Method for initializing an electro-optical material and system for capturing a fingerprint image

Abstract

A fingerprint image capture system comprises an electro-optical material which captures a static fingerprint image and an apparatus for converting the static fingerprint image into an electronic signal. The image capture system includes an electrode for contacting a finger, and a bias supply for creating an electric field where epidermal ridges contact the electro-optical material. A transistor array senses charge or optical density variations in the electro-optical material to create an electronic representation of the fingerprint image. An initialization electrode places the electro-optical material into a uniform condition prior to acquisition of the fingerprint image. A physical artifact of the fingerprint image can be archived by removing the electro-optical material from the system following the fingerprint image acquisition.

What is claimed is: 
     
         1 . A method for initializing an electro-optical material prior to acquiring a fingerprint image using the electro-optical material, the method comprising:
 coupling a first bias supply terminal to an electrode layer on a first side of the electro-optical material;   coupling a second bias supply terminal to an initialization electrode which is mechanically brought into contact with a second side of the electro-optical material, the second side being opposed to the first side; and   coupling a direct current bias supply to the first bias supply terminal and the second bias supply terminal.   
     
     
         2 . The method of  claim 1 , wherein the initialization electrode is a flexible conductive film. 
     
     
         3 . The method of  claim 1 , wherein the electro-optical material is an electrophoretic display material. 
     
     
         4 . A method for initializing an electro-optical material prior to acquiring a fingerprint image using the electro-optical material, the method comprising:
 illuminating the electro-optical material while the electro-optical material is electrically floating and able to reach a uniform electrical potential throughout its volume.   
     
     
         5 . The method of  claim 4  wherein the electro-optical material is an electrochromic material. 
     
     
         6 . A system for capturing a fingerprint image, comprising:
 an electro-optical material, said electro-optical material being characterized by producing a change in optical properties in response to an applied electric field;   a bias supply capable of supplying a direct current potential to a first electrode of the electro-optical material;   a flexible initialization electrode coupled to the bias supply and capable of contacting the electro-optical material while applying an electrical bias to bring the electro-optical material into a condition of uniform appearance;   a finger contact electrode coupled to the bias supply and configured to induce an electric potential on a finger while the finger is in contact with the electro-optical material;   a thin film transistor array having gate lines, drain lines, and photodiodes, said transistor array configured to convert an optical signal incident upon a pixel into an electrical charge, the transistor array mechanically coupled to the electro-optical material during an electronic capture of a fingerprint image;   array addressing circuits configured to apply electrical control potentials to gate and drain lines in the thin film transistor array;   charge sense circuits coupled to the thin film transistor array through the array addressing circuits, the charge sense circuits configured to produce an electrical potential in proportion to the amount of charge present on a drain line of the thin film transistor array;   analog to digital conversion circuits coupled to the charge sense circuits, the analog to digital conversion circuits providing a digital representation of the electrical potentials produced by the charge sense circuit;   an illumination source configured to pass light through a fingerprint image present in the electro-optical material, the light emerging onto the thin film transistor array; and   a microprocessor-based control system which coordinates system control functions for bias control, array addressing, illumination, charge sense and digital conversion, image processing and storage.   
     
     
         7 . The system of  claim 6  wherein the electro-optical material is an electrophoretic material capable of being removed and physically archived after the fingerprint image capture is complete. 
     
     
         8 . The system of  claim 6  wherein the illumination source operates at a wavelength invisible to the human eye.