Fingerprint identification system based on raster structure and microprism array

A technology of fingerprint identification and grating structure, which is applied in the direction of prism, diffraction grating, character and pattern recognition, etc. It can solve the problems of difficult miniaturization, difficult miniaturization, and large overall structure, so as to increase the contrast of fingerprint images and reduce finger scattering The effect of precise optical path control

Active Publication Date: 2016-07-13
SHANGHAI JIAO TONG UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The traditional optical fingerprint recognition system generally has three disadvantages: the structure is bulky and difficult to miniaturize; the optical path is greatly affected by the diffuse reflection of fingers, and the imaging quality is not high; the sliding fingerprint scanning method is used, and the user experience is poor
U.S. Patent US5177802 discloses a structure that uses prisms to read fingerprint images. However, due to the use of prisms, this structure is difficult to miniaturize and cannot be used in mobile terminals such as smart phones and tablet computers.
Chinese patent CN1820272A discloses a system that uses an

Method used

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  • Fingerprint identification system based on raster structure and microprism array
  • Fingerprint identification system based on raster structure and microprism array
  • Fingerprint identification system based on raster structure and microprism array

Examples

Experimental program
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Example Embodiment

[0059] Example 1

[0060] From the formula (5), In order to get a smaller thickness h, in L 1 Under certain circumstances, the diffraction angle j should be set as close to 90° as possible. Combining equation (2), considering the lateral propagation, set the diffraction angle j to 85°θ 1 Is 5°, the corresponding grating period is 370nm, and the incident light wavelength is 550nm. For normal incidence of air, the refractive index of air n 0 =1, the most commonly used polymethyl methacrylate is selected as the waveguide material, and its refractive index is n 1 =1.49, the refractive index of the finger surface is about 1.39~1.42, and the combination of formula (13) can get 16.11° Figure 5 As shown, the illuminance of the valley pattern in the fingerprint pattern received by the imaging device is close to 0, and the contrast is close to 95%. As the angle increases, the fingerprint pattern appears slightly blurred, and the contrast also drops to 89%. This is because the smaller the θ...

Example Embodiment

[0061] Example 2

[0062] For normal incidence of air, the refractive index of air n 0 =1, waveguide refractive index n 1 =1.49, the refractive index of the finger surface is about 1.39~1.42, set θ=25°, the diffraction angle j is 85°, θ 1 Set to 5°. When the unit width d of the microprism is different, the fingerprint patterns obtained are also different. Using software simulation to simulate the width of the triangle base of different microprism cross-sections, the results are as follows Image 6 Shown. It is ideal for d=0.05mm. When d is larger than 0.1mm, since the width of the bottom side increases, the depth of the prism section will increase when the θ angle is constant, making it more difficult for the finger to touch, so the fingerprint pattern Streaks will appear. Therefore, for the selection of the unit width d of the microprism, the smaller the better, but considering the limitation of the processing technology, d=0.05mm is more appropriate.

Example Embodiment

[0063] Example 3

[0064] For normal incidence of air, the refractive index of air n 0 =1, waveguide refractive index n 1 =1.49, the refractive index of the finger surface is about 1.39, set θ=25°, diffraction angle j is 85°, d is 0.05mm, when θ 1 When the settings are different, the fingerprint patterns obtained are also slightly different, such as Figure 7 As shown, if θ 1 When the smaller is 1°, then θ 1 The side of the prism where it is located will reflect part of the light, which will reduce the useful light and reduce the image contrast; if θ 1 When the larger is 35°, the fingerprint detection area is more rugged, and the finger is not easy to touch the bottom of the microprism, thus reducing the image contrast and user experience; when θ 1 At 5°, the ruggedness is appropriate, and a high-contrast and clear fingerprint pattern is obtained.

[0065] Experiments show that the present invention uses the diffraction of the grating, the light from the light source is diffracted by...

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Abstract

Provided is a fingerprint identification system based on a raster structure and a microprism array, comprising a light source, an optical waveguide, a microprism array, a raster, a fingerprint detection area and an image device. The system employs a raster structure on the optical path of a light source entering the optical waveguide, allowing the light emitted by the light source to be diffracted by the raster and then propagate horizontally in the optical waveguide so as to form fingerprint detection light, and controls a raster period to avoid overlapping between a fingerprint identification area and a raster area, thereby guaranteeing the signal to noise ratio of a fingerprint graph; in order to more easily damage the total reflection of the fingerprint identification area, the surface of the optical waveguide is provided with a microstructure of a specific shape to change the normal direction of a total reflection surface, thereby substantially increasing a signal to noise ratio of a fingerprint image, meanwhile greatly reducing the thickness of the optical waveguide, and realizing a miniature and ultra-thin system.

Description

technical field [0001] The invention relates to the technical field of optical fingerprint imaging, in particular to a fingerprint identification system based on a grating structure and a microprism array. Background technique [0002] Fingerprint identification technology can be classified into three categories: optical, capacitive, and radio frequency, according to the way of fingerprint image collection. When the finger touches, the corresponding sensor detects the corresponding physical quantity and converts it into an electrical quantity to form a fingerprint image for comparison and identification. [0003] The biological radio frequency method transmits a small amount of radio frequency signal through the sensor, penetrates the skin layer of the finger to obtain the texture information of the inner layer, the energy loss of the radio frequency signal caused by the ridges and valleys of the finger fingerprint is different, and the receiver forms a fingerprint image thr...

Claims

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Application Information

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IPC IPC(8): G02B5/18G02B5/04G02B27/42G06K9/00
CPCG02B27/4205G02B5/045G02B5/1842G06V40/1324
Inventor 叶志成马萍
Owner SHANGHAI JIAO TONG UNIV
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