Ultrasound Transducer Polyethylene Matching Layer
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Solution Overview
Problem
Two-dimensional array ultrasound transducers face limitations in bandwidth and sensitivity due to the lack of suitable materials for a three matching layer design, leading to reduced performance in Doppler, color flow, and harmonic imaging modes, primarily because of velocity dispersion and the need for lower impedance matching layers.
Innovation Solution
A three matching layer design is implemented, where the first matching layer is a graphite composite, the second is a polymer loaded with electrically-conductive particles, and the third is a low-density polyethylene (LDPE) film, which extends to surround the piezoelectric element, providing a hermetic seal and eliminating the need for a protective coating, thus reducing production costs and improving acoustic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a three matching layer design is implemented to improve bandwidth and sensitivity, then imaging performance is improved, but the complexity of material selection and manufacturing increases due to the need for progressively lower impedance materials
Solution Approach 1:
The matching layer is divided into three distinct layers with progressively lower acoustic impedances (first layer: 3-10 MRayls, second layer: 2-6 MRayls, third layer: 1.5-4 MRayls), creating a stepped impedance transition that improves bandwidth and sensitivity while maintaining manageable manufacturing complexity through standardized material selection ranges
Solution Approach 2:
The patent employs composite material structures in the matching layers, including polyethylene combined with tungsten powder or barium sulfate, creating materials with tailored acoustic impedance properties that enable the three-layer design to achieve superior imaging performance across diverse frequencies
2Reliability
If low impedance materials are used for matching layers to accommodate 2D array elements, then acoustic coupling is improved, but velocity dispersion occurs causing frequency-dependent sound speed and creating a cutoff frequency
Solution Approach 1:
The patent systematically varies the acoustic impedance parameters across three layers (first layer: 3-10 MRayls, second layer: 2-6 MRayls, third layer: 1.5-4 MRayls) and optimizes thickness parameters (each layer 0.25-1.0 wavelengths thick) to achieve broadband matching while minimizing velocity dispersion effects across the operating frequency range
Solution Approach 2:
Different materials with specific local properties are assigned to each matching layer position: the first layer uses materials like graphite composite or epoxy, the second layer uses polyurethane or silicone rubber, and the third layer uses polyethylene with added density particles, where each material's local acoustic properties are optimized for its specific position in the impedance transition sequence
3Ease of manufacture
If only two matching layers are used due to material limitations, then manufacturing is simplified, but bandwidth and sensitivity are reduced limiting performance in Doppler, color flow, and harmonic imaging
Solution Approach 1:
The three-layer matching structure enables the transducer to dynamically adapt to diverse imaging modes by providing broadband frequency response that accommodates fundamental frequencies for penetration and harmonic frequencies for high-resolution imaging, allowing seamless operation across Doppler, color flow, and harmonic imaging applications
Solution Approach 2:
The matching layer structure with three layers and progressively lower impedances creates a universal acoustic coupling solution that performs optimally across multiple imaging modes and frequency ranges, making the transducer suitable for Doppler, color flow, harmonic imaging, and general B-mode imaging without requiring mode-specific adjustments
4Reliability
If polyethylene is used for the third matching layer, then acoustic performance is improved and hermetic sealing is achieved, but the material requires protection from environmental contamination
Solution Approach 1:
The patent combines the third matching layer function with the hermetic sealing function by integrating polyethylene material that serves dual purposes: providing the required low acoustic impedance (1.5-4 MRayls) for optimal acoustic coupling while simultaneously forming an impermeable barrier against environmental contamination, eliminating the need for separate protective coatings
Solution Approach 2:
The polyethylene third matching layer performs multiple functions simultaneously: acoustic impedance matching, hermetic sealing against moisture and chemicals, and structural protection of the piezoelectric elements, creating a multi-functional component that simplifies the overall transducer design and improves reliability
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 three matching layer design enhances the bandwidth and sensitivity of two-dimensional array ultrasound transducers, improving imaging capabilities while simplifying the production process by eliminating the need for protective coatings and reducing cost.
Implementation Method 1
An ultrasound transducer serves to convert electrical signals into ultrasonic energy and to convert ultrasonic energy back into electrical signals
Implementation Method 2
Acoustic coupling is accomplished, layer-by-layer, in a manner analogous to the functioning of respective anti-reflection coatings for lenses in an optical path. The relatively high acoustic impedance of the piezoelectric material in a transducer in comparison to that of the body is spanned by the intervening impedances of the matching layers
Data Source
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AI summary
A third matching layer (140) affording wide bandwidth for an ultrasound matrix probe is made of polyethylene, and may extend downwardly to surround the array (S360) and attach to the housing to seal the array (S370).