We have developed a numerical simulation methodology that is able to accurately characterize the focusing performance of aerodynamic lens systems.The commercial computational fluid dynamics(CFD)software FLUENT was used to simulate the gas flow field.Particle trajectories were tracked using the Lagrangian approach.Brownian motion of nanoparticles was successfully incorporated in our numerical simulations.This simulation tool was then used to evaluate the performance of an aerodynamic lens assembly that was designed to focus 3 nm spherical unit density particles following the guidelines described in Paper I(Wang et al.2005).Our simulations show that the performance of this lens assembly is close to what is predicted by the design guidelines.The simulations also demonstrate the ability of aerodynamic lenses to focus sub-30 nm spherical unit density particles.
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