Capacitive Sensor Active Electrode Discharge for Biomedical Signals
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Solution Overview
Problem
Capacitive sensors used for contactless measurement of biomedical signals face issues with charge buildup on the sensing electrode, leading to errors and instability in signal processing due to high impedance/resistance circuitry, which affects the accuracy and comfort of unobtrusive monitoring.
Innovation Solution
The capacitive sensor employs monitoring and conditioning circuits to detect charge buildup and actively discharge the electrode by connecting it to a fixed potential via a switch, ensuring accurate signal processing and indicating invalid measurements when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If capacitive sensors are used for contactless measurement, then patient comfort and ease of operation are improved, but charge buildup on the electrode causes measurement errors and reduces reliability
Solution Approach 1:
The monitoring circuit continuously monitors the output signal from the amplification circuit to detect charge buildup on the electrode. When charge buildup is detected (indicated by signal instability or exceeding threshold values), the system activates the discharge circuit to remove the accumulated charge, then resumes normal measurement. This closed-loop feedback mechanism maintains measurement reliability while preserving the contactless comfort advantage.
Solution Approach 2:
A discharge circuit is introduced as an intermediary component between the electrode and ground. This discharge circuit, controlled by the monitoring circuit, periodically removes accumulated charge from the electrode without requiring patient contact or interrupting the measurement process, thus resolving the reliability issue while maintaining ease of operation.
2Measurement precision
If high impedance/resistance circuitry is used in capacitive sensors, then sensitivity to small biomedical charges is improved, but charge buildup on the electrode increases causing measurement errors
Solution Approach 1:
The monitoring circuit provides continuous feedback on the electrode charge state by analyzing the output signal from the high-impedance amplification circuit. When charge buildup is detected through signal threshold monitoring, the system automatically activates the discharge circuit to remove excess charge, then returns to normal high-sensitivity measurement mode, thus maintaining measurement precision while eliminating charge buildup errors.
Solution Approach 2:
The discharge circuit operates periodically based on monitoring circuit detection rather than continuously. The monitoring circuit detects charge buildup conditions and triggers periodic discharge events, allowing the high-impedance circuitry to maintain sensitivity during normal operation while periodically removing harmful charge accumulation that would otherwise degrade measurement precision.
3Reliability
If active discharge circuitry is added to the capacitive sensor, then measurement reliability is improved by preventing charge buildup, but device complexity increases
Solution Approach 1:
The monitoring circuit continuously monitors the amplification circuit output to detect charge buildup conditions. When errors are detected (signal exceeds preset thresholds), the monitoring circuit triggers the discharge circuit to remove accumulated charge. This feedback-based approach activates discharge only when necessary, improving reliability while minimizing the operational impact of the additional circuitry.
Solution Approach 2:
The system performs self-diagnosis through the monitoring circuit, which automatically detects charge buildup conditions and triggers the discharge circuit without external intervention. The system monitors its own operational state and self-corrects measurement errors, reducing the need for external complexity while maintaining high reliability.
4Ease of operation
If contactless capacitive measurement is used, then ease of operation and patient comfort are improved, but measurement precision and stability deteriorate due to charge buildup
Solution Approach 1:
The monitoring circuit provides continuous feedback on signal quality by detecting charge buildup effects on the amplification circuit output. When signal instability or errors are detected, the system activates the discharge circuit to restore signal stability, then resumes normal contactless measurement. This maintains unobtrusive measurement comfort while ensuring signal precision through automatic error correction.
Solution Approach 2:
The discharge circuit acts as an intermediary mechanism that periodically removes charge buildup from the electrode without requiring physical contact with the patient or interrupting the contactless measurement process. This intermediary discharge function resolves the signal stability issue while preserving the ease of operation and patient comfort advantages of contactless measurement.
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 prevents measurement errors caused by charge buildup, maintaining sensor accuracy and comfort during unobtrusive biomedical signal monitoring, such as ECG, EEG, or EMG measurements, by quickly discharging the electrode and signaling invalid data to the system.
Implementation Method 1
capacitive sensor for measuring a small biomedical electrical charge originating from an object under test... an electrode for sensing the charge to provide an output signal... wherein the electrode has no electrical contact with the object
Implementation Method 2
the conditioning circuit elements are configured to be activated for discharging the electrode when the error in the measurement is detected... connecting it to a fixed potential
Data Source
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AI summary
The disclosure is directed to a capacitive sensor for measuring a small biomedical electrical charge originating from an object under test comprising input circuit elements having an electrode for sensing the charge to provide an output signal that is a function of the charge being measured, wherein the electrode has no electrical contact with the object; amplification circuit elements (A) connected to the input circuit elements; processing circuit elements configured for receiving and processing the amplified output signal and to provide the measurement; and conditioning and monitoring circuit elements coupled to at least the input circuit elements comprising monitoring circuit elements and conditioning circuit elements; (Rl) wherein the monitoring circuit elements are configured for monitoring the amplified output signal to detect an error in a measurement that is greater than a preset value caused by charge buildup on the electrode; and wherein the conditioning circuit elements are configured to be activated for. discharging the electrode when the error in the measurement is detected by the monitoring circuit elements and the conditioning circuit elements are configured to be deactivated, when the error in the measurement is no longer detected.