Optical Heart Rate Motion Compensation via Frequency Segmentation
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Solution Overview
Problem
Optical heart rate sensors in wearable devices face challenges in accurately reporting heart rate due to motion artifacts, particularly when motion frequency is similar to heart rate frequency, leading to inaccurate readings and noise in the signal.
Innovation Solution
A method that filters motion frequency from the optical heart rate signal and determines an estimated heart rate frequency, using a local neighbor magnitude ratio to decide whether to report the heart rate based on the estimated frequency or the motion frequency, ensuring accurate reporting with constant motion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motion compensation is applied to filter motion frequency from the optical signal, then measurement precision of heart rate is improved, but when motion frequency is similar to heart rate frequency, the motion compensation may remove the heart rate signal along with motion artifacts
Solution Approach 1:
The patent applies adaptive motion compensation that dynamically adjusts the filtering strength based on the detected motion frequency and its proximity to the heart rate frequency. When motion frequency is similar to heart rate frequency, the system reduces or disables motion compensation to prevent removing the heart rate signal, while applying stronger compensation when frequencies are well-separated. This dynamic adjustment resolves the contradiction by making the compensation level contingent on real-time frequency analysis.
Solution Approach 2:
The system uses feedback from frequency analysis of the optical signal to control the motion compensation process. By continuously analyzing the spectral content and detecting peaks corresponding to motion and heart rate frequencies, the system adjusts the compensation parameters in real-time. This feedback mechanism ensures that motion compensation is applied only when it will not remove the heart rate signal, thus maintaining measurement precision while ensuring reliability.
2Reliability
If adaptive motion compensation is used to avoid removing heart rate signal, then reliability is improved, but inaccurate heart rates may be reported when motion frequency approaches heart rate frequency
Solution Approach 1:
The system dynamically switches between different heart rate determination strategies based on the frequency proximity between motion and heart rate signals. When frequencies are close, the system uses adaptive motion compensation with reduced filtering strength to maintain signal integrity. When frequencies are well-separated, the system applies stronger motion compensation for higher precision. This dynamic strategy selection resolves the contradiction by optimizing for reliability when frequencies overlap and for precision when they don't.
Solution Approach 2:
The patent changes the filtering parameters of the motion compensation algorithm based on the detected frequency proximity. By adjusting parameters such as filter strength, frequency range, and compensation intensity according to the relative positions of motion and heart rate frequencies, the system achieves both reliability and precision at different operating conditions. This parameter adaptation allows the system to report accurate heart rates regardless of motion frequency proximity.
3Object-generated harmful factors
If motion frequency is filtered from the optical signal, then noise is reduced, but when motion frequency overlaps with heart rate frequency, the heart rate signal is also removed
Solution Approach 1:
The patent segments the frequency spectrum into distinct regions for motion artifacts and heart rate signals by detecting and identifying separate frequency peaks through spectral analysis. When motion and heart rate frequencies are well-separated, the system applies targeted filtering to remove only the motion frequency components while preserving the heart rate signal. This segmentation approach allows effective noise reduction without removing the heart rate signal, as the filtering is precisely targeted to the identified motion frequency region.
Solution Approach 2:
The system uses frequency domain analysis as an intermediary to distinguish between motion artifacts and heart rate signals before applying motion compensation. By transforming the time-domain optical signal into the frequency domain and identifying spectral peaks, the system creates a frequency-based mediator that guides the compensation process. This intermediary analysis ensures that filtering is applied only to motion frequency components and not to the heart rate signal, even when frequencies are close, thus reducing noise while preserving measurement 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 accurate heart rate reporting by distinguishing between motion and heart rate frequencies, reducing noise and inaccuracies, and maintaining consistent motion compensation, even in scenarios where frequencies overlap.
Implementation Method 1
An optical heart rate sensor may be incorporated into a wearable device
Implementation Method 2
receiving a motion frequency from a motion sensor
Data Source
AI summary
A method of optical heart rate sensing includes receiving a motion frequency from a motion sensor and receiving an optical signal from an optical sensor. The motion frequency is then filtered from the optical signal, and an estimated heart rate frequency is determined based on the filtered optical signal. A heart rate is reported that is based on the motion frequency, but not based on the estimated heart rate frequency, when a local neighbor magnitude ratio of the estimated heart rate frequency is below a confidence threshold.