PPG Sensor Antireflective Interface for Signal-to-Noise Ratio
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Solution Overview
Problem
Current photoplethysmography (PPG) sensors face challenges in achieving high signal-to-noise ratios and efficient light transmission due to the integration of a 'transparent layer interface' for shielding, leading to reduced performance and assembly tolerance issues, especially in reflective PPG sensors used for wrist-based blood pressure monitoring.
Innovation Solution
The PPG sensor incorporates an antireflective interface within a transparent interface element, enhancing light transmission to over 99% by minimizing reflection and maximizing transmittance, while maintaining shielding from the external environment through a flexible interfacing structure, allowing for improved assembly tolerances and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a transparent layer interface is integrated to shield the sensing portion from external environment, then shielding protection is improved, but light transmission is reduced leading to lower signal-to-noise ratio
Solution Approach 1:
The patent introduces an optical coupling medium with refractive index matching between the transparent layer interface and the skin tissue. This intermediary material reduces optical reflection at the interface, allowing the shielding function to be maintained while improving light transmission and signal-to-noise ratio by minimizing optical losses at the boundary between different media.
Solution Approach 2:
The patent modifies the optical parameters of the transparent layer interface by applying an antireflective coating with specific refractive index properties. This parameter change reduces the reflection coefficient at the interface, thereby improving light transmission efficiency and signal-to-noise ratio while preserving the shielding protection function.
2Object-affected harmful factors
If a transparent layer interface is integrated for shielding, then environmental protection is improved, but assembly tolerances become more difficult to achieve
Solution Approach 1:
The patent employs a flexible optical coupling medium that can accommodate variations in assembly tolerances. This flexible material maintains optimal optical contact between the transparent layer interface and the skin surface despite manufacturing variations, making the assembly process more tolerant to dimensional deviations while preserving environmental shielding.
3Measurement precision
If light transmission is maximized by removing the transparent layer interface, then signal-to-noise ratio is improved, but shielding from external environment is lost
Solution Approach 1:
The patent uses an optical coupling medium as an intermediary between the transparent layer interface and the skin tissue. This mediator enables high light transmission by matching refractive indices, achieving signal-to-noise ratio improvement while the transparent layer interface maintains its shielding function against environmental contaminants.
4Loss of energy
If antireflective interface is added to enhance light transmission, then transmittance is improved to over 99%, but device complexity increases
Solution Approach 1:
The patent achieves over 99% light transmittance by modifying the optical parameters of the transparent layer interface through an antireflective coating. This parameter change approach, while adding a layer, uses a simple conformal coating process that does not significantly increase device complexity or manufacturing difficulty.
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 results in a higher signal-to-noise ratio for PPG signals, enabling more accurate cardiovascular parameter monitoring with reduced power consumption and improved manufacturing feasibility, facilitating cuffless and beat-to-beat blood pressure monitoring.
Implementation Method 1
an optical emitter (101) configured to emit an emitted light (201) toward a tissue of the user's body (300)
Implementation Method 2
an optical detector (102) for detecting a detector light (202) reflected or scattered from the tissue
Implementation Method 3
The transparent interface element (104) comprises an antireflective interface (106) configured such that a ratio of the transmitted intensity (I2) on the emitted intensity (I1) of the emitted light (201) is larger than or equal to 99%
Implementation Method 4
through which the emitted light (201) is transmitted when travelling from the optical emitter (101) toward the tissue, and through which the detector light (202) is transmitted when travelling from the tissue to the optical detector (102)
Data Source
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AI summary
A photoplethysmography (PPG) sensor (100) configured to be worn on a user's body (300), the PPG sensor (100) comprising: a sensing portion (110) comprising an optical emitter (101) configured to emit an emitted light (201) toward the user's body (300), and an optical detector (102) for detecting a detector light (202) reflected or scattered from the tissue, such as to provide a PPG signal; and an interfacing portion (120) comprised between the sensing portion (110) and the user's body (300), the interfacing portion (120) comprising a transparent interface element (104)through which the emitted light (201) is transmitted when travelling from the optical emitter (101) toward the body (300), and through which the detector light (202) is transmitted when travelling from the body (300) to the optical detector (102), wherein the transparent interface element (104)has an interface transmittance (T1); the transparent interface element (104) comprising an antireflective interface (106) being configured such that an antireflective interface transmittance (T2) of the transparent interface element (104) comprising the antireflective interface (106) is larger than the interface transmittance (T1) by at least 4%.