Steve Klein publishes paper in Measurement Science and Technology on “Improvement in two-frame correlations by confocal microscopy for temporally resolved micro particle imaging


An investigation of two-frame micro particle image velocimetry (?PIV) correlations is
presented that utilizes a high-speed, spinning disk confocal micro particle image velocimetry
(SD?PIV) system. The system uses Nipkow disk confocal epifluorescence microscopy and a
high-speed camera to capture unsteady microscale flows using two-frame cross correlations.
In ?PIV, ensemble averaging is often used to reduce errors due to noise from out-of-focus
particles. However, unsteady non-periodic flows require two-frame correlations which can be
difficult to achieve with acceptable accuracy using ?PIV. The confocal microscope uses
pinhole spatial filtering to remove much of the light originating from outside the focal plane,
reducing light from out-of-focus particles and improving the accuracy of two-frame cross
correlation ?PIV. Improvements to two-frame PIV correlations provided by the confocal
system are evaluated using the correlation peak signal to noise ratio and universal outlier
detection in steady Poiseuille flow as a function of particle volume fraction and focal depth into
the channel. We find that the confocal system increases the mean correlation signal to noise
ratio for all cases and reduces the fraction of erroneous vectors under conditions where there is
a large number of out-of-focus particles. Time-resolved high-speed PIV is demonstrated
through the measurement of an example unsteady flow created by an electrokinetic