Digital Fresnel Reflection Holography for Fluid Flow Resolution
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Solution Overview
Problem
Digital Inline Holography (DIH)-based Particle Image Velocimetry (PIV) techniques face limitations in longitudinal resolution and signal-to-noise ratio due to longitudinal elongation and signal truncation, as well as high particle concentration requirements, which hinder the analysis of complex near-wall turbulent flows.
Innovation Solution
The implementation of Digital Fresnel Reflection Holography (DFRH) systems, which capture backscattered light from particles within a sample using a reference wave reflected from an imaging window, allowing for higher particle concentration analysis and improved signal-to-noise ratio without the need for additional reference light sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If Digital Inline Holography (DIH) is used to capture forward scattered light, then the system is compact and low-cost, but longitudinal resolution deteriorates due to longitudinal elongation and signal truncation
Solution Approach 1:
The patent inverts the conventional DIH approach by capturing backscattered light instead of forward scattered light. This fundamental reversal allows the reference wave to be reflected from the imaging window while the object wave is backscattered from particles, eliminating the longitudinal elongation problem inherent in forward-scattering configurations and achieving superior longitudinal resolution without compromising system compactness.
Solution Approach 2:
The patent changes the scattering direction parameter from forward scattering to backscattering, and modifies the optical path by using a beam splitter to separate reference and object waves. This parameter change transforms the interference pattern characteristics, eliminating signal truncation and longitudinal elongation while maintaining the compact, single-camera architecture.
2Measurement precision
If particle concentration is increased to achieve high spatial resolution, then spatial resolution improves, but signal-to-noise ratio deteriorates due to cross interference and speckle patterns
Solution Approach 1:
By inverting the scattering geometry to capture backscattered light, the patent fundamentally changes the interference mechanism. The backscattered reference wave interferes with the backscattered object wave in a way that maintains high contrast even at high particle concentrations, eliminating the speckle pattern problem that plagues conventional DIH and allowing accurate particle tracking at shadow densities exceeding 100%.
3Use of energy by moving object
If forward scattering is used to lower laser power requirements, then energy consumption decreases, but longitudinal resolution deteriorates due to extended depth-of-focus
Solution Approach 1:
The patent inverts the scattering direction to backscattering, which naturally provides a tighter depth-of-focus due to the geometry of backscattered light collection. This inversion maintains low laser power requirements while simultaneously improving longitudinal resolution by reducing the extended depth-of-focus effect inherent in forward-scattering configurations.
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
DFRH achieves enhanced particle tracking efficiency and resolution, with peak extraction efficiency of 0.7 at high shadow densities, compared to DIH's 0.2, enabling more accurate 3D flow field measurements in complex fluid dynamics.
Implementation Method 1
The beam splitter is configured to direct the received incident light onto a sample via an imaging window and to direct reflected light to the camera for capture as two-dimensional holograms
Implementation Method 2
a single digital camera to capture interference between forward scattered light (from tracers) and the undiffracted portion of a beam as a hologram
Implementation Method 3
an objective lens, which focuses the reflected light and provides it to a camera for capture of a two-dimensional (2D) hologram
Implementation Method 4
The hologram is numerically reconstructed by convolving with a diffraction kernel (e.g., Raleigh Sommerfeld or Kirchhoff—Fresnel kernel) which simulates the propagation of light
Data Source
AI summary
Systems, devices, and methods are described herein for performing digital holography to analyze dynamics of fluid flow. According to some aspects of this disclosure, a Digital Fresnel Reflection Holography (DFRH) system, which is arranged to utilize light backscattered from particles in a fluid chamber to create a hologram that may be processed to analyze characteristics of fluid flow. The DFRH system may utilize light reflected from an imaging window disposed between a light source and a sampling volume, to be analyzed as a reference wave, to form an interference pattern and resultant hologram. According to some aspects of this disclosure, the DFRH techniques may provide simple, cost-effective mechanisms with improved performance over other techniques for analyzing fluid flow using holography.