Self-Tuning External Device for Wireless Recharging Implantable Medical Devices
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Solution Overview
Problem
External devices for wirelessly recharging implantable medical devices face efficiency issues due to changes in resonant frequency caused by environmental factors like changes in coil loading from nearby metal objects, leading to reduced power transfer efficiency and complex power monitoring.
Innovation Solution
The external device self-tunes its drive circuitry to maintain unity power factor by monitoring current direction and controlling switches within the tank circuit, ensuring efficient energy transfer even with unpredictable changes in resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the tank circuit is designed with high-Q for efficient power transfer, then power transfer efficiency is improved, but the resonant frequency becomes highly sensitive to loading changes causing the system to operate away from resonance
Solution Approach 1:
The patent applies dynamics by making the drive frequency adjustable and adaptive rather than fixed. The system continuously monitors the tank circuit's resonant frequency and dynamically adjusts the drive frequency to track changes caused by loading variations, maintaining operation at or near resonance despite environmental changes.
Solution Approach 2:
The patent implements feedback by monitoring the phase angle between voltage and current in the tank circuit and using this information to adjust the drive frequency. The system measures the actual resonant frequency through phase detection and feeds this information back to the frequency control mechanism, creating a closed-loop system that maintains optimal power transfer efficiency.
2Device complexity
If the drive frequency is fixed and differs from the changing resonant frequency, then device complexity is reduced, but power transfer efficiency plummets and phase angle control becomes inaccurate
Solution Approach 1:
The patent applies self-service by enabling the system to automatically detect and track its own resonant frequency without requiring complex external tuning equipment. The tank circuit itself provides the information needed for frequency adjustment through its phase characteristics, allowing the system to self-correct and maintain optimal operation autonomously.
3Measurement precision
If the phase angle between voltage and current becomes substantial, then power monitoring accuracy is compromised, but the system becomes more tolerant of frequency variations
Solution Approach 1:
The patent applies preliminary action by proactively maintaining the phase angle near zero through continuous frequency adjustment before significant efficiency losses occur. Rather than reacting to large phase deviations, the system continuously tracks resonant frequency changes and adjusts the drive frequency in advance to prevent substantial phase angles from developing, ensuring both accurate power monitoring and efficient power transfer.
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 maintains a phase angle of 10 degrees or less between voltage and current, achieving efficient power transfer and accurate power monitoring, thereby minimizing recharge time and energy wastage.
Implementation Method 1
External devices that provide wireless recharging for implantable medical devices through inductive coupling
Implementation Method 2
the resonant frequency of a tank circuit that includes the coil
Data Source
AI summary
External device circuitry self-tunes so that current is being driven through a coil at a resonant frequency of the tank circuit including the coil. The self-tuning nature of the driver circuitry enables adaptation within a cycle to changes in the resonant frequency such as those due to changing loads on the coil from environmental factors. The self-tuning circuitry monitors the direction of current flow in the tank circuit so that during a non-driven phase of a two-phase cycle, the circuitry detects the current naturally changing directions and then activates the driver circuitry to drive current into the tank circuit in phase with the natural direction of current flow. Unity power factor is approximated while driving the coil despite changes in resonance. Power being driven into the tank circuit may then be measured at the approximation of unity power factor to control the amount of power being applied.