Lateral Resonant Doppler OCT for Flow Velocity Measurement
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Solution Overview
Problem
Existing methods for determining characteristics of flowing fluids using optical coherence tomography (OCT) are limited by phase wrapping, interferometric fringe washout, and increased uncertainty in diffusion coefficient estimation at higher flow speeds.
Innovation Solution
The method involves using Fourier domain optical coherence tomography (FD-OCT) to estimate the local velocity of a flowing fluid and control an optical scanner to move the OCT beam in synchronization with the fluid flow, thereby increasing the measurable velocity range and reducing decorrelation due to flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-resolved Doppler OCT is used for flow velocity measurement, then axial velocity can be detected, but the measurement is limited by phase wrapping due to large axial motion
Solution Approach 1:
Instead of measuring axial velocity directly with phase-resolved Doppler OCT which suffers from phase wrapping, the invention measures transverse velocity components using lateral resonant Doppler OCT. By inverting the measurement approach from axial to transverse direction, the system avoids the phase wrapping problem while still obtaining flow velocity information through the relationship between transverse and axial velocity components in laminar flow.
Solution Approach 2:
The invention changes the measurement parameter from axial phase shift to transverse frequency shift. By using lateral resonant Doppler OCT that measures transverse velocity at resonant frequencies, the system transforms the measurement into a domain where phase wrapping does not occur, thereby expanding the measurable velocity range.
2Measurement precision
If correlation-based measurements are used, then velocity range depends on maximum decorrelation rate, but axial velocity is limited by interferometric fringe washout
Solution Approach 1:
The invention avoids correlation-based measurements that are limited by fringe washout by instead using lateral resonant Doppler OCT. This approach measures transverse velocity directly through frequency domain analysis at resonant frequencies, inverting the measurement strategy to bypass the interferometric fringe washout limitation that constrains axial velocity measurement in correlation-based methods.
3Measurement precision
If DLS-OCT is used to measure particle diffusion, then diffusion coefficient can be estimated, but uncertainty rapidly increases with increasing flow speeds
Solution Approach 1:
The invention extracts transverse velocity information separately using lateral resonant Doppler OCT, then uses this extracted information to correct or account for flow effects in the diffusion measurement. By separating the flow measurement function from the diffusion measurement function, the system can maintain accurate diffusion coefficient estimation even at higher flow speeds by compensating for the extracted flow velocity.
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
This approach significantly enhances the maximum measurable velocity range and allows for more accurate determination of diffusion coefficients and particle sizes, even at higher flow speeds, compared to standard Doppler OCT and DLS-OCT methods.
Implementation Method 1
sense a signal of interference of light scattered back along the optical path mixed with reference reflected light
Implementation Method 2
light scattered back along the optical path
Implementation Method 3
phase-resolved Doppler OCT... Utilizing Doppler phase changed relation in a complex interference signal caused by moving samples
Implementation Method 4
obtain simultaneous depth-resolved information about diffusive and translational motion of particles. This information may be extracted from the temporal autocorrelation of the OCT signal
Data Source
AI summary
A method for determining a characteristic of a flowing fluid having particles in a sample space by Fourier domain optical coherence tomography includes estimating a velocity of the fluid in the sample space; controlling an optical scanner to radiate a beam of light along an optical path to the fluid in the sample space and to sense a signal of interference of measurement light scattered back along the optical path mixed with reference reflected light, while moving the optical scanner, where the beam of light is moved with a scanner velocity being aligned with a velocity component of the velocity of the fluid perpendicular to the optical axis of the beam of light, processing the signal into a corresponding complex-valued optical path length resolved OCT signal, where the OCT signal represents the fluid in the sample space; determining the characteristic of the fluid based on the OCT signal.