Dual-Thickness Bragg Mirror for Multi-Frequency Shear Wave Reflection
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Solution Overview
Problem
Conventional Bragg mirrors are ineffective in reflecting multiple frequencies of acoustic waves, primarily designed to reflect a specific wavelength, which limits their ability to handle acoustic waves and harmonics developed by piezoelectric resonators.
Innovation Solution
A Dual Mode Bragg mirror is introduced, featuring additional shear wave bi-layers that are λS/2 thick, allowing for efficient reflection of both longitudinal and shear waves by incorporating bi-layers of varying thicknesses to accommodate different wavelengths, thereby improving acoustic isolation and reducing energy loss into substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional Bragg mirror is designed to reflect a specific wavelength, then reflection efficiency for that wavelength is improved, but the ability to reflect multiple frequencies of acoustic waves deteriorates
Solution Approach 1:
The Bragg mirror is segmented into multiple bi-layer stacks, each designed with different layer thicknesses corresponding to different wavelengths. This segmentation allows each bi-layer stack to specialize in reflecting a specific frequency range, while collectively the mirror can reflect multiple frequencies simultaneously
Solution Approach 2:
Different regions of the Bragg mirror (different bi-layer stacks) have different local properties - specifically, different layer thicknesses optimized for different wavelengths. This local quality variation enables the mirror to handle multiple frequencies with appropriate reflection efficiency for each
2Device complexity
If Bragg mirror layers are made thinner to reduce device complexity, then manufacturing ease is improved, but acoustic isolation performance deteriorates
Solution Approach 1:
The invention changes the parameter of layer thickness from uniform to varied, with specific thickness ratios optimized for different wave modes. The bi-layers are designed with thicknesses that are approximately one-quarter the wavelength of the target acoustic mode, creating optimal acoustic isolation while maintaining manageable device dimensions
3Adaptability or versatility
If additional bi-layers are added to reflect multiple wavelengths, then multi-frequency reflection capability is improved, but device complexity increases
Solution Approach 1:
Each bi-layer stack is designed to serve multiple functions: reflecting longitudinal waves at specific frequencies while also providing some reflection of shear waves. This multi-functionality reduces the need for completely separate structures for different wave modes, thereby limiting the increase in overall 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 Dual Mode Bragg mirror achieves high reflection efficiency for both longitudinal and shear waves, reducing insertion loss and ripple, and enhancing the quality factor and pass-band characteristics of filters, while maintaining low transmissivity of shear waves.
Implementation Method 1
Each interface between the two materials contributes a Fresnel-type reflection. For the design wavelength, the optical path length difference between reflections from subsequent interfaces is one half the wavelength; in addition, the reflection coefficients for the interfaces have alternating signs. Therefore, all reflected components from the interfaces interfere constructively
Implementation Method 2
all reflected components from the interfaces interfere constructively, which results in a strong reflection
Implementation Method 3
piezoelectric resonators are used for a number of purposes but are primarily used in the electronics industry for signal filtering and reference oscillators
Data Source
AI summary
In an embodiment, set forth by way of example and not limitation, a Bragg mirror includes a first bi-layer of a first thickness and a second bi-layer of a second thickness which is different from the first thickness. In this exemplary embodiment, the first bi-layer consists essentially of a first high impedance layer and a first low impedance layer, and the second bi-layer of a second thickness which is different from the first thickness, the second bi-layer consisting essentially of a second high impedance layer and a second low impedance layer. Preferably, the first bi-layer is configured to substantially reflect a first wavelength and the second bi-layer is configured to substantially reflect a second wavelength different from the first wavelength.