Reflective PPG Photodetector Layout for Motion Artifact Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing photodetector apparatuses face challenges in reducing motion artifacts and improving sensor sensitivity, particularly in photoplethysmographic (PPG) sensors used for physiological measurements.
Innovation Solution
The apparatus incorporates a reflective element configured to direct incident light to a focus point, with a predefined angle of incidence, and a photodetector positioned to receive this light, optionally with a collimating element to collimate the light before detection, enhancing light collection and reducing sensitivity to ambient light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional photodetector apparatus is used without a reflective element, then the device complexity is low, but the light detection sensitivity is insufficient
Solution Approach 1:
The reflective element employs a curved (concave) surface geometry to focus incident light onto the photodetector. This curvature enables efficient light collection from multiple directions and concentrates the light at the focal point, thereby enhancing detection sensitivity without requiring complex multi-component optical systems
Solution Approach 2:
The reflective element is positioned in a spaced relationship from both the light source and photodetector, creating a three-dimensional optical path. This spatial arrangement allows the reflective element to collect light from a broader angular range and direct it to the photodetector, improving sensitivity while maintaining a relatively simple device structure
2Measurement precision
If the reflective element is positioned close to the focus point and light source, then the device size is reduced, but the ability to collect light from multiple directions is compromised
Solution Approach 1:
The concave curved surface of the reflective element is specifically designed to focus light from multiple incident angles onto a single focal point. This geometric configuration maximizes light collection efficiency while maintaining a compact form factor, as the curvature naturally concentrates divergent light rays without requiring a large physical footprint
Solution Approach 2:
The reflective element is positioned at an optimized distance from the focus point and light source, creating a specific spaced relationship. This parameter optimization balances the trade-off between device volume and light collection efficiency, allowing sufficient angular coverage while maintaining a compact overall device size
3Measurement precision
If ambient light is not filtered, then the device complexity is low, but measurement accuracy is reduced due to unwanted wavelengths
Solution Approach 1:
The reflective element is configured with specific optical properties (reflectivity for certain wavelengths, absorption for others) to selectively direct desired light wavelengths to the photodetector while filtering out unwanted ambient light. This local optical filtering enhances measurement accuracy without requiring additional complex filtering components
Solution Approach 2:
The reflective element's geometry and optical properties are designed to naturally reject ambient light from certain directions and wavelengths, converting the potential harm of ambient light interference into a beneficial selective light collection mechanism that improves signal-to-noise ratio
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 configuration increases light detection sensitivity and reduces motion artifacts, allowing for more accurate physiological measurements, such as heart rate and respiration, by collecting light from multiple directions and filtering out unwanted wavelengths.
Implementation Method 1
a reflective element configured to direct at least part of the received incident light to a focus point
Implementation Method 2
a photodetector configured to receive light from the focus point
Implementation Method 3
a collimating element configured to collimate the light directed to the focus point prior to the photodetector receiving the light
Data Source
AI summary
An apparatus, such as a photoplethysmographic sensor, including a light source configured to illuminate a target, wherein the apparatus is configured to receive incident light reflected from or transmitted through the target. The apparatus includes also a reflective element configured to direct at least part of the received incident light to a focus point, and a photodetector configured to receive light from the focus point.