Fingerprint Scanner Optics for Moisture-Resistant Pore Imaging
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Solution Overview
Problem
Conventional fingerprint scanners struggle to reliably capture images of pores on fingers due to moisture interference, leading to indistinguishable pores from friction ridges, especially with varying moisture levels.
Innovation Solution
A high-resolution optical system with Moisture Discriminating Optics (MDO) and a precision optical chassis using carbon fiber raceway plates and crossmembers, capable of capturing 3D images to differentiate between closed and open pores, even in the presence of water-like fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical scanners are used to capture fingerprint images, then the imaging process is simple and fast, but moisture on the finger surface causes pores to become indistinguishable from friction ridges, reducing identification accuracy
Solution Approach 1:
The patent changes the optical parameters by using multiple wavelengths of light and adjusting the angle of light incidence. The sensor detects light at angles greater than the critical angle for water-like fluids, which causes total internal reflection at moisture interfaces while allowing light to pass through dry skin. This parameter change enables differentiation between moist and dry regions, making pores visible even when moisture is present on the finger surface.
Solution Approach 2:
The optical system uses a composite approach by combining multiple light sources emitting different wavelengths with a sensor array configured at specific angles. This composite optical system processes both reflected and transmitted light components separately, then combines the information to produce images where pores are distinguished from ridges regardless of moisture presence.
2Measurement precision
If high-resolution imaging is implemented to capture pore details, then identification accuracy improves, but the system becomes more sensitive to environmental effects and optical path variations
Solution Approach 1:
The sensor array is segmented into multiple independent detection elements positioned at different angles relative to the platen surface. Each sensor element captures light from a specific angular range, allowing the system to process information from multiple perspectives. This segmentation enables high-resolution pore imaging while reducing sensitivity to environmental variations through redundant measurement paths.
Solution Approach 2:
The patent introduces an intermediary optical processing stage that includes multiple light sources and a complex optical path with mirrors and lenses. This intermediary system transforms the raw light interactions into standardized sensor signals, isolating the high-resolution detection from environmental disturbances and simplifying the overall system control.
3Reliability
If the sensor detects light at angles greater than the critical angle for water-like fluids, then moisture discrimination capability is achieved, but the optical path design becomes more complex
Solution Approach 1:
The system transitions from conventional normal-incidence optical detection to angular-dimensional detection. By positioning sensors to detect light at angles greater than the critical angle for water-like fluids, the system exploits the dimensional difference in light propagation paths. This angular dimension provides natural moisture discrimination through total internal reflection effects without requiring complex additional optical components.
Solution Approach 2:
The optical system is designed with multi-functionality by using the same light sources and sensor array to perform both fingerprint imaging and moisture discrimination simultaneously. The angular configuration serves dual purposes: capturing high-resolution pore images and detecting moisture presence through differential light reflection, eliminating the need for separate moisture sensing hardware.
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
Enables consistent and accurate imaging of fingerprint pores, enhancing identification accuracy by leveraging pore location, reducing variability, and minimizing environmental effects on optical path integrity.
Implementation Method 1
the sensor and the platen are positioned relative to one another so that the sensor detects light propagating from the platen surface at an angle relative to a surface normal of the platen, wherein the angle is greater than the critical angle corresponding to an interface of the platen and water
Data Source
AI summary
In general, one aspect disclosed features a fingerprint scanner, comprising: a platen comprising a light-reflecting surface; a light source configured to emit light rays to illuminate a finger placed in proximity to the light-reflecting surface of the platen; and a sensor configured to capture image data of the finger in proximity to the light-reflecting surface of the platen; wherein the sensor and the platen are positioned relative to one another so that the sensor detects light having an axis of propagation which is at an angle relative to a surface normal of the platen, wherein the angle is greater than the critical angle corresponding to an interface of the platen and water, and less than the critical angle corresponding to an interface of the platen and the finger being imaged.