Drift Compensation for Implanted Capacitance Pressure Transducers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitance-based pressure sensors used in monitoring ambient pressure in living organs face significant drift over time due to aging or tissue build-up, and the noisy, time-varying nature of cardiac pressure measurements complicates accurate calibration.
Innovation Solution
A method and apparatus that apply a calibration voltage to the pressure sensor, modifying its capacitance and isolating the contribution of this voltage from the ambient pressure waveform, allowing for real-time calibration of the pressure-capacitance dependence, using either direct application to the sensor or modification of an oscillator circuit's operating point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitance-based pressure sensor is used to monitor ambient pressure in a living organ, then the sensor can detect pressure changes, but the sensor experiences significant drift over time due to aging or tissue build-up
Solution Approach 1:
The system performs preliminary calibration actions by applying calibration voltages at specific time intervals to establish baseline capacitance values before drift occurs. The calibration process proactively identifies and compensates for drift by comparing current sensor readings against previously calibrated reference values, thereby maintaining accuracy over extended periods.
Solution Approach 2:
The system implements feedback mechanisms by continuously monitoring sensor output and comparing it against expected pressure-capacitance relationships. When drift is detected through deviation from calibrated values, the system automatically adjusts or triggers recalibration, creating a closed-loop system that maintains reliability despite aging or tissue changes.
2Measurement precision
If calibration is performed to compensate for drift, then measurement accuracy is improved, but the noisy and time-varying nature of cardiac pressure measurements complicates accurate calibration
Solution Approach 1:
The system employs periodic calibration actions by applying calibration voltages at specific, predetermined time intervals or during specific phases of the cardiac cycle. This periodic approach allows the system to distinguish calibration signals from physiological pressure variations, enabling accurate calibration despite the noisy and time-varying nature of cardiac measurements.
Solution Approach 2:
The calibration voltage acts as an intermediary signal that temporarily overrides normal pressure sensing to establish known reference points. By introducing this controlled intermediary signal, the system can accurately measure and characterize the pressure-capacitance relationship without being confounded by simultaneous physiological variations, thereby simplifying the calibration measurement process.
3Manufacturing precision
If calibration voltage is applied to modify capacitance, then the pressure-capacitance dependence can be calibrated, but the calibration signal must be isolated from the ambient pressure waveform
Solution Approach 1:
The system segments the measurement process into distinct phases: normal pressure sensing mode and calibration mode. During calibration mode, the calibration voltage is applied and the resulting waveform is isolated from ambient pressure variations through phase-based separation. This segmentation allows precise calibration without the complexity of continuously separating overlapping signals throughout all measurement time.
Solution Approach 2:
The calibration voltage is applied periodically at specific phases of the cardiac cycle when the ambient pressure waveform has predictable characteristics. By timing the calibration signal to occur during specific periodic phases, the system can easily isolate the calibration contribution from the ambient pressure waveform, reducing signal isolation complexity while maintaining calibration precision.
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 provides highly accurate compensation for drift and noise in pressure measurements, ensuring the sensor's accuracy remains high over extended periods without performance degradation, even in noisy and time-varying environments.
Implementation Method 1
sensing the ambient pressure using a pressure sensor, which has a capacitance that varies in response to the ambient pressure
Implementation Method 2
A calibration voltage, which modifies the capacitance and thus the time-varying waveform, is applied to the pressure sensor
Data Source
AI summary
A method includes, in a living organ (28) in which an ambient pressure varies as a function of time, sensing the ambient pressure using a pressure sensor (36, 90, 174), which has a capacitance that varies in response to the ambient pressure, so as to produce a time-varying waveform. A calibration voltage, which modifies the capacitance and thus the time-varying waveform, is applied to the pressure sensor. The time-varying waveform is processed so as to isolate and measure a contribution of the calibration voltage to the waveform. A dependence of the capacitance on the ambient pressure is calibrated using the measured contribution of the calibration voltage.