Coaxial cable
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-26
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026051857_13082026_PF_FP_ABST
Abstract
Description
[0001] P29151 PC00
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[0003] Coaxial Cable
[0004] FIELD OF THE DISCLOSURE
[0005] The present disclosure relates to a coaxial cable for cryogenic applications as well as to a method for producing such a coaxial cable.
[0006] BACKGROUND OF THE DISCLOSURE
[0007] In modern quantum computing setups, hundreds or even thousands of microwave lines are needed to control the qubits of a quantum processor in a cryogenic environment. Krinneret al. (EPJ Quantum Technology 2019, 6(2)) have provided a comprehensive study of the design principles for the wiring of such a cryogenic setup, in order to minimize active and passive heat loads and properly manage the heat budget. To minimize passive heat load within cryogenic setups, cable materials with low thermal conductivity are required. Except for superconductors, low thermal conductivity goes along with poor electrical conductivity.
[0008] Known types of coaxial cables for cryogenic applications include stainless steel cables and niobium titanium (NbTi) cables. In known quantum computing setups, stainless steel cables are used for the drive lines where large attenuation is needed. Niobium titanium cables are superconducting below 10 K and therefore have very low attenuation below 10 K, which is why they are used for output lines in the sections between the 4 K and mixing-chamber (MXC) stages. The heat flows associated with these two cable types are dominated by their outer conductor, which has a cross-sectional area that is by a factor of up to 10 times largerP29151 PC00
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[0010] than the cross-sectional area of the inner (center) conductor. An alternative to stainless steel cables are cupronickel (CuNi) cables. Their passive heat load is about 50% larger than the heat load of stainless steel cables.
[0011] SUMMARY OF THE DISCLOSURE
[0012] Various kinds of coaxial cables for multiple applications are known. Coaxial cables typically at least comprise an inner conductor, a circumferentially arranged outer conductor and a dielectric spacer arranged therebetween. A special kind of coaxial cables are so called semi-rigid coaxial cables, which are more a tube than a flexible cable. Semi-rigid coaxial cables typically comprise an inner conductor, which is in form of a solid wire as well as an outer conductor in form of a solid metal outer sheath. Semi-rigid coaxial cables offer superior screening compared to cables with a braided outer conductor, especially at higher frequencies as the outer shield has no voids as they cannot be avoided in a braided shield between the individual wires. The advantage of semi-rigid coaxial cables is that the radiation leakage and attenuation, especially at higher frequencies (in the GHz range), is lower than with conventional coaxial cables. Their use is nevertheless limited to applications where no mechanical mobility of the coaxial cable is necessary.
[0013] A special kind of semi-rigid coaxial cables are superconducting semi-rigid coaxial cables, which are for example used in a cryogenic environment of cryogenic quantum computers. In particular in read-out lines, to allow single photon detection of a superconducting qubit. These readout lines should provide perfect shielding against any electromagnetic interferer, while not disturbing or evenP29151 PC00
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[0015] attenuating the weak single photon signal. This requires superconducting inner-and outer conductors and an ultra-low loss dielectric.
[0016] Special cable designs for coaxial cables are required in cryogenic environments. A core objective is to avoid heat dissipation to keep noise low. A problem with known coaxial cables in quantum computing applications is passive heat load (sometimes called heat leak or parasitic heat load). Passive heat load is defined as energy transfer between temperature stages due to conduction, convection, and / or radiation. Passive heat load may occur through any heat-conductive path including air, insulation and electrical wiring. In applications where there is no active heat generation, the passive heat load will represent the entire heat load on the cooling system.. To minimize passive heat load, low heat conduction is desired, especially where a multitude of lines is needed. Currently, due to cost and procurement reasons, coaxial cables with stainless steel or copper-nickel conductors are often used. These cables have the advantage that they can transfer heat very poorly between different stages in a dilution refrigerator.
[0017] Today, superconducting semi-rigid cables typically comprise an inner (center) and / or outer conductor made from a superconducting material like niobium or niobium titanium alloys (NbTi). Niobium titanium alloys are superconducting at temperatures below about 8 K. Besides avoiding dissipation loss caused by resistivity, superconductivity has the advantage of low thermal conductivity, which is essential to reduce the passive heating between two temperature stages in a cryostat. Especially when hundreds, thousands or even more signal lines, needed to control the qubits, connect the temperature stages thermally.P29151 PC00
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[0019] Although niobium or niobium titanium alloys have favorable superconducting properties at temperatures below about 8K, these alloys are difficult to plastically deform. Forming can only be done sequentially with several small drawing steps with subsequent annealing after each step. This makes especially thin diameter capillary tubes, as required for thin diameter cables e.g. for quantum computers, expensive. Known coaxial cables for cryogenic applications are made by providing an inner conductor and a low loss dielectric material which is extruded around the inner conductor to form an insulating layer. Depending on the material, an evaporation and sintering step needs to be applied afterwards. The inner conductor with thereto extruded insulating layer is typically inserted into a metal tube with slightly larger inner diameter than the insulating layer. In the following drawing process, the metal tube is reduced in diameter, so that the inner diameter encompasses the insulating layer without clearance, thereby forming the outer conductor of the coaxial cable.
[0020] The problem with these methods is that after applying the insulating layer, which is typically made from a polymer material, annealing is not possible anymore as the polymer material would be harmed by the annealing temperature. The insulating layer would at least partially melt or even degrade. Therefore, drawing the diameter of the outer conductor is very limited. A known alternative method for making the outer conductor is to wrap a metal foil around the insulating layer and weld the seam, resulting in a welded tube. But also here the problem is that due to the insulating layer the heat input has to be limited, which limits the degree of freedom for the welding process.P29151 PC00
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[0022] An objective of the present disclosure can be seen in providing a coaxial cable for cryogenic applications, which overcomes the above-described disadvantages of the prior art.
[0023] A coaxial cable for cryogenic applications according to the present disclosure typically comprises an inner conductor having a first outer diameter, which forms a cable core and extends along a longitudinal direction, and an insulating layer, made from a dielectric material and encompassing the inner conductor along the longitudinal direction and having a second outer diameter. The inner conductor is preferably in form of a solid drawn wire. The coaxial cable typically further comprises an outer conductor, which encompasses the insulating layer along the longitudinal direction and preferably comprises a first conductive layer arranged circumferentially on an outer surface of the insulating layer, and a second conductive layer arranged circumferentially on an outer surface of the first conductive layer and having a third outer diameter. The first conductive layer is typically made of a material that is superconducting at temperatures below 8 K, in particular below 4 K, more particular below 1 K, most particular below 100 mK. The first conductive layer can be made from a material which is at room temperature electrically conductive or electrically non-conductive. The first conductive layer can have a critical temperature above 1 K, in particular above 4 K, more particular above 8 K, most particular above 35 K.
[0024] Operating such a design in superconducting mode allows to reduce the outer diameter of the coaxial cable not affecting dissipation loss, which allows for a reduction of the required space not only for the coaxial cable, but also for the pitch. The pitch is to be understood as the distance between adjacent coaxialP29151 PC00
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[0026] cables between individual or ganged connectors. The insulating layer is typically made from a low loss dielectric material for coaxial cables, typically chosen from the group consisting of non-polar polymers, like polyolefins, such as polyethylene and polypropylene. If higher temperature resistance is required, fluoropolymers like PTFE can be chosen, which provide low loss performance. Alternatively, ceramic materials can provide low loss radio frequency (RF) performance and temperature stability. The insulating layer may be extruded onto the outer surface of the inner conductor.
[0027] One advantage of applying the first conductive layer in form of a coating is that, other than the prior art, no solid niobium or niobium titanium tubes are necessary. A cable design according to the present disclosure allows for a faster and more cost-efficient cable production, as applying a coating is easier to fabricate compared to rolling or drawing a tube in several iterations with an annealing step after each forming step. The first conductive layer can be a multi-layered structure which comprises layers of different materials, with the goal to combine multiple material properties in a layer structure. For example, materials with varying thermal conductivity and electrical conductivity can be combined, and a good electrical and / or thermal contact to the second conductive layer can be achieved with a layer of corrosion resistant material. This can be e.g. beneficial to re-route the electrical path from the superconductive first layer to the conductive second layer in case of micro-cracks in the superconductive first layer.
[0028] Good results can be achieved when the thermal conductivity of the outer conductor comprising the first conductive layer and the second conductive layer is at 8 K below 20 W m-1K-1, particularly below 10 W-nr'-K’1, more particularly belowP29151 PC00
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[0030] 5 W nr' K’1, most particular below 2 W m-1K-1. A low thermal conductivity is favorable to reduce the passive heat load between two temperature stages in a cryostat. Especially when hundreds, thousands or even more signal lines, needed to control the qubits, connect the temperature stages thermally.
[0031] The first conductive layer may be made from a material selected from the group consisting of, preferably low temperature metallic superconductors, like for example niobium, titanium, tantalum, tin, aluminum, lead, yttrium, barium, vanadium, alloys thereof and copper oxide. Alternatively, a high temperature superconductor may be used. In this case the second conductive layer can provide electrical conductivity when operating at room-temperature during set-up, where the high temperature superconductor is an insulator. The advantage of using superconducting materials versus materials for conventional electrical conductors, like copper, silver or gold is that these materials, when operated below their critical temperature, have a low active heat generation because the electrical resistance in the superconducting state is almost zero and they possess a low thermal conductivity.
[0032] Especially niobium-titanium alloys have the advantage of a comparatively high critical temperature in the group of metallic superconductors. These alloys can be operated above critical temperature as well, but with higher losses. Furthermore, the superconductive state can be maintained, even in the presence of a high magnetic field (e.g. compared to pure niobium, the critical magnetic field strength can be improved by an order of magnitude).P29151 PC00
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[0034] The thickness of the first conductive layer can be chosen according to the so-called London penetration depth. When a superconductor is subjected to an alternating magnetic field or an alternating current (AC), the London penetration depth becomes relevant. The London penetration depth is a measure of how deeply a magnetic field can penetrate into a superconductor. The skin depth in superconductors is very small, leading to a rapid decrease in the magnetic field strength within the material. While superconductors can carry alternating currents without resistance, they still exhibit a form of skin effect characterized by a very shallow penetration of the magnetic field. Superconductors do show skin effects related to their unique electromagnetic properties, particularly influenced by the London penetration depth. For choosing the thickness of the coating, the London penetration depth should therefore be considered. Good results can be achieved when the first conductive layer has a thickness of which is at least as thick as the London penetration depth, in particular 2 times the London penetration depth, more particularly 5 times the London penetration depth.
[0035] The thickness of the first conductive layer is preferably between 25 nanometers and 5000 nanometers, in particular between 100 nanometers and 3000 nanometers, more particular between 150 nanometers and 1500 nanometers. In a superconducting state, good results can be achieved with a layer with a thickness of 100 nanometers to 3000 nanometers, to provide zero Ohm conductivity and perfect electrical shielding.
[0036] The first conductive layer may be applied by a physical vapor deposition (PVD) or a chemical vapor deposition (CVP) process. Good results can be achieved if the first conductive layer is applied via sputtering, also known as cathodeP29151 PC00
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[0038] sputtering, whereby atoms are released from a solid body by bombarding it with high-energy ions and transferred into the gas phase. Sputtering allows to apply the desired materials as a coating with a thickness in the nanometer range in an economical fashion. The first conductive layer is used directly as a functional (highly conductive) layer in the finished coaxial cable, not only as a contactable layer for galvanic build-up (auxiliary layer for manufacturing process).
[0039] Alternatively or in addition, the first conductive layer may be a coating arranged on the outer surface of the insulating layer or a coating on a substrate layer, which is arranged on the outer surface of the insulating layer. The substrate layer may be a foil or a polymer layer. The first conductive layer can also be a coating arranged on an inner surface of the second conductive layer. The first conductive layer may be applied, e.g. via sputtering to a substrate, e.g. a foil which is then applied to the insulating layer. The foil or polymer layer may be wrapped around the insulating layer and welded, either with or without overlapping. The foil or a polymer layer may be welded parallel to the longitudinal direction. For greater flexibility, a foil or a polymer layer may be applied which is wrapped around the insulation layer forming a spiral, preferably without welding or gluing. In case of a second conductive layer comprising a braiding, a plastic sheath may be applied to hold the braiding in place and establish contact with the first conductive layer.
[0040] The first conductive layer may be applied onto the insulating layer without an adhesion layer between them. Good results can be achieved if the first conductive layer is applied directly on the ultra-low loss dielectric without any adhesion layer (dielectric or metallic) to avoid dissipation introduced by this layer (dielectric loss or resistive). In addition, the coating process of the first conductive layer mayP29151 PC00
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[0042] include multiple steps allowing to build a multiple material stack, for example a precious metal layer above a superconductive metal layer providing a good and reliable electrical contact between the first conductive layer and the second conductive layer.
[0043] The second conductive layer may comprise a metal tube, which is applied via a metal drawing or rolling process. The second conductive layer can be made of stainless steel, which is of comparatively low cost and has a low heat conductivity. While silver or copper would possess desirable electrical conductivity, these materials are also good heat conductors, which is undesired for the given field of application. A massive niobium or niobium titanium tube would be desirable regarding electrical conductivity and low heat conductivity but has the disadvantages of high price and poor manufacturability, as stated above. To overcome this dilemma, the solution is to apply a first conductive layer in form of a highly conductive layer and a mechanically supporting second conductive layer, which gives mechanical integrity to the cable and protects the first conductive layer. This layer structure of the outer conductor leads to a separation into an electrical outer conductor (first conductive layer) and supporting outer conductor (second conductive layer).
[0044] The second conductive layer can protect the relatively thin first conductive layer and may bridge possible microcracks in the first conductive layer. These microcracks can potentially occur when the coaxial cable is bent. The second conductive layer therefore preferably provides a mechanical protection for the first conductive layer. Compared to known designs, a coaxial cable with a first conductive layer and a second conductive layer encompassing the first conductiveP29151 PC00
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[0046] layer is easier to manufacture and avoids multi-staged forming, annealing or welding steps. The second conductive layer enables dimensionally stable bending as known from known semirigid coaxial connectors. Alternatively, instead of a semirigid design, the coaxial cable may comprise a second conductive layer comprising a metal braid or a metal tape or metallized sheet, which is wound about the first conductive layer. Such a design increases the flexibility of the coaxial cable and may be used in applications where semirigid cables are too rigid. Additional dielectric jacket around the cable may be applied for protection of the cable.
[0047] The second conductive layer is preferably made of a material selected from the group consisting of copper, aluminum and steel and alloys thereof. The second conductive layer can be applied by a tube drawing process using the above described metals as commonly used in semirigid cables as they possess good forming properties. Stainless steel is often used in cryogenic applications due to the low thermal conductivity, but with the drawback of higher resistive losses. These resistive losses can be minimized with the proposed design, as the first conductive layer is the layer where the signal propagates. Further, this additional tube can bridge distortion by potential occurring micro-cracks in the first conductive layer, while theoretically introducing marginal resistive losses for the very short distance of the bridging micro crack.
[0048] The second conductive layer may allow to build a coaxial cable with high-temper-ature superconducting ceramic materials, where the second conductive layer provides a good performance above the critical temperature when the cryostat is setup under room temperature conditions allowing to check cable routing.P29151 PC00
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[0050] Good results can be achieved, when the second outer diameter of the insulating layer is between 2 times and 4 times, preferably between 2.5 times and 3.5 times, more preferably 3 times the first outer diameter (D1) of the inner conductor (2) and / or the third outer diameter (D3) of the second conductive layer (42) is between 3 times and 5 times, preferably between 3.5 times and 4.5 times, more preferably 4 times the first outer diameter (D1) of the inner conductor (2). Such a design is favorable regarding manufacturability, isolation between inner and outer conductor and offers favorable elastic properties for bending such a coaxial cable into shape.
[0051] The coaxial cable may comprise a cable jacket which is typically arranged circumferentially on an outer surface of the second conductive layer. Especially in a cryogenic environment the coefficient of thermal expansion (CTE) of the jacket material may apply contraction tension pressing the second conductive layer against the first metallic layer especially in case of non-rigid second layer like braid or wrapped metal tape.
[0052] The present disclosure further relates to a coaxial connector assembly which typically comprises a coaxial cable according to the present disclosure and a coaxial connector comprising an outer contact which is connected to the second conductive layer of the coaxial cable and an inner contact interconnected to the inner conductor of the coaxial cable. Multiple different connector types are commercially available which allow to terminate the coaxial cable keeping the void free screen (e.g. with soldered or crimped cable entries). The second conductive layer may ease the connection between the outer conductor and a connector. As for example niobium titanium is almost impossible to solder, before solderingP29151 PC00
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[0054] niobium titanium cable ends typically need to be galvanically coated with e.g. a copper layer. By using a second outer conductive layer, a connector can be more easily attached to the coaxial cable.
[0055] The present disclosure further relates to a method for producing a coaxial cable for cryogenic applications, comprising at least the following method steps:
[0056] • Producing an inner conductor by forming a cable core, in particular by drawing a wire along a longitudinal direction to a desired outer diameter of the inner conductor;
[0057] • Applying, e.g. by extrusion or tape wrapping, an insulating layer made from a dielectric material onto an outer surface of the inner conductor along the longitudinal direction;
[0058] • Applying a first conductive layer circumferentially on an outer surface of the insulating layer;
[0059] • Applying a second conductive layer circumferentially on an outer surface of the first conductive layer,
[0060] wherein the first conductive layer is made of a material that is superconducting at temperatures below 35 K, in particular below 8 K, more particular below 4 K, most particular below 1 K.
[0061] The thermal conductivity at cryogenic operation condition of the second conductive layer material is preferably below 20 W-nr'-K’1, particularly below 10P29151 PC00
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[0063] W m-1K-1, more particularly below 5 W m-1K-1, most particular below 2 W rrr1K"1. The first conductive layer can have a thickness between 25 nanometers and 5000 nanometers, preferably between 100 nanometers and 3000 nanometers.
[0064] The inner conductor is preferably massive, coated with a single-layer or coated by a multilayer coating. The first conductive layer may be applied by a physical vapor deposition (PVD) or chemical vapor deposition (CVP) process. The first conductive layer may be a single layer or multilayer arrangement. The first conductive layer can be a coating arranged on the outer surface of the insulating layer or a coating on a substrate layer which is arranged on the outer surface of the insulating layer. Alternatively or in addition, the first conductive layer can be a coating arranged on an inner surface of the second conductive layer. The first conductive layer may be applied onto the insulating layer without an adhesion layer between them.
[0065] The second conductive layer can comprise a metal tube which is applied via a metal drawing or rolling process. Alternatively, the second conductive layer can comprise a metal braid or a metallized sheet, which is wound about the first conductive layer.
[0066] It is to be understood that both the foregoing general description and the following detailed description present embodiments, are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrateP29151 PC00
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[0068] various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.
[0069] BRIEF DESCRIPTION OF THE DRAWINGS
[0070] The herein described disclosure will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be considered limiting to the disclosure described in the appended claims. The drawings are showing:
[0071] Fig. 1 shows a coaxial cable known from the prior art;
[0072] Fig. 2 shows a first embodiment of a coaxial cable according to the present disclosure;
[0073] Fig. 3 shows a second embodiment of a coaxial cable according to the present disclosure;
[0074] Fig. 4 shows a third embodiment of a coaxial cable according to the present disclosure;
[0075] Fig. 5 shows a fourth embodiment of a coaxial cable according to the present disclosure;
[0076] Fig. 6 shows a first embodiment of a coaxial cable assembly comprising a coaxial connector, according to the present disclosure;P29151 PC00
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[0078] Fig. 7 shows the application of the first conductive layer via sputtering;
[0079] Fig. 8 shows the application of the first conductive layer in form of a foil;
[0080] Fig. 9 shows the application of the second conductive layer in form of a foil;
[0081] Fig. 10 shows the application of the second conductive layer in form of a braid.
[0082] DESCRIPTION OF THE EMBODIMENTS
[0083] Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.
[0084] Examples
[0085] Coaxial cables according to the present disclosure can be realized according to the following examples:
[0086] Example 1 :
[0087] Outer Diameter inner conductor (D1 ): 0.2 mm
[0088] Material inner conductor: niobium-titanium
[0089] Outer diameter insulating layer (D2): 0.66 mmP29151 PC00
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[0091] Material insulating layer: perfluoroalkoxy alkanes (PFA)
[0092] Thickness first conductive layer (T1): 1000 nanometers
[0093] Material first conductive layer: niobium-titanium
[0094] Structure I manufacturing method first conductive layer: PVD sputtering Outer diameter second conductive layer (D3): 0.86 mm
[0095] Material second conductive layer: stainless steel
[0096] Structure / manufacturing method second conductive layer: drawn tube
[0097] Example 2:
[0098] Outer diameter inner conductor (D1 ): 0.227 mm
[0099] Material inner conductor: copper
[0100] Outer diameter insulating layer (D2): 0.72 mm
[0101] Material insulating layer: foamed polyethylene
[0102] Thickness first conductive layer (T1): 700 nanometers
[0103] Material first conductive layer: aluminum
[0104] Structure / manufacturing method first conductive layer: PVD (evaporation deposition)
[0105] Outer diameter second conductive layer (D3): 0.83 mm
[0106] Material second conductive layer: silver plated copper tape
[0107] Structure / manufacturing method second conductive layer: tape wrapping Outer diameter outer jacket (D4): 1.08 mm
[0108] Material outer jacket: FEP
[0109] Manufacturing method outer jacket: extrusion
[0110] Example 3:
[0111] Outer diameter inner conductor (D1 ): 0.2 mmP29151 PC00
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[0113] Material inner conductor: yttrium barium copper oxide (YBCO)
[0114] Outer diameter insulating layer (D2): 0.7 mm
[0115] Material insulating layer: fluorinated ethylene propylene (FEP)
[0116] Thickness first conductive layer (T1): 5000 nanometers
[0117] Material first conductive layer: yttrium barium copper oxide (YBCO) Structure / manufacturing method first conductive layer: CVD Sputtering Outer diameter second conductive layer (D3): 0.92 mm
[0118] Material second conductive layer: copper-nickel
[0119] Structure / manufacturing method second conductive layer: drawn tube
[0120] Figure 1 shows a coaxial cable 1 known from the prior art. The shown coaxial cable 1 is in the form of a superconducting semi-rigid cable, compromising an inner conductor 2 and an outer conductor 4 made from a superconducting material like niobium or a niobium titanium alloy. The inner conductor 2 is in form of a wire and the outer conductor 4 in form of a tube. Although niobium or niobium titanium alloys have favorable superconducting properties at temperatures below about 8K, these alloys are difficult to plastically deform. Forming can only be done sequentially with several small drawing steps with subsequent annealing after each step. This makes especially thin diameter capillary tubes, as required for thin diameter cables e.g. for quantum computers, expensive.
[0121] The shown coaxial cable 1 comprises a drawn inner conductor 2 in form of a wire which extends along the longitudinal direction x. Between the inner conductor 2 and the outer conductor 4 a low loss dielectric material is arranged around the inner conductor 2 to form an insulating layer 3. For applying the outer conductor 4, the inner conductor 2 with thereto extruded insulating layer 3 is inserted into aP29151 PC00
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[0123] metal tube 4 with slightly larger inner diameter than the insulating layer 3. In the following drawing process, the metal tube is reduced in diameter, so that the inner diameter ends exactly on the required value, thereby forming the outer conductor 4 of the coaxial cable 1. The degree of plastic deformation during the drawing step is limited, as annealing is not possible after the insulating layer 3 has been applied to the inner conductor 2 as the annealing temperature is significant above the temperature low loss polymer can withstand without deterioration. This limitation requires tight diameter- and form-tolerances of the inner diameter of the outer conductor 4 and the insulating layer 3. The insertion process is therefore delicate and almost impossible with coiled tubes or a semi-finished inner conductor 2 with insulating layer 3, as commonly used in cable manufacturing.
[0124] Figure 2 shows a first embodiment of a coaxial cable 1 according to the present disclosure with an outer conductor 4 comprising a first outer conductor 41 and a second outer conductor 42. The shown coaxial cable 1 for cryogenic applications comprises an inner conductor 2, which forms the cable core and extends along a longitudinal direction x. The inner conductor 2 has a first outer diameter D1. The inner conductor 2 is encompassed by an insulating layer 3, which comprises a second outer diameter D2 and is made from a dielectric material and encompassing the inner conductor 2 along the longitudinal direction x. The shown coaxial cable 1 further comprises an outer conductor 4 which encompasses the insulating layer 3 along the longitudinal direction x and comprises a first conductive layer 41 in form of a coating, having a coating thickness T1 and being arranged circumferentially on an outer surface 31 of the insulating layer 3. The outer conductor 4 further comprises a second conductive layer 42 arranged circumferentially on an outer surface 411 of the first conductive layer 41 and having a third outerP29151 PC00
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[0126] diameter D3. The shown first conductive layer 41 is a coating 412 and made of a material that is superconducting at temperatures below 8 K. Such a design allows to produce a coaxial cable 1 with a smaller overall outer diameter, as the restriction to only one small drawing step for the outer conductor 4 due to the brittleness of superconducting material is not in place. This allows for a reduction of the required space not only for the coaxial cable 1 , but also of the connector pitch.
[0127] The shown coaxial cable 1 is made by extruding the insulating layer 3 made from a polymer material onto the inner conductor 2. Afterwards the outer conductor 4 is made by applying the first conductive layer 41 directly onto the outer surface 31 of the insulating layer 3 by a vapor deposition process. The shown second conductive layer 42 is in form of a metal tube, which is applied via a metal drawing or rolling process onto the outer surface 411 of the first conductive layer 41. The second conductive layer 42 is made of stainless steel, which is of comparatively low cost and has a low heat conductivity and comparatively good ductility. The first conductive layer 41 in form of a coating 412 is a highly conductive layer and the second conductive layer 42 works as a supporting layer.
[0128] The shown coaxial cable 1 further comprises a cable jacket 5 which is arranged circumferentially on the outer surface 421 of the second conductive layer 42. The cable jacket 5 is made from a thermoplastic polymer which is extruded onto the outer surface 421 of the second conductive layer 42 and has a fourth outer diameter D4.
[0129] Figures 3 to 5 show three embodiments of the coaxial cable 1 according to the present disclosure.P29151 PC00
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[0131] Figure 3 shows an embodiment with a sputtered first conductive layer 41. The coating 412 is applied by applying atoms of the substrate material directly onto the outer surface 31 of the insulating layer 3. The atoms are hereby released from a solid body by bombarding it with high-energy ions and transferred into the gas phase. This allows to form a first conductive layer 41 with a thickness T 1 between 100 nanometers and 3000 nanometers. In a superconducting state the layer of a superconducting material provides zero Ohm conductivity and perfect electrical shielding.
[0132] Figure 4 shows an embodiment with a first conductive layer 41 in form of a metallized sheet. A coating 412 is applied on a substrate layer 413 which is arranged on the outer surface 31 of the insulating layer 3. The metallized sheet is made from a substrate layer 413 in form of a polymer foil which is coated with a superconductive coating 412 with a thickness between 100 nanometers and 3000 nanometers. The conductive layer is first applied to the substrate by a vapor deposition process and the coated foil is subsequently wound about the outer surface 31 of the insulating layer 3.
[0133] Figure 5 shows an embodiment in which the first conductive layer 41 corresponds to that of Figure 3, with the second conductive layer 42 being in form of a metal sheet 424 which is wrapped around the outer surface 411 of the first conductive layer 41.
[0134] Figure 6 shows a coaxial connector assembly 10 which comprises a coaxial cable 1 as shown by Figure 2 and a coaxial connector 6 comprising an outer contact 61 which is connected to the second conductive layer 42 of the coaxial cable 1P29151 PC00
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[0136] as well as an inner contact 62 which is connected to the inner conductor 2 of the coaxial cable 1. Multiple different connector types are commercially available which allow to terminate the coaxial cable 1 keeping the void free screen (e.g. with soldered, conductive glued or crimped cable entries).
[0137] Figures 7 and 8 show the application of the first conductive layer 41 to the insulating layer 3.
[0138] Figure 7 shows the application of the first conductive layer 41 via sputtering onto the outer surface 31 of the insulating layer 3. Sputtering, also known as cathode sputtering applies atoms of the substrate material which are released from a solid body by bombarding it with high-energy ions and transferred into the gas phase. Sputtering allows to apply the desired material as a coating 412 with a thickness in the nanometer range in an economical fashion. The first conductive layer 41 is used directly as a functional (highly conductive) layer in the finished coaxial cable 1 , not only as a contactable layer for galvanic build-up (auxiliary layer for manufacturing process).
[0139] Figure 8 shows the application of the first conductive layer 41 in form of a coated foil. The shown first conductive layer 41 is a substrate layer 413 with thereon arranged coating 412. The first conductive layer 41 is applied onto the outer surface 31 of the insulating layer 3 without an adhesion layer between them.
[0140] Figures 9 and 10 show the application of the second conductive layer 42 to the outer surface 411 of the first conductive layer 41.P29151 PC00
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[0142] Figure 9 shows the application in form of a metal sheet 424. The metal sheet or coated foil 424 is wound about the outer surface 411 of the first conductive layer 41 and soldered, welded or glued along the parting line. The second conductive layer 42 enables dimensionally stable bending as known from known semirigid coaxial cables. Alternatively, instead of a semirigid design, the coaxial cable 1 may comprise a second conductive layer 42 in form of a metal braid 423 as shown by Figure 10, which is braided about the outer surface 411 of the first conductive layer 41. Such a design increases the flexibility of the coaxial cable 1 and may be used in application where semirigid cables are too rigid.
[0143] Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the Spirit and scope of the disclosure.P29151PC00
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[0145] LIST OF DESIGNATIONS
[0146] 1 Coaxial cable 425 Inner surface
[0147] 2 Inner conductor (second outer conductor) 21 Outer surface 5 Cable jacket
[0148] (inner conductor) 25 6 Coaxial connector 3 Insulating layer 61 Outer contact
[0149] 31 Outer surface 62 Inner contact (insulating layer) 10 Coaxial cable assembly 4 Outer conductor x Longitudinal direction 41 First conductive layer 30 D1 First diameter (outer di411 Outer surface ameter inner conductor)
[0150] (first outer conductor) D2 Second diameter (outer 412 Coating diameter insulating layer) 413 Substrate layer D3 Third diameter (outer di- 414 35 ameter second conduc42 Second conductive layer tive layer)
[0151] 421 Outer surface D4 Fourth diameter (outer di(second outer conductor) ameter outer jacket) 422 Metal tube T 1 Thickness first conductive 423 Metal braid 40 layer
[0152] 424 Metal sheet
Claims
P29151 PC0025 / 31PATENT CLAIMS1. A coaxial cable (1 ) for cryogenic applications, comprising:a. an inner conductor (2) forming a cable core, having a first outer diameter (D1) and extending along a longitudinal direction (x);b. an insulating layer (3) made from a dielectric material and encompassing the inner conductor (2) along the longitudinal direction (x) and having a second outer diameter (D2);c. an outer conductor (4) encompassing the insulating layer (3) along the longitudinal direction (x) and comprisingi. a first conductive layer (41 ) arranged circumferentially on an outer surface (31) of the insulating layer (3), andii. a second conductive layer (42) arranged circumferentially on an outer surface (411 ) of the first conductive layer (41 ) having a third outer diameter (D3),wherein the first conductive layer (41 ) is made of a material that is superconducting at temperatures below 35 K, in particular below 8 K, more particular below 4 K, most particular below 1 K.
2. The coaxial cable (1 ) according to claim 1 , wherein the first conductive layer (41) is made from a material selected from the group consisting of niobium,P29151 PC0026 / 31titanium, tantalum, tin, aluminum, lead, yttrium, barium, vanadium, alloys thereof and copper oxide.
3. The coaxial cable (1 ) according to claim 1 or 2, wherein the first conductive layer (41 ) has a critical temperature above 1 K, in particular above 4 K, more particular above 8 K, most particular above 35 K.
4. The coaxial cable (1 ) according to at least one of claims 1 to 3, wherein the first conductive layer (41 ) has a thickness between 25 nanometers and 5000 nanometers, in particular between 100 nanometers and 3000 nanometers, more particular between 150 nanometers and 1500 nanometers.
5. The coaxial cable (1) according to at least one of the preceding claims, wherein the first conductive layer (41 ) is applied by a physical vapor deposition (PVD) or a chemical vapor deposition (CVP) process.
6. The coaxial cable (1 ) according to at least one of claims 1 to 5, wherein the first conductive layer (41) is a coating (412) arranged on the outer surface (31) of the insulating layer (3) or a coating (412) on a substrate layer (413) which is arranged on the outer surface (31 ) of the insulating layer (3).
7. The coaxial cable (1 ) according to at least one of claims 1 to 5, wherein the first conductive layer (41) is a coating (412) arranged on an inner surfaceP29151 PC0027 / 318. The coaxial cable (1) according to at least one of the preceding claims, wherein the first conductive layer (41 ) is applied directly onto the insulating layer (3) without an adhesion layer between them.
9. The coaxial cable (1) according to at least one of the preceding claims, wherein the second conductive layer (42) comprises a metal tube (422) applied via a metal drawing or rolling process.
10. The coaxial cable (1) according to at least one of the preceding claims, wherein the second conductive layer (42) comprises a metal braid (423) or a metallized sheet (424) wound about the first conductive layer (41).
11. The coaxial cable (1) according to at least one of the preceding claims, wherein the second conductive layer (42) is made of a material selected from the group consisting of copper, aluminum, steel and alloys thereof.
12. The coaxial cable (1) according to at least one of the preceding claims, wherein a cable jacket (5) is arranged circumferentially on an outer surface (421) of the second conductive layer (42).
13. The coaxial cable (1) according to at least one of the preceding claims, wherein the second outer diameter (D2) of the insulating layer (3) is between 2 times and 4 times, preferably between 2.5 times and 3.5 times, more preferably 3 times the first outer diameter (D1 ) of the inner conductor (2) and / or the third outer diameter (D3) of the second conductive layer (42) is between 3 times and 5 times, preferably between 3.5 times and 4.5 times,P29151 PC0028 / 31more preferably 4 times the first outer diameter (D1 ) of the inner conductor (2).
14. A coaxial connector assembly (10) comprising a coaxial cable (1 ) according to at least one of claims 1 to 13 and a coaxial connector (6) comprising an outer contact (61) which is interconnected to the second conductive layer (42) of the coaxial cable (1) and an inner contact (62) interconnected to the inner conductor (2) of the coaxial cable (1 ).
15. A method for producing a coaxial cable (1 ) for cryogenic applications, preferably according to at least one of claims 1 to 13, the method comprising at least the following method steps:a. Producing an inner conductor (2) by forming a cable core, in particular by drawing a wire along a longitudinal direction (x) to a desired outer diameter (D1 ) of the inner conductor (2);b. Extruding an insulating layer (3) made from a dielectric material onto an outer surface (21 ) of the inner conductor (2) along the longitudinal direction (x);c. Applying a first conductive layer (41) circumferentially on an outer surface (31) of the insulating layer (3);d. Applying a second conductive layer (42) circumferentially on an outer surface (411 ) of the first conductive layer (41 ),P29151 PC0029 / 31wherein the first conductive layer (41 ) is made of a material that is superconducting at temperatures below 35 K, in particular below 8 K, more particular below 4 K, most particular below 1 K.
16. The method according to claim 15, wherein the first conductive layer (41) has a thickness between 25 nanometers and 5000 nanometers, preferably between 100 nanometers and 3000 nanometers.
17. The method according to at least one of claims 14 to 16, wherein the first conductive layer (41) is applied by a physical vapor deposition (PVD) or chemical vapor deposition (CVP) process.
18. The method according to at least one of claims 14 to 17, wherein the first conductive layer (41) is a coating (412) arranged on the outer surface (31) of the insulating layer (3) or a coating (412) on a substrate layer (413) which is arranged on the outer surface (31 ) of the insulating layer (3).
19. The method according to at least one of claims 14 to 17, wherein the first conductive layer (41) is a coating (412) arranged on an inner surface (425) of the second conductive layer (42).
20. The method according to at least one of claims 14 to 19, wherein the first conductive layer (41) is applied onto the insulating layer (3) without an adhesion layer between them.P29151 PC0030 / 3121. The method according to at least one of claims 14 to 20, wherein the second conductive layer (42) is in form of a metal tube (422) applied via a metal drawing or rolling process.
22. The method according to any of claims 14 to 20, wherein the second con- ductive layer (42) is in a metal braid (423) or a metallized sheet wound (424) about the first conductive layer (41 ).