PPG Sensor Curved Nozzle Arrangement for Wavelength Penetration
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Solution Overview
Problem
Existing photoplethysmography (PPG) sensors are limited in their ability to use wavelengths that are far apart on the electromagnetic spectrum, and they often require a long nozzle for ear-based applications, which can be uncomfortable and unsafe for users.
Innovation Solution
A PPG sensor design featuring an earbud nozzle with a curved surface, where the emitters and optical sensor are arranged to allow for the use of far-apart wavelengths and a shorter nozzle, ensuring more comfortable wear and similar trajectories for light penetration, enhancing the comparability of absorption readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If emitters and optical sensor are arranged in a linear fashion along the length of the nozzle, then the device can accommodate multiple components, but the nozzle becomes long and uncomfortable for users
Solution Approach 1:
The patent transitions from a one-dimensional linear arrangement of emitters and optical sensor along the nozzle length to a two-dimensional arrangement on the curved surface. The emitters are positioned at different angular locations around the circumference, allowing multiple components to be accommodated without increasing the nozzle's axial length, thus resolving the contradiction between component accommodation and user comfort.
2Measurement precision
If light of different wavelengths is used to measure specific analytes, then higher quantification resolution is achieved, but the trajectories of light through tissue become significantly different making readings incomparable
Solution Approach 1:
The patent positions different emitters at specific angular locations on the curved surface to create localized measurement zones. By arranging emitters and optical sensors at carefully selected angular positions, the light trajectories for different wavelengths are made to converge on similar tissue paths, ensuring that local tissue properties are sampled consistently across wavelengths while maintaining the ability to measure different analytes.
3Ease of operation
If the nozzle is made short for user comfort, then ease of operation is improved, but there is insufficient space to arrange multiple emitters and optical sensors
Solution Approach 1:
The patent utilizes the curved surface geometry to arrange components in a two-dimensional configuration rather than a one-dimensional linear layout. Multiple emitters and optical sensors are positioned at different angular locations around the circumference of the curved surface, maximizing space utilization and accommodating all necessary components within a compact, short nozzle length that ensures user comfort.
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 design enables the use of far-apart wavelengths for monitoring blood analytes, providing higher quantification resolution and comfort for users, while maintaining the ability to compare absorption readings meaningfully.
Implementation Method 1
The light is scattered by the tissue, such that some of the light reaches the optical sensor
Implementation Method 2
The wavelength of light emitted by one emitter can be absorbed by tissue components not including the target analyte. The wavelength of light emitted by the other emitter can be absorbed by tissue components including the target analyte.
Data Source
AI summary
A PPG sensor that comprises two emitters each emitting in a different wavelength and at least one optical sensor. The emitters are placed to emit through a body part of the user to the optical sensor in the same direction. However, the emitter of the shorter wavelength is placed further from the optical sensor, so as to force the emission to travel deeper into the tissue before reaching the optical sensor. This resolves the natural difference in penetration depths of the two wavelengths, especially if the two wavelengths are so far apart on the electromagnetic spectrum that their respective absorption mechanisms are different.