PPG Sensor Light Arrival Angle Control at Detector
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Solution Overview
Problem
Wearable devices struggle to obtain high-quality photoplethysmographic (PPG) signals due to motion noise and non-pulsatile signal artifacts, as they are sensitive to light from all angles, making it difficult to determine optimal sensor placement for accurate heart rate and oxygen saturation monitoring.
Innovation Solution
The development of wearable devices equipped with a PPG sensor array that includes an illumination system and a detection system, featuring a viewing component configured to receive light at specific angles associated with high pulsatile signals, thereby optimizing perfusion index and reducing noise from non-pulsatile signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a typical PPG detector is used that is sensitive to light from all angles, then the device can detect light signals, but the signal quality deteriorates due to inclusion of non-pulsatile signal artifacts and motion noise
Solution Approach 1:
The detector is segmented into multiple photodetector elements, each associated with a specific viewing angle through a viewing component. This segmentation allows the system to separate and selectively detect light signals from different angles, enabling the exclusion of harmful non-pulsatile signals while preserving useful pulsatile signals.
Solution Approach 2:
Different portions of the detector are assigned different viewing angles through the viewing component structure. Each photodetector element has a specific local viewing angle that is optimized for detecting light from particular tissue layers, allowing the system to achieve high signal quality by selecting appropriate local viewing angles.
2Illumination intensity
If the detector is made sensitive to light from all angles to capture maximum light signal, then the light detection capability is improved, but the perfusion index measurement accuracy deteriorates
Solution Approach 1:
The detector is divided into multiple photodetector elements with different viewing angles. This segmentation allows the system to capture light signals from multiple angles simultaneously while being able to select and process only the signals from angles that provide accurate perfusion index measurements, thus maintaining both light detection capability and measurement accuracy.
Solution Approach 2:
The system adds the dimension of viewing angle to the traditional intensity-based detection. By incorporating angular information through the viewing component, the system can distinguish between light signals that provide useful physiological information versus those that provide spurious data, thereby maintaining measurement accuracy while preserving light detection capability.
3Measurement precision
If the sensor placement is optimized to find a monitoring site with high perfusion index, then the PPG signal quality is improved, but the device complexity increases due to the need for site evaluation and repositioning
Solution Approach 1:
The viewing component is pre-configured with multiple viewing angles that are optimized for detecting light from different tissue layers. This preliminary configuration eliminates the need for manual site evaluation and repositioning, as the device is already set up to capture signals from the optimal angles upon initial placement.
Solution Approach 2:
The device performs self-optimization by automatically selecting the best viewing angles through its multi-element photodetector array with different viewing angles. The system can identify and process signals from the optimal tissue layers without requiring user intervention for site evaluation or repositioning, thereby reducing operational complexity while maintaining high signal quality.
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 solution enables the acquisition of high-quality PPG signals by preferentially receiving light at angles with high perfusion index, improving the accuracy of heart rate and oxygen saturation measurements while minimizing noise from internal tissue motion and non-pulsatile artifacts.
Implementation Method 1
The illumination system may be configured to project light to a tissue layer within the body region, and the detection system may comprise a viewing component configured to receive light reflected from the tissue layer at a preset viewing angle
Implementation Method 2
Most soft tissue will transmit and reflect both visible and near-infrared radiation. Thus, if light is projected onto an area of skin and the reflected light detected after its interaction with the skin, blood, and other tissues, 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 (PPG) signal. The wearable devices and methods described herein are capable of obtaining PPG signals by employing a PPG sensor array configured to receive light at angles associated with a high perfusion index. Viewing components may be coupled to the PPG sensor array to effect transmission of light at these preferential angles.