Direct Optical Fingerprint Scanner With Contrast Aperture Layer
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Solution Overview
Problem
Direct optical scanners face challenges in achieving high contrast between skin peaks and valleys, especially under unfavorable conditions, due to their design without prisms or lens-based optics, leading to lower Michelson contrast compared to classic prism-based devices, making them less robust against ambient light and varying skin types.
Innovation Solution
A layer sequence is designed with a contrast aperture layer that selectively transmits light at large angles of incidence, blocking light at small angles, ensuring each light-sensitive element is covered by the contrast aperture to enhance contrast, and includes a spacer layer to adjust the distance between the aperture and the element, along with an illumination layer to suppress total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If direct optical scanning without prisms or lens-based optics is used, then device size and weight are reduced, but image contrast between skin peaks and valleys deteriorates
Solution Approach 1:
An aperture layer is introduced as an intermediary component between the sensor layer and cover layer. This aperture layer selectively transmits light at large angles of incidence while blocking light at small angles, serving as a mediator to enhance contrast without requiring heavy prism components. The aperture layer acts as the key intermediary element that enables direct scanners to achieve high contrast imaging.
2Device complexity
If direct optical scanning without prisms or lens-based optics is used, then device complexity is reduced, but robustness against ambient light deteriorates
Solution Approach 1:
The aperture layer is designed with spatially varying properties where each aperture's position and size are locally optimized to control light from specific directions. This local quality approach allows the system to selectively block ambient light from certain angles while maintaining sensitivity to reflected light from the skin surface, enhancing robustness without increasing overall system complexity.
3Measurement precision
If aperture layer is designed to transmit light at large angles of incidence, then contrast between skin peaks and valleys is enhanced, but light sensitivity of individual pixels is reduced
Solution Approach 1:
The aperture layer blocks a portion of the light (excessive action) to enhance contrast by eliminating unwanted small-angle light. Although this reduces the total light reaching each pixel, the contrast enhancement is prioritized as the partial action of blocking certain angles produces superior image quality that outweighs the reduction in overall light sensitivity.
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
The solution enhances brightness differences between skin peaks and valleys to match or exceed the contrast of classic FTIR systems, ensuring high-quality imaging even under poor conditions, and allows for capturing documents with sufficient contrast using the same sensor.
Implementation Method 1
The illumination layer is configured to suppress total internal reflection at the contact surface of the cover layer
Implementation Method 2
A contrast aperture layer is provided in the layer sequence above the sensor layer, the contrast aperture layer comprising non-transparent and transparent areas for limiting the angle of incidence of light that is remitted from the object to be recorded through the contact surface into the layer sequence
Data Source
Figure 1~2a
Figure 2b~3
Figure 4a~4b
AI summary
The invention relates to a device for directly optically recording security-relevant objects, such as at least skin prints but also documents. The problem of producing, in case of direct optical sensors for recording skin prints, a contrast between skin peaks and skin valleys that lies in the contrast range of classical systems having frustrated total internal reflection is solved according to the invention by providing a contrast aperture layer (403) having contrast apertures, each light-sensitive element (303) of the sensor layer (406) being assigned exactly one contrast aperture (301) of the contrast aperture layer (403), the assigned contrast aperture (301) being arranged above the light-sensitive element (303) at a distance and having an area that is at least as large as an active region (305) of the light-sensitive element (303), and the contrast aperture (301) being arranged at a distance above the light-sensitive element (303) in such a way that the active region (305) of the light-sensitive element (303) is at least 60% covered, and the illumination layer (409) containing a plurality of point light sources (306), which emit toward the contact surface (102) in a limited angle range in order to avoid total internal reflection.