Self-Mixing Interferometry Laser for Liquid Property Measurement
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Solution Overview
Problem
Existing optical flow measurement systems using self-mixing interferometry have low sensitivity and are influenced by the chemical/physical properties of fluids, temperature variations, and conduit geometry, limiting their applicability to fluids with high scattering levels.
Innovation Solution
A method and apparatus utilizing a semiconductor laser source with multiple photodiodes positioned downstream and upstream of the laser cavity, along with a processing unit, to detect and process the self-mix signal, enhancing signal-to-noise ratio and allowing measurement of fluid properties like speed, flow rate, and particle characteristics independently of fluid properties and conduit geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-mixing interferometry is used to measure fluid flow, then the measurement can be performed non-invasively, but the sensitivity is low and strongly influenced by fluid scattering properties
Solution Approach 1:
The patent introduces an external reference cavity as an intermediary element that mediates between the laser source and the fluid measurement. By comparing the self-mixing signal from the reference cavity with the signal from the fluid-containing conduit, the system eliminates the dependency on fluid scattering properties while maintaining measurement sensitivity. The reference cavity serves as a stable benchmark that decouples the measurement sensitivity from the variable optical properties of different fluids.
2Measurement precision
If a monitor photodiode is placed at the laser cavity to detect self-mix signal, then the flow speed can be measured, but the measurement is affected by temperature variations and conduit geometry
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the self-mixing signal from an external reference cavity and using this information to compensate for environmental disturbances. The system compares the reference signal with the measurement signal and adjusts accordingly, providing real-time feedback that stabilizes the measurement against temperature variations and conduit geometry changes while maintaining accurate flow speed measurement.
3Measurement precision
If the laser beam angle relative to flow direction is optimized for Doppler shift, then flow measurement is possible, but the system complexity increases with multiple photodiodes and processing units
Solution Approach 1:
The patent combines multiple measurement functions into a single integrated optical path. By using an external reference cavity and detecting both self-mixing signals through a coordinated photodiode system, the invention merges reference measurement and fluid measurement into one unified setup. This approach maintains the necessary Doppler shift detection capability while reducing overall system complexity compared to separate reference and measurement systems.
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 improves measurement sensitivity and accuracy, enabling the characterization of a wide range of fluids, including those with low scattering, and provides real-time, non-invasive monitoring of fluid properties without being affected by temperature or conduit geometry, with reduced costs and complexity.
Implementation Method 1
inside the transparent conduit 5 the power of the laser light beam 30 is modulated due to the retro-reflection of the laser light beam 30 towards the laser cavity 32 caused by the suspended particles moving inside the liquid 7. This phenomenon is known as self-mixing interferometry.
Implementation Method 2
the retro-reflection of the laser light beam 30 towards the laser cavity 32 caused by the suspended particles moving inside the liquid 7
Implementation Method 3
detecting, through a first photodiode 9 arranged downstream of the transparent conduit 5, the power of the laser light beam 30 modulated due to said retro-reflection
Implementation Method 4
The measurement of the flowing speed of the fluid along the conduit is based on the Doppler shift caused by the diffusion ('scattering') due to the presence of moving particles inside the fluid.
Data Source
AI summary
A method and an apparatus for measuring the properties of a liquid that exploit the power modulation a laser light beam undergoes due to the retro-reflection of the laser light beam itself towards the laser cavity from which the laser is generated when this laser light is directed towards a transparent conduit through which the liquid for which the properties are to be measured flows, where this power modulation is detected by at least one photodiode arranged downstream of the transparent conduit.