Self-Mixing Interferometry Sensor Module for Motion-Noise Separation
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Solution Overview
Problem
Wearable electronic devices face challenges in accurately measuring physiological parameters due to noise interference from unwanted body movements, such as respiratory motions and muscle contractions, which affect the accuracy of self-mixing interferometry sensors.
Innovation Solution
Employing two identical light emitters, such as VCSEL laser diodes, rigidly connected and separated by a specific distance, to generate a difference signal that reduces noise interference by treating signal and noise components differently, eliminating the need for additional motion sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light emitter is used for SMI measurement, then the device structure is simple, but the measurement precision deteriorates due to noise from body movements
Solution Approach 1:
The patent divides the single light emitter into two separate light emitters (first and second light emitters) that emit light at different angles to the skin surface. This segmentation allows the system to capture different signal components, where one emitter primarily captures physiological signals and the other captures motion artifacts, enabling subsequent noise cancellation through differential processing while maintaining relatively simple device structure
Solution Approach 2:
The patent introduces an intermediary processing mechanism that compares output signals from two light emitters and generates a difference signal. This intermediary step acts as a mediator to separate physiological signals from motion noise by exploiting the angular difference in light emission, thereby improving measurement precision without significantly complicating the overall system
2Measurement precision
If additional motion sensors are added to compensate for body movement noise, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent implements a self-service mechanism where the optical measurement system itself generates the reference signal needed for noise cancellation. By using two light emitters at different angles, one of which primarily captures motion artifacts, the system creates its own motion reference without needing external motion sensors, thereby maintaining measurement precision while avoiding additional hardware complexity
Solution Approach 2:
The patent makes the light emitter system multi-functional by having it serve both as the primary physiological signal source and as the motion artifact reference source. The same optical system performs dual functions: capturing blood flow signals and capturing motion noise, eliminating the need for separate motion sensing hardware and reducing overall device complexity
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 proposed solution significantly improves the signal-to-noise ratio, allowing for precise measurement of movements and physiological parameters like heart rate and blood flow without additional hardware, by effectively separating noise and signal components.
Implementation Method 1
self-mixing interference relates to light waves emitted from the laser being reflected back into a resonant cavity of a light emitter, such as a laser, by an external object and interfering with the light waves in the resonant cavity
Implementation Method 2
Each light emitter is operable to emit coherent electromagnetic radiation out of the sensor module
Implementation Method 3
The detector unit is operable to detect an optical power output or a junction voltage of the light emitters, respectively
Data Source
AI summary
A self-mixing interferometry sensor module includes at least two light emitters of the same type, a detector unit and an electronic processing unit. Each light emitter is operable to emit coherent electromagnetic radiation out of the sensor module and undergo self-mixing interference (SMI) caused by reflections of the emitted electromagnetic radiation from an external object outside the sensor module. The detector unit is operable to generate output signals indicative of the SMI of the light emitters, respectively. The electronic processing unit is operable to generate a difference signal from the output signals indicative of a movement of the external object.