Coaxial cable refers to a cable with two concentric conductors, and the conductor and shield share the same axis. The most common PE /PP Physical Foaming Material For Coaxial Cable is composed of copper conductor isolated by insulating material. Outside the inner insulating material is another layer of circular conductor and its insulator, and then the whole cable is covered by PVC sheath. The insulating layer of coaxial cable is usually made of foamed PVC. So what are the benefits of using foamed insulation? Let’s first understand what is “dielectric constant”.
1.What is dielectric constant
When a medium is applied with an electric field, it will generate an induced charge and weaken the electric field. The ratio of the original applied electric field (in vacuum) to the electric field in the medium is the relative permittivity or dielectric constant, which is related to the frequency. Permittivity is the product of relative permittivity and absolute permittivity in vacuum. It is an important data of electrical properties of dielectric or insulating materials.
It means that if a material with high dielectric constant is placed in an electric field, the strength of the electric field will decrease significantly in the dielectric. The relative permittivity of an ideal conductor is infinite, because the internal field strength in the conductor is always zero, and the skin depth is zero due to the infinite conductivity, and electromagnetic shielding is formed in the conductor.
The transmission speed of signal in dielectric materials will decrease with the increase of dielectric constant. Therefore, in order to obtain high signal transmission speed, the dielectric constant of the material must be reduced. At the same time, in order to obtain high signal transmission speed, high characteristic impedance value must be used. But the high characteristic impedance must choose the low dielectric constant material.
2.Purpose of foaming
The purpose of foaming of general materials is to lighten the cable, strengthen the heat insulation and interference of the cable, and reduce the cost of materials. The purpose of foaming coaxial cable material is to reduce the dielectric constant of the material, so as to obtain high-speed signal transmission speed.
3.Material foaming mode
In order to increase the transmission capacity and speed, the best way is to reduce the medium constant of the material, which can be achieved by using foamed PE material. Generally, there are two ways of material foaming: chemical foaming and physical foaming (nitrogen foaming).
To sum up, the transmission speed of signal in the dielectric material will decrease with the increase of its dielectric constant, and the high-speed signal transmission speed can be obtained by reducing the dielectric constant of the coaxial cable using foaming insulating material, so as to ensure that the machine equipment can transmit the signal quickly and increase the working efficiency. Because the foaming of materials will lead to the decrease of material strength, it is necessary to control the foaming degree of insulating materials.
