BOS Setup Generator

'BOS setup generator' is an app specifically developed to quickly define the optimum setup for background oriented schliern measurements.

App overview

BOS Setup Generator is an app developed to perform (and speed up) the setup design process of a Background Oriented Schlieren experiment.

The app allows to control all the typical parameters of a BOS entocentric setup, providing the necessary tools to find the best trade-off between system resolution and system sensitivity. It is organized in two configurations, 'Computational configuration' and 'Comparison configuration', which can be easily activated through the 'Comparison switch' placed in the 'Resolution section'.

• The 'Computation configuration' allows to compute, given certain inputs entered in the section 'BOS setup characteristics', the setup performance. The performance are evaluated in terms of system sensitivity, resolution and effective FOV which and are shown to the user through plots and numerical output in the sections 'Resolution' and 'Setup characteristics'.
• The 'Comparison configuration' allows to compare, in terms of sensitivity, resolution and effective FOV, different setups (with a maximum of 3) previously computed and saved.

The app offers many ways to save, extract and load different session, data and plots. Those functions are available on the 'Menu' tab and a detailed explanation of these features is available in the attached manual ('BOS Setup Generator MANUAL.pdf').

Theoretical Model

Setup sensitivity

The sensitivity equation defining the expected displacement is defined as:

where:

• is the displacement,
• G is the Gladstone-Dale constant,
• is the distance between the background and the density gradient plane,
• M is the entocentric system magnification defined by in which is the size of the camera sensor and is the FOV size
• is the thickness of the density gradient region,
• is the pixel size,
• is the density gradient.

Setup resolution

The optical resolution () is modelled by the equation:

where:

• δ is the uncertainty region size on the camera sensor and is defined by in which is the diameter of the Airy disk produced by diffraction,
• is the objective lens distance from the background and is defined by in which f is the focal length.

The image processing resolution is defined as half of the size of the interrogation window (IW) projection on the background. In symbols:

This definition is made considering an image processing algorithm set with a 50 % overlap between interrogation windows. In case of different settings, it is recommended to adjust (considering the above equation) the value of the IW to obtain the real image processing resolution.

References

In this app it is used the function copyUIAxes available in the MathWorks File Exchange link:

• Adam Danz (2022). copyUIAxes (https://www.mathworks.com/matlabcentral/fileexchange/73103-copyuiaxes), MATLAB Central File Exchange. Retrieved January 24, 2022.

A more detailed description of the theoretical model and a possible use of the app will be provided in a future publication. As soon as it will be published the reference link will be updated here.