Channelling optics for high quality imaging of sensory hair

Bearbeiter:Dipl.-Phys. Christoph Skupsch


A long distance microscope (LDM) is extended by a lens and aperture array. This newly formed channelling LDM is superior in high quality, high-speed imaging of large field of views (FOV). It allows imaging the same FOV like a conventional LDM, but at improved magnification. The optical design is evaluated by calculations with the ray tracing code ZEMAX. High-speed imaging of a 2x2mm² FOV is realized at 3.000 frames per second and 1µm per pixel image resolution.

Fig.1: Cross-sectional image of a wall jet in still air issuing a nozzle. Micro-pillars are attached to the wall in order to detect the wall shear stress. The maximum streamwise velocity is u=7m/s, the jet Reynolds number is Re=1200. The flow direction is from left to right. In combination with flow sensitive hair the optics forms a wall shear stress sensor. The optics images the direct vicinity of twenty-one flow sensitive hair distributed in a quadratic array. The hair consists of identical micro-pillars that are 20µm in diameter, 390µm in length and made from polydimethylsiloxane (PDMS), see figure 1. Sensor validation in conducted in the transition region of a wall jet in air. The wall shear stress is calculated from optically measured micro-pillar tip deflections. 2D wall shear stress distributions in a wall jet are obtained with high spatiotemporal resolution. The footprint of coherent vortical structures far away from the wall is recovered in the Fourier spectrum of wall shear stress fluctuations. High energetic patterns of 2D wall shear stress distributions are identified by proper orthogonal decomposition (POD).

The complete work is published in Review of Scientific Instruments (AIP) and may be found at C. Skupsch et al., Rev. Sci. Instrum. 83, 045001 (2012).

Copyright (2011) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

This work is performed within the Cluster of Excellence "Structure Design of Novel High-Performance Materials via Atomic Design and Defect Engineering (ADDE)" that is financially supported by the European Union (EU) (European regional development fund) and by the Ministry of Science and Art of Saxony (SMWK).