Spatial Light Modulator PPG Sensor for Signal Noise Reduction
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Solution Overview
Problem
Conventional PPG sensors face challenges in achieving a high signal-to-noise ratio due to inefficient light irradiation on blood vessels, motion artifacts, and environmental changes, particularly when used as wearable devices, leading to poor signal quality and noise interference.
Innovation Solution
The integration of a spatial light modulator (SLM) in PPG sensors, which actively modulates light amplitude and phase to improve light irradiation efficiency and adapt to moving blood vessels, reducing noise and enhancing signal quality by controlling light output through a two-dimensional array of pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional simple irradiation-type PPG sensor directly irradiates the user's skin with light, then the light emission is simple and the device structure is simple, but only about 10% of light reaches the blood vessel and the signal-to-noise ratio is low
Solution Approach 1:
The patent employs a spatial light modulator (SLM) that dynamically adjusts light irradiation patterns in real-time. The SLM can change the spatial distribution of light to continuously track and focus on moving blood vessels, adapting to physiological changes and motion artifacts. This dynamic adjustment capability enables the system to maintain high signal-to-noise ratio even when blood vessel positions change due to heartbeat or body movement.
Solution Approach 2:
The SLM applies local quality enhancement by concentrating light energy precisely on the blood vessel region while leaving other areas unaffected. Instead of uniform irradiation, the system creates a focused light pattern that matches the spatial distribution of the target blood vessel, thereby maximizing the proportion of useful light (10% or more) that reaches the blood vessel and minimizing noise from surrounding tissues.
2Adaptability or versatility
If a PPG sensor employs a lens or waveguide to focus light on a desired portion, then light focusing capability is improved, but the sensor becomes vulnerable to artifacts due to motion of the body and cannot respond to changes in sensor or blood vessel position
Solution Approach 1:
The SLM provides dynamic adaptability by continuously adjusting light irradiation patterns in response to detected blood vessel positions. When motion causes the blood vessel to move or the sensor to shift, the SLM recalculates and updates the light focusing pattern in real-time, ensuring the light always reaches the correct location. This dynamic response eliminates motion artifacts that plague static lens-based systems.
Solution Approach 2:
The system implements a feedback mechanism where the detected blood vessel position information is fed back to the SLM control algorithm. The SLM then adjusts its light modulation pattern based on this feedback, creating a closed-loop control system that automatically compensates for positional changes. This feedback-driven adaptation ensures reliable operation even during body movement or improper wearable device fitting.
3Ease of operation
If the PPG sensor is not completely in contact with the skin, then wearability is improved and comfort is enhanced, but background noise due to reflection or external light source increases and signal-to-noise ratio is reduced
Solution Approach 1:
The SLM compensates for incomplete skin contact by creating a highly focused local light pattern that concentrates energy precisely on the blood vessel region. Even when the sensor is not fully pressed against the skin, the localized light focusing ensures that sufficient light reaches the target blood vessel while minimizing stray light and background noise from reflection or external sources. This local concentration approach maintains measurement precision regardless of contact pressure.
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 SLM enhances the signal-to-noise ratio and allows for accurate biometric information detection, particularly in wearable devices, by effectively focusing light on blood vessels and minimizing noise interference, even under varying environmental conditions.
Implementation Method 1
The SLM may have a two-dimensional array and may actively modulate the property of light when an electrical signal is applied. For example, the SLM may modulate an amplitude and/or phase of light output from the light-emitting device by an electrical signal to adjust the direction of the light
Implementation Method 2
photoplethysmography (PPG), among such biometric information detection techniques, is an optical technique that can be used to measure volumetric changes in the body. In photoplethysmography, the skin may be irradiated with light emitted from a light source so that a difference in light absorption due to a change in the volume of a blood vessel in the skin is expressed in the form of the intensity of reflected or transmitted light
Data Source
AI summary
According to various embodiments, an electronic device may comprise: a housing comprising an inner space; a sensor structure positioned in the housing and exposed through a part of the housing, the sensor structure comprising a substantially transparent plate comprising a first surface facing away from the inner space and a second surface facing away from the first surface; a support structure positioned in the inner space so as to face the transparent plate; at least one light-emitting element mounted on the support structure while being spaced apart from the second surface and inserted between the second surface and the support structure; a spatial light modulator (SLM) disposed between the transparent plate and the LED while being spaced apart from the light-emitting element; a light-receiving element mounted on the support structure and positioned between the second surface and the support structure while being adjacent to a side surface of the light-emitting element; and a processing circuit comprising at least one electrical path electrically connected to the SLM, the processing circuit being operatively connected to the light-receiving element and configured to generate photoplethysmogram (PPG) data by using the light-emitting element. Other embodiments are possible.