EP1177562B1 - Use of a cable as low pass cable - Google Patents

Description

The present invention relates to a use of a cable for producing a low-pass cable.

an electric transmission cable is intended to convey signals within an electrical or electronic system or between two such systems 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 to propagate signals whose frequency is below a certain limit called cable cut-off frequency.

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

Low-pass shielded cables are already known in which, in addition to the usual metal braid shielding, an intermediate magnetic absorption layer is formed which, in these known cables, is made of ferrite. Such low-pass cables have a cut-off frequency of the order of 100 MHz in the sense mentioned above. Such a cutoff frequency is considered permissible for a number of applications. However, when it is desired to have a useful transmission of the signal without it being affected by disturbances conducted by the cable or resulting from external radiation of better quality, it would be desirable to have low-pass shielded cables having a substantially 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 that must pass through the cable.

In any case it is desirable to have cables with their own shielding or not, whose cutoff frequency is very substantially less than 100 MHz, cutoff frequency that is obtained with the low-pass cables of the state of the technical.

An object of the present invention is to provide a low-pass cable whose cutoff frequency, i.e. the frequency corresponding to an attenuation of 4.3 dB per meter is substantially less than 100 MHz, typically less than or equal to equal to 20 MHz.

Another object of the invention is to provide a cable of this type in which the cable transfer impedance Zt does not strongly increase with the frequency of external interfering signals to provide effective protection against electromagnetic interference.

Finally, it is highly desirable that the cable retain its magnetic absorption properties in a temperature range corresponding to its current use, i.e., typically up to 260 ° C.

• une âme conductrice ;
• une première couche diélectrique ;
• une couche d'absorption magnétique en un alliage métallique amorphe ferromagnétique ; et
• une gaine isolante.

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

• a conductive soul;
• a first dielectric layer;
• a magnetic absorption layer of a ferromagnetic amorphous metal alloy; and
• an insulating sheath.

• A_80±10% B_20±10%

A représentant le pourcentage total exprimé en atomes des éléments ferromagnétiques de l'alliage choisis dans le groupe comprenant Co, Fe, Mn et Ni ; et
B représentant le pourcentage total exprimé en atomes des éléments métalloïdes de l'alliage choisis dans le groupe comprenant B, Si et P. Le composé est du type amorphe.Preferably, said ferromagnetic alloy has the following composition:

• At _{80 ± 10%} B _{20 ± 10%}

Where A is the total atomic percentage of the ferromagnetic elements of the alloy selected from the group consisting of Co, Fe, Mn and Ni; and
B represents the total percentage expressed as atoms of the metalloid elements of the alloy selected from the group consisting of B, Si and P. The compound is of the amorphous type.

• A_{75±10 %} B_20±10% C_5±3%

• A représente les éléments ferromagnétiques Co, Fe, Mn et Ni entrant dans la composition soit seul, soit à plusieurs sous forme combinée ;
• B représente les éléments métalloïdes B, Si et P entrant dans la composition soit seul, soit à plusieurs sous forme combinée ; et
• C représentant le pourcentage total exprimé en atomes d'un élément métallique choisi dans le groupe comprenant le Cu et le Nb ou du mélange des deux.

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

• At _{75 ± 10%} B _{20 ± 10%} C _{5 ± 3%}

• A represents the ferromagnetic elements Co, Fe, Mn and Ni entering the composition either alone or in several combined form;
• B represents the metalloid elements B, Si and P used in the composition either alone or in several combined form; and
• C represents the total percentage expressed as atoms of a metal element selected from the group consisting of Cu and Nb or a mixture of both.

Thanks to the presence of the magnetic absorption layer made of a ferromagnetic amorphous or nano-crystalline metallic alloy preferably having the composition indicated above, the reduction frequency is effectively lowered at a lower value or at the same time. equal to 20 MHz for attenuation of 4.3dB / m and a decrease in the transfer impedance increase for high frequencies.

• la figure 1 est une vue en perspective partiellement arrachée d'un câble passe-bas ;
• la figure 2 est une vue en coupe transversale du câble de la figure 1 ;
• la figure 3 représente des courbes qui montrent l'atténuation du câble correspondant à l'exemple 1 en fonction de la fréquence ;
• la figure 4 est une vue similaire pour le câble de l'exemple 2 ;
• la figure 5 montre des courbes donnant les variations d'impédance de transfert en fonction de la fréquence pour les quatre exemples de câbles correspondant à l'exemple 6 ;
• les figures 6A à 6D montrent des courbes représentant l'efficacité de blindage en fonction de la fréquence pour les quatre câbles définis dans l'exemple 6 ;
• la figure 7 montre la courbe d'atténuation (A) du câble correspondant aux exemples du tableau II en fonction de la fréquence (F) ; et
• la figure 8 montre la variation de la partie imaginaire de la perméabilité du matériau absorbant en fonction de la fréquence.

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:

• Figure 1 is a partially cutaway 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 transfer impedance variations as a function of frequency for the four cable examples corresponding to example 6;
• Figs. 6A-6D show curves showing the shielding efficiency as a function of frequency for the four cables defined in Example 6;
• Figure 7 shows the attenuation curve (A) of the cable corresponding to the examples in Table II as a function of the frequency (F); and
• Figure 8 shows the variation of the imaginary part of the permeability of the absorbent material as a function of frequency.

Referring first to Figures 1 and 2, the general structure of the cable will be described. The cable is constituted first of a conductive core 10 which can be constituted of course by several conductive strands for example silver-plated copper. This conductive core can be 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 formed according to an essential feature of the invention a magnetic absorption layer 14. A second layer 16 of dielectric material is then found, followed by a standard shielding metal braid 18 and finally an insulating outer sheath 20. In FIG. 2, the external diameters of these different layers have been labeled from D1 to D6.

It should now be mentioned that according to some 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 that will include an overblanking, that is to say, shielding means common to the entire cable bundle.

Alternatively, the conductive core 10 could be constituted by a plurality of 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, constituted by the different insulations. The magnetic absorption layer is formed around the assembly constituted by the various isolated 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 already explained briefly and as will be demonstrated by reference to the attached curves to obtain a very significant reduction in the cutoff frequency corresponding to the attenuation of 4.3 dB / m, which makes it possible to obtain a transmission of the useful signal under greatly improved conditions since thus obtaining a filtering of the non-useful induced or radiated frequencies, as well as a significant improvement in the transfer impedance.

• A_80±10% B_20±10%

et le matériau ferromagnétique nano-cristallin a la composition suivante :

• A_75±10% B_20±10% C_5±3%

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

• At _{80 ± 10%} B _{20 ± 10%}

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

• At _{75 ± 10%} B _{20 ± 10%} C _{5 ± 3%}

• A représente les éléments ferromagnétiques Co, Fe, Mn et Ni entrant dans la composition soit seul, soit à plusieurs sous forme combinée ;
• B représente les éléments métalloïdes B, Si et P entrant dans la composition soit seul, soit à plusieurs sous forme combinée ;
• C représente les éléments métalliques Cu et Nb entrant dans la composition soit seul, soit à plusieurs sous forme combinée.
• Le pourcentage est en atome et nominal.
• La tolérance en pourcentage représente la plage dans laquelle les caractéristiques électromagnétiques pour l'application câble passe-bas sont satisfaisantes.

In these formulas:

• A represents the ferromagnetic elements Co, Fe, Mn and Ni entering the composition either alone or in several combined form;
• B represents the metalloid elements B, Si and P used in the composition either alone or in several combined form;
• C represents the Cu and Nb metal elements entering the composition either alone or in several combined form.
• The percentage is atomic and nominal.
• The percent tolerance represents the range in which the electromagnetic characteristics for the low-pass cable application are satisfactory.

In fact, the component of type A determines the intrinsic ferromagnetic properties of the materials, while that of the type B makes it possible to obtain during the solidification of the alloy the amorphous state that only component A can not obtain. As for the type C, it serves as a buffer between crystallization and amorphous solidification, and allows 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 nano-crystalline state. TABLE I Alloy Composition State of the alloy I Fe ₈₀ B ₂₀ Amorphous II Fe ₇₇ Si ₈ B ₁₅ Amorphous III Fe ₆₅ CO ₁₀ Si ₁₀ B ₁₅ Amorphous IV Fe ₆₅ Mn ₁₀ Si ₁₀ B ₁₅ Amorphous V CO ₈₀ Si ₁₀ B ₁₀ Amorphous VI CO ₆₉ Fe ₅ Si ₁₂ B ₁₅ Amorphous VII CO ₆₉ Mn ₆ Si ₁₅ B ₁₀ Amorphous VIII CO ₆₉ Mn ₅ Fe ₁ Si ₁₃ B ₁₂ Amorphous IX Ni ₆₀ Fe ₂₀ P ₂₀ Amorphous X CO ₇₁ Fe ₄ Nb ₄ Si ₁₅ B ₆ Amorphous + nano-crystalline XI Fe ₇₄ Cu ₁ Nb ₃ Si ₁₃ B ₉ Amorphous + nano-crystalline XII Fe _0.8 Mn _5.6 Ni _0.2 B _6.5 Si ₁₄ Co _72.6 Amorphous XIII Fe _0.8 Mn ₆ Ni _0.1 B _5.7 Si _13.9 Co _79.5 Amorphous XIV Co ₆₈ Fe ₄ Si ₁₂ B ₁₅ Mn ₁ Amorphous

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 of 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.

Several embodiments of the low-pass cable according to the first embodiment will now be described.

Example 1

A first cable was made according to the characteristics defined in the table below. For the production of the magnetic absorption layer, a beam of 32 micro-wires made of an alloy having the composition of line XII of Table 1 is used. This magnetic absorption layer is obtained by wrapping a cord constituted by the beam of 32 micro-son. A substantially adjacent micro-son layer is obtained. The covering pitch is 1 mm. The attenuation measurement of the cable 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 100 MHz cutoff frequency of the state. of the technique. Component Materials Implementation Driver D1 = 0.76 mm Silver plated AWG22 Dielectric D2 = 0.88 mm EFF Extrusion Absorption layer D3 = 1.00 mm Beam 32 micro-son wrapping Braid shield D5 = 1.55 mm Silver plated ∅ = 0.102 mm Braiding Sheath D6 = 2.00 mm EFF Extrusion

More generally, the beam 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 wrapping pitch of the ferromagnetic amorphous metallic material micro-wires 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 of 4.3 dB / m since this frequency is of the order of 3 MHz.

Example 3

A third cable was made which differs from the preceding examples only in that the diameter D 3 of the absorption layer is 1.10 mm instead of 1 mm, that is to say that the micro-wires have a diameter of the order of 20 microns. The other parameters are unchanged. The attenuation measurement of this cable shows that the cutoff 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, the presence of the second dielectric layer 16 between the absorbent layer 14 and the shielding braid 18 is indeed present. The results are similar to those obtained in the case of Example 2. Component Materials Implementation Driver D1 = 0.76 mm Silver plated AWG22 Dielectric D2 = 0.88 mm EFF Extrusion Absorption layer D3 = 1.00 mm Beam 32 micro-son wrapping Dielectric D4 = 1.37 mm EFF Extrusion Braid shield D5 = 1.82 mm Silver Cu ∅ = 0.102 mm Braiding Sheath D6 = 2.30 mm EFF Extrusion

Example 5

Another cable similar to that of Example 4 was made except for the dielectric material used to make the two dielectric layers and the outer sheath. The FEP is replaced by a PTFE / polyimide / PTFE composite film or a polyimide / PTFE composite film. The results of the attenuation measurement show performance in terms of attenuation and cutoff frequency similar to those of Example 2. Component Materials Implementation Driver D1 = 0.76 mm Tinned Cu AWG22 Dielectric D2 = 0.88 mm Polyimide film / .PTFE Wrapping Absorption layer D3 = 1.10 mm Beam 32 micro-son wrapping Dielectric D4 = 1.35 mm Polyimide / PTFE film Wrapping Braid shield D5 = 1.80 mm Tinned Cu ∅ = 0.102 mm Braiding Sheath D6 = 2.30 mm Polyimide / PTFE film Wrapping

Example 6

In the following example, 4 cables numbered 1, 2, 3 and 4 were respectively made to show the efficiency in terms of improving the transfer impedance of the cables according to the invention with respect to the cable of the state. of the technique. The table below shows the composition of cables 1, 2, 3 and 4. Component Materials Cable 1 Cable 2 Cable 3 Cable 4 Driver D1 = 0.76 mm Silver plated AWG22 Dielectric D2 = 0.88 mm EFF Absorption layer D3 = 1.00 mm EFF ferrite micro-son 1 micro-son 2 Dielectric D4 = 1.37mm EFF Braid shield D5 = 1.82mm Silver Cu wire 0.102 mm 16x3 Sheath D6 = 2.30 mm EFF

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

The cable 1 does not include a magnetic absorption layer, the cable 2 comprises a ferrite magnetic absorption layer according to the state of the art, the cable 3 comprises an absorption layer according to the invention, the alloy ferromagnetic amorphous metal is in accordance with the composition given in Example XIII of Table I.

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

In addition, FIGS. 6A-6D show the shielding efficiency A expressed in dB / m as a function of the frequency F expressed in MHz for the cables 1 to 4 in a high frequency range of 500 MHz to 2 GHz. The comparison of FIGS. 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 (10 to 20 dB / m) than that obtained with the cables 1 and 2 according to the state of the art.

These measurements were made using the reverberation chamber technique in accordance with Mil-STD 1344

Example 7

A cable is made 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 the AWG08 type.

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

According to a second embodiment, the magnetic absorption layer is made from one or more ribbons constituted by an amorphous or nano-crystalline ferromagnetic material of which different compositions have been given previously.

The ribbon may be manufactured by the Spinning Fast Spinning technique or the Planar Flow Casting (Planar Flow Casting) technique.

These techniques consist in projecting, through a nozzle of very small thickness, the alloy in liquid form on a wheel rotating at a speed of the order of 2500 rpm. The liquid alloy spreads around the periphery of the wheel. By solidifying, the alloy forms a ribbon that can be very thin.

Ribbons were manufactured from alloys I to XI of Table I. Table II below gives, for each alloy, an embodiment of the ribbon by specifying its dimensions and method of preparation. TABLE II Alloy Ribbon size State Technical Elaboration Thickness μm Width mm I 4.0 0.3 Amorphous Melt Spinning II 6.0 0.5 Amorphous Melt Spinning III 10.5 1.2 Amorphous Planar flow Casting IV 14.5 2.0 Amorphous Planar flow Casting V 15.0 3.0 Amorphous Planar flow Casting VI 5.0 3.6 Amorphous Planar flow Casting VII 25.5 1.0 Amorphous Planar flow Casting VIII 12.0 3.5 Amorphous Planar flow Casting IX 30.5 0.8 Amorphous Planar flow Casting X 10.0 1.0 Amorphous + nano-cristaliin Planar flow Casting XI 12.5 0.8 Amorphous + nano-crystalline Planar flow Casting

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 called tape-cutting commonly used in the cable industry.

The tape can be made using a single tape, the turns overlapping each other, or successively with two ribbons with contiguous turns, spiralages of the two layers being reversed

From the ribbons defined by Table II, shielded cables according to the invention were made.

The conductive core is made by concentric stranding or roplay stranding from copper wires coated with Ag, Sn or Ni gauges AwG 8 to 26.

The dielectric layer or layers are made of fluorinated thermoplastics by extrusion, polyolefin or PVC by extrusion or polyimide film by taping.

The magnetic absorption layer is made, as already indicated, by taping using the ribbons defined in Table II.

Preferably the magnetic absorption layer is made with at least one ribbon 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: Cable I including a 23 μm thick ribbon Cable II including 2 strips of thickness 23 μm superimposed Frequency (MHz) Attenuation (dB / m) Attenuation (dB / m) 10 6.38 11.8 50 15.9 26.6 100 24.8 41.3 150 32.4 53.2 200 39.2 68.1

Thus, it is possible, by varying the number of ribbons and / or the thickness of the ribbon (s), to adapt the absorption effect to the conditions of use of the cable. It is the same when the absorbent layer is made with micro-son.

The shield, if it exists, is made, by means of 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 polyimide film by taping.

The high frequency filtering and transfer impedance measurements made on the previously described cables using amorphous or nanocrystalline ribbon gave results similar to those obtained for cables made from microfilts.

Figure 7 shows the attenuation of the cable A expressed in dB / m as a function of the frequency F expressed in MHz. Curve 1 corresponds to the cables of the state of the art and curve II corresponds to the cables of Table II.

Various measurements have been made, in particular for the examples of ferromagnetic alloy composition 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 be seen that these temperatures are much higher than the normal cable operating temperatures which do not exceed nearly 260 ° C.

FIG. 8 shows, for different alloys, the value of the imaginary part of the permeability (μ ") as a function of the frequency F expressed in MHz.The curves A, B and C respectively correspond 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 (12)

1. Use of a cable comprising in succession, from its centre to its periphery, a conducting core (10), a first dielectric layer (12), a magnetic absorption layer made of a ferromagnetic metal alloy with an amorphous or nanocrystalline structure (14) and an insulating sleeve (20) for producing a low-pass cable characterised in that said low-pass cable has a cut-off frequency, corresponding to an attenuation of 4.3 dB/m, lower than 20 MHz and usable up to a temperature of 260°C.
2. Use of a cable according to Claim 1, characterised in that it further comprises a shielding layer (18) produced over the absorption layer.
3. Use of a cable according to Claim 2, characterised in that it further comprises a second dielectric layer (16) placed between the absorbing layer (14) and the shielding (18).
4. Use of a cable according to any one of Claims 1 to 3, characterised in that said ferromagnetic alloy has the following composition:

   A_80±10% B_20±10%

   A representing the total percentage expressed as 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 as atoms of the metalloid elements of the alloy chosen from the group comprising B, Si and P.
5. Use of a cable according to any one of Claims 1 to 3, characterised in that said ferromagnetic alloy has the following composition:

   A_75±10% B_20±10% C_5±3%

   - A represents the ferromagnetic elements Co, Fe, Mn and Ni contained in the composition either alone, or as a plurality in a combined form;

   - B represents the metalloid elements B, Si and P contained in the composition either alone, or as a plurality in combined form; and

   - C representing the total percentage expressed as atoms of a metallic element chosen from the group comprising Cu and Nb or of the mixture of the two.
6. Use of a cable according to any one of Claims 1 to 5, characterised in that said magnetic absorption layer is constituted by wires of said ferromagnetic alloy with a diameter comprised between 9 and 22 micrometers.
7. Use of a cable according to Claim 6, characterised in that each wire is covered with a layer of glass.
8. Use of a cable according to any one of Claims 6 and 7, characterised in that said absorbent layer is constituted by wrapping with a bundle that comprises 30 to 35 of said wires at a pitch comprised between 0.25 mm and 1.1 mm.
9. Use of a cable according to any one of Claims 1 to 5, characterised in that said magnetic absorption layer is constituted by at least one ribbon of said ferromagnetic alloy, the width of which is comprised between 0.3 and 4.00 mm and the thickness of which is comprised between 2 and 100 microns.
10. Use of a cable according to any one of Claims 1 to 9 characterised in that said dielectric layer(s) are made of FEP or PTFE.
11. Use of a cable according to any one of Claims 1 to 10, characterised in that the conducting core (10) is constituted by a plurality of conducting elements and in that the first dielectric layer (12) is constituted by a plurality of insulating coatings, each coating covering one of said conducting elements.
12. Use of a cable according to any one of Claims 1 to 11, characterised in that its temperature of use is equal to no more than 260°C.

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