Investigation of High-Efficiency Wireless Power Transfer Criteria of Resonantly-Coupled Loops and Dipoles through Analysis of the Figure of Merit

Abstract

The efficiency of a Wireless Power Transfer (WPT) system is greatly dependent on both the geometry and operating frequency of the transmitting and receiving structures. By using Coupled Mode Theory (CMT), the figure of merit is calculated for resonantly-coupled loop and dipole systems. An in-depth analysis of the figure of merit is performed with respect to the key geometric parameters of the loops and dipoles, along with the resonant frequency, in order to identify the key relationships leading to high-efficiency WPT. For systems consisting of two identical single-turn loops, it is shown that the choice of both the loop radius and resonant frequency are essential in achieving high-efficiency WPT. For the dipole geometries studied, it is shown that the choice of length is largely irrelevant and that as a result of their capacitive nature, low-MHz frequency dipoles are able to produce significantly higher figures of merit than those of the loops considered. The results of the figure of merit analysis are used to propose and subsequently compare two mid-range loop and dipole WPT systems of equal size and operating frequency, where it is shown that the dipole system is able to achieve higher efficiencies than the loop system of the distance range examined.

A Study on the Wireless Power Transfer Efficiency of Electrically Small, Perfectly Conducting Electric and Magnetic Dipoles

“…(16). This result shows that the WPT efficiency between coupled electric and magnetic dipoles is identical when they are electrically short and perfectly conducting.…”

“…Previous studies involving electric and magnetic dipoles have used them to analyse near-field WPT between magnetostatic resonators [13], ferrite loop antennas [14], into dispersive tissue [15], in terms of their resonant frequency and geometric characteristics [16] and in the presence of metamaterial slabs [17,18]. In contrast to previous work in the area, this paper presents a general theoretical analysis to study the WPT efficiency between electrically short, PEC electric and magnetic dipoles of equal size and orientation † .…”

A Review on the Fundamentals and Practical Implementation Details of Strongly Coupled Magnetic Resonant Technology for Wireless Power Transfer

“…As can be observed, for a more precise model, the resistances of the coils are included. Considering the typical operational frequency, these resistances are due to two physical effects leading to the ohmic resistance and the radiation resistance [15]. These two effects are assumed to be independent so the equivalent resistance of the coils is computed as the sum of the ohmic and the radiation resistances.…”

Frequency-Splitting-Free Synchronous Tuning of Close-Coupling Self-Oscillating Wireless Power Transfer

“…Recently, the magnetic coupling resonant WPT has found widespread applications, such as wireless sensors, electrical vehicles, and wireless household appliances [1][2][3][4]. This type of WPT system is non-radiative with ignorable radiative loss [5], and often operates in the close-coupling condition where the transfer range is approximately equal to the diameter of the coils.…”