Micromachined membrane particle filters

Particle membrane filters (8 x 8 mm(2)) with circular, hexagonal and rectangular through holes are designed, fabricated and tested. By varying hole dimensions from 6 to 12 mu m, opening factors from 4 to 45% are achieved. In order to improve the filter robustness, a composite silicon nitride/Parylene membrane technology is developed, and the burst pressure of the filters is increased more than 4 times. More importantly, fluid dynamic performance of the filters is also studied by both experiments and numerical simulations. It is found that the gaseous flow through the filters depends strongly on opening factors, and the measured pressure drops are much lower than that from numerical calculation using the Navier-Stokes equation. Interestingly, surface velocity slip can only account for a minor part of the discrepancy. This suggests that a very interesting topic for micro fluid mechanics research is identified. (C) 1999 Elsevier Science S.A. All rights reserved.