PTFE Sheath with Air Cells for Low Dielectric Constant
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Solution Overview
Problem
Existing electric cables with insulating sheaths made from materials like polyethylene (PE) and polytetrafluoroethylene (PTFE) face challenges in achieving low dielectric constants and sufficient mechanical strength, especially when forming cables with multiple conductors, and require special precautions during soldering due to material melting issues.
Innovation Solution
The use of PTFE with continuous air-filled cells in the sheath, combined with a method involving extrusion and sintering, allows for the creation of electric cables with a dielectric constant less than 1.7 and improved mechanical strength, enabling cables of small diameter with enhanced dielectric performance and resistance to high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a solid sheath made of PTFE or PE is formed around the conductor, then the dielectric constant is reduced, but the mechanical strength and resistance to high temperatures are insufficient
Solution Approach 1:
The patent applies porous materials by incorporating air-filled cells within the PTFE sheath structure. The air-filled porous structure reduces the overall dielectric constant of the sheath while the PTFE matrix maintains mechanical strength and thermal resistance. This resolves the contradiction by using the low dielectric constant of air (ε≈1) combined with the structural integrity of PTFE.
Solution Approach 2:
The patent uses composite materials by combining PTFE with air-filled cells to create a sheath that achieves both low dielectric constant and adequate mechanical strength. The composite structure leverages the low dielectric properties of air and the mechanical/thermal properties of PTFE, resolving the contradiction between dielectric performance and mechanical strength.
2Quantity of substance
If thermoplastic materials like FEP or PE are used for the sheath, then the dielectric constant is reduced, but the materials melt under soldering heater elements
Solution Approach 1:
The patent applies parameter changes by transitioning from thermoplastic materials (FEP, PE) to thermosetting PTFE material. This fundamental material parameter change enables resistance to soldering temperatures while maintaining low dielectric constant through the air-filled cell structure. PTFE's high melting point and thermal stability resolve the temperature vulnerability of thermoplastics.
3Volume of moving object
If the cable diameter is reduced to fit multiple cables in small spaces, then the space requirement is reduced, but the mechanical strength and dielectric performance may deteriorate
Solution Approach 1:
The patent uses air-filled porous cells within the sheath to reduce the effective dielectric constant, which improves signal transmission at high frequencies. This allows for optimized cable design that maintains performance even at reduced diameters, as the low dielectric constant compensates for the smaller cross-sectional area available for conductors and insulation.
Solution Approach 2:
The composite PTFE-air structure enables reduced cable diameter while maintaining mechanical and dielectric performance. The PTFE provides structural integrity at small scales, while the air cells optimize electrical properties, allowing multiple cables to be installed in confined spaces without sacrificing performance.
4Quantity of substance
If cells are formed in the sheath wall to reduce dielectric constant, then the dielectric constant is reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent implements air-filled cells within the sheath using a manufacturing process that creates a porous structure. This approach reduces dielectric constant while the integration of cell formation into the sheath fabrication process minimizes additional manufacturing complexity. The porous structure is created as part of the sheath formation rather than as a separate complex assembly step.
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 resulting cables exhibit remarkable dielectric properties, allowing for multiple cables to be installed in small spaces and providing flexibility and mechanical strength, while the method is simple and industrially reliable, avoiding the need for complex air or fluid delivery systems.
Implementation Method 1
the sheath is made of PTFE and includes at least one continuous cell... the dielectric constant ε of which is less than 1.7... By using PTFE, the intrinsic properties of PTFE are combined with the contribution of one or more air-filled cells, so that the resulting electric cable possesses dielectric properties that are remarkable
Implementation Method 2
a method of sheathing at least one conductor in a PTFE sheath while forming at least one continuous cell... compressing a lubricant-impregnated PTFE powder in a converging chamber arranged in an extrusion die and around a guide for guiding said at least one conductor, the impregnated PTFE powder thus being thrust towards an extrusion orifice to form an extrudate
Implementation Method 3
sintering the resulting assembly so as to stabilize the material of the sheath
Implementation Method 4
extracting the lubricant by evaporation
Data Source
AI summary
An electric cable for conveying signals, the cable having a diameter of less than 2 mm and comprising at least one conductor in an insulating sheath, the sheath having a dielectric constant ε of less than 1.7. To achieve this, the sheath is made of PTFE and it includes at least one continuous cell. Fabrication is preferably by performing the following operations:compressing a lubricant-impregnated PTFE powder in a converging chamber arranged in an extrusion die and around a guide for guiding said at least one conductor, the impregnated PTFE powder thus being thrust towards an extrusion orifice to form an extrudate;causing said extrudate to pass from said orifice along an extrusion passage inside the die, in which it is shaped around the conductor(s), and of inside section that corresponds to the outline desired for the sheath;passing said extrudate around at least one solid bar presenting, at least over a distance within the extrusion passage, the same section as said cell and thereby preventing the extrudate from occupying the section that is to be occupied by said cell, the cell(s) being formed from the downstream end surface(s) of the bar(s) and extending downstream therefrom;extracting the lubricant by evaporation; andsintering the resulting assembly.