Manufacture of high aspect ratio micro-pillar wall shear stress sensor arrays

Abstract

In the field of experimental fluid mechanics the measurement of unsteady, distributed wall shear stress has proved historically challenging. Recently, sensors based on an array of flexible micro-pillars have shown promise in carrying out such measurements. Similar sensors find use in other applications such as cellular mechanics. This work presents a manufacturing technique that can manufacture micro-pillar arrays of high aspect ratio. An electric discharge machine (EDM) is used to manufacture a micro-drilling tool. This micro-drilling tool is used to form holes in a wax sheet which acts as the mold for the micro-pillar array. Silicone rubber is cast in these molds to yield a micro-pillar array. Using this technique, micro-pillar arrays with a maximum aspect ratio of about 10 have been manufactured. Manufacturing issues encountered, steps to alleviate them and the potential of the process to manufacture similar micro-pillar arrays in a time-efficient manner are also discussed.

A study of directional MEMS dual-fences gauge

“…The measurement principle based on arrays of hairlike flexible micro-pillars [10] on the surface has become more attractive as it can be used on curved surfaces with a sufficient resolution. Similar approaches were published earlier by Grobe S [11] and by the group of Gnanamanickam E P [12,13]. When micro-pillar shear-stress sensor (MPS3) is placed in a boundary layer flow, the pillars are bent until reaching the equilibrium between the drag force and the internal elastic strain, resulting in a tip displacement, which is directly proportional to the wall shear stress.…”

Wetting of soft superhydrophobic micropillar arrays

“… 8 , 9 Polydimethylsiloxane (PDMS) micropillars have been used as force sensors to measure drag and shear in microfluidic devices, as they show significant bending with forces in the nanonewton range. 10 – 12 The softness of PDMS allows control of the shape and orientation by external fields, e.g. for smart surfaces with directional wettability, magnetic pillars, 13 and measurement of cell adhesion forces.…”

Accurate Measurements of Wall Shear Stress on a Plate with Elliptic Leading Edge

“…It can be used to evaluating flow fluctuations, developments of turbulent boundary layer, and so on. For now, wall shear stress can be measured by Preston tubes [ 3 ], hot wires/films [ 4 , 5 ], micro-pillars [ 6 , 7 ], sub-layer fences [ 8 ], and micro-floating element wall shear stress sensors [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. These techniques have been developed for many years and have been proved a good prospect in aerodynamic measurements.…”