Force Sensor for PPG Motion Noise Filtering
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Solution Overview
Problem
Wearable devices measuring photoplethysmographic signals face challenges in accurately filtering out motion noise caused by internal tissue forces, which can lead to erroneous physiological signal determinations, such as heart rate and oxygen saturation, due to the inability to detect flexion and other internal tissue movements.
Innovation Solution
Incorporating a force sensor into wearable devices to detect internal tissue forces and use this information to condition or disqualify the photoplethysmographic signal, thereby improving measurement accuracy by filtering out motion noise and providing feedback for optimal device positioning and pressure adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a force sensor is added to detect internal tissue forces, then measurement precision of PPG signal is improved, but device complexity increases
Solution Approach 1:
A force sensor is introduced as an intermediary component between the PPG sensor and the processing system. The force sensor detects internal tissue forces that cause motion artifacts in PPG signals, and this force information is used as a mediator to identify and filter out contaminated PPG measurements, thereby improving measurement precision without requiring direct modification of the PPG sensing mechanism itself.
2Reliability
If force sensing is used to filter PPG signals, then reliability of physiological parameter determination is improved, but loss of information increases due to disqualification of PPG signals
Solution Approach 1:
The system employs feedback by continuously monitoring force sensor output and using this information to evaluate the quality of simultaneously acquired PPG signals. When the force sensor detects internal tissue forces exceeding a threshold, the system feedback-indicates that the corresponding PPG signal should be disqualified or filtered. This feedback mechanism ensures that only reliable PPG measurements are used for physiological parameter determination, improving overall reliability while minimizing information loss by retaining valid signals.
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
The use of a force sensor enhances the quality of photoplethysmographic signals by effectively filtering out internal tissue motion noise, leading to more accurate physiological parameter measurements and improved user feedback for optimal device operation.
Implementation Method 1
a force sensor configured to detect a force signal
Implementation Method 2
time varying changes in light absorbance can be observed
Data Source
AI summary
The present disclosure generally relates to wearable devices and methods for measuring a photoplethysmographic signal. The wearable devices and methods may include a force sensor that provides input used for motion-noise filtering to obtain improved PPG signals. Feedback from the force sensor may also be used to indicate whether the amount of pressure exerted by the device should be adjusted, or whether the device should be switched to a locked state.