Planar Light Guide Plate for Multi-Finger Fingerprint Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current fingerprint scanning devices using disturbed total reflection struggle with achieving high image quality while maintaining a compact, flat size, especially when recording multiple fingers or hands, due to issues with illuminance distribution and mechanical complexity, leading to suboptimal contrast and resolution.
Innovation Solution
The device employs a light source that emits light in a limited angular range to maximize total reflection, combined with a mirror layer for light homogenization and a thick protective body, allowing for simultaneous recording of multiple fingers with improved illuminance distribution and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a prism is used for capturing fingerprints with disturbed total reflection, then high image quality is achieved, but the device size and mass increase
Solution Approach 1:
The patent extracts the light-guiding function from a traditional large prism and implements it using a planar light guide plate with controlled total internal reflection. The light guide plate is integrated directly into the sensor substrate, removing the need for a separate bulky prism component while maintaining the disturbed total reflection mechanism for high-quality fingerprint capture.
Solution Approach 2:
The invention transitions from a three-dimensional prism structure to a two-dimensional planar light guide plate. By changing the geometric dimensionality, the patent achieves the same optical function (disturbed total reflection) with a much smaller footprint and reduced mass, enabling compact device design without sacrificing image quality.
2Measurement precision
If a prism is used for capturing fingerprints with disturbed total reflection, then high image quality is achieved, but the device becomes less flat and more complex
Solution Approach 1:
The patent merges the light guide function with the sensor substrate by integrating the light guide plate directly into the fingerprint sensor structure. This consolidation eliminates the need for separate mechanical components and complex assembly mechanisms, reducing device complexity while maintaining the optical principles needed for high-quality imaging.
Solution Approach 2:
The invention replaces complex mechanical adjustment mechanisms with an optically integrated light guide plate that uses controlled total internal reflection. The optical path is defined by the refractive index differences and geometric configuration of the planar structure rather than mechanical components, simplifying the overall system design and reducing mechanical complexity.
3Productivity
If multiple fingers are recorded simultaneously, then throughput is improved, but illuminance distribution becomes non-uniform
Solution Approach 1:
The patent applies local quality by varying the light guide plate thickness or refractive index properties at different locations to compensate for the natural decline in illuminance with distance from the light source. This ensures that fingers at different positions on the sensor surface receive uniform illuminance, enabling simultaneous recording of multiple fingers with consistent image quality across the entire active area.
4Productivity
If the light guide is made larger to support multiple fingers, then simultaneous recording is enabled, but the device size increases
Solution Approach 1:
The patent uses a thin-film light guide plate that can be made large in area while maintaining a minimal thickness profile. This thin-film structure enables the light guide to cover a large active area for simultaneous multi-finger recording without significantly increasing the device's vertical height or overall footprint, maintaining a compact form factor despite the expanded functional area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables high-quality fingerprint imaging for multiple fingers or hands with uniform illuminance and reduced mechanical complexity, meeting stringent quality standards while allowing for document scanning and user guidance.
Implementation Method 1
The light guide is designed in the form of a plane-parallel plate and has a lower large side and an upper large side arranged parallel thereto... One of the narrow sides of the light guide is designed as a coupling surface for illumination light
Implementation Method 2
The sensor layer comprises arrayed, light-sensitive sensor elements for detecting light of at least one predetermined wavelength range... optical systems that operate according to the principle of disturbed total internal reflection
Data Source
Figure 1
Figure 2a~2b
Figure 2c~2d
AI summary
The invention relates to a device for the contact-based simultaneous recording of impressions of several vascularized skin areas of human autopodia by means of disturbed total internal reflection. Viewed from the direction of a contacting skin area, the device comprises a protective body (103) of a predetermined thickness with a contact surface (102), wherein the contact surface (102) has a size that allows the simultaneous contact of several autopodia. This is followed by a sensor layer (104) which comprises array-arranged, light-sensitive sensor elements (201) for detecting light of at least one predetermined wavelength range, wherein transmission areas (202) are arranged between the sensor elements (201) which are transparent to light of at least one predetermined illumination wavelength range.Finally, the device also includes an optical fiber (106) made of a material transparent to light of the specified illumination wavelength range, wherein the optical fiber (106) is designed in the form of a plane-parallel plate. The plane-parallel plate has a lower large side (155) and an upper large side (156) arranged parallel to it, which faces the sensor layer (104). The large sides (155, 156) are connected by several narrow sides, one of which is designed as an input surface (158) for illumination light, which is emitted by a light source (112) along a longitudinal direction of the input surface (158). According to the invention, the light source (112) emits light within a limited angular range around a preferred direction (113).The preferred direction (113) forms an angle of incidence with the large sides (155, 156) such that light emitted within this angle would be totally reflected at the large sides (155, 156) after entering the light guide (106) if the medium in contact with it had a refractive index of air. A reflective layer (105) is arranged between the sensor layer (104) and the light guide (106), which reflects part of the illumination light back into the light guide (106) and transmits another part. The device includes means for homogenizing the illuminance of the illumination light that exits the light guide (106) through its upper large side (156) and strikes the contact surface (102).Additionally or alternatively, the device also includes means for homogenizing a quantity of light to be detected depending on the illuminance of the illuminating light striking the support surface (102) from the protective body (103), wherein the homogenization takes place depending on the distance to the light source (112).