Ultra-lightweight, stable phase radio frequency coaxial cable and method of making same

Abstract

The application provides a kind of ultra-light stable phase radio frequency coaxial cable, including sequentially arranged from inside to outside in cross-sectional direction inner conductor, insulating layer, outer conductor, shielding isolation layer and outer protective layer;Inner conductor adopts Ag / FEP composite material, and conductive silver layer floats on the surface of fluoroplastic FEP;Outer conductor adopts Ag / PI / Ag composite material, and conductive silver layer is distributed around polyimide to form airtight conductive layer;Shielding isolation layer is woven shielding structure formed by weaving polyimide fiber with surface silver layer, and the surface of single polyimide fiber in it is covered with surface silver layer, and outer protective layer is FEP / PI / FEP outer protective layer or PFA outer protective layer.The ultra-light stable phase radio frequency coaxial cable provided by the application uses the principle of skin effect of high frequency signal, uses composite material containing surface silver layer, and uses non-metallic material with smaller density to replace metal material not participating in signal transmission part, reduces material weight on the basis of ensuring signal transmission demand, and reduces cable weight by more than 50%.

Description

TECHNICAL FIELD

[0001] The present application relates to coaxial cable technology field, and in particular to an ultra-light stable phase radio frequency coaxial cable and a preparation method thereof. BACKGROUND

[0002] With the development of aerospace equipment, the weight requirements of various devices and components are becoming more and more stringent. As a link transmission medium in communication, tracking, warning, navigation, and electronic countermeasure radio frequency equipment, the radio frequency coaxial cable is widely used in aerospace equipment. Therefore, there is a new demand for ultra-light stable phase radio frequency coaxial cable.

[0003] Traditional stable phase radio frequency coaxial cables generally use silver-plated copper metal materials as the inner conductor, outer conductor, and shielding layer of the cable to play a conductive role. However, the density of the commonly used silver-plated copper material is 8.89 g / cm 3 , which makes the overall weight of the traditional stable coaxial cable relatively high. Moreover, the outermost protective layer of the traditional stable coaxial cable is produced by extrusion, and the extrusion thickness is relatively large, which also increases the weight of the traditional stable coaxial cable, which is undesirable. SUMMARY

[0004] The present application aims to provide an ultra-light stable phase radio frequency coaxial cable and a preparation method thereof. By utilizing the skin effect principle of high-frequency signals and replacing the metal materials that do not participate in signal transmission with non-metal materials of smaller density, the weight of the materials is reduced while ensuring the signal transmission requirements, thereby reducing the weight of the cable by more than 50%.

[0005] According to the first aspect of the present application, an ultra-light stable phase radio frequency coaxial cable is provided, which includes an inner conductor, an insulating layer, an outer conductor, a shielding isolation layer, and an outer protective layer arranged in order from inside to outside in the cross-sectional direction.

[0006] The inner conductor is made of Ag / FEP composite material, and the conductive silver layer is floating on the surface of the fluoroplastic FEP.

[0007] The outer conductor is made of Ag / PI / Ag composite material, and the conductive silver layer is distributed around the polyimide to form a closed conductive layer.

[0008] The shielding isolation layer is a woven shielding structure formed by weaving polyimide fibers with a surface silver layer. The surface of each polyimide fiber of the woven shielding structure is covered with a surface silver layer.

[0009] According to the second aspect of the present application, a preparation method of an ultra-light stable phase radio frequency coaxial cable is also provided, which includes the following steps:

[0010] Step 1: preparing an Ag / FEP composite material inner conductor

[0011] A conductive silver layer is prepared on the surface of the fluoroplastic FEP, and the thickness of the conductive silver layer is 10-15 μm;

[0012] Step 2, preparing an insulating layer on the outer layer of the inner conductor

[0013] A plurality of low-density polytetrafluoroethylene insulating tapes are wrapped outside the insulating layer to form a polytetrafluoroethylene insulating layer, wherein the wrapping directions of adjacent two polytetrafluoroethylene insulating tapes are opposite;

[0014] Step 3, preparing an outer conductor of Ag / PI / Ag composite material on the outer layer of the insulating layer

[0015] The conductive silver layers on both sides of the Ag / PI / Ag composite material are respectively distributed on the upper and lower surfaces of the polyimide material to form an Ag / PI / Ag conductive tape, and the Ag / PI / Ag conductive tape is wound on the outer layer of the insulating layer to form a closed conductive layer;

[0016] Step 4, preparing a shielding isolation layer on the outer layer of the outer conductor

[0017] The polyimide fibers are used to cover the outer layer of the outer conductor in a multi-strand cross-weaving manner to prepare a woven shielding structure, and the surface of each polyimide fiber of the woven shielding structure is covered with a surface silver layer;

[0018] Step 5, preparing an outer protective layer on the outer layer of the shielding isolation layer, and the outer protective layer is an FEP / PI / FEP outer protective layer or a PFA outer protective layer

[0019] The preparation process of the FEP / PI / FEP outer protective layer is as follows: the FEP / PI / FEP composite material is uniformly and multi-layer wound outside the shielding isolation layer to form a relatively closed tubular structure, and through a heat treatment process, the fluoroplastic FEP in contact with each other during the winding process is melted to form a sealed protective layer, and the thickness of the outer protective layer is reduced to 0.1 mm;

[0020] The preparation process of the PFA outer protective layer is as follows: the PFA material is uniformly extruded and wrapped outside the shielding isolation layer to form a PFA outer protective layer.

[0021] Through the above technical scheme, the ultra-light stable phase radio frequency coaxial cable adopts a new type of composite material, which greatly reduces the weight of the product under the condition of ensuring signal transmission, so that the weight of the stable phase radio frequency coaxial cable is reduced by more than 50%, and the stable phase performance, low loss performance, and bending performance of the product are improved, so that the light weight of the aerospace equipment can be realized.

[0022] It is to be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter. Additionally, all combinations of claimed subject matter are contemplated as part of the inventive subject matter.

[0023] The foregoing and other aspects, embodiments and features of the present teachings are more fully described and understood by reference to the following description taken in conjunction with the accompanying drawings. Other aspects, features, and embodiments of the present teachings will become apparent with reference to the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical, or nearly identical, component that is illustrated in various figures is represented with a like numeral. For purposes of clarity, not every component is called out in every drawing. Embodiments of various aspects of the present teachings will now be described, by way of example, with reference to the drawings, in which:

[0025] Figure 1 is a schematic diagram of the cross-sectional structure of the ultra-lightweight stable phase radio frequency coaxial cable proposed by the present application. DETAILED DESCRIPTION

[0026] For a more complete understanding of the present application, reference is now made to the following description taken in conjunction with the accompanying drawings in which:

[0027] Aspects of the present application are described in the disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The described embodiments of the present application are not necessarily meant to include all aspects of the present application. It is to be understood that the various concepts and embodiments introduced above and those described in greater detail below can be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any particular implementation. Additionally, some aspects of the present application can be utilized independently, or in any suitable combination with other aspects of the present application.

[0028] In conjunction Figure 1 The ultra-lightweight stable phase radio frequency coaxial cable of the illustrated example includes, in cross-sectional order from inner to outer, an inner conductor 10, an insulating layer 20, an outer conductor 30, a shielding isolation layer 40, and an outer protective layer 50.

[0029] The inner conductor is made of Ag / FEP composite material, in which the conductive silver layer floats on the surface of fluoroplastic FEP.

[0030] The outer conductor is made of Ag / PI / Ag composite material, in which the conductive silver layer is distributed around the polyimide to form a closed conductive layer.

[0031] The shielding isolation layer is a woven shielding structure formed by weaving polyimide fibers with a surface silver layer, and the surface of each polyimide fiber of the woven shielding structure is covered with a surface silver layer.

[0032] Thus, by using the new composite material for the inner conductor 10, the outer conductor 30 and the shielding isolation layer 40, and by using the skin effect principle of high-frequency signals, that is, when alternating current or alternating magnetic field exists in the conductor, the current distribution in the conductor is uneven, the current is concentrated on the surface of the conductor, and the current density on the conductor is greater, the skin phenomenon is formed, by using the composite material containing the surface silver layer, the metal material not participating in signal transmission is replaced by the non-metal material with smaller density, the material weight is reduced on the basis of ensuring the signal transmission requirement, thereby the cable weight is reduced by more than 50%, and the stable phase performance, low loss performance and mechanical performance index of the stable phase radio frequency coaxial cable are ensured, and the lightweight application in aerospace equipment is realized.

[0033] Inner conductor

[0034] In the embodiment of the present application, the typical value of the density of the Ag / FEP composite material is 2.2 g / cm 3 The thickness of the conductive silver layer is 10-15 μm.

[0035] In the embodiment of the present application, according to the calculation of the skin depth, when the signal frequency reaches the minimum use frequency 100 MHz of the cable, the signal skin depth is 8 μm, the Ag / FEP composite material meets the signal transmission requirement, and the density is only 2.2 g / cm 3 , thereby reducing the weight of the inner conductor by 75%.

[0036] In the production process, the production of the inner conductor 10 uses a small-tension active pay-off device, the outer diameter of the guide wheel and the traction dancing wheel needs to be more than 200 times of the outer diameter of the inner conductor, the pay-off tension is 1 N-20 N, and the pay-off tension fluctuation is less than ±0.15 N. In the pay-off process, by using the active pay-off mode with small tension and large bending radius, the continuity of the conductive layer of the inner conductor is effectively ensured, and the continuity of the signal transmission on the inner conductor is ensured.

[0037] Insulation layer

[0038] In the embodiment of the present application, the insulating layer 20 is formed by winding a plurality of polytetrafluoroethylene insulating tapes on the outside of the insulating layer, the winding directions of the adjacent two polytetrafluoroethylene insulating tapes are opposite, and the lap rate is controlled to be 40%-80%.

[0039] In the embodiment of the present application, the polytetrafluoroethylene material is uniformly distributed with air by the puffing or micropore technology, so that the density of the low-density polytetrafluoroethylene insulating layer is controlled to be 0.6-0.7 g / cm3 .

[0040] The insulating layer 20 has a stable relative dielectric constant, so that the phase of the coaxial cable changes less with temperature, thereby having a stable phase effect. Moreover, the insulating layer is produced by using a high-precision concentric wrapping form of active tape laying, the thickness of the low-density polytetrafluoroethylene insulating tape is less than 0.254 mm, the cladding rate is less than 80%, the number of wrapping layers is selected to be an even number, the wrapping directions of adjacent two layers are opposite, and the stress generated in the wrapping forming process of the low-density polytetrafluoroethylene insulating tape is offset through the opposite wrapping directions, so that the overall insulation is stable.

[0041] Outer conductor

[0042] In the embodiment of the present application, the typical value of the density of the Ag / PI / Ag composite material is selected as 5.83 g / cm 3 wherein the conductive silver layers are distributed on the upper and lower sides of the PI, and the thickness of the conductive silver layers is controlled to be 10-15 μm.

[0043] In the embodiment of the present application, the Ag / PI / Ag composite material is uniformly distributed in the form of a thin layer on the outside of the insulating layer to form an outer conductor layer.

[0044] The polyimide PI material has the characteristics of high temperature resistance and high strength, so that the outer conductor has high strength and is superior to the traditional silver-plated copper material in processing.

[0045] In the embodiment of the present application, the Ag / PI / Ag composite material is uniformly distributed on the outside of the insulating layer in the form of winding. In order to ensure the consistency of the cable impedance in the winding process, the outer diameter can be finely adjusted by a precision mold after winding, so as to reduce the outer diameter fluctuation caused by winding and ensure the consistency of the inner diameter of the outer conductor, thereby improving the consistency of the cable impedance and avoiding signal reflection in the transmission of the cable, which affects the signal quality.

[0046] The key performance of the outer conductor material is shown in the following table:

[0047] Performance Unit Typical value Thickness tolerance mm ±0.003 Width tolerance mm ±0.040 Density g / cm 3 ]] 5.83 DC resistance Ω·mm 2 / m]] 1.39 Tensile strength MPa 220 Elongation at break ％ 20 Conductive silver layer μm 10 Service temperature ℃ -60～250

[0048] Shielding barrier layer 40

[0049] In the embodiment of the present application, the polyimide fibers with a surface silver layer in the woven shielding structure are covered on the outer layer of the outer conductor by multi-strand cross weaving, and the covering density is greater than or equal to 97%, so that the shielding isolation layer has a relatively optimal shielding efficiency, the shielding efficiency can reach more than 95 dB, thereby ensuring the shielding property of the cable and making the signal transmission process not be disturbed by the outside.

[0050] The silver layer on the surface of the polyimide fiber monofilament has a thickness of 1-2 μm.

[0051] Outer protective layer 50

[0052] In the embodiment of the present application, the outer protective layer 50 serves as a sheath layer and plays a protective role. The outer protective layer 50 can be realized by two technical solutions, i.e., an FEP / PI / FEP outer protective layer or an FPA outer protective layer.

[0053] When the outer protective layer uses FEP / PI / FEP, the FEP / PI / FEP composite material is uniformly wound in multiple layers outside the shielding isolation layer to form a relatively closed tubular structure, and through a heat treatment process, the fluoroplastic FEP in contact with each other during the winding process is melted to form a sealing protective layer.

[0054] When the outer protective layer uses PFA, the FPA material is extruded and formed on the outer layer of the shielding isolation layer.

[0055] Solution (1): The outer protective layer uses FEP / PI / FEP composite material to be uniformly wound on the shielding layer, and through a heat treatment process, the fluoroplastic layer in contact with each other during the winding process is melted to form a sealing protective layer. The thickness of the outer protective layer can be reduced to 0.1 mm, and the weight is reduced by more than 60%.

[0056] The outer protective layer uses a 30%-50% overlap rate winding process, and the overlapping winding can make the FEP / PI / FEP composite material form a relatively closed tubular structure. After heat treatment, the overlapping parts are melted together to play a sheath protection role.

[0057] The heat treatment temperature of the optional embodiment of the present application is as follows (unit: Celsius):

[0058] Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 585±10 580585±10 550585±10 590585±10 590585±10 515585±10 515585±10 550585±10

[0059] The performance of the prepared outer protective layer is shown in the table:

[0060] Performance Unit Typical value Thickness tolerance ％ ±15 Width tolerance ％ ±3 Tensile strength (23°C) MPa 152 Tensile modulus MPa 2100 Elongation at break ％ 60 Dielectric constant (1 kHz) - 1.5～4 Dielectric loss tangent (1 kHz) - 1.5 x 10 -3 ]]> Dielectric strength kV / mm 200 Volume resistivity (23°C) Ω·cm 1.5 x 10 16 ]]

[0061] Solution (2): The outer protective layer uses PFA material to be uniformly extruded and wrapped on the shielding isolation layer. Through a heat extrusion process, a fluoroplastic extruder is used, the stretching ratio is 20-250, and the stretching balance is 1.02-1.35.

[0062] The temperature of each zone of the extruder during extrusion is controlled as follows:

[0063] Zone 1: (340±10) °C;

[0064] Zone 2: (355±10) °C;

[0065] 3 zone (365 ± 10) °C;

[0066] 4 zone (370 ± 10) °C;

[0067] 5 zone (330 ± 10) °C;

[0068] 6 zone (385 ± 15) °C;

[0069] 7 zone (390 ± 15) °C.

[0070] Preferably, the PFA material of the outer protective layer should be pre-dried at (200 ± 5) °C before overmolding.

[0071] The typical properties of the PFA outer protective layer are shown in the following table.

[0072] Performance Unit Typical value Melt index g / 10 min 11～18 Melting point ℃ 300～308 Tensile strength MPa 23～33 Elongation at break ％ 400～550

[0073] In combination with the disclosed embodiments, a method for preparing the ultra-lightweight stable-phase radio frequency coaxial cable is also proposed, comprising the following steps:

[0074] Step 1, preparing an inner conductor of Ag / FEP composite material

[0075] An electrically conductive silver layer is prepared on the surface of the fluoroplastic FEP, with a thickness of 10-15 μm;

[0076] Step 2, preparing an insulating layer outside the inner conductor

[0077] A plurality of low-density polytetrafluoroethylene insulating tapes are wrapped outside the insulating layer to form a polytetrafluoroethylene insulating layer, wherein the wrapping directions of the adjacent two polytetrafluoroethylene insulating tapes are opposite;

[0078] Step 3, preparing an outer conductor of Ag / PI / Ag composite material outside the insulating layer

[0079] The electrically conductive silver layers on both sides of the Ag / PI / Ag composite material are respectively distributed on the upper and lower surfaces of the polyimide material to form Ag / PI / Ag conductive tapes, and the Ag / PI / Ag conductive tapes are wound outside the insulating layer to form a closed conductive layer; the thickness of each electrically conductive silver layer is 10-15 μm;

[0080] Step 4, preparing a shielding isolation layer outside the outer conductor

[0081] The polyimide fibers are used to cover the outer layer of the outer conductor in a multi-strand cross-weaving manner to prepare a woven shielding structure, and the surface of each polyimide fiber of the woven shielding structure is covered with a surface silver layer;

[0082] Step 5, preparing an outer protective layer on the outer layer of the shielding isolation layer, the outer protective layer being an FEP / PI / FEP outer protective layer or a PFA outer protective layer

[0083] The preparation process of the FEP / PI / FEP outer protective layer is as follows: the FEP / PI / FEP composite material is uniformly and multi-layer wound outside the shielding isolation layer to form a relatively closed tubular structure, and through a heat treatment process, the fluoroplastic FEP in contact with each other during the winding process is melted to form a sealed protective layer, and the thickness of the outer protective layer is reduced to 0.1 mm; wherein the lap rate of the winding is 30-50%.

[0084] The preparation process of the PFA outer protective layer is as follows: the PFA material is uniformly extruded and wrapped outside the shielding isolation layer to form a PFA outer protective layer.

[0085] Taking a 3449 specification precision radio frequency coaxial cable as an example, the improved structure and process of the application is prepared, and the specific design is as follows:

[0086] (1) an Ag / FEP composite material with an outer diameter of 1.40 mm is used, and the thickness of the conductive silver layer on the outer surface is 10 μm, which is used as an inner conductor,

[0087] (2) the insulating layer uses a 0.6 g / cm3 PTFE microporous tape, and the structure is as follows:

[0088] Tier Specification (width x thickness, mm) Overlap rate 1 9×0.127 66％ 2 13×0.127 66％ 3 15×0.152 66％

[0089] The wrapping environment temperature is 23.2℃, the wrapping tension is 5N, the overall thickness of the insulation is 1.195 mm, and the outer diameter is 3.79 mm;

[0090] (3) the outer conductor uses a 2.5x0.04 specification Ag / PI / Ag composite material, and the thickness of the conductive silver layer is 12 μm.

[0091] Among them, the wrapping tension is 9.5N, the lap rate is 50%, the thickness of the outer conductor is 0.08mm, and the outer diameter of the outer conductor is 3.95mm;

[0092] (4) the shielding isolation layer uses a 300D specification surface silver layer polyimide fiber, and is prepared by using a 24 spindle braiding machine, the braiding solution is 15 mm, the braiding density is 98%, and the braided outer diameter is 4.35 mm; the thickness of the silver layer on the surface of the polyimide fiber monofilament is controlled to be 1-2 μm;

[0093] (5) the outer protective layer uses a PFA material uniformly extruded and wrapped outside the shielding isolation layer, and the temperature of each zone of the extruder during extrusion is controlled as follows:

[0094] 1 zone 340℃, 2 zone 355℃, 3 zone 365℃, 4 zone 370℃, 5 zone 325℃, 6 zone 380℃, 7 zone 390℃.

[0095] The PFA material is pre-dried at 200±110 DEG C before extrusion.

[0096] The outer protective layer has a thickness of 0.23 mm, and the cable has an outer diameter of 4.80 mm.

[0097] Thus, the ultra-lightweight stable-phase RF coaxial cable is prepared by the typical process, and performance test comparison with the existing CXN3449 type RF coaxial cable (Gore) is shown in the following table:

[0098]

[0099] It can be seen that the ultra-lightweight stable-phase RF coaxial cable designed and optimized by the application uses the principle of skin effect of high-frequency signals, uses a composite material containing a surface silver layer, and uses a non-metallic material with smaller density to replace the metal material not participating in signal transmission, thereby reducing the material weight, reducing the cable outer diameter size, and reducing the cable weight by more than 50% on the basis of ensuring the signal transmission requirement.

[0100] Although the application has been disclosed as above with preferred embodiments, it is not intended to limit the application. Those skilled in the art can make various modifications and improvements without departing from the spirit and scope of the application. Therefore, the protection scope of the application shall be subject to the definition of the claims.

Claims

1. An ultralight, phase-stable radio frequency coaxial cable, characterized in that, It includes an inner conductor, an insulating layer, an outer conductor, a shielding and isolation layer, and an outer protective layer arranged sequentially from the inside to the outside in the cross-sectional direction; The inner conductor is made of Ag / FEP composite material, in which the conductive silver layer floats on the surface of the fluoroplastic FEP. The outer conductor is made of Ag / PI / Ag composite material, in which a conductive silver layer is distributed around the polyimide to form a closed conductive layer. The shielding layer is a woven shielding structure formed by weaving polyimide fibers with a surface silver layer. The surface of each polyimide fiber in the woven shielding structure is covered with a surface silver layer. The insulation layer is formed by wrapping multiple layers of polytetrafluoroethylene (PTFE) insulating tape around the outside of the insulation layer. The wrapping directions of adjacent layers of PTFE insulating tape are opposite, and the overlap rate is controlled between 40% and 80%. The polytetrafluoroethylene (PTFE) material is treated with expansion or microporous technology to ensure uniform air distribution within the PTFE material, thereby controlling the density of the low-density PTFE insulation layer to be 0.6–0.7 g / cm³. 3 .

2. The ultralightweight stable phase radio frequency coaxial cable according to claim 1, characterized in that, The thickness of the conductive silver layer in the Ag / FEP composite material is 10~15μm.

3. The ultralight stable phase radio frequency coaxial cable according to claim 1, characterized in that, The thickness of the conductive silver layer in the Ag / PI / Ag composite material is 10~15μm.

4. The ultralight stable phase radio frequency coaxial cable according to claim 1, characterized in that, The Ag / PI / Ag composite material is uniformly distributed on the outside of the insulation layer by winding.

5. The ultralightweight stable phase radio frequency coaxial cable according to claim 1, characterized in that, In the braided shielding structure, polyimide fibers with a surface silver layer are covered on the outer layer of the outer conductor by multi-strand cross-weaving, with a coverage density of greater than or equal to 97%.

6. The ultralight stable phase radio frequency coaxial cable according to claim 1, characterized in that, The outer protective layer is an FEP / PI / FEP outer protective layer, wherein the FEP / PI / FEP composite material is uniformly wound in multiple layers around the outside of the shielding and isolation layer to form a relatively closed tubular structure. Through a heat treatment process, the fluoroplastic FEP that comes into contact with each other during the winding process melts to form a sealed protective layer.

7. The ultralight stable phase radio frequency coaxial cable according to claim 1, characterized in that, The outer protective layer is a PFA outer protective layer, which is extruded and formed on the outer layer of the shielding and isolation layer.

8. A method for manufacturing an ultralight, phase-stable radio frequency coaxial cable as described in claim 1, characterized in that, Includes the following steps: Step 1: Preparation of the inner conductor of Ag / FEP composite material A conductive silver layer with a thickness of 10~15 μm was prepared on the surface of fluoroplastic FEP. Step 2: Prepare an insulating layer on the outer layer of the inner conductor. Multiple layers of low-density polytetrafluoroethylene (PTFE) insulating tape are wrapped around the outside of the insulation layer to form a PTFE insulation layer, wherein the wrapping directions of adjacent PTFE insulating tape layers are opposite. Step 3: Prepare an outer conductor of Ag / PI / Ag composite material on the outer layer of the insulating layer. The conductive silver layers on both sides of the Ag / PI / Ag composite material are distributed on the upper and lower surfaces of the polyimide material, forming Ag / PI / Ag conductive strips. The Ag / PI / Ag conductive strips are wound around the outer layer of the insulating layer to form a closed conductive layer. Step 4: Prepare a shielding isolation layer on the outer layer of the outer conductor. A braided shielding structure is prepared by covering the outer layer of the outer conductor with polyimide fibers in a multi-strand cross-weaving manner, wherein the surface of each polyimide fiber of the braided shielding structure is covered with a surface silver layer. Step 5: Prepare an outer protective layer on the outer layer of the shielding and isolation layer. The outer protective layer is an FEP / PI / FEP outer protective layer or a PFA outer protective layer. The fabrication process of the FEP / PI / FEP outer protective layer is as follows: FEP / PI / FEP composite material is uniformly wound in multiple layers around the outside of the shielding and isolation layer to form a relatively closed tubular structure. Through a heat treatment process, the fluoroplastic FEP that comes into contact with each other during the winding process melts to form a sealed protective layer, reducing the thickness of the outer protective layer to 0.1 mm; the overlap rate of the winding is 30%~50%. The manufacturing process of the PFA outer protective layer is as follows: PFA material is uniformly extruded onto the outside of the shielding and isolation layer to form the PFA outer protective layer.

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