Electric cable for communication
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- AUTONETWORKS TECH LTD
- Filing Date
- 2025-11-17
- Publication Date
- 2026-07-30
Smart Images
Figure JP2025040037_30072026_PF_FP_ABST
Abstract
Description
Communication wire
[0001] The present disclosure relates to a communication wire.
[0002] In fields such as automobiles, the demand for high-speed communication is increasing. In particular, in recent years, with the progress of autonomous driving technology and the high functionality of in-vehicle devices, the performance required for communication wires has been increasing. For example, it is required to maintain high transmission characteristics over a wide band and to suppress signal loss to a low level. As an example, in Patent Document 1, as a communication wire capable of suppressing a phenomenon (sackout) in which signal transmission characteristics rapidly deteriorate when transmitting a high-frequency signal, an intervening material made of a predetermined resin material is provided around a twisted pair cable, and a shield tape is provided around the intervening material, and a low-voltage differential signal transmission cable is disclosed.
[0003] Japanese Patent Application Laid-Open No. 2017-142959
[0004] As described above, in communication wires for automobiles, applicability to a wide band (widebanding) and reduction of signal loss (low loss) are required. As communication wires aiming at widebanding and / or low loss, various communication wires such as those in Patent Document 1 have been developed, but it is not easy to achieve both widebanding and low loss.
[0005] In a communication wire including a twisted pair wire formed by twisting a pair of insulated wires as a signal wire, in order to enhance the applicability to the high-frequency region for widebanding, it is effective to shorten the twist pitch of the twisted pair wire. By reducing the outer diameter of the insulated wire constituting the twisted pair wire, it becomes easier to shorten the twist pitch. On the other hand, in order to achieve low loss, the conductor diameter of the insulated wire constituting the twisted pair wire may be increased, but then the diameter of the insulated wire becomes large, and it becomes difficult to shorten the twist pitch of the twisted pair wire. Thus, since the size of the outer diameter of the insulated wire constituting the twisted pair wire shows opposite contributions to widebanding and low loss, it is difficult to achieve both widebanding and low loss in a communication wire.
[0006] Furthermore, reducing the outer diameter of the insulated wire in order to shorten the twist pitch of twisted pair wires in order to achieve wider bandwidth can reduce the differential characteristic impedance, potentially making impedance matching difficult. It could also be considered as an effective means of widening bandwidth by forming a parallel signal line without twisting a pair of insulated wires, thereby eliminating the periodicity caused by the twisted structure. However, this would lead to increased mode conversion losses and reduced handling of the signal line.
[0007] In view of the above, the objective is to provide a communication cable that exhibits high transmission characteristics over a wide bandwidth while reducing signal loss.
[0008] The communication wire of this disclosure comprises a conductor with an outer diameter of 0.55 mm or more, an insulating sheath having an elastic modulus of 1600 MPa or less and covering the outer circumference of the conductor, a twisted pair wire formed by twisting together a pair of insulated wires with an outer diameter of 1.4 mm or less at a twist pitch of 14 mm or less, an inner sheath made of an insulator and covering the outer circumference of the twisted pair wire, a film-like shield made of metal foil and arranged longitudinally with respect to the axis of the twisted pair wire and covering the outer circumference of the inner sheath, a braided shield made of a braided body of metal strands and covering the outer circumference of the film-like shield, and an outer sheath made of an insulator and covering the outer circumference of the braided shield.
[0009] The communication cable described herein exhibits high transmission characteristics over a wide bandwidth and reduces signal loss.
[0010] Figure 1 is a cross-sectional view showing a communication wire according to one embodiment of the present disclosure. Figure 2 is a diagram comparing insertion losses when the stacking order of the shield portion is different. Figure 3 is a diagram showing the relationship between the resin ratio in the region surrounded by the inner sheath and the differential characteristic impedance. Figure 4 is a diagram showing the relationship between the thickness of the inner sheath and the mode conversion loss. Figure 5 is a diagram comparing insertion losses when the outer diameter of the conductor constituting the insulated wire is different.
[0011] [Description of Embodiments of the Disclosure] First, embodiments of the disclosure will be listed and described.
[0012] [1] The communication wire of the present disclosure comprises a conductor with an outer diameter of 0.55 mm or more, an insulating sheath having an elastic modulus of 1600 MPa or less and covering the outer circumference of the conductor, a twisted pair wire formed by twisting together a pair of insulated wires with an outer diameter of 1.4 mm or less at a twist pitch of 14 mm or less, an inner sheath made of an insulator and covering the outer circumference of the twisted pair wire, a film-like shield made of metal foil and arranged longitudinally with respect to the axis of the twisted pair wire and covering the outer circumference of the inner sheath, a braided shield made of a braided body of metal strands and covering the outer circumference of the film-like shield, and an outer sheath made of an insulator and covering the outer circumference of the braided shield.
[0013] In the communication wire of this disclosure having the above configuration, an inner sheath is provided between the twisted pair wires that serve as signal lines and the shield portion, which is composed of a film-like shield and a braided shield. The inner sheath ensures a distance between the conductors of the insulated wires constituting the twisted pair wires and the shield portion, thereby suppressing mode conversion losses in the communication wire. Furthermore, by providing an inner sheath, it becomes easier to secure the required size of differential characteristic impedance, and impedance matching becomes easier even when the outer diameter of the insulated wires is reduced to 1.4 mm or less. By reducing the outer diameter of the insulated wires, the twist pitch of the twisted pair wires can be shortened, and as a result, the signal transmission characteristics in the high-frequency band can be improved, and the communication wires can be made wider bandwidth. In addition to making the outer diameter of the insulated wires 1.4 mm or less, by making the insulating coating constituting the insulated wires flexible with an elastic modulus of 1600 MPa or less, it becomes easy to reduce the twist pitch to 14 mm or less. By shortening the twist pitch to 14 mm or less, the drop in signal transmission characteristics in the high-frequency range is suppressed, making it easier to apply communication wires to a wide bandwidth.
[0014] In communication cables, high noise shielding performance can be achieved by providing both a film shield and a braided shield as shielding. In particular, arranging the film shield in a longitudinal manner is highly effective in improving noise shielding performance and reducing signal loss. By arranging the longitudinally arranged film shield inside the braided shield, covering the surface of the inner sheath, the film shield can be arranged with high smoothness. The increased smoothness of the film shield further enhances the effect of reducing transmission signal loss due to the reduction of electrical resistance in the shield and the contribution of the skin effect. The fact that the conductor diameter of the insulated wires constituting the twisted pair wire is large, such as 0.55 mm or more, also contributes to the reduction of signal loss.
[0015] Thus, in the communication wire according to this disclosure, an inner sheath is provided, and the shielding section has a structure in which a vertically arranged film-like shield is provided on the inside and a braided shield is provided on the outside. Furthermore, the parameters related to the dimensions and physical properties of each part are controlled within a predetermined range, thereby achieving both a wide bandwidth of applicable frequencies and a reduction in signal loss. In addition, although the vertical arrangement of the film-like shield contributes to increasing mode conversion loss, the provision of an inner sheath weakens the electromagnetic coupling between the conductor of the insulated wire constituting the twisted pair wire and the shielding section, thereby keeping mode conversion loss to a minimum.
[0016] [2] In the embodiment of [1] above, the metal foil constituting the film-like shield may be made of copper or a copper alloy. This provides a high level of effectiveness in shielding noise and suppressing signal loss.
[0017] [3] In the embodiment of [1] or [2] above, in a cross section perpendicular to the axial direction of the communication wire, it is preferable that the area occupied by the constituent material of the inner sheath in the space enclosed by the circle circumscribing the twisted pair wire and the outer surface of the twisted pair wire is 60% or less. This ensures a sufficient gap between the inner sheath and the twisted pair wire, making it easier to maintain the differential characteristic impedance of the communication wire in a sufficiently large range, such as 100 ± 5 Ω, and to perform impedance matching.
[0018] [4] In any of the embodiments described in [1] to [3] above, the thickness of the inner sheath is preferably in the range of 0.40 ± 0.15 mm. This allows the inner sheath to effectively suppress mode conversion losses and improve the handling of the communication wire. Impedance matching also becomes easier.
[0019] [5] In any of the embodiments described in [1] to [4] above, it is preferable that the dielectric loss tangent of the inner sheath be 0.01 or less. This enhances the effect of suppressing signal loss.
[0020] [6] In any of the embodiments described in [1] to [5] above, the modulus of elasticity of the inner sheath is preferably 100 MPa or more and 500 MPa or less. This improves the flexibility and bending resistance of the communication wire.
[0021] [7] In any of the embodiments described in [1] to [6] above, the melting point of the inner sheath is preferably 140°C or higher. This improves the heat resistance of the inner sheath.
[0022] [8] In any of the embodiments described in [1] to [7] above, the conductor may be made of soft copper. The high flexibility of soft copper makes it easier to twist insulated wires with a short twist pitch, which is advantageous for widening the bandwidth.
[0023] [9] In any of the embodiments described in [1] to [8] above, the conductor is configured as a stranded wire made by twisting together multiple metal strands, and the twist pitch of the strands is preferably 9 mm or less. This makes it possible to effectively suppress mode conversion loss in communication wires.
[0024]
[10] In any of the embodiments described in [1] to [9] above, the relative permittivity of the insulating coating is preferably 2.4 or less. This makes it easier to ensure a sufficiently large differential characteristic impedance, such as 100 ± 5 Ω, and to perform impedance matching.
[0025]
[11] In any of the embodiments described in [1] to
[10] above, it is preferable that the dielectric loss tangent of the insulating coating be 0.001 or less. This makes it possible to effectively reduce the loss of the transmitted signal in the communication wire.
[0026]
[12] In any of the embodiments of [1] to
[11] above, it is preferable that the elastic modulus of the insulating coating is 1200 MPa or less. Then, due to the flexibility of the insulating coating, even when the twist pitch is shortened, the effect of stably forming and maintaining a twist structure of a predetermined pitch is further enhanced. As a result, it becomes even easier to broaden the bandwidth by reducing the twist pitch.
[0027]
[13] In any of the embodiments described in [1] to
[12] above, it is preferable that the differential characteristic impedance is in the range of 100 ± 5 Ω. This makes it easier for the communication wire to satisfy the differential characteristic impedance required by standards, etc., and to perform impedance matching.
[0028] [Details of Embodiments of this Disclosure] The communication wire according to embodiments of this disclosure will be described in detail below with reference to the drawings. In this specification, various material properties that depend on the measurement frequency and / or measurement environment, such as dielectric loss tangent and elastic modulus, are specified for the communication frequency to which the communication wire is applied, for example, a frequency in the range of 1 to 10 GHz, and are values measured at room temperature in air, unless otherwise specified. In this specification, unless otherwise specified, the cross-section of the communication wire refers to a cross-section perpendicular to the axial direction of the communication wire. Also, unless otherwise specified, characteristic impedance refers to differential characteristic impedance.
[0029] <Overall Configuration of Communication Cable> Figure 1 shows a cross-sectional view of a communication cable 1 according to one embodiment of the present disclosure. The communication cable 1 has a twisted pair wire 10, which is formed by twisting together a pair of insulated wires 11, 11, as a signal wire. Each insulated wire 11 has a conductor 12 and an insulating coating 13 that covers the outer circumference of the conductor 12.
[0030] An inner sheath 20 is provided on the outside of the twisted pair wire 10, covering the outer circumference of the twisted pair wire 10. Outside the inner sheath 20, a shield portion 30 is provided, which includes a film-like shield 31 and a braided shield 32. The film-like shield 31 is arranged longitudinally and covers the outer circumference of the inner sheath 20. The braided shield 32 covers the outer circumference of the film-like shield 31. Further outside the braided shield 32, an outer sheath 40 is provided, covering the outer circumference of the braided shield 32.
[0031] In the communication cable 1, the inner sheath 20, film shield 31, braided shield 32, and outer sheath 40 are arranged coaxially around the twisted pair wire 10, and each continuously covers the outer circumference of the inner component over a full circle. In the communication cable 1, it is not prohibited to provide other layers between the components listed above, but it is preferable that the components listed above are in direct contact without other layers in between. However, a polymer tape such as PET having an adhesive layer may be appropriately provided on the inner circumferential surface of the inner sheath 20 and / or outer sheath 40.
[0032] The communication cable 1 has a characteristic impedance determined by the material and dimensions of each component. From the viewpoint of satisfying standards and impedance matching, it is preferable that the characteristic impedance of the communication cable 1 is in the range of 100 ± 5 Ω. The components of the communication cable 1 will be described in detail below.
[0033] <Twisted Pair Wire> The communication wire 1 has a twisted pair wire 10, as described above, in which a pair of insulated wires 11, 11 are twisted together, as a signal line for transmitting differential signals. Each insulated wire 11 has a conductor 12 and an insulating coating 13 that covers the outer circumference of the conductor 12.
[0034] (1) In the twisted pair wire 10, a pair of insulated wires 11, 11 are twisted together with a twist pitch of 14 mm or less. In general twisted pair wires, due to the periodicity of the twist structure, the signal transmission characteristics drop sharply in the region of frequencies higher than a certain frequency, making it difficult to use in the high-frequency range. However, by keeping the twist pitch at 14 mm or less, the frequency at which the signal transmission characteristics drop is pushed to the high-frequency range, and the effect of the drop is suppressed over a wide frequency band, making it possible to obtain high transmission characteristics. In this way, by shortening the twist pitch, the communication wire 1 can be made wider bandwidth. From the viewpoint of further enhancing this effect, it is more preferable that the twist pitch be 13 mm or less, and even more preferably 10 mm or less.
[0035] When considering increasing the bandwidth of a communication cable 1, if a parallel structure is used in the communication cable 1, in which two insulated wires 11, 11 are run parallel to each other without being twisted together, the effects of periodicity can be eliminated. However, this tends to increase mode conversion loss and worsen the handling of the signal wire. By using a twisted pair wire 10 with a twisted structure, mode conversion loss can be suppressed and the handling of the signal wire can be improved.
[0036] In the twisted pair wire 10, there is no specific lower limit for the twist pitch. However, from the viewpoint of improving the twistability, that is, forming a twisted structure with a stable pitch and stably maintaining the formed twisted structure, it is preferable to set it to 6 mm or more.
[0037] (2) Structure of the insulated wires The outer diameter of each insulated wire 11 constituting the twisted pair wire 10 is 1.4 mm or less. By keeping the outer diameter of the insulated wire 11 to 1.4 mm or less, it becomes easier to twist a pair of insulated wires 11, 11 together with a short twist pitch in the twisted pair wire 10. As described above, by shortening the twist pitch, the communication wire 1 can be made to have a wider bandwidth. In addition, if the insulation coating 13 is made thicker and the outer diameter of the insulated wire 11 is made larger in the twisted pair wire 10, the characteristic impedance will increase, but by keeping the outer diameter of the insulated wire 11 to 1.4 mm or less, it becomes easier to keep the characteristic impedance of the communication wire 1 within the range of 100 ± 5 Ω. From the viewpoint of enhancing these effects, it is even more preferable that the outer diameter of the insulated wire 11 be 1.3 mm or less.
[0038] There is no specific lower limit for the outer diameter of the insulated wire 11. However, if the outer diameter of the insulated wire 11 becomes smaller, the characteristic impedance of the communication wire 1 will decrease. Therefore, from the viewpoint of avoiding an excessive decrease in characteristic impedance, it is preferable to set the outer diameter of the insulated wire 11 to 1.0 mm or more.
[0039] (3) Conductor structure In this embodiment, the conductor 12 constituting each insulated wire 11 has an outer diameter of 0.55 mm or more. By setting the outer diameter of the conductor 12 to 0.55 mm or more, the electrical resistance of the conductor 12 can be kept low. As a result, the insertion loss (transmission loss) of the communication wire 1 can be kept low, and the communication wire 1 can be made to have low loss. From the viewpoint of further enhancing this effect, it is even more preferable that the outer diameter of the conductor 12 be 0.6 mm or more.
[0040] There is no specific upper limit for the outer diameter of the conductor 12. However, if the outer diameter of the conductor 12 increases, the distance between a pair of conductors 12 (the distance connecting the centers of the conductors 12) increases, and the characteristic impedance of the communication wire 1 decreases. From the viewpoint of avoiding an excessive decrease in characteristic impedance, it is preferable to keep the outer diameter of the conductor 12 to 0.65 mm or less.
[0041] The conductor 12 that constitutes the insulated wire 11 may be composed of a single wire, but from the viewpoint of enhancing flexibility during bending and the like, it is preferably composed of a stranded wire in which a plurality of metal strands are twisted together. In this case, after twisting the strands, compression molding may be performed to form a compressed stranded wire. When the conductor 12 is composed of a stranded wire, the twist pitch of the strands is preferably 9 mm or less. Then, since the looseness of the twist structure of the conductor is suppressed, the mode conversion loss of the communication wire 1 can be suppressed. Although the lower limit of the twist pitch is not particularly defined, from the viewpoint of productivity, it is advisable to set it to 6 mm or more. When the conductor 12 is composed of a stranded wire, the outer diameter of the conductor 12 is determined as the average value of the diameters in each direction in the cross section, that is, the length of a straight line passing through the center of the conductor 12 and crossing the conductor 12 in each direction.
[0042] The material that constitutes the conductor 12 of the insulated wire 11 is not particularly limited, but it is preferably copper or a copper alloy. In particular, it is preferably soft copper. When the conductor 12 is composed of soft copper, due to the high flexibility of the soft copper, the twistability of the insulated wire 11 is increased, and it becomes easier to form a twisted pair wire 10 with a short twist pitch. As a result, it contributes to the broadbanding of the communication wire 1.
[0043] (4) Configuration of the insulation coating The insulation coating 13 that constitutes each insulated wire 11 is made of an insulating material containing a polymer material. The constituent material of the insulation coating 13 has a modulus of elasticity suppressed to 1600 MPa or less. Since the insulation coating 13 has a low modulus of elasticity such as 1600 MPa or less and high flexibility, when forming the twisted pair wire 10, by utilizing its flexibility, it becomes easier to twist a pair of insulated wires 11, 11 with a short twist pitch. Even when the insulated wires 11, 11 are twisted with a short twist pitch, the variation in the twist pitch is suppressed to a small value, forming a stable twisted structure at a predetermined twist pitch and being more easily maintained. By being able to stably perform twisting with a short twist pitch, it becomes easier to achieve broadbanding due to the shortening of the pitch. From the viewpoint of further enhancing this effect, it is more preferable that the modulus of elasticity is 1200 MPa or less. In this specification, the modulus of elasticity refers to the flexural modulus of elasticity.
[0044] There is no particular lower limit specified for the elastic modulus of the constituent material of the insulating coating 13. However, from the perspective of suppressing wire deformation due to stress applied during twisting and ensuring mechanical strength such as abrasion resistance, it is advisable to set it at 1000 MPa or more.
[0045] The constituent material of the insulating coating 13 preferably has a relative permittivity suppressed to 2.4 or less. By using a material with a low relative permittivity for the insulating coating 13, the characteristic impedance of the communication wire 1 increases. By setting the relative permittivity of the insulating coating 13 to 2.4 or less, it becomes easier to ensure a sufficient characteristic impedance such as 100 ± 5 Ω. The lower limit of the relative permittivity is not particularly defined, but the relative permittivity of polymer materials that can be realistically used to form the insulating coating 13 of the insulated wire 11 is generally 1.3 or more.
[0046] Furthermore, the constituent material of the insulating coating 13 preferably has a dielectric loss tangent of 0.001 or less. By using a material with a low dielectric loss tangent for the insulating coating 13, the attenuation of the transmission signal can be significantly suppressed, promoting low loss. The lower limit of the dielectric loss tangent is not particularly defined.
[0047] The polymer material constituting the insulating coating 13 is not particularly limited, but from the perspective of suppressing both the elastic modulus, relative permittivity, and dielectric loss tangent to low levels, it is preferable to use a material with low molecular polarity, particularly a non-polar material. Examples of such low-polarity or non-polar polymer materials include polyolefins such as polyethylene and polypropylene, polystyrene, and polytetrafluoroethylene. Among these, it is preferable to use polyolefins, particularly polypropylene. The polymer materials may be used as a mixture of multiple types. The polymer material constituting the insulating coating 13 may be crosslinked or foamed. In addition to the polymer material, the insulating coating 13 may appropriately contain additives such as flame retardants. The thickness of the insulating coating 13 is not particularly limited, but it is necessary to determine the thickness within a range where the outer diameter of the conductor 12 is 0.55 mm or more and the outer diameter of the entire insulated wire 11 is suppressed to 1.4 mm or less.
[0048] <Inner Sheath> The inner sheath 20 is made of an insulating material containing a polymer material and covers the outer circumference of the twisted pair wire 10. By providing the inner sheath 20 to the communication wire 1, a region not occupied by conductive material is formed between the conductor 12 constituting the twisted pair wire 10 and the shield portion 30, thereby increasing the characteristic impedance of the communication wire 1. As a result, even if the outer diameter of the insulated wire 11 constituting the twisted pair wire 10 is reduced to 1.4 mm or less, a characteristic impedance of the required size, such as 100 ± 5 Ω, can be secured, and impedance matching can be performed. As described above, by reducing the outer diameter of the insulated wire 11, the twist pitch of the twisted pair wire 10 can be shortened, so by providing the inner sheath 20, it is possible to shorten the twist pitch while securing the characteristic impedance and broaden the bandwidth of the communication wire 1. Furthermore, the interposition of the inner sheath 20 between the twisted pair wire 10 and the shield portion 30 weakens the electromagnetic coupling between the twisted pair wire 10 and the shield portion 30, thereby reducing mode conversion loss.
[0049] The thickness of the inner sheath 20 is preferably in the range of 0.40 ± 0.15 mm. This effectively suppresses mode conversion loss in the communication wire 1. It also improves the handling of the communication wire 1. Impedance matching is also made easier. More preferably, the thickness of the inner sheath 20 is 0.40 mm or more. The thickness of the inner sheath 20 is defined as the average value of the thickness over the entire circumferential direction of the cross-section.
[0050] The resin content in the region enclosed by the inner sheath 20 is preferably 60% or less. Here, the resin content in the region enclosed by the inner sheath 20 refers to the proportion of the area occupied by the constituent material of the inner sheath 20 within the space enclosed (sandwiched) between a circle circumscribing the twisted pair wire 10 (i.e., a hypothetical circle whose diameter is the longest straight line crossing the twisted pair wire 10) and the outer surface of the twisted pair wire 10 in cross-section. A low resin content means that there are many voids between the twisted pair wire 10 and the inner sheath 20 that are not occupied by the constituent material (resin material) of the inner sheath 20. Since resin material has a higher dielectric constant than air, a higher proportion of voids occupied by air rather than resin material increases the characteristic impedance of the communication wire 1, making impedance matching easier. If the resin content is 60% or less, it becomes easier to secure a sufficiently large characteristic impedance, such as 100 ± 5 Ω. More preferably, the resin content is 40% or less. While there is no specific lower limit for the resin content, it is advisable to keep it at, for example, 10% or more to prevent the characteristic impedance from becoming too high.
[0051] The dielectric loss tangent of the constituent material of the inner sheath 20 is preferably kept below 0.01. By using a material with a low dielectric loss tangent as the inner sheath 20, the attenuation of the transmitted signal can be kept to a minimum, promoting low loss. There is no particular lower limit for the dielectric loss tangent.
[0052] Furthermore, the elastic modulus of the constituent material of the inner sheath 20 should be 100 MPa or higher. This will improve the bending resistance of the communication wire 1. On the other hand, the elastic modulus of the constituent material of the inner sheath 20 should be kept below 500 MPa. This will improve the flexibility of the communication wire 1.
[0053] Furthermore, it is preferable that the constituent material of the inner sheath 20 has a melting point of 140°C or higher. This results in the inner sheath 20 and the entire communication wire 1 having high heat resistance. There is no need to crosslink the polymer material constituting the inner sheath 20 in order to improve heat resistance. Although there is no particular upper limit set for the melting point, the melting points of polymer materials that can be practically used to constitute the inner sheath 20 are generally 200°C or lower.
[0054] The polymer material constituting the inner sheath 20 is not particularly limited, but examples include polyolefins such as polyethylene and polypropylene, polystyrene, and polytetrafluoroethylene. Among these, polyolefins, particularly polypropylene, are preferred. These polymer materials tend to provide the preferred properties such as dielectric loss tangent, elastic modulus, and melting point listed above. Multiple types of polymer materials may be mixed and used. The polymer material constituting the inner sheath 20 may be crosslinked or foamed, but keeping it uncrosslinked makes it easier to obtain an elastic modulus within the above range. In addition to the polymer material, the inner sheath 20 may contain additives such as flame retardants as appropriate.
[0055] <Shielding Section> The shielding section 30 is configured as a laminate of a film-like shield 31 that covers the outer circumference of the inner sheath 20 and a braided shield 32 that covers the outer circumference of the film-like shield 31. The film-like shield 31 is a film-like (sheet-like, tape-like) member equipped with metal foil, and is arranged longitudinally with respect to the axis of the twisted pair wire 10. That is, with the axial direction of the twisted pair wire 10 and the longitudinal axis of the surface of the elongated film-like shield 31 aligned, the surface of the film-like shield 31 surrounds the outer circumference of the assembly of the twisted pair wire 10 and the inner sheath 20 along the circumferential direction of the twisted pair wire 10. The braided shield 32 is a cylindrical member configured as a braided body of metal strands.
[0056] (1) Structure of the shielded section In a communication wire 1, by providing a shielded section 30 on the outside of the twisted pair wire 10, noise can be shielded from the twisted pair wire 10, which is a signal line. In other words, it is possible to suppress the intrusion of external noise into the twisted pair wire 10 and the emission of noise from the twisted pair wire 10 to the outside. By providing two types of shielding materials, a film-like shield 31 and a braided shield 32, in layers as the shielded section 30, the noise shielding performance can be improved. In particular, by arranging the film-like shield 31 in a vertical manner, leakage of the electric field in the shielded section 30 can be suppressed, and the noise shielding performance can be effectively improved. By arranging the film-like shield 31 in a vertical manner, the transmission path length of the shielded section 30 is shortened, the resistance of the shielded section is reduced, and it is also effective in reducing loss.
[0057] In the shield section 30, when the vertically aligned film shield 31 is placed on the inside and the braided shield 32 is placed on the outside, the film shield is placed in contact with the smooth outer surface of the inner sheath 20. Compared to the case where the braided shield 32 is placed on the inside and the film shield 31 is placed on the outside, the film shield 31 can be placed vertically while maintaining a highly smooth surface, with reduced effects of wrinkles and folds. By increasing the smoothness of the film shield 31, the transmission path length of the shield section 30 can be shortened, and the electrical resistance of the shield section 30 can be reduced. This makes it possible to keep signal loss in the communication wire 1 low. Furthermore, in the shield section 30, due to the skin effect, the current distribution tends to be biased toward the center of the communication wire 1, i.e., toward the inner layer, in the high-frequency range. However, because the film shield 31, which has a continuous metal foil and is placed in a highly smooth state, is located on the inside, the skin effect can be effectively utilized in the communication wire 1 to keep signal loss transmitted to the twisted pair wire 10 low. Thus, as a result of reducing the transmission path length and utilizing the skin effect, a high level of loss reduction can be achieved in the communication cable 1.
[0058] (2) Structure of the film-like shield The film-like shield 31 can be any form as long as it has a metal foil, and may be in the form of a single metal foil or in the form of a composite material formed by combining a metal foil with other materials such as a substrate. As a composite material, a polymer-metal composite film is a suitable example in which a polymer film as a substrate and a metal foil are combined by vapor deposition, plating, bonding, etc. When the film-like shield 31 is constructed as a composite material, it is preferable to place the film-like shield 31 on the outer circumference of the inner sheath 20 with the side on which the metal foil is arranged facing outwards, and to keep the side of the metal foil in contact with the braided shield 32.
[0059] The specific metals used in the film-like shield 31, either as a standalone metal foil or as a metal foil within a composite material, are not particularly limited, but examples include copper, copper alloys, aluminum, and aluminum alloys. In particular, using copper or copper alloys, especially copper, is excellent in reducing signal loss in the twisted pair wire 10.
[0060] (3) Structure of the braided shield The braided shield 32 is composed of a braided body formed by braiding together multiple metal wires to create a hollow cylindrical shape. Suitable metal wires for the braided shield 32 include fine wires made of metal materials such as copper, copper alloys, aluminum, and aluminum alloys, or fine wires made of materials with plating applied to the surface of these metal materials.
[0061] <Outer Sheath> The outer sheath 40 is a layer that covers the outer circumference of the braided shield 32 that constitutes the shield portion 30, and is made of an insulating material containing a polymer material. The outer sheath 40 plays a role in physically protecting the film-like shield 31 and the braided shield 32 that constitute the shield portion 30, as well as the internal twisted pair wires 10 and the inner sheath 20.
[0062] The materials used to construct the outer sheath 40 are not particularly limited; for example, any materials that can be used for the insulating coating 13 of the insulated wire 11 or for constructing the inner sheath 20 may be used as appropriate.
[0063] <Characteristics of the communication cable> The communication cable 1 according to this embodiment, having the above configuration, is applicable to a wide bandwidth and has reduced signal loss. In addition, it exhibits a characteristic impedance suitable for impedance matching, such as 100 ± 5 Ω, has high noise shielding properties, and is excellent in suppressing mode conversion loss.
[0064] In particular, by keeping the outer diameter of the insulated wire 11 of the twisted pair wire 10 to 1.4 mm or less, and by setting the elastic modulus of the insulating coating 13 constituting the insulated wire 11 to 1600 MPa or less, it is possible to shorten the twist pitch and easily form the twisted pair wire 10. Shortening the twist pitch suppresses the drop in signal transmission characteristics in the high-frequency range and enables wider bandwidth. On the other hand, by setting the outer diameter of the conductor 12 constituting the insulated wire 11 to 0.55 mm or more, and by arranging the film-like shield 31 in a vertical manner inside the braided shield 32 in the shield section 30, the loss of transmitted signals is reduced.
[0065] Furthermore, the inner sheath 20 provided between the twisted pair wire 10 and the shield section 30 increases the characteristic impedance and suppresses mode conversion loss. The smaller the outer diameter of the insulated wire 11 constituting the twisted pair wire 10, the lower the characteristic impedance of the communication wire 1. However, by providing the inner sheath 20, it is possible to reduce the outer diameter of the insulated wire 11 to 1.4 mm or less while ensuring a sufficiently large characteristic impedance, and to utilize this for widening the bandwidth by reducing the twist pitch.
[0066] Examples of the present disclosure are shown below. However, the present invention is not limited to these examples. In these examples, unless otherwise specified, all evaluations were performed at room temperature in air.
[0067] [1] Relationship between wire configuration and characteristics of communication wires First, multiple communication wires were fabricated by changing the configuration, and the relationship between the parameters related to the wire configuration and the characteristics of the communication wires was verified.
[0068] [Sample Preparation] Multiple soft copper strands were twisted together to create a conductor. By selecting the diameter of the strands used, the outer diameter of the conductor was varied as shown in Table 1. Polypropylene resin was extruded onto the outer circumference of the obtained conductor to form an insulating coating, thereby obtaining an insulated wire. In this process, the elastic modulus of the insulating coating was varied depending on the type of resin used, as shown in Table 1, and the outer diameter of the insulated wire was controlled by the thickness of the insulating coating.
[0069] Two insulated wires were twisted together at the twist pitch shown in Table 1 to form a twisted pair wire. For each sample except samples B1 and B2, an inner sheath was then provided around the outer circumference of the twisted pair wire by extrusion molding. Polypropylene resin was used as the material for the inner sheath. The resin content in the area surrounded by the inner sheath was 0% (hollow).
[0070] For all samples except samples B1 and B2, a film-like shield was placed longitudinally on the outer circumference of the inner sheath, and for samples B1 and B2, it was placed longitudinally on the outer circumference of the twisted pair wire. As shown in Table 1, the film-like shield used had a metal foil made of copper or aluminum. Furthermore, a braided shield was provided on the outer circumference of the film-like shield by weaving metal strands into a tubular shape. Finally, an outer sheath made of polypropylene resin was formed on the outer circumference of the braided shield by extrusion molding to obtain the communication wires of samples A1 to A4 and B1 to B4.
[0071] In sample A1, the wire configuration other than that shown in Table 1 was as follows. For the other samples, the same wire configuration as sample A1 was used as a base, with the configuration modified as shown in Table 1. • Conductor twist pitch: 8.0 mm • Relative permittivity of insulation coating: 2.1 • Dielectric loss tangent of insulation coating: 0.0002 • Resin content in the area surrounded by the inner sheath: 0% • Thickness of inner sheath: 0.40 mm • Dielectric loss tangent of inner sheath: 0.002 • Elastic modulus of inner sheath: 330 MPa • Melting point of inner sheath: 165°C
[0072] [Evaluation Method] - Measurement of Characteristic Impedance The differential characteristic impedance was measured for the communication wires of each sample. The measurement was performed using a network analyzer and the time-domain reflection method (TDR method).
[0073] - Insertion loss and bandwidth evaluation: Using a network analyzer, insertion loss was measured in the range of 0.001 to 8 GHz. The frequency at which insertion loss increased sharply was identified, and this frequency was set as the upper bandwidth limit. If the upper bandwidth limit is 6 GHz or higher, the communication cable can be considered to have sufficient bandwidth.
[0074] Furthermore, for each sample, the insertion loss value at 8 GHz was expressed as a ratio based on the value of sample A1, and this was defined as the loss degradation rate. If the loss degradation rate is less than 1.1, the communication cable can be considered to have sufficiently low loss.
[0075] [Test Results] Table 1 below shows the wire configurations applied to samples A1-A4 and B1-B4, along with the evaluation results of their wire characteristics.
[0076]
[0077] According to Table 1, all samples A1 to A4 have an inner sheath. The conductor outer diameter is 0.55 mm or more, the elastic modulus of the insulation coating is 1600 MPa or less, the outer diameter of the insulated wire is 1.4 mm or less, and the twist pitch is 14 mm or less. A characteristic impedance of 100 Ω was obtained for these samples A1 to A4. In addition, the upper limit of the bandwidth evaluated by insertion loss is 6 GHz or more, and it can be considered that sufficient broadbanding has been achieved. Furthermore, the loss degradation rate is kept below 1.1, and it can be considered that sufficient low loss has been achieved. Thus, it has been confirmed that by applying the above parameters to a communication wire having an inner sheath and a film-like shield arranged longitudinally inside a braided shield, it is possible to broaden the bandwidth of the communication wire and further reduce loss while ensuring a characteristic impedance of 100 ± 5 Ω.
[0078] Here, we compare samples A1 to A4 with each other. In samples A1 to A3, the metal foil constituting the film-like shield is made of copper, while in sample A4, it is made of aluminum. When sample A4 is compared with samples A1 to A3, and especially sample A1, where all parameters except the metal material constituting the film-like shield are the same, the rate of loss deterioration is slightly higher. From this, it can be said that using highly conductive copper as the metal constituting the metal foil of the film-like shield is particularly effective in reducing insertion loss and the resulting broadening of bandwidth.
[0079] Samples A1 and A2 differ from each other in the twist pitch of their twisted pair wires. Comparing their evaluation results, sample A2, with its shorter twist pitch, shows a higher upper bandwidth limit. This indicates that shortening the twist pitch is highly effective in broadening the bandwidth. The 10 mm twist pitch of sample A2 is the practical minimum twist pitch at which insulated wires can be stably twisted together without variation, assuming an elastic modulus of 1500 MPa for the insulating coating.
[0080] In sample A3, the elastic modulus of the insulating coating is lower than in samples A1 and A2. This allows for twisting the insulated wires at an even shorter pitch than in sample A2, resulting in a twist pitch of 9 mm. In response to the shorter pitch, sample A3 has an even higher upper limit of bandwidth than sample A2, achieving a high degree of broadband operation.
[0081] Unlike samples A1 to A4, samples B1 and B2 do not have an inner sheath on the communication wire. Sample B2, in particular, differs from sample A1 only in that it does not have an inner sheath. In sample B2, the characteristic impedance is 75 Ω, which is significantly lower than 100 Ω. On the other hand, sample B1 increases the characteristic impedance to 100 Ω by increasing the outer diameter of the insulated wire without providing an inner sheath. In sample B1, the outer diameter of the insulated wire is 1.65 mm, which exceeds 1.4 mm. Due to this increased outer diameter of the insulated wire, it became impossible to stably twist the insulated wires together with the same 13 mm twist pitch as samples A1 and B2, so the twist pitch was increased to 16 mm. In response to the increase in twist pitch, the upper limit of the bandwidth became 5 GHz, which is lower than 6 GHz. In other words, sufficient broadband cannot be achieved. A comparison of sample A1 with samples B1 and B2 confirms that the inner sheath improves the characteristic impedance, enabling the securing of a sufficient characteristic impedance even when the outer diameter of the insulated wire is reduced to shorten the pitch of the twisted pair wires.
[0082] In sample B3, the elastic modulus of the insulating coating constituting the insulated wire is high, exceeding 1600 MPa. In this case, due to the rigidity of the insulated wire, it becomes impossible to stably twist the insulated wires together with the same 13 mm twist pitch as in sample A1, etc., and the twist pitch is increased to 16 mm. Consequently, corresponding to the increase in twist pitch, the upper limit of the bandwidth becomes 5 GHz, falling below 6 GHz. In other words, sufficient broadband is no longer achievable.
[0083] In sample B4, the outer diameter of the conductor constituting the insulated wire is less than 0.55 mm. In this case, the loss deterioration rate is a large value exceeding 1.1. From this, it can be said that increasing the outer diameter of the conductor to 0.55 mm or more is important for reducing loss.
[0084] [2] Influence of the arrangement order of the shielding section Next, we investigated the relationship between the arrangement order of the film shield and the braided shield in the shielding section and the signal loss.
[0085] [Test Method] Based on sample A1 from the above test [1], two types of samples were prepared with different arrangements of the film-like shield and the braided shield. Specifically, sample A1 itself, with the film-like shield on the inside and the braided shield on the outside, was designated as the sample with the metal foil on the inside. On the other hand, sample A1 was modified so that the metal braid was on the inside and the film-like shield was on the outside, and this was designated as the sample with the braid on the inside. Insertion loss was then measured for both samples in the same manner as in the above test [1].
[0086] [Test Results] Figure 2 shows the measurement results of insertion loss (IL) for each frequency (f) for samples with metal foil placed inside and braided material placed inside. A smaller absolute value of the insertion loss (higher on the graph) indicates a reduction in loss.
[0087] As shown in Figure 2, across the entire frequency range, the insertion loss is lower with the metal foil on the inside than with the braided shield on the outside. Furthermore, the difference in insertion loss between the two increases with higher frequencies. For example, at 8 GHz, the insertion loss is -2.4 dB / m with the metal foil on the inside and -3.3 dB / m with the braided shield on the inside. In other words, the braided shield on the inside has an insertion loss value that is approximately 35% higher. From these test results, it is confirmed that a high level of signal loss reduction can be obtained by placing a film-like shield with metal foil on the inside and a braided shield on the outside as the shielding section.
[0088] [3] Influence of resin ratio in the region surrounded by the inner sheath Next, we examined the relationship between the resin ratio in the region surrounded by the inner sheath and the characteristic impedance.
[0089] [Test Method] Based on sample A1 from the above test [1], several samples with different resin ratios in the region surrounded by the inner sheath were prepared. The resin ratio was varied according to the extrusion molding conditions of the inner sheath. The differential characteristic impedance was measured for each obtained sample in the same manner as in the above test [1].
[0090] [Test Results] Figure 3 shows the relationship between the resin ratio and differential characteristic impedance (CIDM) obtained from actual measurements. A resin ratio of 0% corresponds to a state in which the inner surface of the inner sheath has a shape that can be considered circular in cross-section and is a hollow state that is circumscribing the twisted pair wire. On the other hand, a resin ratio of 100% corresponds to a state in which the entire inner surface of the inner sheath is in contact with the surface of the insulated wire that makes up the twisted pair wire.
[0091] As shown in Figure 3, the characteristic impedance increases as the resin content decreases and the proportion of voids not occupied by the resin material within the inner sheath increases. By keeping the resin content below 60%, a characteristic impedance of approximately 100 ± 5 Ω can be secured.
[0092] [4] Influence of inner sheath thickness Next, we examined the relationship between the thickness of the inner sheath and the mode conversion loss.
[0093] [Test Method] Based on sample A1 from the above test [1], several samples with different inner sheath thicknesses were prepared. For each obtained sample, the mode conversion loss (transmission mode conversion) was measured using a network analyzer. Generally, if the mode conversion loss is below -20 dB, it can be considered that the mode conversion loss is sufficiently suppressed.
[0094] [Test Results] Figure 4 shows the relationship between the inner sheath thickness and mode conversion loss obtained by actual measurement. A smaller value for mode conversion loss (lower on the graph) indicates that the mode conversion loss is reduced. The sample with an inner sheath thickness of 0 mm corresponds to a configuration without an inner sheath (i.e., sample B2).
[0095] As shown in Figure 4, the mode conversion loss decreases as the thickness of the inner sheath increases. Furthermore, when the thickness of the inner sheath exceeds 0.3 mm, the mode conversion loss falls below -20 dB. From this, it can be said that to sufficiently suppress mode conversion loss, the thickness of the inner sheath should be kept to around 0.40 ± 0.15 mm.
[0096] [5] Influence of dielectric loss tangent of insulating coating Next, we examined the relationship between the dielectric loss tangent of the insulating coating constituting the insulated wire and the signal loss.
[0097] [Test Method] Based on sample A1 from the above test [1], samples with different dielectric loss tangents of the insulating coating constituting the insulated wire were prepared. Here, two types of samples with different dielectric loss tangents were prepared by changing the material used for the insulating coating. Then, the insertion loss was measured for each of the obtained samples in the same manner as in the above test [1].
[0098] [Test Results] Table 2 below shows the relationship between the dielectric loss tangent of the insulating coating and the insertion loss value at 8 GHz.
[0099]
[0100] Table 2 shows that insertion loss is greater when the dielectric loss tangent is large. －３ In this case, the value of the insertion loss is when the dielectric loss tangent is 2 × 10⁻⁶. －４ This is approximately 20% larger compared to the previous case. These test results confirm that reducing the dielectric loss tangent of the insulating coating that makes up the insulated wire can achieve lower losses.
[0101] [6] Influence of conductor outer diameter Next, we examined the relationship between the outer diameter of the conductor constituting the insulated wire and signal loss.
[0102] [Test Method] Based on sample A1 from the above test [1], two types of samples with different outer diameters of conductors constituting the insulated wire were prepared. The outer diameters of the conductors were 0.6 mm and 0.48 mm. These samples correspond to samples A1 and B4, respectively. For each sample, the insertion loss was measured in the same manner as in the above test [1].
[0103] [Test Results] Figure 5 shows the measurement results of insertion loss (IL) at each frequency (f) for two types of samples with different conductor outer diameters. According to Figure 5, across the entire frequency range, the insertion loss is lower when the conductor outer diameter is 0.6 mm than when it is 0.48 mm. Furthermore, the difference in insertion loss between the two increases with increasing frequency. For example, at 8 GHz, the insertion loss is -2.4 dB / m for the conductor outer diameter of 0.6 mm and -2.7 dB / m for the conductor outer diameter of 0.48 mm. In other words, the insertion loss is approximately 12% higher when the conductor outer diameter is 0.48 mm. This corresponds to the loss degradation rate of 1.12 for sample B4 in Table 1. From the above test results, it is confirmed that loss reduction can be achieved by increasing the outer diameter of the conductor constituting the insulated wire.
[0104] [7] Influence of Outer Diameter of Insulated Wires Finally, we examined the relationship between the outer diameter of the insulated wires constituting the twisted pair wire, the twist pitch, and the applicable bandwidth.
[0105] [Test Method] Based on sample A2 from the above test [1], several samples with different outer diameters of insulated wires were prepared by changing the thickness of the insulation coating. Two insulated wires of each outer diameter were then twisted together to form a twisted pair wire. During the formation process of the twisted pair wire, the minimum twist pitch that allows for twisting with a stable pitch without variation was estimated. Furthermore, the upper limit of the bandwidth was estimated for a communication wire containing the twisted pair wire having the minimum twist pitch, in the same manner as in the above test [1].
[0106] [Test Results] Table 3 below shows the relationship between the outer diameter of the insulated wire, the twist pitch, and the upper limit of the bandwidth.
[0107]
[0108] Table 3 shows that the twist pitch increases as the outer diameter of the insulated wire increases. Consequently, the upper limit of the bandwidth decreases, making it difficult to achieve wider bandwidth. Generally, by keeping the outer diameter of the insulated wire to 1.4 mm or less, it is possible to twist the insulated wires together with a twist pitch of 14 mm or less with ample margin. This allows for achieving a bandwidth upper limit of 6 GHz or more, enabling wider bandwidth for communication wires.
[0109] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.
[0110] 1. Communication wire 10. Twisted pair wire 11. Insulated wire 12. Conductor 13. Insulation coating 20. Inner sheath 30. Shielding section 31. Film shield 32. Braided shield 40. Outer sheath
Claims
1. A communication wire comprising: a conductor with an outer diameter of 0.55 mm or more; an insulating sheath having an elastic modulus of 1600 MPa or less and covering the outer circumference of the conductor; a pair of insulated wires with an outer diameter of 1.4 mm or less, twisted together with a twist pitch of 14 mm or less; an inner sheath made of an insulator and covering the outer circumference of the twisted pair wire; a film-like shield comprising metal foil, arranged longitudinally with respect to the axis of the twisted pair wire and covering the outer circumference of the inner sheath; a braided shield made of a braided body of metal strands and covering the outer circumference of the film-like shield; and an outer sheath made of an insulator and covering the outer circumference of the braided shield.
2. The communication wire according to claim 1, wherein the metal foil constituting the film-like shield is made of copper or a copper alloy.
3. The communication wire according to claim 1 or 2, wherein, in a cross-section perpendicular to the axial direction of the communication wire, the proportion of the area occupied by the constituent material of the inner sheath within the space enclosed by a circle circumscribing the twisted pair wire and the outer surface of the twisted pair wire is 60% or less.
4. The communication wire according to claim 1 or claim 2, wherein the thickness of the inner sheath is in the range of 0.40 ± 0.15 mm.
5. The communication wire according to claim 1 or claim 2, wherein the dielectric loss tangent of the inner sheath is 0.01 or less.
6. The communication cable according to claim 1 or claim 2, wherein the elastic modulus of the inner sheath is 100 MPa or more and 500 MPa or less.
7. The communication wire according to claim 1 or claim 2, wherein the melting point of the inner sheath is 140°C or higher.
8. The communication wire according to claim 1 or claim 2, wherein the conductor is made of soft copper.
9. The communication wire according to claim 1 or claim 2, wherein the conductor is configured as a stranded wire made by twisting together a plurality of metal strands, and the twist pitch of the strands is 9 mm or less.
10. The communication wire according to claim 1 or claim 2, wherein the relative permittivity of the insulating coating is 2.4 or less.
11. The communication wire according to claim 1 or claim 2, wherein the dielectric loss tangent of the insulating coating is 0.001 or less.
12. The communication wire according to claim 1 or claim 2, wherein the elastic modulus of the insulating coating is 1200 MPa or less.
13. A communication wire according to claim 1 or claim 2, wherein the differential characteristic impedance is in the range of 100 ± 5 Ω.