Abstract:
A fingerprint optical input apparatus comprises a contact image sensor for viewing a moving finger and providing a high contrast image. A narrow strip of the fingerprint touching a transparent platen is illuminated by sheet of collimated light normal to or at an oblique angle to the surface. The fingerprint image is viewed at an oblique angle by partially scattered light or by frustrated total internal reflection by a GRIN rod lens array and projected onto a linear array sensor. Various embodiments of the platen provide a compact design by using TIR or mirror reflections of the fingerprint image.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a method of creating electronic images of a finger or other object with ridges and the like, and a compact optical apparatus to project high contrast image slices of a fingerprint onto sensors.  
         BACKGROUND  
         [0002]    The prior art for contact image sensors is exemplified by U.S. Pat. No. 5,214,273 (“the &#39;273 patent”) which issued May 25, 1993 for an invention called “Contact Image Sensor.” A second example of prior art is U.S. Pat. No. 5,331,146 (“the &#39;146 patent”) which issued Jul. 19, 1994 for an invention called “Contact-type Image Sensor for Generating Electric Signals Corresponding to an Image Formed on a Document.” Unlike the present invention, the &#39;273 patent and the &#39;146 patent do not employ frustrated total internal reflection (FTIR) to view a high contrast fingerprint.  
           [0003]    The prior art for fingerprint sensors is exemplified by U.S. Pat. No. 4,784,484 (“the &#39;484 patent”) which issued Nov. 15, 1988 for an invention called “Method and Apparatus for Automatic Scanning of Fingerprints.” Unlike the present invention, the &#39;484 patent uses a separate sensing means to measure the speed of finger motion. Also, unlike the present invention, the &#39;484 patent does not teach the use of FTIR to view a high contrast image of the fingerprint. Finally, unlike the present invention, the &#39;484 patent does not employ a gradient index rod lens array or an array of relay lens pairs.  
           [0004]    The prior art for fingerprint sensors is also exemplified by U.S. Pat. No. 5,619,586 (“the &#39;586 patent”) which issued Apr. 8, 1997 for an invention called “Method and Apparatus for Producing a Directly Viewable Image of a Fingerprint.” The &#39;586 patent shows prior art employing FTIR to obtain a high contrast fingerprint image. However, unlike the present invention, the &#39;586 patent shows imaging of the entire fingerprint at once as an area image, instead of a narrow strip image projected onto a linear array sensor. Also, unlike the present invention, the &#39;586 patent does not show the use of gradient index rod lenses or relay lenses to image the fingerprint.  
           [0005]    The prior art for fingerprint sensors is also exemplified by U.S. Pat. No. 5,096,290 (“the &#39;290 patent”) which issued Aug. 27, 1990 for an “Apparatus for Imaging Fingerprint Using Transparent Optical Means Having Elastic Material Layer.” Unlike the present invention, the &#39;290 patent is covers an elastic layer for the entire area of the fingerprint, rather than a narrow strip of the fingerprint.  
           [0006]    The prior art of fingerprint sensors is also exemplified by U.S. Pat. No. 5,448,649 (the &#39;649 patent”), which issued Sep. 5, 1995, for an “Apparatus for Imaging Fingerprint or Topographical Relief Pattern on the Surface of an Object”. Unlike the present invention, the &#39;649 patent fails to disclose a stationary lens array and sensor array, does not include a platen with complex geometry and incorporates a physical separation between the platen and the lens array.  
           [0007]    The prior art of fingerprint sensors is yet further exemplified by an article entitled “Fingerprint Input Based on Scattered-light Detection”, in Applied Optics, Dec. 10, 1997, Opt. Soc. of America, 36(35), 9152-9156. Unlike the present invention, this article fails to disclose the use of stationary lens and sensors, fails to use the light source to illuminate the entire finger, and incorporates a physical separation between the platen and the lens array.  
         SUMMARY OF INVENTION  
         [0008]    The invention provides a fingerprint image optical input apparatus in the form of a contact image sensor (CIS) which projects high contrast image slices onto a linear array sensor. Novel optics are employed to provide a high contrast image by means of FTIR or direct illumination of ridges of the fingerprint which is projected by a GRIN (GRadient INdex of refraction) lens array onto a linear array sensor.  
           [0009]    The generally preferred embodiment is a miniaturized CIS sensor arranged to view the width of the moving fingerprint as it is wiped over the optically transparent platen of the sensor. To view the fingerprint, light must be introduced inside the platen. Light from the light source may be introduced inside the transparent platen through a flat or curved surface, which acts as a lens to direct the light and help collimate the light so that it forms a flat sheet of light the width of the linear array sensor. Once introduced, the light may optionally be directed inside the platen by using total internal reflection (TIR) or reflections from a mirror-like surface or surfaces. The use of reflections to direct the light inside the platen allows the light source to be located anywhere convenient, such as on a printed circuit board; the location of the light source can alter the form of the platen, or allow the platen to be made more compactly. The reflective surfaces or TIR surfaces of the platen can be slightly rough, not perfectly flat, to partially diffuse the light beam and thus cause more even lighting of the fingerprint.  
           [0010]    A high contrast image may be obtained by viewing the fingerprint through the transparent platen at an oblique angle; the fingerprint image is then focused by a GRIN lens array onto a linear sensor array. Alternatively, the GRIN lens or other focusing means can be arranged to view reflected images of the fingerprint, and to project reflected images onto the linear array sensor. To provide a high contrast image of the fingerprint, light is directed at an angle to the top interior surface of the platen (typically 45 degrees or more to a line normal to the surface of the platen, depending on the index of refraction of the platen, which is advantageously greater than 1.5), where it is reflected by TIR if no fingerprint is present. Where the fingerprint ridges touch the top surface of the platen, light is not reflected, due to FTIR at the surface of the platen causing absorption of light, resulting in a dark pattern for the fingerprint ridges and bright light at the fingerprint valleys, which are reflected by TIR from the interior of the platen. Foreshortening effects can be accommodated by image processing.  
           [0011]    A high contrast image may also be obtained by viewing the fingerprint through the transparent platen at an oblique angle, but with direct illumination of the finger by light directed substantially normal to the internal imaging surface of the platen. The fingerprint image is then focused by a GRIN lens array onto a linear sensor array. Alternatively, the GRIN lens or other focusing means can be arranged to view reflected images of the fingerprint, and to project reflected images onto the linear array sensor. When no finger is present, the light escapes through the surface of the platen, while the GRIN lens sees a black surface by TIR from the platen. A high contrast image of the fingerprint is obtained by when a finger is placed on the platen and the fingerprint ridges are selectively illuminated due to physical contact with the surface of the platen. Where the fingerprint ridges touch the top surface of the platen, the fingerprint ridges glow with scattered light, resulting in a bright pattern for the fingerprint ridges and darker regions at the fingerprint valleys. The oblique viewing angle of the GRIN lens enhances contrast, while allowing limited viewing of fingerprint ridge details that are near to, but not touching, the platen.  
           [0012]    The angled surface of the platen can be a raised strip to increase the pressure of the finger on the imaging surface, thereby giving better contact for total internal reflection. The platen surface or raised portion can also be constructed of silicone or some other material with optical wetting or low friction properties to improve imaging or finger movement respectively. A liquid reservoir can be integrated into the platen or an adjacent surface to allowing wetting of the finger with oil or other liquid to improve the total FTIR or fingerprint ridge glow imaging, as well as lubricating the finger for smooth motion. The platen itself can be part of the protective housing of the sensing elements. Surfaces of the platen can be coated in a light absorbing material to absorb stray light, thus reducing the noise at the sensor element.  
           [0013]    The high contrast fingerprint image is viewed by a GRIN lens array, or alternatively a relay lens pair array, or any other functionally equivalent means that creates a series of coherent overlapping images. The GRIN lens array looks at an oblique angle to the platen; the narrow fingerprint strip image is focused by the GRIN lens array onto the width of a linear array sensor, which may have one linear array of light sensing pixels or two or more parallel linear arrays of light sensing pixels. The advantages of this arrangement are that a very compact optical system can be achieved which provides fingerprint images which have low distortion, high resolution and large format size.  
           [0014]    The CIS sensor for fingerprint imaging can be arranged in several novel configurations, which can be optimized for different applications and manufacturing techniques. For those skilled in the art of design of optical components, the different features of various configurations may be utilized or combined, and other materials, components or technologies may used or combined to achieve substantially similar fingerprint imaging systems. 
       
    
    
     BRIEF DESCRIPTION OF FIGURES  
       [0015]    Further objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following description of the invention when taken in conjunction with the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1A shows a cut-away, isometric depiction of a side view of the prior art contact image sensor, similar to those commonly used in facsimile machines, viewing a horizontally moving sheet of paper through a GRIN rod lens array and projecting a narrow strip image onto a linear array sensor.  
         [0017]    [0017]FIG. 1B shows a comparison of a prior art GRIN rod lens array with a functionally equivalent array of relay lens pairs, with an optical ray diagram which depicts the well known image transfer function of relay lenses.  
         [0018]    [0018]FIG. 2 shows a cross-sectional depiction of a side view of a GRIN lens array at 45 degrees viewing a fingerprint image illuminated at 45 degrees, providing a high contrast strip image on a linear array sensor.  
         [0019]    FIG. 3  shows a cross-sectional depiction of a side view of a illuminated fingerprint, with light introduced from the bottom and reflected by total internal reflection, a GRIN lens array mounted at an angle less than 45 degrees to the horizontal, with the projected high contrast image from the GRIN lens array reflected one time by total internal reflection and then directed onto a linear array sensor.  
         [0020]    [0020]FIG. 4 shows a cross-sectional depiction of a side view of a vertically mounted GRIN lens array viewing a fingerprint, with light introduced from the bottom and reflected by total internal reflection to the fingerprint, the image of the fingerprint reflected to the GRIN lens array by total internal reflection, which then projects a high contrast image of a fingerprint directly onto the linear array sensor.  
         [0021]    [0021]FIG. 5 shows a view of an optical system identical to that in FIG. 4, with the exception that an array of small relay optics lens pairs has been substituted equivalently for the GRIN lens.  
         [0022]    [0022]FIG. 6 shows a cross-sectional depiction of a side view of a horizontally deployed GRIN lens array viewing an illuminated fingerprint, with light introduced horizontally from the side and reflected by total internal reflection to the fingerprint, and the image of the fingerprint reflected by total internal reflection to the GRIN lens array and thereafter reflected again by total internal reflection down onto the linear array sensor.  
         [0023]    [0023]FIG. 7 shows a cross-sectional depiction of a side view of a horizontally deployed GRIN lens array viewing an illuminated fingerprint, with light introduced from the bottom and reflected by total internal reflection to the fingerprint, and the high contrast image of the fingerprint reflected by total internal reflection to the GRIN lens array and thereafter reflected again by total internal reflection down onto the linear array sensor.  
         [0024]    [0024]FIG. 8 shows a cross-sectional perspective view of an optical system identical to that shown in FIG. 7.  
         [0025]    [0025]FIG. 9 shows a cross-sectional view of an optical system similar to that shown in FIG. 7, with the exception that the GRIN lens array is supported by two transparent optical elements.  
         [0026]    [0026]FIG. 10 shows a cross-sectional view of an optical system similar to that shown in FIG. 7, with the exception that the linear array sensor is mounted directly on the PC board, as a chip-on-board mounting, eliminating the need for a package for the linear array sensor.  
         [0027]    [0027]FIG. 11 shows a cross-sectional view of an optical system similar to that shown in FIG. 7, with the exception that the optical elements are attached directly to the PC board, and the linear array sensor is mounted as a flip-chip on the opposite side of the PC board, over a slot in the board, which allows light to reach the linear array sensor surface.  
         [0028]    [0028]FIG. 12 shows a cross-sectional view of an optical system similar to that shown in FIG. 3, with a side view of a illuminated fingerprint, with light introduced from the bottom and refracted in the direction substantially normal to the imaging surface of the platen, a GRIN lens array mounted at an angle of approximately 45 degrees to the platen, with the projected high contrast image from the GRIN lens array reflected one time by total internal reflection and then directed onto a linear array sensor. 
     
    
     DESCRIPTION  
       [0029]    In FIG. 1A a basic CIS (Contact Image Sensor) is shown, which is commonly used in prior art facsimile machines and sheet-feed document scanners. A CIS imager is comprised of four basic components, which include a transparent platen, light source, lens array, and linear array sensor.  
         [0030]    In FIG. 1A the platen  1  is made of transparent glass or plastic, or other suitable transparent material. The light source  2 , is conveniently an array of light emitting diodes (LEDs) or any other suitable source of light such as an electro-luminescent strip or miniature fluorescent tube. The lens system is typically a GRIN lens array  3 , or it could be replaced by a relay lens array  6  as shown in FIG. 1B. The linear array optical sensor  4 , with a single linear array, or two or more parallel rows of light sensing pixels, may use CCD (charge coupled device) pixels, or may use CMOS (complementary metal oxide semiconductor) APS (active pixel sensing) pixels, photo-diode pixels, or any other linear array of light sensing or infrared sensing pixel technology. The width of platen  1 , light source  2 , GRIN lens array  3  and linear array sensor  4  may be any convenient length, suited to the imaging task at hand.  
         [0031]    In FIG. 1A, the CIS sensor is shown imaging a printed sheet of paper  5  which is moved across the platen  1 . For facsimile machines and document scanners, paper  5  is mechanically moved across the platen; alternatively, the CIS sensor may be mechanically moved beneath paper  5  on a fixed platen. In the generic configuration of the CIS sensor, light source  2  shines light beam  2   a  through transparent platen  1  and illuminates the object, such as printed letters on paper  5 . Some light  2   b  is then scattered and reflected from paper  5  and is viewed by GRIN lens array  3  and focused as light  2   c  onto linear array sensor  4 . An electronic gray scale image is gathered line by line by the linear array sensor  4 , and is subsequently stored, altered, processed, interpreted, transmitted, displayed, printed or otherwise used.  
         [0032]    When a finger is dragged across platen  1  of FIG. 1A (instead of a paper document), an additional sensing means must be used to measure the speed of the finger across the platen and the fingerprint image which is obtained by the CIS sensor will have very low contrast between the fingerprint ridges and valleys. The low contrast causes difficulties in interpreting the significant features of the fingerprint image, making such an image not optimum for fingerprint matching or verification. However, image enhancement techniques may by used to produce a fingerprint imaging system using a standard CIS sensor.  
         [0033]    [0033]FIG. 1B compares GRIN lens array  3  with relay lens array  6 , which is comprised of a linear array of relay lens pairs. In this diagram, relay lens array  6  is the functional equivalent of GRIN lens array  3 , which is a 1:1 imager (no magnification, de-magnification or image inversion). The GRIN lens array  3  and relay lens array  6  both create a series of overlapping coherent images to create a single narrow image the width of the array. The general optical properties of a relay lens is shown schematically with relay lens pair  7 , whereby an image is transmitted, or relayed, to the focal plane without change in size or orientation. In contrast, GRIN lens array  3  utilizes optical fibers as rod lenses to refract the image, to achieve the same optical result. For all CIS imaging systems, including those designed for imaging the fingerprint, a suitably designed relay lens array may be substituted for a GRIN lens array.  
         [0034]    In FIG. 2, a general embodiment of the fingerprint sensor is shown. Surface mount technology (SMT) is used to mount the electronic components of linear array sensor package  8  and linear array light emitting diode (LED) light source  2  onto printed circuit board (PCB)  9 . The linear array sensor  4  silicon chip is supported by sensor package  8 , and connected by wire bonds  4   a . Linear array sensor  4  may have one linear array of light sensing pixels, or two or more parallel linear arrays. Sensor package  8  also supports transparent platen  1 . Platen  1  also serves as a cover for package  8 , providing a sealed enclosure for linear array sensor  4 . GRIN lens array  3  is fitted or otherwise attached to platen  1  such that GRIN lens array  3  is at the appropriate position that it is able to focus on interior surface  1   a  of platen  1  and also on linear sensor array  4 . [Since GRIN lens array  3  projects a narrow strip image onto linear array sensor  4 , the orientation of linear array sensor  4  may be varied from that depicted in FIG. 2; for example, the pixel sensing surface of linear array sensor  4  may also tilted so that it is normal to the axis of light  2   c  coming from GRIN lens array  3 .] The top surface of platen  1  of the fingerprint sensor protrudes slightly through a hole in cover surface  12 , which may be part of an enclosure for the sensor. A finger with fingerprint  5  is wiped over the top of the sensor platen to obtain a fingerprint image.  
         [0035]    In the embodiment shown in FIG. 2, linear array LED light source  2  generates light beam  2   a , which ideally is a collimated sheet of monochromatic light which is the width of the fingerprint. Light beam  2   a  shines upward into the transparent platen  1  where it is reflected by TIR on interior surface  1   c  and then is directed towards the top interior surface  1   a  of the transparent platen  1 . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a , which causes FTIR where the fingerprint ridges touch the platen, resulting in dark regions for fingerprint ridges and bright regions for fingerprint valleys. The linear strip of high contrast fingerprint image  2   b  is directed towards GRIN lens array  3 , which then focuses light  2   c  of the fingerprint strip on the width linear array sensor  4 .  
         [0036]    [0036]FIG. 2 also shows several optional refinements which can improve performance. The top of platen  1  has a slightly raised strip  1   b  which provides increased pressure of the fingerprint on the platen, improving image quality by causing the skin to contact the platen more firmly. Interior surface  1   c  of platen  1  is roughened to act as a reflective diffuser to light beam  2   a  to provide more constant illumination across the width of the fingerprint. Surface  1   f  of platen  1  is blackened to eliminate stray light from reaching linear array  4 . On the top surface of platen  1  is sponge or other absorbent or capillary material  11 , which optionally is glued into a recess in platen  1  and which can be loaded with water or oil or other lubricating fluid. The function of sponge  11  is to wet the skin of fingerprint  5  before it passes over platen  1  on raised strip  1   b , providing a higher contrast image and compensating for dry skin on the fingerprint. A particular advantage of sponge  11  is that it automatically lubricates the finger in a single swiping motion, as the fingerprint image is being taken.  
         [0037]    In FIG. 2, and in all embodiments of the invention shown in FIG. 3 through FIG. 11, linear array sensor  4  generates an electronic signal representative of the current strip of the fingerprint image being viewed by the CIS optical system in platen  1 . However, unlike a document scanner, where paper  5  is moved over the CIS sensor at a predetermined regular speed by an electric motor, a CIS sensor for fingerprint imaging must accommodate variable and unknown speed of motion of the finger as it is wiped over platen  1 . A simple method to measure the speed of motion of the finger is to employ an external sensor. The measurement of the speed of finger motion can used to rectify the image data from linear array sensor  4  to obtain geometrically correct fingerprint images. A second preferred method of measuring finger speed is to compare successive scans of parallel linear arrays in linear array sensor  4 . This method of estimating finger speed from linear array sensors is disclosed in commonly owned U.S. patent application Ser. No. 08/892,577 filed Jul. 16, 1997 for an invention called “Linear Sensor Imaging Method and Apparatus.” 
         [0038]    [0038]FIG. 3 shows a cross sectional view of another practical embodiment of a fingerprint sensor, employing through-hole technology electronic components of linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 . The linear array sensor  4  silicon chip is supported by sensor package  8 , which also supports transparent platen  1 . GRIN lens array  3  is fitted or otherwise attached to platen  1  such that the focal distance is appropriate for imaging the fingerprint onto linear array sensor  4 . Platen  1  also serves as a cover for package  8 , providing a sealed enclosure for linear sensor array  4 . The top surface of platen  1  of the fingerprint sensor protrudes slightly through a hole in cover surface  12 , which represents part of the sensor enclosure. In this embodiment, the linear array LED light source  2  shines collimated sheet of light  2   a  upward into the transparent platen  1  where it is bounced by TIR or mirror reflection on interior surface  1   c  towards interior surface  1   a . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a , which causes FTIR reflection of a linear strip of the fingerprint image  2   b  towards GRIN lens array  3 . Light  2   c  from GRIN lens array  3  is reflected by TIR or a mirrored surface on the interior surface  1   e  of platen  1 , and is then directed downward and focused across the width of linear array sensor  4 . If a mirrored surface is employed at surface  1   e , the reflective layer may be applied to the external surface of platen  1 . The optical design shown in FIG. 3, with a single TIR or mirrored reflection of the fingerprint image on the interior surface  1   e  of platen  1 , causes the image of the fingerprint on linear array sensor  4  to be both foreshortened and directionally reversed in relation to the direction of motion of the fingerprint; the foreshortening and directional reversal are easily characterized and accommodated for by adjustments in the electronic readout of linear array sensor  4 .  
         [0039]    [0039]FIG. 3 also shows several optional refinements which can improve performance. The top of platen  1  has a slightly raised strip  1   b , made from silicone rubber or other flexible or rigid transparent material, which provides increased local pressure of the fingerprint on the platen and also increased optical contact between the fingerprint and the flexible top of the platen, improving image quality. Surface  1   f  of platen  1  is blackened to reduce stray light reaching linear array  4 . Lastly, surface  1   g  inside platen  1  acts as a barrier to eliminate stray light from beam  2   a  reaching linear array  4 .  
         [0040]    [0040]FIG. 4 shows a cross sectional view of another practical embodiment of a fingerprint sensor, employing through-hole technology electronic components: linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 . The linear array sensor  4  silicon chip is supported by sensor package  8 , which also supports transparent platen  1 . GRIN lens array  3  is fitted or otherwise attached to platen  1 . Platen  1  also serves as a cover for package  8 , providing a sealed enclosure for linear sensor array  4  and GRIN lens array  3 . The top surface of platen  1  of the fingerprint sensor protrudes slightly through a hole in cover surface  12 , which encloses the sensor. In this embodiment, the linear array LED light source  2  shines collimated sheet of light  2   a  upward into the transparent platen  1  where it is bounced by TIR on interior surface  1   c  towards interior surface  1   a . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a , which causes FTIR reflection of a linear strip of the fingerprint image  2   b  towards interior surface  1   d  where it is reflected by TIR or a mirrored surface towards GRIN lens array  3 . If a mirrored surface is employed at surface  1   d , the reflective layer may be applied to the external surface of platen  1 . Light  2   c  from GRIN lens array  3  is then directed downward and focused across the width of linear array sensor  4 . The optical design shown in FIG. 4, with a single TIR or mirror reflection of the fingerprint image on the interior surface  1   d  of platen  1 , causes the image of the fingerprint on linear array sensor  4  to be both foreshortened and directionally reversed, in relation to the direction of motion of the fingerprint; the foreshortening and directional reversal are easily characterized and accommodated for by adjustments in the electronic readout of linear array sensor  4 .  
         [0041]    [0041]FIG. 4 also shows two optional refinements which can improve performance. Surface  1   f  of platen  1  is blackened to reduce stray light reaching linear array  4 . Interior surface  1   c  of platen  1  is roughened to act as a reflective diffuser to light beam  2   a  to provide more constant illumination across the width of the fingerprint.  
         [0042]    [0042]FIG. 5 shows a cross sectional view of another practical embodiment of a fingerprint sensor, employing through-hole technology electronic components of linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 . The linear array sensor  4  silicon chip is supported by sensor package  8 , which also supports transparent platen  1 . Relay lens array  6  is fitted or otherwise attached inside platen  1  such that it projects an image of fingerprint  4  on linear array sensor  4 . Platen  1  also serves as a cover for package  8 , providing a sealed enclosure for linear sensor array  4  and relay lens array  6 . In this embodiment, the fingerprint image is acquired in a manner identical to FIG. 4, with the exception that relay lens array  6  is used in place of a GRIN lens array. As an optional refinement, surface  1   f  of platen  1  is blackened to reduce stray light reaching linear array  4 .  
         [0043]    [0043]FIG. 6 shows a cross sectional view of a more compact embodiment of a fingerprint sensor. The linear array sensor  4  silicon chip is sealed inside sensor package  8  by transparent glass or plastic cover  10 . Platen  1  is held in place over sensor package  8  and cover  10  by glue or other attachment or supporting means. GRIN lens array  3  and linear array LED light source  2  are fitted or otherwise attached to platen  1 . Linear array LED light source  2  shines collimated light sheet  2   a  sideways into the transparent platen  1  where it is bounced by TIR or mirror reflection on interior surface  1   c  towards the top interior surface  1   a  of the transparent platen  1 . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a  which causes a linear strip of the fingerprint image to be reflected by FTIR from  1   a  towards interior surface  1   d , where it is again reflected by TIR or a mirror surface towards GRIN lens array  3 . The light from GRIN lens array  3  is then reflected by TIR or mirror reflection by interior surface  1   e , which then directs the light downward through cover  10  where the image is focused across the width of linear array sensor  4 . If a mirrored surface is employed at surface  1   e  and/or  1   d , the reflective layer may be applied to the external surface of platen  1 . The optical design shown in FIG. 6, with two TIR or mirror reflections of the fingerprint image on interior surfaces  1   d  and  1   e  of platen  1 , causes the image of the fingerprint on linear array sensor  4  to be foreshortened in relation to the direction of finger motion but not directionally reversed; the foreshortening is easily characterized and accommodated by adjustments in the electronic readout of linear array sensor  4 .  
         [0044]    [0044]FIG. 7 shows a cross sectional view of another compact embodiment of a fingerprint sensor, employing through-hole technology electronic components of linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 . The linear array sensor  4  silicon chip is sealed inside sensor package  8  by transparent plastic or glass cover  10 . Platen  1  is supported over cover  10  by glue or other attachment or support means. GRIN lens array  3  is fitted or otherwise attached to platen  1 . Linear array LED light source  2  shines upward into the transparent platen  1 , through curved surface  1   h , which serves as a lens to collimate light inside platen  1 , increasing the amount of light available for imaging the fingerprint. Light from light source  2  is bounced by TIR or mirror reflection on interior surface  1   c  towards the top interior surface  1   a  of the transparent platen  1 . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a , which causes a linear strip of the fingerprint image to be reflected by FTIR from  1   a  towards interior surface  1   d , where it is again reflected by TIR or mirror reflection towards GRIN lens array  3 . The narrow strip image from GRIN lens array  3  is then reflected by TIR or mirror reflection on interior surface  1   e , which directs the image downward through cover  10  where it is focused across the width of linear sensor array  4 . If a mirrored surface is employed at surface  1   e  and/or  1   d , the reflective layer may be applied to the external surface of platen  1 . In this embodiment, the upper interior surface  1   a  of the platen  1  is contained in a slightly raised strip  1   b  which provides increased pressure of the fingerprint onto the platen imaging surface above  1   a , improving image quality. As in FIG. 6, the image on linear array  4  is foreshortened but not reversed in direction.  
         [0045]    [0045]FIG. 8 shows a perspective view of the embodiment shown in FIG. 7, with the electronic components of linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 ; in this perspective view, the ends of the sensor package are cut off for display purposes. In this view, the width of the fingerprint sensor, as measured along the width of transparent platen  1  and raised strip  1   b , is about 19 mm, or the approximate width of the human finger, although variations in this dimension will also function satisfactorily. GRIN lens array  3  is at least the width of linear sensor array  4  and is fitted or otherwise attached to platen  1  to properly focus the fingerprint image on linear sensor array  4 . Light source  2  can be seen as a linear bar of multiple linear array LEDs, or any other elongated light source, providing an upwardly directed sheet of approximately collimated light  2   a , which is also the width of the fingerprint sensor. The sheet of light of light beam  2   a  is directed into platen  1  and reflected internally by TIR or mirror reflection at internal surface  1   c  in platen  1  onto interior surface  1   a , illuminating the width of raised strip  1   b  of platen  1 . When the skin of a fingerprint is pressed against the raised surface of strip  1   b , the fingerprint ridges cause FTIR and absorb light at position  1   a , while the valleys of the fingerprint do not touch the platen and thus allow light to be reflected by TIR from interior surface  1   a . The narrow strip fingerprint image from the width surface  1   a  is reflected by TIR or mirror reflection along the width of interior surface  1   d  and is directed towards GRIN lens array  3 . GRIN lens array  3  acts in the manner of a relay lens and refracts the fingerprint strip image and sends the image to be reflected again by TIR or mirror reflection along the width interior surface  1   e , which then directs the image downward through glass or plastic cover  10  where the image of the narrow fingerprint strip is focused across the width of linear sensor array  4 . If a mirrored surface is employed at surface  1   e  and/or  1   d , the reflective layer may be applied to the external surface of platen  1 .  
         [0046]    [0046]FIG. 9 shows a cross sectional view of a practical embodiment similar to that shown in FIG. 7, employing through-hole technology electronic components of linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 . In this embodiment, the function of the transparent platen is separated into two parts. Platen  1  is attached to cover  10  by glue or other attachment means. The linear array sensor  4  silicon chip is sealed inside sensor package  8  by transparent plastic or glass cover  10 , which also serves as part of the optical path to reflect the fingerprint image from interior surface  1   e . GRIN lens array  3  is fitted or otherwise attached between platen  1  and cover  10 ; opaque layer  1   f  serves to limit unwanted light from reaching linear array sensor  4 . The top surface of platen  1  of the fingerprint sensor protrudes slightly through a hole in cover surface  12 , which is part of an enclosure for the sensor. Linear array LED light source  2  shines upward into the transparent platen  1 . The collimated sheet of light  2   a  is bounced by TIR or mirror reflection on interior surface  1   c  towards top interior surface  1   a  of the transparent platen  1 . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a , which causes a linear strip of the fingerprint image to be reflected by FTIR from  1   a  towards interior surface  1   d , where it is again reflected by TIR or mirror reflection towards GRIN lens array  3 . The narrow strip image from GRIN lens array  3  is then reflected by TIR or mirror reflection on interior surface  1   e , which directs the image downward through cover  10  where it is focused across the width of linear sensor array  4 . If a mirrored surface is employed at surface  1   e  and/or  1   d , the reflective layer may be applied to the external surface of platen  1 . As in FIG. 7, the image on linear array  4  is foreshortened but not reversed in direction.  
         [0047]    [0047]FIG. 10 shows a cross sectional view of a practical miniaturized embodiment, employing chip-on-board (COB) mounting with wire-bonding  4   a  for the linear array sensor  4  and SMT for the linear array LED light source  2 , both attached to PCB  9 . The elimination of a package for linear array sensor  4  allows for further miniaturization of the fingerprint sensor. In this embodiment, platen  1  is designed to be glued or otherwise attached to PCB  9  and to completely cover linear array sensor  4 , protecting it from the environment. GRIN lens array  3  is fitted or otherwise attached to platen  1 . The fingerprint is optically sensed in a manner identical to that shown in FIG. 7. In this embodiment, the upper interior surface  1   a  of the platen  1  is contained in a slightly raised strip  1   b  which provides increased pressure of the fingerprint onto the platen imaging surface above  1   a , improving image quality. As in FIG. 2, a sponge or other absorbent or capillary material  11  serves to supply a fluid to the skin of the fingerprint, providing increased optical contact with platen  1 . The top surface of platen  1  of the fingerprint sensor protrudes slightly through a hole in cover surface  12 , which encloses the sensor.  
         [0048]    [0048]FIG. 11 show a cross sectional view of a practical sub-miniaturized fingerprint sensor. Components are mounted on both sides of PCB  9 . On the bottom surface of PCB  9  is mounted linear array LED light source  2 , which shines a sheet of light upward through a slotted hole  9   a  or multiple single holes. Also on the bottom surface of PCB  9  is linear array sensor  4 , which is mounted using “flip-chip” technology, which either bonds the chip to the printed circuit board with pressure-welds which also provide the required electrical contacts, or is mounted using special conductive glue to bond the electrical contacts and hold the chip to the printed circuit board; epoxy coating  4   b , or other suitable material, may be used to protect linear array sensor  4 . Since linear array sensor  4  must be bonded to the PCB with pixels directed towards the opposite side of the board, slotted hole  9   b  is provided to allow light to shine on the pixels. On the top surface of PCB  9  is glued or otherwise mounted platen  1 . GRIN lens array  3  is fitted or otherwise attached to platen  1 . In this configuration, the optical path is otherwise similar to that shown in FIG. 7.  
         [0049]    [0049]FIG. 12 shows a cross sectional view of another practical embodiment of a fingerprint sensor, employing surface-mount technology electronic components of linear array sensor package  8  and linear array LED light source  2  soldered to PCB  9 . The linear array sensor  4  silicon chip is supported by sensor package  8 , which is sealed by transparent cover  10  which also supports transparent platen  1 . GRIN lens array  3  is fitted or otherwise attached to platen  1  such that the focal distance is appropriate for imaging the fingerprint onto linear array sensor  4 . The top surface of platen  1  of the fingerprint sensor protrudes slightly through a hole in cover surface  12 , which represents part of the sensor enclosure. In this embodiment, the linear array LED light source  2  shines through refractive surface  1   h  upward into the transparent platen  1  providing a substantially collimated sheet of light  2   a  that is substantially normal to the interior platen surface  1   a . The skin of fingerprint  5  touches the exterior surface of the platen  1  above position  1   a , which causes the fingerprint ridges to glow from light source  2   a . The GRIN lens array  3  views a linear strip of the fingerprint image at  1   a  along light path  2   b . The fingerprint image from  1   a  is not viewed by means of TIR or FTIR, but rather by scattered light from the fingerprint ridges. A high contrast image of the fingerprint is obtained by positioning the GRIN lens to view platen surface  1   a  at an oblique angle, typically 45 degrees, so that very little light from the fingerprint valleys is transmitted. Light  2   c  from GRIN lens array  3  is reflected by TIR or a mirrored surface on the interior surface  1   e  of platen  1 , and is then directed downward and focused across the width of linear array sensor  4 . If a mirrored surface is employed at surface  1   e , the reflective layer may be applied to the external surface of platen  1 . The optical design shown in FIG. 12, with a single TIR or mirrored reflection of the fingerprint image on the interior surface  1   e  of platen  1 , causes the image of the fingerprint on linear array sensor  4  to be both foreshortened and directionally reversed in relation to the direction of motion of the fingerprint; the foreshortening and directional reversal are easily characterized and accommodated for by adjustments in the electronic readout of linear array sensor  4 .  
         [0050]    [0050]FIG. 12 also shows several optional refinements which improve performance. Surface  1   f  of platen  1  is blackened to reduce stray light reaching linear array  4  when no finger is present on platen  1 . Lastly, surface 1 g inside platen  1  acts as a barrier to eliminate stray light from beam  2   a  reaching linear array  4 .  
         [0051]    The above descriptions of apparatus are examples of means to implement the method of creating an electronic image of a finger.  
         [0052]    While the principles of the invention have now been made clear in the illustrated embodiments, there will be immediately obvious to those skilled in the art, many modifications of structure, arrangements, proportions, the elements, materials and components used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operational requirements without departing from those principles. The claims are therefore intended to cover and embrace such modifications within the limits only of the true spirit and scope of the invention. In particular, it will be appreciated that while a finger has been described for the creation of an electronic image of a fingerprint, other objects having ridges or varied surfaces (e.g. toes, noses and other human parts as well as inanimate surfaces) are encompassed by the present invention.