Claims for Patent: 7,316,067

Summary for Patent: 7,316,067

Title:	Forming a perforate membrane by laser drilling and a subsequent electro-polishing step
Abstract:	A method of forming a perforate membrane (1) is disclosed for use in a liquid transport device. The membrane has at least plural nozzles (10) formed therethrough. Each of those nozzles has a throat portion (12) opening at opposite end through opposite surface (2') of the perforate membrane and a smoothly curved outwardly diverging portion (11) extending from the first end of the throat portion to the first surface (2) of the perforate membrane. Laser energy is applied selectively to the first surface (2) of the membrane in the form of a pulsed, focused beam to form the nozzles (10) and thereafter the first surface (2) of the membrane and the surface of the diverging portion (11) of the nozzles (10) are electro-polished to remove surface imperfections. The electro-polishing is controlled so as to remove material from the surface of the diverging portion (11) of the nozzles to a depth less than the length of the throat portion (12).
Inventor(s):	Blakey; David Mark (Herts, GB)
Assignee:	The Technology Partnership (Melbourn Royston, Hertz, GB)
Application Number:	10/489,327
Patent Claims:	1. A method of forming a perforate membrane for use in a liquid transport device, by applying laser energy selectively to a first surface of the membrane in the form of a pulsed, focused beam to form a plurality of nozzles each having a throat portion opening of a selected diameter at one end through the opposite surface of the perforate membrane and a smoothly curved outwardly diverging portion extending from the other end of the throat portion to the first surface of the perforate membrane, and further comprising the steps of: thereafter electro-polishing the first surface of the membrane and the surface of the diverging portion of the nozzles to remove surface imperfections, and controlling the electro-polishing so as to remove material from the surface of the diverging portion of the nozzles to a depth within the membrane less than the length of the throat portion so that the diameter of the throat portion is unchanged by the electro-polishing step. 2. A method according to claim 1, wherein the laser energy is applied selectively to the first surface of the membrane in the form of a pulsed, focused beam. 3. A method according to claim 2, wherein, for forming each nozzle, a focused laser beam is applied to the first surface of the membrane positioned at a distance from the laser focus, to remove material of the membrane in order to form the diverging portion, and thereafter the distance between the laser focus and the first surface is decreased and/or the pulse energy of the laser beam is reduced, in order to form the throat portion extending from the diverging portion to the opposite surface of the membrane. 4. A method according to claim 3, wherein the distance between the laser focus and the first surface of the membrane and/or pulse energy of the laser beam is adjusted during the step of forming the diverging portion. 5. A method according to claim 3, wherein the distance between the laser focus and the first surface of the membrane and/or pulse energy of the laser beam is adjusted during the step of forming the throat portion. 6. A method according to claim 2, wherein the laser energy is applied in two steps to form each nozzle, between which steps the distance between the laser focus and the first surface of the membrane and/or the pulse energy of the laser beam is adjusted. 7. A method according to claim 1, further comprising electro-polishing the opposite surface of the membrane to remove surface imperfections. 8. A method according to claim 1, wherein the position of the laser focus relative the first surface of the membrane and/or the relative laser pulse energy is controlled by comparison of the number of the pulses required respectively to form the diverging portion or throat portion with a predetermined respective number. 9. A perforate membrane for use in a liquid transport device, the perforate membrane comprising: a first surface and an opposite surface; a plurality of pulsed, focused laser energy formed nozzles, each nozzle having a throat portion of a selected diameter and being open at one end through the opposite surface and having a smoothly curved outwardly diverging portion extending from the other end of the throat portion to the first surface of the perforate membrane; and wherein the first surface of the membrane and the surface of the diverging portion of the nozzles having been electro-polished to a depth of less than the length of the throat portion so that the diameter of the throat portion is unchanged by the electro-polishing. 10. A membrane according to claim 9, wherein the outwardly diverging portion of each nozzle is concave. 11. A membrane according to claim 10, wherein the concave portion is part spherical. 12. A membrane according to claim 9, wherein the throat portion is substantially cylindrical. 13. A membrane according to claim 9, wherein the throat portion is divergent towards the one surface of the membrane. 14. A fluid transport device including a perforate membrane according to claim 9. 15. An aerosol generator incorporating a membrane according to claim 9. 16. A pump incorporating a membrane according to claim 9. 17. A filter incorporating a membrane according to claim 9. 18. A membrane according to claim 9 wherein the throat portion has a selected length extending directly through the plate.