Geiger-mode photodiode array for covert fingerprint detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for remote and covert fingerprint detection, such as 3-D Laser Detection and Ranging (LADAR) sensors, face challenges in accurately differentiating fingerprint ridges and valleys due to insufficient contrast and require cooperation from the suspect, making them impractical for covert terrorist identification scenarios.
Innovation Solution
A system utilizing a photoreceptor array with at least a first and second photoreceptor configured to detect the relative difference in the time of arrival of electromagnetic radiation, allowing for the detection of textured surfaces like fingerprints without cooperation, using a fast charge-scavenging photodiode array that desensitizes regions to delayed radiation pulses, enabling contrast detection between ridges and valleys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 3-D Laser LADAR sensors are used for fingerprint detection, then range measurement capability is provided, but the sensor lacks the range resolution necessary to measure the height difference between fingerprint ridges and valleys
Solution Approach 1:
The patent changes the operational parameter of the photodetector from continuous detection to Geiger-mode operation with single-photon sensitivity. This parameter change enables the detection of extremely subtle range differences (sub-millimeter accuracy) by detecting the time-of-flight of individual photons, achieving the required measurement precision without proportionally increasing device complexity
Solution Approach 2:
The system uses pulsed laser illumination with specific timing characteristics to illuminate the target. By controlling the pulse duration and timing, and combining this with the Geiger-mode photodetector's single-photon detection capability, the system achieves high range resolution for fingerprint ridge-valley height measurement
2Measurement precision
If passive sensors are used for fingerprint detection, then the system is simple and covert, but there is insufficient contrast to differentiate ridges from valleys in the dermal papillae
Solution Approach 1:
The patent changes the detection parameter from intensity-based detection to time-of-flight-based detection. By measuring the time difference for photons to return from ridges versus valleys, the system achieves high contrast differentiation without requiring intense illumination or complex active illumination systems, maintaining both simplicity and effectiveness
Solution Approach 2:
The patent replaces traditional optical contrast mechanisms (which rely on illumination intensity and reflectivity differences) with a time-based measurement mechanism. This substitution allows ridge-valley differentiation based on the time-of-flight difference of photons, achieving high measurement precision without requiring high illumination intensity or complex optical setups
3Measurement precision
If commercial ladar sensors with binary range sensing are used, then sharp fingerprint detail can be obtained, but the suspect must place their finger on a flat optical surface requiring cooperation
Solution Approach 1:
The system is designed to automatically detect and image the fingerprint without requiring the suspect's cooperation or deliberate action. The Geiger-mode photodetector array passively detects the time-of-flight of photons reflected from the fingerprint surface, automatically generating a high-resolution image without requiring the suspect to place their finger on a specific surface or cooperate with the imaging process
4Measurement precision
If coherent ladar with high modulation bandwidth is used for texture pattern sensing, then effective fingerprint detection is achieved, but the system becomes very complex, bulky, and costly
Solution Approach 1:
The patent extracts and utilizes only the essential function needed for fingerprint detection - time-of-flight measurement of photons - without implementing the full coherent ladar system with high modulation bandwidth. By using Geiger-mode photodetectors that are inherently sensitive to single photons and can measure time-of-flight directly, the system achieves texture pattern detection accuracy without the complexity, size, and cost of a complete coherent ladar system
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 high-quality fingerprint imaging independently of dermal irregularities and finger orientation, providing a covert and non-cooperative means for fingerprint detection, suitable for terrorist identification and tracking.
Implementation Method 1
the photoreceptor array is configured to detect an image of the textured surface based on the relative difference between the time of arrival of the signals from the first and second photoreceptors
Implementation Method 2
A 3-D image may be created by associating the measured range from a small region of the target with the position of that region in sensor angular coordinates
Implementation Method 3
an in-band optical receiver to measure the time-of-flight of the photons to and from the target
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
A system (200) for imaging a textured surface (100) comprising includes a photoreceptor array (235) having: at least a first photoreceptor and a second photoreceptor, each configured to receive electromagnetic radiation (228) reflected from the textured surface (100) and to generate a signal corresponding thereto; wherein the photoreceptor array (235) is configured to detect an image of the textured surface (100) based on the relative difference between the time of arrival of the signals from the first and second photoreceptors. Methods for imaging a textured surface (100) and fabricating a photoreceptor array structure for imaging a textured surface (100) are also provided.