Optical Heart Rate Sensor Motion Artifact Removal
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Solution Overview
Problem
Existing heart rate monitoring technologies in wearable devices face challenges with high power consumption and interference from user movements, leading to inaccurate bioinformation calculations.
Innovation Solution
An optical sensing apparatus with a processor that calculates heart rate values using a PPG signal, incorporating a motion sensor to eliminate interference and adjust calculation methods based on signal quality, allowing for both hardware and software calculations to optimize power usage and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If optical sensing apparatus is used for continuous heart rate monitoring, then heart rate information can be obtained continuously, but power consumption increases
Solution Approach 1:
The optical sensing apparatus performs heart rate measurements at periodic intervals rather than continuously, allowing the device to enter low-power states between measurements. The system activates the light source and photodetector only during measurement cycles, significantly reducing overall power consumption while maintaining continuous monitoring capability over extended periods
Solution Approach 2:
The measurement frequency and depth are dynamically adjusted based on activity level detection. During periods of low motion (detected by accelerometers or gyroscopes), the system reduces measurement frequency to conserve power. During high-activity periods, measurement frequency increases to capture accurate heart rate data, optimizing the balance between monitoring continuity and power consumption
2Measurement precision
If traditional heart rate calculation methods are used, then heart rate values can be obtained, but accuracy is reduced due to motion interference
Solution Approach 1:
The system separates motion artifact signals from the photoplethysmogram (PPG) signal by detecting motion using accelerometers or gyroscopes. The motion characteristics are extracted and used to identify and remove corresponding interference components from the PPG signal, leaving only the pure cardiac-related waveform for accurate heart rate calculation
Solution Approach 2:
Motion sensors serve as intermediary devices that detect user movement and provide correction data to the heart rate calculation algorithm. The motion information acts as a mediator that enables the system to compensate for motion-induced signal distortions, maintaining measurement accuracy during physical activity
3Speed
If hardware calculation is used for heart rate values, then calculation speed is improved, but device complexity increases
Solution Approach 1:
The heart rate calculation system is segmented into multiple processing stages: signal acquisition by photodetector, analog preprocessing (amplification, filtering), digital signal processing for PPG waveform extraction, motion artifact removal, and peak detection for heart rate determination. This segmentation allows critical time-sensitive operations to be performed in hardware while less time-critical operations use software processing
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 enables continuous, accurate heart rate monitoring with reduced power consumption, allowing the device to be used for extended periods without frequent charging and providing reliable bioinformation under various operating conditions.
Implementation Method 1
a first calculator in a processor and from a light receiver, a PPG signal
Data Source
AI summary
A method for obtaining a heart rate value by an optical sensing apparatus includes: receiving, by a first calculator in a processor and from a light receiver, a PPG signal; receiving, by a second calculator in the processor and from a motion sensor, a motion signal; determining, by the first calculator, a first heart rate value; determining, by the first calculator, a validity indicator according to the PPG signal; and determining, by the second calculator, a second heart rate value according to the PPG signal and the motion signal. When the validity indicator is determined to satisfy a predetermined requirement, the processor outputs the first heart rate value as the heart rate value. When the validity indicator is determined to not satisfy the predetermined requirement, the processor outputs the second heart rate value as the heart rate value.