PMUT Membrane Cavity Design for High-Frequency Ultrasonic Imaging
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Solution Overview
Problem
Conventional piezoelectric ultrasonic transducers face limitations in achieving high frequency oscillations and efficient acoustic signal generation due to membrane thickness and radius constraints, which affect displacement and area utilization, and struggle with spurious reflections and image pixel density in ultrasonic sensing applications.
Innovation Solution
The development of a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) device with a substrate, edge support structure, and an interior support structure, featuring a membrane with a piezoelectric layer and electrodes, allowing for high-frequency operation and improved acoustic signal generation and sensing, along with phase delayed transmission and beamforming techniques to enhance image pixel density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If membrane thickness and radius are reduced to achieve high frequency oscillations, then frequency response is improved, but displacement and area utilization deteriorate
Solution Approach 1:
The patent changes the physical parameters of the membrane by introducing a cavity beneath it, which fundamentally alters the membrane's mechanical behavior. This cavity structure allows the membrane to achieve larger displacement at high frequencies without requiring reduction in thickness or radius, thus resolving the contradiction between frequency response and displacement capability
Solution Approach 2:
The invention adds a vertical dimension by creating a cavity beneath the membrane, transforming the problem from a two-dimensional membrane surface issue to a three-dimensional volume utilization issue. This dimensional change allows the membrane to exploit the cavity space for enhanced displacement while maintaining high frequency operation
2Speed
If membrane thickness and radius are reduced to achieve high frequency oscillations, then frequency response is improved, but area utilization deteriorates
Solution Approach 1:
By introducing the cavity parameter, the system changes how area is utilized. The membrane can maintain larger radius and thickness while the cavity volume provides additional effective area for acoustic signal generation, thus improving area utilization without sacrificing high frequency response
Solution Approach 2:
The cavity adds vertical space utilization, converting a two-dimensional area constraint into a three-dimensional volume advantage. This allows the membrane to maintain larger horizontal dimensions for better area utilization while the cavity provides additional acoustic generation space
3Device complexity
If conventional ultrasonic transducers are used, then device simplicity is maintained, but spurious reflections and image pixel density issues occur
Solution Approach 1:
The transducer is segmented into distinct functional zones: the membrane for high-frequency oscillation, the cavity for acoustic signal generation and amplification, and the backing material for reflection rejection. This segmentation allows each component to be optimized independently, improving acoustic signal quality while maintaining overall device simplicity
Solution Approach 2:
The cavity acts as an intermediary between the membrane and the backing material, serving multiple functions: amplifying acoustic signals from the membrane, providing acoustic isolation to reduce spurious reflections, and enabling better coupling to the surrounding medium. This intermediary structure improves reliability without significantly increasing 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 PMUT device operates at high frequencies with reduced acoustic diffraction, shortens ring-up and ring-down times for better reflection rejection, and increases image pixel density by combining multiple beamforming patterns, effectively addressing the limitations of conventional transducers.
Implementation Method 1
The membrane includes a piezoelectric layer and first and second electrodes coupled to opposing sides of the piezoelectric layer
Implementation Method 2
Piezoelectric materials are widely utilized in piezoelectric ultrasonic transducers to generate acoustic waves based on an actuation voltage applied to electrodes
Data Source
AI summary
A method for generating a composite image having an increased image pixel density by an array of ultrasonic transducers having a given spatial density is provided. The method comprises capturing a first set of pixels at an ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of ultrasonic transducers of the ultrasonic sensor. The method further comprises capturing a second set of pixels at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers. The first beamforming pattern and the second beamforming pattern are different. Pixels of the second set of pixels correspond to positions between pixels of the first set of pixels. The method additionally comprises combining the first and second sets of pixels to form the composite image. An electronic device and a method of generating an image of a fingerprint are also provided.