Shielded Passive Transponder Coil for Implantable Medical Devices
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Solution Overview
Problem
Passive transponders experience poor signal-to-noise ratios and reduced quality factor when used in liquid media like blood due to electrical properties of the medium, leading to attenuated signal coupling and eddy current losses.
Innovation Solution
A passive transponder design featuring a solenoid coil with electrically conductive shielding that covers both sides of the coil turns except for a central area, incorporating interruptions in the shielding to prevent current flow and an electrically insulating layer to minimize interaction with the surrounding medium, allowing magnetic fields to induce current in the coil while maintaining electromagnetic field concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the implant is made thinner to avoid obstructing blood flow, then the device profile is improved, but the signal-to-noise ratio deteriorates due to increased proximity to the conductive medium
Solution Approach 1:
An electrically insulating layer is introduced as an intermediary between the coil and the blood medium. This layer prevents direct electrical interaction between the coil and the conductive blood, reducing eddy current losses and improving the signal-to-noise ratio while allowing the implant to maintain a thin profile
Solution Approach 2:
The conductive properties of blood, which cause eddy current losses, are mitigated by introducing the insulating layer. The harmful electrical interaction is converted into a beneficial configuration where the insulating layer directs the magnetic field coupling through the coil while blocking parasitic current paths in the blood
2Adaptability or versatility
If coils are used in the human body to establish inductive coupling, then wireless communication is enabled, but the quality factor decreases dramatically due to eddy current losses in the surrounding medium
Solution Approach 1:
The insulating layer acts as a mediator that allows magnetic field penetration for inductive coupling while blocking electrical current paths that would otherwise cause eddy current losses in the blood medium, thereby preserving the quality factor
Solution Approach 2:
A thin film insulating layer is applied to the coil structure, providing electrical isolation from the conductive medium while maintaining the flexibility and thin profile required for implantable devices. This thin film prevents energy losses without compromising the inductive coupling function
3Length of moving object
If the coil is placed close to the blood medium for implantability, then the device profile is reduced, but parasitic capacitance increases due to the different dielectric properties of blood compared to air
Solution Approach 1:
The insulating layer serves as a dielectric intermediary between the coil and the blood medium, controlling and stabilizing the parasitic capacitance by providing a consistent dielectric barrier that prevents direct electrical interaction with the high-permittivity blood medium
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
Enhances inductive coupling and signal quality in liquid media by reducing parasitic capacitance and eddy current losses, maintaining signal strength and quality factor comparable to air environments.
Implementation Method 1
coils are used in the human body or blood to establish an inductive coupling between an implanted transponder and an external readout device
Implementation Method 2
The reduction in the coil's quality factor is caused by eddy current losses. These losses, occurring in close proximity to the coil windings, result in losses in the medium
Data Source
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AI summary
The invention relates to a passive transponder having at least one coil, the transponder having an electrically conductive shield which covers the windings of the coil from both sides. A central region of the coil around which the windings are wound is not covered by the shield. In the surfaces, in which the shield covers the windings, the shield has at least one discontinuity by which a current flow in the shield can be prevented.