WO2018011317A1

WO2018011317A1 - Functionalized cellular substrate and sandwich composite structure incorporating such a substrate

Info

Publication number: WO2018011317A1
Application number: PCT/EP2017/067638
Authority: WO
Inventors: Patrick Parneix; Kevin RUBRICE; Mohammed HIMDI; Xavier Castel
Original assignee: Naval Group; Universite De Rennes 1; Centre National De La Recherche Scientifique
Priority date: 2016-07-13
Filing date: 2017-07-12
Publication date: 2018-01-18
Also published as: FR3054079A1; EP3485533A1; FR3054079B1

Abstract

Cellular substrate (20) of honeycomb type extending between a first end face and a second end face, the cellular substrate (20) comprising a plurality of tubular cells having a polygonal cross section, each cell comprising a plurality of walls (11) delimiting said cell, the walls (11) extending from the first end face to the second end face, the walls (11) being formed from a dielectric material, characterized in that said plurality of cells comprises at least one conductive cell (9c), said conductive cell (9c) comprising at least one electrically or thermally conductive element (22), which element is positioned in at least one of the walls (11) of said conductive cell (9c) or on a surface of at least one of the walls (11) of said conductive cell (9c).

Description

Functionalized alveolar substrate and sandwich composite structure incorporating such a substrate

The present invention relates to a honeycomb-like honeycomb substrate, said honeycomb substrate extending between a first end face and a second end face, the honeycomb substrate comprising a plurality of tubular cells with a polygonal section, each cell comprising a plurality of walls defining said cell, the walls extending from the first end face to the second end face, the walls being formed of a dielectric material.

Such substrates are used in the field of composite materials as a core for producing sandwich structures. The tubular configuration of the cells makes it possible to confer on the core specific mechanical characteristics that are very interesting, particularly in terms of compressive rigidity and shear strength, associated with a reduced density. Mechanical performance is therefore the primary functionality of such substrates. Other natural or non-natural performance can be sought, for example thermal or sound insulation.

In the electromagnetic field, composite sandwich structures are used in microwave systems. They are particularly used for producing radomes, as structural walls transparent to electromagnetic waves, structural walls incorporating electromagnetic shielding functions, stealth (mainly in the radar field), or antennal functions.

In each of these applications, the role of the material forming the core of the sandwich structure is essential both for the mechanical strength of the sandwich structure, but also for the targeted electromagnetic performance.

For example, a microwave system may consist of an antenna and a wall formed of a composite sandwich material, which is for example the carrier wall or the antenna support or the radome. The reconfigurability of such a microwave system is generally provided by the antenna, via the use of active and electrically controllable components such as pin diodes, varicaps, transistors and / or MEMS, the substrate made of composite material having a totally passive function.

It has been proposed to use in the wall, reconfigurable active materials, for example by depositing thin layers of versatile materials, whose dielectric parameters are controllable, on a specific passive substrate. Reconfigurability the microwave system is then no longer provided by the antenna itself but by the associated active thin layer.

Such a solution is not entirely satisfactory. In particular, the use of such walls incorporating thin active layers is reserved on a local scale, because of the many constraints related to these walls which limit their use on a larger scale. In particular, these walls are unsuitable for the realization of large structures such as naval structures.

An object of the invention is therefore to provide a functionalized alveolar substrate, in particular a control vector, that is to say capable of providing an electromagnetic function, which is suitable both for use as a wall carrier of an antenna or as a radome, or as an antenna system itself, and for use on a large scale as a structural panel, including a naval, land or air carrier.

For this purpose, the subject of the invention is a cellular substrate of the aforementioned type, characterized in that said plurality of cells comprises at least one conducting cell, said conducting cell comprising at least one electrically or thermally conductive element disposed in at least one one of the walls of said conductive cell or on a surface of at least one of the walls of said conductive cell.

The alveolar substrate according to the invention may comprise one or more of the following characteristics, taken alone or in any technically possible combination:

said conductive element is metallic;

said conductive element extends between a first end and a second end, from the first end face to the second end face;

said conductive element is a resistive element, said conductive element being adapted to dissipate heat when a current intensity is applied between its first end and its second end;

said conductive element is selected from the group consisting of a resistive ink printed on the surface of said wall, a metallized meander line, a metallized film, a metallized wire and a conductive pattern printed on the surface of said wall;

- The cellular substrate further comprises a plurality of active charges dispersed in the conductive cell, the active charges being made of a pyroelectric material having dielectric characteristics modifiable by applying a thermal or electrical control to said active charges;

the active charges consist of a pyroelectric material having dielectric characteristics that can be modified by applying a thermal command said active charges, and said conductive member is adapted to apply thermal control to said active charges when a current intensity is applied between its first end and its second end;

said active charges consist of a pyroelectric and ferroelectric material having modifiable dielectric characteristics by applying an electrical command to said active charges, said conducting cell comprises at least two electrically conductive elements, arranged in or on the surface of two distinct walls; said conductive cell, and said conductive members are configured to electrically control said active charges when a potential difference is applied between said conductive members;

the conducting element is a microwave circuit, in particular chosen from the group consisting of a micro-ribbon line, a coplanar line, a microwave coupler, a microwave phase-shifter and a microwave filter;

at least two conductive elements are arranged in or on the surface of two distinct walls, said at least two distinct walls being walls of a single conducting cell or at least two distinct conducting cells, and said at least two conductive elements; form a microwave circuit, in particular a Wilkinson divider;

said conductive element comprises an element of an antenna system, in particular a planar antenna.

The invention furthermore relates to a sandwich composite structure comprising a core interposed between a first and a second skin, said core comprising a cellular substrate according to the invention.

The sandwich composite structure according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:

said first skin is contiguous with the first end surface of the alveolar substrate, and the second end surface is contiguous with the second end surface of the cellular substrate;

said core comprises a cellular substrate in which the conductive element is a microwave circuit, in particular chosen from the group consisting of a microstrip line, a coplanar line, a microwave coupler, a microwave phase shifter and a microwave filter, or in which at least two conductive elements are arranged in or on the surface of two distinct walls, said at least two distinct walls being walls of a single conducting cell or at least two distinct conducting cells, said at least two conductive elements forming a microwave circuit, in particular a Wilkinson divider, and at least one of the first and second skins comprises a microwave device, in particular a planar antenna, electrically connected to said conductive element.

The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which:

- Figure 1 is a diagram of a sandwich composite structure,

Figure 2 schematically illustrates a cellular substrate forming the core of the composite sandwich structure of Figure 1;

- Figure 3 is a perspective view of a portion of a cellular substrate according to a first embodiment;

FIG. 4 is a graph illustrating the variation of the reflection coefficient Su of the cellular substrate of FIG. 3 as a function of frequency and temperature;

- Figure 5 is a diagram illustrating a meandering line;

FIG. 6 is a perspective view of a portion of a cellular substrate according to a first variant of a second embodiment;

Figure 7 is a perspective view of a portion of a composite sandwich structure incorporating the cellular substrate of Figure 6;

FIG. 8 is a front view, in perspective, of a portion of a cellular substrate according to a second variant of the second embodiment;

- Figure 9 is a rear view, in perspective, of a detail of the cellular substrate of Figure 8;

Figure 10 is a diagram illustrating a set of conductive elements forming a Wilkinson line;

- Figure 1 1 is a perspective view of a portion of a cellular substrate according to a third embodiment;

- Figures 12 and 13 respectively illustrate a front side and a back side of a sheet for the manufacture of a cellular substrate according to one embodiment of the invention; and

- Figure 14 illustrates the bonding of four sheets during the manufacture of a cellular substrate according to one embodiment of the invention.

A sandwich composite structure 1 is illustrated in FIG.

The composite sandwich structure 1 comprises a core 3 interposed between a first and a second skin 5a, 5b. The skins 5a and 5b are sometimes referred to as "sole". Each skin 5a is made of a rigid material, for example a "monolithic" composite material (single skin) comprising an impregnating resin and a set of fibrous reinforcements, which provide the mechanical reinforcement of the material.

The impregnating resin is preferably an organic, thermosetting or thermoplastic resin, for example a polymer resin such as an epoxy resin, a polyester resin, vinylester, etc.

The fibrous reinforcements are made of an organic or inorganic material. This is for example fiberglass or carbon.

The skins 5a and 5b extend in planes substantially parallel to each other.

The core 3, which is illustrated in more detail in FIG. 2, is formed of a cellular substrate 7.

The cellular substrate 7 extends between the skins 5a, 5b, between a first end face and a second end face. The first and second end faces extend in planes substantially parallel to the skins 5a and 5b. The first and second end faces are for example contiguous to the first 5a and the second 5b skins respectively.

The longitudinal plane will be referred to as a plane parallel to the first and second end surfaces, and a transverse plane or direction (e) a plane or an orthogonal direction (e) to the first and second end faces.

The cellular substrate 7 comprises a plurality of polygonal section tubular cells 9, each extending from the first end face to the second end face.

By tubular polygonal section is meant that the longitudinal section, i.e. by a longitudinal plane as previously defined, of each cell is preferably a polygon of constant section.

Preferably, this polygon is a regular polygon.

In the illustrated example, the longitudinal section of each cell is a regular hexagon.

As a variant, this longitudinal section is, for example, square or rectangular.

The cells 9 are contiguous to each other, forming a pavement preferably regular.

Each cell 9 comprises a plurality of transverse walls 1 1 delimiting this cell, each wall 1 1 extending transversely from the first end face to the second end face. In the example shown, each cell 9 is bounded by six walls. At least some of the walls 1 1 may be common to two cells 9.

Subsequently, the term "width" of a wall 1 1, the dimension of a wall in a longitudinal direction, and "depth" of a wall 1 1 or the cellular substrate 7 the dimension of a wall 1 1 or the cellular substrate 7 in the transverse direction.

The walls 1 1 are formed of a dielectric material, for example aramid paper, a thermoplastic material such as polypropylene, or polyimide.

The material forming the walls is chosen as a function of the desired application, in particular the properties of temperature resistance, mechanical strength and permittivity desired.

Each cell 9 thus forms a transverse duct passing through, that is to say opening transversely on either side of the alveolar substrate 7.

According to the invention, the cellular substrate 7 is functionalized by integrating, in or on the surface of at least one wall 1 1 of at least one cell 9, an electrically or thermally conductive element.

By extension, the term "conductive cell" 9c will henceforth denote a cell, of which at least one wall 11 integrates, on its inner surface or within this wall 11, such a conductive element. By inner surface of a wall, relative to a given cell, is meant the surface of this wall facing towards the inside of this cell.

The conductive element is preferably metallic.

Preferably, the conductive element is flush with at least one of said first and second end faces. In particular, the conductive element extends between a first end and a second end, from the first end face to the second end face.

According to a first embodiment, the conductive element (s) is / are actuators intended to apply electrical or thermal control to an active element disposed in the conductive cell (s).

For example, the active element comprises an active material having dielectric characteristics that can be modified under the effect of electrical and / or thermal control.

Thus, the conductive element (s) is / are actuators intended to apply an electrical or thermal control to the active material disposed in the conductive cell (s), in order to control the dielectric characteristics of the active charges, and therefore of the alveolar substrate 7 and the composite sandwich structure 1. Preferably, the active material comprises a plurality of active charges dispersed in the conducting cell. These active charges consist of a material having dielectric characteristics modifiable by applying a thermal or electrical control to these active charges.

As a result, the dielectric characteristics of the cellular substrate 7 and of the composite sandwich structure 1 including these charges are themselves modifiable and therefore reconfigurable by application of this command.

In particular, the active charges are characterized by a complex dielectric permittivity ε * = ε '+ I' ', where ε' and ε "are respectively the real component and the imaginary component of the complex dielectric permittivity ε * of the material constituting the charges active.

The factor or tangent of losses tan δ of these active loads is defined as: tan δ = ε "I ε '.

The complex dielectric permittivity of the active charges, therefore of the cellular substrate and of the composite structure integrating them, can be modified by applying a suitable control, so as to vary the absorption and reflection properties by the cellular substrate or by the composite structure of incident electromagnetic waves on this substrate or structure.

In particular, the complex dielectric permittivity of the active charges depends on the electrical voltage to which the charges are subjected. The complex dielectric permittivity of the active charges is thus modifiable by application of an electric control.

Preferably, the active charges are made of a ferroelectric material that also has pyroelectric properties, or a non-ferroelectric pyroelectric material.

Thus, the complex electrical permittivity of the active charges is modifiable by application to the active charges of an electrical or thermal control, or only thermal, respectively.

The active charges can be dispersed in all the cells 9 of the cellular substrate 7. Thus, the dielectric characteristics of the whole of the cellular substrate 7 and the sandwich composite structure 1 are reconfigurable. In this case, each cell 9 is a conductive cell, that is to say comprises at least one wall in or on which a conductive element is integrated.

Alternatively, the active charges are dispersed locally, in some cells 9 only, these cells being conductive cells 9c. In this case, dielectric characteristics of the portion (s) of the cellular substrate 7 and the composite sandwich structure 1 comprising active charges are reconfigurable.

The active charges are formed of a ferroelectric material which is preferably selected from the family of perovskites, the ilmenite family, the family of pyrochlores, the family of quadratic bronzes, the family of Aurivillius phases, the optionally chosen doped material.

In particular, the ferroelectric material is, for example, a material of the perovskite family, for example BaTiO ₃ , CaTiO ₃ , KTaO ₃ , YMnO ₃ , PbTiO ₃ , etc.

The ferroelectric material can also be:

an ilmenite, for example LiNbO ₃ ,

a pyrochlore, in particular Cd ₂ Nb ₂ 0 ₇ ,

a quadratic bronze, in particular PbNb ₂ 0 ₆ ,

an Aurivillius phase, in particular BiTi ₃ 0 ₁₂ or SrBi ₂ Ta ₂ 0 ₉ , etc.

The ferroelectric material may be a doped phase of one of the above materials, for example Ba 2 Sr 3 O 5, KTai-xNbxTiO 5, AgTai.xNbxOa, 5η_ _χ Βίχ ^" Π0 ₃ , Ρ ^ - _Χ 8Γ _Χ ^" Π0 ₃ , Β3Ζη ^" Π _χ 0 ₃ etc.

The value of the coefficient x may be chosen between 0 and 1, depending in particular on the desired Curie temperature for the material.

The ferroelectric material may also be a multiferroic material, for example BiFe0 ₃ , having several ferroic properties. For example, the material is both ferroelectric, ferroelastic and ferromagnetic.

For example, the active charges are made of a ferroelectric material and therefore pyroelectric, having dielectric characteristics, including a complex dielectric permittivity, modifiable by applying a thermal control to these active charges. According to this example, each conductive element, disposed on or in a wall 1 1 of a conductive cell, is adapted to apply a thermal control to the active charges contained in this conductive cell, when a current intensity is applied between its first end and its second end. In particular, each conductive element is adapted to dissipate heat when a current intensity is applied between its first end and its second end.

According to this example, each conductive element is preferably a resistive ink, printed on the inner surface of a wall of the conductive cell, a metallized meander line, which can be fixed on the inner wall of the conducting cell or integrated in this wall, or a film or conductive wire, which can also be fixed on the inner wall of the conducting cell or integrated in this wall. According to one variant, each conducting cell comprises at least two electrically conductive elements, arranged in or on the surface of two distinct walls of the conducting cell. These electrically conductive elements are disjoint from each other.

The conductive elements of each conductive cell are then configured to apply electrical control to the active charges contained in this conductive cell when a potential difference is applied between these conductive elements.

According to this variant, the conductive elements are, for example, conducting wires or films.

According to this first embodiment, the application of a potential difference between the conductive elements makes it possible to vary the dielectric characteristics, in particular the complex dielectric permittivity, of the active charges contained in the conducting cell (s) 9c, and thus of modify the electromagnetic response of all or part of the cellular substrate 7, therefore of the composite sandwich structure.

According to a second embodiment, the conductive element is intended to be coupled to one or more controllable microwave device (s), in particular a planar antenna or patch antenna, for example disposed on one of the skins. 5a, 5b or integrated (s) to one of the skins 5a, 5b. In particular, the conductive element is a transmitter configured to supply and / or control one or more microwave device (s).

For example, each conductive element forms a microwave circuit, in particular a microstrip line, a coplanar line, a microwave coupler, a microwave phase shifter or a microwave filter.

According to a variant, at least two conductive elements are arranged in or on the surface of two distinct walls, these distinct walls being walls of a single conducting cavity or of at least two distinct conducting cells, and forming a set of elements. conductors, this set of conductive elements forming a microwave circuit, including a Wilkinson divider for example.

According to a third embodiment, the conductive element (s) comprises an element of an antenna system, in particular a planar antenna or patch antenna.

Thus, FIG. 3 shows a portion of a cellular substrate 20 according to the first embodiment.

The elements of Figure 3 identical to the corresponding elements of Figure

2 are designated by identical references. In this first embodiment, the cellular substrate 20 comprises a plurality of active charges 21 dispersed in a conducting cell 9c.

These active charges 21 consist of a ferroelectric and pyroelectric material, or only pyroelectric, having dielectric characteristics modifiable by application of an electrical or thermal control, or only thermal to the active charges, respectively.

For example, the active charges 21 are introduced into the conducting cell 9c in the form of powder of ferroelectric material and pyroelectric material, or pyroelectric material. In this case, the powder formed of active charges is directly introduced into the conducting cell 9c.

Alternatively, the active charges are introduced into the conducting cell 9c in the form of ceramic.

The active charges 21 may also be dispersed in an organic resin, for example an epoxy resin, or in an expanded material introduced into the conducting cell 9c. In particular, the charge rate in active charges in this resin is chosen so as to optimize the reconfigurability of the cellular substrate 7.

In this example, each of the walls 1 1 of the conductive cell 9c is covered with a conductive element 22 in the form of a metal film, covering the entire wall. Each metal film is fixed on the inner surface of a wall January 1.

Each conductive element 22 extends between a first transverse end and a second transverse end.

Each conductive member 22 is configured to dissipate heat when current is applied to it by a suitable device. This device is for example a current generator configured to apply a current intensity between the first end and the second end of the conductive element.

In addition, each conductive element 22 is configured to transmit the heat thus generated to the active charges dispersed in the conducting cell 9c, causing a rise in temperature of the active charges and thus a modification of their complex dielectric permittivity. The absorption and reflection properties of the alveolar substrate 20 of incident electromagnetic waves on this substrate are thus modified.

FIG. 4 thus shows the reflection coefficient Su of a cellular substrate, one cell of which in two directions in the two directions of the longitudinal plane contains periodically active charges and constitutes a conductive cell, as a function of the frequency, for two different temperatures T1 and T2 (T2> T1) applied to the active charges by means of the conductive elements.

There is indeed a change in the reflectivity of the composite sandwich structure, both in amplitude and in frequency.

Alternatively, the conductive member for dissipating heat may be a meandering line, as illustrated by way of example in Figure 5.

Figures 6 and 7 illustrate a portion of a sandwich composite structure 30 according to a first variant of the second embodiment.

The sandwich composite structure 30 is similar to the sandwich composite structure 1 described with reference to Figures 1 and 2. The identical elements of these Figures are therefore designated by identical references.

In the example shown, a planar antenna or patch antenna 32 is integrated in one of the skins 5a. In particular, the planar antenna 32 is formed on a portion of the skin 5a disposed opposite a conductive cell 9c.

This conductive cell 9c is provided, on one of its walls 1 1, with a conductive element 34 formed of a microstrip line extending transversely from the first face to the second face of the cellular substrate. In this example, the microstrip line is a 50 ohm line. The mass of the microstrip line is formed by conductive elements disposed on an outer surface 36 of the wall 1 1 comprising the conductive element 34.

The conductive element 34 is configured to feed the planar antenna 32.

The insertion of such a conductive element 34, for feeding the planar antenna 32, thus makes it possible to integrate such a planar antenna with the sandwich composite structure 30.

Figures 8 and 9 illustrate a portion of a composite sandwich structure comprising a cellular substrate 40 according to a second variant of the second embodiment.

In these Figures, the skins are not shown, for simplification. The sandwich composite structure is similar to the sandwich composite structure 1 described with reference to Figures 1 and 2. The identical elements of these Figures are therefore designated by identical references.

In this second variant, a dipole antenna 42 is made on an end face of the cellular substrate 40, that is to say on or integrated within one of the skins, the outer face of this skin serving radome to said dipole antenna. In particular, the dipole antenna 42 is arranged facing at least one conducting cell 9c. As illustrated in FIG. 9, this conducting cell 9c is provided, on one of its walls 11, with a conductive element 44 formed, for example, of a microstrip line extending transversely from the first face to the second face. The conductive element 44 is configured to feed the dipole antenna 42.

Alternatively, in this second embodiment, a Wilkinson divider may be formed by a set of conductive elements formed on the surface of a plurality of adjacent walls 1 1 of one or more cells of a cellular substrate. This Wilkinson divider is intended to be coupled to a microwave system such as an antenna disposed on or in a skin of the composite sandwich structure integrating the cellular substrate.

Such a Wilkinson divider is illustrated in FIG. 10. In the example illustrated in this FIGURE, there is shown a set 50 of conductive elements intended to be printed on a portion of a sheet used for the manufacture of a substrate. alveolar, as described below. This set 50 of conductive elements comprises metallized patterns forming a Wilkinson divider 52.

Thus, according to the second embodiment, the conductive elements inserted in or on the surface of the conducting cell walls make it possible to feed or send a command to a microwave system disposed on a surface of one of the skins or integrated in one of the skins.

Figure 11 illustrates an exemplary foam substrate according to the third embodiment.

In this example, a conducting cell 9c comprises a conductive element 62 forming a patch antenna powered by a microstrip line.

Thus, in this embodiment, a microwave radiating system is incorporated within the cellular substrate itself.

A method of manufacturing a cellular substrate comprising conductive elements will now be described with reference to Figures 12 to 14.

This cellular substrate is made from sheets of a suitable dielectric material, for example aramid paper sheets or polypropylene sheets, cut in a coil.

The sheets have for example a thickness of 0.150 mm.

The leaves are of the same length L and of the same width I.

According to a first embodiment of the manufacturing method, conductive elements are integrated with the sheets or some of the sheets during their manufacture. In this first embodiment, the conductive elements are, for example, conductive frames. According to a second embodiment of the manufacturing method, conductive elements are printed on at least one surface of the sheets or of certain sheets during their manufacture. In this second embodiment, the conductive elements are for example formed of a conductive ink.

According to a third embodiment of the manufacturing method, conductive elements are fixed on at least one surface of the sheets or of certain sheets. In this third embodiment, the conductive elements comprise for example metallized films or wires, microwave circuits, or elements of microwave systems such as planar antennas.

In these three embodiments, the conductive elements are integrated on or in the sheets at specific locations, which are determined according to the desired position of the conductive elements in the cellular substrate subsequently made from these sheets.

In FIGS. 12 and 13, FIGS. 12 and 13 show the front sides 70a and 70b of a sheet 70 for producing a honeycomb substrate whose cells are hexagonal in cross-section.

In these figures, the dotted lines delimit fold zones of the sheet. Each strip located between two folding zones is of width a (in the direction of the length of the sheet) equal to the width of a wall. In the example described, walls of width 4 mm are considered.

The length L and the width I of the sheets are chosen according to the desired final geometry for the cellular substrate and the number of alveolar substrates that it is desired to form from these sheets.

In particular, as described below, the sheets being intended to be cut lengthwise, the width of the sheets depends on the number of cellular substrates that it is desired to form from these sheets and the thickness of each alveolar substrate.

On the front side 70a of the sheet 70 illustrated in FIG. 12, are integrated, in particular fixed, two sets 72, 74 of conductive elements, each formed of a strip whose width is for example equal to the thickness of a honeycomb substrate.

Each set of conductive elements 72, 74 covers an area of the sheet 70 corresponding to several distinct walls of the final cellular substrate.

Each set of conductive elements forms for example a microwave circuit such as a Wilkinson divider. In the latter case, a metallization on the back of the sheet is necessary because of the microstructure structure of the aforementioned circuit. Nevertheless, in the example illustrated, no conductive element is integrated on the back of the sheet 70.

Furthermore, strips 76 of adhesive are applied to each of the front faces 70a and 70b of the sheet 70. The width of these strips 76 of adhesive is equal to the width of a wall of a cell of the substrate.

The positioning of these adhesive strips depends on the desired geometry of the cells.

In this case, the cells being hexagonal, the strips 76 of glue are separated from each other by a strip of width equal to three times the width of a wall. In addition, each band 76 of adhesive applied to the front side of the sheet is separated from adhesive strips applied on the back side by a strip of width equal to the width of a wall.

In the third embodiment of the manufacturing method, the adhesive strips 76 are for example applied after the fixing of the sets 72, 74 of conductive elements.

Then, each sheet 70 provided with strips of glue is attached to a sheet 70 'devoid of adhesive strips, thus alternating the sheets provided with strips of glue with sheets devoid of tape glue, as shown in Figure 14.

Of course, the conductive elements may be present on only one or some of these sheets.

The stack of glued sheets is compacted to form a block.

The block is cut lengthwise, i.e. orthogonal to the adhesive strips 76, to form at least two slices.

Each slice is then stretched in a direction orthogonal to the plane of the sheets forming this slice, to obtain a cellular substrate. The thickness of each alveolar substrate is equal to the width of the wafer from which the substrate was obtained.

The cellular substrate thus obtained comprises conducting elements which may be present in the walls of all the cells, or in the walls of certain cells only.

Thus, the alveolar substrate according to the invention can be functionalized as required.

In particular, when the conductive elements are intended to control the dielectric properties of an active material inserted into certain cells, the dielectric properties of the active material in each cell can be controlled independently of the other cells. In particular, if the conductive elements are heating elements, the temperature of each cell can be controlled independently of that of other cells.

The cellular substrate and the sandwich composite structure according to the invention, thus functionalized, provide an electromagnetic function, for example in terms of electromagnetic shielding, radio-transparency, absorption of electromagnetic waves, integration or decoupling antennas, or even as an antenna, without their mechanical performance, their mass or the method of manufacture being impacted.

In addition, the invention makes it possible to functionalize sandwich composite structures that are usually passive, and this, over large areas

In particular, the cellular substrate and the sandwich composite structure according to the invention are suitable for use on a large scale, for example as a structural panel, in particular of a naval, land or air carrier, and on a smaller scale.

Moreover, the additional cost associated with the integration of the conductive elements is moderate.

The cellular substrate and the sandwich composite structure according to the invention provide a modular or active character to the electromagnetic performance of the systems integrating them.

In particular, a sandwich composite structure whose conductive elements are used as control of the dielectric characteristics of active charges dispersed in conductive cells can be integrated into various systems, such as antennal systems dedicated to communications applications, including naval applications ( in buildings of surface, masts) or terrestrial (within vehicles, buildings) or in the field of the energy.

Such a composite sandwich structure can also be used:

as an active radome wall, associated with an antenna, and / or as a supporting structure, for example a structure carrying an antenna,

as a structural wall of a naval, land or air carrier incorporating an antenna,

- in a jammer, an electronic card, a phase-shifter, a filter, in a radar or a goniometer,

as a substrate of a printed circuit in the electronic field.

The embodiments and variants described above may further be combined. In particular, different types of conductive elements described above can be combined in the same cellular substrate.

Claims

1 .- Respirable honeycomb-shaped honeycomb substrate (7; 20; 40), said cellular substrate (7; 20; 40) extending between a first end face and a second end face, the honeycomb substrate. (7; 20; 40) comprising a plurality of tubular cells (9) with polygonal section, each cell (9) comprising a plurality of walls (1 1) delimiting said cell (9), the walls (1 1) s' extending from the first end face to the second end face, the walls (1 1) being formed of a dielectric material,

the cellular substrate (7; 20; 40) being characterized in that said plurality of cells (9) comprises at least one conductive cell (9c), said conductive cell (9c) comprising at least one element (22; 34; 52, 62) electrically or thermally conductive, disposed in at least one of the walls (1 1) of said conductive cell (9c) or on a surface of at least one of the walls (1 1) of said conductive cell (9c) .

The alveolar substrate (7; 20; 40) according to claim 1, characterized in that said conductive element (22; 34; 44; 52; 62) is metallic.

3. - alveolar substrate (7; 20; 40) according to any one of claims 1 or 2, characterized in that said conductive element (22; 34; 44; 52; 62) extends between a first end and a second end, from the first end face to the second end face.

4. - cellular substrate (7; 20) according to claim 3, characterized in that said conductive element (22) is a resistive element, said conductive element (22) being adapted to dissipate heat when a current intensity is applied between its first end and its second end.

5. A cellular substrate (7; 20) according to claim 4, characterized in that said conductive element (22) is selected from the group consisting of a resistive ink printed on the surface of said wall (1 1), a line metallized meander, a metallized film, a metallized wire and a conductive pattern printed on the surface of said wall (1 1).

6. -Alveolar substrate (7; 20) according to any one of claims 1 to 5, characterized in that it further comprises a plurality of active charges (21) dispersed in the conducting cell (9c), the charges active elements (21) consisting of a pyroelectric material having modifiable dielectric characteristics by applying a thermal or electrical command to said active charges (21).

7.- alveolar substrate (7; 20) according to claim 6 and any one of claims 4 or 5, characterized in that the active charges (21) consist of a pyroelectric material having modifiable dielectric characteristics by applying thermal control to said active charges (21), and in that said conductive element (22) is adapted to apply thermal control to said active charges (21) when a intensity of current is applied between its first end and its second end.

8. - alveolar substrate (7) according to claim 6, characterized in that:

said active charges (21) consist of a pyroelectric and ferroelectric material having modifiable dielectric characteristics by applying an electrical command to said active charges,

said conductive cavity (9c) comprises at least two electrically conductive elements, arranged in or on the surface of two distinct walls of said conducting cell, and

said conductive elements are configured to apply electrical control to said active loads (21) when a potential difference is applied between said conductive elements.

9. - cellular substrate (7; 40) according to any one of claims 1 to 3, characterized in that the conductive element (34; 44) is a microwave circuit, in particular selected from the group consisting of a micro-line ribbon, a coplanar line, a microwave coupler, a microwave phase shifter and a microwave filter.

10. - alveolar substrate (7) according to any one of claims 1 to 3, characterized in that at least two conductive elements are arranged in or on the surface of two walls (1 1) distinct, said at least two walls (1 1) being walls of a single conducting cell (9c) or at least two distinct conducting cells (9c), and in that said at least two conducting elements form a microwave circuit (52), in particular a Wilkinson divider.

1 1. - Cellular substrate (7) according to any one of claims 1 to 3, characterized in that said conductive element (62) comprises an element of an antennal system, including a planar antenna.

12.- sandwich composite structure (1; 30), comprising a core interposed between a first (5a) and a second (5b) skins, said core comprising a cellular substrate (7; 20; 40) according to any one of the claims 1 to 1 1.

13.- sandwich composite structure (1; 30) according to claim 12, characterized in that said first skin (5a) is contiguous to the first end surface of the cellular substrate (7), and the second end surface is contiguous with the second end surface of the cellular substrate (7).

14. A sandwich composite structure according to any one of claims 12 or 13, characterized in that said core comprises a cellular substrate (7; 40) according to any one of claims 9 or 10, and in that at least one of the first (5b) and second (5b) skins comprises a microwave device, in particular a planar antenna, electrically connected to said conductive element (34; 44).