Dual-Mode Bragg Mirror Structure for Shear Wave Reflection
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Solution Overview
Problem
Conventional Bragg mirrors are ineffective in reflecting multiple frequencies of acoustic waves, particularly failing to efficiently reflect shear waves and harmonics, leading to energy loss and reduced performance in devices like piezoelectric resonators.
Innovation Solution
A Dual Mode Bragg mirror is designed by adding shear wave bi-layers to the conventional Bragg mirror stack, with each bi-layer configured to reflect specific wavelengths, including both longitudinal and shear wave modes, using alternating high and low acoustic impedance layers of different thicknesses to enhance reflection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional Bragg mirror with uniform bi-layers is used, then the structure is simple and easy to manufacture, but it fails to efficiently reflect multiple frequencies including shear waves and harmonics
Solution Approach 1:
The Bragg mirror is segmented into distinct regions: a first plurality of bi-layers for reflecting longitudinal waves at a first frequency, and a second plurality of bi-layers for reflecting longitudinal waves at a second frequency. This segmentation allows each region to be optimized for specific frequency reflection, enabling multi-frequency operation while maintaining a systematic structure.
Solution Approach 2:
Different regions of the Bragg mirror are given different local properties. The first bi-layers have specific thickness ratios optimized for the first frequency, while the second bi-layers have different thickness ratios optimized for the second frequency. This local differentiation enables the mirror to reflect multiple frequencies efficiently without requiring a completely new uniform structure.
2Reliability
If the Bragg mirror is designed to reflect multiple wavelengths with different bi-layer thicknesses, then reflection efficiency improves, but manufacturing precision requirements increase
Solution Approach 1:
The invention changes the parameters of the bi-layers systematically. The first bi-layers have thicknesses where the low impedance layer is approximately 0.25 to 0.35 times the wavelength and the high impedance layer is approximately 0.15 to 0.25 times the wavelength. The second bi-layers have different thickness ratios optimized for a different frequency. These parameter variations are calculated based on the desired reflection frequencies, allowing efficient multi-frequency reflection while providing clear manufacturing targets.
3Adaptability or versatility
If shear wave bi-layers are added to the Bragg mirror stack, then shear wave reflection improves, but device complexity increases
Solution Approach 1:
The Bragg mirror is designed to perform multiple functions: reflecting longitudinal waves at the operating frequency, reflecting longitudinal waves at harmonic frequencies, and reflecting shear waves. By incorporating bi-layers with specific thickness ratios, the same structure achieves multi-functionality without requiring separate independent reflection systems for each wave type and frequency.
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 solution achieves improved isolation and reduced transmissivity of shear waves, maintaining low insertion loss and ripple, thereby increasing the quality factor and pass-band performance of filters and resonators.
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, which results in a strong reflection.
Implementation Method 2
all reflected components from the interfaces interfere constructively, which results in a strong reflection
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.