PPG Motion Artifact Compensation via Sequential Adaptive Filtering
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Solution Overview
Problem
Wearable heart-rate monitors using photoplethysmogram (PPG) sensors face challenges due to motion-induced artifacts from arm movements, which current methods attempt to address with high complexity and battery drainage through methods like accelerometers and real-time FFT computations.
Innovation Solution
A PPG system employing an adaptive digital filter operated sequentially in a daisy-chain fashion, utilizing multiple sensors to reduce motion artifacts, optimizing filter parameters, and performing only one FFT computation per heart-rate update, thereby minimizing noise and conserving battery life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If accelerometers and real-time FFT computations are used to reduce motion artifacts, then motion artifact reduction is improved, but computational complexity and battery drainage increase
Solution Approach 1:
The patent segments the motion artifact reduction process into multiple sequential filter stages, each processing specific frequency components. Instead of performing a complete FFT and processing all frequency components simultaneously, the system divides the spectrum into multiple bands and processes them sequentially through cascaded filters, reducing the computational burden while maintaining effective motion artifact reduction.
Solution Approach 2:
The patent implements periodic action by updating filter parameters at specific intervals rather than continuously. The adaptive filter parameters are updated periodically based on detected motion patterns, and the system alternates between filtering modes based on detected activity states, reducing computational requirements while maintaining effectiveness.
2Measurement precision
If accelerometers and real-time FFT computations are used to reduce motion artifacts, then motion artifact reduction is improved, but battery drainage increases
Solution Approach 1:
The patent segments the motion artifact reduction process into multiple sequential filter stages, each processing specific frequency components. Instead of performing a complete FFT and processing all frequency components simultaneously, the system divides the spectrum into multiple bands and processes them sequentially through cascaded filters, reducing the computational burden and energy consumption while maintaining effective motion artifact reduction.
Solution Approach 2:
The patent applies partial action by selectively applying full FFT processing only when motion artifacts are detected, and using simplified filtering approaches during low-motion periods. The system performs partial processing on only the necessary frequency components rather than processing the entire spectrum continuously, reducing battery drainage while maintaining effectiveness when needed.
3Measurement precision
If multiple filter stages are applied sequentially, then motion artifact reduction is improved, but processing time increases
Solution Approach 1:
The patent segments the motion artifact reduction process into multiple sequential filter stages, each processing specific frequency components. By dividing the spectrum into multiple bands and processing them sequentially through cascaded filters, the system reduces the computational burden at each stage, allowing faster processing compared to a single comprehensive FFT approach.
Solution Approach 2:
The patent implements preliminary action by performing initial motion detection and pre-processing before applying the full multi-stage filtering. The system detects motion patterns first and prepares filter parameters in advance, so that when full filtering is needed, the processing can proceed more efficiently with pre-configured parameters and known motion characteristics.
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 solution effectively reduces motion-induced noise in PPG signals, improving heart-rate monitoring accuracy while reducing computational complexity and battery drainage.
Implementation Method 1
A source of light (typically a Light-Emitting-Diode (LED)) illuminates the skin and underlying tissue and a light-intensity sensor (typically a photo-diode) measures the amount of light either transmitted or reflected. The intensity of the transmitted or reflected light corresponds to the amount of blood volume.
Implementation Method 2
The processor includes an adaptive digital filter operated sequentially in a daisy-chain fashion. At each stage, the adaptive digital filter processes sensor signals to reduce motion artifacts from the PPG signal.
Data Source
AI summary
A photoplethysmogram system includes a plurality of sensors, each sensor capable of providing a sensor signal, and an adaptive filter capable of receiving a first input signal and computing an output. The photoplethysmogram system is capable of operating the filter in sequential stages, such that at each different stage the first input signal is a different sensor signal.