PPG Sensor Layout Using Reflective and Transmissive Light Paths
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Solution Overview
Problem
Existing PPG sensors face challenges in achieving high signal-to-noise ratio (SNR) when measuring thin tissues due to limited modulation depth, particularly in transmission-based sensors, and size constraints in reflection-based sensors.
Innovation Solution
A PPG sensor system that combines transmissive and reflective ray paths by positioning the optical source and detector on one side of the tissue and using a reflector on the opposite side to reflect transmitted light back towards the detector, allowing for enhanced detection of both ray paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmission-based sensors are used to measure thin tissues, then the full thickness of tissue can be measured, but the modulation depth is limited and signal-to-noise ratio is degraded
Solution Approach 1:
The patent combines transmission-based and reflection-based measurement modes into a single sensor system. The optical detector is positioned to receive optical radiation via both transmission path (through the full thickness of tissue) and reflection path (from the reflector on the opposite side), thereby merging the advantages of both modes to achieve high modulation depth and signal-to-noise ratio in thin tissue measurements
Solution Approach 2:
The patent introduces a spatial dimension by positioning the reflector on the opposite side of the tissue from the optical source and detector. This creates an additional optical path dimension where light can travel through the tissue, reflect off the reflector, and return to the detector, effectively doubling the tissue interaction path length and enhancing the measurement signal
2Measurement precision
If reflection-based sensors increase separation between light source and light detector, then modulation depth can be achieved, but the device size is constrained
Solution Approach 1:
The patent merges transmission and reflection measurement modes in a compact configuration. The optical detector receives light through both the transmission path (directly through tissue) and reflection path (via the reflector on the opposite side), allowing high modulation depth to be achieved without requiring large separation distances between source and detector, thus maintaining small device size
Solution Approach 2:
The patent uses the reflector to create an additional optical path dimension, allowing the light to effectively travel through the tissue twice (forward and reflected back), thereby achieving high modulation depth equivalent to larger source-detector separations while maintaining a compact sensor geometry
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 the signal level and SNR, enabling more accurate monitoring and assessment of oxygen saturation in thin tissues by leveraging both reflective and transmissive ray paths.
Implementation Method 1
a reflector coupled to the support structure and configured to reflect optical radiation incident on the reflector
Implementation Method 2
optical radiation emitted by the optical source arrangement is received at the optical detector arrangement via both transmissive and reflective ray paths through the bodily tissue
Implementation Method 3
an optical detector arrangement configured to detect optical radiation incident on the optical detector arrangement
Data Source
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AI summary
Proposed concepts thus aim to provide schemes, solutions, concepts, designs, methods, and systems pertaining to a PPG sensor system comprising an optical source arrangement, a reflector, and an optical detector arrangement for measuring oxygen saturation of blood within bodily tissue. In particular, embodiments aim to provide a PPG sensor system configured such that optical radiation emitted by the optical source arrangement is received at the optical detector arrangement via both transmissive and reflective ray paths through bodily tissue.