Capacitive Electrophysiological Sensing with Coupling Estimation
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Solution Overview
Problem
Capacitive electrophysiological sensors face challenges in reliably monitoring electrode-to-skin coupling quality without injecting electrical currents and are hindered by motion artifacts, especially in real-life applications where static charges and tribo-electric discharges are prevalent.
Innovation Solution
A sensing system utilizing two sensing circuits with distinct transfer functions to determine coupling capacitance without injecting electrical currents, allowing for assessment of electrode-to-body coupling and compensation for body motion, thereby improving the reliability of electrophysiological signal measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical current is injected through the electrode to skin interface to track coupling quality, then the coupling quality can be monitored, but safety issues arise and device complexity increases
Solution Approach 1:
The patent replaces the electrical current injection method with a capacitive sensing method. Instead of injecting current through the electrode-skin interface, the system uses a capacitive sensor to detect changes in capacitance that occur when the electrode couples with the skin. This substitution eliminates the safety risks associated with current injection while maintaining the ability to monitor coupling quality.
Solution Approach 2:
The patent introduces a capacitive sensor as an intermediary between the electrode and the measurement system. This sensor indirectly detects coupling quality by measuring capacitance changes without requiring direct electrical contact or current injection into the body, thus avoiding safety issues while providing reliable monitoring.
2Reliability
If electrical current is injected through the electrode to skin interface to track coupling quality, then the coupling quality can be monitored, but device complexity increases
Solution Approach 1:
The patent replaces the complex current injection and measurement system with a simpler capacitive sensing system. The capacitive sensor directly measures coupling quality through capacitance changes without requiring current sources, safety circuits, or complex signal processing, thereby reducing device complexity while maintaining monitoring reliability.
3Ease of operation
If capacitive sensing is used to eliminate galvanic contact, then patient comfort and mobility improve, but motion artifacts increase
Solution Approach 1:
The patent uses feedback from the capacitive coupling measurements to detect and compensate for motion artifacts. By continuously monitoring capacitance changes and comparing them against expected patterns, the system can distinguish between legitimate physiological signals and motion-induced artifacts, thereby maintaining signal quality while preserving patient comfort and mobility.
4Ease of operation
If dry electrodes are used to eliminate gel, then patient comfort improves, but measurement stability deteriorates
Solution Approach 1:
The patent replaces the galvanic contact mechanism (which requires gel and prolonged stabilization) with a capacitive sensing mechanism. This substitution allows dry electrodes to achieve immediate measurement stability without requiring gel application or extended equilibration time, thereby maintaining patient comfort while improving measurement readiness.
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
Enables reliable and safe monitoring of electrophysiological signals by determining coupling capacitance and compensating for signal variations caused by movement, enhancing the quality of capacitive coupling without the need for galvanic contact and reducing motion artifacts.
Implementation Method 1
a sense electrode arrangement (14) for capacitive coupling to a surface (16) of a body such that the sense electrode arrangement (14) and the body define a coupling capacitance (Ce)
Data Source
AI summary
A sensing system and method uses a sense electrode arrangement for coupling to a surface of a body such that the sense electrode arrangement and the body (and the spacing between them) define a coupling capacitance. First and second sensing circuits have different transfer functions and generate first and second outputs. These outputs are processed to determine the coupling capacitance. The electrophysiological signal being monitored is also acquired by one or both of the sensing circuits. In this way, the quality of the electrode coupling can be determined in a simple and passive manner.