Seeing the invisible with schlieren imaging

Abstract

Schlieren imaging is a method for visualizing differences in refractive index as caused by pressure or temperature non-uniformities within a medium, or as caused by the mixing of two fluids. It is an inexpensive yet powerful and straightforward tool for sensitive and high-resolution visualization of otherwise invisible phenomena. In this article, application of the method to liquid membranes, sonar pulses and microscopic gas flows is used to illustrate its usefulness and versatility in physics education and research.

Schlieren imaging of microthruster exhausts for qualitative and quantitative analysis

“…Its use is by no means limited to microthruster exhausts. Due to its capability of resolving differences in refractive index, it can be used for the study of mixing chemicals, temperature changes, pressure waves, homogeneity within materials, etc [14]. As long as the medium is transparent, and the setup is properly adjusted to resolve the differences in refractive index, the magnification is easily adapted for resolution down to micrometres, making it a suitable tool for microfluidics.…”

Observation of gas flow around plants using Schlieren imaging system and high-refractive-index gas

“…Their use in shock wave, sound wave, and microfluid observations has been reported [3][4][5][6]. The Schlieren and shadowgraph methods are suitable as observation methods in science education, and in some studies, they have been used as teaching tools [7][8][9][10][11]. However, the observations using the Schlieren method often use artificial shape objects such as airplanes or only gas flow as a sample, although there are also examples of the application of these methods to the observation of living organisms.…”