Optical Fiber Fingerprint Sensor for Fake Detection
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Solution Overview
Problem
Fingerprint identification systems face challenges in reliably distinguishing between genuine and fake fingerprints, particularly in cases of severed fingers or copied fingerprints, due to the limitations of existing capacitive and optical surface-area sensors.
Innovation Solution
The use of an optical fiber-based device that illuminates the surface with a light source and measures the reflected light through the same fiber, leveraging the refractive index difference between human skin and air to differentiate real fingers from fakes, while also detecting elevations and depressions using incident light, which is less affected by ambient light and surface thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitive or optical surface-area sensors are used for fingerprint identification, then the device structure is simple, but the system cannot reliably distinguish between genuine and fake fingerprints
Solution Approach 1:
The patent divides the measurement surface into multiple independently measurable zones, each with its own optical fiber and photosensor. This segmentation allows the system to detect elevations and depressions at multiple discrete points across the fingerprint surface, enabling reliable differentiation between genuine and fake fingerprints through multi-point topographic analysis rather than relying on a single complex sensor.
Solution Approach 2:
The patent introduces optical fibers as intermediary elements between the light source and the measurement surface. These optical fibers transmit light to illuminate the fingerprint and simultaneously collect reflected light to carry measurement signals back to the photosensors. This intermediary optical transmission system enables non-contact, multi-point measurement that reliably detects fingerprint topography without requiring complex direct sensor contact.
2Measurement precision
If transmitted-light method is used to measure surface elevations, then the measurement can penetrate through the surface, but the method is highly affected by ambient light and surface thickness variations
Solution Approach 1:
The patent inverts the traditional transmitted-light approach by using incident light illumination. Instead of shining light through the surface from below to detect transmitted light patterns, the system illuminates the surface from above and detects the reflected light. This inversion makes the measurement independent of surface thickness and ambient light conditions, as the reflected light intensity depends only on the local surface topography at each measurement point.
3Reliability
If glass plate surface is used for measurement, then the surface is smooth and easy to manufacture, but scratches and wear affect measurement values over time
Solution Approach 1:
The patent replaces the traditional rigid glass plate with a flexible measurement surface composed of numerous thin optical fibers arranged in a grid pattern. This fiber-optic membrane is inherently more durable because individual fiber failures do not compromise the entire surface - other fibers continue to function independently. The flexible film structure also better accommodates repeated contact and cleaning without developing scratches that would affect measurements.
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 approach provides enhanced security by accurately differentiating real fingers from fakes through dynamic changes in brightness and color, offering improved contrast and resistance to sabotage, with the ability to detect fake attempts within a short time frame.
Implementation Method 1
The optical characteristic of optical fibers, wherein the light beam at the output is coupled into the medium located there better or worse depending on the refractive index of the medium, is taken advantage of, and therefore less or more light is reflected back into the glass fiber of the fiber optics. Human skin behaves like a medium with a higher refractive index than air.
Implementation Method 2
the brightness of the reflected light is measured with a photosensor through the same optical fiber
Data Source
AI summary
In a device for measuring elevations and/or depressions of a flexible surface which is at least partially transmissive to light, for measurement purposes, the surface is illuminated by a fiber-optical means (3) by way of a light source (7) and the brightness of the reflected light is measured by the same fiber-optical means using a photosensor (1).