On the calibration of astigmatism particle tracking velocimetry for microflows

Abstract

Astigmatism particle tracking velocimetry (APTV) is a method to determine three components (3C) of the velocity field in a volume (3D) using a single camera. The depth position of the particles is coded by optical distortions caused by a cylindrical lens in the optical setup. This technique is particularly suited for microfluidic applications as measurement errors due to spatial averaging and depth of correlation, typically encountered with μPIV approaches, are eliminated so that the measurement precision is enhanced. Unfortunately, the current state of the technique is limited by the small measurement region achievable with the current calibration procedures as well as by higher order image aberrations (Cierpka et al 2010 Meas. Sci. Technol. 21 045401). In order to extend the size of the measurement volume and to account for all image aberrations, a new intrinsic calibration procedure, based on the imaging function of the particles, is proposed in the paper at hand. It provides an extended measurement depth, taking into account all image aberrations. In this work, the calibration procedure was applied to a μPIV arrangement but could also be implemented on macroscopic experimental setups. The calibration procedure is qualified with synthetic data as well as Poiseuille flow in a straight rectangular micro-channel with a cross-sectional area of 200 × 500 µm2. The three-dimensional velocity distribution of the whole channel was resolved via APTV with uncertainties of 0.9% and 3.7% of the centerline velocity, uc, for the in-plane and out-of-plane components, respectively. Further investigations using different cylindrical-lens focal lengths, magnifications and particle sizes provide information about achievable measurement depths and help to design and adapt the optimal system for the desired experiment.

Ultrasound-induced acoustophoretic motion of microparticles in three dimensions

“…A fully three-dimensional evaluation of the particle trajectories and velocities was performed by means of the astigmatism particle tracking velocimetry (APTV) technique [33,34] coupled to the temperature-controlled and automated setup presented in Ref. [28].…”

Particle focusing by AC electroosmosis with additional axial flow

“…The basic principle of astigmatism µ-PTV is that due to the anamorphic effect by inserting a cylindrical lens, particle images are deformed into ellipses. This ellipticity is directly related to the particle position normal to the focal plane (Liu et al 2014a;Cierpka et al 2010Cierpka et al , 2011Cierpka and Kähler 2012). A fluorescence microscope with a 20× Zeiss objective lens (numerical aperture of 0.4 and focal length of 7.9 mm) was used.…”

“…1 3 (Liu et al 2014a;Cierpka et al 2010Cierpka et al , 2011Cierpka and Kähler 2012). The vorticity is analyzed as function of the axial background velocity and the results are compared to a numerical model developed before (Liu et al 2014b).…”

Numerical simulation of 3D boundary-driven acoustic streaming in microfluidic devices

“…Experimental investigations have shown that μPIV [11][12][13] and PTV 14,15 are powerful tools for analysing 2D microchannel acoustophoresis. Fully 3D particle tracking has been demonstrated using μPIV with depth of correlations 16 and astigmatism particle tracking velocimetry [17][18][19] . On the other hand, numerical simulations of acoustophoretic motion of microparticles can provide efficient prediction of experiments and provide effective guidance and optimization on the design of acoustofluidic devices to enhance or improve experiments.…”