Interlocking Photodetector Areas for Motion Artifact Reduction
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Solution Overview
Problem
Optical sensors for physiological measurements, such as heart rate monitoring, face challenges due to motion artifacts caused by user movement, which corrupt the measurement signals and lead to inaccurate readings, especially in wearable devices like wrist straps where maintaining stability is difficult.
Innovation Solution
A detector arrangement featuring co-planar interlocking photodetector areas with an optical blocking filter, where one area detects all wavelengths and the other area is filtered to block specific wavelengths, allowing for signal subtraction to reduce noise and artifacts, and potentially using fractal space-filling curves or genetic algorithms to define the shapes of the photodetector areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single photodetector area is used for optical sensing, then the device structure is simple, but motion artifacts corrupt the measurement signal leading to inaccurate readings
Solution Approach 1:
The photodetector area is segmented into multiple sub-areas (first photodetector area, second photodetector area, third photodetector area) with different optical filtering characteristics. Each sub-area detects light in different wavelength ranges, allowing the system to separate motion artifact signals from physiological signals through differential measurement, thereby improving measurement accuracy while maintaining reasonable structural complexity
Solution Approach 2:
Different regions of the photodetector area are assigned different optical filtering properties. The first photodetector area has no optical blocking filter (detects all wavelengths), the second photodetector area has an optical blocking filter (blocks specific wavelengths), and the third photodetector area has a different optical blocking filter. This local differentiation enables selective detection of specific wavelength components to isolate physiological signals from motion artifacts
2Reliability
If the wrist strap is kept tight to stabilize the sensor, then motion artifacts are reduced, but blood circulation may be stopped or deteriorated causing the measurement signal to disappear
Solution Approach 1:
Multiple photodetector areas with different optical filtering characteristics serve as intermediaries to detect different components of the light signal. By comparing signals from these intermediate detection channels, the system can identify and compensate for motion artifacts without requiring excessive mechanical constraint on the wrist strap, thus maintaining both sensor stability and blood circulation
Solution Approach 2:
The system uses feedback from multiple photodetector areas to continuously monitor and differentiate between motion-induced signal changes and physiological signal changes. This feedback mechanism allows the sensor to maintain reliability through signal processing rather than mechanical constraint, avoiding blood circulation obstruction
3Measurement precision
If motion artifacts are completely avoided by stabilizing the sensor, then measurement accuracy improves, but user comfort deteriorates and blood circulation may be compromised
Solution Approach 1:
The system converts motion artifacts, which are harmful to measurement accuracy, into useful information. By using multiple photodetector areas with different optical filtering characteristics, the system can detect motion artifacts in specific wavelength ranges and use this information to compensate for their effects, thereby improving measurement accuracy without restricting user movement or comfort
Solution Approach 2:
The system changes the optical parameters (wavelength detection ranges) of different photodetector areas to detect the same physiological signal through different spectral pathways. This parameter differentiation allows the system to maintain measurement accuracy across varying motion conditions without compromising user comfort
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 arrangement improves the accuracy of physiological measurements by reducing noise and motion artifacts, enhancing the reliability of wearable optical sensors by ensuring comparable signal detection across different angles and light conditions, and enabling effective noise cancellation.
Implementation Method 1
an optical blocking filter configured to filter light incident on the second photodetector area
Implementation Method 2
a photodetector area comprising a first photodetector area and a second photodetector area
Data Source
Figure 1~3
Figure 4A~4C
Figure 5A~5C
AI summary
An apparatus with a photodetector area comprising a first photodetector area and a second photodetector area, the first and second photodetector areas having coplanar interlocking shapes, and an optical blocking filter configured to filter light incident on the second photodetector area.