Background-Oriented Schlieren Imaging Without Separate Reference Frames

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Solution Overview

Problem

Existing background-oriented schlieren systems require expensive retroreflective materials and time-consuming setup adjustments, are sensitive to vibrations, and need separate reference measurements, limiting their flexibility and efficiency.

Innovation Solution

A real-time reference-free background oriented schlieren system using a display device to project an image pattern onto a retroreflective background, with a beam splitter to transmit and reflect image portions to reference and signal imaging sensors, allowing on-the-fly pattern adjustments and eliminating the need for separate reference measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If retroreflective material with pre-applied speckle pattern is used, then the background provides stable reflection, but the setup time increases and pattern changes require replacing entire sheets

Engineering Contradiction:

Improvereflection stabilityVSAvoidsetup time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The speckle pattern is separated from the retroreflective material by projecting it dynamically through a display device, allowing independent control of pattern and reflection properties without requiring permanent attachment of pattern to material

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The speckle pattern is made dynamic through projection onto the retroreflective material, enabling real-time changes to pattern size and density without physical replacement of the retroreflective sheet itself

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If laser speckle projection is used, then pattern changes are possible without replacing material, but the system becomes sensitive to vibrations and requires laser safety permits

Engineering Contradiction:

Improvepattern adjustabilityVSAvoidvibration sensitivity

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces expensive, vibration-sensitive laser systems with a more robust display device that projects the speckle pattern, eliminating vibration sensitivity while maintaining pattern adjustability capabilities

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The display device allows dynamic adjustment of speckle pattern parameters including size and density through software control, providing versatility without the physical constraints or safety issues of laser systems

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If reference images are captured separately, then accurate density measurements are achieved, but the measurement process time increases

Engineering Contradiction:

Improvedensity measurement accuracyVSAvoidmeasurement speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent combines reference image capture and test image capture into a single simultaneous imaging operation, where the display device projects the speckle pattern and both reference and test images are captured in real-time, eliminating sequential processing delays

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The system maintains continuous real-time imaging where reference and test images are continuously captured simultaneously, enabling ongoing density measurements without interruption or sequential processing gaps

Inventive Principle:

Principle #20Continuity of useful action

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

Reduces setup and adjustment time, eliminates the need for expensive retroreflective materials, and enables rapid switching between schlieren and shadowgraph imaging techniques, enhancing system flexibility and efficiency.

Implementation Method 1

The retroreflective background may be configured to reflect the projected image pattern back through the beam splitter and onto a signal imaging sensor

Methodology Applied

Scientific EffectRetroreflection: Retroreflector

Implementation Method 2

A beam splitter may be used to transmit a portion of the projected image pattern towards a reference image sensor and another portion of the image pattern towards the retroreflective background

Methodology Applied

Scientific EffectLight reflection and transmission: Reflection

Data Source

PatentUS12590891B2Real-time, reference-free background oriented schlieren imaging system

Publication Date: 2026.03.31 UNITED STATES OF AMERICA AS REPRESENTED BY THE ADMINISTRATOR NAT AERONAUTICS & SPACE ADMINISTRATION

AI summary

A real-time reference free background oriented schlieren system is provided. One embodiment includes a display device capable of generating an image pattern projected onto a retroreflective background. A beam splitter is used to transmit a portion of the projected image pattern towards a reference image sensor and another portion of the image pattern towards the retroreflective background and past a density object. The retroreflective background reflects the projected pattern back through the beam splitter and onto a signal imaging sensor. Collected data from the reference image sensor and the signal image sensor may be processed in real-time. The image pattern may be altered as necessary without requiring a new reference image, reducing the amount of time required to set up and adjust the system. A display device may be capable of switching between a schlieren visualization capability to a shadowgraph system allowing for the use of two different imaging techniques.