Patent Publication Number: US-2022215988-A1

Title: Cable

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a cable, and more particularly to a cable used to transmit high frequency signals. 
     2. Description of Related Arts 
     U.S. Pat. No. 10,950,369, issued on Mar. 16, 2021, discloses a twin-axial cable including a pair of inner cables arranged side-by-side, or parallel to one another. Each of the inner cables includes a center conductor, a first dielectric layer surrounding the center conductor, and a middle conductor surrounding the first dielectric layer. The twin-axial cable also include one or more second dielectric layers surrounding each inner cable, an outer conductor surrounding the one or more second dielectric layers, and a protective outer jacket surrounding the outer conductor. 
     With the development and popularization of electronic technology products, signal cables are widely used in household appliances, instrumentation, automation equipment, data centers, servers, switches, cloud computing and 5G as a tool for signal transmission. However, in the signal transmission process, the cable is susceptible to interference from external electromagnetic signals, so it is often necessary to use a shielding structure to eliminate or reduce the interference of the external electromagnetic field, and to prevent the leakage of the transmission signal. Therefore, it is necessary to provide an improved cable with strong anti-interference performance, stable signal transmission, reliability. 
     SUMMARY OF THE INVENTION 
     A main object of the present invention is to provide a cable which has good shielding effect and stable signal transmission capability. 
     To achieve the above-mentioned object, a cable comprises: a pair of core wires; a shielding layer covering the pair of core wires; and an outer insulating layer covering the shielding layer; wherein each of the core wires includes an inner conductor, an inner insulating layer covering the inner conductor, and a first shielding layer covering the inner insulating layer, and each core wire includes only one inner conductor. 
     Compared to prior art, the present invention has the advantage that the double shielding of the first shielding layer covering the core wire and the shielding layer covering the pair of core wires improves the shielding effect of the cable and ensures the reliability of signal transmission. Also, the cable of the present invention has the ability to transmit high-speed data signals with a frequency greater than 40 GHz. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a front view of a first embodiment of a cable of the present invention; 
         FIG. 2  is a front view of a second embodiment of the cable of the present invention; 
         FIG. 3  is the curve of differential insertion loss tested with the structure in  FIG. 1  and American Wire Gauge (AWG) 30 cable; 
         FIG. 4  is the curve of single-ended insertion loss tested with the structure in  FIG. 1  and AWG 30 cable; and 
         FIG. 5  is the curve of single-ended insertion loss attenuation difference in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows the first embodiment of a cable  100  of the present invention. The cable  100  includes a pair of core wires  10 , a shielding layer  30  covers the pair of core wires  10 , an outer insulating layer  50  covers the shielding layer  30  and a ground wire  60  is located between the shielding layer  30  and the pair of core wires  10 . 
     In this embodiment, Each core wire  10  includes an inner conductor  1  and an inner insulating layer  2  covering the inner conductor  1 , a first shielding layer  3  covering the inner insulating layer  2 , a second shielding layer  4  covering the first shielding layer  3  and an heat-adhesive PET (polyethylene terephthalate) layer  5  covering the second shielding layer  4 . The inner conductor  1  is used for transmitting high-speed signal. The inner insulating layer  2  of each core wire  10  is extruded and molded to cover the inner conductor  1 . The inner insulating layer  2  can be one of PP (polypropylene), PE (polyethylene), FEP (Fluorinated ethylene propylene), and PFA (Polyfluoroalkoxy). The first shielding layer  3  is a pure metal tape. The second shielding layer  4  is a metal wire. Preferably, in this embodiment, the first shielding layer  3  is a metal copper tape or a metal aluminum tape. The second shielding layer  4  is pure copper wire. The first shielding layer  3  covers the inner insulating layer  2  in a longitudinal wrapping way. The pure copper wire wraps the first shielding layer  3  in a spiral winding way. The heat-adhesive PET layer  5  fixes the second shielding layer  4 . The heat-adhesive PET layer  5  wraps the second shielding layer  4  in a spiral winding way. The shielding layer  30  can be any one of aluminum foil, copper foil, metal copper tape or metal aluminum tape. The upper and lower sides between the shielding layer  30  and the pair of core wires  10  forms air gaps  70 . The ground wire  60  is provided in the upper side air gap  70  between the shielding layer  30  and the core wire  10 . The outer insulating layer  50  can be provided as one layer or multiple layers, and its material can be PET tape. In the embodiment, each core wire  10  adopts the double-layer shielding of the first shielding layer  3  of pure metal and the second shielding layer  4  wound by metal wires, so the shielding effect is better, and the pure metal shielding layer can meet the attenuation requirements of higher frequencies. 
       FIG. 2  shows the second embodiment of the cable  100 . Compared with the first embodiment, in this embodiment, the second shielding layer  4  and the heat-adhesive PET layer  5  in the first embodiment are reduced. The cable  100  reduces the second shielding layer  4  and the heat-adhesive PET layer  5 , which makes the cable lighter, simpler in structure, more convenient to manufacture, and cheaper in price. 
     Refer to  FIGS. 3-5 , which is the performance test curve of the cable, using the cable structure in the first embodiment and 30 AWG as the test sample. The abscissa is the frequency, in GHz, and the ordinate is the loss, in dB. 
       FIG. 3  is the SDD 21  (Differential Insertion Loss) curve of the cable. It can be seen that as the frequency increases, the differential insertion loss has no cliff-like attenuation before 40 GHz, and the attenuation is less than −16 dB at 40 GHz. 
       FIG. 4  is the curve of SEIL (single-ended insertion loss). The curve measured by one conductor of the cable is curve  1 , and the curve measured by the other conductor is curve  2 . It can be seen that the single-ended insertion loss of the two conductors of the cable has no cliff-type attenuation at 22 GHz, and the attenuation is less than −35 dB at 22 GHz, and the single-ended attenuation consistency of the two wires is better. 
       FIG. 5  is the curve of SEILD (single-ended insertion loss attenuation difference). It is the absolute value of curve  1  minus the value of curve  2  in  FIG. 4 , and it can be seen that the absolute value is below 2.5 dB at 22 GHz. 
     The cable of the present invention is provided with a first shielding layer on each core wire, and then a shielding layer covering the pair of core wires is arranged outside the pair of core wires. With the double shielding layer, the shielding effect is better and the anti-interference ability is stronger. The cable of the present invention has a high-speed data transmission capability with a signal transmission frequency greater than 40 GHz. 
     The above are only some of the embodiments of the present invention, but not all of the embodiments. Any equivalent changes to the technical solutions of the present invention by those skilled in the art by reading the description of the present invention are covered by the claims of the present invention.