Ultrasonic Fingerprint Sensor Multipath Reflection Correction
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Solution Overview
Problem
Ultrasonic fingerprint sensors face challenges in producing high-quality fingerprint images due to multipath reflections, which introduce noise and can be caused by reflections within the sensor stack and substrate, making it difficult to distinguish real from fake fingers.
Innovation Solution
A multipath correction system is implemented using characteristics of multipath reflection signals to analyze and correct acoustic signals received at the ultrasonic sensor, identifying primary and multipath signal contributions, and generating templates to isolate and remove multipath reflections, thereby improving image quality and spoof detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ultrasonic signals are transmitted to image a fingerprint, then fingerprint imaging is achieved, but multipath reflection noise is introduced
Solution Approach 1:
The patent performs preliminary characterization of the sensor stack to determine multipath reflection characteristics before actual fingerprint imaging. By measuring and storing the multipath template during a calibration phase, the system prepares correction data in advance that can be applied during normal operation to remove multipath noise from the fingerprint images.
Solution Approach 2:
The patent converts the harmful multipath reflection signals into useful information by characterizing their patterns and creating correction templates. Instead of simply filtering out multipath noise, the system analyzes the noise characteristics and uses them to construct a template that can be subtracted from the received signals, thereby transforming the harmful multipath reflections into a known correctable pattern.
2Object-affected harmful factors
If multipath correction is performed, then noise reduction is achieved, but system complexity increases
Solution Approach 1:
The complex multipath characterization is performed once during an initial calibration phase rather than continuously during operation. By pre-computing the multipath template and storing it for later use, the system reduces the computational burden during actual fingerprint imaging while still achieving effective noise reduction.
Solution Approach 2:
The patent creates a template copy of the multipath reflection pattern that can be reused for correction. Instead of performing complex real-time analysis, the system uses a pre-generated template that replicates the multipath characteristics, simplifying the correction process to a matter of template matching and subtraction.
3Ease of manufacture
If multipath characteristics are determined without target interaction, then calibration is simplified, but accuracy may be compromised
Solution Approach 1:
The sensor stack performs self-characterization by measuring its own multipath reflection characteristics in a controlled manner during calibration. The system uses the sensor's own transmitted and received signals to determine the multipath template without requiring external targets or complex setup, making the calibration process self-contained and simple.
Solution Approach 2:
The patent measures multipath characteristics at multiple different times of flight and combines these measurements to create a comprehensive template. By varying the measurement parameters (time of flight) and aggregating the results, the system achieves accurate multipath characterization while maintaining a simple calibration procedure that can be performed without target interaction.
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 effectively reduces multipath noise, enhancing the accuracy of fingerprint recognition and distinguishing real from fake fingers by isolating primary signals from multipath reflections, leading to improved user authentication and security.
Implementation Method 1
Ultrasonic fingerprint sensors operate by transmitting ultrasonic signals onto a finger and imaging a fingerprint using the reflected ultrasonic signals
Implementation Method 2
Transmitting ultrasonic signals also causes multipath signals other than the desired ultrasonic signals that reflect off the target finger
Data Source
AI summary
In a method for multipath reflection correction of acoustic signals received at an ultrasonic sensor, characteristics of multipath reflection signals of the ultrasonic sensor are accessed, wherein the characteristics of the multipath reflection signals include a relationship of primary signal contributions to multipath reflection signal contributions for acoustic signals received at the ultrasonic sensor at a plurality of times of flight for a plurality of locations of the ultrasonic sensor. Acoustic signals are received at the ultrasonic sensor over a time of flight range while a target is interacting with the ultrasonic sensor, wherein the acoustic signals include a primary signal contribution and a multipath reflection signal contribution. The characteristics of the multipath reflection signals are compared to received acoustic signals. The primary signal contribution of the received acoustic signals is determined at a plurality of times of flight of the time of flight range based on the characteristics of the multipath reflection signals.