Segmented Capacitive Shielding for Implant Charging Noise Reduction
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Solution Overview
Problem
Current wireless charging technologies for medical implants face challenges in minimizing the impact of electric fields on biological tissue, which can induce parasitic capacitance and interfere with the measurement of small electrical voltages or currents, particularly in neural devices.
Innovation Solution
A capacitively shielded magnetic inductive coupling apparatus featuring a transmitter coil with a conductive ring and radial fingers, and a receiver coil with a conductive annulus and ribs, forming a Faraday cage to suppress electric fields and prevent capacitive coupling with tissue, allowing for the measurement of microvoltages and microamperes while enabling simultaneous charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If wireless charging is implemented for medical implants, then power transfer efficiency is improved, but electric field induced currents in tissue increase causing measurement interference
Solution Approach 1:
The shield is segmented into multiple radial fingers that are electrically isolated from each other, preventing continuous eddy current paths while maintaining electric field blocking capability. This segmentation allows the shield to reduce measurement interference without significantly impeding power transfer.
Solution Approach 2:
A capacitive shield structure is introduced as an intermediary component between the transmitter coil and the tissue/implant. This shield mediates the electric field interaction by providing a grounded conductive barrier that redirects electric field lines, reducing induced currents in tissue while allowing magnetic field coupling for power transfer to continue.
2Object-affected harmful factors
If a continuous conductive shield is used to block electric fields, then parasitic capacitance is reduced, but eddy currents are generated in the shield itself
Solution Approach 1:
The continuous conductive shield is divided into multiple discrete radial fingers that are electrically isolated from one another. This segmentation interrupts the formation of large-scale eddy current loops in the shield material while maintaining the overall capacitive shielding effect through the distributed structure of the fingers.
Solution Approach 2:
Different portions of the shield structure serve different functions: the radial fingers provide electric field blocking and parasitic capacitance reduction, while the gaps between fingers prevent eddy current formation. The grounding structure at the base provides a reference potential without creating continuous conductive paths that would generate eddy currents.
3Object-affected harmful factors
If the shield is made more extensive to improve field blocking, then electric field suppression is improved, but device complexity increases
Solution Approach 1:
The shield is implemented as a set of discrete radial fingers rather than a continuous structure, which simplifies fabrication and assembly. The segmented design achieves effective field blocking through the distributed arrangement of conductive elements, reducing the amount of material and structural complexity required compared to a solid shield.
Solution Approach 2:
The shield provides sufficient electric field blocking with a partial structure (radial fingers) rather than requiring a complete continuous enclosure. This partial shielding approach achieves the necessary reduction in parasitic capacitance and electric field suppression while minimizing device complexity and material usage.
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 solution effectively reduces eddy currents and charging noise, enabling safe and precise measurement of small electrical signals in tissue while allowing for efficient power transfer, supporting medical implants that require accurate voltage and current detection.
Implementation Method 1
a capacitive shield efficient at containing electric fields created by alternating current (AC) voltage of charging coils... A grounded, capacitive shield is efficient at containing electric fields created by alternating current (AC) voltage of charging coils
Implementation Method 2
Resonant inductive coupling between a transmitter coil and receiver coil is an efficient way to transfer power over short distances... an alternating current (AC) is driven in the transmitter coil, which causes a magnetic ('B') field in the volume around it. When close enough to the receiver coil, the magnetic field passes through it and induces current in the receiver coil
Implementation Method 3
The implant ground is separate from any precision sensor grounds for electronics within the device. The receiver shield suppresses an electric field emanating from the receiver coil... A ground plane for the electronics can cap off one side of the shield, forming a full Faraday cage around the receiver coil
Data Source
AI summary
A set of shielded coils for wireless power transmission into a medical implant is described in which the external, power transmission coil is blocked at least on one side by a shield with a broken ring and radial fingers while the power receiver coil inside the medical implant is surrounded by a shield having a broken ring connecting radial fingers and ribs around its circumference. The finger and rib configurations minimizes eddy currents in the shields. A ground plane of the implant's internal circuitry, which is within the shield along with the receiver coil, can cap off the cupped receiver shield to form a Faraday cage with it. The metal or other conductive shielding prevents large electric fields from the coils from penetrating into the tissue of the subject while simultaneously allowing magnetic fields inductively couple the coils for charging. An implant with sensitive electrodes that measure minute voltages from a brain or other tissues is protected from capacitively driven voltage swings or other transients during charging.