Multi-Layer Magnetic Shield for Wireless Power Coil Efficiency
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Solution Overview
Problem
Wireless power systems suffer from reduced efficiency due to stray magnetic flux not captured by the receive coil, which is trapped as eddy currents in conductive substrates, leading to a decrease in the quality factor of the coils and undesirable effects such as heating.
Innovation Solution
A multi-layer magnetic shield is implemented, comprising a first layer of low-loss material like ferrite and a second layer of higher-loss, high permeability material, arranged to capture stray magnetic flux where the field is weaker, improving the quality factor and overall efficiency of the wireless power system without increasing shield thickness or introducing gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer magnetic shield is used, then the shield thickness is reduced, but the quality factor improvement is insufficient
Solution Approach 1:
The patent employs a multi-layer magnetic shield structure where each layer is made of different magnetic materials with distinct permeability characteristics. The first layer uses a high permeability material to capture strong magnetic flux near the coil, while the second layer uses a lower permeability material to capture weaker flux further away. This composite structure optimizes the overall shielding effectiveness and improves the quality factor more than a single-layer shield could achieve alone.
Solution Approach 2:
The magnetic shield is designed with spatially varying material properties - the first layer positioned closer to the receive coil uses high permeability material where the magnetic field is strongest, while the second layer positioned farther away uses lower permeability material where the field is weaker. This local optimization of material properties maximizes the shielding effect at each position, thereby improving the quality factor and power transfer efficiency.
2Reliability
If shield thickness is increased, then stray magnetic flux is better captured, but device profile becomes thicker
Solution Approach 1:
By using a multi-layer composite structure with different material permeabilities, the patent achieves effective stray flux capture with reduced total thickness. The high permeability first layer captures the majority of strong flux close to the coil, while the thinner second layer with lower permeability captures the remaining weaker flux, eliminating the need for a single thick shield layer.
Solution Approach 2:
The magnetic shield is segmented into multiple thin layers rather than one thick layer. Each layer is optimized for its specific position and function - the first layer handles strong flux near the coil, the second layer handles weaker flux farther away. This segmentation allows the total shield thickness to be reduced while maintaining or improving shielding effectiveness.
3Ease of manufacture
If gaps are introduced in the shield, then manufacturing is easier, but magnetic flux trapping is reduced
Solution Approach 1:
The multi-layer composite structure provides manufacturing flexibility where each layer can be fabricated separately and then assembled. The different material properties of each layer allow for optimized manufacturing processes for each individual layer while maintaining overall magnetic shielding effectiveness through the composite structure.
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
The multi-layer magnetic shield effectively traps and returns stray magnetic flux, enhancing the quality factor of the receive coil and improving the efficiency of the wireless power system, while maintaining a thin device profile suitable for electronic devices.
Implementation Method 1
the magnetic shield includes a first layer comprising a first material and a second layer comprising a second material, wherein the second material has a higher permeability than the first material
Implementation Method 2
The oscillating magnetic field induces an AC voltage into the tuned receive coil 12 of wireless power receiver 3 in accordance with Faraday's law
Implementation Method 3
The inverter, in conjunction with transmitter matching network 8, generates an AC current in transmit coil 10. The AC current in the transmit coil 10 generates an oscillating magnetic field in accordance with Ampere's law
Implementation Method 4
stray magnetic flux not captured by the receive coil, which is trapped as eddy currents in conductive substrates
Data Source
AI summary
A wireless power assembly including a multi-layer magnetic shield is described. The wireless power assembly includes a wireless power coil and the multi-layer magnetic shield arranged adjacent to the wireless power coil. The magnetic shield includes a first layer comprising a first material and a second layer comprising a second material, wherein the second material has a higher permeability than the first material.