Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
  • H01Q17/008—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with a particular shape
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
  • H01Q17/007—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with means for controlling the absorption

Definitions

• the present invention relates to the radiofrequency functionalization of composite structural elements integrating core elements in the form of a honeycomb, in order to confer on them various functionalities, for example absorbing, communicating, reflecting and/or focusing functions for electromagnetic waves.
• the present invention also relates to associated methods and devices, namely a manufacturing method, an optimization method, a composite structure, a computer program product and a readable information medium.
• Such performance is generally accompanied by an increase in the weight of these devices and by a more complex integration of these devices in the vehicle or carrier.
• the description describes an absorbent structure, the absorbent structure being a honeycomb type honeycomb structure extending between a first end face and a second end face, the honeycomb structure comprising a plurality of tubular cells, each cell comprising a plurality of walls delimiting said cell, the walls extending from the first end face to the second end face, the walls being formed of a dielectric material, at least one cell comprising at least one strip of electrically conductive coating arranged in at least one wall or on a surface of at least one wall, the cell structure being characterized by parameters, the parameters of the cell structure being chosen so that the absorbent structure provides an attenuation of at least 10 dB for each incident wave of a range of frequencies having a frequency range greater than or equal to 15 GHz.
• the absorbent structure has one or more of the following characteristics, taken separately or according to all the technically possible combinations:
• the parameters are the dielectric and geometric parameters of each cell and the electrical and geometric parameters of each strip.
• the at least one cell has two separate coating strips with a separate resistance per square.
• the resistance per square of two contiguous strips differs by an interval of resistance per square comprised between 10 Ohms/sq and 500 Ohms/sq, preferably between 50 Ohms/sq and 150 Ohms/sq.
• At least one strip has a height, said height varying in a direction perpendicular to the plane.
• the width of the strip varies according to a stepwise variation or according to a strictly monotonous variation in a direction perpendicular to the plane.
• the space between two contiguous bands is between 100 micrometers and 1000 micrometers, preferably between 400 micrometers and 600 micrometers.
• the height of the wall in a direction perpendicular to the plane is between 5 millimeters and 50 millimeters, preferably between 7 millimeters and 25 millimeters.
• the description also relates to a sandwich composite structure comprising a core interposed between a first skin and a second skin, said core comprising at least one absorbent structure as previously described.
• the description also describes a method of manufacturing an absorbent structure, the absorbent structure being a honeycomb structure, the honeycomb structure being characterized by parameters, the parameters being chosen so that the absorbent structure provides an attenuation of at least 10 dB for each incident wave of a frequency range having a frequency range greater than or equal to 15 GHz, the method comprising the steps of printing strips of electrically conductive coating, depositing a layer of adhesive on a surface of at least one blade made of dielectric material, for bonding the blades to the layers of adhesive, for assembling the blades to form a plurality of tubular cells, each cell comprising a plurality of walls delimiting said cell, the walls extending from a first end face to a second end face of the honeycomb-like honeycomb structure extending between a first end face and a second end face, for expanding the assembled blades
• the description also relates to a method for optimizing an absorbent structure, the absorbent structure being a honeycomb-type alveolar structure extending between a first end face and a second end face, the alveolar structure comprising a plurality of tubular cells, each cell comprising a plurality of walls delimiting said cell, the walls extending from the first end face to the second end face, the walls being formed of a dielectric material, at least a cell comprising at least one strip of electrically conductive coating placed in at least one wall or on a surface of at least one wall, the cellular structure being characterized by parameters, the method comprising a step of choosing initial parameters for the structure alveolar, and a step of optimizing the parameters of the alveolar structure according to an optimization technique implemented by successive iterations on r current sets of parameters, the first set of parameters being the set of initial parameters and the set of parameters of an iteration being the set of parameters obtained at the previous iteration, the optimization technique being implemented under the constraint that the absorbing structure provides an attenuation
• the description also relates to a radio frequency lens comprising a plurality of conductive studs, each stud being a honeycomb assembly comprising at least one tubular honeycomb, each honeycomb comprising a plurality of walls delimiting said honeycomb, the walls extending from a first face of end to a second face end, the walls being formed of a dielectric material, at least one cell comprising at least one strip of electrically conductive coating placed in at least one wall or on a surface of at least one wall, each cell assembly having parameters , the parameters of each honeycomb assembly being chosen so that the radiofrequency lens has a spatial variation of predefined effective refractive index.
• the radiofrequency lens has one or more of the following characteristics, taken separately or according to all the technically possible combinations:
• the lens has a center and the spatial variation of the effective refractive index corresponds to a gradient from the center of the lens.
• the studs are divided into several zones, the parameters of the cell assemblies in the same zone being identical.
• each honeycomb assembly the parameters of each honeycomb assembly are chosen so that the lens has a gain greater than 5 dBi over a range extending from 8 GigaHertz to 12 GigaHertz.
• the parameters of each cell assembly are the dielectric and geometric parameters of each cell and the electrical and geometric parameters of each strip.
• the description also describes a method for manufacturing a radiofrequency lens comprising a plurality of conductive pads, each pad being a honeycomb assembly, each honeycomb assembly having parameters, the parameters being chosen so that the radiofrequency lens has a spatial variation of index of predefined effective refraction, the method comprising, for each stud, the steps of printing strips of electrically conductive coating, of depositing a layer of adhesive on a surface of at least one strip of dielectric material, of bonding the blades on the layers of adhesive, assembling the blades to form a plurality of tubular cells, each cell comprising a plurality of walls delimiting said cell, the walls extending from a first end face to a second face end of the honeycomb-like alveolar structure extending between a first end face and a second end face, of ex panning of the assembled blades, to obtain a structure to freeze, and firing of the structure to freeze to obtain the final radiofrequency lens.
• the description also relates to a method for optimizing a radiofrequency lens comprising a plurality of conductive pads, each pad being a honeycomb assembly comprising at least one tubular honeycomb, each honeycomb comprising a plurality of walls delimiting said honeycomb, the walls extending from a first end face to a second end face, the walls being formed of a dielectric material , at least one cell comprising at least one strip of electrically conductive coating arranged in at least one wall or on a surface of at least one wall, each cell assembly having parameters, the method comprising a step of choosing initial parameters for the radiofrequency lens, and a step of optimizing the parameters of each honeycomb assembly according to an optimization technique implemented by successive iterations on sets of current parameters, the first set of parameters being the set of initial parameters and the set of parameters of an iteration being the set of parameters obtained at the previous iteration, the optimization technique being implemented under the constraint that the radiofrequency lens has a spatial variation of predefined effective index of refraction.
• the description also relates to an antenna system comprising at least one part which is a honeycomb type honeycomb structure extending between a first end face and a second end face, the honeycomb structure comprising a plurality of tubular cells, each cell comprising a plurality of walls delimiting said cell, the walls extending from the first end face to the second end face, the walls being formed of a dielectric material, at least one cell comprising at at least one strip of electrically conductive coating disposed in at least one wall or on a surface of at least one wall, the plurality of walls being transparent, the part of the antenna system having parameters, the parameters being chosen so that the antenna system has an optical transmittance of at least 80% for an electromagnetic wave belonging to the visible range and having an incidence substantially normal to a plane parallel to at least one of the two end faces.
• the antenna system has one or more of the following characteristics, taken in isolation or according to all technically possible combinations:
• the parameters are the dielectric and geometric parameters of each cell and the electrical and geometric parameters of each strip.
• the part of the antenna system is chosen from an antenna and a reflector plane.
• the antenna system is chosen from a wire antenna, a patch antenna and a reflective plane antenna.
• the antenna system further comprises a complementary strip of electrically conductive coating placed in at least one wall or on a surface of at least one wall, the complementary strip being placed between the at least one strip of coating and a face end so as to form a ground plane and/or a reflective plane for the antenna system.
• At least one strip has a height defined for each cell, said height of the strip varying between 10 micrometers to the height of the cell comprising the wall in or on which the strip is arranged, said height of the strip preferably varying between 10 micrometers and 500 micrometers.
• the part presents parameters, the parameters being chosen so that the antenna system presents a desired radiation pattern.
• the radiation pattern is such that each cell in combination with the other cells of the plurality presents sector-type radiation thanks to the supply of the antenna elements according to a cardinal sine law.
• the description also describes a method of manufacturing an antenna system comprising at least one part which is a honeycomb-type alveolar structure extending between a first end face and a second end face, the antenna system having parameters, the parameters being chosen so that the antenna system has an optical transmittance of at least 80% for an electromagnetic wave belonging to the visible range and having an incidence substantially normal to the foreground, the method comprising, for each plot, the steps of printing strips of electrically conductive coating, of depositing a layer of adhesive on a surface of at least one strip of dielectric material, of bonding the strips to the layers of adhesive, of assembling blades to form a plurality of tubular cells, each cell having a plurality of walls delimiting said cell, the walls extending from a first outer face attached to a second end face of the honeycomb-type alveolar structure extending between a first end face and a second end face, for expansion of the assembled blades, to obtain a structure to be fixed, and firing the structure to be fixed to obtain the final antenna system.
• the description also relates to a method for optimizing an antenna system comprising at least one part which is a honeycomb-type honeycomb structure extending between a first end face and a second end face, the part of the antenna system having parameters, the parameters being chosen so that the antenna system has an optical transmittance of at least 80% for an electromagnetic wave belonging to the visible range and having an incidence substantially normal to a plane parallel to at least one of the two end faces, the method comprising a step of choosing initial parameters for the part of the antenna system, and of optimizing the parameters of part of the antenna system according to a technique optimization implemented by successive iterations on current sets of parameters, the first set of parameters being the set of initial parameters and the set of parameters of an iteration being the set of parameters obtained at the previous iteration, the optimization technique being implemented under the constraint that a part of the antenna system has an optical transmittance of at least 80% for an electromagnetic wave belonging to the visible range and having an incidence substantially normal to a plane parallel to at least one of the two end faces.
• the description also relates to a computer program product comprising a readable information medium, on which is stored a computer program comprising program instructions, the computer program being loadable on a data processing unit and implementing an optimization method according to claim when the computer program is implemented on the data processing unit.
• the description also relates to a readable information medium comprising program instructions forming a computer program, the computer program being loadable on a data processing unit and implementing an optimization method as previously described when the computer program is implemented on the data processing unit.
• FIG. 1 is a schematic three-dimensional representation of a honeycomb structure
• FIG. 2 is a schematic top view of a cell of a honeycomb structure
• FIG. 3 is a schematic representation in enlarged three-dimensional view of a wall element of a cell of a honeycomb structure
• FIG. 4 to 11 are figures obtained in the context of experiments relating to absorbent structures comprising a honeycomb structure of the type of those of Figures 1 to 3,
• Figures 12 to 17 are figures obtained in the context of experiments relating to radiofrequency lenses comprising a honeycomb structure of the type of those of Figures 1 to 3, and
• Figures 18 to 26 are figures obtained in the context of experiments relating to antenna systems comprising a honeycomb structure of the type of those of Figures 1 to 3.
• This basic structure is an alveolar structure which is presented first.
• the interest of the alveolar structure is shown for three distinct devices: an absorbent structure, part of the antenna system and a radiofrequency lens.
• FIG. 1 is a three-dimensional representation
• Figure 2 a top view of part of the honeycomb structure 10
• Figure 3 an enlarged three-dimensional view of another part of the honeycomb structure 10.
• the honeycomb structure 10 is of the honeycomb or nida type, the two terms being equivalent.
• the honeycomb structure 10 extends between a first end face and a second end face not shown in Figure 1 to make the interior of the honeycomb structure 10 visible.
• the assembly of the honeycomb structure 10 and the skins forms a composite sandwich structure.
• the first and second end faces are intended to be arranged to extend in planes parallel to the skins.
• the first and second end faces are for example contiguous to the first and to the second skin respectively.
• a longitudinal plane is a plane parallel to the first and second end surfaces and a transverse plane is a plane orthogonal to the first and second end surfaces.
• a first longitudinal direction denoted X in a longitudinal plane is defined, a second longitudinal direction denoted Y and perpendicular to the first longitudinal direction X in the same longitudinal plane and a transverse direction denoted Z which is orthogonal to the two longitudinal directions X and Y.
• the honeycomb structure 10 comprises a plurality of cells 12.
• the cells 12 are contiguous to each other, forming a preferably regular paving.
• Each cell 12 extends between the first end face and the second end face.
• Each cell 12 comprises a plurality of walls 14 delimiting this cell 12, each wall 14 extending transversely from the first end face to the second end face.
• Each cell 12 is tubular and may have a polygonal section along a longitudinal plane.
• each cell 12 is tubular with a polygonal section.
• the polygonal section is constant when the cell 12 is traversed along the transverse direction.
• each cell 12 is a regular hexagon, but for the device examples, the longitudinal section is a non-regular hexagon.
• each cell 12 is delimited by six walls 14, some walls 14 being common with other cells 12.
• the section of a cell 12 is, for example, of square, rectangular, circular or elliptical geometry.
• the walls 14 are formed from a dielectric material.
• the dielectric material is, for example, an aramid sheet, or a cellulose paper or else a thermoplastic material such as polyethylene, polypropylene, polyimide, polycarbonate or polyethylene terephthalate.
• At least one cell 12 comprises at least one strip 16 of electrically conductive coating disposed in at least one wall 14 or on a surface of at least one wall 14.
• the strip 16 of electrically conductive coating is, for example, made of a metallic material or a conductive organic material.
• An organic material is a material comprising at least one bond forming part of the group consisting of the covalent bonds between a carbon atom and a hydrogen atom, the covalent bonds between a carbon atom and a nitrogen atom, or even bonds between a carbon atom and an oxygen atom.
• Polyaniline or poly(3,4-ethylenedioxythiophene): polystyrene sulfonate) also denoted PEDOT/PSS
• PEDOT/PSS polystyrene sulfonate
• conductive inks with low resistivity loaded with particles can be envisaged.
• Particles of micrometric (each dimension less than 1 mm) and nanometric (each dimension less than 1 ⁇ m) size are examples of such particles.
• Said particles are, for example, silver, copper, gold, aluminum, carbon black, graphene, carbon nanotubes or a mixture of the preceding elements.
• the internal and/or external faces of the cells 12 are made radioelectrically functional, in particular conductive by depositing an electrically conductive coating.
• the band 16 can extend over all or part of the wall 14.
• Such strips 16 can be obtained by subtractive (especially chemical etching) or additive manufacturing processes. Screen printing is preferred without being exclusive.
• the production of the strip 16 remains easy as evidenced by the following description of an example of a process for manufacturing a honeycomb structure 10 using a screen printing technique.
• the manufacturing process first includes a step of printing strips 16 of electrically conductive coating.
• the deposition by serigraphy is done via a precise mask whose image is engraved using a photosensitive capillary exposed on a canvas.
• the insulated canvas and frame set forms the silkscreen screen.
• the nature of the capillary and of the fabric will make it possible to control the thickness of the deposits and their geometries.
• the deposition also includes a pulling operation during which a doctor blade put under pressure on the fabric is moved in a horizontal translation.
• the ink is then transferred from the top of the screen onto the support through the open pores of the screen.
• a layer of adhesive is then deposited on a surface of at least one blade of dielectric material.
• the adhesive is, depending on the case, reported in the form of double-sided, a transfer adhesive or a printed adhesive.
• the nature of the adhesive is chosen according to the honeycomb structure 10 to be produced.
• the method includes a step of gluing the strips of dielectric material comprising the strips 16 printed.
• the blades are then assembled to form the plurality of tubular cells 12 with polygonal section.
• the process also includes a step of expanding the assembled blades, to obtain a structure to freeze. This expansion step can take place in a controlled atmosphere.
• temperature, humidity, stretching force or stretching speed can be controlled.
• the structure to be set is then baked during a baking step to obtain the final honeycomb structure.
• honeycomb structure 10 mechanical or thermal
• dipping in particular in a resin bath
• chemical deposition under vacuum or physical deposition under vacuum are implemented.
• a first example of a parameter for the honeycomb structure 10 is a geometry parameter for each cell 12.
• angles such as the angle formed by a wall 14 and one of the longitudinal directions, for example the angle 0 corresponding to the angle between the wall 14 and the longitudinal direction Y.
• the thickness of a wall t or t' is another example of a parameter used to characterize the geometry of a cell 12.
• the dimension along the transverse direction Z is another parameter independent of the other preceding parameters. This dimension will be called “height” in what follows.
• a second example of a parameter is an electrical parameter of a band 16.
• a conductivity value, an electrical resistivity value or else a resistance value per square of strip 16 is a particular example of an electrical parameter.
• the relative arrangement of the strips 16 with respect to the walls 14 is another parameter likely to influence the behavior of the honeycomb structure 10.
• the strip 16 is not necessarily printed over the entire height of the cell 12.
• a fourth example of a parameter relates to the materials used, in particular to produce the walls 14.
• the optimization method then comprises an optimization step during which the parameters of the honeycomb structure 10 are optimized according to an optimization technique implemented by successive iterations on sets of current parameters, the first set of parameters being the set of initial parameters and the set of parameters of an iteration being the set of parameters obtained at the previous iteration, the optimization technique being implemented under the constraint that the honeycomb structure 10 or the device comprising the honeycomb structure 10 exhibits the desired electromagnetic emission, electromagnetic transmission or electromagnetic absorption properties.
• One such method is a computer-implemented method.
• the computer is an electronic computer suitable for manipulating and/or transforming data represented as electronic or physical quantities in registers of the computer and/or memories into other similar data corresponding to physical data in memories. , registers or other types of display, transmission or storage devices.
• the computer has a processor comprising a data processing unit, memories and an information carrier reader.
• the calculator also includes a keyboard and a display unit.
• the computer program product comprises a readable carrier of information.
• a readable information medium is a medium readable by the computer, usually by the reader.
• the readable information carrier is a medium suitable for storing electronic instructions and capable of being coupled to a bus of a computer system.
• the readable information medium is a diskette or floppy disk (from the English name "floppy disk"), an optical disk, a CD-ROM, a magneto-optical disk, a ROM memory, a RAM memory, an EPROM memory, an EEPROM memory, a magnetic card or an optical card.
• a computer program comprising program instructions.
• the computer program is loadable on the data processing unit and is adapted to cause the implementation of the optimization method.
• honeycomb structure 10 which has just been presented is its use to produce an absorbing structure 20 for electromagnetic waves and more specifically radiofrequency waves.
• the absorbent structure 20 is then formed by the honeycomb structure 10 then used for its absorption properties.
• a single strip 16 of electrically conductive coating covers all of the walls 14.
• the coating strip 16 has a resistance per square of 900 Ohms per square (Q/sq).
• each cell 12 is 11 millimeters (mm).
• the intercell space (distance between two contiguous cells 12 of the same line) is 10 mm, the angle a of a cell 12 of 70°, the angle p of a cell 12 of 145°, the length of an end face on which the honeycomb structure 10 rests is 72.54 mm and the width of said end face is 23.44 mm.
• FIG. 4 is a graph presenting the evolution of the attenuation in reflectivity provided by the absorbent structure 20 as a function of the frequency.
• the absorbent structure 20 has an attenuation of 10 dB over a wide frequency band (of the order of 16 GHz, dashed lines) with attenuation levels markedly higher than those known in the state of the art (solid line).
• the second example corresponds to the structure shown in Figure 5.
• each cell 12 comprises three distinct coating strips 16 having a distinct resistance per square but of the same thickness.
• the variation of the resistance per square of the strips 16 is strictly monotonous when the wall 14 of the cell 12 is traversed in the transverse direction.
• such an example corresponds to the deposition of gradient electrically conductive coatings.
• the interval of resistance per square between two contiguous bands 16 is the same and equal to 100 Q/sq.
• the first strip 16 has a resistance per square of 300 Q/sq
• the second strip 16 has a resistance per square of 400 Q/sq. sq
• the third strip 16 has a resistance per square of 500 ⁇ /sq.
• Each strip 16 also has the same height of 3.3 mm.
• space 18 between two contiguous bands 16 is identical and is equal to 500 micrometers (pm).
• each cell 12 is 10.9 mm
• the intercell space is 10 mm
• the angle a of a cell 12 is 70°
• the angle p of a cell 12 is 145°
• the length of the end face is 72.54 mm
• the width of the end face is 23.44 mm.
• the two graphs in figure 6 show the evolution of the absorption of the structure according to example 2 in normal incidence (top graph) and in oblique incidence (bottom graph).
• three curves are represented: a first curve in solid lines corresponding to normal incidence (0°), a second curve in dotted lines corresponding to an incidence of ⁇ 20° and a third curve in dashed lines corresponding to an angle of attack of ⁇ 40°.
• the absorbent structure 20 has an attenuation of 10 dB over a very wide frequency band (of the order of 25 GHz) compared to that of Example 1.
• This frequency band width is obtained by the increase in the attenuation of the absorbent structure 20 at low frequencies linked to the presence of the resistance gradient per square.
• the performance of the absorbing structure 20 improves with the incidence and the decrease in frequency.
• EXAMPLE 3 The absorbent structure 20 according to the third example has the same characteristics as that of the second example which are not repeated, so that only the differences with the absorbent structure 20 of the second example are now described.
• a fourth additional strip 16 is added in addition to the three strips 16.
• This fourth strip 16 has a resistance per square of 200 Q/sq and is placed above the first strip 16.
• the heights of the bands 16 and the height of the cell 12 are different compared to the second example.
• the height of the first, second and fourth bands 16 is 4.9 mm and the height of the third band 16 is 3.9 mm.
• the height of the cell 12 is 20.1 mm.
• the length of the end face is 72.54 mm and the width of the end face is 23.34 mm.
• the two graphs in figure 7 show the evolution of the absorption of the structure according to example 3 in normal incidence (top graph) and in oblique incidence (bottom graph).
• the absorbent structure 20 according to the fourth example has the same characteristics as that of the third example which are not repeated, so that only the differences with the absorbent structure 20 of the third example are now described.
• the heights of the strips 16 and the height of the cell 12 are different from the third example. More precisely, the height of the bands 16 is the same for all and is equal to 2.4 mm.
• the height of the cell 12 is 11.1 mm.
• the two graphs in figure 8 show the evolution of the absorption of the structure according to example 4 in normal incidence (top graph) and in oblique incidence (bottom graph).
• the absorbent structure 20 according to the fifth example has the same characteristics as that of the first example which are not repeated, so that only the differences with the absorbent structure 20 of the first example are now described.
• strip 16 is continuous over the entire height of wall 14 of cell 12.
• the strip 16 has a width which varies along the longitudinal directions.
• FIG. 9 presents a set of patterns corresponding to a variation of possible widths for the band 16 at constant height.
• the variation is a variation in stair steps according to 7 levels and in a constant manner.
• the variation corresponds to a variation in the shape of a pyramid, by noting "a” the width at the top of the pyramid and “b" the width at the foot of the pyramid, each of the cases A, B and C is characterized by different values of width at the top "a", the width at the foot "b” being fixed at 8 mm.
• the width at the top is 7.86 mm (which corresponds to an a/b ratio of 0.98); for case B, the width at the top is 6.81 mm (which corresponds to an a/b ratio of 0.85) and for case C, the width at the top is 2.33 mm (which corresponds to a a/b ratio of 0.29).
• Cases D and E correspond to the inverse of cases B and C.
• the width of the strip 16 varies according to the pattern of case B with a resistance per sheet of the conductive coating equal to 400 ⁇ /sq.
• the height of a cell 12 is 8.0 mm and the intercell space 12 is 8.0 mm.
• the length of the end face is 174.15mm and the width of the end face is 55.38mm.
• the two graphs in figure 10 show the evolution of the absorption of the structure according to example 5 in normal incidence (top graph) and in oblique incidence (bottom graph).
• the absorbent structure 20 according to the sixth example has the same characteristics as that of the third example which are not repeated, so that only the differences with the absorbent structure 20 of the third example are now described.
• the heights of the bands 16 and the height of the cell 12 are different from the third example.
• the height of the bands 16 is the same for all and is equal to
• the height of the cell 12 is 17.6 mm.
• the width of the strip 16 varies according to the strip 16 considered, the fourth strip 16 has a width of 10 mm, the first strip 16 a width of
• the fourth strip 16 has a resistance per square of 500 Q/sq
• the first strip 16 has a resistance per square of 260 Q/sq
• the second strip 16 has a square resistance of 340 ⁇ /sq
• the third strip 16 has a square resistance of 420 ⁇ /sq.
• the intercell space is 10 mm
• the angle a of a cell 12 is 70°
• the angle p of a cell 12 is 145°
• the length of the end face is 72.5mm
• the width of the end face is 23.3mm.
• the two graphs in FIG. 11 show the evolution of the absorption of the structure according to Example 6 at normal incidence (top graph) and at oblique incidence (bottom graph).
• This good absorption performance is also maintained over a wide frequency band of at least 20 GHz.
• the use of the basic structure offers the freedom to allow the desired absorption to be obtained for the absorbent structure 20 by adapting the parameters of each honeycomb assembly. More precisely, the parameters of the honeycomb structure 10 are chosen so that the absorbent structure 20 provides an attenuation of at least 10 dB for each incident wave of a range of frequencies having a frequency range greater than or equal to 15 GHz.
• the frequency range is greater than or equal to 20 GHz, and even better if possible greater than or equal to 25 GHz.
• the attenuation is at least 15 dB, or even 20 dB.
• the frequency range over which the attenuation takes place starts from the frequency of 10 MHz.
• alveolar structures participate in the mechanical robustness of composite sandwich structures.
• the mass associated with these alveolar structures is also low.
• the proposed absorbing structure 20 makes it possible to obtain very high and durable attenuation performance in terms of attenuation level, frequency bandwidth and stability in oblique incidences.
• honeycomb structure 10 is hollowed out at its core, a gain in mass is obtained compared to other absorbent structures of the state of the art.
• the method for manufacturing a honeycomb structure 10 presented above is indeed applicable here to obtain the absorbent structure 20.
• the absorbent structure 20 can easily be integrated into a wall 14.
• Such an absorbent structure 20 is advantageous for many applications involving electromagnetic discretion and/or problems of electromagnetic compatibility between radio frequency systems.
• a radiofrequency lens 30 using the same basic honeycomb structure 10 is now described with reference to Figures 12 to 14.
• a radiofrequency lens 30 is a device capable of converging or diverging beams of incident electromagnetic waves. In the case of convergence, the term “focusing lens” or “focusing device” may be used.
• the radio frequency lens 30 comprises a plurality of pads 32 conductors.
• a pad 32 can be seen as an obstacle generally cylindrical in the broad sense (including any basic shape for the cylinder).
• the dimensions of the pads 32 and their mutual distances are usually small compared to the band at which the radiofrequency lens 30 operates.
• the distance between these studs 32 and their height constitute an equivalent medium with a variable index.
• the studs 32 make it possible to reproduce the same propagation effect as in a conventional dielectric medium in which the refractive index varies from 2 to the limit lower than unity, starting from the peripheral to the center of the radio frequency lens 30.
• a pad 32 is therefore a part of the radiofrequency lens 30 which comprises several of them to obtain such an effect.
• the material of the pads 32 is different from that forming the medium surrounding the pads 32.
• Each pad 32 is a honeycomb assembly having said honeycomb structure 10.
• each cell assembly comprises at least one tubular cell 12 with polygonal section along a plane parallel to at least one of the end faces, said first plane, each cell 12 comprising a plurality of walls 14 delimiting said cell 12, the walls 14 extending from a first end face to a second end face, the walls 14 being formed of a dielectric material, at least one cell 12 comprising at least one strip 16 of electrically conductive coating arranged on at least least one wall 14.
• each honeycomb assembly has parameters.
• the parameters of each cell assembly are the geometric and dielectric parameters of each cell 12 and the electrical, dielectric and geometric parameters of each strip 16.
• a center O is defined for the radiofrequency lens 30.
• the pads 32 are distributed in several zones Z1, Z2, Z3, Z4, Z5, Z6, the parameters of the honeycomb assemblies of the same zone Z1, Z2, Z3, Z4, Z5, Z6 being identical.
• each pad 32 of the same zone Z1, Z2, Z3, Z4, Z5, Z6 has the same height.
• the zones Z1, Z2, Z3, Z4, Z5, Z6 are concentric, the center of the zones Z1, Z2, Z3, Z4, Z5, Z6 being the center O of the radio frequency lens 30.
• the first zone Z1 is a disc and the other zones Z2, Z3, Z4, Z5, Z6 are rings surrounding the previous zone.
• the lens comprises five annular zones Z2, Z3, Z4, Z5, Z6 so that the total number of zones Z1, Z2, Z3, Z4, Z5, Z6 is 6.
• the surface of the radiofrequency lens 30 is a disc having a radius R.
• the radius is equal to 250 mm.
• Each zone Z1, Z2, Z3, Z4, Z5, Z6 can be identified by its geographical position relative to the center of the radio frequency lens 30.
• a pad 32 of the first zone Z1 is located at a distance x between 0 and 0.4 ⁇ R from the center of the radiofrequency lens 30; a pad 32 of the second zone Z2 is located at a distance x between 0.4 ⁇ R and 0.54 ⁇ R from the center of the radiofrequency lens 30; a pad 32 of the third zone Z3 is located at a distance x of between 0.54 ⁇ R and 0.68 ⁇ R from the center of the radiofrequency lens 30; a pad 32 of the fourth zone Z4 is located at a distance x comprised between 0.68 ⁇ R and 0.78 ⁇ R from the center of the radiofrequency lens 30; a pad 32 of the fifth zone Z5 is located at a distance x of between 0.78xR and 0.88xR from the center of the radiofrequency lens 30 and a pad 32 of the sixth zone Z6 is located at a distance x of between 0.88xR and 1.0xR from the center of the radio frequency lens 30.
• the height of studs 32 varies from one zone Z1, Z2, Z3, Z4, Z5, Z6 to another. More specifically, in the first zone Z1, the studs 32 have a height of 4.86 mm; a height of 4.57 mm in the second zone Z2; a height of 4.24 mm in the third zone Z3; a height of 3.85 mm in the fourth zone Z4; a height of 3.25 mm in the fifth zone Z5 and a height of 1 mm in the sixth zone Z6.
• the studs 32 are arranged in an evenly distributed manner on the surface of the radiofrequency lens 30.
• Such a configuration of the pads 32 makes it possible to obtain an equivalent medium with a variable refractive index, that is to say to obtain a spatial variation of effective refractive index.
• the medium surrounding the pads 32 is preferably not made using a honeycomb assembly.
• the effective refractive index is 1.4; in the second zone Z2, the effective refractive index is 1.33; in the third zone Z3, the effective refractive index is 1.27; in the fourth zone Z4, the effective refractive index is 1.2; in the fifth zone Z5, the effective refractive index is 1.14 and in the sixth zone Z6, the effective refractive index is 1.02.
• radio frequency lens 30 to achieve an effective index gradient corresponding to a spatial variation of the refractive index from 1.4 to 1, the variation following the mathematical law 2 - % 2 where x is representative of the position of the zone Z1, Z2, Z3, Z4, Z5, Z6 considered.
• At least one source is integrated into the honeycomb at the focal point of the lens (see figure 12).
• Figure 15 shows the evolution of the adaptation of the lens as a function of the frequency when the source is at the focal point of the lens (curve in solid line) and for a displacement of the source of a few millimeters with respect to the focal point of the lens (curve in dotted lines).
• This figure shows that the radio frequency lens 30 has good operation between 8 GHz and 12 GHz even if the source is slightly offset.
• figure 16 was obtained with a prototype for which the radius of the radiofrequency lens 30 was 50 mm instead of 250 mm for the simulation of figure 15.
• Figure 16 has three graphs.
• the graph at the top left is a radiation diagram representing the revolution of the amplitude of the electromagnetic field in the H plane as a function of the azimuth angle.
• the frequency is fixed at 9.4 GHz.
• the graph at the top right is a radiation diagram representing the evolution of the amplitude of the electromagnetic field in the E plane as a function of the elevation angle.
• the frequency is fixed at 9.4 GHz.
• the bottom graph represents the evolution of the gain as a function of the frequency (solid line curve) as well as the evolution of the efficiency as a function of the frequency (dotted curve).
• the gain G is the ratio between the power density radiated in one direction and the power density which would be radiated by an antenna with isotropic radiation in this same direction.
• An isotropic antenna is an antenna ideal consisting of a point source which radiates the same power in all directions in space (gain equal to 1).
• the directivity D represents the ratio between the power radiated in a given direction and the average power radiated by the antenna.
• the difference between the directivity and the gain takes into account the losses of the antenna. In the case of a lossless antenna, the directivity will therefore be equal to the gain.
• Figure 17 presents other results obtained by simulation for a lens with a radius of 250 mm.
• Figure 17 includes a graph at the top showing the variation of the gain in the H plane at 9.4 GHz after crossing the lens as a function of the azimuth angle.
• the shift of the source by a few millimeters (curve in dashed lines) in relation to the focal point of the lens (curve in solid line) has no influence on the focusing of the gain.
• the bottom graph shows the variation of the gain in the far field after crossing the lens, but this time as a function of the frequency.
• FIGS. 16 and 17 show that the performance of the radiofrequency lens 30 is satisfactory.
• Such a lens therefore performs the desired function.
• the parameters of each honeycomb assembly are chosen so that the lens has a spatial variation of predefined effective refractive index, in particular a gradient from the center of the lens.
• each honeycomb assembly is chosen so that the lens has a gain greater than 5 dBi over a range extending from 8 GHz to 12 GHz.
• the conductive pad 32 formed of a honeycomb assembly is hollowed out at its heart, which implies a gain in mass.
• the method of manufacturing a honeycomb structure 10 presented above is indeed applicable for each of the pads 32. Furthermore, the radiofrequency lens 30 can easily be integrated into a wall element made of composite materials.
• This integration can also be improved by printing the excitation sources of the radiofrequency lens 30. This notably makes it possible to simplify the mechanics associated with its radiofrequency power supply.
• Such a radiofrequency lens 30 is particularly advantageous in the field of telecommunications and detection.
• each antenna system 40 comprising at least one part which is a honeycomb structure 10 as previously proposed.
• the plurality of walls 14 are optically transparent.
• each wall 14 has an optical transmittance greater than 80% at at least one wavelength belonging to the visible range.
• the optical transmittance is defined by the ratio of the light intensities before and after crossing the wall 14 and the visible range is defined as bringing together all the wavelengths between 400 nanometers (nm) and 800 nm.
• the walls 14 are made of a polymer made from polyethylene terephthalate (PET) having such properties of optical transparency.
• PET polyethylene terephthalate
• a first example of antenna system 40 is presented with reference to Figures 18 and 19.
• Each cell 12 is then a radiating structure thanks to the addition of at least one strip 16 of electrically conductive coating.
• Figure 18 illustrates a pattern particularly suitable for this case.
• This is a wall 14 having a central recess 42, a conductive strip 16 surrounding the wall 14 so that in the central recess 42 two portions 44 of conductive strip 16 face one another.
• honeycomb structure 10 having only three rows 46 of honeycomb cells 12 as shown in Figure 19 is particularly suitable.
• control law applied to the antenna system 40 is a phase supply of each radiating structure.
• Figure 20 has three graphs.
• the graph at the top left of Figure 20 is a radiation diagram representing the evolution of the amplitude of the electromagnetic field in the plane E (plane orthogonal to the surface of the antenna and including its main length) as a function of its elevation angle.
• the working frequency is fixed at 9.3 GHz.
• the graph at the top right of Figure 20 is a radiation diagram representing the evolution of the amplitude of the electromagnetic field in the H plane (plane orthogonal to the surface of the antenna and including its main width) as a function of the angle of elevation.
• the frequency is fixed at 9.3 GHz.
• the bottom graph of FIG. 20 represents the adaptation of the antenna system 40 as a function of the frequency. Its adaptation is optimal at 9.3 GHz.
• the second example corresponds to a grid antenna array with sectoral radiation.
• Such a network is physically identical to the network shown in Figures 18 and 19.
• FIGS. 21 to 23 The performances of this second example of antenna system 40 are presented in FIGS. 21 to 23 on the one hand and FIG. 24 on the other hand.
• Figure 21 has three graphs.
• the graph at the top of figure 21 is a diagram giving schematically the position of the antenna elements within the honeycomb along the longitudinal direction, the graph in the middle gives the current distribution applied to these antenna elements and the graph below gives the (normalized) directivity resulting from such a feed.
• the directivity is satisfactory because, as shown in FIGS. 22 and 23, a cardinal sine control law both in phase and in amplitude supplies the various antenna elements.
• FIG. 23 presents the current distribution along the cells 12 of the central line marked in FIG. 22 from the notation A' to the notation R' (top graph in this figure 23) and for a line located in end identified in figure 22 by the notation A to the notation R (bottom graph in this figure 23).
• Figure 24 represents the evolution of the gain as a function of the elevation angle.
• the evolution of the gain is presented for two planes: plane E (curve in thick lines in figure 24) and plane H (curve in thin lines in figure 24).
• the working frequency is fixed at 9.3 GHz.
• This figure 24 shows the advantage of using the honeycomb structure 10 in this case. Indeed, it is thus obtained from a sector antenna without the need for additional equipment such as phase shifters or attenuators to apply the command, which simplifies assembly.
• the third example corresponds to a grid antenna of the patch or slot type.
• the antenna system 40 seen from the side is shown schematically in Figure 25.
• the antenna system 40 comprises the honeycomb structure 10 positioned on a reflector plane 50, itself in contact with a coaxial probe 52 which feeds the patch-type grid antenna.
• the reflective plane 50 is the carbon skin of the composite sandwich structure associated with the antenna system 40.
• the reflective plane 50 is produced similarly to the radiating element positioned in the upper part of the honeycomb structure 10 except that the strips of conductive coating are arranged at the base of each of the cells constituting the honeycomb structure 10 and form a network of conductive crowns then providing a reflection function.
• Figure 26 has three graphs.
• the graph at the top left of figure 26 is a radiation diagram representing the evolution of the amplitude of the electromagnetic field in the E plane as a function of the elevation angle.
• the frequency is fixed at 2.4 GHz.
• the graph at the top right of Figure 26 is a radiation diagram representing the evolution of the amplitude of the electromagnetic field in the H plane as a function of the elevation angle.
• the frequency is fixed at 2.6 GHz.
• the bottom graph of FIG. 26 represents the evolution of the adaptation of the antenna system 40 as a function of the frequency.
• FIG. 26 shows that the antenna system 40 is perfectly suited (reflection coefficient Su less than -15 dB) at two operating frequencies (2.4 GHz and 2.62 GHz) allowing higher gains to be obtained. to 5 dBi at these two frequencies (6.1 dBi and 8.4 dBi, respectively).
• each cell 12 is chosen so that the antenna system 40 has an optical transmittance of at least 80% for an electromagnetic wave belonging to the visible range and having a substantially normal incidence in the foreground.
• the parameters are chosen so that the antenna system 40 has a desired radiation pattern.
• the radiation pattern is such that each cell 12 in combination with the other cells 12 of the plurality presents radiation of the sector type (see FIG. 24) thanks to the supply of the antennal elements according to a cardinal sine law.
• the antenna system 40 advantageously comprises a complementary strip 16 of electrically conductive coating disposed in at least one wall 14, the complementary strip 16 being disposed between the at least one strip 16 of coating and an end face so to form a ground plane and/or a reflective plane for the antenna system 40.
• the height of the strip 16 varies between 10 micrometers at the height of the cell 12 comprising the wall 14 in or on which is arranged the strip 16, said height of the strip 16 preferably varying between 10 micrometers and 500 micrometers.
• Such technology is compatible with any type of antenna, and in particular a wire antenna, a patch antenna or an antenna requiring a reflector plane.
• the antenna system 40 formed of a honeycomb assembly is hollowed out at its heart, which implies a gain in mass.
• This mass saving can be obtained without significant complexity in the manufacture of the antenna system 40.
• the manufacturing method of a honeycomb structure 10 can effectively be used directly.
• the antenna system 40 can easily be integrated into a wall element made of composite materials.
• such antenna systems can be used in the field of transport, in particular air, rail or naval transport.
• the best integration of the antenna systems makes it possible to obtain a significant gain in aerodynamics.
• the devices obtained allow better integration into a wearer while remaining easy to manufacture and exhibiting for some of them performances unequaled by the other known solutions. This is particularly the case for the absorbent structure 20.

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• Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
• Laminated Bodies (AREA)
• Aerials With Secondary Devices (AREA)

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• 2020
  • 2020-10-21 FR FR2010790A patent/FR3115230B1/fr active Active
• 2021
  • 2021-10-21 KR KR1020237013667A patent/KR20230130607A/ko unknown
  • 2021-10-21 US US18/249,893 patent/US20230395989A1/en active Pending
  • 2021-10-21 WO PCT/EP2021/079256 patent/WO2022084465A1/fr active Application Filing
  • 2021-10-21 EP EP21798368.3A patent/EP4233129A1/de not_active Withdrawn
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