Aerosol penetrations through fibrous filters with pinholes were studied theoretically and experimentally. An equivalent thin filter layer (ETFL) model assuming a virtual filter layer was proposed to account for penetration through filters with pinholes. From one to thirty pinholes per filter were made on HEPA filter media using columnar pins of 0.195, 0.150 or 0.130 mm in diameter. Aerosol penetration through these filters was measured using monodisperse NaCl aerosols ranging from 0.05 to 0.3 μm in diameter at air flow face velocities of 0.00775, 0.0233 and 0.0698 m/s. Net penetration through the pinholes increased in proportion to the pinhole number and size. But there was no change in pressure drops across the filters. As a result of analysis based on the ETFL model, the layer thickness was estimated to range from 1/5 to 1/12 of the normal filter thickness. The predicted penetration curves were confirmed to agree well with the measured curves.
A new technique which determines the location, behavior and velocity of particles with different shapes and sizes has been developed based on a Multiplexed Matched Spatial Filter (MMSF). The technique can be used in the manipulation or discrimination of the blood cells and the living cells in the liquid flow. The particles passing through on the frontal focal plane of the Fourier transform lens, the auto-correlation peaks can be observed skew-symmetri- cally for the input location at each observing field on the back focal plane of the imaging lens. The velocity of particles in each shape or size has been determined from the velocity of the displace- ment of auto-correlation peaks obtained by the MMSF method.