Biometric Sensor Card Coating for Capacitance Homogenization
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Solution Overview
Problem
Biometric sensor cards face issues with aesthetic appearance and sensor protection due to visible light exposure between the sensor and card body, leading to potential degradation and impact on fingerprint recognition accuracy.
Innovation Solution
A biometric sensor card with a capacitive fingerprint sensor coated using a layered material system, where different dielectric materials with specific thicknesses and patterns are applied to the external surface, homogenizing capacitance and protecting the sensor while enhancing tactile identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is deposited on the capacitive sensor, then the sensor is protected from external aggression and visual demarcation is reduced, but the fingerprint image quality may be degraded
Solution Approach 1:
The patent applies a composite coating structure with multiple layers having different dielectric properties. The first layer has a first dielectric constant and the second layer has a second dielectric constant, where the ratio of dielectric constants compensates for the ratio of layer thicknesses. This composite structure provides both protection and optical uniformity while maintaining sensor performance.
Solution Approach 2:
The patent controls the dielectric parameters of the coating layers to achieve capacitance homogenization. By adjusting the dielectric constants and thicknesses of the layers according to the relationship (ε1/d1) ≈ (ε2/d2), the coating becomes electrically transparent to the capacitive sensor, allowing protection without degrading fingerprint image quality.
2Reliability
If a coating is deposited on the capacitive sensor, then the sensor is protected from external aggression, but the capacitance uniformity may be altered
Solution Approach 1:
The patent uses a composite multi-layer coating where each layer has specifically controlled dielectric properties. The combination of layers with different dielectric constants compensates for thickness variations, maintaining uniform capacitance across the sensor surface while providing comprehensive protection.
Solution Approach 2:
The patent applies different dielectric materials in different layers to achieve local compensation of capacitance variations. The first layer addresses certain thickness variations while the second layer compensates for remaining non-uniformities, ensuring overall capacitance homogeneity.
3Shape
If the sensor surface is coated to unify appearance, then visual demarcation is reduced, but tactile identification may be affected
Solution Approach 1:
The patent applies the coating only on specific regions of the sensor surface, leaving certain areas uncovered or differently treated. This allows the coated areas to provide visual uniformity while the uncovered areas maintain tactile characteristics for user identification.
Solution Approach 2:
The patent applies coating partially on the sensor surface rather than completely covering it. This partial application provides sufficient visual unification while preserving tactile feedback areas, achieving the desired balance between appearance and usability.
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 coating minimizes fingerprint quality degradation, protects the sensor from external aggression, and unifies the appearance by reducing visual demarcation between the sensor and card body, thereby improving recognition accuracy and user experience.
Implementation Method 1
said sensitive film being configured to form a capacitor with the user's finger
Implementation Method 2
said coating comprising at least a first part made of a first material of a first dielectric value and having a first thickness, said sensitive film covered with said at least one first part being configured to form a capacitor of a first capacitance
Data Source
Figure 1~2
Figure 3~4
AI summary
Biometric sensor card comprising a body and a capacitive fingerprint sensor, said sensor comprising a sensitive film configured to form a capacitor with a user's finger and a dielectric film covering the sensitive film and defining an external surface of the sensor, the card comprising a coating covering at least the external surface and comprising at least a first part, the sensitive film covered by at least a first part being configured to form a capacitor of a first capacitance with the user's finger applied to this first part, said coating comprising at least a second part, said sensitive film covered by said at least a second part being configured to form a capacitor of a second capacitance with the user's finger applied to this second part, the second capacitance having a value between 0.9 and 1.1 times that of the first capacitance.