Inductive Charger Magnetic Shielding for Implantable Devices
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Solution Overview
Problem
Existing wireless external chargers for implantable medical devices face inefficiencies due to excessive heating and eddy currents in the battery casing caused by the close proximity of the charging coil, leading to reduced charging efficiency and increased power requirements.
Innovation Solution
A compact, low-profile external charger design with a magnetic shield made of high permeability material, such as ferrite plates, is introduced, where the magnetic shield is placed between the battery and the coil to redirect magnetic field lines and minimize eddy current heating, allowing for improved energy transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the charging coil is placed close to the battery for compact design, then the device size is reduced, but eddy current heating in the battery casing increases
Solution Approach 1:
A magnetic shield made of high permeability material (ferrite plates) is introduced as an intermediary component between the charging coil and the battery. This magnetic shield redirects magnetic field lines away from the battery casing, preventing eddy current generation while allowing the coil and battery to remain in close proximity for compact design.
Solution Approach 2:
The harmful magnetic field interaction is extracted and isolated from the battery by placing the magnetic shield between the coil and battery. The shield captures and redirects the magnetic flux, effectively removing the harmful effect from the battery area while maintaining the compact integrated structure.
2Device complexity
If the charging coil is placed close to the battery, then the device complexity is reduced, but charging efficiency decreases due to heat loss
Solution Approach 1:
The magnetic shield serves as a mediator that improves energy transfer efficiency by directing magnetic field lines away from the battery and toward the implantable device. This reduces energy loss through eddy currents in the battery casing while maintaining the simple integrated structure.
Solution Approach 2:
The introduction of the magnetic shield changes the magnetic field distribution parameters, redirecting flux lines to improve the quality factor of the coil and reduce energy loss. This allows the system to maintain high charging efficiency despite the compact integrated design.
3Loss of energy
If a magnetic shield is added to reduce eddy current heating, then charging efficiency improves, but device complexity increases
Solution Approach 1:
The magnetic shield is constructed from ferrite plates, which are composite magnetic materials with high permeability. These materials provide effective magnetic shielding while maintaining a relatively simple structural form that integrates well with the existing charger components.
Solution Approach 2:
The magnetic shield is implemented as thin ferrite plates rather than bulky shielding structures. This thin-film approach provides effective magnetic field redirection while adding minimal complexity and volume to the integrated charger design.
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 magnetic shield enhances charging efficiency, reduces heat loss, and increases the quality factor of the coil, resulting in faster charging rates, increased patient safety, and a smaller form factor.
Implementation Method 1
a magnetic shield within the housing comprising a plate or plates made of a high permeability material, in which the magnetic shield is located between the battery and the coil
Implementation Method 2
excessive heating and eddy currents in the battery casing caused by the close proximity of the charging coil
Implementation Method 3
the coil is used to provide power to an implantable medical device
Data Source
AI summary
To recharge an implanted medical device, an external device, typically in the form of an inductive charger, is placed over the implant to provide for transcutaneous energy transfer. The external charging device can be powered by a rechargeable battery. Since the battery is in close proximity to the charge coil, the large magnetic field produced by the charge coil induces eddy currents that flow on the battery's metallic case, often resulting in undesirable heating of the battery and reduced efficiency of the charger. This disclosure provides a means of shielding the battery from the magnetic field to reduce eddy current heating, thereby increasing efficiency. In one embodiment, the magnetic shield consists of one or more thin ferrite plates. The use of a ferrite shield allows the battery to be placed directly over the charge coil as opposed to outside the extent of the charge coil.