Stepped Shield Ferrite for Wireless Power Eddy Current Reduction
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Solution Overview
Problem
Existing power transfer systems experience eddy current losses due to interlinkage of magnetic flux between coils and shields in contactless power transfer systems, leading to inefficiencies in power reception and transmission.
Innovation Solution
The configuration of a power reception and transmission apparatus with a ferrite and a shield, where the coil is placed on one principal face of the ferrite and the shield on the other, with a stepped portion between them, allowing magnetic flux to return to the ferrite and reducing interlinkage with the shield, thereby minimizing eddy current losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the shield is placed on the outer periphery of the ferrite core, then the shield provides electromagnetic shielding, but the magnetic flux from the coil hits the shield causing eddy current loss
Solution Approach 1:
The invention introduces a stepped portion that creates a vertical dimension (height difference) between the shield and the outer periphery of the ferrite core. This dimensional change allows the magnetic flux to return to the ferrite through the exposed surface without hitting the shield, thereby reducing eddy current loss while maintaining shielding effectiveness.
Solution Approach 2:
The shield is segmented into different levels by the stepped portion, creating distinct zones: one zone for electromagnetic shielding and another zone (exposed ferrite surface) for magnetic flux return. This segmentation allows the shield to perform its shielding function without interfering with the magnetic flux path.
2Power
If the coil is placed on the ferrite surface, then power transfer is enabled, but magnetic flux interlinkage with the coil itself causes energy loss
Solution Approach 1:
The invention extracts the harmful interlinkage effect by providing an external return path for the magnetic flux through the exposed ferrite surface. This allows the magnetic flux to complete its cycle outside the coil, preventing it from interlinking with the coil itself and causing energy loss.
3Object-affected harmful factors
If the shield covers the entire ferrite core, then shielding is maximized, but magnetic flux cannot return to the ferrite causing increased loss
Solution Approach 1:
The invention applies local quality by making only the necessary portion of the ferrite surface exposed (where the stepped portion is provided) rather than leaving the entire surface exposed. This localized exposure is sufficient for magnetic flux return while maintaining shielding effectiveness in other areas.
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 effectively reduces eddy current losses by guiding magnetic flux back to the ferrite, enhancing the efficiency of power transfer and maintaining resonance strength in the power transfer system.
Implementation Method 1
a magnetic flux generated from the coil is easily led to return to the ferrite from those exposed parts of the first principal face and the second principal face
Implementation Method 2
it is possible to reduce an eddy current loss due to interlinkage of a magnetic flux generated from an inner-peripheral-portion side of the coil with the coil itself and the shield
Implementation Method 3
a power transfer system including the power reception apparatus that receives power from the power transmission apparatus in a contactless manner
Data Source
AI summary
A power reception apparatus to which power is transferred from a power transmission apparatus in a contactless manner includes: a ferrite provided in a plate shape and having a first principal face and a second principal face; an annular coil provided on the first principal face of the ferrite; and a shield provided on the second principal face of the ferrite, wherein an outer peripheral portion of the coil is placed on an inner side relative to an outer peripheral portion of the ferrite, such that part of the first principal face is exposed on an outer-peripheral-portion side of the ferrite, and an outer peripheral side of the shield includes a stepped portion provided at a position away from the second principal face of the ferrite, such that part of the second principal face is exposed on the outer-peripheral -portion side of the ferrite.