Co-linear LED Illumination for Schlieren Imaging
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Solution Overview
Problem
Existing imaging systems for wind tunnels and similar applications face challenges such as window reflections and shadow formation due to refractive index gradients, which affect the accuracy of density gradient measurements in schlieren and background-oriented schlieren techniques.
Innovation Solution
A compact imaging system utilizing a co-linear, high-intensity LED illumination unit with an optical beam splitter and diffusing lens, which minimizes shadows and reflections by directing light coaxially with the camera's optical axis, allowing for more accurate capture of density gradients and pressure variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a direct line-of-sight through the test section with a point illumination source is used, then schlieren imaging can be performed, but window reflections and shadow formation occur that reduce measurement accuracy
Solution Approach 1:
A beam splitter is introduced as an intermediary component between the light source and the test section. The beam splitter directs light through the test section at an angle and reflects it into the camera, eliminating the need for direct line-of-sight through windows and preventing reflections and shadows from interfering with measurements.
Solution Approach 2:
The illumination geometry is changed from a direct one-dimensional path through the test section to a two-dimensional angular path using the beam splitter. This dimensional change allows light to traverse the test section without requiring direct optical access through windows, thereby eliminating reflection and shadow artifacts.
2Measurement precision
If conventional schlieren techniques with point illumination sources are used, then density gradients can be visualized, but the system complexity increases due to requirements for high quality lenses or mirrors
Solution Approach 1:
The complex mechanical optical system requiring high-quality lenses and mirrors is replaced with a simpler system using a beam splitter and extended light source. This substitution maintains the ability to visualize density gradients while significantly reducing optical component requirements and system complexity.
Solution Approach 2:
Instead of using a point illumination source that requires complex optical elements, an extended light source is used that naturally provides the necessary illumination. The beam splitter creates the required light paths without needing additional lenses or mirrors, effectively copying the functional outcome with simpler components.
3Adaptability or versatility
If background-oriented schlieren techniques are used with arbitrary field-of-view scaling, then measurement flexibility increases, but sensitivity to window reflections and shadows increases
Solution Approach 1:
The beam splitter serves as a mediator that decouples the camera's line-of-sight from the light path through the test section. This allows the camera to be positioned at angles that avoid window reflections while maintaining arbitrary field-of-view scaling, as the beam splitter creates the necessary optical paths without requiring direct camera-to-test-section alignment through windows.
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 configuration enhances the accuracy of background-oriented schlieren and shadowgraph imaging by reducing window reflections and shadow effects, enabling precise 2D and 3D tomographic reconstructions of fluid dynamics in wind tunnels and other applications.
Implementation Method 1
The optical beam splitter is configured to direct light from the light source along the optical axis of the digital camera
Implementation Method 2
an optional diffusing lens that is configured to diffuse and concentrate light from the LED light source
Implementation Method 3
shadows projected onto the image plane, which may arise from refractive index gradients in the measurement region
Data Source
AI summary
One aspect of the present disclosure is an imaging system including an optical sensor defining an optical axis. The system further includes a light source. The system may include an optical beam splitter, and may also include an optional diffusing lens that may be configured to diffuse and/or collimate light from the light source and direct light exiting the diffusing lens to the optical beam splitter. The optical beam splitter is configured to direct light from the light source along the optical axis of the optical sensor.