Surface Acoustic Wave Filter With Phononic Crystal Wave Guiding
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Solution Overview
Problem
Existing acoustic filters in radiofrequency transmission systems, particularly for mobile telephone systems, face challenges in achieving efficient impedance and mode conversion while minimizing internal electrical reflections and manufacturing complexity, often requiring cumbersome multi-layer stacking and expensive balun systems.
Innovation Solution
The use of acoustically coupled Bulk Acoustic Wave resonators with integrated phononic crystal structures for impedance and mode conversion, allowing for better energy control and wave channeling without internal reflections, and simplifying the manufacturing process by using surface variations instead of thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If balun systems are used to ensure connection between ground-referenced and differential parts, then electrical isolation is achieved, but device complexity and cost increase significantly
Solution Approach 1:
The invention extracts the electrical isolation function from external balun components and integrates it directly into the filter structure through acoustic coupling between resonators. The acoustic wave path provides inherent galvanic isolation, eliminating the need for separate balun components while maintaining the required electrical isolation between ground-referenced input and differential output stages.
Solution Approach 2:
The invention introduces acoustic waves as an intermediary medium to transfer signal energy between the input and output resonators without direct electrical connection. The acoustic coupling acts as a mediator that enables signal transmission while maintaining electrical isolation, replacing the traditional electrical coupling method used in baluns.
2Adaptability or versatility
If CRF filters with stacked resonators are used for impedance and mode conversion, then conversion efficiency improves, but manufacturing complexity increases due to multiple layers and masking levels
Solution Approach 1:
The invention transitions from vertical stacking of resonators (requiring multiple deposition layers and masking levels) to a planar arrangement where resonators are positioned side-by-side on the same substrate. Acoustic coupling is achieved through lateral wave propagation rather than vertical acoustic paths, dramatically simplifying the manufacturing process while maintaining impedance conversion capability.
Solution Approach 2:
The invention replaces the complex multi-layer deposition and masking process with a simpler planar fabrication approach. Instead of building vertical stacks requiring precise layer alignment, the resonators are fabricated in a single substrate plane, reducing manufacturing steps and improving ease of production.
3Adaptability or versatility
If resonators of different thicknesses are stacked for impedance conversion, then impedance ratios can be achieved, but manufacturing complexity and area requirements increase
Solution Approach 1:
The invention achieves impedance conversion by varying the surface area of resonators in the planar dimension rather than changing thickness in the vertical dimension. Resonators are arranged side-by-side with different footprints, allowing impedance transformation while maintaining a compact planar structure that requires minimal substrate area.
4Productivity
If two filter sections are connected at lower resonators with different impedances, then filter selectivity is improved, but internal electrical reflections increase degrading performance
Solution Approach 1:
The invention uses acoustic waves as a temporary, disposable medium for signal transmission between filter sections. The acoustic coupling allows energy to pass through the isolation barrier without creating persistent electrical connections that would cause reflections. The acoustic path exists only during the brief moment of energy transfer, eliminating the need for complex impedance matching networks.
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 enables flexible impedance ratios, reduces internal reflections, and simplifies the manufacturing process, improving filter performance and reducing costs compared to traditional methods.
Implementation Method 1
said resonators being acoustically coupled to each other
Implementation Method 2
at least one first phononic crystal structure between said input and output resonators allowing control of the amount of energy exchanged between said two resonators
Implementation Method 3
comprising at least one layer of piezoelectric or electrostrictive material
Implementation Method 4
comprising at least one layer of piezoelectric or electrostrictive material
Implementation Method 5
mainly bulk acoustic wave (BAW) resonators
Implementation Method 6
acoustic resonators
Data Source
Figure 1~2a
Figure 2b
Figure 3~4
AI summary
The invention relates to a surface acoustic wave band-pass filter comprising at least a first, input surface acoustic wave resonator (R1E), having an output face, and a second, output surface acoustic wave resonator (R2S), having an input face, said resonators being coupled together along a defined direction, the input and output faces being substantially opposite each other, characterized in that it further includes at least a first phononic crystal structure (CP1) between said input and output resonators and/or a second phononic crystal structure (CP2) on the periphery of said resonators so as to guide the surface acoustic waves generated by said input resonator to said output resonator along said defined direction, the resonators allowing impedance and/or mode conversion.