Ultrasonic Fingerprint Resonator Stack for Under-Display Wave Transmission
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Solution Overview
Problem
Designing an under-display ultrasonic sensor system for devices like foldable displays poses challenges due to attenuation of ultrasonic waves by layers such as display stiffeners, which affects performance and requires innovative solutions to enhance wave transmission and authentication processes.
Innovation Solution
Incorporating an ultrasonic sensor stack with an acoustic resonator that includes higher-impedance and low-impedance layers, where the low-impedance layers have thicknesses corresponding to multiples of wavelengths at peak frequencies, to enhance ultrasonic wave transmission and reduce attenuation, allowing for effective authentication processes without modifying existing device structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If display stiffener layers are added to protect foldable displays, then display strength and reliability are improved, but ultrasonic wave transmission is attenuated
Solution Approach 1:
An acoustic resonator structure is introduced as an intermediary component between the ultrasonic sensor and the display stack. This resonator includes alternating high-impedance and low-impedance layers with specific thicknesses (multiples of quarter-wavelengths) that create acoustic coupling effects, enabling ultrasonic waves to pass through the display stiffener with reduced attenuation while maintaining display protection
Solution Approach 2:
The acoustic resonator utilizes controlled changes in acoustic impedance parameters through alternating high-impedance and low-impedance layers. The specific thickness parameters of these layers (configured as multiples of quarter-wavelengths at the operating frequency) are optimized to enhance ultrasonic transmission through the display stack while preserving display structural integrity
2Measurement precision
If ultrasonic frequency is increased to improve fingerprint sensor resolution, then measurement precision is improved, but wave attenuation by display layers increases
Solution Approach 1:
The acoustic resonator is designed with layer thicknesses specifically configured as multiples of quarter-wavelengths at the desired operating frequency. This parameter optimization enables high-frequency ultrasonic waves to transmit through the display stack with minimal attenuation, maintaining both measurement precision and wave transmission efficiency
Solution Approach 2:
The acoustic resonator utilizes mechanical vibration and resonance principles to amplify and sustain ultrasonic wave transmission through the display stack. The alternating impedance layers create constructive interference patterns that enhance wave transmission at specific resonant frequencies, improving both precision and transmission
3Loss of energy
If acoustic resonator with multiple layers is added to enhance ultrasonic transmission, then wave transmission is improved, but device complexity increases
Solution Approach 1:
The acoustic resonator structure is integrated and merged with the existing display stack architecture. The alternating high-impedance and low-impedance layers are incorporated into the display's existing layer structure, allowing ultrasonic transmission enhancement without requiring separate, additional components that would increase device 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
The solution enhances ultrasonic wave transmission in the frequency range suitable for ultrasonic fingerprint sensors, improving authentication processes and maintaining the integrity of foldable displays by minimizing wave attenuation, thus providing effective and cost-efficient solutions for under-display sensor systems.
Implementation Method 1
the acoustic resonator may include one or more higher-impedance layers having a thickness corresponding to a multiple of a half wavelength at a peak frequency of the acoustic resonator
Implementation Method 2
each layer of the one or more first low-impedance layers may have a lower acoustic impedance than an acoustic impedance of one or more higher-impedance layers
Implementation Method 3
enhances ultrasonic wave transmission in the frequency range suitable for ultrasonic fingerprint sensors
Data Source
AI summary
Some disclosed implementations include an ultrasonic sensor stack and an acoustic resonator. The acoustic resonator may be configured to enhance ultrasonic waves transmitted by the ultrasonic sensor stack in an ultrasonic frequency range that is suitable for ultrasonic fingerprint sensors. In some examples, the acoustic resonator may include one or more low-impedance layers residing between a first higher-impedance layer and a second higher-impedance layer. Each of the one or more low-impedance layers may have a lower acoustic impedance than an acoustic impedance of the first higher-impedance layer or an acoustic impedance of the second higher-impedance layer. At least one low-impedance layer may have a thickness corresponding to a multiple of a half wavelength at a peak frequency of the acoustic resonator. The peak frequency may be within a frequency range from 1 MHz. to 20 MHz.