1 Micron - Resolution Particle Image Velocimetry

During the past five years, significant progress has been made in the development and application of micron-resolution Particle Image Velocimetry (μPIV). Developments of the technique have extended typical spatial resolutions of PIV from order 1-mm to order 1-μm. These advancements have been obtained as a result of novel improvements in instrument hardware and post processing software. Theory describing the limits of in-plane and out-of-plane spatial resolution are presented. The basis of the theory for in-plane spatial resolution extends the original work of Adrian & Yao (1985). The theory for out-of-plane spatial resolution closely follows the recent work of Olsen & Adrian (2000a). The desire for high spatial resolution dictates that the flow tracing particles typically range between 200 – 700 nm in diameter. The effect of Brownian forces on particle motion is discussed in detail. Guidelines are given to determine optimal particle size and to estimate particle flow following fidelity. Advances in post processing algorithm provide improvements in velocity accuracy and spatial resolution. The correlation-averaging algorithm increases the effective particle concentration, while maintaining sufficiently low particle concentration in the working fluid. Central difference interrogation provides second order accurate estimates of velocity, which becomes important in regions containing high spatial variations in velocity. These post-processing techniques are particularly useful in challenging micro length scales, and can also be extended to macroscopic flows. The utility of μPIV is demonstrated by applying it to flows in microchannels, micronozzles, BioMEMS, and flow around cells. While the technique was initially developed for microscale velocity measurements, it has been extended to measure wall positions with tens of nanometers resolution, the deformation of hydrogels, micro-particle thermometry, infrared-PIV, and particle tracking velocimetry.