SBIR-STTR Award

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

This Small Business Innovation Research (SBIR) Phase II project is aimed at the development of a wall shear stress sensor based on micro-optical resonators. The core element of the sensor, the micro-optical stress gauge (MOSG), consists of a micro-optical spherical resonator and optical fibers through which tunable laser light is coupled into and out of the sphere. By monitoring shifts of the resonator spectrum, that are a function of the deformation of the sphere, forces can be measured over more than four orders of magnitude with minute deformation of the resonator (< 1 nm). This capability allows a MOSG to be incorporated within a shear stress sensor in which the motion of a floating element in contact with the fluid is minimal. In Phase I, a breadboard version of the sensor was fabricated and successfully tested in a model flow between two parallel plates, where measurements were in close agreement with computational predictions. Phase II research will focus on advancing the technology by improving measurement rate, sensitivity, and dynamic range, along with decreasing vibration susceptibility, and improving robustness. Sensor prototypes will be tested on high shear industrial mixers with the aim of commercialization for the process mixing market. The broader impact/commercial potential of this project will include the advancement of the understanding of the fundamental processes occurring in boundary layers of flows. For non-Newtonian or otherwise rheologically complex fluids, wall shear stress cannot be reliably calculated or, especially for non-transparent flows, measured. The proposed sensor fills a need for shear stress measurement in the fields of fluid dynamics, aerodynamics and medical research. The largest impact is expected to be in the chemical and pharmaceutical industries that are suffering from an inability to scale and predict processing equipment performance. Knowledge of wall shear stress will provide means to improve process control, quality and throughput of products including drugs and other pharmaceutical products, foods, paints, inks and dyes, cosmetics, and many others