Foil-Type Wireless Power Coils with Arcuate Corners
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Solution Overview
Problem
Wireless power transfer systems face reduced power transfer efficiency due to high eddy current losses, which are exacerbated by the skin effects of winding conductors at high frequencies, limiting their application to niche uses.
Innovation Solution
The use of foil-type transmitter/receiver coils with specific arcuate-shaped corners and configurations, including odd integers of turns with concave surfaces and ferrite shielding, to minimize eddy current losses by aligning magnetic flux lines parallel to the coil surfaces, reducing the impact of skin effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional winding conductors are used in resonant tank circuits operating at high frequency, then the system can be constructed with standard components, but eddy current losses become unacceptably high due to skin effects
Solution Approach 1:
The patent changes the geometric parameters of the conductor from conventional round wires to foil-type conductors with specific dimensions (thickness t and width w). By controlling the thickness to be less than the skin depth at operating frequency, the conductor geometry is optimized to minimize skin effect losses while maintaining manufacturability through standard foil fabrication processes.
Solution Approach 2:
The patent employs composite construction by stacking multiple insulated foil layers to form the winding conductor. This composite structure combines thin foil layers (each thinner than skin depth) with insulation material, creating a conductor that reduces eddy current losses while maintaining the necessary current-carrying capacity and mechanical strength.
2Loss of energy
If foil-type conductors are used to reduce eddy current losses, then power transfer efficiency increases, but the configuration and layout must comply with ICNIRP guidelines to limit human exposure to time-varying EMFs
Solution Approach 1:
The patent applies curvature to the foil conductor edges, specifically rounding the corners and edges of the foil layers. This curvature distributes the current density more uniformly and reduces concentrated eddy currents at sharp edges, thereby reducing EMF exposure while maintaining the low eddy current loss benefits of foil conductors.
Solution Approach 2:
The patent implements different geometric characteristics at different locations of the conductor. The foil layers have varying thickness distributions and edge curvatures optimized for local current density management. This local optimization reduces EMF exposure in critical areas while maintaining overall power transfer efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces eddy current losses, enhancing power transfer efficiency and compliance with safety guidelines by minimizing human exposure to EMFs, as demonstrated by comparative studies showing lower eddy current losses compared to conventional coil designs.
Implementation Method 1
Some wireless power transfer systems use near-field electromagnetic coupling (e.g., mutual inductance) to charge electronic devices by transferring power from a transmitter winding ('primary winding') located external to a device to a receiver winding ('secondary winding’) within the device
Implementation Method 2
because a resonant tank circuit within the power transfer system may operate at relatively high frequency, the skin effects of winding conductors should be minimized; otherwise, eddy current losses may be unacceptably high
Implementation Method 3
the skin effects of winding conductors should be minimized; otherwise, eddy current losses may be unacceptably high and power transfer efficiency may be unacceptably low
Data Source
AI summary
Wireless power transfer systems include at least one foil-type transmitter/receiver coil with a plurality of turns, which is configured to reduce eddy current losses therein when energized to conduct an alternating current that supports inductive power transfer including coil-to-coil power electrical transfer, inductive heating, etc. The plurality of turns includes at least an outermost turn with a first arcuate-shaped corner having a concave inner surface, which faces an immediately adjacent one of the plurality of turns. The immediately adjacent one of the plurality of turns may also have a second arcuate-shaped corner with a concave inner surface facing an innermost one of the plurality of turns. The first arcuate-shaped corner may have a non-uniform radius of curvature and/or an innermost one of the plurality of turns may have an arcuate-shaped corner, which is a mirror image of the first arcuate-shaped corner when the coil is view in transverse cross-section.