Dual Self-Mixing Interferometry for Calibration-Free Rotation Sensing
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Solution Overview
Problem
Conventional self-mixing interferometry (SMI) devices face issues with dark speckle, which reduces signal amplitude, and require calibration to determine angular velocity accurately, leading to manufacturing difficulties and costs.
Innovation Solution
A dual SMI device using two electromagnetic radiation sources, such as vertical cavity surface emitting lasers, positioned at a known distance on a common die, allows for the determination of rotational movement by analyzing the frequency difference between their signals, eliminating the need for calibration and reducing speckle-related signal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser is used in conventional SMI devices, then the device structure is simple, but dark speckle reduces signal amplitude causing detection errors
Solution Approach 1:
The patent divides the single laser system into multiple laser sources (first and second electromagnetic radiation devices) positioned at different locations. Each laser independently illuminates the rotating target and generates its own SMI signal. By segmenting the measurement function across multiple sources, the system ensures that when one signal experiences dark speckle, another may still provide reliable detection, thus resolving the contradiction between structural simplicity and detection reliability.
Solution Approach 2:
The patent changes the spatial parameter by positioning multiple lasers at different locations (with a predetermined distance between them) and directs them to different regions on the rotating target. This parameter change in spatial distribution allows the system to overcome the amplitude reduction caused by dark speckle in any single location, maintaining reliable signal detection without significantly increasing overall device complexity.
2Measurement precision
If conventional SMI sensors are calibrated to determine angular velocity, then measurement accuracy is improved, but manufacturing difficulties and costs increase
Solution Approach 1:
The patent implements a self-calibrating system where the multiple lasers and their corresponding SMI signals work together to automatically determine the radius of rotation and calculate angular velocity without external calibration. The system uses the known distance between lasers and the relationship between their signals to self-determine measurement parameters, eliminating the need for manual calibration procedures and reducing manufacturing complexity while maintaining high measurement precision.
Solution Approach 2:
The patent employs feedback mechanisms where the processor analyzes the relationship between multiple SMI signals to continuously determine the radius of rotation and angular velocity. The system uses the feedback from multiple signal sources to self-correct and maintain accurate measurements without requiring external calibration, thus resolving the contradiction between measurement precision and ease of manufacture.
3Power
If fringe-counting method is used to determine rotational velocity, then computational demand is reduced, but dark speckle causing amplitude loss leads to counting errors
Solution Approach 1:
The patent segments the fringe-counting measurement function across multiple laser sources. Each laser independently provides fringe information, and the processor combines these segmented measurements. This segmentation ensures that when dark speckle affects one signal's amplitude, other signals still provide valid fringe information for counting, maintaining measurement precision while keeping computational requirements low through simple fringe counting rather than complex FFT analysis.
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 dual SMI device effectively determines rotational velocity and angular velocity without calibration, overcoming speckle-induced signal loss and manufacturing errors, thus improving accuracy and reducing complexity.
Implementation Method 1
the reflected electromagnetic radiation fD (or Doppler frequency) undergoes a Doppler shift that depends on the instantaneous rotational velocity of the portion of the rotating target
Implementation Method 2
Some of this Doppler shifted, reflected electromagnetic radiation fD is received at the source (e.g. in the laser cavity) and is coherently added to (e.g. modulates) newly generated electromagnetic radiation
Data Source
AI summary
A detection device includes a first electromagnetic radiation device, configured to emit first electromagnetic radiation at a first time period, receive a reflection of the first electromagnetic radiation emitted at the first time period from a target, and modulate first electromagnetic radiation emitted at a second time period by the received reflection of the first electromagnetic radiation; a second electromagnetic radiation device, configured to emit second electromagnetic radiation at the first time period, receive a reflection of the second electromagnetic radiation emitted at the first time period from the target, and modulate second electromagnetic radiation emitted at a second time period by the received reflection of the second electromagnetic radiation; and a processor, configured to determine a rotational movement of the target based on the modulated first electromagnetic radiation, the modulated second electromagnetic radiation, and a predetermined distance between the first electromagnetic radiation device and the second electromagnetic radiation device.