Acoustic Wave Electrode Layout for Unwanted Resonance Suppression

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Solution Overview

Problem

Acoustic wave devices, particularly longitudinally coupled resonator-type filters, suffer from unwanted resonance that degrades filter characteristics, especially in the attenuation region, due to increased intensity of longitudinal modes.

Innovation Solution

Incorporating nonuniform duty ratio and average width ratio areas in the interdigital transducer electrodes and reflectors, with random duty ratios and widths, to reduce phase coherence of signal reflections and suppress unwanted resonance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If uniform duty ratio is used in all electrode fingers, then manufacturing is simple, but unwanted resonance occurs and filter characteristics are degraded

Engineering Contradiction:

Improveelectrode fabrication simplicityVSAvoidfilter characteristics

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by varying the duty ratio of electrode fingers in specific local regions rather than uniformly across all fingers. The interdigital transducer electrode includes a first region and a second region with different duty ratios, and reflectors have alternating high and low duty ratio sections. This localized variation suppresses unwanted resonance while maintaining overall manufacturability through a systematic design approach.

Inventive Principle:

Principle #3Local quality

2Reliability

If nonuniform duty ratio is used to suppress unwanted resonance, then filter characteristics improve, but device complexity increases

Engineering Contradiction:

Improvefilter characteristicsVSAvoidelectrode structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the electrode structure into distinct regions with different duty ratios. The interdigital transducer electrode is divided into a first region with a first duty ratio and a second region with a second duty ratio. Reflectors are segmented into alternating high and low duty ratio sections. This segmentation systematically manages complexity while achieving resonance suppression.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces asymmetry by using different duty ratios in different regions of the same electrode type. The interdigital transducer has asymmetric duty ratios between its first and second regions, and reflectors have asymmetric alternating patterns. This asymmetry disrupts the phase coherence of reflected signals, suppressing unwanted resonance.

Inventive Principle:

Principle #4Asymmetry

3Loss of energy

If longitudinal mode intensity is increased to improve pass band characteristics, then insertion loss improves, but response level in attenuation region degrades

Engineering Contradiction:

Improveinsertion lossVSAvoidresponse level in attenuation region

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent converts the harmful effect of strong longitudinal modes (which cause unwanted resonance in the attenuation region) into a beneficial effect. By using nonuniform duty ratios in the interdigital transducer and reflectors, the patent suppresses the unwanted resonance caused by longitudinal modes while maintaining their useful contribution to pass band characteristics. The varied duty ratios disrupt the phase coherence of reflected signals, transforming the harmful resonance into suppressed responses in the attenuation region.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

Improves response level in the attenuation region outside the pass band by suppressing unwanted resonance, thereby enhancing filter performance.

Implementation Method 1

an acoustic wave device includes a piezoelectric substrate, an interdigital transducer (IDT) electrode on the piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

acoustic wave device includes a piezoelectric substrate, an interdigital transducer (IDT) electrode on the piezoelectric substrate

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Data Source

PatentUS12407324B2Acoustic wave device

Publication Date: 2025.09.02 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a piezoelectric substrate, a first interdigital transducer electrode on the piezoelectric substrate, and a first reflector and a second reflector. The first interdigital transducer electrode, the first reflector, and the second reflector each include a plurality of electrode fingers. At least one of the first interdigital transducer electrode, the first reflector, and the second reflector has a nonuniform duty ratio area where three successive electrode fingers in an acoustic wave propagation direction all have different duty ratios.