Apparatus and method for electronically acquiring fingerprint images with low cost removable platen and separate imaging device

Claims

What is claimed is:

1. An optical subsystem for a direct fingerprint reader, comprising:

a housing having an imaging aperture;

a light source for directing light toward said imaging aperture;

an imaging device for receiving light reflected from a fingertip or other portion of a body visible through said imaging aperture and electronically sensing the image in said reflected light;

a low cost, easily replaceable, disposable platen for placement in said imaging platen aperture and having a generally flat, thin configuration and having a first surface upon which a portion of a body such as a fingertip is placed when said platen is in use and a second surface which is generally parallel to said first surface and which includes a plurality of projections comprising an optical structure, said projections being small enough to maintain the generally flat, thin configuration of said disposable platen and comprised of material through which light can pass said plurality of projections of said optical structure having optical characteristics so as to function to prevent light rays originating at said light source arriving at said second surface from being reflected off said second surface toward said imaging device but instead causing said light rays to enter said disposable platen and travel through said disposable platen so as to reach said first surface without the need for guiding within the platen by total internal reflection, the shape of said first surface being such that the angle of incidence between light rays arriving at said first surface and a normal to said first surface is such that said light rays are refracted back toward said second surface from all portions of said first surface not in contact with flesh from the portion of body placed upon said first surface, and such that light rays arriving at portions of said first surface in contact with flesh of the portion of said body placed in contact with said first surface escape therefrom, the configuration of said projections being such that most light rays refracted toward said second surface from portions of said first surface not in contact with flesh exit said first surface and travel generally toward said imaging device.

2. The apparatus of claim 1 wherein said platen is comprised of plastic and wherein said projections of said optical structure comprise an array of parallel rows of microprisms each of which has an input surface having a normal pointing in a direction such that light arriving from said light source impinges on said first surface at portions thereof not in contact with flesh at an angle which is greater than the critical angle defined by Snell's law and are refracted toward said second surface but light which impinges on said first surface at portions thereof in contact with flesh impinge at an angle which is less than the critical angle defined by Snell's law such that these light rays escape said platen, each microprism also having an output surface having a normal pointing in a direction such that most light rays refracted from said first surface toward said second surface impinge upon said output surface at an angle which is less than the critical angle defined by Snell's law thereby escaping said platen and becoming available for imaging by said imaging device, and wherein the dimensions of each said microprism are such that said microprisms can be manufactured using stamping, pressure forming, injection molding or other processes substantially less expensive that semiconductor photolithography processes.

3. The apparatus of claim 1 wherein said disposable platen is made of plastic and wherein said plurality of projections have dimensions suitable for fabrication using pressure forming, stamping or injection molding.

4. The apparatus of claim 1 wherein said plurality of projections are triangular cross-section microprisms placed edge to edge at their bases in parallel rows across said second surface.

5. The apparatus of claim 4 wherein there are at least 50 parallel rows of microprisms per millimeter.

6. The apparatus of claim 1 manufactured by the process of stamping.

7. The apparatus of claim 1 manufactured by the process of injection molding.

8. A method of acquiring a working image of a fingerprint, comprising:

placing a portable, disposable fingerprint platen included as part of the structure of a credit card, identification card or passport on a direct fingerprint reader imaging device which does not have its own platen, said platen being generally flat and thin and of a size suitable for carrying in a wallet, and having an underside and a top side;

placing a finger or other portion of the body on said top side of said platen;

illuminating said underside of said portable fingerprint platen with a light source;

capturing the working image of the fingerprint in an imaging device from light rays reflected back into said direct fingerprint reader from said top side of said platen upon which the finger or other portion of the body was placed; and

using an optical structure on said underside of said platen, preventing reflection of non working light rays originating from said light source and travelling toward the underside of said platen which bear no fingerprint image information from being reflected from the underside of said platen toward said imaging device by refracting the rays first arriving from said light source at said underside so that the rays substantially all enter said platen and travel to said top side, said refraction at said underside being such that said light rays first arriving at said top side arrive at such an angle such that substantially all light rays which first arrive at portions of said top side in contact with flesh such as the ridges of a fingerprint exit said platen and escape whereas substantially all light rays which first arrive at portions of said top side which are not in contact with flesh such as the grooves of a fingerprint are refracted by the interface of said top side and the substance filling the grooves of said fingerprint back toward said underside, and preventing, at said underside, refraction or reflection away from said imaging device of light rays bearing fingerprint or other identification information which are first arriving at said underside after refraction from said top side.

9. A disposable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said disposable platen when said disposable platen is positioned in said fingerprint reader, comprising:

a thin, flat, light-transmitting, disposable platen having a a first surface upon which a finger or other portion of the body is to be placed when said disposable platen is placed in said fingerprint reader and a fingerprint is to be read, said platen having a second surface which is illuminated by light rays from said light source when said disposable platen is placed in said fingerprint reader said second surface having formed thereon a plurality of small microprisms which causes refraction of most of said light rays from said light source such that they pass through said second surface and propagate to said first surface at an angle relative to the normal of said first surface so as to be refracted from portions of said first surface not in contact with flesh back toward said second surface, said angle of said light rays arriving from said second surface relative to a normal to said first surface being such that most light rays which impinge upon portions of said first surface in contact with flesh escape therethrough thereby forming a working image, said second surface also being the surface through which light rays carrying said working image of said fingerprint passes enroute to said imaging device;

and wherein said said plurality of small microprisms on said second surface are formed in such as way such that a normal thereof points generally in the direction of said first surface and is oriented relative to the angle of arrival of said working ray refracted toward said second surface from said first surface such that most of said working rays pass through said second surface so that the image of the portion of the body in contact with said first surface may be detected by said imaging device.

10. A disposable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device, comprising:

a light transmitting generally flat, generally thin platen having a a first surface upon which a fingertip or other portion of the body is to be placed when said disposable platen is placed in said fingerprint reader and a fingerprint is to be read, and having a second surface illuminated by said light source when said disposable platen is placed in said fingerprint reader, said second surface being the surface through which light passes carrying an image of said fingerprint to said imaging device;

and wherein said second surface has formed thereon optical structure means for refracting light from said light source through said second surface toward said first surface such that said light arrives at said first surface without the need to be guided through said platen by total internal reflection, and arrives at said first surface at an angle relative to a normal to said first surface such that light rays impinging on portions of said first surface in contact with flesh escapes said platen while light rays that impinge upon said first surface not in contact with flesh are refracted back toward said second surface where said light rays arrive at an angle relative to a normal of a surface of said optical means such that most of said light rays escape said platen where they are focussed on said imaging device.

11. A disposable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device, comprising:

a thin, flat, light-transmitting, disposable platen having a first surface upon which a finger or other portion of the body is to be placed when said disposable platen is placed in said fingerprint reader and a fingerprint is to be read, said platen having a second surface which is illuminated by light rays from said light source when said disposable platen is placed in said fingerprint reader, said second surface having formed thereon a plurality of small microprisms which causes refraction of most of said light rays from said light source such that they pass through said second surface and propagate to said first surface at an angle relative to the normal of said first surface so as to be refracted from portions of said first surface not in contact with flesh back toward said second surface, said angle of said light rays arriving from said second surface relative to a normal to said first surface being such that most light rays which impinge upon portions of said first surface in contact with flesh escape therethrough thereby forming a working image, said second surface also being the surface through which light rays carrying said working image of said fingerprint passes enroute to said imaging device;

and wherein said said plurality of small microprisms on said second surface are formed in such as way such that a normal thereof is oriented relative to the angle of arrival of light refracted from said first surface toward said second surface such that most of said working rays pass through said second surface so as to make available to said imaging device the image of the portion of the body in contact with said first surface, and

wherein said platen has template data encoded thereon in a spatially distributed pattern of light and dark areas, said template data encoding the x, y and theta values of minutiae in the fingerprint of the rightful owner of the card.

12. A portable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a transparent plate having a a first surface upon which a finger is placed when said portable platen is placed in said fingerprint reader and a fingerprint is to be read, and having a second surface illuminated by said light source when said portable platen is placed in said fingerprint reader, and said second surface being the surface through which light carrying an image of said fingerprint passes enroute to said imaging device;

and wherein said second surface has formed thereon optical structures for preventing immediate reflection off said second surface toward said imaging device of nonworking light rays that originated from said light source and which are impinging on said second surface for the first time after being emitted from said light source and that bear no information about the working image of a fingerprint in contact with said first surface thereby preventing interference between non working light rays carrying no image information reflected from said second surface upon encountering said second surface for the first time after emission from said light source and working light rays carrying a working image of said fingerprint which are reflected from said first surface toward said imaging device and which pass through said second surface upon encountering said second surface for the first time after reflection from said first surface, said optical structures also for preventing reflection away from said imaging device at said second surface of working light rays carrying a working image of said fingerprint which are reflected from said first surface toward said imaging device and which are impinging on said second surface for the first time since reflection from said first surface, said optical structures being small enough to allow said transparent plate to be carried easily and comfortably in a wallet with other credit cards and identification cards,

and wherein said portable platen has template data encoded thereon in a spatially distributed pattern of light and dark areas said template data encoding the x, y and theta values of minutiae in the fingerprint of the rightful owner of the card,

and wherein said spatially distributed pattern of light and dark areas is a two dimensional barcode.

13. The apparatus of claim 12 wherein said template data is enciphered prior to encoding in said spatially distributed pattern of light and dark areas.

14. A portable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a transparent plate having an imaging surface upon which a finger is placed when said portable platen is placed in said fingerprint reader and a fingerprint is to be read, and having an undersurface illuminated by said light source when said portable platen is placed in said fingerprint reader, said undersurface being the surface through which light carrying an image of said fingerprint passes enroute to said imaging device;

and wherein said undersurface has formed thereon optical structures for preventing immediate reflection off said undersurface toward said imaging device of nonworking light rays that originated from said light source and which are impinging on said undersurface for the first time after being emitted from said light source and that bear no information about the working image of a fingerprint in contact with said first surface thereby preventing interference between nonworking light rays carrying no image information reflected from said undersurface upon encountering said undersurface for the first time after emission from said light source and working light rays carrying a working image of said fingerprint which are reflected from said imaging surface toward said imaging device and which pass through said undersurface upon encountering said undersurface for the first time after reflection from said imaging surface, said optical structures also for preventing reflection away from said imaging device at said undersurface of working light rays carrying a working image of said fingerprint which are reflected from said imaging surface toward said imaging device and which are impinging on said undersurface for the first time since reflection from said imaging surface, said optical structures being small enough to allow said transparent plate to be carried easily and comfortably in a wallet with other credit cards and identification cards, and

wherein said portable platen transparent plate is part of a credit card, identification card or passport, and

wherein said portable platen is configured for insertion into a direct fingerprint reader having an imaging aperture but no platen over said imaging aperture and having a light source which directs light toward said imaging aperture and having an optical path including an imaging device for receiving light from said imaging aperture and guiding said light to and focussing said light upon said imaging device, said transparent plate being positioned on said portable platen such that when said card is placed in said direct fingerprint reader, said transparent plate is located over said imaging aperture of said direct fingerprint reader, and wherein said optical structures comprise a plurality of microprisms each of which has a triangular cross-section having first and second faces, said first face having a normal which generally points at said light source and said second face having a normal which generally points at the region of said imaging surface upon which said finger or other portion of a body is placed.

15. The apparatus of claim 14 wherein each said microprism has an elongated shape with a long axis which extends all the way across said transparent portion of said portable platen and which is parallel to the long axis of each other microprism, said microprisms being placed edge to edge.

16. The apparatus of claim 15 wherein the density of said microprisms 50 microprisms per millimeter.

17. The apparatus of claim 16 wherein the imaging surface of said portable platen is coated with a transparent layer of rubber polyurethane.

18. The apparatus of claim 16 wherein the medium surrounding said portable platen when said card is placed in said direct fingerprint reader is air and wherein at each of said first and second faces of each microprism and at said imaging surface of said portable platen there is a critical angle defined by the Snell's law relationship ##EQU2## where n.sub.b =the index of refraction of the medium above the surface or face, and

n.sub.a =the index of refraction of the medium below the surface or face, and

.phi..sub.crit =the critical angle of total internal reflection wherein the angle of refraction is equal to 90.degree. such that the refracted light ray does not leave the medium it is travelling in but is refracted at an angle so as to travel parallel to said face or surface, and wherein the included angle between said first and second faces of each said microprism is such relative to the placement of said light source and said optical path that the angle of incidence of a light ray travelling from said light source toward said first face of said microprism when said light ray impinges on said first face of said microprism is less than said critical angle at said first face for light attempting to enter said transparent plate from said surrounding air thereby causing said light rays from said light source to enter said transparent plate and not be reflected or refracted away therefrom, and wherein the angle of incidence of a light ray refracted from said first face of said microprism on which it impinges is such that said light rays arriving at said imaging surface at locations thereof in contact with flesh arrive at less than the critical angle but also such that said light rays arriving at portions of said imaging surface in not in contact with flesh at an angle greater than the critical angle and are refracted toward a second face of a microprism such that when said light rays reach said second, the angle they arrive at is less than said critical angle for light travelling in said transparent plate and attempting to enter the surrounding air below said portable platen thereby causing said light rays to escape said transparent plate.

19. A portable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a transparent plate having a a first surface upon which a finger is placed when said portable platen is placed in said fingerprint reader and a fingerprint is to be read, and having a second surface illuminated by said light source when said portable platen is placed in said fingerprint