Capacitive Fingerprint Sensor with Grounded Peripheral Electrodes
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Solution Overview
Problem
Current fingerprint sensing systems for smartcards face challenges with high power consumption, high costs due to memory requirements, and slow verification speeds, particularly in developing regions where contact-based infrastructure limits access and compatibility with mobile devices.
Innovation Solution
A capacitive fingerprint sensing system using a two-dimensional array of sensor capacitors with central and peripheral electrodes, where the peripheral electrodes are connected to ground potential, allowing for efficient detection of fingerprint topology without the need for an external metal ring, reducing power consumption and data storage needs through selective capacitance measurement and data compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional capacitive sensor array with surrounding metal ring is used, then fingerprint detection is achieved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts and removes the surrounding metal ring (bezel) from the conventional capacitive sensor array design. The sensor electrodes are directly patterned on the smartcard surface without requiring an external metal ring structure, thereby simplifying the device construction while maintaining fingerprint detection capability
Solution Approach 2:
The smartcard itself serves multiple functions: it acts as both the substrate and the sensor structure. The conductive layers on the smartcard surface function as both the card identifier and the capacitive sensor electrodes, eliminating the need for separate sensor components
2Measurement precision
If conventional capacitive fingerprint sensing is used, then fingerprint verification is achieved, but power consumption increases
Solution Approach 1:
The patent implements selective area scanning where only specific regions of the fingerprint are scanned based on their information content. Areas with rich fingerprint details are scanned at full resolution while other areas are scanned at reduced resolution or skipped entirely, thereby reducing the total number of sensor readings and power consumption
Solution Approach 2:
The system dynamically adjusts scanning parameters such as resolution and scan area based on the detected fingerprint features. The sensor operates at different capacitance measurement levels depending on the required verification accuracy, optimizing power consumption for each scanning operation
3Loss of information
If full area scan of fingerprint is performed, then complete fingerprint data is obtained, but memory requirements and cost increase
Solution Approach 1:
The patent extracts only the essential fingerprint features from the complete fingerprint image. Instead of storing all sensor data, the system identifies and extracts key characteristics such as ridge patterns, minutiae points, and other discriminative features, storing only this extracted information in memory
Solution Approach 2:
The system applies different data processing and storage strategies to different regions of the fingerprint. Areas containing critical verification information are captured at high detail and stored, while regions with redundant information are processed at lower resolution or discarded, optimizing memory utilization
4Reliability
If conventional fingerprint processing is performed, then verification is achieved, but processing time increases
Solution Approach 1:
The patent performs preliminary processing of fingerprint data during the scanning phase itself. The sensor system pre-identifies regions of interest and extracts key features during acquisition, so that when verification is needed, the data is already prepared and organized, eliminating the need for extensive post-processing
Solution Approach 2:
The system processes only the necessary portions of fingerprint data at full computational intensity. By identifying and focusing computational resources on critical fingerprint regions and features, the system achieves accurate verification without processing the entire fingerprint image at maximum resolution
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 system enables fast, low-power, and cost-effective fingerprint verification, suitable for mobile devices like smartcards, with reduced data storage requirements and improved verification speed by focusing on detail-rich areas for enhanced authentication accuracy.
Implementation Method 1
changes of the electric (stray) fields between each of the central electrode and the peripheral electrode of the plural sensor capacitors upon positioning a finger close to the sensor system is used to detect the fingerprint
Implementation Method 2
changes of the electric (stray) fields between each of the central electrode and the peripheral electrode
Data Source
AI summary
It is described an arrangement (560, 660, 760) for fingerprint sensing/verification, comprising: a sensor system (100) comprising plural sensor capacitors (101), each sensor capacitor including a central electrode (103) and a peripheral electrode (105) annularly surrounding the central electrode and being connected to a ground potential; wherein changes of the electric fields between each of the central electrode and the peripheral electrode of the plural sensor capacitors upon positioning a finger (317) close to the sensor system is used to detect the fingerprint.