MEMS Phononic Membrane Structure for Bulk Acoustic Isolation
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Solution Overview
Problem
There is a need for bulk wave acoustic bandgap devices fabricated using microelectromechanical systems (MEMS) technologies to operate in the ultrasonic, VHF, or UHF regime, as existing technologies are limited to large structures and surface acoustic wave devices with energy leakage issues.
Innovation Solution
A microfabricated bulk wave acoustic bandgap device is created with a substrate, a membrane of matrix material, and a two-dimensional periodic array of scatterers with different density and/or elastic constants, causing destructive interference and acoustic isolation, fabricated using MEMS materials and technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large hand-assembled structures are used for acoustic bandgap devices, then acoustic isolation is achieved at low frequencies, but device size becomes impractically large and fabrication complexity increases
Solution Approach 1:
The device is segmented into a periodic array of scatterers embedded in a matrix material, creating a phononic crystal structure. This segmentation enables acoustic bandgap formation through destructive interference while allowing microfabrication techniques to be used instead of large-scale hand assembly
Solution Approach 2:
The invention transitions from one-dimensional quarter-wave acoustic reflectors to two-dimensional phononic crystal structures. This dimensional change enables broader acoustic bandgaps and allows the use of planar microfabrication techniques, reducing fabrication complexity while maintaining acoustic isolation performance
2Ease of manufacture
If surface acoustic wave devices are used, then integration with solid substrates is achieved, but energy leakage into the substrate causes loss in cavities and waveguides
Solution Approach 1:
A suspended membrane structure acts as an intermediary between the acoustic wave and the substrate. The membrane confines acoustic energy to propagate in bulk waves within the membrane plane, preventing energy leakage into the substrate while still allowing the device to be fabricated using standard substrate-based MEMS processes
3Length of moving object
If microfabricated structures are used to reduce device size, then miniaturization is achieved, but operating frequency range is limited
Solution Approach 1:
The acoustic bandgap frequency is tuned by changing the lattice constant (periodicity) of the phononic crystal structure. This parameter can be adjusted during microfabrication to operate at different frequencies from ultrasonic to VHF to UHF regimes, enabling a small device to cover a broad frequency range
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 device achieves high acoustic attenuation and wide bandgaps, enabling phononic integrated circuits and overcoming energy leakage issues, with potential applications in communications and non-destructive testing.
Implementation Method 1
the periodicity of the array causes destructive interference of the acoustic wave within an acoustic bandgap
Data Source
AI summary
A microfabricated bulk wave acoustic bandgap device comprises a periodic two-dimensional array of scatterers embedded within the matrix material membrane, wherein the scatterer material has a density and/or elastic constant that is different than the matrix material and wherein the periodicity of the array causes destructive interference of the acoustic wave within an acoustic bandgap. The membrane can be suspended above a substrate by an air or vacuum gap to provide acoustic isolation from the substrate. The device can be fabricated using microelectromechanical systems (MEMS) technologies. Such microfabricated bulk wave phononic bandgap devices are useful for acoustic isolation in the ultrasonic, VHF, or UHF regime (i.e., frequencies of order 1 MHz to 10 GHz and higher, and lattice constants of order 100 μm or less).