Ultrasonic Sensor Array Receiver Bias Electrode
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Solution Overview
Problem
Capacitive touch sensors and fingerprint sensors in mobile devices face limitations such as low resolution and incompatibility with thick glass displays, making it difficult to accurately detect user inputs and fingerprints through a cover glass.
Innovation Solution
An ultrasonic sensor array with a receiver bias electrode that transitions between hold, block, and sample voltage values to accurately transmit and receive ultrasonic waves perpendicular to the display surface, enhancing detection accuracy by stacking the piezoelectric transmitter and receiver layers for improved signal acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive touch sensors are used in mobile devices, then the device can detect user inputs, but the resolution is limited and detailed fingerprint features cannot be detected through thick cover glass
Solution Approach 1:
The patent replaces capacitive sensing with ultrasonic sensing. The ultrasonic transmitter generates acoustic waves that propagate through the cover glass and interact with the finger, while the receiver detects reflected waves. This mechanical/acoustic substitution enables detection through thick glass that capacitive sensors cannot penetrate effectively.
Solution Approach 2:
The patent transitions from surface-level capacitive detection to volumetric ultrasonic detection. By using acoustic waves that propagate through the thickness of the cover glass, the system accesses information from a different dimensional space, enabling fingerprint detection through materials that block electrical field-based capacitive sensing.
2Measurement precision
If ultrasonic waves are transmitted and received simultaneously, then the system can detect reflections, but the outgoing wave interferes with the received signal
Solution Approach 1:
The patent implements periodic transmission and reception cycles. The transmitter operates in bursts followed by reception windows, creating a time-division multiplexed operation. This periodic action separates the harmful outgoing wave from the desired received signal in time, allowing accurate detection of reflected ultrasonic waves from the finger.
Solution Approach 2:
The system performs preliminary actions by transmitting the ultrasonic wave before attempting to receive the reflection. The transmitter activates first to establish the acoustic field, then the receiver is enabled after the outgoing pulse has propagated and reflected, ensuring the detection window occurs before interference from subsequent transmissions occurs.
3Measurement precision
If the receiver bias voltage is maintained at a constant value, then the circuit is simple, but the receiver cannot differentiate between outgoing and reflected waves
Solution Approach 1:
The patent applies dynamic voltage control to the receiver bias electrode, transitioning from constant voltage to time-varying voltage. The bias voltage is adjusted in synchronization with the transmission-reception cycle, being high during transmission to block outgoing waves and low during reception to enable detection of reflected waves. This dynamic adjustment allows the simple receiver circuit to discriminate between different wave types without complex filtering.
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 allows for precise detection of user inputs and fingerprints, even through thick glass, improving accuracy and compatibility with mobile device designs compared to traditional capacitive touch sensors.
Implementation Method 1
a piezoelectric transmitter layer that generates an ultrasonic wave
Implementation Method 2
a piezoelectric receiver layer that may detect a reflection of the ultrasonic wave
Data Source
AI summary
A method of operation of an ultrasonic sensor array includes receiving a receiver bias voltage at a receiver bias electrode of the ultrasonic sensor array to bias piezoelectric sensor elements of the ultrasonic sensor array. The method further includes receiving a transmitter control signal at the ultrasonic sensor array to cause an ultrasonic transmitter of the ultrasonic sensor array to generate an ultrasonic wave. The method further includes generating data samples based on a reflection of the ultrasonic wave. The receiver bias voltage and the transmitter control signal are received from an integrated circuit that is coupled to the ultrasonic sensor array.