Research Projects

Background-Oriented Schlieren (BOS) is an optical flow visualization technique that detects refractive index variations by measuring the apparent displacements in a patterned background. Originally developed for macroscopic applications, BOS offers a simple, cost-effective alternative to traditional schlieren methods, requiring only a camera, a patterned background, and a light source. While BOS has demonstrated exceptional capabilities for large-scale flow visualization, its adaptation to microscopic domains remains largely unexplored. Microscale systems (such as microfluidic devices and lab-on-chip platforms) also produce refractive index gradients due to thermal, chemical, or concentration variations, which can similarly deflect light rays and be captured using BOS principles. Extending BOS to microscopy would involve using a patterned substrate or background beneath a transparent microchannel and capturing images through a microscope. By analyzing the apparent displacements in the background pattern, induced by refractive index gradients, flow fields at the microscale can be qualitatively and quantitatively visualized. Moreover, many biological cells and microscale flows are optically translucent and remain invisible under conventional bright-field microscopy. Imaging such specimens typically requires expensive and complex techniques like phase-contrast or fluorescence microscopy. In contrast, BOS microscopy would offer a simple, label-free alternative by leveraging refractive index gradients to render otherwise invisible cells detectable. This promises a non-invasive, full-field measurement technique with minimal hardware requirements, potentially enabling portable and cost-effective solutions for microfluidics, biomedical diagnostics, and cellular studies. Under this research, we will build a BOS microscopy system that is capable of imaging a wide range of samples. The initial collection of samples would be from the biological world, and it would consist of low contrast samples such as micro-organisms, water planktons, insect larvae, and other specimens. The second group of samples would be from the industrial world which would be focused on fluid flow in micro flames, and study of micro-shockwaves. A third group of samples would be targeted towards environment friendliness by detecting the presence of microplastics in the waterways.