Line Method
In this paper, we designed and analyzed a 3D isotropic bulk structure consisting of thin wires and SRR's(Split Ring Resonator) with which the permittivity and permeability can be controlled at the same time. For the 3D isotropic bulk structure, first of all, the geometry seen by three main axes must look alike. Thus, we adopted the orthogonal thin wires and symmetrical SRR's. As a result, we constructed metamaterial bulk structures of which effective relative permittivity and permiability are about -0.6 and -1.5, respectively. Its refractive index is about -0.95 in each direction(, and direction). The computed Brillouin dispersion diagram also showed that the proposed structure is almost near isotropic.
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