Smartcard Fingerprint Sensor Dummy Finger Detection Circuit
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Solution Overview
Problem
Fingerprint sensors on smart cards, such as payment cards, are vulnerable to fraudulent authentication attempts using fake or replicated fingers, as existing technologies lack effective methods to distinguish between human and dummy fingers.
Innovation Solution
A smart card with a detection circuit comprising a first and second electrode forming an open circuit, a filter circuit, and processing means that generate and analyze signals to differentiate between human and dummy fingers based on impedance and phase shift characteristics, using reference data from real human fingers to validate authenticity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fingerprint sensor is used for authentication, then user convenience is improved, but security against fraudulent authentication deteriorates
Solution Approach 1:
The patent applies parameter changes by measuring electrical impedance characteristics of the finger at multiple frequencies and comparing them against reference values. The system varies the measurement frequency parameter to detect differences between real and fake fingers, thereby maintaining convenience while improving security against fraudulent authentication attempts
Solution Approach 2:
The patent implements feedback by continuously monitoring impedance measurements and comparing them against stored reference data. The system provides real-time feedback to determine whether the finger is genuine or fake, enabling dynamic security verification that maintains user convenience while preventing fraud
2Device complexity
If simple fingerprint sensing is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the impedance measurement into multiple frequency components (different measurement frequencies). This allows the system to extract more detailed information about the finger's electrical characteristics without requiring a single complex sensor, thereby improving measurement precision while keeping device complexity manageable
Solution Approach 2:
The patent implements universality by using a multi-frequency impedance measurement system that can serve multiple detection purposes. The same measurement circuitry is used to detect various characteristics of the finger (impedance, phase, frequency response), making the system more precise without proportionally increasing complexity
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
Enhances the security of fingerprint-based authentication by accurately distinguishing between genuine and fake fingers, thereby preventing unauthorized access.
Implementation Method 1
The loop, which extends between the end of the first finger, for example the thumb of one hand of the individual, and the end of the second finger, for example the index finger of the same hand, forms a filter whose the impedance is very different depending on whether the two fingers are human fingers or include a dummy finger.
Implementation Method 2
the first signals comprise sinusoidal signals each having a distinct transmission frequency, the processing means being arranged to acquire a second signal for each frequency resignation
Implementation Method 3
the processing means are arranged to estimate a phase shift of each second signal, to produce a phase shift signal as a function of the transmission frequency
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Smart card comprising a fingerprint sensor and a detection circuit (5) including at least a first electrode (6) and a second electrode (7) insulated from each other and forming an open circuit (8), the first electrode and the second electrode being arranged so that, when a user applies a first finger to the fingerprint sensor and uses a second finger to grasp the smart card, the first finger is in contact with the first electrode and the second finger with the second electrode so as to form a loop closing the open circuit, the detection circuit (5) further comprising a filtering circuit (10) connected to the first electrode and the second electrode, a generator (17) arranged to generate first signals across the terminals of the filtering circuit,and processing means (18) arranged to acquire second signals and to detect from the second signals whether the first and second fingers include a dummy finger.