EP1177562A1

EP1177562A1 - Low pass cable

Info

Publication number: EP1177562A1
Application number: EP00927330A
Authority: EP
Inventors: Ning Yu; Bruno Giacomini
Original assignee: Axon Cable SA
Current assignee: Axon Cable SA
Priority date: 1999-05-11
Filing date: 2000-05-11
Publication date: 2002-02-06
Anticipated expiration: 2020-05-11
Also published as: WO2000068959A1; FR2793594B1; EP1177562B1; DE60033513D1; DE60033513T2; FR2793594A1

Abstract

The invention concerns a low pass cable, comprising successively from its centre towards its periphery: a conductive core (10); a first dielectric layer (12); a magnetic absorption layer in ferromagnetic alloy with amorphous or nanocrystalline structure (14); and an insulating sheath (20).

Description

Low pass cable

The present invention relates to a low pass cable.

The purpose of an electrical transmission cable is to convey the signals within an electrical or electronic system or between two systems of this type in a wide frequency range of these signals.

A low-pass transmission cable has a low frequency bandwidth, that is to say that it only allows signals whose frequency is less than a certain limit called the cable cut-off frequency to propagate.

According to the American standard MIL-C-85 485, the cutoff frequency is defined as being that for which the attenuation is equal to 4.3 dB per meter.

Shielded low-pass cables are already known in which, in addition to the usual shielding by metallic braid, an intermediate magnetic absorption layer is produced which is made of ferrite in these known cables. Such low-pass cables have a cut-off frequency of the order of 100 MHz in the sense mentioned above. Such a cut-off frequency is considered admissible for a certain number of applications. However, when it is desired to have a useful signal transmission without it being affected by disturbances conducted by the cable or resulting from external radiation of better quality, it would be desirable to have shielded low-pass cables having a significantly lower cutoff presence, for example at most equal to a few tens of MHz.

It goes without saying that this cut-off frequency must be adapted to the maximum frequency of the electrical signals which must pass through the cable. In any case, it is desirable to have cables having their own shielding or not, whose cutoff frequency is very substantially less than 100 MHz, cutoff frequency which is obtained with low-pass cables of the state of the technical.

An object of the present invention is to provide a low-pass cable whose cut-off frequency, that is to say the frequency corresponding to an attenuation of 4.3 dB per meter is substantially less than 100 MHz, typically lower or equal to 20 MHz. Another object of the invention is to provide a cable of this type in which the transfer impedance Zt of the cable does not increase strongly with the frequency of external parasitic signals to ensure effective protection against electromagnetic interference. Finally, it is very desirable that the cable retains its magnetic absorption properties in a temperature range corresponding to its current use, that is to say typically up to 260 ° C.

To achieve these two objects according to the invention, the low-pass shielded cable is characterized in that it successively comprises from its center towards its periphery

- a conductive core;

- a first dielectric layer;

- a magnetic absorption layer of an amorphous ferromagnetic metal alloy; and

- an insulating sheath.

Preferably, said ferromagnetic alloy has the following composition: 8o + ιo% B ₂ o + ιo%

A representing the total percentage expressed in atoms of the ferromagnetic elements of the alloy chosen from the group comprising Co, Fe, Mn and Ni; and

B representing the total percentage expressed in atoms of the metalloid elements of the alloy chosen from the group comprising B, Si and P. The compound is of the amorphous type.

As a variant, said ferromagnetic alloy has the following composition:

- A represents the ferromagnetic elements Co, Fe, Mn and Ni entering into the composition either alone or in several in combined form;

- B represents the metalloid elements B, Si and P entering into the composition either alone, or in several in combined form; and - C representing the total percentage expressed in atoms of a metallic element chosen from the group comprising Cu and Nb or of the mixture of the two.

Thanks to the presence of the magnetic absorption layer made of an amorphous or nano-crystalline ferromagnetic metal alloy preferably having the composition indicated above, one effectively obtains, simultaneously, a lowering of the cut-off frequency to a lower value or equal to 20 MHz for an attenuation of 4.3 dB / m and a decrease in the increase in the transfer impedance for high frequencies.

The present invention also relates to a method of manufacturing a low-pass cable which makes it possible to obtain, under attractive economic conditions, a low-pass shielded cable having the characteristics set out above. The magnetic absorption layer can be produced either from micro-wires of the amorphous or nano-crystalline material, or from ribbons of this material.

Other characteristics and advantages of the invention will appear better on reading the following description of several embodiments of the invention given by way of non-limiting example. The description refers to the appended figures in which: FIG. 1 is a partially cut away perspective view of a low-pass cable; Figure 2 is a cross-sectional view of the cable of Figure 1; FIG. 3 represents curves which show the attenuation of the cable corresponding to example 1 as a function of the frequency; Figure 4 is a similar view for the cable of Example 2; FIG. 5 shows curves giving the variations in transfer impedance as a function of the frequency for the four examples of cables corresponding to example 6; FIGS. 6A to 6D show curves representing the shielding efficiency as a function of the frequency for the four cables defined in Example 6; FIG. 7 shows the attenuation curve (A) of the cable corresponding to the examples in Table II as a function of the frequency (F); and FIG. 8 shows the variation of the imaginary part of the permeability of the absorbent material as a function of the frequency.

Referring first to Figures 1 and 2, we will describe the general structure of the cable. The cable consists first of all of a conductive core 10 which can of course be made up of several conductive strands, for example of silver copper. This conductive core can range from AWG08 to AWG26. Around the conductive core 10, there is a first layer of dielectric material 12. On the first dielectric layer 12 is produced according to an essential characteristic of the invention a layer 14 of magnetic absorption. There is then a second layer 16 of dielectric material then a metal braid of shielding 18 of standard type and finally an external insulating sheath 20. In FIG. 2, the external diameters of these different layers have been identified from D1 to D6.

It should now be mentioned that according to certain embodiments, the cable may not include the second dielectric layer 16 interposed between the magnetic absorption layer 14 and the shielding braid 18.

Alternatively, the cable may also not have its own shielding layer. In this case, most often, it is a bundle of these cables which will include a shielding, that is to say shielding means common to the entire bundle of cables.

Alternatively, the conductive core 10 could consist of several conductive elements, each conductive element being surrounded by its own insulation of dielectric material. These conductive elements are preferably twisted. The first layer of dielectric material 12 is then, in this case, formed by the different insulations. The magnetic absorption layer is produced around the assembly formed by the various insulated conductive elements.

According to an essential characteristic of the invention, the magnetic absorbent layer is made of a ferromagnetic metal alloy of the amorphous or nano-crystalline type. This characteristic allows, as has already been explained briefly and as will be demonstrated by reference to the appended curves, to obtain a very significant reduction in the cut-off frequency corresponding to the attenuation of 4.3 dB / m, which therefore makes it possible to obtain transmission of the useful signal under very improved conditions since this results in filtering of the non-useful frequencies induced or radiated, as well as a significant improvement in the transfer impedance.

Preferably, the ferromagnetic material of the amorphous type has the following composition:

and the nano-crystalline ferromagnetic material has the following composition:

A _7% ιo 5 + B ₂ O +% C5 ιo _{± _3/0}

In these formulas:

- B represents the metalloid elements B, Si and P entering into the composition either alone, or in several in combined form;

- C represents the metallic elements Cu and Nb used in the composition either alone or in several in combined form. - The percentage is in atom and nominal.

- The percentage tolerance represents the range in which the electromagnetic characteristics for the low-pass cable application are satisfactory.

In fact, the constituent of type A determines the intrinsic ferromagnetic properties of the materials, while that of type B makes it possible to obtain, during the solidification of the alloy, the amorphous state that, only, constituent A cannot obtain. As for that of type C, it serves as a buffer between crystallization and amorphous solidification, and makes it possible to create a so-called nano-crystalline state in which the ferromagnetic characteristics are just as interesting as in the amorphous state. Special alloys have been developed to test their effectiveness as a magnetic absorption layer. Table I below provides several alloy compositions with their amorphous or nanocrystalline state.

TABLE I

According to a first embodiment, the absorption layer is preferably obtained by covering micro-wires made with the amorphous or nano-crystalline metal alloy, having a diameter between 9 microns and 22 microns and preferably covered individually of glass. The layer thus obtained preferably has a thickness of between 50 and 150 microns. We will now describe several exemplary embodiments of the low-pass cable according to the first embodiment.

Example 1

A first cable was made according to the characteristics defined in the table below. For the realization of the magnetic absorption layer, a bundle of 32 micro-wires made with an alloy having the composition of line XII of table I is used. This magnetic absorption layer is obtained by wrapping a bead constituted by the bundle of 32 micro-wires. A substantially contiguous layer of micro-wires is obtained. The covering pitch is 1 mm. The cable attenuation measurement shown in Figure 3 shows that for an attenuation of 4.3 dB / m the cutoff frequency is 20 MHz, which is much lower than the cutoff frequency of 100 MHz in the state of technique.

More generally, the bundle comprises 30 to 35 micro-wires and the guide pitch is between 0.25 mm and 1.1 mm.

Example 2 Another cable was made by adopting the same manufacturing techniques as in Example 1 and the same structure for the cable. The difference lies in the fact that the covering pitch of the micro-wires made of ferromagnetic amorphous metallic material is 0.3 mm instead of 1 mm. As shown in Figure 4, the cable has a cutoff frequency which is further lowered for attenuation by 4.3 dB / m since this frequency is of the order of 3 MHz.

Example 3 A third cable was produced which differs from the previous examples only in that the diameter D3 of the absorption layer is 1.10 mm to 1 mm, that is to say that the microphones -wires have a diameter of the order of 20 microns. The other parameters are unchanged. The attenuation measurement of this cable shows that the cut-off frequency at 4.3 dB / m is pushed back below 1 MHz. Example 4 Another cable was made according to the specifications indicated in the table below. It can be seen that in this case, there is effectively the presence of the second dielectric layer 16 between the absorbent layer 14 and the shielding braid 18. The results are similar to those obtained in the case of Example 2.

Example 5

Another cable similar to that of Example 4 was produced, except as regards the dielectric material used to produce the two dielectric layers and the outer sheath. The FEP is replaced by a composite PTFE / polyimide / PTFE film or a composite polyimide / PTFE film. The results of the attenuation measurement show performances in terms of attenuation and cutoff frequency similar to those of Example 2.

Example 6 In the following example, 4 cables numbered 1, 2, 3 and 4 were respectively produced to show the efficiency in terms of improving the transfer impedance of the cables according to the invention compared to the cable of the state of the art The table below shows the composition of cables 1, 2, 3 and 4

The difference between cables 3 and 4 lies in the chemical composition of the micro-wires used, the first corresponding to alloy XII of table 1 and the second to alloy XIII of this same table

Cable 1 does not have a magnetic absorption layer, cable 2 has a ferrite magnetic absorption layer according to the prior art, cable 3 has an absorption layer according to the invention, the alloy ferromagnetic amorphous metal conforms to the composition given in Example XIII of Table I

FIG. 5 shows that a very significant improvement in the transfer impedance is obtained for cables 3 and 4, that is to say for cables according to the invention. These measurements were carried out according to the tπaxial method.

In addition, FIGS. 6A to 6D show the shielding efficiency A expressed in dB / m as a function of the frequency F expressed in MHz for cables 1 to 4 in a high frequency range from 500 MHz to 2 GHz. Figures 6A and 6B on the one hand and 6C and 6D on the other hand shows that at these high frequencies, the shielding efficiency cables 3 and 4 according to the invention is much higher (from 10 to 20 dB / m) than that obtained with cables 1 and 2 according to the state of the art.

These measurements were carried out using the reverberation chamber technique in accordance with Standard Mil-STD 1344

Example 7

A cable is produced according to the same characteristics as those of Example 4 but with a conductive core of the AWG26 type. The other construction parameters being identical. Similar performances are obtained in the case of the preceding examples. It would be the same if the conductive core was of type AWG08.

In examples 1 to 7, the cable has its own shielding. As already explained, the cable may not have a shielding braid.

According to a second embodiment, the magnetic absorption layer is produced from one or more ribbons constituted by an amorphous or nano-crystalline ferromagnetic material, of which different compositions have been given previously. The ribbon can be manufactured by the rapid solidification technique by spinning (in English Melt Spinning) or by the rapid solidification technique by planar flow (in English Planar Flow Casting).

These techniques consist in projecting, through a very thin nozzle, the alloy in liquid form on a wheel rotating at a speed of the order of 2,500 revolutions per minute. The liquid alloy spreads around the periphery of the wheel. When solidifying, the alloy forms a ribbon which can have a very small thickness.

Ribbons were produced from alloys I to XI of table I. Table II below gives, for each alloy, an embodiment of the ribbon, specifying its dimensions and its method of production. TABLE II

These ribbons were then integrated into the cables according to the invention, with a pitch ranging from 0.1 to 1.5 mm, by the technique known as taping commonly used in the cable industry.

The taping can be carried out using a single tape, the turns overlapping each other, or successively using two tapes with contiguous turns, the spirals of the two layers being inverted From the tapes defined by Table II shielded cables were produced in accordance with the invention.

The conductive core is produced by concentric stranding or roplay stranding from copper wires coated with Ag, Sn or Ni with AwG 8 to 26 gauges. The dielectric layer or layers are made of extruded fluoroplastics, of polyolefin. or PVC by extrusion or in polyimide film by taping.

The magnetic absorption layer is produced, as already indicated, by taping using the tapes defined in Table II. Preferably, the magnetic absorption layer is produced with at least one strip of the ferromagnetic alloy whose width is between 0.3 and 4.0 mm and whose thickness is between 2 and 100 microns.

In addition, the measurements made on the cables show that the attenuation increases as a function of the thickness of the layer of absorbent material. This is shown in the following table:

Thus, it is possible, by varying the number of ribbons and / or the thickness of the ribbons, to adapt the absorption effect to the conditions of use of the cable. The same applies when the absorbent layer is produced with micro-threads.

The shielding, if it exists, is carried out, using a copper wire coated with Ag, Sn or Ni, by braiding or wrapping. Finally, the outer sheath can be made of fluorinated thermoplastics, thermoplastic elastomer or PVC by extrusion or even in polyimide film by taping.

The high frequency filtering and transfer impedance measurements carried out on the cables described above and using an amorphous or nanocrystalline ribbon gave results similar to those obtained for cables made from microfilms.

Figure 7 shows the attenuation of cable A expressed in dB / m as a function of frequency F expressed in MHz. Curve I corresponds to the cables of the prior art and curve II corresponds to the cables of Table II. Various measurements have been made, in particular for the examples of composition of ferromagnetic alloy VI, VII and XIV of Table I above.

These measurements show that, for alloy VI, the Curie temperature is equal to 350 ° C. and the crystallization temperature is 510 ° C. For alloy VII, these temperatures are respectively 320 ° C and 500 ° C and for alloy XIV, they are respectively 300 ° C and 490 ° C.

For the other alloys, these measurements are of the same order. It can therefore be seen that these temperatures are much higher than the normal temperatures for using the cable which do not practically exceed 260 ° C.

In FIG. 8, the value of the imaginary part of the permeability (μ ") as a function of the frequency F expressed in MHz has been represented for different alloys. The curves A, B and C correspond respectively to the alloys VI, VII and These curves show that the imaginary part of the permeability, which best represents the magnetic absorption effect, has a very marked maximum around a frequency equal to 10 MHz.

Claims

1. Low-pass cable having a cut-off frequency, corresponding to an attenuation of 4.3 dB / m, less than 10 MHz, characterized in that it successively comprises from its center towards its periphery

- a conductive core (10),

- a first dielectric layer (12),

- a magnetic absorption layer of a ferromagnetic metal alloy with an amorphous or nano-crystalline structure (14); and

- an insulating sheath (20).

2. Cable according to claim 1, characterized in that it further comprises a shielding layer (18) produced on the absorption layer.

3. Cable according to claim 2, characterized in that it further comprises a second dielectric layer (16) interposed between the absorbent layer (14) and the shield (18).

4. Cable according to any one of claims 1 to 3, characterized in that said ferromagnetic alloy has the following composition:

A8o + ιo% B ₂ o + ιo%

B representing the total percentage expressed in atoms of the metalloid elements of the alloy chosen from the group comprising B, Si and P.

5. Cable according to any one of claims 1 to 3, characterized in that said ferromagnetic alloy has the following composition:

A ₇ 5+ 10% B ₂ 0 + 10% C5 _{± 3} o / ₀

- A represents the ferromagnetic elements Co, Fe, Mn and Ni entering into the composition either alone or in several in combined form; - B represents the metalloid elements B, Si and P entering into the composition either alone, or in several in combined form; and

- C representing the total percentage expressed in atoms of a metallic element chosen from the group comprising Cu and Nb or of the mixture of the two.

6. Cable according to any one of claims 1 to 5, characterized in that said magnetic absorption layer consists of wires of said ferromagnetic alloy with a diameter between 9 and 22 micrometers.

7. Cable according to claim 6, characterized in that each wire is coated with a layer of glass.

8. Cable according to any one of claims 6 and 7, characterized in that said absorbent layer is formed by covering with a bundle which comprises 30 to 35 of said wires at a pitch between 0.25 mm and 1.1 mm.

9. Cable according to any one of claims 1 to 5, characterized in that said magnetic absorption layer consists of at least one strip of said ferromagnetic alloy whose width is between 0.3 and 4.00 mm and of which the thickness is between 2 and 100 microns.

10. Cable according to any one of claims 1 to 9 characterized in that the said dielectric layer or layers are made of FEP or PTFE.

11. Cable according to any one of claims 1 to 10, characterized in that the conductive core (10) is constituted by a plurality of conductive elements and in that the first dielectric layer (12) is constituted by a plurality of insulating coatings, each coating covering one of said conductive elements.

12. Cable according to any one of claims 1 to 11, characterized in that its operating temperature is at most equal to

260 ° C.

13. A method of manufacturing a low-pass cable according to any one of claims 1 to 4, characterized in that it comprises the following steps: a) a first layer of dielectric material is produced by extrusion or tape a conductive core; b) a magnetic absorption layer is formed on said dielectric material by covering with a bundle of a plurality of micro-wires made of a ferromagnetic amorphous metallic material; and c) an external insulating sheath is produced by extrusion.

14. Method according to claim 13, characterized in that between steps c) and d), an shielding layer is produced by braiding.

15. Method according to any one of claims 13 and

14, characterized in that between steps c) and d) a second layer of dielectric material is produced by extrusion or tape on said layer of absorbent material.

16. Method according to any one of claims 13 to

15, characterized in that the covering with the aid of the bundle of micro-wires is produced in such a way that the micro-wires are substantially contiguous.

17. A method of manufacturing a low-pass shielded cable according to any one of claims 1 to 4, characterized in that it comprises the following steps: a) a first layer of dielectric material is produced by extrusion or tape on a conductive core; b) a magnetic absorption layer is formed on said dielectric material by tape using at least one tape made of a ferromagnetic alloy; and c) an external insulating sheath is produced by extrusion.

18. The method of claim 17, characterized in that between steps c) and d) a second layer of dielectric material is produced by said extrusion or tape on said layer of absorbent material.

19. The method of claim 18, characterized in that between steps c) and d), a shielding layer is produced by braiding.