Resonant Cavity Surface Wave Filter With Segmented Reflection Gratings

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Solution Overview

Problem

Surface elastic wave filters with resonant cavities often exhibit high-amplitude secondary lobes in the rejection or transition band, particularly when attempting to widen the passband, which is undesirable for telecommunications applications.

Innovation Solution

A surface elastic wave filter design featuring a composite substrate with a piezoelectric upper layer and a base substrate, incorporating an internal reflective structure with distinct reflection gratings and separation distances, along with external mirrors, to reduce the amplitude of lobes in the rejection or transition band.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the passband width is widened, then the filter's frequency range is improved, but the amplitude of secondary lobes in the rejection or transition band increases

Engineering Contradiction:

Improvepassband widthVSAvoidamplitude of secondary lobes

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The internal reflective structure is divided into multiple reflection gratings with different periods (first period and second period, where first period > second period). These gratings are separated by different distances (first distance and second distance, where first distance < second distance), creating segmented reflective zones that independently control different frequency components. This segmentation allows the filter to widen the passband while suppressing secondary lobes through distributed reflection control.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the internal reflective structure are assigned different reflective properties through varying grating periods and separation distances. The first structure with larger period and smaller separation distance handles specific frequency ranges, while the second structure with smaller period and larger separation distance handles other ranges. This local differentiation enables precise control over the frequency response, reducing secondary lobe amplitudes while maintaining wide passband coverage.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If conventional filter structures are used, then manufacturing is simplified, but unwanted signal rejection with high-amplitude lobes occurs

Engineering Contradiction:

Improvefilter structure fabricationVSAvoidunwanted signal rejection

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The filter employs a composite internal reflective structure combining multiple reflection grating types with different periods and spacing configurations. This composite approach integrates the functionality of multiple simpler structures into one unified device, achieving superior signal rejection characteristics while maintaining manufacturability through standardized fabrication processes for each grating component.

Inventive Principle:

Principle #40Composite materials

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 proposed filter structure effectively reduces the amplitude of secondary lobes by at least 5 dB, even for high passband widths, improving the filter's performance by minimizing unwanted signal rejection and maintaining a wide passband.

Implementation Method 1

at least two, respectively input and output, electroacoustic transducers 2a, 2b... arranged on a piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

two external reflection gratings 3a, 3b... typically Bragg mirrors... at least one internal reflection grating 4

Methodology Applied

Scientific EffectBragg diffraction: Bragg Diffraction

Data Source

PatentUS12255634B2Surface elastic wave filter with resonant cavities

Publication Date: 2025.03.18 SOITEC SA

AI summary

A surface elastic wave filter has resonant cavities and comprises a composite substrate formed of a base substrate and a piezoelectric upper layer; at least one input electroacoustic transducer and an output electroacoustic transducer, arranged on the upper layer, and at least one internal reflecting structure, arranged between the input electroacoustic transducer and the output electroacoustic transducer. The internal reflecting structure comprises a first structure comprising at least one reflection grating having a first period and a second structure comprising at least one reflection grating having a second period, the first period being greater than the second period.