Ultrasonic Fingerprint Sensor Non-Uniform Contact Layer Correction
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Solution Overview
Problem
Current fingerprint sensors face challenges in accurately imaging fingers through non-flat or non-uniform surfaces, as existing technologies require specialized manufacturing to conform to these surfaces, which is costly and limits their adoption in commodity devices.
Innovation Solution
An ultrasonic fingerprint sensor with a substantially flat two-dimensional array of ultrasonic transducers and a non-uniform contact layer that adjusts operating parameters to correct for surface non-uniformity, using time-of-flight maps and gain maps to generate accurate images without modifying the transducer array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the sensor uses a flat transducer array, then manufacturing cost is reduced and ease of manufacture is improved, but the ability to image through non-flat surfaces deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the contact layer's thickness and material composition rather than changing the transducer array geometry. The contact layer is designed with non-uniform thickness (varying from 0.1mm to 1.0mm) and can include multiple materials with different acoustic properties, allowing the system to compensate for surface non-uniformity while keeping the transducer array flat and simple to manufacture
Solution Approach 2:
The contact layer serves as an intermediary element between the flat transducer array and the non-flat finger surface. This intermediate layer absorbs and compensates for surface irregularities, enabling accurate imaging through non-flat surfaces without requiring the transducer array itself to conform to the surface geometry
2Adaptability or versatility
If the contact layer is made non-uniform, then adaptability to non-flat surfaces is improved, but device complexity increases
Solution Approach 1:
The contact layer implements local quality by having different thicknesses and material compositions in different regions. This allows each local area of the contact layer to be optimized for its specific position on the sensor surface, providing adaptability to local surface variations while maintaining an overall simple device architecture
Solution Approach 2:
The system uses parameter changes in the contact layer (thickness, material composition) to achieve adaptability without increasing the complexity of the transducer array or requiring specialized manufacturing processes for the entire device
3Measurement precision
If operating parameters are adjusted to correct surface non-uniformity, then imaging accuracy is improved, but device complexity increases
Solution Approach 1:
The system implements feedback by measuring the actual thickness and acoustic properties of the contact layer using time-of-flight measurements, then using this information to adjust operating parameters such as gain and timing. This closed-loop approach improves imaging accuracy while keeping the device complexity manageable through software-based correction
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 accurate fingerprint imaging through non-flat or non-uniform surfaces without the need for specialized manufacturing, improving the sensor's adaptability and reducing costs, while maintaining high signal-to-noise ratios and contrast-to-noise ratios.
Implementation Method 1
transmit ultrasonic signals using the two-dimensional array of ultrasonic transducers for reflection from an object in contact with the non-uniform contact layer
Implementation Method 2
receive reflected ultrasonic signals at the two-dimensional array of ultrasonic transducers
Implementation Method 3
obtain non-uniformity data characterizing the non-uniform contact layer... generate an image of the object in contact with the non-uniform contact layer based on the reflected ultrasonic signals, wherein the image is corrected for non-uniformity of the non-uniform contact layer
Data Source
AI summary
A sensor device comprising a two-dimensional array of ultrasonic transducers, wherein the two-dimensional array of ultrasonic transducers is substantially flat, a non-uniform contact layer overlying the two-dimensional array of ultrasonic transducers, and a sensor processor is described. The sensor device is configured to: transmit ultrasonic signals using the two-dimensional array of ultrasonic transducers for reflection from an object in contact with the non-uniform contact layer, wherein the ultrasonic signals traverse the non-uniform contact layer, receive reflected ultrasonic signals at the two-dimensional array of ultrasonic transducers, obtain non-uniformity data characterizing the non-uniform contact layer, control operating parameters of the sensor device based on the non-uniformity data, and generate an image of the object in contact with the non-uniform contact layer based on the reflected ultrasonic signals, wherein the image is corrected for non-uniformity of the non-uniform contact layer.