Design considerations for asymmetric magnetically coupled resonators used in wireless power transfer applications

Abstract

Abstract-Magnetic resonance coupling is a widely used technique for wireless power transfer (WPT) in biomedical and consumer electronics applications. For specific applications, device size limits the overall size of the transmit and receive coils. In this work, design considerations for an asymmetrical 4-element WPT system are investigated. For either a target efficiency or a desired WPT range, the optimal coil parameters such as Q and coupling coefficient are defined and these design considerations are experimentally verified. The results can be used to design an optimal set of coils for various WPT applications.

Directional Characteristics of Wireless Power Transfer via Coupled Magnetic Resonance

“…The directivity of a coupling coil can be expressed by the angular deviation of a coaxial receiving coil. It is reported that the CMR system can be almost "non-directional" in [24]. However, [24] did not give a specific explanation from the perspective of simulations or experiments, nor did it analyze the directional characteristics.…”

“…It is reported that the CMR system can be almost "non-directional" in [24]. However, [24] did not give a specific explanation from the perspective of simulations or experiments, nor did it analyze the directional characteristics. In [25], formulas were given to calculate the axial distance, radial distance, deflection angle, and the mutual inductance between arbitrary transmitting and receiving coils at any position in a space.…”

Two‐port network approach for a wireless power transfer link using a cascade of inductively coupled resonators

“…More recently, to extend the distance covered by the wireless link, the use of relay resonators interposed between the transmitter and the receiver (indirect feed) has been suggested. [12][13][14][15][16][17][18][19] In particular, the case of a link using 3 resonators has been studied in previous studies, 14,15 while the case of an indirect feed/load implemented by means of 4 resonators has been studied in other studies. [16][17][18][19] In more detail, in 1 study, 14 the coupled mode theory has been used to analyze the efficiency in the case where a single relay resonator is added to a direct link; it is demonstrated that the presence of the intermediate resonator allows improving the efficiency of the link even in the case of noncoaxially arranged resonators.…”

“…[12][13][14][15][16][17][18][19] In particular, the case of a link using 3 resonators has been studied in previous studies, 14,15 while the case of an indirect feed/load implemented by means of 4 resonators has been studied in other studies. [16][17][18][19] In more detail, in 1 study, 14 the coupled mode theory has been used to analyze the efficiency in the case where a single relay resonator is added to a direct link; it is demonstrated that the presence of the intermediate resonator allows improving the efficiency of the link even in the case of noncoaxially arranged resonators. As per the case of a WREL using 4 resonators (ie, a WREL obtained by adding 2 relay resonators to a direct feed), the configuration that is generally adopted is the one suggested in another study 16 ; according to this configuration, the wireless power transfer occurs between the relay resonators, which have a mutual distance determined by the specific application, while the distance between the transmitting/receiving resonator and the relay resonators is set to match the source/load to the WREL link.…”

Adjustable wireless power transfer system using port-selective switching coils

“…The frequency tracking method finds the frequency that achieves maximum power transfer, and transmits at this frequency to maintain high efficiency when the transfer distance changes at short distances ; however, this method requires wide bandwidth and a high‐speed controller to sweep a frequency range promptly. The varying coupling method adaptively changes the coupling between the drive and main resonant coil in a 4‐coil system ; this method achieves impedance matching at most distances at a single frequency, but increases the number of coils and it is not practical because the physical distance between the coils should be changed to vary the coupling. The LC matching circuit method achieves impedance matching adaptively using additional combinations of lumped elements in front of coils ; this method can be used with the minimum number (two) of coil at a single frequency, but requires many combinations of lumped elements and therefore may incur additional power loss.…”