SBIR Phase I: Shear Stress Sensor Based on Optical Micro-Spring Technology

This Small Business Innovation Research Phase I project is aimed at the development of a wall shear stress sensor with an Optical Micro-Spring (OMS) as its core element. The OMS, a miniature fiber-based load cell, relies on the morphology-dependent optical resonances known as Whispering Gallery Modes (WGM) realized in a microcavity. A miniature and robust sensor is proposed that is capable of direct measurement of wall shear stress in either transparent or opaque media. Due to high quality factor of WGM technology, displacements of the sensing element as small as a hundredth of a nanometer can be detected. The sensor therefore virtually does not have any moving parts while detecting sensing element displacements within more than four orders of magnitude of the shear force. The project will advance the understanding of the fundamental processes occurring in the boundary layer of a flow. For non-Newtonian or otherwise rheologically complex fluids the wall shear stress can not be easily calculated or, especially for non-transparent flows, measured. The chemical and pharmaceutical industries suffer from an inability to scale and predict mixing equipment performance. Direct measurements of wall shear stress would significantly improve existing CFD models and provide a means to increase process control, quality and throughput for high intensity mixing devices and to reduce the cost of the final product.