Patent EA-001876-B1 (EA)
Title: Microstructured filter
Inventor: KADEL KLAUS
IPC: B01D46/12
Filed: 1998-08-28
Abstract: 1. A microstructured filter having an inlet for unfiltered fluid and an outlet for filtered fluid, a filter chamber  being partly defined by a substantially flat base plate (1) and a cover plate that is securable thereto, the surface of the base plate is provided with a plurality of projections which form passages for liquid via the filter chamber from said inlet to said outlet, said plurality of projections said plurality of projections are arranged in at least two rows to extend in a zig-zag configuration (34) and in a mutually juxtaposed relationship across the filter chamber; and the inlet and the outlet each comprise an elongate slot for unfiltered and filtered fluid respectively each of said slots being substantially as wide as the filter chamber and substantially as high as the projections on the inlet and outlet sides of the filter body respectively. 2. A filter according to Claim 1, wherein a spacing between the base plate and the cover plate is approximately as large as the width of the passages (8) between adjacent projections (7). 3. A filter according to Claim 1, wherein:  - a plurality of rows (3) of projections (7) are arranged in cascade form, - the cross-section of the passages (8) perpendicularly to the direction of flow of the fluid - as viewed in the direction of flow - decreases from row to row, - the projections (3) which are arranged closer to the inlet side of the filter are larger than the projections (3) which are arranged more at the outlet side of the filter, and - the spacing between the base plate and the cover plate in the area around each row of projections (7), which row is arranged in a cascade form, is approximately as large as the width of the passages on the side of the projections (7), on which the fluid passes into the row of passages. 4. A filter according to any of claims 1 to 3, wherein said cover plate is substantially flat. 5. A filter according to any of claims 1 to 4, wherein said inlet slot (5) has a ratio of height to width from 1:5 to 1:1000, and said outlet slot has a ratio of height to width from 1:5 to 1:1000. 6. A filter according to any of claims 1 to 5, wherein: - a spacing between the base plate (1) in the area around the projections (7) and the cover plate within a row (3) of projections (7) is between half and double the passage width on the side of the projections, on which the fluid passes into the row of passages (8). 7. A filter according to any of claims 1 to 6, comprising: - a collecting chamber of elongate cross-section between the inlet slot (5) and a first row of projections (4), into which the unfiltered fluid is passed and out of which the fluid flows into all passages between the projections of the first row, and - a collecting chamber of elongate cross-section between a last row of projections and the outlet slot, into which the fluid flows out of all passages of the last row and out of which the filtered fluid is passed. 8. A filter according to any of claims 1 to 7, wherein said projections are either in the form of lands (11, 12, 13, 14, 15) which - as viewed in the flow direction- are straight or curved; or are in the form of columns (16, 17, 18, 19). 9. A filter according to any of claims 1 to 8, wherein said passages (8) are of substantially constant cross-section, and have a length that is at least twice as great as their height on the entry side of the fluid. 10. A filter according to any of claims 1 to 9, wherein said passages (8) are of an approximately constant cross-section over the passage length, and are of a length of 5 μm to 50 μm, a height of 2.5 μm to 25 μm and a width of 2.5 μm to 25 μm. 11. A filter according to Claim 10, wherein said passages have a substantially square cross-section. 12. A filter according to any of claims 1 to 10, wherein said passages have a barrel-shaped or trapezoidal cross-section. 13. A filter according to Claim 12, wherein a longer side of the trapezoidal passages is formed by the cover plate. 14. A filter according to any of claims 1 to 10, wherein the passages (8) have an approximately square cross-section on the entry side of the filter that becomes wider towards the exit side of the filter. 15. A filter according to any of claims 1 to 14, wherein a spacing between the rows of projections is preferably twice as great as the passage width on the entry side. 16. A filter according to any of claims 1 to 15, wherein said projections are arranged in rows (31) extending parallel to each other. 17. A filter according to any preceding claim, wherein said zig-zag configuration comprises rows of projections inclined relative to each other through an angle alpha of between 2 degree  to 25 degree . 18. A filter according to any of claims 1 to 17, wherein the spacing between the base plate (1) in the area around the projections (7) and the cover plate within a row (3) of projections is substantially constant. 19. A filter according to any of claims 1 to 17, wherein the spacing between the base plate (1) in the area around the projections (7) and the cover plate within a row (3) of projections (7) is greater in the region of the end of the row which is in the proximity of the outlet of the filter than in the region of the end of the row which is in the proximity of the inlet of the filter. 20. A filter according to any of claims 1 to 17, wherein a spacing between the flat base plate (1) in the area around the projections (7) and the flat cover plate within a row of projections linearly increases from the region of the end of the row which is in the proximity of the inlet side of the filter in a direction towards the region of the end of the row which is in the proximity of the outlet side of the filter. 21. A filter according to any of claims 1 to 20, wherein said base plate (1) has been structured by isotropic or anisotropic wet or dry etching or a combination of those processes, preferably by anisotropic dry etching. 22. A filter according to any of claims 1 to 21, wherein said base plate (1) is of silicon and said cover plate is of glass, said base plate being joined to said cover plate by anodic bonding. 23. A nebuliser for inhalation therapy, the nebuliser comprising a microstructured filter for fluid having an inlet for unfiltered fluid and an outlet for filtered fluid, the filter comprising the base plate having a plurality of projections (7) which are arranged in at least two rows (3) in mutually juxtaposed relationship, wherein the passages form a plurality of through paths fof fluid from the inlet to the outlet and a cover plate that is securable to the base plate (1) to cover the projections and the passages (8), wherein said input and output passeges are elongate slots for passing for the unfiltered fluid and filtered fluids being substantially as high as the projections on the inlet and outlet sides of the filter. 24. A nebuliser according to Claim 23, comprising a nozzle (6) connected to said outlet.