CN115938657A

CN115938657A - Transmission cable, core wire and core wire preparation method

Info

Publication number: CN115938657A
Application number: CN202211731382.6A
Authority: CN
Inventors: 曹树钊; 王峰
Original assignee: XFusion Digital Technologies Co Ltd
Current assignee: XFusion Digital Technologies Co Ltd
Priority date: 2022-12-30
Filing date: 2022-12-30
Publication date: 2023-04-07
Also published as: WO2024139369A1

Abstract

The embodiment of the application discloses a transmission cable, a core wire and a core wire preparation method. The core wire comprises a conductor and a dielectric layer coated outside the conductor, and a plurality of closed cavity structures which are arranged at intervals are arranged in the dielectric layer. While the medium loss of the core wire is effectively reduced, each independent cavity structure can construct and form a closed space for blocking water vapor from entering, so that the moisture absorption risk of the medium layer can be reduced; for a high-speed cable applied in a humid environment with large temperature difference change, insertion loss fluctuation can be effectively avoided, and the SI performance of high-speed cable transmission is met. By applying the scheme, based on the arrangement of the medium layer inner sealing cavity structure, the weight can be reduced, the flexibility of the cable is improved, the assembly operation of the high-speed cable is facilitated, and the advantages are particularly remarkable in the application scene of more system high-speed cable wiring.

Description

Transmission cable, core wire and core wire preparation method

Technical Field

The embodiment of the application relates to the technical field of communication interconnection, in particular to a transmission cable, a core wire and a core wire preparation method.

Background

The development of communication technology has higher and higher requirements on system bandwidth, and good SI (Signal Integrity) performance is ensured through the requirement of high-speed performance parameters of a system full link from a sending chip to a receiving chip. Taking the field of servers as an example, the chip and the matched PCIE interface both provide a product specification of 32Gbps bandwidth, so that specific parameter index requirements are provided for passive parameters such as full link insertion loss and crosstalk.

For a high-speed link of a product, the reasonable control of design indexes such as insertion loss performance, flexibility and weight of a high-speed cable becomes a research and development direction of important attention in the industry. In the existing typical cable structure, an insulation medium layer is formed outside a conductor by adopting an FEP (Fluorinated ethylene propylene) foaming process, and a plurality of cavity pores are formed in the medium layer, so that the flexibility of the cable can be improved to a certain degree, and the dead weight is reduced. However, the pores of the cavity formed in the dielectric layer based on the foaming process are in a disordered communication state, the impedance is increased after water vapor in the environment enters the pores of the cavity, and the insertion loss fluctuation is large due to the change of the dielectric constant.

Disclosure of Invention

The embodiment of the application provides a transmission cable, a core wire and a core wire preparation method, the moisture absorption capacity of a dielectric layer can be reduced through structural optimization, insertion loss fluctuation is effectively avoided, and a technical guarantee is provided for improving the signal integrity transmission performance of the transmission cable.

The first aspect of the embodiments of the present application provides a core wire, where the core wire includes a conductor and a dielectric layer coated outside the conductor, and a plurality of closed cavity structures arranged at intervals are provided in the dielectric layer. By the arrangement, the core wire dielectric loss is effectively reduced, and meanwhile, each independent cavity structure can construct a closed space for blocking water vapor from entering, so that the moisture absorption risk of the dielectric layer can be reduced; therefore, for the high-speed cable applied to the environment with large changes of humidity and temperature difference, the insertion loss fluctuation can be effectively avoided, and the SI performance of high-speed cable transmission is improved.

In addition, based on the arrangement of the medium layer inner sealing cavity structure, the weight can be reduced, the flexibility of the cable is improved, the assembly operation of the high-speed cable is facilitated, and the advantages are particularly obvious in the application scene of more system high-speed cable wiring.

Based on the first aspect, an embodiment of the present application further provides a first implementation manner of the first aspect: the dielectric layer comprises a substrate and low-dielectric closed cavity filler arranged in the substrate, wherein the closed cavity structure is formed by the low-dielectric closed cavity filler.

In practical application, the low dielectric closed cavity filler is made of a material with a dielectric constant less than 2.0, so that the core wire dielectric loss can be further reduced on the basis of reducing the moisture absorption capacity of the dielectric layer, and the insertion loss performance and reliability of the core wire can be ensured.

Based on the first implementation manner of the first aspect, the present application provides a second implementation manner of the first aspect: the low dielectric closed cavity filler is hollow glass beads, has better manufacturability and controllable process implementation cost.

In practical application, the hollow glass beads have the particle size of 5-250 microns and the wall thickness of 1-2 microns. The core wire body has good strength; meanwhile, the influence of the local thinning of the pressed dielectric layer on the coating integrity can be avoided, and dielectric loss fluctuation is avoided.

Based on the first aspect, the embodiments of the present application further provide a third implementation manner of the first aspect: the closed cavity structure is formed by a substrate body of the dielectric layer; that is to say, the substrate body of the dielectric layer is utilized to form a closed cavity structure, so that the material cost can be further reasonably controlled.

In practical application, a plurality of closed cavity structures tend to be uniformly distributed in the medium layer, and the overall performance and reliability are higher.

Based on the first aspect, or the first implementation manner of the first aspect, or the second implementation manner of the first aspect, or the third implementation manner of the first aspect, the examples of the present application further provide a fourth implementation manner of the first aspect: the volume of the plurality of closed cavity structures in the medium layer is not less than 10%. Therefore, on the basis of obtaining good dielectric layer insulation performance, stable insertion loss fluctuation can be further kept in a damp application scene.

Illustratively, the closed cavity structure may be relatively uniformly arranged within the dielectric layer, such as, but not limited to, a uniform arrangement in dimensions such as a core circumferential direction and/or a core running direction, to achieve more reliable core performance.

Based on the first aspect, or the first implementation manner of the first aspect, or the second implementation manner of the first aspect, or the third implementation manner of the first aspect, the examples of the present application further provide a fourth implementation manner of the first aspect: the material of the substrate of the dielectric layer is fluoroplastic, such as but not limited to FEP, and has good dielectric characteristics and processing property. Therefore, the moisture absorption capacity of the dielectric layer is effectively reduced, and the process implementation cost of the core wire is low.

In practical applications, the material of the dielectric layer substrate may be a mixture of an organic compound and a silicon oxide compound, or may be a carbon-doped silicon oxide formed by chemical vapor deposition.

A second aspect of embodiments of the present application provides a transmission cable comprising a core wire as described above. The moisture absorption capability of the medium layer is reduced due to the configuration of the closed cavity structure in the medium layer based on the core wire. Like this, when this high-speed cable is in humid environment, can avoid steam to get into in the dielectric layer, effectively avoid the dielectric layer moisture absorption to lead to the insertion loss undulant to promote the signal integrality transmission performance of cable, avoid signal distortion as far as possible, can the wide application in the high-speed cable module of different scenes.

The high-speed cable provided by the embodiment has excellent attenuation performance, low time delay and anti-interference performance, and can be widely applied to data center interconnection scenes such as SATA storage equipment, RADI system scenes and core routers.

Based on the second aspect, the embodiments of the present application further provide a first implementation manner of the second aspect: this transmission cable includes two heart yearn, a shielded wire, shielding layer and overcoat layer, two heart yearns are arranged side by side, and the shielded wire is located between two heart yearns, and shielding layer and overcoat layer cladding are in proper order in the outside of two heart yearns and shielded wire. That is to say, the transmission cable may be a high-speed cable having two conductors, the two conductors are matched with the differential pair, and the shielding layer is wrapped outside the two core wires to weaken electromagnetic interference; for example, but not limited to, the shielding layer may be formed by coating a metal foil such as an aluminum foil, a copper foil, or a tin foil, and the coating manner may be a wrapping manner or a longitudinal wrapping manner. The outer sleeve layer is coated outside the shielding layer and isolated from the environment; for example, but not limited to, the outer jacket layer 30 is formed by winding a PET (polyethylene terephthalate) film, a PTFE (polytetrafluoroethylene) film, or the like.

In practical application, this transmission cable can include two heart yearns, two shielded wires, shielding layer and overcoat layer, and two heart yearns are arranged side by side, and two shielded wires are located two respectively the outside of heart yearn, shielding layer and overcoat layer cladding in proper order are in the outside of two heart yearns and two shielded wires. In addition, this transmission cable can also include two heart yearns, shielding layer and overcoat layer, and two heart yearns are arranged side by side, and shielding layer and overcoat layer cladding in proper order are in the outside of two heart yearns.

In other practical applications, the conventional cable may also be a coaxial cable having a conductor, and the core wire is externally covered with a shielding layer and an outer sheath layer. For example, but not limited to, the shielding layer may be a metal textile and the outer jacket layer may be an insulating plastic.

In a third aspect of the embodiments of the present application, there is provided a method for manufacturing a core wire, including the steps of:

preparing materials: adding low-dielectric closed cavity filler into a base material of the dielectric layer, and mixing to form a dielectric layer material; wherein, the mass percentage of the low dielectric closed cavity filler in the base material is 5 to 80 percent; specifically, stirring may be performed by screw rotation, so that the hollow glass beads can be uniformly dispersed within the FEP base material.

Core wire molding: and (3) feeding the conductor of the core wire and the dielectric layer material obtained in the material preparation step into extrusion equipment to form the core wire coated with the dielectric layer outside the conductor, and forming a plurality of closed cavity structures arranged at intervals in the dielectric layer.

In practical application, the filling mass percentage of the hollow glass beads can be 30% -50%, and by the arrangement, good dielectric property and cable strength can be effectively considered.

Drawings

FIG. 1 is a schematic cross-sectional view of a core wire according to an embodiment of the present invention;

FIG. 2 is a schematic view of a process system for manufacturing a core wire according to an embodiment of the present invention;

FIG. 3 is a comparative graph of simulation test data based on examples of the present application and comparative examples;

FIG. 4 is a cross-sectional schematic view of a high-speed cable provided by an embodiment of the present invention;

FIG. 5 is a cross-sectional schematic view of another high-speed cable provided by an embodiment of the present invention;

FIG. 6 is a cross-sectional schematic view of yet another high-speed cable provided by an embodiment of the present invention;

fig. 7 is a schematic cross-sectional view of a coaxial cable according to an embodiment of the present invention.

Detailed Description

The embodiment of the application provides a core wire for a transmission cable, and through the structural optimization of the dielectric layer, the moisture absorption capacity of the dielectric layer is reduced, the insertion loss fluctuation can be effectively avoided, different high-speed transmission application scenes can be met, and the requirement of high-speed performance parameters of the whole link of the system is ensured.

In a typical high-speed cable structure in the prior art, a medium material FEP with a lower dielectric constant is adopted, a core wire medium layer with a more pore structure is formed by a foaming process, the dielectric constant and the medium loss of the core wire medium layer can be reduced, and the high-speed cable structure has the characteristics of better flexibility and lighter weight. However, the pore structure formed by the foaming process is in disorder connection, and the cable formed by the process generates serious insertion loss fluctuation in a humid environment.

Another typical high-speed cable structure in the prior art also utilizes a dielectric material FEP with a lower dielectric constant to form a core dielectric layer of a solid structure, and the cable using the core has higher hardness and relative weight. For the application scene that the system uses a large number of cables, the assembly bending difficulty is large.

Based on this, this application embodiment provides a heart yearn, and this heart yearn includes the conductor and the cladding in the outside dielectric layer of conductor, has a plurality of airtight cavity structures of interval arrangement in this dielectric layer. Based on the arrangement of the plurality of closed cavity structures, the core wire dielectric loss is effectively reduced, and meanwhile, each independent closed cavity structure can construct a closed space for blocking water vapor from entering, so that the moisture absorption capacity of the dielectric layer can be reduced; like this, to the high-speed cable of using in humid environment, can effectively avoid appearing the insertion loss fluctuation, satisfy the SI performance of high-speed cable transmission.

In addition, based on the arrangement of the sealing cavity structure in the dielectric layer, the weight can be reduced, the flexibility of the cable is improved, the assembly operation of the high-speed cable is facilitated, and the cable has a remarkable advantage in an application scene that the high-speed cable of the system is more in wiring.

In order to better understand the technical solutions and effects of the present application, without loss of generality, specific embodiments will be described in detail below with reference to the accompanying drawings.

Referring to fig. 1, a schematic cross-sectional structure diagram of a core wire provided by an embodiment of the invention is shown.

The dielectric layer 1 of the core wire 10 is coated outside the conductor 2, and the insulation requirement of the conductor 2 is met through the insulation performance of the dielectric layer 1. The medium layer 1 comprises a plurality of hollow glass beads 3, each hollow glass bead 3 occupies space in the medium layer 1 to form a closed cavity structure, and water vapor is difficult to enter the hollow glass beads 3, so that the moisture absorption capacity of the medium layer can be effectively reduced, the medium layer 1 can keep a stable dielectric constant, insertion loss fluctuation can be avoided, and the SI performance of high-speed cable transmission is met. Meanwhile, the weight of the core wire is reduced, and the core wire has good flexibility and is beneficial to assembly and wiring operation.

The hollow glass bead mainly comprises borosilicate, has the characteristics of high compressive strength, high melting point, high resistivity, small thermal conductivity coefficient, small thermal shrinkage coefficient and the like, and has good high-humidity high-temperature stability. In a specific implementation, hollow glass microspheres with a particle size of 5-250 μm and a wall thickness of 1-2 μm can be used. Therefore, the core wire has good strength, and meanwhile, the influence of local thinning of the pressed medium layer on the coating integrity can be avoided, and medium loss fluctuation is avoided.

In a specific implementation, the hollow glass beads 3 can be arranged in the dielectric layer 1 in a disordered manner or in a regular manner. Compared with the prior art, the disordered hollow glass beads 3 can reduce the process realization difficulty and reasonably control the core wire manufacturing cost, and the hollow glass beads 3 are added and mixed in the base material of the dielectric layer before the core wire is manufactured and molded.

In other specific implementations, as the low dielectric closed cavity filler added in the base material of the dielectric layer, a closed hollow structure made of other low dielectric constant materials may also be used, and it should be noted that the "low dielectric constant" dielectric material herein refers to a dielectric material with a relatively low dielectric constant (lower than silicon dioxide), and can meet the functional requirements of the dielectric layer of the corresponding transmission cable, and does not particularly refer to a certain numerical value. For example, but not limited to, a material having a dielectric constant less than 2.0, and may also fill the space occupied in the dielectric layer 1; on the basis of reducing the temperature absorption capacity of the dielectric layer, the dielectric loss of the core wire can be further reduced.

In addition, the low dielectric constant material for preparing the hollow structure also needs to have high temperature resistance. Taking a high-speed cable applied to a high-density layout server as an example, the low-dielectric-constant material needs to have the capability of resisting the high temperature of 350 ℃, so that the hollow structure can keep stable and reliable characteristics in the application scene of the high-speed cable, and lower dielectric loss of a high-speed core wire is realized.

The base material of the dielectric layer 1 may be made of a material with good insulating property, such as Fluorinated Ethylene Propylene (FEP), polyvinyl Chloride (PVC), polypropylene (PP), polyethylene (PE), and the like. For another example, the substrate of the dielectric layer 1 may be a mixture of organic and silicon oxide, or a chemical vapor deposition carbon-doped silicon oxide.

The conductor 2 is a single or multi-strand metal wire, the metal wire is any one of bare copper, silver-plated copper, tin-plated copper, silver-plated copper-clad steel and silver-plated copper-clad aluminum conductor, and the cross section of the metal wire can be a circle as shown in the figure, or can be any one of an ellipse, a flat or other shapes. Based on this, the cross-sectional shape of the core wire 10 of the present embodiment may be circular as shown in the drawings, or may be oblate or the like.

The extrusion molding method of the core wire will be described below by taking the FEP as the base material of the dielectric layer 1 and the hollow glass beads as the filler. Please refer to fig. 2, which is a schematic view of a process system for manufacturing the core wire according to the embodiment of the present application.

S1, preparing a dielectric layer material. The hollow glass beads are added into the FEP material, and the FEP material and the hollow glass beads are fully and uniformly mixed to form the modified material.

Here, the FEP material may be added with 5% to 80% by mass of hollow glass beads. In a specific implementation, the stirring can be performed by the rotation of the screw, so that the hollow glass beads can be uniformly dispersed in the FEP base material.

It should be noted that, according to different requirements of the cable usage scenario for bending, the filling ratio of the hollow glass beads can be adjusted according to actual requirements. In particular, the core wire will have a better strength on the premise that a dielectric constant of less than 2.0 is achieved. Under the common use condition, the filling mass percentage of the hollow glass beads is 30-50%, and the balance between dielectric property and strength can be realized.

And S2, finishing extrusion forming of the core wire based on the manufacturing process equipment shown in the figure 2.

As shown in fig. 2, the conductor wire coil continuously conveys the conductor to the preheating machine, and the preheated conductor enters the vacuum extruder; and meanwhile, injecting the FEP modified material mixed with the hollow glass beads prepared in the step S1 into a feeding port of a vacuum extruder to form a core wire with a dielectric layer coated outside the conductor.

And cooling the core wire formed by the vacuum extruder, detecting, and winding the finished product core wire on a winch. It should be noted that the specific functional structure of each process device in the process system shown in fig. 2 can be implemented by using the prior art for those skilled in the art, and therefore, the detailed description thereof is omitted here.

Compared with the FEP foaming manufacturing process of the existing core wire, the medium layer material of the core wire does not need to be subjected to foaming treatment, and N can be omitted from being injected into a vacuum extruder ₂ The working procedure of (2) effectively reduces the difficulty of extruding and processing the core wire while constructing and forming a reliable closed cavity structure in the medium layer; further, the process control of the process can be simplified on the basis of improving the manufacturability of the core wire, for example, but not limited to, saving N ₂ And controlling the cost of the parameters with high precision.

In addition, based on the existing FEP foaming process system, the core wire coating forming process in the embodiment does not need to replace main production equipment, the process equipment for removing injected N2 can be simply adjusted, the improvement cost is low, and the popularization and the application are facilitated.

In the foregoing embodiment, the closed cavity structures in the dielectric layer are constructed by low dielectric closed cavity fillers, and in other specific implementations, a plurality of closed cavity structures may also be constructed based on a process treatment of a substrate of the dielectric layer.

In order to control dielectric loss, for a dielectric layer with unit volume, the volume ratio of the closed cavity structures such as low dielectric closed cavity filler is not less than 10%, and stable insertion loss fluctuation can be kept in a damp application scene. The wall thickness of the dielectric layer may be 0.2mm to 0.3mm. It will be appreciated that in order to obtain more reliable core performance, the closed cavity structure may be arranged relatively uniformly within the dielectric layer, for example, but not limited to, in dimensions such as the core circumference and/or the core extension direction.

In the following, simulation tests are performed in combination with the embodiments and comparative examples of the present application, and the design targets of the embodiments of the present application are verified based on the same conductor arrangement. Please refer to fig. 3 together with a comparison of simulation test data of the examples and comparative examples.

Example (b): as shown in the embodiment of fig. 1, the substrate of the dielectric layer 1 is FEP, the low dielectric closed cavity filler is hollow glass beads 3, and the volume percentage of the hollow glass beads 3 in the dielectric layer is 45%, a simulation test is performed to obtain a loss curve shown as L1 in fig. 3, the abscissa in fig. 3 is represented as frequency (GHz), and the ordinate in fig. 3 is represented as loss (DB).

Comparative example: a simulation test was performed using a core wire formed by the prior FEP foaming process to obtain a loss curve shown as L2 in fig. 3.

From simulation results, it can be seen that under the same working frequency, the core wire loss can be effectively reduced by arranging the hollow glass beads 3 in the dielectric layer for occupation, wherein based on comparison of characteristic points with the frequency of 28GHz in FIG. 3, the core wire loss described in the embodiment is-6.17507 DB, and the core wire loss described in the comparative example is-7.07764 DB. Therefore, the effect on the insertion stability of the optimized core wire is significant.

In addition to the core wires described in the previous embodiments, the examples of the present application further detail the implementation of a transmission cable using the above-described core wires.

Please refer to fig. 4, which is a schematic cross-sectional view of a high-speed cable according to an embodiment of the present application.

As shown in fig. 4, the high-speed cable 100 includes two cores 10 and a shield wire 40, the conductors 2 inside the two cores 10 and the differential pairs are matched with each other, and the shield wire 40 is interposed between the two cores 10. The high-speed cable 100 further comprises a shielding layer 20 and an outer jacket layer 30, wherein the shielding layer 20 is coated outside the two core wires 10 and the shielding wire 40 to reduce electromagnetic interference; for example, but not limited to, the shielding layer 20 may be formed by coating a metal foil such as an aluminum foil, a copper foil, or a tin foil, and the coating method may be wrapping or longitudinal wrapping. The outer sleeve layer 30 is coated outside the shielding layer 20 and isolated from the environment; for example, but not limited to, the outer jacket layer 30 may be formed by winding a PET (polyethylene terephthalate) film, a PTFE (polytetrafluoroethylene) film, or the like.

The core wire 10-based closed cavity structure configuration in the dielectric layer 1 reduces the moisture absorption capacity of the dielectric layer; when the high-speed cable 100 is in a humid environment, water vapor can be prevented from entering the medium layer, insertion loss fluctuation caused by moisture absorption of the medium layer is effectively avoided, and therefore the signal integrity transmission performance of the cable is improved, and signal distortion is avoided as far as possible. The high-speed cable provided by the embodiment has excellent attenuation performance, low time delay and anti-interference performance, and can be widely applied to data center interconnection scenes such as SATA storage equipment, RADI system scenes and core routers.

For high speed cables, shielding may be configured in certain implementations based on the strength requirements for interference resistance, such as, but not limited to, two shielding wires 40. Please refer to fig. 5, which is a schematic cross-sectional view of another high-speed cable according to an embodiment of the present application. In order to clearly illustrate the differences and connections between this embodiment and the embodiment described in the foregoing fig. 4, the same functional components or structures are illustrated in the drawings with the same reference numerals.

As shown in fig. 5, the high-speed cable 100a includes two core wires 10 and two shield wires 40, and the two shield wires 40 are respectively located on both sides of the two core wires 10. Similarly, the shield layer 20 and the jacket layer 30 are sequentially coated outside the core wire 10 and the shield wire 40, forming a high-speed cable 100a matched with the differential pair. This embodiment can not occupy the space on the high-speed cable direction of height, does benefit to the flattening design of high-speed cable.

In addition, only two core wires 10 may be disposed in the shielding layer 20 according to the configuration requirements of different application scenarios. Please refer to fig. 6, which is a schematic cross-sectional view of another high-band cable according to an embodiment of the present application. In order to clearly illustrate the differences and connections between this embodiment and the previously described embodiments of fig. 4 and 5, the same functional components or structures are illustrated in the figures with the same reference numerals.

As shown in fig. 6, the high speed cable 100b includes two core wires 10, and the shielding layer 20 and the outer sheath 30 are sequentially coated outside the core wires 10 to form a high speed cable 100b matched with the differential pairs.

Further, the core wire 10 described based on the foregoing embodiment can be applied to a coaxial cable. Please refer to fig. 7, which is a schematic cross-sectional view of a coaxial cable according to an embodiment of the present application. In order to clearly illustrate the differences and connections between the present embodiment and the foregoing embodiments, the same functional configurations or structures are illustrated in the drawings with the same reference numerals.

As shown in fig. 7, the coaxial cable 100c includes a single core wire 10, the conductor 2 of the core wire 10 is a central conductor, and further includes a shield layer 20c and an outer jacket layer 30c covering the core wire 10. Here, the shielding layer 20c may be a metal textile, and the outer sheath layer 30c may be an insulating plastic.

It should be noted that the core wires described in the foregoing embodiments can be applied to other types of transmission cables, implement corresponding signal transmission functions, and can improve the signal integrity transmission performance of the cables. The technical advantages described above are even more pronounced, especially for application scenarios where the environment is humid.

The above is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, a plurality of modifications and embellishments can be made without departing from the principle of the present invention, and these modifications and embellishments should also be regarded as the protection scope of the present invention.

Claims

1. A core wire is characterized by comprising a conductor and a dielectric layer coated outside the conductor, wherein a plurality of closed cavity structures are arranged in the dielectric layer at intervals.

2. The core wire of claim 1 wherein the dielectric layer comprises a substrate and a low dielectric closed cavity filler embedded in the substrate, the closed cavity structure being formed from the low dielectric closed cavity filler.

3. The core wire of claim 2 wherein said low dielectric closed cavity filler is made of a material having a dielectric constant of less than 2.0.

4. The core wire of claim 2 wherein the low dielectric closed cavity filler is hollow glass microspheres.

5. The core wire according to claim 4, wherein the hollow glass microspheres have a particle size of 5 μm to 250 μm and a wall thickness of 1 μm to 2 μm.

6. The core wire of claim 1, wherein the closed cavity structure is formed by a substrate body of the dielectric layer.

7. The core wire of any one of claims 1 to 6 wherein the volume fraction of said plurality of closed cavity structures within said dielectric layer is not less than 10%.

8. The core wire of any one of claims 1 to 7 wherein the material of the substrate of the dielectric layer is a fluoroplastic, or a mixture of an organic and a silicon oxide compound, or a chemical vapor deposition of carbon doped silicon oxide.

9. A transmission cable comprising a core wire according to any one of claims 1 to 8.

10. The transmission cable according to claim 9, wherein the transmission cable comprises two core wires, a shield wire, a shield layer and an outer jacket layer, the two core wires are arranged side by side, the shield wire is located between the two core wires, and the shield layer and the outer jacket layer are sequentially coated outside the two core wires and the shield wire.

11. The transmission cable according to claim 9, wherein the transmission cable includes two core wires, two shield wires, a shield layer and an outer jacket layer, the two core wires are arranged side by side, the two shield wires are respectively located at outer sides of the two core wires, and the shield layer and the outer jacket layer are sequentially coated outside the two core wires and the two shield wires.

12. The transmission cable according to claim 9, wherein the transmission cable comprises two of the core wires, a shielding layer and an outer jacket layer, the two core wires are arranged side by side, and the shielding layer and the outer jacket layer are sequentially coated outside the two core wires.

13. A method of making a core wire, comprising the steps of:

preparing materials: adding low-dielectric closed cavity filler into a base material of the dielectric layer, and mixing to form a dielectric layer material; wherein the mass percentage of the low-dielectric closed cavity filler in the base material is 5-80%;

core wire forming: and feeding the conductor of the core wire and the dielectric layer material obtained in the material preparation step into extrusion equipment to form the core wire coated with the dielectric layer outside the conductor, and forming a plurality of closed cavity structures arranged at intervals in the dielectric layer.