Method and apparatus for measuring structures in a fingerprint

• US 20040213441A1
• Filed: 05/19/2004
• Published: 10/28/2004
• Est. Priority Date: 06/16/1997
• Status: Active Grant

• Current Assignee: SINTEF
• Original Assignee: SINTEF
• Inventors: Tschudi, Jon
• Granted Patent: US 7,054,471 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: A61B 5/1172 using fingerprinting
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/1335 Combining adjacent partial images (e.g. slices) to create a composite input or reference pattern; Tracking a sweeping finger movement

Abstract

A plurality of images of portions of a fingerprint surface is generated by measuring structural features the portions of the surface with a sensor array as the surface is moved relative to the array. A two-dimensional image of the fingerprint surface is constructed from a portion of the plurality of images. In one embodiment, a varying voltage is applied to a finger positioned over an exciting electrode and a capacitive sensor array, and the capacitance or impedance through the finger is measured between the electrode and the array to detect variations in capacitance or impedance caused by variations in the structural features of the fingerprint surface. In one embodiment, the speed of the fingerprint surface relative to the sensor array is determined by sensing features of the fingerprint surface at two spaced-apart sensing elements and determining the speed from the distance between the sensing elements and the time lapse between passage of identical features of the fingerprint surface from one of the sensing elements to the other.

Claims

1. A method for sensing a fingerprint comprising:

generating a plurality of images of different portions of a fingerprint surface by measuring structural features of the fingerprint surface at given intervals of time with an essentially one-dimensional sensor array as the fingerprint surface is moved relative to the sensor array in a direction that is generally perpendicular to the sensor array; and

constructing a two-dimensional image of the fingerprint surface from a portion of the plurality of images obtained from said generating step;

wherein said portion of the plurality of images is defined by neglecting selected images of the plurality of images generated during said generating step and thereafter constructing the two-dimensional image from the remaining images.

2. The method of claim 1, wherein the selected images are images containing measurement data that is redundant with the measurement data of a previous image generated during said generating step.

3. The method of claim 1, wherein the remaining images consist of each second or third image of the plurality of images generated during said generating step.

4. The method of claim 1, wherein said measuring is performed at each of a plurality of equally spaced measuring points arranged in at least one line corresponding to the essentially one-dimensional sensor array.

5. The method of claim 1, wherein said measuring is performed simultaneously at each of a plurality of equally spaced measuring points arranged in at least two generally parallel lines spaced apart by a distance different from the distance separating the measuring points, wherein the measuring points of one line are shifted longitudinally with respect to the measuring points of the next line, and wherein said generating is performed from measurements performed at one of the at least two lines.

6. A method for sensing a fingerprint comprising:

generating a plurality of images of different portions of a fingerprint surface by measuring structural features of the fingerprint surface at given intervals of time with a sensor array as the fingerprint surface is moved relative to the sensor array;

ascertaining the speed of movement of the fingerprint surface relative to the sensor array by sensing structural features of the fingerprint surface moved over two sensing elements spaced apart by a predetermined distance and determining the speed from the predetermined distance and a time lapse between passage of identical structural features of the fingerprint surface from one of the two sensing elements to the other; and

forming a two-dimensional image of the fingerprint surface using a portion of the plurality of images,

wherein the portion of the plurality of images is defined by neglecting images at regular specified intervals as determined by the ascertained speed and thereafter forming the two-dimensional image from the remaining images.

7. The method of claim 6, wherein the remaining images consist of each second or third image of the plurality of images generated during said generating step.

8. The method of claim 6, wherein one of the two sensing elements comprises a sensor in the sensor array.

9. The method of claim 6, wherein each of the two sensing elements is disposed in a different one of two groups of sensing elements arranged in two spaced-apart, generally parallel lines of sensing elements.

10. A method for sensing a fingerprint comprising:

applying a varying voltage to a finger positioned over an electrode;

measuring the capacitance or impedance between the electrode and an essentially one-dimensional capacitive sensor array through a fingerprint surface positioned over both the electrode and the capacitive sensor array, wherein the capacitive sensor array is separately disposed from the electrode and the array of capacitive sensors is adapted to detect variations in capacitance or impedance across the array caused by structural features of a portion of the fingerprint surface positioned over the array;

generating a plurality of images of different portions of a fingerprint surface by measuring structural features of the fingerprint surface at given intervals of time with the capacitive sensor array as the fingerprint surface is moved relative to the sensor array in a direction that is generally perpendicular to the sensor array;

ascertaining the speed of movement of the fingerprint surface relative to the sensor array by sensing structural features of the fingerprint surface moved over two sensing elements spaced apart by a predetermined distance and determining the speed from the predetermined distance and a time lapse between passage of identical structural features of the fingerprint surface over the two sensing elements; and

constructing a two-dimensional image of the fingerprint surface from a portion of the plurality of images obtained from said generating step,

wherein said portion of the plurality of images is defined by neglecting selected images of the plurality of images generated during said generating step and thereafter constructing the two-dimensional image from the remaining images.

11. The method of claim 10, wherein said portion of the plurality of images is defined by neglecting images at regular specified intervals as determined by the ascertained speed.

12. The method of claim 11, wherein the remaining images consist of each second or third image of the plurality of images generated during said generating step.

13. The method of claim 10, wherein the selected images are images containing measurement data that is redundant with the measurement data of a previous image generated during said generating step.

14. An apparatus for sensing a fingerprint comprising:

an essentially one-dimensional sensor array and associated circuitry constructed and arranged to generate a plurality of images of different portions of a fingerprint surface by measuring structural features of the fingerprint surface at given intervals of time as the fingerprint surface is moved relative to said sensor array in a direction that is generally perpendicular to said sensor array;

at least one pair of sensing elements, where the sensing elements in each pair are spaced apart by a predetermined distance and are constructed and arranged to sense structural features of the fingerprint surface moved over said two sensing elements of each pair, to determine a time lapse between passage of identical structural features over one sensing element and then the other, and to determine the speed of movement of the fingerprint surface relative to the sensor array from the predetermined distance and the time lapse; and

means for constructing a two-dimensional image of the fingerprint surface from a portion of the plurality of images generated by said sensor array,

wherein said portion of the plurality of images is defined by neglecting selected images of the plurality of images generated during said generating step and thereafter constructing the two-dimensional image from the remaining images.

15. The apparatus of claim 14, wherein the selected images are images containing measurement data that is redundant with the measurement data of a previous image generated during said generating step.

16. The apparatus of claim 14, wherein the remaining images consist of each second or third image of the plurality of images generated during said generating step.

17. The apparatus of claim 14, further comprising an electrode and associated circuitry constructed and arranged to apply a varying voltage to a finger positioned over said electrode, wherein said sensor array is separately disposed from said electrode, and wherein said sensor array is a constructed and arranged to measure the capacitance or impedance between said electrode and said sensor array through a fingerprint surface positioned over both said electrode and said sensor array and to detect variations in capacitance or impedance across said array caused by structural features of a portion of the fingerprint surface positioned over said array.

18. The apparatus of claim 14, wherein one of the two sensing elements of each pair comprises a sensor in the sensor array.

19. The apparatus of claim 14, wherein each of the two sensing elements of each pair is disposed in a different one of two groups of sensing elements arranged in two spaced-apart, generally parallel lines of sensing elements.