Gap-Short Electro Acoustic Resonator for Transversal Mode Suppression
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Solution Overview
Problem
Electro acoustic resonators face challenges in suppressing transversal gap mode excitations and reducing transversal modes, which affect the performance of RF filters, especially in material systems like TFSAW where conventional piston mode approaches are insufficient.
Innovation Solution
The electro acoustic resonator incorporates a gap short structure with conductor strips that electrically shorts areas within the transversal gaps, reducing electrical fields and suppressing transversal gap mode excitations. This design also modifies the acoustic velocity barrier and its shape to further improve transversal mode suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transversal gap with higher wave velocity is used to reduce leakage of acoustic waves, then acoustic wave leakage is reduced, but transversal modes are excited due to wave diffraction
Solution Approach 1:
The patent converts the harmful effect of wave diffraction that excites transversal modes into a beneficial effect by intentionally designing diffraction gratings at the edges of the transversal gap. These gratings use diffraction to redirect acoustic energy back into the longitudinal propagation mode, transforming the harmful diffraction-induced transversal modes into useful acoustic energy confinement.
Solution Approach 2:
The patent introduces diffraction gratings as intermediary structures at the transversal gap edges. These gratings act as mediators that interact with the acoustic waves, selectively diffracting longitudinal modes while suppressing transversal modes, thus resolving the contradiction between reducing wave leakage and preventing transversal mode excitation.
2Ease of manufacture
If conventional piston mode approach is used in TFSAW material systems, then manufacturing is simplified, but transversal gap mode excitations cannot be sufficiently suppressed
Solution Approach 1:
The patent applies local quality by modifying only the edge regions of the transversal gap with diffraction gratings, while maintaining the conventional piston mode structure in the central region. This localized modification suppresses transversal gap mode excitations without requiring complete redesign of the entire resonator structure, thus preserving manufacturing simplicity while improving performance.
Solution Approach 2:
The patent segments the transversal gap region into a central piston mode area and edge regions with diffraction gratings. This segmentation allows different functional zones to coexist: the central region maintains conventional simple manufacturing characteristics while the edge regions provide specialized transversal mode suppression functionality.
3Power
If electrode fingers have extension in transversal direction to convert between electromagnetic and acoustic RF signals, then signal conversion is enabled, but transversal modes are excited
Solution Approach 1:
The patent converts the harmful transversal mode excitations generated by extended electrode fingers into beneficial effects by introducing diffraction gratings that use the same extension geometry to create constructive interference for longitudinal modes while creating destructive interference for transversal modes. The electrode finger extension that originally caused harm is now part of the solution.
Solution Approach 2:
The patent modifies the geometric parameters of the electrode fingers and introduces periodic structures (diffraction gratings) with specific pitch and width parameters. By carefully selecting these parameters to match the acoustic wavelength, the system achieves enhanced signal conversion capability while simultaneously suppressing transversal modes through parametric control of the diffraction process.
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 implementation of the gap short structure effectively suppresses transversal gap mode excitations and reduces transversal modes, leading to improved passband performance and transition steepness between passband and stopband in filters, while maintaining manufacturability with conventional processes.
Implementation Method 1
Electro acoustic resonators have an electrode structure and a piezoelectric material. Due to the piezoelectric effect an electro acoustic resonator converts between electromagnetic RF signals and acoustic RF signals.
Implementation Method 2
The gap short structure has conductor strips and is arranged inside the transversal gaps. The gap short structure effectively suppresses transversal gap mode excitations by reducing electrical fields
Implementation Method 3
The acoustic waves propagate in the longitudinal direction that is mainly orthogonal to the extension direction of the electrode fingers. The acoustic waves propagate at the surface or at the interface of the piezoelectric material.
Data Source
AI summary
An electro acoustic resonator is provided. The resonator has a gap short structure (GSS) to electrically short at least an area of the transversal gap to suppress transversal gap mode excitations. The gap short structure may be provided by a conductive stripe in the gap and parallel to or inclined with respect to the bus bar (BB) shorting adjacent IDT fingers. Additional connectors between the stripe and the bus bar may be provided. The connectors may have different pitch or metallization ratio with respect to the ID fingers. The connectors may be offset from the position of the fingers and my be inclined with respect to the bus bars. Multiple parallel stripes in the gap may provide a transversal reflector. By using a gap short structure a further improved transversal mode suppression of piston mode designs can be achieved.