PMUT Ultrasonic Sensor Beamforming and Cavity Design
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Solution Overview
Problem
Conventional piezoelectric ultrasonic transducers face limitations in achieving high-frequency membrane oscillations due to constraints on membrane thickness and radius, which affect displacement and acoustic diffraction, and require improved designs for efficient ultrasonic wave generation and sensing applications.
Innovation Solution
The development of a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) device with a substrate, edge support structure, and interior support structure, featuring a membrane with piezoelectric layers and electrodes, allowing for high-frequency operation and efficient acoustic signal generation and sensing, including phase delayed transmission and beamforming patterns for improved signal resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If membrane thickness and radius are reduced to achieve high-frequency oscillations, then frequency is improved, but displacement and acoustic diffraction performance deteriorate
Solution Approach 1:
The patent introduces a vertical dimension by creating a cavity beneath the membrane, allowing the membrane to oscillate with greater amplitude in the vertical direction without being constrained by planar dimensions. This enables high-frequency oscillations to maintain adequate displacement by utilizing the third dimension (depth) for movement space.
Solution Approach 2:
The transducer is segmented into distinct functional layers: the oscillating membrane, the cavity space, and the support structure. This segmentation allows each component to be optimized independently - the membrane for high-frequency oscillation and the cavity for providing displacement space, thereby resolving the contradiction between frequency and displacement.
2Speed
If membrane thickness and radius are reduced to achieve high-frequency oscillations, then frequency is improved, but acoustic diffraction is worsened
Solution Approach 1:
By utilizing the vertical cavity dimension, the patent enables the membrane to maintain an effective radiating area despite reduced planar dimensions. The cavity allows the acoustic energy to be directed more efficiently, reducing unwanted diffraction effects while maintaining high-frequency operation.
Solution Approach 2:
The patent changes the operational parameters by introducing a controlled cavity environment beneath the membrane. This modifies the acoustic boundary conditions, allowing high-frequency oscillations to occur with reduced diffraction by altering the pressure distribution and acoustic impedance in the cavity space.
3Ease of manufacture
If conventional transducer design is used, then manufacturing is simpler, but signal efficiency and fill-factor are reduced
Solution Approach 1:
The membrane serves multiple functions: it acts as both the piezoelectric actuator for generating ultrasonic waves and as the radiating surface for acoustic signal transmission. This multi-functionality increases the fill-factor and signal efficiency while maintaining a relatively simple layered structure that can be manufactured using standard thin-film deposition techniques.
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 enables efficient ultrasonic wave generation and sensing with reduced acoustic diffraction, high fill-factor for large signals, and shorter ring-up/ring-down times, effectively addressing limitations in existing transducers for applications like fingerprint sensing and medical imaging.
Implementation Method 1
Piezoelectric materials facilitate conversion between mechanical energy and electrical energy. Moreover, a piezoelectric material can generate an electrical signal when subjected to mechanical stress, and can vibrate when subjected to an electrical voltage.
Implementation Method 2
Piezoelectric materials are widely utilized in piezoelectric ultrasonic transducers to generate acoustic waves based on an actuation voltage applied to electrodes of the piezoelectric ultrasonic transducer.
Data Source
AI summary
An ultrasonic sensor includes a two-dimensional array of ultrasonic transducers. A signal generator is configured to generate a plurality of transmit signals, wherein each transmit signal of the plurality of transmit signals has a different phase delay relative to other transmit signals of the plurality of transmit signals. A plurality of shift registers is configured to store a beamforming space including a beamforming pattern to apply to the two-dimensional array, wherein the beamforming pattern identifies a transmit signal of the plurality of transmit signals that is applied to each ultrasonic transducer of the beamforming space that is activated during a transmit operation. An array controller is configured to control activation of ultrasonic transducers during a transmit operation according to the beamforming pattern and configured to shift a position of the beamforming space within the plurality of shift registers such that the beamforming space moves within the two-dimensional array.