Composite cable

Abstract

The invention provides a composite cable which is small in outer diameter and capable of reducing delay inequality. A composite cable (1) is provided with an integrated core (3) configured by twisting a plurality of sub-stranded wires (2) into a plurality of layers, and a sheath (6) covering the periphery of the integrated core (3), the integrated core (3) includes the plurality of sub-stranded wires (2), each sub-stranded wire (2) includes a four-strand stranded wire (21) formed by twisting two pairs of differential signal wires (210) for transmitting differential signals, and a plurality of four-strand stranded wires (21) are included in one layer of the integrated core (3).

Description

Technical Field

[0001] This invention relates to composite cables. Background Technology

[0002] With the aim of increasing the communication speed and image quality of ultrasonic probes, research is underway on ultrasonic probes using digital transmission methods. The cables used in digital transmission ultrasonic probes are required to transmit differential signals. As cables for transmitting differential signals, twisted-pair cables, consisting of a pair of signal lines for differential signals (hereinafter referred to as differential signal lines), are typically used.

[0003] Conventionally, in the transmission of differential signals, twisted-pair cables with an overall shielding layer are used. However, in composite cables used for ultrasonic probes, mechanical stresses such as bending and twisting are repeatedly applied. Therefore, in composite cables containing twisted-pair cables with an overall shielding layer, there are problems such as breakage of the metal wires constituting the overall shielding layer and displacement of the differential signal lines. If a breakage occurs in the overall shielding layer or the displacement of the differential signal lines becomes large, performance degradation such as impedance shift and attenuation deterioration may occur, and countermeasures are desired. Therefore, shielded coaxial cables are used for the differential signal lines, and a pair of coaxial cables are twisted together (for example, see Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-176567 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, composite cables used for ultrasonic probes require not only differential signal lines but also a combination of various wires such as control signal lines and power lines. In particular, cables containing multiple differential signal lines require multiple twisted pairs of coaxial differential signal lines bundled together, resulting in an increased cable outer diameter.

[0009] In order to reduce the outer diameter of the cable, it is also considered to twist the differential signal line together with other wires without twisting. However, in this case, a physical length difference will be generated between the pairs of differential signal lines, resulting in the problem of deterioration of the time delay difference (skew).

[0010] The purpose of this invention is to provide a composite cable with a small outer diameter and reduced time delay difference.

[0011] Methods for solving problems

[0012] To address the aforementioned issues, this invention provides a composite cable comprising a core, a surrounding area covering the core, and a sheath. The core comprises multiple stranded wires and is constructed by twisting multiple stranded wires into multiple layers. Each stranded wire includes multiple four-strand wires formed by twisting two pairs of differential signal lines for transmitting differential signals. One layer of the core contains multiple of these four-strand wires.

[0013] Invention Effects

[0014] According to the present invention, a composite cable with a small outer diameter and reduced time delay difference can be provided. Attached Figure Description

[0015] Figure 1 In the diagram, (a) is a cross-sectional view of a composite cable perpendicular to the length direction according to one embodiment of the present invention, and (b) is a cross-sectional view of a differential signal line perpendicular to the length direction.

[0016] Figure 2 This is a cross-sectional photograph of the composite cable of Example 1.

[0017] Explanation of reference numerals in the attached figures

[0018] 1…Composite cable, 2…Structured wire, 21…Four-strand wire, 210…Differential signal line, 211…Inner conductor, 211a…Metal wire, 3…Collective core, 31…Inner layer, 32…Outer layer, 4…Bundling tape, 5…Overall shielding layer, 6…Sheath, 7…Clamping material. Detailed Implementation

[0019] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0020] (Overall structure of composite cable 1)

[0021] Figure 1 (a) is a cross-sectional view showing the composite cable 1 of this embodiment, perpendicular to its length. The composite cable 1 is, for example, a probe cable for an ultrasonic probe used in a digital transmission mode, and is a medical cable. The composite cable 1 is repeatedly subjected to bending, twisting, swinging, and other actions (referred to as bending and other actions).

[0022] The composite cable 1 includes a core 3 formed by twisting multiple strands 2 together and a sheath 6 covering the periphery of the core 3. In this embodiment, the composite cable 1 includes a binding strap 4 wound around the core 3 and a general shielding layer 5 disposed around the binding strap 4. The sheath 6 is disposed to cover the periphery of the general shielding layer 5. Details of each part will be described below.

[0023] (Core 3)

[0024] The core 3 is constructed by twisting multiple sub-strands 2 into multiple layers. In this embodiment, the core 3 has a two-layer structure of an inner layer 31 and an outer layer 32. The inner layer 31 is constructed by twisting three sub-strands 2 around a clamping element 7 made of tensile fibers. Furthermore, the outer layer 32 is constructed by twisting seven sub-strands 2 around the inner layer 31. It should be noted that the number of layers of the core 3 and the number of sub-strands 2 in each layer are not limited to the numbers shown in the figure.

[0025] The twisting directions of the multiple layers constituting the core 3 (in this case, the twisting directions of the inner layer 31 and the outer layer 32) can be the same. With this configuration, when the composite cable 1 is subjected to bending or other actions, the overall twisting of the core 3 can tighten or loosen, thus dispersing stress and improving resistance to bending and other actions. It should be noted that the twisting directions of the inner layer 31 and the outer layer 32 refer to the direction in which the stranded wires 2 rotate from one end to the other when viewed from one end of the composite cable 1.

[0026] Furthermore, for the same reason, it is preferable that the twisting direction of each sub-strand 2 is the same as the twisting direction of each layer of the core 3. It should be noted that the twisting direction of the sub-strand 2 is the direction in which the wires constituting the sub-strand 2 (differential signal line 210, power line 220, 230 or signal line 240, 250, described later) rotate from one end to the other when viewed from one end of the sub-strand 2.

[0027] The core 3 includes various sub-strands 2. Additionally, the core 3 includes four-stranded wires 21 formed by twisting two pairs of differential signal lines 210 that transmit differential signals as sub-strands 2. In this embodiment, the core 3 includes six four-stranded wires 21, one first power line unit 22, one second power line unit 23, one first signal line unit 24, and one second signal line unit 25, totaling ten wires and five sub-strands 2. Furthermore, the inner layer 31 is constructed by twisting the clamping element 7, one first power line unit 22, one second power line unit 23, and one first signal line unit 24 together. The outer layer 32 is constructed by twisting six four-stranded wires 21 and one second signal line unit 25 around the inner layer 31.

[0028] (4-strand twisted wire 21)

[0029] In this embodiment, instead of using twisted-pair cables for differential signal transmission, a four-strand twisted-wire 21 is used, consisting of two pairs (i.e., four strands) of differential signal lines 210 twisted together. This configuration reduces the outer diameter of the composite cable 1 compared to using twisted-pair cables, and also suppresses the time delay difference to the same level as when using twisted-pair cables. More specifically, for example, when using four differential signal lines 210, if twisted-pair cables were used, two twisted-pair cables with an outer diameter twice that of the differential signal lines 210 would be required. In contrast, with the four-strand twisted-wire 21, only one four-strand twisted-wire 21 with an outer diameter approximately 2.4 times that of the differential signal lines 210 is needed. Therefore, when using multiple differential signal lines 210 (specifically, using 8 or more, preferably 12 or more, more preferably 16 or more differential signal lines 210), the outer diameter of the composite cable 1 can be reduced by using four-strand twisted wire 21. Furthermore, the time delay difference when forming four-strand twisted wire 21 can be the same as the time delay difference when forming twisted pair wire. It should be noted that in this embodiment, the core 3 does not include a twisted pair formed by twisting the differential signal lines 210 together.

[0030] In this embodiment, all the multiple four-strand wires 21 are included in one layer of the core 3 (here, the outer layer 32). More specifically, the outer layer 32 of the core 3 is formed by twisting multiple (here, 6) four-strand wires 21 and other sub-stranded wires 2 (here, one second signal line unit 25) into a loop. Moreover, the inner layer 31 does not contain four-strand wires 21. With this configuration, the four-strand wires 21 are arranged side by side in the outer layer 32, so the sub-stranded wires 2 can be arranged in a balanced and good manner in the core 3, and the increase in time delay difference caused by the shape deformation of the core 3 can be suppressed. In addition, by arranging the four-strand wires 21 side by side in the outer layer 32, stress concentration when the composite cable 1 is subjected to bending or other actions can be suppressed, and the resistance to bending and other actions can be improved. Furthermore, compared with the case where the four-strand wires 21 are arranged in the inner layer 31, the flattening of the differential signal line 210 can be suppressed, and the degradation of transmission characteristics can be suppressed. It should be noted that, for a better balanced configuration and to further improve resistance to bending and other actions, the outer layer 32 is preferably composed of only four strands 21. Furthermore, the number of sub-strands 2 other than the four strands 21 in the outer layer 32 is preferably two or less. Moreover, the number of four strands 21 in the outer layer 32 is preferably four or more.

[0031] In the four-strand wire 21, the ratio of its twisting pitch P1 to the core diameter Pd1, i.e., P1 / Pd1, can be greater than 30 and less than 50. This configuration reduces the cable's outer diameter and suppresses time delay differences. It should be noted that if P1 / Pd1 of the four-strand wire 21 is less than 30, the shape of the four-strand wire 21 is difficult to deform, making it difficult to reduce the cable's outer diameter by allowing the differential signal line 210 to enter the gap. Conversely, if P1 / Pd1 of the four-strand wire 21 is greater than 50, the shape of the four-strand wire 21 is too easily deformed, potentially creating physical length differences between the paired differential signal lines 210, which could worsen the time delay difference.

[0032] Regarding the outer layer 32 containing the four strands 21, the ratio of its twisting pitch P2 to the core diameter Pd2, i.e., P2 / Pd2, can be 30 or more and 45 or less. This configuration reduces the cable's outer diameter and also suppresses time delay differences. It should be noted that if P2 / Pd2 of the outer layer 32 is less than 30, the twisted shape of the outer layer 32 is difficult to deform, making it difficult to properly fill the gaps between the sub-strands 2 through appropriate deformation of the twisted shape, thus hindering the reduction of the cable's outer diameter. Conversely, if P2 / Pd2 of the outer layer 32 is greater than 45, the twisted shape of the outer layer 32 becomes too easily deformable, potentially worsening the time delay difference due to deformation of the outer layer 32's twisted shape.

[0033] It should be noted that, preferably, both P1 / Pd1 of the four-strand twisted wire 21 and P2 / Pd2 of the outer layer 32 are within the above-mentioned value range. However, even if only either P1 / Pd1 of the four-strand twisted wire 21 or P2 / Pd2 of the outer layer 32 is within the above-mentioned value range, the above-mentioned effect, namely the reduction of cable outer diameter and time delay difference, can still be obtained.

[0034] In this embodiment, during the twisting of the core 3, the twisting of each layer and the twisting of the sub-strands 2 are moderately deformed (to a degree that the time delay difference will not worsen), filling the gaps in the core 3. Therefore, the actual outer diameter of the core 3 is smaller than the outer diameter of the core 3 assumed based on the concentric circles of each sub-strand 2 during the design (i.e., the outer diameter of the core 3 assumed according to the attached drawings). In addition, by moderately deforming the twisted shape of the core 3, the shape of the core 3 can easily become an aesthetically pleasing circular shape.

[0035] (Differential signal line 210)

[0036] Figure 1 (b) is a cross-sectional view showing the differential signal line 210 perpendicular to its length direction. For example... Figure 1As shown in (b), the differential signal line 210 is composed of a coaxial line and has an inner conductor 211, an insulator 212 covering the periphery of the inner conductor 211, an outer conductor 213 covering the periphery of the insulator 212, and an outer sheath 214 covering the periphery of the outer conductor 213.

[0037] The internal conductor 211 of the differential signal line 210 is composed of a compressed stranded conductor, which is formed by lightly compressing multiple (in this case, seven) metal wires 211a after twisting them together, resulting in a roughly circular cross-sectional shape. This configuration allows for a larger maintenance of the conductor cross-sectional area and a smaller conductor outer diameter, contributing to the miniaturization of the differential signal line 210 and the overall miniaturization of the composite cable 1. Furthermore, the increased contact area between adjacent metal wires 211a reduces contact resistance, thereby improving the conductivity of the internal conductor 211 and enhancing its electrical characteristics.

[0038] The metal wire 211a constituting the inner conductor 211 can be a copper alloy with a tensile strength of 320 MPa or higher and a conductivity of 75% or higher. In this embodiment, silver-plated copper alloy wire with a high conductivity silver plating is used as the metal wire 211a constituting the inner conductor 211. With this configuration, mechanical strength can be improved while suppressing the decrease in conductivity, and an inner conductor 211 that is not easily broken even with a small diameter can be formed.

[0039] As the insulator 212 of the differential signal line 210, a thin-walled and moldable fluoropolymer can be used. Here, as the insulator 212, an insulator made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) is used.

[0040] The outer conductor 213 of the differential signal line 210 uses a transversely wound shielding member formed by winding multiple metal wires 213a into a spiral around the insulator 212. This configuration improves resistance to bending and other actions, and also prevents the outer conductor 213 from becoming thicker and the differential signal line 210 from becoming larger in diameter. The metal wires 213a constituting the outer conductor 213, like the metal wires 211a constituting the inner conductor 211, are silver-plated copper alloy wires with high conductivity and high mechanical strength.

[0041] In addition, in this embodiment, to further improve noise immunity, a metal strip 215 is wound around the outer conductor 213. The metal strip 215 is wound into a spiral shape with a portion of its width direction overlapping. As the metal strip 215, a metal strip with a copper layer formed on one side of a strip member made of polyester can be used. In this case, the metal strip 215 is wound with the copper layer on the inside (the copper layer is in contact with the outer conductor 213).

[0042] The outer sheath 214 of the differential signal line 210 is formed by winding a polyester tape. The polyester tape is wound into a spiral shape with a portion overlapping in the width direction. The outer diameter of the outer sheath 214, i.e., the outer diameter of the differential signal line 210, is 0.73 mm.

[0043] (Sub-strand 2 other than the four-strand strand 21)

[0044] The inner layer 31 of the core 3 is formed by twisting together a first power line unit 22, a second power line unit 23 and a first signal line unit 24.

[0045] The first power line unit 22, located in the inner layer 31, is constructed by twisting together four power lines 220. Similarly, the second power line unit 23, also located in the inner layer 31, is constructed by twisting together five power lines 230. Although not shown, the power lines 220 and 230 are insulated wires with an insulator formed around the conductor. While the same structure is used for the power lines 220 and 230, different structures are also possible. Furthermore, the number of power lines 220 and 230 included in the power line units 22 and 23 is not limited to the number shown in the figure. In this embodiment, the power lines 220 and 230 are only located in the inner layer 31. The outer diameter of the power lines 220 and 230 is smaller than the outer diameter of the differential signal line 211. Here, insulated wires with an outer diameter of 0.44 mm are used for the power lines 220 and 230.

[0046] The first signal line unit 24, located in the inner layer 31, is constructed by twisting together six signal lines 240. The second signal line unit 25, located in the outer layer 32, is constructed by twisting together sixteen signal lines 250. Although not shown, the signal lines 240 and 250 are made of coaxial cable. The outer diameters of the signal lines 240 and 250 are smaller than the outer diameter of the differential signal line 210 and smaller than the outer diameters of the power lines 220 and 230. Here, coaxial cable with an outer diameter of 0.34 mm is used as the signal lines 240 and 250. Furthermore, the second signal line unit 25 in the outer layer 32 contains fewer signal lines 250 than the first signal line unit 24 in the inner layer 31.

[0047] Thus, in composite cable 1, all power lines 220 and 230 are arranged in the inner layer 31. Signal lines 240 and 250 are arranged in the inner layer 31 and the outer layer 32, with more lines arranged in the outer layer 32 than in the inner layer 31. Furthermore, all differential signal lines 210 are arranged in the outer layer 32. The inner layer 31 contains a mixture of power lines 220, 230, and signal lines 240, while the outer layer 32 is entirely composed of differential signal lines 210 and signal lines 250 for signal transmission.

[0048] (4 straps)

[0049] The binding tape 4 is a component used to prevent the twisted core 3 from unraveling, and it is wrapped around the core 3. The binding tape 4 is spirally wound around the core 3 with a portion of its width overlapping. Resin tape can be used as the binding tape 4. In this embodiment, a binding tape 4 made of PTFE (polytetrafluoroethylene) is used.

[0050] (Total shielding layer 5)

[0051] The overall shielding layer 5 is used to improve the noise immunity of the differential signal line 21 (and signal lines 240, 250), and is connected to the so-called chassis ground. It should be noted that the outer conductor 213 of the differential signal line 210 (and the outer conductors of signal lines 240, 250) is connected to the so-called signal ground, and its purpose differs from that of the overall shielding layer 5. Here, the overall shielding layer 5 is composed of a braided shield made of multiple braided metal wires. Copper alloy wire with excellent mechanical strength can be used as the metal wire used for the braided shield.

[0052] (Sheath 6)

[0053] The sheath 6 is a layer used to protect the core 3 and the overall shielding layer 5. In this embodiment, the sheath 6 is made of PVC (vinyl chloride resin). The outer diameter of the sheath 6, i.e. the outer diameter of the composite cable 1, is 10 mm or less, more preferably 9 mm or less, and even more preferably 8.5 mm or less.

[0054] (Manufacturing method of composite cable 1)

[0055] In manufacturing the composite cable 1, firstly, each stranded wire 2 is formed. At this time, the twisting pitch P in the four-strand strands 21 is adjusted to a P / Pd ratio of 30 or higher and 50 or lower. Next, one first power line unit 22, one second power line unit 23, and one first signal line unit 24 are twisted together to form an inner layer 31, and six four-strand strands 21 and one second signal line unit 25 are twisted around the inner layer 31 to form an outer layer 32, thus forming the core 3. At this time, the twisting pitch P is adjusted so that the P / Pd ratio of the outer layer 32 is 30 or higher and 45 or lower.

[0056] In this embodiment, to maintain the shape of the core 3 while it is twisted, the twisting of the core 3 and the winding of the strapping 4 are performed simultaneously in the same process. It should be noted that during the twisting of the core 3, the tension of each strand 2 should be kept consistent, adjusted in a way that prevents excessive deformation of the core 3's shape. Next, a comprehensive shielding layer 5 composed of braided shielding is formed around the strapping 4. Then, a sheath 6 is formed around the comprehensive shielding layer 5 by extrusion molding. To prevent the resin constituting the sheath 6 from entering the comprehensive shielding layer 5, the sheath 6 can be formed by tube extrusion molding. Through the above, the following is obtained: Figure 1 (a) Composite cable 1.

[0057] (Measurement of the outer diameter of core 3, the outer diameter of composite cable 1, and the time delay difference)

[0058] Production Figure 1 Composite cable 1, as Example 1, was used to measure the outer diameter of the core 3, the outer diameter of composite cable 1, and the time delay difference. The outer diameter was measured according to JIS C 3005. The time delay difference was measured by propagation delay time difference measurement based on TDR (Time Zone Reflectivity Measurement). The target value of the time delay difference was set to 30 ps / m, and a measured time delay difference value of 30 ps / m or less was considered acceptable. In addition, composite cable 1 of Example 2, in which the inner conductor 211 of the differential signal line 210 is a non-compressed stranded conductor, was manufactured, and the outer diameter of the core 3, the outer diameter of composite cable 1, and the time delay difference were measured in the same manner as in Example 1. The measurement results are summarized in Table 1. In Table 1, the outer diameter of the core 3 assumed according to the attached drawings is also shown. In Example 1, the P1 / Pd1 of the four strands 21 is 39.9, and the P2 / Pd2 of the outer layer 32 is 40.5. In addition, in Example 2, the P1 / Pd1 ratio of the four-strand twisted wire 21 is 40.7, and the P2 / Pd2 ratio of the outer layer 32 is 37.2.

[0059] [Table 1]

[0060]

[0061] As shown in Table 1, the outer diameter of the core 3 is smaller than the outer diameter assumed in the attached diagram based on the concentric circles of each strand 2. This is believed to be because the twisting of the core 3 and the strand 2 causes moderate deformation, filling the gaps in the core 3. Furthermore, the time delay difference was measured at 5 ps / m in Example 1 and 20 ps / m in Example 2, both of which are acceptable. Additionally, it is evident that Example 1, which uses a compressed stranded conductor in the inner conductor 211 of the differential signal line 210, achieves a lower time delay difference compared to Example 2, which uses a conventional stranded conductor.

[0062] A cross-sectional photograph of the composite cable 1 of Example 1 is shown below. Figure 2 .like Figure 2 As shown, in the composite cable 1, the twisting of the core 3 and the stranded wires 2 is moderately deformed, and the outer diameter of the core 3 is also an aesthetically pleasing circular shape. By setting P1 / Pd1 of the four strands 21 to 30 or more and 50 or less, and setting P2 / Pd2 of the outer layer 32 to 30 or more and 45 or less, the deterioration of the time delay difference caused by excessive deformation of the core 3 can be suppressed, and the shape of the core 3 can be moderately deformed to reduce the outer diameter of the composite cable 1.

[0063] (The role and effect of the implementation method)

[0064] As explained above, the composite cable 1 of this embodiment includes a core 3 formed by twisting multiple strands 2 into multiple layers and a sheath 6 covering the periphery of the core 3. The core 3 includes multiple strands 2. As a strand, it includes a four-strand strand 21 formed by twisting two pairs of differential signal lines 210 that transmit differential signals. Multiple four-strand strands 21 are included in one layer of the core 3.

[0065] With this configuration, the outer diameter of the composite cable 1 can be reduced compared to the case of twisted-pair cables using differential signal lines 210. Furthermore, by concentrating the four strands 21 in one layer, the sub-strands 2 can be easily and evenly arranged within the core 3, suppressing the increase in time delay difference caused by shape deformation of the core 3. Additionally, by concentrating the four strands 21 in one layer, stress concentration during bending and other actions can be suppressed, improving resistance to bending and other actions.

[0066] Furthermore, in the composite cable 1, the P1 / Pd1 ratio of the four strands 21 is set to 30 or more and 50 or less, and the P2 / Pd2 ratio of the outer layer 32 is set to 30 or more and 45 or less. This allows for appropriate deformation of the shape of the core 3, suppressing the deterioration of the time delay difference and reducing the cable's outer diameter. That is, according to this embodiment, a composite cable 1 with a small diameter, high resistance to bending and other actions, and low time delay difference can be realized.

[0067] (Summary of implementation methods)

[0068] Next, the technical ideas learned from the embodiments described above will be described by reference to the accompanying reference numerals and the like. However, the reference numerals and the like in the following description do not limit the constituent elements in the claims to the components specifically shown in the embodiments.

[0069] [1] A composite cable (1) having a core (3) and a sheath (6) wherein the core (3) is formed by twisting multiple strands (2) into multiple layers and the sheath (6) covers the periphery of the core (3); the core (3) includes multiple strands (2), including a four-strand strand (21) formed by twisting two pairs of differential signal lines (210) for transmitting differential signals, and multiple strands (21) are included in one layer of the core (3).

[0070] [2] According to the composite cable (1) described in [1], the ratio of the twisting pitch P1 of the above-mentioned four strands (21) to the core diameter Pd1, i.e., P1 / Pd1, is 30 or more and 50 or less.

[0071] [3] According to the composite cable (1) described in [1], the above-mentioned core (3) is a two-layer structure of inner layer (31) and outer layer (32), and the outer layer (32) contains multiple of the above-mentioned four-strand strands (21) and other above-mentioned sub-strands (2).

[0072] [4] According to the composite cable (1) described in [3], the ratio of the stranding pitch P2 of the outer layer (32) to the core diameter Pd2, i.e., P2 / Pd2, is 30 or more and 45 or less.

[0073] [5] According to the composite cable (1) described in [1], the differential signal line (210) is composed of a coaxial line having an inner conductor (211), which is composed of a compressed stranded conductor formed by twisting together multiple metal wires (211a).

[0074] [6] According to the composite cable 1 described in [5], the metal wire (211a) constituting the internal conductor (211) is made of a copper alloy with a tensile strength of 320 MPa or more and a conductivity of 75% or more.

[0075] (Postscript)

[0076] The embodiments of the present invention have been described above, but the embodiments described above do not limit the invention as defined in the claims. Furthermore, it should be noted that the combinations of features described in the embodiments are not necessarily all necessary for the method to solve the problems of the invention. In addition, the present invention can be implemented with appropriate modifications without departing from its spirit.

Claims

1. A composite cable comprising: A core is formed by twisting multiple sub-wires together into multiple layers, and A sheath covering the periphery of the core assembly; The core assembly includes various types of stranded wires. The sub-twisted wire includes a four-strand wire formed by twisting two pairs of differential signal lines that transmit differential signals together. One layer of the core comprises multiple strands of the four-strand wires.

2. The composite cable according to claim 1, wherein, The ratio of the twisting spacing P1 of the four strands to the core diameter Pd1, i.e., P1 / Pd1, is more than 30 and less than 50.

3. The composite cable according to claim 1, wherein, The core is a two-layer structure consisting of an inner layer and an outer layer, with the outer layer containing multiple strands of the four-strand wires and other sub-strand wires.

4. The composite cable according to claim 3, wherein, The ratio of the outer layer's stranding pitch P2 to the core diameter Pd2, i.e., P2 / Pd2, is greater than 30 and less than 45.

5. The composite cable according to claim 1, wherein, The differential signal line includes a coaxial line with an inner conductor, the inner conductor being a compressed stranded conductor formed by twisting together and compressing multiple metal wires.

6. The composite cable according to claim 5, wherein, The metal wire constituting the internal conductor comprises a copper alloy with a tensile strength of 320 MPa or more and a conductivity of 75% or more.

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