Light Homogenizing Apparatus for Photoplethysmography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional photoplethysmographic devices face challenges in achieving homogeneous light distribution across a small aperture, leading to measurement errors due to varying optical paths and high light transmission losses, which affect signal accuracy and require increased input power, resulting in shorter device lifetimes and heat generation.
Innovation Solution
A light homogenizing apparatus comprising one or more light guides and a light mixing element with a diffuser followed by an internally reflective light guide, which disperses and reflects light to achieve a homogeneous mixture with high optical throughput, ensuring consistent light intensity across the output aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a diffuser is placed some distance from the LEDs to homogenize light, then light homogeneity is improved, but light transmission losses increase and device lifetime decreases
Solution Approach 1:
The patent introduces a light guide as an intermediary component between the LEDs and the diffuser. This light guide conducts light from the LEDs to the diffuser, allowing the diffuser to be positioned closer to the LEDs while still achieving effective light homogenization. The light guide mediates the light transmission process, reducing the distance light must travel through air and minimizing transmission losses while maintaining the homogenizing function of the diffuser.
Solution Approach 2:
The patent transitions from a simple linear arrangement of LEDs and diffuser to a three-dimensional light guide structure. The light guide extends the light path in multiple dimensions, allowing light to be distributed more efficiently across the diffuser surface. This dimensional change enables better light homogeneity to be achieved with shorter physical distances, reducing overall light transmission losses.
2Illumination intensity
If input power is increased to compensate for light losses, then light intensity is improved, but heat generation increases and device lifetime decreases
Solution Approach 1:
The light guide acts as an intermediary that efficiently transports light from the LEDs to the diffuser with minimal losses. By improving the efficiency of light transmission, the system maintains adequate light intensity at the tissue interface without requiring excessive input power, thereby reducing heat generation and extending device lifetime.
Solution Approach 2:
The patent changes the physical parameters of light transmission by introducing the light guide, which has optimized optical properties. This parameter change improves light coupling efficiency and reduces transmission losses, allowing the system to achieve the required light intensity with lower input power, thus reducing heat generation.
3Measurement precision
If LEDs are positioned closely together to minimize different optical paths, then measurement accuracy is improved, but light homogeneity at the aperture deteriorates
Solution Approach 1:
The patent segments the light transmission path by introducing a light guide that separates the LED positioning function from the light homogenization function. This segmentation allows LEDs to be positioned closely together for measurement accuracy while the light guide and diffuser work together to achieve uniform light distribution at the aperture, resolving the conflict between these two requirements.
Solution Approach 2:
The light guide serves as an intermediary that decouples the spatial relationship between LEDs from the light distribution pattern at the aperture. This intermediary component allows close LED positioning for accuracy while maintaining light homogeneity through its guiding and distributing function.
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
The solution provides accurate, high-resolution photoplethysmographic measurements with improved optical efficiency, reducing measurement errors and extending device lifetimes by minimizing light losses and heat generation.
Implementation Method 1
one or more light guides conducting light from at least one laser
Implementation Method 2
a diffuser followed by an internally reflective light guide
Implementation Method 3
an internally reflective light guide which disperses and reflects light to achieve a homogeneous mixture
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
An embodiment of a light homogenizing apparatus having one or more emitters (110, 120) incident on a light mixing element. The emitters including at least one laser light source. The light mixing element comprising a diffuser (130) followed by an internally reflective light guide (160). This apparatus substantially homogenizes light from all emitters (110, 120) before light exits light guide (160) where it could then be incident on living tissue for use in photoplethysmographic measurement. Other embodiments are described and shown.