The application environment of microwave cable components is becoming increasingly challenging, such as exposure to extreme temperature changes; Exposure to chemicals often results in friction and bending. There are also some other challenges, such as requiring cable components to be not only compact and lightweight, but also economical and durable. In order to ensure the integrity of the signal and the reliability of the product, we must evaluate the electrical, mechanical, environmental, and specific application constraints that affect the overall performance of the cable. These variables have a direct impact on cable insulation, cable sheath, and cable construction. Meanwhile, experimentation and data analysis are key to determining whether these cables are still reliable in specific environments.
To ensure high-quality and stable signals, it is necessary to evaluate the insulation and sheath material characteristics of the cable, as these properties play a decisive role in whether the cable can meet strict requirements. The dielectric material used in signal cables not only affects the integrity of the signal, but also affects the durability of the cable.
silicone
Silicone is mainly used for cable sheaths and can maintain high flexibility even in low temperature environments. However, it is prone to breakage and its adhesive surface generates relatively high friction, making it unsuitable for cleanroom environments. The tensile strength and tear resistance of silicone are relatively low, so the sheath made of this material is thicker than other materials. Silicone has excellent radiation resistance, but the grade of silicone that can be used to make cable sheaths is well known, as silicone oil leakage can occur in vacuum applications, such as in hot vacuum chambers. If weight factor needs to be considered, then silicone is not the best choice.
polyurethane
Polyurethane is a good sheath material, but due to its lower voltage resistance compared to other materials, it is not used as insulation. Mechanically speaking, polyurethane has good flexibility and is highly resistant to wear and tear. In terms of environment, polyurethane is resistant to solvents, ultraviolet radiation, radiation, and mold. Polyurethane has a narrow temperature range and becomes brittle at around -40 ℃, with an upper temperature limit of around 100 ℃.
polyethylene
Polyethylene is most suitable for conductor insulation, as the polyethylene sheath is relatively hard and affects the flexibility of the cable. Polyethylene has good dielectric properties when used with foam materials. From the perspective of mechanical mechanics, high molecular weight polyethylene has the characteristics of wear resistance and low friction. The application temperature range of polyethylene is also very small, making it difficult to combine chemical resistant materials with polyethylene cable sheaths. The mechanical properties of polyethylene will decrease after flame retardant treatment.
fluoropolymer
Fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), and polytetrafluoroethylene (PTFE), among other fluorinated polymers, are excellent sheath materials. Among all insulation materials, fluorinated polymer materials have the highest pressure resistance. Fluorinated polymers can withstand extreme temperatures, but each material has its own application temperature range: Fluorinated ethylene propylene (FEP) can withstand temperature differences from -250 ° C to 150 ° C, while perfluoroalkoxy (PFA) can withstand temperature differences from -250 ° C to 200 ° C.
Polytetrafluoroethylene (PTFE) does not lose its flexibility even at low temperatures up to 260 ° C. Fluorinated polymers are resistant to chemicals, acids, and corrosive substances, and they are all non flammable. Polytetrafluoroethylene and its polymers also have the advantage of low degassing, which is particularly important for ultra-high vacuum (UHV) environments. Most fluoropolymers are flexible, but like their temperature resistance, their flexibility may vary depending on the material used. Perfluoroalkoxy is the hardest, followed by fluorinated ethylene propylene and polytetrafluoroethylene. Meanwhile, the sheath made of polytetrafluoroethylene has the best flexibility.
Engineering Fluorinated Polymers
One of the drawbacks of fluorinated polymers is their weak resistance to wear and tear. Some fluorinated polymers can be improved in their physical, chemical, and electromagnetic properties through engineering treatments, thereby enhancing their ability to meet special requirements in microwave applications. Tetrafluoroethylene (ETFE) can improve its mechanical properties and chemical resistance through irradiation, but irradiation can enhance its hardness, thereby greatly reducing its flexibility. The natural properties of polytetrafluoroethylene are heat resistance and chemical inertness. Therefore, when improving its electrical or mechanical properties, its temperature and chemical properties will not change significantly.
