A miniaturized optical package was developed for a floating-element shear stress sensor that permits the direct measurement of skin friction based on geometric Moiré interferometry. Aluminum gratings are placed on a silicon floating element and a Pyrex support structure to generate a Moiré fringe pattern, which is used to optically amplify the floating element deflections. The Moiré fringe is discretely sampled and modeled as a sinusoid. Several fringe estimation techniques are evaluated to track the phase of the Moiré fringe. Initial static characterization of the device using conventional large-scale optics indicates a shear stress sensitivity of 59 nm/Pa with linearity designed up to 5 Pa. The overall size of the optical components and packaging is significantly reduced by using an optical fiber array instead of an optical lens system to reflect light off of the Moiré fringe patterns on the shear stress sensor for optical detection.
