Surface Stimulation Device Impedance Compensation
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Solution Overview
Problem
Existing surface-based stimulation devices face challenges in ensuring consistent nerve stimulation due to changing skin impedance, which can result in inadequate stimulus duration and power consumption issues.
Innovation Solution
The solution involves increasing the internal impedance of the stimulation device and generating a stimulation waveform with a non-zero slope during current decay to prolong the stimulus duration, ensuring consistent nerve stimulation without increasing the amplitude or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amplitude of the stimulation signal is increased to ensure action potential firing, then the reliability of nerve stimulation is improved, but the power consumption increases
Solution Approach 1:
The patent changes the temporal parameters of the stimulation signal by extending its duration to match the widened Chronaxie period, rather than increasing the amplitude. This parameter transformation allows reliable nerve stimulation while maintaining lower power consumption levels.
Solution Approach 2:
The patent introduces dynamic adjustment of the stimulation signal duration based on the measured skin impedance and calculated Chronaxie value. The system dynamically extends or reduces the stimulus pulse width to optimize the balance between stimulation reliability and power consumption for each user condition.
2Reliability
If the stimulus duration is extended to compensate for current decay, then the reliability of nerve stimulation is improved, but the power consumption increases
Solution Approach 1:
The patent transforms the static fixed-duration stimulus into a dynamic variable-duration signal that adapts to skin impedance changes. By calculating Chronaxie based on measured impedance and extending the stimulus to match this calculated duration, the system ensures consistent nerve stimulation without unnecessarily prolonged activation.
3Adaptability or versatility
If the internal impedance is increased to widen Chronaxie, then the adaptability to skin impedance changes is improved, but the device complexity increases
Solution Approach 1:
The patent introduces an intermediary computational layer that measures skin impedance, calculates Chronaxie using the established formula, and uses this calculation to determine the optimal stimulus duration. This intermediary processing step enables sophisticated impedance compensation without requiring complex hardware modifications.
Solution Approach 2:
The system implements a feedback loop where skin impedance is continuously measured, Chronaxie is recalculated based on the measured impedance, and the stimulus duration is adjusted accordingly. This closed-loop feedback mechanism enables real-time adaptation to changing skin conditions while maintaining manageable device complexity.
4Reliability
If the stimulus current amplitude is maintained high to overcome impedance decay, then the reliability of action potential firing is improved, but the safety and comfort decrease
Solution Approach 1:
The patent shifts from amplitude-based stimulation to duration-based stimulation. By maintaining a moderate, comfortable current amplitude while extending the stimulus duration to match the widened Chronaxie, the system achieves reliable action potential firing without the skin irritation and discomfort associated with high-amplitude brief pulses.
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 effectively widens the Chronaxie time period, ensuring action potential firing irrespective of skin-to-electrode impedance, while minimizing power consumption and avoiding unnecessary activation of non-target tissues.
Implementation Method 1
increasing the internal impedance of the stimulation device so as to widen a Chronaxie time period... by adding an in-line series impedance on the electrode interface side
Implementation Method 2
employing a stimulus waveform envelope having a non-zero slope or rate of change at least during substantially the duration of current decay so that the average current is non-zero
Data Source
AI summary
A method and associated stimulation device for ensuring firing of an action potential in an intended physiological target activated by a stimulus pulse generated by an electrode of a non-invasive surface based stimulation device irrespective of skin-to-electrode impedance by: (i) increasing internal impedance of the stimulation device so as to widen a Chronaxie time period thereby ensuring firing of the action potential of the intended physiological target irrespective of the skin-to-electrode impedance; and/or (ii) generating a stimulation waveform that optimizes a non-zero average current (e.g., non-zero slope of the envelope of the stimulation waveform) during preferably substantially the entire current decay of the stimulus pulse.