Capacitive and Optical Sensor Edge Matching for Spoof Detection
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Solution Overview
Problem
Fingerprint sensors face challenges in distinguishing between live and spoof fingers, leading to potential unauthorized access, as spoof fingers can mimic live fingerprints, compromising security.
Innovation Solution
A method combining a capacitive fingerprint sensor with an optical sensor, where both sensors capture images of neighboring portions of a finger, with edge matching and multi-wavelength optical imaging used to differentiate between live and spoof fingers, enhancing authentication security without requiring overlapping image regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single capacitive fingerprint sensor is used, then the device size and power consumption are kept low, but the authentication security is insufficient due to vulnerability to spoof fingers
Solution Approach 1:
The patent combines a capacitive fingerprint sensor and an optical sensor into a single integrated sensor system. The capacitive sensor array and optical sensor array are positioned adjacent to each other, sharing common structural elements such as the substrate, protective layer, and signal processing circuitry. This merging approach enables spoof detection through multi-modal sensing while maintaining a compact form factor and avoiding the complexity of completely separate sensor systems.
Solution Approach 2:
The integrated sensor system performs multiple functions: the capacitive sensor captures ridge-valley patterns for traditional fingerprint authentication, while the optical sensor detects subsurface blood flow patterns for liveness verification. This multi-functionality allows the system to authenticate both fingerprint identity and finger liveness, making it resistant to spoof attacks while using a unified sensor structure.
2Reliability
If a capacitive fingerprint sensor is used, then the form factor is small, but the ability to detect spoof fingers is limited
Solution Approach 1:
The patent transitions from single-modal surface sensing to multi-modal sensing that includes subsurface detection. The optical sensor penetrates through the fingerprint ridges and valleys to detect blood flow patterns beneath the skin surface, adding a depth dimension to the sensing capability. This enables spoof detection without significantly increasing the lateral sensor area, as the optical sensor shares the same footprint as the capacitive sensor array.
3Measurement precision
If edge matching between capacitive and optical images is performed, then spoof detection accuracy is improved, but the processing complexity increases
Solution Approach 1:
The patent divides the fingerprint verification process into distinct segments: the capacitive sensor captures ridge-valley pattern data, the optical sensor captures subsurface blood flow data, and a processing unit performs edge matching between the two image types. This segmentation allows for specialized processing of each sensor type's output and simplifies the overall algorithm by focusing comparison efforts on the border regions where spoof artifacts are most apparent.
Solution Approach 2:
The processing unit acts as an intermediary that receives raw data from both sensors, performs edge matching analysis, and generates authentication decisions. This intermediary layer abstracts the complex comparison operations from the sensor hardware itself, allowing the sensors to remain simple while enabling sophisticated spoof detection through software-based image correlation and feature matching at the image boundaries.
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 improves authentication security by accurately differentiating between live and spoof fingers, reducing unauthorized access through enhanced edge matching and optical properties analysis, while maintaining a compact sensor structure.
Implementation Method 1
All capacitive fingerprint sensors provide an indicative measure of the capacitance between several sensing elements and a finger placed on the surface of the fingerprint sensor
Implementation Method 2
an optical sensor arranged side-by-side with the capacitive fingerprint sensor, the optical sensor comprising an array of optical sensor units arranged adjacent to the array of sensing structures in the sensing structure plane, the optical sensor being configured to obtain an optical image of a second portion of the user's finger
Data Source
AI summary
The present invention generally relates to authenticating a user of an electronic device comprising a capacitive fingerprint sensor and an optical sensor arranged side-by-side with the capacitive fingerprint sensor. In accordance with the present invention a first image of at least a first portion of an object is acquired using the capacitive fingerprint sensor and an optical image of at least a second portion of the object is acquired using the optical sensor, the optical image and the first image being representative of neighboring portions of the object. An edge portion of the first image is matched with at least an edge portion of the optical image, where the edge portions represent the object at the border between the capacitive fingerprint sensor and the optical sensor. When there is a match, a fingerprint authentication procedure may be performed.