Optical Concentrator Pulse Sensor for Thin High-SNR Detection
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Solution Overview
Problem
Conventional pulse sensors have low efficiency and low ratio R, resulting in a weak signal-to-noise ratio due to limited light reaching the detector and insufficient modulation, while maintaining a thin form factor is necessary for applications like wristwatches.
Innovation Solution
Incorporation of an optical concentrator and/or decoupling body to guide and concentrate scattered light towards the detector, using materials with high refractive index and internal total reflection to enhance light collection and minimize losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance between the LEDs and the light detector is increased and/or partition walls are widened, then the ratio R increases, but the efficiency decreases
Solution Approach 1:
The patent introduces a microlens array that adds an optical focusing dimension to the light path. Instead of simply increasing the distance between LED and detector (one-dimensional solution), the microlens array refracts and focuses light rays in multiple dimensions, directing scattered light toward the detector while maintaining compact geometry. This resolves the contradiction by achieving both high ratio R and high efficiency through optical path manipulation rather than geometric expansion.
Solution Approach 2:
The patent changes the optical parameters of the system by introducing microlenses with specific focal lengths and refractive indices. By adjusting these optical parameters, the system can focus scattered light effectively without increasing the physical distance between components. This allows simultaneous achievement of high ratio R (through focused light paths) and high efficiency (through maintained component proximity).
2Loss of energy
If the distance between the LEDs and the light detector is reduced, then the efficiency increases, but the ratio R decreases
Solution Approach 1:
The microlens array acts as an optical intermediary between the LED and the light detector. It mediates the light path by collecting scattered light from the LED and redirecting it toward the detector. This intermediary component enables short distances (high efficiency) while maintaining high ratio R through optical focusing, as the microlens compensates for the reduced geometric path length.
Solution Approach 2:
The microlens array introduces curved optical surfaces that refract light rays in controlled paths. The spherical or aspherical geometry of the microlenses bends light trajectories to converge at the detector position, enabling effective light collection even at short distances. This curvature-based optical path control achieves high ratio R without requiring large component separations.
3Length of moving object
If the pulse sensor is made thinner, then the form factor improves, but the light path length decreases reducing modulation
Solution Approach 1:
The microlens array introduces an optical focusing dimension that compensates for the reduced physical thickness. By refracting and converging light paths through the microlens geometry, the system achieves sufficient modulation depth in a thin profile. The optical path length (determined by refraction angles and focal points) can be extended within the thin physical constraint, maintaining modulation quality while achieving thin form factor.
Solution Approach 2:
The patent changes the optical parameters (refractive index, focal length, lens diameter) of the microlens array to optimize performance for thin sensor design. By carefully selecting these parameters, the system achieves adequate light modulation within a reduced thickness while maintaining high detection efficiency through the microlens focusing effect.
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 significantly increases the efficiency and ratio R of light detection, allowing for a more accurate pulse measurement with a thin sensor design.
Implementation Method 1
using materials with high refractive index
Implementation Method 2
internal total reflection to enhance light collection
Data Source
AI summary
In an embodiment a pulse sensor includes at least one light source configured to emit light in a direction of a blood-perfused tissue of a living being, at least one light detector including a light-sensitive surface configured to sense at least one part of a light scattered by the blood-perfused tissue, wherein the scattered light is modulated depending on a pulse of the living being and an optical concentrator arranged in a light path of the scattered light between the tissue and the light-sensitive surface of the light detector, the optical concentrator configured to concentrate the scattered light, wherein the optical concentrator has a first entry surface, through which the scattered light is able to enter the optical concentrator, and a first exit surface, through which the concentrated scattered light is able to exit from the optical concentrator toward the light-sensitive surface, the first exist surface being parallel to the first entry surface, wherein the optical concentrator is transparent to the scattered light, wherein the first entry surface is larger than the first exit surface and is larger than the light-sensitive surface of the light detector, wherein the optical concentrator is in optical contact with the light detector via the first exit surface, and wherein a sectional surface of the optical concentrator, perpendicular to the first entry surface and the first exit surface, is shaped trapezoidal.