Method of fabricating radar chaff

Abstract

The present invention is a method for making radar chaff consisting of metal rings having varying diameters, using photolithographic processes. One aspect of the invention has the steps of: providing a metal foil having a thickness suitable for use in radar chaff; overcoating the metal foil with a photoresist, to form a layered structure; undercoating the metal foil with a removable backing; exposing the photoresist to a quantity of actinic radiation for chemically modifying the photoresist into a photoproduct suitable for subsequent development, where the actinic radiation is patterned into a series of concentric rings; developing the photoresist, to expose the underlying metal in a series of concentric rings; removing the exposed metal to form a series of concentric metal rings on the removable backing; and removing the removable backing. Another aspect of the invention is a metal chaff precursor, comprising: a removable backing, coated with a plurality of concentric metal foil rings.

What is claimed is: 
     
       1. A method for making radar chaff comprising metal rings having varying diameters, comprising the steps of: providing a metal foil having a thickness suitable for use in radar chaff;   overcoating said metal foil with a photoresist, thereby forming a layered structure;   undercoating said metal foil with a removable backing;   exposing said photoresist to a quantity of actinic radiation for chemically modifying said photoresist into a photoproduct suitable for subsequent development, wherein said actinic radiation is patterned into a series of concentric rings;   developing said photoresist, thereby exposing said underlying metal in a series of concentric rings;   removing said exposed metal to form a series of concentric metal rings on said removable backing; and   removing said removable backing.   
     
     
       2. The method of claim 1, wherein said removable backing comprises an etch-resistant lacquer, and said step of removing said removable backing comprises contacting said removable backing with a solvent for said etch-resistant lacquer. 
     
     
       3. The method of claim 1, wherein said step of undercoating said metal foil is conducted after said steps of overrcoating said metal foil with a photoresist, exposing said photoresist, and developing said photoresist. 
     
     
       4. The method of claim 1, wherein said step of undercoating said metal foil is conducted before said step of overrcoating said metal foil with a photoresist. 
     
     
       5. The method of claim 1, wherein said step of undercoating said metal foil with a removable backing comprises coating a removable plastic film onto said metal foil. 
     
     
       6. The method of claim 5, wherein said step of exposing said photoresist to patterned actinic radiation comprises exposing said photoresist to light through a mask patterned with a series of concentric rings. 
     
     
       7. The method of claim 5, wherein said step of removing said metal comprises etching away said metal. 
     
     
       8. The method of claim 5, further comprising the step of: opening a channel through said layered structure, normal to the plane of said layered structure, at about the center of said concentric rings.   
     
     
       9. The method of claim 5, wherein said plastic film comprises polyacetyl. 
     
     
       10. The method of claim 5, further comprising the step of: exposing said plastic film to nitric acid fumes after said step of removing said exposed metal, thereby removing said plastic film.   
     
     
       11. The method of claim 5, wherein said plastic film comprises a substrate plastic layer and a degradable plastic layer interposed between said substrate plastic layer and said metal, wherein said substrate plastic layer is stable under conditions that will degrade said degradable plastic layer. 
     
     
       12. The method of claim 11, further comprising the step of: removing said degradable plastic layer from said metal rings, thereby forming metal chaff.   
     
     
       13. The method of claim 11, wherein said substrate plastic layer is nonadherent to said metal foil or to another substrate plastic layer. 
     
     
       14. The method of claim 11, wherein said substrate plastic layer is selected from the group consisting of teflon and polyethylene. 
     
     
       15. The method of claim 5, further comprising the step of: prior to said step of overcoating said metal foil with said photoresist, overcoating said metal foil with a ceramic layer.   
     
     
       16. The method of claim 15, wherein said ceramic layer comprises a ceramic selected from the group consisting of oxides, carbides, nitrides, and borides. 
     
     
       17. The method of claim 15, wherein said ceramic layer is electrostatically charged. 
     
     
       18. A method for making radar chaff consisting of metal rings having varying diameters, comprising the steps of: (a) coating a plastic film with a metal foil;   (b) overcoating said metal foil with a photoresist, thereby forming a layered structure;   (c) exposing the photoresist to a quantity of actinic radiation for chemically modifying said photoresist into a photoproduct suitable for subsequent development, wherein said actinic radiation is patterned into a series of concentric rings;   (d) developing said photoresist, thereby exposing said underlying metal in a series of concentric rings;   (e) removing said exposed metal to form a series of concentric metal rings on said plastic film;   (f) repeating said steps (a) through (e) a plurality of times, thereby forming a plurality of patterned layered structures; and   (g) coaxially stacking said plurality of said patterned layered structures.   
     
     
       19. A metal chaff precursor, comprising: a removable backing, coated with a plurality of concentric metal foil rings.   
     
     
       20. The metal chaff precursor of claim 19, wherein said concentric metal foil rings have circumferences selected to correspond to the wavelengths of selected radars. 
     
     
       21. The metal chaff precursor of claim 19, wherein said concentric metal foil rings have circumferences ranging from about 1.0" to about 0.1". 
     
     
       22. The metal chaff precursor of claim 19, wherein said concentric metal foil rings have cross sections of about 0.001"×0.001".