PVDF Annular Array Transducer Fabrication via Ball-Bearing Compression

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Solution Overview

Problem

High-frequency ultrasound imaging is limited by the small depth of field and high two-way insertion loss of single element transducers, which restricts image resolution and depth of field, and existing methods struggle to fabricate high-frequency annular array transducers due to material limitations and complexity.

Innovation Solution

A high-frequency ultrasound annular array transducer is fabricated using a polyvinylidene fluoride (PVDF) film bonded with a copperclad polyimide film and epoxy, formed into a concave shape using a ball-bearing compression method, allowing for improved acoustic impedance matching and electronic focusing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If single element focused transducers are used for HFU applications, then fabrication is simple, but depth of field is limited and image resolution is restricted to a small axial range

Engineering Contradiction:

Improvefabrication simplicityVSAvoidimage resolution

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The transducer is divided into multiple independent annular elements that can be individually controlled. This segmentation allows electronic focusing and imaging across a larger depth of field while maintaining fabrication simplicity through modular construction using standard PVDF materials and techniques.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention transitions from a single-element design to a multi-element annular array configuration. This dimensional change from one element to multiple concentric rings enables electronic beam forming and focusing capabilities that extend the depth of field while preserving the simplicity of PVDF-based fabrication.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If PVDF membranes are used as the active acoustic layer, then fabrication is simple, but two-way insertion loss is high (≈40 dB)

Engineering Contradiction:

Improvefabrication simplicityVSAvoidinsertion loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The invention optimizes PVDF transducer performance by changing key parameters including increasing piezoelectric coefficients through material composition adjustments, optimizing thickness ratios between PVDF layers and backing materials, and tuning electrical matching networks to compensate for the inherent high insertion loss of PVDF while maintaining fabrication simplicity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The transducer employs composite material structures combining PVDF with optimized backing layers, matching layers, and electrode configurations. These composite designs improve acoustic impedance matching and reduce insertion loss while preserving the ease of PVDF-based fabrication processes.

Inventive Principle:

Principle #40Composite materials

3Loss of energy

If ceramic materials are used for HFU transducers, then insertion loss is reduced, but fabricating curved shapes is difficult

Engineering Contradiction:

Improveinsertion lossVSAvoidshaping capability

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The invention changes the material parameter from ceramic to PVDF, which inherently possesses the flexibility to be formed into curved shapes through simple bending and bonding processes. This material substitution maintains low insertion loss through optimized PVDF composition and structure while dramatically improving ease of manufacturing curved transducer geometries.

Inventive Principle:

Principle #35Parameter changes

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 provides a transducer with enhanced axial resolution, reduced lateral beamwidth, and improved depth of field, enabling two-dimensional imaging with a limited number of elements and reduced insertion loss, while maintaining the advantages of PVDF materials in acoustic impedance matching.

Implementation Method 1

a PVDF film on the epoxy... The assembly of materials are then pressed to bond the polyvinylidene fluoride film to the copperclad polyimide film

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

depositing a copperclad polyimide film... The area behind the copperclad polyimide film surface is filled with a second epoxy

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

bonded with a copperclad polyimide film and epoxy, formed into a concave shape... allowing for improved acoustic impedance matching

Methodology Applied

Scientific EffectAcoustic impedance matching: Acoustic Absorption

Data Source

PatentUS7356905B2Method of fabricating a high frequency ultrasound transducer

Publication Date: 2008.04.15 RIVERSIDE RES INST

AI summary

Techniques for fabricating high frequency ultrasound transducers are provided herein. In one embodiment, the fabrication includes depositing a copperclad polyimide film, a layer of epoxy on the copperclad polyimide film, and a polyvinylidene fluoride film on the epoxy. The assembly of materials are then pressed to bond the polyvinylidene fluoride film to the copperclad polyimide film and to form an assembly. The polyvinylidene fluoride film being one surface and the copperclad polyimide film being the other surface. The area behind the copperclad polyimide film surface is filled with a second epoxy, and then cured to form an epoxy plug.