Ring-Shaped PMUT with Differential Circuitry for Noise Rejection
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Solution Overview
Problem
Existing piezoelectric micromachined ultrasonic transducers (PMUTs) face challenges in reducing noise sensitivity to electromagnetic interference, managing resonance frequency variations due to stress, and minimizing electrical connections for cost and complexity, particularly when used as both transmitters and receivers.
Innovation Solution
A ring-shaped PMUT design with a flexible membrane supported by a substrate, featuring equal parasitic capacitances and reduced piezoelectric material on the surface to minimize stress sensitivity and electrical connections, along with a circuitry system using switches to manage noise and voltage polarity for improved signal transmission and reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional piezoelectric transducer design with full surface piezoelectric material is used, then the transducer generates strong acoustic output, but the resonance frequency is highly sensitive to stress variations from residual stress, packaging stress, and thermal stress
Solution Approach 1:
The piezoelectric material is segmented into a ring-shaped region rather than covering the entire surface. This segmentation creates a design where the piezoelectric material is positioned away from the high-stress center region, reducing stress sensitivity while maintaining acoustic output capability through the distributed ring structure.
Solution Approach 2:
The design transitions from a two-dimensional full surface coverage to a one-dimensional ring-shaped annular region. This dimensional change allows the piezoelectric material to be positioned strategically in a ring pattern that maintains acoustic generation while being less susceptible to stress variations that affect the center region.
2Object-affected harmful factors
If a differential amplifier circuit with two transducers and load resistors is used, then common mode noise rejection is improved, but the cost, complexity and size are doubled and thermal noise increases
Solution Approach 1:
A single piezoelectric transducer is designed to perform both transmitting and receiving functions, eliminating the need for separate transducers. The ring-shaped electrode configuration enables the same device to operate in both modes, reducing overall system complexity while maintaining differential signal processing capabilities.
Solution Approach 2:
The transmitting and receiving functions are merged into a single piezoelectric transducer device. The ring-shaped electrode structure serves dual purposes: generating acoustic waves during transmission and detecting acoustic signals during reception, thereby reducing the number of components and simplifying the overall circuit design.
3Object-affected harmful factors
If four electrical connections are made to achieve good common mode noise rejection, then noise rejection is improved, but the cost and complexity increase
Solution Approach 1:
The electrode design uses asymmetric ring-shaped electrodes with different configurations for transmitting and receiving operations. The first and second ring-shaped electrodes are positioned and dimensioned to create inherent differential signaling capabilities, achieving common mode noise rejection with fewer connections by exploiting the asymmetric geometric configuration.
Solution Approach 2:
Different regions of the ring-shaped electrodes are optimized for different functions: the first ring-shaped electrode is optimized for transmitting operations while the second is optimized for receiving operations. This local quality differentiation allows the system to achieve both transmission and reception with a minimal connection structure.
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 new design significantly reduces resonance frequency sensitivity to stress variations, enhances operational frequency bandwidth, and achieves effective common-mode noise rejection with fewer electrical connections, improving both manufacturing efficiency and signal quality.
Implementation Method 1
a piezoelectric layer 502 positioned on the flexible membrane 501
Implementation Method 2
a PMUT transmits and receives ultrasound in a frequency band centered at its flexural resonance frequency
Data Source
AI summary
An apparatus comprises an ultrasonic transducer having a first and second electrode and switches which configured to selectively connect the first and second electrodes to a transmit voltage source or to a receive amplifier. The switches are configured to selectively connect a first input of the amplifier to the first electrode of the transducer and to selectively connect a second input of the amplifier to the second electrode of the transducer. The switches are also configured to selectively connect the voltage source to the first and second electrodes of the transducer. The transducer may include a piezoelectric layer attached to and sandwiched between the first electrode and the second electrode, and a flexible membrane attached to the first electrode. The piezoelectric layer may be patterned to form an annular ring at the outer diameter of the flexible membrane.