cMUT Array With Massive Isolation Plate Suppressing Substrate Coupling
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Solution Overview
Problem
Capacitive micromachined ultrasonic transducer (cMUT) arrays face issues with acoustic coupling of reverberation energy to the substrate, leading to spurious signals and reduced image quality due to low acoustic loss materials like silicon, which compromise lateral resolution and beam steering capabilities.
Innovation Solution
The implementation of a cMUT array with acoustically isolated elements using a massive plate supported by small, low-stiffness posts, and optionally filled with a compliant material like PDMS, to oppose the acoustic force and minimize substrate coupling, thereby reducing unwanted motion and energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cMUT elements are directly mounted on a low acoustic loss substrate like silicon, then the substrate provides strong mechanical support, but acoustic coupling occurs causing spurious signals and image artifacts
Solution Approach 1:
A massive isolation plate is introduced as an intermediary component between the cMUT elements and the substrate. This plate has high mass to provide strong mechanical support while being acoustically isolated from the substrate through small support posts, thereby blocking the transmission of spurious acoustic signals to the substrate
Solution Approach 2:
The support structure is segmented into multiple small support posts distributed across the isolation plate. These posts provide necessary mechanical support while minimizing acoustic coupling area, effectively separating the mechanical support function from the acoustic coupling path
2Object-generated harmful factors
If the substrate is thinned to prevent lateral wave propagation, then acoustic coupling is reduced, but mechanical strength and structural integrity are compromised
Solution Approach 1:
The massive isolation plate serves as an intermediary that blocks lateral wave propagation without requiring substrate thinning. The plate's high mass and isolation from the substrate prevent acoustic energy from coupling into and traveling along the substrate, maintaining substrate integrity
3Object-generated harmful factors
If acoustic backing is added behind the substrate to deaden unwanted energy, then spurious signals are reduced, but device complexity increases
Solution Approach 1:
The solution extracts the acoustic isolation function from the substrate and relocates it to a dedicated massive isolation plate positioned between the cMUT elements and the substrate. This separates the isolation function from the substrate, preventing acoustic coupling without adding complexity behind the substrate
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 approach significantly attenuates substrate excitation forces, improving image quality by reducing clutter and enhancing the acceptance angle and beam steering capabilities of the ultrasound system.
Implementation Method 1
The acoustic force of transmission of a MUT element is opposed by a relatively significant mass which supports the MUT element
Implementation Method 2
a plurality of support members of small size and/or low stiffness which provide low coupling from the support mass to the substrate
Implementation Method 3
a membrane is vibrated by a variable capacitive effect, in the manner of the diaphragm of a drum
Implementation Method 4
Forces applied to the substrate, typically a very low acoustic loss material such as silicon, generate one or more of several acoustic wave types
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~5
AI summary
An array of cMUT cells are formed on individually isolated massive plates on a substrate. The mass of each plate provides an inertial force in opposition to the force and motion of transmission by the cell which reduces the resultant translation of motion in the plate. The reduction in motion results in less coupling of acoustic energy into the substrate and contamination of the signals of adjacent cMUT cells by lateral waves. The unwanted wave coupling into the substrate can be further damped by compliant or sparse periodic mounting of the massive plates on the substrate.