EP3465815B1 - Waveguide comprising a thick conductive layer - Google Patents

Description

Technical area

The present invention relates to a waveguide device, a method for manufacturing said waveguide and an information medium for manufacturing said waveguide.

State of the art

Radio frequency (RF) signals can propagate either in free space or in waveguide devices. These waveguide devices are used to channel RF signals or to manipulate them in the spatial or frequency domain.

• Les dispositifs basés sur le guidage d'ondes à l'intérieur de canaux métalliques creux, couramment appelés guides d'ondes.
• Les dispositifs basés sur le guidage d'ondes à l'intérieur de substrats diélectriques.
• Les dispositifs basés sur le guidage d'ondes au moyen d'ondes de surface sur des substrats métalliques tels que des circuits imprimés PCB, des microstrips, etc.

In particular, the present invention relates to passive RF devices which enable radio frequency signals to be propagated and manipulated without the use of active electronic components. Passive waveguides can be divided into three distinct categories:

• Devices based on guiding waves inside hollow metal channels, commonly called waveguides.
• Devices based on guiding waves inside dielectric substrates.
• Devices based on waveguiding by means of surface waves on metal substrates such as PCB printed circuits, microstrips, etc.

The present invention relates in particular to the first category above, hereinafter collectively referred to as guides. of waves. Examples of such devices include waveguides as such, filters, antennas, mode converters, etc. They can be used for signal routing, frequency filtering, signal separation or recombination, transmission or reception of signals in or from free space, etc.

An example of a conventional waveguide is shown on the figure 1 . It consists of a hollow device, the shape and proportions of which determine the propagation characteristics for a given wavelength of the electromagnetic signal. Conventional waveguides used for radiofrequency signals have internal openings of rectangular or circular section. They make it possible to propagate electromagnetic modes corresponding to different distributions of electromagnetic field along their section. In the example illustrated the waveguide has a height B along the y axis and a width A along the x axis.

The figure 2 schematically illustrates the electric E and magnetic H field lines in such a waveguide. The dominant mode of propagation is in this case the electric transverse mode called TE ₁₀ . The index 1 indicates the number of half wavelengths across the width of the guide, and 0 the number of half wavelengths along the height.

The figures 3 and 4 illustrate a circular section waveguide. Circular transmission modes can propagate in such a waveguide. Arrows on the figure 4 illustrate the TE11 transmission mode; the more or less vertical arrows show the electric field, the more horizontal arrows the magnetic field. The orientation of the field changes across the waveguide section.

Apart from these examples of rectangular or circular waveguide openings, other forms of opening have been imagined or can be imagined within the framework of the invention and which allow to maintain an electromagnetic mode at a given signal frequency in order to transmit an electromagnetic signal. Examples of possible waveguide apertures are shown on the figure 5 . The illustrated surface corresponds to the section of the opening of the waveguide, delimited by electrically conductive surfaces. The shape and the area of the section may further vary along the main direction of the waveguide device.

The manufacture of waveguides with complex sections is difficult and expensive. Recent work, however, has demonstrated the possibility of making waveguide components, including antennas, waveguides, filters, converters, etc., using additive manufacturing methods, e.g. 3d printing. In particular, the additive manufacturing of waveguides comprising both non-conductive materials, such as polymers or ceramics, and conductive metals is known.

Waveguides comprising ceramic or polymer walls manufactured by an additive method and then covered with a metal plating have in particular been suggested. The internal surfaces of the waveguide must indeed be electrically conductive to operate. The use of a non-conductive core makes it possible on the one hand to reduce the weight and the cost of the device, on the other hand to implement 3D printing methods adapted to polymers or ceramics and making it possible to produce parts. high precision with low roughness.

For example, the article by Mario D'Auria et al, "3-D PRINTED METAL-PIPE RECTANGULAR WAVEGUIDES", August 21, 2015, IEEE Transactions on components, packaging and manufacturing technologies, Vol. 5, No 9, pages 1339-1349 , describes in paragraph III a process for manufacturing the core of a waveguide by deposition of molten wire (FDM, Fused deposition modeling). This document recognizes that the resolution obtained by this process is limited by the diameter of the extrusion nozzle, which is 400 micrometers. It thus produces a relatively rough core. A 3 micron primer layer is deposited on this core; the thickness of this layer, relative to the resolution of the core printing process and relative to the roughness Ra of the core, is insufficient to produce significant smoothness. A conductive layer of 27 micrometers of copper is then deposited on this priming layer.

The document WO2016030490 describes a method for making articles by additive manufacturing. In it, the surface pores generated by additive manufacturing are covered with a non-stick coating, which prevents the adhesion of any substances that come into contact with the surface. Thus, it is not possible to deposit an additional layer on this coating, for example a conductive layer.

The document US 3,195,079 describes a waveguide comprising an epoxy resin core covered with a single metal layer, without an initiating layer or smoothing layer.

An example of a waveguide 1 produced by additive manufacturing is illustrated on the figure 6 . It comprises a non-conductive core 3, for example of polymer or ceramic, which is manufactured for example by stereolithography, by selective laser melting or by another additive process and which defines an internal opening 2 for the propagation of the RF signal. In this example, the window has a rectangular section of width a and height b. The internal walls of this core around the opening 2 are coated with an electrically conductive coating 4, for example with a metal plating. In this example, the outer walls of the waveguide are also coated with a metal cladding 5 which may be of the same metal and of the same thickness. This external coating reinforces the waveguide against external mechanical or chemical stresses.

The figure 7 illustrates a waveguide variant similar to that of the figure 6 , but without the conductive coating on the outer faces.

• des pressions et des températures extrêmes qui varient de façon importante ce qui induit des chocs thermiques répétés;
• un stress mécanique, le guide d'ondes étant intégré dans un engin qui subit des chocs, des vibrations et des charges qui impactent le guide d'ondes;
• des conditions météorologiques et environnementales hostiles dans lesquels évoluent les engins équipés de guide d'ondes (vent, gel, humidités, sable, sels, champignons/bactéries) ;

Waveguides are typically used outdoors, for example in aerospace (airplane, helicopter, drone) to equip a spacecraft in space, on a ship at sea or on an underwater vehicle, on machines moving in the desert or in high mountains, each time in hostile or even extreme conditions. In these environments, waveguides are particularly exposed to:

• extreme pressures and temperatures which vary considerably, which induces repeated thermal shocks;
• mechanical stress, the waveguide being integrated into a device which is subjected to shocks, vibrations and loads which impact the waveguide;
• hostile meteorological and environmental conditions in which devices equipped with waveguides operate (wind, frost, humidity, sand, salts, fungi / bacteria);

To meet these constraints, waveguides are known formed by assembling previously machined metal plates, which make it possible to manufacture waveguides capable of operating in hostile environments. On the other hand, the manufacture of these waveguides is often difficult, expensive and difficult to adapt to the manufacture of light waveguides with complex shapes.

As regards waveguides assembled by additive manufacturing, existing techniques do not allow the manufacture of waveguides that are sufficiently resistant to operate in hostile environments. The existing waveguides, manufactured by additive manufacturing of a polymer core whose internal surface is covered with metal, do not exhibit mechanical and structural characteristics which allow satisfactory use in hostile environments where the waveguides. Exposed to significant variations in pressure or temperature, the structure of these waveguides is unstable and tends to degrade which disturbs the transmission of the RF signal. In addition, the existing waveguides, manufactured by additive manufacturing of a conductive material, such as a metallic material, have surface states of too low quality, in particular too much roughness, which degrades the RF performance of the waveguide. wave and makes additive manufacturing difficult to use for this application.

Brief summary of the invention

An aim of the present invention is to provide a waveguide device free from or minimizing the limitations of known devices.

Another object of the invention is to provide a waveguide device by additive manufacturing which can be used in hostile conditions.

• une âme fabriquée par fabrication additive en matériau conducteur ou de préférence non conducteur, comprenant des parois latérales avec des surfaces externes et internes, les surfaces internes délimitant un canal de guide d'ondes les surfaces internes de l'âme comprenant des irrégularités qui définissent un valeur de rugosité,
• une couche de lissage recouvrant la surface interne de l'âme, réalisée de manière à lisser au moins partiellement les irrégularités de la couche de la surface interne de l'âme l'épaisseur de ladite couche de lissage étant supérieure ou égale à la rugosité de l'âme,
• une couche conductrice métallique recouvrant la couche de lissage, ladite couche conductrice étant formée d'un métal caractérisé par une profondeur de peau δ à la fréquence f,

According to the invention, these aims are achieved in particular by means of a device with a waveguide device for guiding a radiofrequency signal at a determined frequency f, the device comprising:

• a core made by additive manufacturing of a conductive or preferably non-conductive material, comprising side walls with external and internal surfaces, the internal surfaces delimiting a waveguide channel the internal surfaces of the core comprising irregularities which define a roughness value,
• a smoothing layer covering the internal surface of the core, produced so as to at least partially smooth the irregularities of the layer of the internal surface of the core, the thickness of said smoothing layer being greater than or equal to the roughness of blade,
• a metallic conductive layer covering the smoothing layer, said conductive layer being formed of a metal characterized by a skin depth δ at the frequency f,

the conductive layer having a thickness at least five times equal to said skin depth δ, preferably at least equal to twenty times said skin depth.

dans laquelle µ est la perméabilité magnétique du métal plaqué, f est la fréquence radio du signal à transmettre et σ est la conductivité électrique du métal plaqué. Intuitivement, il s'agit de l'épaisseur de la zone où se concentre le courant dans le conducteur, à une fréquence donnée.The skin depth δ is defined as: $$\delta =\sqrt{\frac{2}{\mathrm{<figure-callout\; id="2"\; label="\mu "\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">\mu </figure-callout>}2\mathit{\pi f}\sigma }}$$

where µ is the magnetic permeability of the plated metal, f is the radio frequency of the signal to be transmitted and σ is the electrical conductivity of the plated metal. Intuitively, this is the thickness of the area where the current is concentrated in the conductor, at a given frequency.

This solution has the particular advantage over the prior art of providing waveguides assembled by additive manufacturing which are more resistant to the stresses to which they are exposed (thermal, mechanical, meteorological and environmental stresses).

In waveguides assembled by additive manufacturing according to existing methods, the structural, mechanical, thermal and chemical properties depend essentially on the properties of the core. Typically, waveguides are known in which the conductive layer deposited on the core is very thin, less than the skin depth of the metal constituting the conductive layer. Thus, it was generally accepted that in order to improve the structural and mechanical properties of waveguides it was necessary to increase the thickness and / or the rigidity of the core. It was also recognized that it is necessary to reduce the thickness of the conductive film layer, in order to lighten the structure.

The inventors have discovered that by increasing the thickness of the conductive layer so that the latter reaches a thickness at at least five times equal to the skin depth δ of the metal of the conductive layer, preferably at least equal to twenty times this depth, the structural, mechanical, thermal and chemical properties of the waveguide depend mainly, or even almost exclusively, on the conductive layer. This surprising behavior is observed although the thickness of the conductive layer remains significantly less than the thickness of the core.

In one embodiment, the resistance of the device chosen from the resistance in traction, in torsion, in bending or a combination of these resistances is conferred mainly by the conductive layer. For example, one way to characterize the resistance of a device is to measure Young's modulus. It is accepted that for a material, the higher the Young's modulus, the more rigid the material. For example, steel has a higher Young's modulus than rubber. According to one embodiment, the conductive layer is made of metal and is thinner than the core and yet it is the metal layer which provides most of the rigidity of the device. Thus, it is possible to reduce the thickness of the core, and thus its dimensions, while improving the tensile, torsional and bending resistance of the device (cf. figure 12 ). It is advantageous to be able to reduce the thickness of the walls, and thus the dimensions of the waveguide, while increasing the tensile strength (for example the rigidity), in torsion, in bending of the waveguide, in particular for spacecraft or submarine or when the space available for each component is limited.

In one embodiment, the resistance of the device chosen from the resistance in traction, in torsion, in bending or a combination of these resistances being conferred mainly by the conductive layer over the operating temperature range of the device. By operating temperatures, we mean temperatures between -150 ° C and + 150 ° C. This temperature range makes it possible to cover the majority of temperatures where the device according to the invention is liable to change (space, desert, deep water, etc.).

In one embodiment, the conductive layer has a thickness between twenty times and sixty times the skin depth δ. This embodiment makes it possible to reduce, or even eliminate, the roughness of the conductive surface. This also makes it possible to reinforce the tensile, torsional and bending resistance of the device, for example the rigidity of the waveguide.

In one embodiment, the conductive layer has a thickness of between sixty times and a thousand times the skin depth δ. Such a thickness of conductive layer makes it possible in particular to reinforce the tensile, torsional and bending resistance of the device, for example the rigidity of the waveguide.

The device comprises a smoothing layer between the core and the conductive layer. At the end of the additive manufacturing of the core, it has been observed that the additive manufacturing process creates a strong roughness (for example hollows and bumps), in particular on the edges and surface of the core, in particular on slanted edges. These hollows and bumps can take the form of stair treads, with each tread representing the addition of a layer of non-conductive material during additive manufacturing. It was observed that after covering the core with a thin conductive layer, the roughness of the core persisted so that the surface after metallization still exhibited a roughness which disturbed the transmission of the RF signal. In this case, the addition of a smoothing layer between the core and the conductive layer makes it possible to reduce, or even eliminate, this roughness, which improves the transmission of the RF signal. The smoothing layer can be of a conductive or non-conductive material.

The thickness of this smoothing layer is preferably between 5 and 500 microns, preferably between 10 and 150 microns, preferably between 20 and 150 microns. In the case of manufacturing the core by stereolithography or by selective laser melting, this thickness makes it possible to effectively smooth the surface irregularities due to the printing process.

The thickness of said smoothing layer is greater than or equal to the roughness (Ra) of the core.

The thickness of said smoothing layer is preferably greater than or equal to the resolution of the process for manufacturing the core.

When the smoothing layer comprises a weakly conductive material, for example nickel, the transmission of the RF signal is ensured essentially by the outer metallic conductive layer, the influence of the smoothing layer is negligible, and in this case the outer conductive layer must have a thickness at least five times equal to said skin depth δ, preferably at least 20 times equal to this skin depth.

In one embodiment, the resistance of the device chosen from the resistance in traction, in torsion, in bending or a combination of these resistances is conferred mainly by the conductive layer comprising the smoothing layer.

In one embodiment, the resistance of the device chosen from the resistance in traction, in torsion, in bending or a combination of these resistances is conferred mainly by the conductive layer comprising the smoothing layer over the operating temperature range of the device.

The use of a conductive layer thicker than what would be required by the skin thickness also helps to smooth the roughness of the core due to the resolution of the 3D printer. Thus, the conductive layer also makes it possible to reduce, or even eliminate, the roughness of the core.

This smoothing layer also improves the structural, mechanical, thermal and chemical properties of the waveguide device.

In one embodiment, the device comprises a tie (or primer) layer between the core and the conductive layer. Preferably, the tie layer is on the inner surface of the core. The bonding layer can be made of a conductive or non-conductive material. The tie layer improves the adhesion of the conductor to the core. Its thickness is preferably less than the roughness Ra of the core, and less than the resolution of the additive manufacturing process of the core.

In one embodiment, the device successively comprises a non-conductive core produced by additive manufacturing, a tie layer, a smoothing layer and a conductive layer. Thus, the bonding layer and the smoothing layer make it possible to reduce the roughness of the surface of the waveguide channel. The bonding layer makes it possible to improve the adhesion of the core, conductive or non-conductive, with the smoothing layer and the conductive layer.

In one embodiment, the metallic layer comprises several sublayers of metals. When the conductive layer comprises several successive layers of highly conductive metals, for example Cu, Au, Ag, the skin depth δ is determined by the properties of the materials of all the layers in which the skin current is concentrated.

When the conductive layer comprises several successive sublayers of metals, at least one of which is a weak conductor, for example Ni, the skin depth δ of the weakly conductive sublayer is negligible in the calculation of the thickness of the conductive layer, the main part of the transmission of the RF signal being ensured by the sublayers of highly conductive metals deposited over the sublayer of weakly conductive materials.

In one embodiment, the conductive metal layer also covers the outer surface of the core. When the device is covered with a metal layer, the rigidity of the device is improved.

According to one embodiment, the core comprises at least one layer of polymer and / or ceramic.

In one embodiment, the core is formed from a metal or an alloy. For example, the metal or alloy is selected from Cu, Au, Ag, Ni, Al, stainless steel, brass or a combination of these choices.

In one embodiment, the metallic layer comprises a metal selected from Cu, Au, Ag, Ni, Al, stainless steel, brass.

In one embodiment, the bonding layer optionally comprises a metal chosen from Cu, Au, Ag, Ni, Al, stainless steel, brass, a non-conductive material, for example a polymer or a ceramic, or a combination of these choices. .

In one embodiment, the smoothing layer optionally comprises a metal chosen from Cu, Au, Ag, Ni, Al, stainless steel, brass, a non-conductive material, for example a polymer or a ceramic or a combination of these choices. .

In one embodiment, the device successively comprises a core, a bonding layer, a smoothing layer of nickel, and said metallic conductive layer.

According to one embodiment, the device successively comprises a non-conductive core, a first layer of copper, a layer of nickel, a second layer of copper. The tie layer comprises the first layer of copper. The smoothing layer includes the Ni layer. The metallic layer comprises the second layer of Cu.

The invention also relates to a method of manufacturing a waveguide device for guiding a radiofrequency signal at a determined frequency f, the method comprising steps according to claim 12.

According to one embodiment, the deposition of the conductive layer on the core is carried out by electrolytic or electroplating deposition, chemical deposition, vacuum deposition, physical vapor deposition (PVD), deposition by printing, deposition by sintering.

In one embodiment of the method, the conductive layer comprises several layers of metals and / or non-metals deposited successively.

In one embodiment, the manufacture of said core comprises an additive manufacturing step. The term “additive manufacturing” means any process for manufacturing parts by adding material, according to computer data stored on a computer medium and defining a model of the part. In addition to stereolithography and selective laser melting, the expression also designates other manufacturing methods by hardening or coagulation of liquid or powder in particular, including without limitation methods based on jets ink (binder jetting), DED (Direct Energy Deposition), EBFF (Electron beam freeform fabrication), FDM (fused deposition modeling), PFF (plastic freeforming), by aerosols, BPM (ballistic particle manufacturing), powder bed, SLS (Selective Laser Sintering), ALM (additive Layer Manufacturing), polyjet, EBM (electron beam melting), photopolymerization, etc. Manufacturing by stereolithography or by selective laser melting is however preferred because it makes it possible to obtain parts with relatively clean surface states, with low roughness, which reduces the stresses on the smoothing layer.

1. 1) l'introduction de données représentant la forme d'une âme pour dispositif à guide d'ondes, l'âme comportant des parois latérales avec des surfaces externes et internes,
2. 2) l'utilisation de ces données pour réaliser par fabrication additive une âme de dispositif à guide d'ondes,
3. 3) la déposition d'une couche conductrice sur ladite âme, la couche conductrice étant caractérisée par une profondeur de peau δ à la fréquence f, de manière à recouvrir les surfaces internes de l'âme pour définir un canal guide d'ondes,
4. 4) caractérisé en ce que lesdites données représentant la forme d'une âme sont déterminée en tenant compte de l'épaisseur de la couche conductrice de manière à ce que le guide d'onde soit optimisé pour la transmission de signal RF à la fréquence f, la couche conductrice ayant une épaisseur d'au moins cinq fois, de préférence vingt fois, la profondeur de peau δ.

An example which does not form part of the invention shows a manufacturing process comprising:

1. 1) input of data representing the shape of a core for a waveguide device, the core having side walls with outer and inner surfaces,
2. 2) the use of these data to achieve by additive manufacturing a core of a waveguide device,
3. 3) the deposition of a conductive layer on said core, the conductive layer being characterized by a skin depth δ at the frequency f, so as to cover the internal surfaces of the core to define a waveguide channel,
4. 4) characterized in that said data representing the shape of a core is determined taking into account the thickness of the conductive layer so that the waveguide is optimized for RF signal transmission at the frequency f , the conductive layer having a thickness of at least five times, preferably twenty times, the skin depth δ.

The dimensions of the waveguide channel are determined as a function of the frequency of the wave to be transmitted. It is necessary that know the thickness of the conductive layers and the thickness of the walls of the core to calculate the dimensions (width and height) of the waveguide channel. In the method according to the invention, the thickness of the core which is manufactured is calculated taking into account the unusual thickness of the conductive layer which will be deposited subsequently on the core to obtain a guide channel of waves to the required dimensions.

The invention also relates to a computer data medium containing data intended to be read by an additive manufacturing device in order to manufacture an object, said data representing the shape of a core for a waveguide device, said core comprising walls. sides with outer and inner surfaces, the inner surfaces defining a waveguide channel.

The computer data medium can consist, for example, of a hard disk, a flash memory, a virtual disk, a USD key, an optical disk, a storage medium in a network or of cloud type, etc.

The embodiments of the waveguide device apply mutatis mutandis to the manufacturing methods and to the data medium according to the invention and vice versa.

In the context of the invention, the terms “conductive layer”, “conductive coating”, “metallic conductive layer” and “metallic layer” are synonymous and interchangeable.

Brief description of the figures

• La figure 1 illustre une vue en perspective tronquée d'un dispositif guide d'onde conventionnel à section rectangulaire.
• La figure 2 illustre les lignes de champ magnétiques et électriques dans le dispositif de la figure 1.
• La figure 3 illustre une vue en perspective tronquée d'un dispositif guide d'ondes conventionnel à section circulaire.
• La figure 4 illustre les lignes de champ magnétiques et électriques dans le dispositif de la figure 3.
• La figure 5 illustre différentes sections possibles de canaux de transmission dans des dispositifs à guide d'ondes.
• La figure 6 illustre une vue en perspective tronquée d'un dispositif guide d'onde à section rectangulaire produit par fabrication additive et dont les parois internes et externes sont toutes deux recouvertes d'une déposition de matériau électrique conducteur.
• La figure 7 illustre une vue en perspective tronquée d'un dispositif guide d'ondes à section rectangulaire produit par fabrication additive et dont seules les parois internes sont recouvertes d'une déposition de matériau électrique conducteur.
• Les figures 8A et 8B illustrent un dispositif selon un exemple qui ne fait pas partie de l'invention dans lequel l'âme est recouverte d'une seule couche conductrice sur la face interne et, respectivement, sur la face interne et externe.
• Les figures 9A et 9B illustrent un dispositif selon un mode de réalisation dans lequel l'âme est recouverte d'une couche de lissage puis d'une couche conductrice sur la face interne et, respectivement, sur la face interne et externe.
• Les figures 10A et 10B illustre un dispositif selon un autre mode de réalisation dans lequel l'âme est recouverte d'une couche d'accrochage, d'une couche de lissage puis d'une couche conductrice sur la face interne et, respectivement, sur la face interne et externe.
• La figure 11 représente une vue en coupe longitudinale d'une portion de la surface rugueuse de l'âme de la couche de lissage et conductrice sur cette âme.
• La figure 12 est un tableau comparatif des modules de Young pour un guide d'ondes selon l'art antérieur et un guide d'onde selon la présente invention.

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

• The figure 1 illustrates a cutaway perspective view of a conventional rectangular section waveguide device.
• The figure 2 illustrates the magnetic and electric field lines in the device of the figure 1 .
• The figure 3 illustrates a cutaway perspective view of a conventional circular section waveguide device.
• The figure 4 illustrates the magnetic and electric field lines in the device of the figure 3 .
• The figure 5 illustrates different possible sections of transmission channels in waveguide devices.
• The figure 6 illustrates a cutaway perspective view of a rectangular section waveguide device produced by additive manufacturing and both inner and outer walls of which are coated with a deposit of electrically conductive material.
• The figure 7 illustrates a cutaway perspective view of a waveguide device with a rectangular section produced by additive manufacturing and only the internal walls of which are covered with a deposit of electrically conductive material.
• The figures 8A and 8B illustrate a device according to an example which does not form part of the invention in which the core is covered with a single conductive layer on the inner face and, respectively, on the inner and outer face.
• The figures 9A and 9B illustrate a device according to an embodiment in which the core is covered with a layer of then smoothing a conductive layer on the inner face and, respectively, on the inner and outer face.
• The figures 10A and 10B illustrates a device according to another embodiment in which the core is covered with a tie layer, a smoothing layer and then a conductive layer on the internal face and, respectively, on the internal and external face .
• The figure 11 represents a view in longitudinal section of a portion of the rough surface of the core of the smoothing and conductive layer on this core.
• The figure 12 is a comparative table of Young's moduli for a waveguide according to the prior art and a waveguide according to the present invention.

Example (s) of embodiment of the invention

The figures 9 and 10 show two embodiments of a waveguide device 1 according to the invention, each time with two sub-variants. The waveguide 1 comprises a core 3, for example a core made of metal (aluminum, titanium or steel), or optionally of polymer, epoxy, ceramic, or organic material.

The core 3 is manufactured by additive manufacturing, preferably by stereolithography or by selective laser melting in order to reduce the roughness of the surface. The material of the core can be non-conductive or conductive. The thickness of the walls of the core is for example between 0.5 and 3 mm, preferably between 0.8 and 1.5 mm.

The shape of the core can be determined by a computer file stored in a computer data medium.

The core can also be made up of several parts formed by stereolithography or by selective laser melting and assembled together before plating, for example by bonding or thermal fusion or mechanical assembly.

This core 3 delimits an internal channel 2 intended for guiding waves, and the section of which is determined according to the frequency of the electromagnetic signal to be transmitted. The dimensions of this internal channel a, b and its shape are determined as a function of the operational frequency of the device 1, that is to say the frequency of the electromagnetic signal for which the device is manufactured and for which a stable mode of transmission and optionally with a minimum of attenuation is obtained.

The core 3 has an internal surface 7 and an external surface 8, the internal surface 7 covering the walls of the opening of rectangular section 2.

In an example which does not form part of the invention illustrated on figure 8A , the internal surface 7 of the polymer core 3 is covered with a conductive metallic layer 4, for example of copper, silver, gold, nickel, etc., plated by chemical deposition without electric current. The thickness of this layer is for example between 1 and 20 micrometers, for example between 4 and 10 micrometers.

The thickness of this conductive coating 4 must be sufficient for the surface to be electrically conductive at the chosen radio frequency. This is typically obtained using a conductive layer whose thickness is greater than the skin depth δ.

This thickness is substantially constant on all internal surfaces in order to obtain a finished part with precise dimensional tolerances for the channel. According to the invention, the thickness of this layer 4 is at least twenty times greater than the skin depth in order to improve the structural, mechanical, thermal and chemical properties of the device.

On the example of figure 8A , the outer surface 8 of the core is bare. In order to protect it, following the example of the figure 8B , this external surface is also covered with a conductive layer 5, which also contributes to improving the structural, mechanical, thermal and chemical properties of the device.

The deposition of conductive metal 4,5 on the internal 7 and possibly external 8 faces is carried out by immersing the core 3 in a series of successive baths, typically 1 to 15 baths. Each bath involves a fluid with one or more reagents. The deposition does not require applying a current to the core to be covered. Stirring and regular deposition are obtained by stirring the fluid, for example by pumping the fluid in the transmission channel and / or around the device or by vibrating the core 3 and / or the fluid tank, for example with a device ultrasonic vibrating to create ultrasonic waves.

In the embodiment illustrated in figure 9A , the internal surface 7 of the polymer core 3 is covered with a smoothing layer 9, for example an Ni layer. The thickness of the smoothing layer 9 is at least equal to the roughness Ra of the internal surface 7, or at least equal to the resolution of the 3D printing process used to manufacture the core (the resolution of the printing process 3D determining the roughness Ra of the surface). In one embodiment, the thickness of this layer is between 5 and 500 micrometers, preferably between 10 and 150 micrometers, preferably between 20 and 150 micrometers. This smoothing layer also determines the mechanical and thermal properties of the device 1. The Ni layer 9 is then covered with the conductive layer 4, for example made of copper, silver, gold, etc.

The smoothing layer makes it possible to smooth the surface of the core and therefore to reduce the transmission losses due to the roughness of the internal surface.

In this embodiment, the core 3 is therefore covered with a metal layer 4 + 9 formed by a smoothing layer 9 and a conductive layer 4. The total thickness of this layer 4 + 9 is greater or equal to five times, preferably twenty times the skin depth δ. The value of the Young's modulus of the device 1 is mainly conferred by this conductive layer 4 + 9. The thickness of the conductive layer 4 may also alone be greater than or equal to twenty times the depth of skin δ. The most conductive layer is preferably deposited last, at the periphery.

Likewise, on the figure 9B , the internal surface 7 of the non-conductive polymer core 3 is covered with a smoothing layer 9 of Ni, deposited by chemical deposition. The Ni layer 9 is then covered by chemical deposition with a conductive Cu layer 4, the thickness of which is at least equal to twenty skin thicknesses at the nominal transmission frequency of the waveguide. The outer surface 8 of the core 3 is also coated by chemical deposition with a smoothing layer 6 of nickel, which also serves as a structural support. A conductive layer 5, for example copper, can be deposited over this smoothing layer.

In the embodiment illustrated in figure 10A , the waveguide 1 comprises a tie layer 11, for example a Cu layer, over the internal surface 7 of the core 3; this bonding layer facilitates the subsequent deposition of the smoothing layer 9 if such a layer is provided, or of the conductive layer 4. The thickness of this layer is advantageously less than 30 micrometers.

Likewise, on the figure 10B , the waveguide 1 comprises a tie layer 12, for example a Cu layer, over the outer surface 8 of the core 3; this bonding layer facilitates the subsequent deposition of the smoothing layer 6.

The figure 11 is a diagram showing a longitudinal section of a portion of the internal surface 7 of the core 3 of a waveguide device 1 comprising a waveguide channel 2. It can be seen that this internal surface is very irregular or rough due to the additive manufacturing process.

Above the core 3, the waveguide 1 comprises a tie layer 11, for example a Cu layer between 1 and 10 micrometers thick.

A smoothing layer 9, for example an Ni layer, is deposited by chemical deposition and makes it possible to partially smooth the irregularities of the layer of the surface of the core 3. The thickness of this smoothing layer is at least greater than the resolution of the additive printing system and therefore the roughness of Ra of the surface; in one embodiment, the thickness of the smoothing layer 9 is between 5 and 500 micrometers, preferably between 20 and 150 micrometers.

A third conductive layer 4 made of copper or silver is deposited by chemical deposition on the smoothing layer 9; its thickness is preferably greater than or equal to twenty times the skin thickness at the nominal frequency f of the waveguide, so that the surface currents are concentrated mainly, or even almost exclusively, in this layer. The relatively large thickness of this conductive layer 4 also makes it possible to reinforce the mechanical rigidity of the device. In one embodiment, the thickness of this layer is between 5 and 50 micrometers, preferably between 5 and 15 micrometers.

These depositions can be applied mutatis mutandis to the external surface 8.

The table of the figure 12 compares the Young's modulus of an all-Al waveguide 1 with the Young's modulus of a device waveguide 1 according to the invention. The waveguide according to the prior art used for this comparison consists of an Al sheet 500 micrometer thick having a Young's modulus of 72,500 N / mm ² . The waveguide 1 according to the invention used in this example comprises a core 3 of 1 mm thick polymer, a 5 micrometer Cu bond layer 11, a 90 micrometer Ni smoothing layer 9 and a conductive layer 4 of 5 micrometer Cu. The overall thickness of the coating is thus 100 microns for a Young's modulus of 214,000 N / mm ² . The influence of tie layers on Young's modulus is negligible. Note that the flexural strength (flexural rigidity) of the waveguide according to the invention is greater than that of the waveguide entirely made of aluminum according to the prior art, for a reduced weight. <b> Reference numbers used in the figures </b> 1 Waveguide device at Waveguide height b Waveguide width 2 Waveguide channel 3 Soul 4 Internal conductive coating 5 External conductive coating 6 Smoothing or structural layer 7 Internal surface of the core 8 External surface of the web 9 Smoothing layer 11 Internal tack layer 12 External tack layer

Claims (15)

1. Waveguiding device (1) for guiding a radiofrequency signal at a set frequency f, the device (1) comprising:

   - a core (3) manufactured by additive manufacturing and comprising sidewalls with external (8) and internal (7) surfaces, the internal surfaces (7) bounding a waveguide channel (2), the internal surfaces (7) of the core (3) comprising irregularities that define a roughness value (Ra),

   - a smoothing layer (9) covering the internal surface (7) of the core (3), which is produced so as to at least partially smooth the irregularities of the layer of the internal surface of the core, the thickness of said smoothing layer (9) being greater than or equal to the roughness (Ra) of the core,

   - a conductive metal layer (4) covering the smoothing layer, said conductive metal layer (4) being formed from a metal characterized by a skin depth δ at the frequency f, the conductive metal layer (4) having a thickness at least equal to five times said skin depth δ.
2. Waveguiding device (1) according to Claim 1, the thickness of said smoothing layer (9) being comprised between 5 and 500 microns, preferably between 10 and 150 microns, preferably between 20 and 150 microns.
3. Waveguiding device (1) according to either of Claims 1 and 2, the thickness of said smoothing layer (9) being greater than or equal to the resolution of the process for manufacturing the core.
4. Waveguiding device (1) according to one of Claims 1 to 3, the core being formed from a metal or from an alloy.
5. Waveguiding device (1) according to one of Claims 1 to 4, the core (3) being produced by stereolithography or by selective laser melting.
6. Waveguiding device (1) according to one of Claims 1 to 5, the metal layer (4) comprising any metal selected from Cu, Au, Ag, Ni, Al, stainless steel, brass or a combination of these metals.
7. Waveguiding device (1) according to one of Claims 1 to 6, the thickness of said conductive metal layer (4) being at least equal to twenty times said skin depth δ.
8. Waveguiding device according to one of Claims 1 to 7, furthermore comprising a bond layer (11) between said core and said smoothing layer.
9. Waveguiding device (1) according to Claim 1 to 8, the strength of the device (1), which strength is chosen from tensile strength, torsional strength, flexural strength or a combination of these strengths, being mainly conferred by the conductive layer (4).
10. Waveguiding device (1) according to Claim 9, the strength of the device (1), which is chosen from tensile strength, torsional strength, flexural strength or a combination of these strengths, being mainly conferred by the conductive layer (4) and by the smoothing layer (9) .
11. Waveguiding device (1) according to one of Claims 1 to 10, comprising a metal layer (5) covering the external surface (8) of the core (3).
12. Process for manufacturing a waveguiding device (1) for guiding a radiofrequency signal at a set frequency f, the process comprising:

    - manufacturing a core (3) comprising sidewalls with external (8) and internal (7) surfaces, the internal surfaces (7) bounding a waveguide channel (2), the internal surfaces (7) of the core (3) comprising irregularities that define a roughness value (Ra),

    - depositing, on the internal surface (7) of the core (3), in succession, a smoothing layer (9) and a conductive layer (4), the thickness of the smoothing layer being greater than or equal to the roughness (Ra) of the core (3) so as to at least partially smooth the irregularities of the layer of the internal surface of the core, said conductive layer (4) being formed from a metal characterized by a skin depth δ at the frequency f, said conductive layer (4) having a thickness at least equal to five times said skin depth δ.
13. Process according to Claim 12, the manufacture of the core comprising a step of additive manufacturing by stereolithography or by selective laser melting.
14. Process according to Claim 13, comprising depositing a bond layer between said core and said smoothing layer.
15. Computational data medium for an additive-manufacturing device, the medium comprising instructions that, when they are executed by the additive-manufacturing device, implement the steps of a method according to one of Claims 12-14.

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