Heterodyne Interferometry for Fluid Interface Deflection Measurement
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Solution Overview
Problem
Existing methods for determining deflections of a fluid interface between media with different refractive indices suffer from low spatial resolution and inability to measure dynamic processes effectively.
Innovation Solution
The method employs heterodyne interferometry, which involves producing a fringe pattern by interference of coherent beams, digitally recording the pattern, and using Fast Fourier Transform (FFT) and Discrete Cosine Transform (DCT) analyses to calculate a relative phase image, thereby resolving phase differences to a fraction of 2π and allowing for dynamic measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Michelson interferometer with phase scanning is used to measure interfacial deflections, then spatial resolution is improved, but dynamic measurements become inaccessible due to required particle immobilization
Solution Approach 1:
The patent replaces the mechanical phase-scanning system (piezo-driven moving mirrors) with a digital image processing system. The heterodyne interferometry produces time-dependent intensity variations that are captured by a camera, and the phase information is extracted through digital signal processing (FFT and phase unwrapping algorithms), eliminating the need for mechanical movement and particle immobilization.
Solution Approach 2:
The patent employs heterodyne interferometry where the object beam and reference beam have different frequencies, creating a time-periodic interference pattern with a beating frequency. This periodic modulation allows the phase information to be encoded in the time-dependent intensity variations, enabling dynamic measurements without mechanical scanning.
2Adaptability or versatility
If synthetic Schlieren method is used to measure interfacial dynamics, then dynamic measurement capability is improved, but spatial resolution deteriorates to micrometric level
Solution Approach 1:
The patent introduces an intermediary reference beam with a different frequency than the object beam. This reference beam mediates the measurement by creating heterodyne interference that encodes the phase information in the time-dependent intensity pattern, allowing both high spatial resolution and dynamic measurement capability.
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 provides high spatial resolution and dynamic range, enabling the measurement of fluid interface deflections and dynamics with unprecedented precision, surpassing the limitations of previous techniques.
Implementation Method 1
producing a fringe pattern by interference of two coherent beams, wherein the two beams are an object beam and a reference beam
Implementation Method 2
calculating a wrapped phase image by applying a Fast Fourier Transform (FFT) analysis, wherein the FFT analysis comprises filtering the recorded fringe pattern by transforming the recorded fringe pattern into frequency space
Implementation Method 3
unwrapping the wrapped phase image, particularly by applying a Discrete Cosine Transform (DCT) analysis, yielding a phase image
Data Source
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AI summary
Method for determining deflections of a fluid interface (1), the method comprising the following steps: a) producing a fringe pattern (2) by interference of two coherent beams, wherein the two beams are an object beam (3) and a reference beam (4), wherein, the object beam passes through the fluid interface or is reflected by the fluid interface before the two beams interfere, wherein the reference beam remains unaffected by the fluid interface; b) digitally recording the fringe pattern by an imaging system (5) focussing on the fluid interface; c) calculating a wrapped phase image (8) by applying a FFT analysis, with filtering the recorded fringe pattern by transforming the recorded fringe pattern into frequency space, selecting a frequency region (21) around a carrying frequency corresponding to a fringe period in the fringe pattern, and transforming the selected frequency region back into real space; d) unwrapping the wrapped phase image, yielding a phase image (9); e) subtracting from the phase image a reference phase image, yielding a relative phase image.