Broadband Ultrasonic Sensor Acoustic Stack Design
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Solution Overview
Problem
Piezoelectric ultrasonic transducers in ultrasonic sensor systems face challenges in maintaining a high signal-to-noise ratio (SNR) over a broad frequency range, especially when accommodating varying multi-layer stack configurations and screen protector installations, which affect their performance in applications like fingerprint and sub-dermis imaging.
Innovation Solution
The ultrasonic sensor system incorporates a substrate, a platen, and an acoustic stack with a piezoelectric layer, including a thin-film transistor (TFT) layer, configured to operate with ultrasonic waves, where the acoustic stack's total thickness is less than half the characteristic wavelength, and the platen and OLED stack have similar acoustic impedance, ensuring a signal-to-noise ratio of at least 4 over a frequency range of 9 to 16 MHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the piezoelectric ultrasonic transducer is configured to operate with varying multi-layer stack configurations and screen protectors, then the adaptability is improved, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent applies parameter changes by designing the acoustic stack with specific thickness parameters (total thickness less than 1/2 the characteristic wavelength, with the piezoelectric layer thickness and acoustic matching layer thickness optimized to specific ranges) to achieve broadband operation across 9-16 MHz while maintaining SNR ≥ 4 across varying multi-layer configurations and screen protector conditions
Solution Approach 2:
The patent employs composite materials through the acoustic stack structure combining piezoelectric materials (PZT, PMN-PT, PVDF, or PVDF-TrFE) with acoustic matching layers having specifically engineered acoustic impedances (Z1 and Z2 within defined ranges) to optimize ultrasonic wave transmission across different platen and screen protector configurations
2Adaptability or versatility
If the piezoelectric layer thickness and acoustic matching layer thickness are optimized for broadband operation, then the frequency range is improved, but the device complexity increases
Solution Approach 1:
The patent resolves this contradiction by establishing specific parameter ranges for the acoustic stack components: the piezoelectric layer thickness is optimized to 50-200 μm, the acoustic matching layer thickness to 50-200 μm, and the total acoustic stack thickness to less than 1/2 the characteristic wavelength. These parameter specifications enable broadband operation across 9-16 MHz while providing clear manufacturing guidelines that control 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
This configuration achieves a high signal-to-noise ratio over a broad frequency range, reducing the need for sensor tuning and enabling reliable operation with various screen protectors, including sub-dermis imaging capabilities.
Implementation Method 1
The piezoelectric layer may convert vibrations caused by ultrasonic reflections into electrical output signals
Data Source
AI summary
An ultrasonic sensor includes a substrate, a platen and an acoustic stack disposed between the substrate and the platen, including at least one piezoelectric layer. The ultrasonic transducer exhibits a signal-to-noise ratio of at least 4 over a frequency range of at least 9 to 16 MHz.