Thermal Fingerprint Sensor Double Integration Method
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Active thermal fingerprint sensors face challenges in distinguishing thermal patterns due to stray phenomena, such as temperature equilibrium and variations caused by the sensor's heating, leading to reduced contrast and noise interference, especially when power constraints limit heating power and measurement duration adjustments.
Innovation Solution
A method involving a thermal pattern sensor with a heating element and reading circuit that implements two measurement phases: a first reading during more than half of the heating phase and a second reading during the cooling phase, calculating the difference between the two readings to enhance contrast and reduce noise, thereby isolating the thermal signals from stray phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the measurement duration is increased to obtain good contrast between ridges and valleys, then the signal level increases compared to noise, but the total capture duration becomes too long and measurements are disturbed by finger movements
Solution Approach 1:
The patent applies periodic action by implementing multiple sequential measurement phases (first measurement phase, second measurement phase) with different integration times. The first phase uses a longer integration time to capture sufficient signal, while the second phase uses a shorter integration time to capture additional signal components. This periodic measurement approach allows the system to achieve good contrast without requiring a single excessively long measurement that would be disrupted by finger movements.
2Measurement precision
If the heating power is increased to improve thermal signal detection, then the thermal signal strength increases, but power consumption increases and stray phenomena become more pronounced
Solution Approach 1:
The patent applies partial or excessive action by implementing measurement integration times that extend beyond the heating duration. The first measurement phase integrates from the start of heating through the heating period and into the cooling period, while the second measurement phase integrates during the cooling period. This allows the system to capture thermal signals without requiring excessive heating power, as the extended integration captures the full thermal response including the cooling phase.
Solution Approach 2:
The patent converts the harmful effect of thermal diffusion and stray phenomena into a benefit by measuring during both the heating and cooling phases. The thermal diffusion that causes stray phenomena during heating also creates a measurable thermal signature during cooling. By integrating measurements across both phases and combining them, the system transforms the problematic thermal diffusion into useful signal information that improves detection without requiring additional power.
3Measurement precision
If the measurement duration is extended to capture thermal patterns, then noise from stray phenomena increases, but shorter measurements reduce the thermal signal quality
Solution Approach 1:
The patent applies segmentation by dividing the measurement process into distinct phases: a first measurement phase with a first integration time that captures signal during and after heating, and a second measurement phase with a second integration time that captures signal during cooling. By segmenting the measurement into these separate phases with different integration characteristics, the system can combine them to achieve high signal quality while suppressing noise from stray phenomena that would be present in a single extended measurement.
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 the contrast between thermal conductivity variations in the fingerprint, effectively reducing noise and stray signals, resulting in clearer thermal pattern captures while maintaining acceptable measurement durations and power efficiency.
Implementation Method 1
at least one heating element configured to heat the heat-sensitive measuring element of at least one pixel during a measurement by the heat-sensitive measuring element of said at least one pixel
Implementation Method 2
These heat detection means may be pyroelectric capacitors, diodes, thermistors, or more generally any heat-sensitive element converting a variation in temperature to which the heat-sensitive element is subjected into a variation in an electrical parameter
Data Source
AI summary
Method for capturing a thermal pattern by a sensor comprising a plurality of pixels each comprising a heat-sensitive measuring element, the method comprising, for each pixel:heating the measuring element;first reading of the electrical charges outputted by the pixel during a first measurement duration and giving a first measurement value x1;second reading of the electrical charges outputted by the pixel during a second measurement duration and giving a second measurement value x2;calculating a difference x1−α·x2, where α is a positive real number,and wherein more than half of the heating duration is implemented during the first measurement duration and less than half of the heating duration is implemented during the second measurement duration.