Reflected Impedance Modulation for Wireless Charging
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Solution Overview
Problem
Existing wireless charging systems for implantable medical devices face inefficiencies in power coupling between external chargers and implantable pulse generators, leading to increased power expenditure and potential overheating, especially in non-ideal alignment conditions.
Innovation Solution
The system employs reflected impedance modulation to assess coupling by periodically pulsing the impedance of the charging coil in the implantable pulse generator, allowing the external charger to adjust output power based on the voltage reflections, thereby optimizing charging without the need for telemetry of coupling parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wireless inductive charging is used for implantable medical devices, then charging convenience is improved, but power coupling efficiency deteriorates leading to increased power expenditure and overheating
Solution Approach 1:
The system implements a feedback mechanism where the implantable device modulates its coil impedance based on received charge current levels. By varying the impedance (e.g., switching between high and low impedance states), the implantable device provides feedback signals that the external charger detects and uses to adjust the charge current, thereby optimizing power transfer and reducing energy loss
Solution Approach 2:
The system dynamically adjusts the charge current based on real-time coupling conditions. The external charger continuously monitors the reflected impedance changes from the implantable device and adapts the charging parameters accordingly, enabling optimal power transfer efficiency under varying alignment and tissue conditions
2Productivity
If high power output is used to improve charging speed, then charging efficiency is improved, but overheating risk increases
Solution Approach 1:
The system employs periodic impedance modulation where the implantable device switches its coil impedance between different states at specific intervals during charging. This periodic action creates detectable variations in the reflected impedance that allow the external charger to monitor charging progress and adjust power levels to maintain optimal charging speed while preventing overheating
Solution Approach 2:
The feedback mechanism enables real-time monitoring of charging conditions through impedance variations. When the system detects suboptimal coupling or rising temperatures, the feedback signals prompt the external charger to reduce power output, thereby preventing overheating while maintaining the highest safe charging speed
3Productivity
If impedance modulation is used to assess coupling, then charging optimization is improved, but device complexity increases
Solution Approach 1:
The impedance modulation mechanism serves multiple functions: it enables coupling assessment, provides charging status feedback, and facilitates communication between the external charger and implantable device. By making the impedance modulation multi-functional, the system achieves charging optimization without adding separate dedicated components for each function
Solution Approach 2:
The implantable device uses its existing coil structure for both wireless power reception and impedance modulation signaling. The coil that receives charging power is also used to generate the impedance variations that convey coupling information, eliminating the need for separate sensing or communication hardware
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 approach enhances charging efficiency by dynamically adjusting power output, reducing the risk of overheating and improving charging speed, while maintaining patient safety by minimizing unnecessary power consumption.
Implementation Method 1
The system employs reflected impedance modulation to assess coupling by periodically pulsing the impedance of the charging coil in the implantable pulse generator
Implementation Method 2
Power transmission from the external charger 50 to the IPG 100 occurs wirelessly, and transcutaneously through a patient's tissue 25, via inductive coupling
Implementation Method 3
Power transmission from the external charger 50 to the IPG 100 occurs wirelessly, and transcutaneously through a patient's tissue 25, via inductive coupling
Data Source
AI summary
The disclosed system for providing closed loop charging between an external charger and an implantable medical device such as an IPG involves the use of reflected impedance modulation, i.e., by measuring at the external charger reflections arising from modulating the impedance of the charging coil in the IPG. During charging, the charging coil in the IPG is periodically pulsed to modulate its impedance. The magnitude of the change in the coil voltage produced at the external charger ΔV as a result of these pulses is assessed and is used by the controller circuitry in the external charger as indicative of the coupling between the external charger and the IPG. The external charger adjusts its output power (e.g., Icharge) in accordance with the magnitude of ΔV, thus achieving closed loop charging without the need of telemetering coupling parameters from the IPG.