Segmented Conductive Enclosure for Wireless Charging EMI Suppression
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Solution Overview
Problem
Wireless charging systems face challenges in suppressing electromagnetic interference (EMI) due to conductive enclosures, which can interfere with the magnetic field necessary for charging, and existing methods like Faraday cages can reduce EMI but also hinder wireless charging efficiency.
Innovation Solution
Implementing a parallel LC resonant filter across gaps in the conductive enclosure to prevent eddy currents at the wireless charging frequency while maintaining EMI shielding at other frequencies, allowing for a continuous conductive enclosure that enables effective wireless charging and EMI suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a continuous conductive enclosure is used for EMI shielding, then EMI suppression is improved, but wireless charging efficiency deteriorates due to eddy currents at the charging frequency
Solution Approach 1:
The continuous conductive enclosure is segmented by introducing gaps at strategic locations. These gaps interrupt the eddy current paths at wireless charging frequency while maintaining EMI shielding effectiveness. The enclosure is divided into multiple conductive sections that are electrically isolated from each other, preventing large-scale eddy current circulation during wireless charging.
Solution Approach 2:
LC resonant filters are introduced as intermediary components across the gaps in the conductive enclosure. These filters act as frequency-selective mediators that block eddy currents at wireless charging frequency while allowing EMI shielding at other frequencies. The LC filter circuit creates a high impedance path specifically at the resonant frequency matching the wireless charging frequency.
2Loss of energy
If gaps are introduced in the conductive enclosure to prevent eddy currents, then wireless charging efficiency is improved, but EMI shielding effectiveness deteriorates
Solution Approach 1:
LC resonant filters serve as intermediary components that restore EMI shielding functionality across the gaps. The filters present a low impedance path for EMI frequencies, effectively bridging the gaps for shielding purposes while maintaining high impedance at wireless charging frequency due to their resonant characteristics.
Solution Approach 2:
The gaps in the conductive enclosure are not uniform but are strategically positioned and sized based on local electromagnetic field analysis. Each gap is optimized for its specific location to minimize impact on EMI shielding while maximizing eddy current interruption. The LC filter values are also locally optimized for each gap position.
3Object-affected harmful factors
If a Faraday cage approach is used for EMI reduction, then electromagnetic radiation compliance is improved, but wireless charging functionality deteriorates
Solution Approach 1:
The Faraday cage structure is segmented into multiple conductive sections with gaps between them. This segmentation allows the structure to maintain EMI shielding and regulatory compliance while permitting the magnetic field necessary for wireless charging to pass through the gaps without being blocked by continuous conductive material.
Solution Approach 2:
The electrical properties of the enclosure are dynamically changed through the LC filter circuits that are frequency-dependent. At wireless charging frequency, the filters present high impedance to block eddy currents, while at EMI frequencies, they present low impedance to maintain shielding effectiveness, thus adapting the enclosure's electromagnetic characteristics to different operational requirements.
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 solution enhances power transfer during wireless charging, integrates the charging coil fully within the product, and ensures compliance with regulatory limits on electromagnetic radiation, while providing immunity to electrostatic discharge.
Implementation Method 1
a parallel LC resonant filter may be connected across each of the gaps to pass all frequencies except for the frequency at which the wireless charging occurs
Implementation Method 2
the conductive enclosure may also reduce the magnetic field within the electronic device as generated by the PTU due to eddy currents circulating through the body of the enclosure
Implementation Method 3
One of the most common techniques to reduce EM interference (EMI) is to create some sort of metallic enclosure around the product, e.g., a Faraday cage
Data Source
AI summary
A computing device includes a charging coil for producing a charging current when placed in a magnetic field of a wireless power transmitter. A wireless charging operating frequency is associated with wireless charging of a battery of the computing device by the charging coil and the wireless power transmitter. An electrically conductive substrate has a plurality of gaps for reducing eddy currents when the electrically conductive substrate is disposed between the charging coil and the wireless power transmitter during charging of the battery. A plurality of filters each electrically bridge a respective one of the gaps. Each filter attenuates signals within a range of frequencies including the wireless charging operating frequency.