PPG Multi-Light Path Layout for Signal Strength and Perfusion Index
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Solution Overview
Problem
Existing PPG systems face a trade-off between signal strength and perfusion index, with separation distance affecting both, and are aesthetically unappealing due to visible components.
Innovation Solution
A multiple light paths architecture with varying emitter-to-detector separation distances and optical configurations for noise cancellation, including lenses and reflectors to obscure components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the separation distance between light emitter and light detector is increased, then perfusion index is improved, but PPG signal strength deteriorates
Solution Approach 1:
The patent divides the single light path into multiple light paths with different separation distances. By segmenting the measurement into multiple paths (e.g., first light path with shorter distance for signal strength, second light path with longer distance for perfusion index), the system can simultaneously capture both high PPG signal strength and high perfusion index measurements that would otherwise be mutually exclusive in a single-path configuration.
2Measurement precision
If multiple light emitters and light detectors are added to the PPG system, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the light emitter and light detector serve multiple functions by configuring them to generate and detect multiple light paths simultaneously. The same light emitter can illuminate through different tissue depths, and the same light detector can receive light from multiple paths, eliminating the need for separate dedicated components for each measurement function and reducing overall device complexity.
3Ease of operation
If light emitters and light sensors are made visible to the user, then optical alignment is simplified, but aesthetic appearance deteriorates
Solution Approach 1:
The patent introduces an optical element (such as a lens or reflector) as an intermediary component positioned between the light emitter and the user's view. This optical element redirects or focuses the light path while remaining substantially invisible to the user, allowing proper optical alignment and functionality to be achieved without compromising the aesthetic appearance of the wearable device.
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
Optimizes PPG signal strength and perfusion index for diverse user conditions while enhancing aesthetics by minimizing visible components.
Implementation Method 1
a light source or light emitter that injects light into the user's tissue and a light detector to receive light that reflects and/or scatters and exits the tissue
Implementation Method 2
The PPG device can further include one or more lenses and/or reflectors to increase the signal strength
Implementation Method 3
The PPG device can further include one or more lenses and/or reflectors to increase the signal strength and/or and to obscure the light emitters, light sensors, and associated wiring from being visible to a user's eye
Data Source
Figure 1A~1C
Figure 2~3A
Figure 3B~3C
AI summary
A photoplethysmographic (PPG) device is disclosed. The PPG device can include one or more light emitters and one or more light sensors to generate the multiple light paths for measuring a PPG signal and perfusion indices of a user. The multiple light paths between each pair of light emitters and light detectors can include different separation distances to generate both an accurate PPG signal and a perfusion index value to accommodate a variety of users and usage conditions. In some examples, the multiple light paths can include the same separation distances for noise cancellation due to artifacts resulting from, for example, tilt and/or pull of the device, a user's hair, a user's skin pigmentation, and/or motion. The PPG device can further include one or more lenses and/or reflectors to increase the signal strength and/or and to obscure the optical components and associated wiring from being visible to a user's eye.