WO2011086298A1

WO2011086298A1 - Reconfigurable hyperfrequency device having a deformable membrane

Info

Publication number: WO2011086298A1
Application number: PCT/FR2011/000020
Authority: WO
Inventors: Philippe Jacques Pernod; Sami Hage-Ali; Nicolas Tiercelin; Philippe Coquet; Ronan Sauleau; Vladimir Preobrazhensky
Original assignee: Centre National De La Recherche Scientifique
Priority date: 2010-01-15
Filing date: 2011-01-14
Publication date: 2011-07-21
Also published as: FR2955319A1; FR2955319B1

Abstract

The invention relates to a reconfigurable hyperfrequency device (1) characterised in that said device includes: a mechanical mounting (2) for at least one elastically deformable membrane (3), said membrane (3) having a modulus of elasticity that is no higher than 500 MPa; at least one first electric conductor (4) arranged on the membrane; at least one dielectric element (91); at least one second electric conductor (5, 21) electrically insulated from the first electric conductor (4); and a means (6) for deforming the membrane (3), said means (6) being suitable for exerting a deformation force capable of modifying the distance H between the first electric conductor (4) and the second electric conductor (5, 21) to at least 100%.

Description

RECONFIGURABLE HYPERFREQUENCY DEVICE WITH DEFORMABLE MEMBRANE

The present invention relates to the field of reconfigurable microwave devices.

By microwave device is meant a device operating at frequencies between 0.3GHz and 300 GHz, which corresponds to wavelengths between 100 cm and 1 mm.

The present invention relates for example to reconfigurable microwave antennas. Among these antennas, the present invention may particularly relate to reconfigurable microwave microstrip antennas.

However, the invention is not limited to these antennas and may relate to other types of microwave devices.

These devices include, but are not limited to, frequency tunable phase shifters, frequency selective surface based cavities, reflector gratings, phased arrays, or frequency tunable filters.

A microwave device can be used for wireless communication applications, for example in a sensor network, or for detecting remote object characteristics, for example anti-collision radars or in autonomous aircraft landing systems. .

Existing reconfigurable microwave devices can be classified into two large families.

We present below frequency tunable microwave antennas belonging to these two families. In the first family, the approach consists in modifying the effective length of the microwave antenna by using active electronic microswitches, for example of the PIN diode, MEMS micro-switch or micro-switch type (for "Micro Electro-Mechanical Systems" according to the English terminology). -saxonne).

For example, the document "Design of Reconfigurable Slot Antennas", D. Peroulis et al., IEEE Transactions on Antennas and Propagation, vol. 53 (2), pp. 645-654, 2005 (D1) provides a microstrip antenna having a plurality of PIN diode switches along the antenna feed ribbon.

The resonant frequency of the antenna is thus adapted as a function of the actuation of the switches. Given the positioning of these switches along the ribbon, it is possible to obtain an antenna capable of transmitting over a wide frequency band. This ability of the antenna to operate on multiple frequencies is called agility.

In the present case, the authors have provided four microswitches to cover a frequency range between 540MHz and 890MHz, but microwave frequencies near GHz could probably be obtained with this antenna.

In general, these devices are expensive in energy because they require active electronic components to reconfigure the antenna in frequency.

In addition, their rise in frequency in the millimeter range or beyond (frequencies above 30 GHz) is problematic, for reasons of increased loss of microswitches, complexity and cost of this type of antennas.

In the second family, the approach consists in modifying its effective permittivity and / or the effective length of the microwave antenna by a mechanical deformation.

For example, the document "Frequency-agile microstrip patch antenna using a reconfigurable ground plane mems", R. Al-Dahleh & al. Microwave and Optical Technology Letters, Vol. 43 (1), pp. 64-67, 2004 (D2) proposes to modify the effective permittivity of a microstrip microwave antenna, by the use of an electrostatically deformable metal membrane.

The radiating element of the antenna is disposed on the upper face of a glass substrate (rigid), which has on its underside the metal membrane. The substrate and the membrane are supported by support means arranged at their circumferences to obtain a volume of air under the membrane. The supports also rest on the upper face of an electrical insulation layer, the latter having on its underside an electrode of the electrostatic actuator, whose mass is the membrane itself.

When the electrostatic actuator is activated, the distance between the electrode and the membrane (ground plane) varies, which results in the modification of the effective permittivity of the antenna.

The authors specify that they were able to obtain a variation of the order of 1GHz (agility) approximately of the resonance frequency of the antenna, between 16.8GHz and 17.82GHz.

Another example is specified in the document "MEMS-based Frequency Switchable Microstrip Patch Antenna Fabricated Using Printed Circuit Processing Techniques", R. Goteti et al., IEEE Antennas and Wirel. Propagated. Lett, vol. 5 (1), pp. 228-230, 2006 (D3).

This document proposes to modify the effective permittivity and the effective length of a microstrip microwave antenna, by the use of a membrane on which is mounted the radiating element of the antenna, the membrane being deformable electrostatically.

More precisely, the radiating element of the antenna is disposed on the upper face of a polyimide membrane (Kapton). The membrane is supported by support means disposed at its circumference to define a volume of air under the membrane. Media also rest on the upper face of an electrical insulation layer, forming a ground plane.

When a voltage is applied between the radiating element and the ground plane, the polyimide membrane deforms under the effect of the force generated by the electrostatic interaction. The distance between the radiating element and the ground plane is then modified, which implies a modification of the effective permittivity of the substrate and therefore of the resonance frequency of the antenna.

The authors specify that they were able to obtain a variation of the order of 0.39GHz of the antenna resonance frequency (agility), between 17.95GHz and 18.34GHz.

The reconfigurable microwave antennas presented in these references are based on a simpler and less expensive principle than reconfigurable antennas using active electronic microswitches. Moreover, they make it possible to obtain reconfigurable microwave antennas at a lower cost for frequencies up to 20 GHz.

However, these antennas have a still limited agility for the intended applications. Moreover, their rise in frequency in the millimeter domain is unproven.

An object of the invention is thus to provide a simple reconfigurable microwave device at reduced cost and to obtain improved reconfiguration capabilities. ,

Another object of the invention is to propose a reconfigurable microwave device which is also capable of obtaining these advantages in the millimetric range, ie typically for microwaves above 30 GHz.

To achieve at least one of these objectives, the invention proposes a reconfigurable microwave device characterized in that it comprises: a mechanical support of at least one elastically deformable membrane, said membrane having an elastic modulus of less than or equal to 500 MPa;

at least one first electrical conductor disposed on the membrane;

at least one dielectric element;

at least one second electrical conductor electrically insulated from the first electrical conductor;

means for deforming the membrane, said means being adapted to exert a deformation force capable of modifying the distance H between the first electrical conductor and the second electrical conductor to at least 100%.

The device may provide other technical features of the invention, taken alone or in combination:

the means for deforming the membrane is selected from electromagnetic, fluidic, magnetoelastic, piezoelectric, electrostrictive, thermal, electrorheological, magnetorheological means, based on a thermal shape memory alloy or a magnetic shape memory alloy;

the membrane is a silicone polymer, for example polydimethylsiloxane (PDMS), or an elastomer;

the membrane is textured or micro-structured;

the operating frequency is greater than or equal to 30GHz;

the mechanical support is made of the same material as the membrane;

the first electrical conductor also has a magnetic function and the means for deforming the membrane is a means for applying a controllable magnetic field for interacting with the first electrical conductor;

the first electrical conductor is a permanent magnet or a ferromagnetic material; the first electrical conductor is made from one of the following: SmCo, AINiCo, FePt, NdFeB, Fe-Ni alloy, Fe-Ni-Mo alloy or other iron alloys;

the first electrical conductor comprises an electrical conduct itself and a magnetic element separate from said conductor and the means for deforming the membrane is a means for applying a controllable magnetic field for interacting with the magnetic element associated with the electrical conductor;

the magnetic element is selected from NdFeB, ferrites, iron compounds and alloys or rare earth compounds;

the deformable membrane also has a magnetic function and the means for deforming the membrane is a means for applying a controllable magnetic field capable of interacting with the membrane;

the deformable membrane comprises a magnetic powder, for example a ferrite powder, NdFeB, FePt, SmCo, Fe, Fe-Ni, Fe-Ni-Mo, Ni, Co, or a powder of iron alloys, alloys of Nickel or cobalt alloys;

the means for applying a controllable magnetic field is a coil, a conductor traversed by an electric current, a movable magnet or a magnetoelectric element;

the means for deforming the membrane is a micropump, for example peristaltic, capable of injecting a dielectric fluid, for example air, liquids or colloidal solutions, between the membrane and its mechanical support;

it comprises at least two dielectric elements, the first dielectric element being a fluid and the second dielectric element being a solid or a multiphase material such as foam;

the second dielectric element is chosen from: alumina, glasses, teflon glasses, quartz, teflon, polyimides, a liquid crystal polymer, a foam or a microwave substrate; it comprises a means for controlling the state of deformation of the membrane disposed thereon, for example a piezo-resistive gauge; it performs one of the following functions: antenna, phase shifter, cavity based frequency selective surfaces, phased array, reflector array, filter.

Other features, objects and advantages of the invention will be set forth in the following detailed description with reference to the following figures:

FIG. 1, which comprises FIGS. 1 (a) to 1 (c), shows a reconfigurable microwave device according to the invention, which has been tested experimentally, FIG. 1 (a) more precisely representing the device without its means. for deforming the diaphragm, Fig. 1 (b) showing the device with its means for deforming the diaphragm and Fig. 1 (c) being a photograph of the test stand;

FIG. 2 represents various intermediate structures obtained during the fabrication process of the reconfigurable microwave device represented in FIG. 1

FIG. 3 represents the evolution of the resonance frequency of the reconfigurable microwave device of FIG. 1, as a function of the distance H between the two electrical conducting elements of the device;

FIG. 4 represents a reconfigurable microwave device according to the invention, whose performances have been determined by numerical simulation;

FIG. 5 shows the evolution of the resonance frequency of the reconfigurable microwave device of FIG. 4, as a function of the distance H between the two electrical conducting elements of the device;

FIG. 6 represents another reconfigurable microwave device according to the invention, namely a phase-shifter whose performance has been determined by digital simulation; FIG. 7 represents another reconfigurable microwave device according to the invention, namely a cavity based on frequency-selective surfaces;

FIG. 8 represents another reconfigurable microwave device according to the invention, namely an array of reflectors;

- Figure 9 shows another reconfigurable microwave device according to the invention, namely a phased array of antennas;

- Figure 10 shows another reconfigurable microwave device according to the invention, namely a frequency filter;

FIG. 11, which comprises FIGS. 11 (a) and 11 (b), shows a reconfigurable microwave device according to the invention, in which the energy supply is carried out by a coplanar waveguide, respectively according to FIG. a sectional view and a partial top view;

- Figure 12 shows another reconfigurable microwave device according to the invention, wherein there is provided an electromagnetic waveguide;

FIG. 13 represents a reconfigurable microwave device according to the invention, in which the means for deforming the membrane is an active means of the peristaltic micropump type;

FIG. 14, which comprises FIGS. 14 (a) to 14 (f), represents various intermediate structures obtained during the fabrication process of the reconfigurable microwave device shown in FIG. 13;

FIG. 15 comprises FIGS. 15 (a) and 15 (b), which respectively represent an alternative embodiment of a means having a magnetic function such as a permanent magnet and an electromagnetic type active medium, such as a coil, to deform the membrane of the device;

FIG. 16, which comprises FIGS. 16 (a) to 16 (f), represents various intermediate structures obtained during the course of method of manufacturing the reconfigurable microwave device shown in Fig. 15 (a).

Whatever the embodiment envisaged, a reconfigurable microwave device 1 according to the invention comprises a mechanical support 2 for at least one elastically deformable membrane 3, a first electrical conductor 4 disposed on the membrane 3, at least one dielectric element 9, 9 ', 31, 32, a second electrical conductor 5, 21 electrically isolated from the first electrical conductor 4 and a means 6 for deforming the membrane 3.

The means 6 is generally a means for actively controlling the deformation of the membrane 3.

The second electrical conductor 5, 21 is generally disposed below the dielectric element 9, 9 '. It is understood that the dielectric element 9, 9 'then makes it possible to electrically isolate the second electrical conductor 5, 21 of the first electrical conductor 4.

In addition, the membrane 3 has an elastic modulus (Young's modulus) less than or equal to 500 MPa, for example between 0.1 MPa and 500 MPa. Preferably, the elastic modulus of the membrane 3 is between 0.1 MPa and 300 MPa, or between 0.1 MPa and 200 MPa, and more preferably between 0.1 MPa and 150 MPa, or even between 0.1 MPa and 10 ^'. 0MPa.

The membrane 3 can be made from a single material or several materials, associated or likely to be in the form of alloys. The membrane 3 may also be made of a textured or micro-machined material. These materials may have isotropic or anisotropic properties.

The elastic modulus is generally defined for an isotropic material. It is conceivable to define an equivalent elastic modulus for anisotropic materials, which it is understood that it could be evaluated by a method similar to that of determining the elastic modulus of an isotropic material. However, throughout the following description, an elastic modulus may relate to an isotropic or anisotropic material.

In all cases, the elastic modulus of the membrane 3 is in accordance with the values mentioned above.

It can be determined by a conventional tensile test. The determination of the elastic modulus then takes place in the zone of linear deformation of the example material, the elastic modulus can be determined by the relation

Given the mechanical properties of the membrane, it can be described as ultrasouple. It turns out to have a much greater flexibility than existing membranes, a solid material type metal or polyimide (Kapton, for example).

An example of a material that may be suitable in the context of the invention is a silicone polymer such as polydimethylsiloxane (PDMS). Another example of a material that may be suitable is an elastomer.

To fix the ideas, it should be noted that the thickness of the membrane 3 can range from micron to a few millimeters. Furthermore, the membrane 3 may have a rectangular, square or other shape, its total surface being related to the frequency at which the reconfigurable microwave device 1 is supposed to work. These data remain related to the intended application.

The means 6 for deforming the membrane 3 is adapted to exert a deformation force on the membrane 3, the value of which can make it possible to exploit to the maximum the deformation properties of this membrane 3.

For example, the means 6 is capable of modifying the distance H between the two electrical conductors 4, 5 to at least 100%.

The means 6 for deforming the membrane 3 may furthermore modify the distance H between the two electrical conductors 4, 5 up to less than 150%, 300%, 500%, 600%, 700%, 800%, 900% or at least 1000%.

To ensure this function, the means 6 for deforming the membrane 3 can be chosen from an electromagnetic, fluidic, magnetoelastic, piezoelectric, electrostrictive, thermal, electrorheological, magnetorheological means, based on a thermal shape memory alloy or a magnetic shape memory alloy.

A first example of a reconfigurable microwave device according to the invention is described below with reference to FIG.

FIG. 1 represents a reconfigurable microwave antenna of microstrip type, according to the invention, which has been experimentally tested. FIG. 1 (a) is a diagram of this device without the actuating means 6, in this case fluidic and FIG. 1 (b) the same device with the actuating means 6. FIG. 1 (c) is as for it a photograph of the test bench used and on which one distinguishes the deformed membrane 3 on which is located the radiating element 7 of the antenna and its ribbon 8 of feeding.

The deformable membrane 3 is made of polydimethylsiloxane (also known by the acronym PDMS). This material can be described as ultra-soft compared to existing membranes made for example of metal or polyimide (Kapton). Indeed, the PDMS has in particular a very weak elastic modulus, of the order of MPa.

The membrane 3 has a thickness of 20μιη.

The mechanical support 2 is also made of PDMS with a thickness of 200 m. This support is also disposed at the periphery of the deformable membrane 3, so that a volume of air 9 '(dielectric) is released under the membrane 3.

The first electrical conductor 4, disposed on the upper face of the membrane 3, comprises a radiating element 7 ("patch") The radiating element 7 has a square shape, side L. In the case in point, the first electrical conductor 4 is gold.

The second electrical conductor 5 forms a ground plane of the antenna, in this case copper. It is disposed under the mechanical support 2. The electrical insulation between the two electrical conductors 4, 5 is therefore via the mechanical support 2 PDMS. Part of this plane of mass 5 therefore extends under the volume of air.

The distance between the two electrical conductors 4, 5 is denoted H.

The mechanical support 2 and the ground plane 5 together form a cavity filled with air. An orifice 12 is made in the ground plane 5 for blowing air into it and ensuring the deformation of the membrane 3.

The fluidic means 6 used in this experiment is a system consisting of a syringe pump 6a, a sealed cavity 6c (non-deformable) disposed under the second electrical conductor 5 forming a ground plane and a fluidic conduit 6b connecting the syringe driver to the sealed cavity 6c. The actuation of the syringe driver 6a makes it possible to inject or withdraw air into the cavity in order to deform the membrane 3.

The amount of air finally introduced into the cavity located between the membrane 3 and the second electrical conductor 5, in combination with the ultrasonic diaphragm finally makes it possible to reach unexpected performances (in particular on the agility of the antenna), as this will be explained in more detail below in support of Figure 3.

The resonance frequency F _res of such an antenna is provided by the relation:

where: it is the celerity of the light in the void, L _e , the effective length of the antenna determined by the relation: L _e = L + 2AL with L the length of the radiating element 7 and, AL the overflow of the electromagnetic field between the two electrical conductors 4, 5, and

ε _β , the effective (relative) permittivity of the antenna between the two electrical conductors 4, 5. Under the action of the fluidic means 6, the distance between the electrical conductors 4,5 varies and consequently the overflow of the AL field, the effective length L _e and the effective permittivity s _e vary. Consequently, a variation of the resonance frequency of the antenna F _res is obtained.

A method for producing this reconfigurable microstrip microwave antenna is shown in FIG.

A sacrificial layer of molybdenum is first deposited on a silicon substrate, FIG. 2 (a).

A gold layer of a few tens of nm is made by evaporation then patterned by a process called "lift-off", using a resin as a mask, Figure 2 (b).

A resin mold is then prepared by photolithography. Gold is deposited by electrolysis in this mold, on the previously deposited gold pattern, in order to form a gold layer of thickness close to the pm, this layer being intended to form the first electrical conductor 4 of FIG. Then, a titanium layer of about ten nm thick is deposited by sputtering or evaporation, and then deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition) according to the English terminology meaning plasma-assisted chemical vapor deposition. ) a layer of Si0 ₂ , a few tens of nm thick. The structure shown in FIG. 2 (c) is then obtained.

Then, the Ti / SiO ₂ bilayer is patterned by a "lift-off" process, Figure 2 (d).

PDMS is spin-coated on the Ti / SiO ₂ bilayer, this bilayer serving as a means of hooking between the PDMS and gold. Then, a PDMS frame, having a cavity, is glued after activation to ultraviolet or oxygen plasma on the PDMS previously coated. The resulting structure is shown in Figure 2 (e).

Finally, the sacrificial layer of molybdenum is removed, for example by etching with hydrogen peroxide, and the silicon substrate removed. The structure thus released is transferred to a copper layer intended to form the second electrical conductor 5 (ground plane of the antenna), FIG. 2 (f).

The fluidic means 6 is then added in the following manner to the structure of Figure 2 (f). A sealed cavity, fluidly connected to the structure of Figure 2 (f) via one or more holes in the ground plane 5, is secured to this structure. Then, a syringe pump is fluidly connected to this sealed cavity.

This production method is more fully detailed in "Millimeter-wave patch array antenna on ultra flexible micromachined Polydimethylsiloxane substrate", S. Hage-Ali et al., IEEE Antennas and Propagation Society International Symposium, 2009 or "Polydimethylsiloxane membranes for millimeter-wave planar ultra flexible antennas ", Tiercelin & al., J. Micromech. And Microeng, vol. 16 (1 1), pp. 2389-2395, 2006.

FIG. 3 represents the evolution of the resonance frequency F _res of the antenna of FIG. 1, as a function of the distance H between the two electrical conducting elements 4, 5. The curve thus obtained is denoted "experiment".

In the absence of any action of the fluidic means 6, the distance H between the two electrical conductors 4, 5 is 200pm.

By injecting air into the cavity, the distance H between the two electrical conductors 4, 5 could evolve between 200 m and 575 μηι (factor 2.875), the resonant frequency of the antenna passing from F _res = 55.5 GHz to F _res = 51 GHz, an absolute agility of 4.5GHz (= 55.5-51 GHz).

For this purpose, the volume of air injected by the fluidic means 6 is a few tens of pl. In the case in point, about 80μΙ of air has been injected to change the distance H from 200μιη to 575μιτι. It is possible to inject a larger volume of air, for example up to 300 μΙ to obtain a value of H of the order of 2 mm, but at the cost of a degradation of the performance of the antenna. The variation of the height H between the two electrical conductors can thus reach 900% (= (2mm-200pm) / 200pm ^* 100%)

The reconfigurable microwave antenna tested has therefore shown that it was able to provide high agility over a frequency band extending over 4.5GHz. Existing mechanical reconfiguration techniques provide much lower agility.

Moreover, this agility is obtained in the millimetric domain (resonance frequency greater than 30 GHz), which is not the case of existing microwave antennas.

It should also be noted that over this entire frequency range, the antenna retains a reflection coefficient of less than -10 dB, bandwidth and gain (> 4 dB) remaining consistent for real use.

FIG. 3 also shows the same evolutions with an analytical model described by Balanis in CA Balanis, Antenna Theory and Design, Wiley, 1982, and numerical simulations carried out with commercial software, namely CST Microwave Studio and Ansoft HFSS. .

This makes it possible in particular to validate the HFSS digital model with respect to the experimental tests carried out.

As a result, a reconfigurable microwave antenna conforming to that of FIG. 1, in which a dielectric layer 9 made of alumina (Al ₂ O ₃ ) was however added between the ground plane 5 and the mechanical support 2, was simulated. The cavity filled with air 9 'is thus sealed in its lower part by the layer of alumina 9. This structure is represented in FIG.

Alumina has a high electrical permittivity (6 _a i _U mine =

9.8). In this case, the thickness of the alumina layer was set at 150μηη.

The results of the simulation with the Ansoft HFSS digital model on the structure represented in FIG. 4 are given in FIG. 5. This FIG. 5 represents the evolution of the resonance frequency F _res of the antenna as a function of the distance H between the two electrical conductors 4, 5.

By changing the distance H between the two electrical conductors 4, 5 between 185μηι and δΟΌμιη, the resonance frequency of the antenna goes from F _res = 44GHz to F _res = 65GHz, an absolute agility of 21 GHz, which corresponds to at a relative agility of 38.5%.

Beyond a height H of δθθμιη, the resonant frequency changes only slightly. Indeed, when the distance H between the two electrical conductors 4, 5 increases, the overflow of the field AL increases (and therefore the effective length L _e of the antenna), which tends to decrease the resonance frequency of the 'antenna. On the other hand, when H increases, the effective permittivity decreases which tends to increase the resonance frequency of the antenna. The effect related to the effective permittivity is greater when a solid dielectric 9 such as alumina is used. The slight evolution thus observed is related to the compensation of the two effects mentioned above.

In this frequency range, the antenna retains a reflection coefficient of less than -10 dB, the bandwidth and gain remaining consistent for actual use.

The performance of this reconfigurable microwave device therefore goes well beyond the current performance of known reconfigurable antennas.

Still thanks to the Ansoft HFSS digital model, a reconfigurable microwave device forming a phase shifter was also simulated. The structure of this reconfigurable microwave phase shifter is shown in FIG.

This structure is consistent with that of the antenna shown in FIG. 4, with the exception of the first electrical conductor 4. Indeed, in the present case, the first electrical conductor 4 is not formed by a radiating element powered by a ribbon but by a microstrip line 71.

This phase shifter was simulated numerically with the Ansoft HFSS software. For this, a microstrip line of 1cm long over 390μηη wide is provided. The other characteristics (thickness of the different elements ...) are identical to the structure of FIG.

The results of the simulation are given in Table 1 below, at a resonance frequency of 60 GHz. The position H = 350 μm (150 μm of alumina + 180 μm of air + 20 μm for the PDMS membrane) corresponds to a position of the membrane for which the means for deforming the membrane exerts no force on the membrane.

These results show a total phase shift of 350 ° with respect to the reference position, which corresponds to a total displacement of 150μπη (= 350μηη - 200μηι) of the deformable membrane 3. The transmission losses and the reflection coefficient remain good over this range of deformation of the membrane 3. Moreover, the merit factor of this phase shifter is 437 dB (350 0.8dB), which is significantly higher than the merit factors obtained with existing reconfigurable microwave phase shifters.

FIGS. 7 to 10 represent four other types of reconfigurable microwave devices according to the invention, namely respectively a cavity based on frequency selective surfaces, a reflector grating, a phased array and a filter.

It will be understood that all the structures represented in these FIGS. 7 to 10 comprise a mechanical support 2 of an elastically deformable membrane 3, a first electrical conductor 4 disposed on the membrane 3, a second electrical conductor 5 electrically isolated from the first electrical conductor 4 and means for deforming the membrane (not shown).

The membrane 3 used in these structures has mechanical characteristics similar to those used in the reconfigurable hyperfrequency device (antenna) tested experimentally (FIG. 1). In particular, the membrane 3 may be made of a silicone polymer such as polydimethylsiloxane.

More precisely, a frequency selective surface base cavity shown in FIG. 7 may comprise two deformable membranes 31, 32 arranged on either side of the mechanical support 2.

The first electrical conductor 4, disposed on the upper membrane 31, can then be formed of an inductive grid, for example continuous or discontinuous capacitive.

The second electrical conductor 5 may be in the form of a grid, continuous or discontinuous, or more simply a reflective plane and is arranged on the lower membrane 32. With respect to the structure shown in FIG. 1, a lower membrane is therefore inserted between the second electrical conductor 5 and the mechanical support 2. The electrical insulation between the two conductors 4, 5 is effected in particular by the membranes 31. , 32 and possibly by the mechanical support 2 itself.

With this type of device, the excitation of the cavity formed by the conductors 4 and 5 can be effected by a plane wave, represented by the arrows "E _inC idente" or by direct excitation with the aid of a waveguide. wave or a printed line.

A reconfigurable microwave reflective grating is shown in FIG.

Such a network may comprise n deformable membranes on each of which is a reflector.

The membranes are supported by the mechanical support 2, which defines a cavity under each deformable membrane 3. This cavity is generally filled with a dielectric fluid 9 'such as air, closed in its lower part by the second electrical conductor 5, or, as shown in FIG. 8, by a layer of solid dielectric such as a layer of alumina disposed between the mechanical support 2 and the second electrical conductor 5.

A means for deforming the membrane 3 can be associated with each of the n membranes individually. It is thus possible to introduce a phase shift between the different beams reflected by each of the n reflectors. This then makes it possible to make beam synthesis. The control of the deformation of each reflector of the network makes it possible to control the direction of reflection of the network.

With this type of device, the excitation of the structure is effected by an electromagnetic wave, represented by the arrows "Evidente"_> this excitation involving an interaction between the two electrical conductors 4, 5. A reconfigurable microwave phased array is shown in FIG.

In this structure, the first electrical conductor 4 may comprise a supply ribbon 8, divided into n parallel parallel microstrip lines each comprising a phase-shifter 10 followed by a radiating element 7.

For each microstrip line, the phase shifter 10 and the radiating element 7 are each arranged on a membrane 3, 3 '. Each deformable membrane 3, 3 'is held by the mechanical support 2 whose shape makes it possible to define a cavity, generally filled with a dielectric fluid such as air, closed in its lower part by the second electrical conductor 5 (plane of mass), or, as shown in FIG. 9, by a solid dielectric layer such as a layer of alumina disposed between the mechanical support 2 and the second electrical conductor 5.

With this structure, it is thus possible to emit waves of the same frequency, but out of phase to perform the functions of misalignment or beam synthesis. Each phase-shifter 10 and / or each radiating element 7 can be controlled by a dedicated means of deformation of the membrane 3, 3 'on which it is arranged.

A reconfigurable microwave filter is shown in FIG.

This structure is the same as that described in support of Figure 4, with the exception of the radiating element and its supply ribbon which are replaced by two microstrips lines facing each other, and likely, as such , to be coupled to each other. By deforming the membrane 3, the coupling between the microstrips is modified, which makes it possible to modify the electrical characteristics of the filter.

It will be noted that the reconfigurable hyperfrequency devices described in support of FIGS. 1, 4, 6, 9 and 10 implement energy transmission technologies based on guided propagation, for example a microstrip line connected to a microwave source. By Moreover, the reconfigurable microwave devices described in support of Figures 7 and 8 implement, in turn, an electromagnetic wave in free space for interacting with the structure.

However, other transmission technologies could quite well be used within the scope of the invention.

By way of nonlimiting example, another possibility is the use of a coplanar waveguide (CPW for CoPlanar Waveguide according to the English terminology) represented in FIG. 11. In this case, the first electrical conductor 4 is constituted by a central ribbon and the second electrical conductor 5 of two-half planes, acting as a ground plane, arranged on either side of the central ribbon 4. comprises in this case, that the membrane 3 can electrically isolate the two electrical conductors 4, 5 from one another.

A third electrical conductor 51, optional, can be provided. The presence of this third electrical conductor 51 constitutes a variant (GBCPW for Ground Backed CoPlanar Waveguide according to the English terminology) of the coplanar technology, which is precisely represented in FIG. 11.

By actuating the means 6 to deform the membrane 3, the couplings between the electrical conductors 4, 5 are modified so as to reconfigure the microwave device. More precisely, when the means 6 for deforming the membrane is actuated, this modifies the distance H between the central ribbon 4 and any one of the two half-planes forming the second electrical conductor 5, which modifies the electrical characteristics of the microwave device. , including the equivalent permittivity.

Another variant, using a waveguide, is shown in FIG.

According to this variant, the first electrical conductor 4 (capacitive load) is disposed on the deformable membrane 3. The deformable membrane 3 rests on a mechanical support 2 via a solid dielectric layer 9, for example alumina. A volume of fluid dielectric 9 'such that the air is provided between the dielectric layer 9 and the deformable membrane 3.

In order to form a waveguide, the mechanical support 2 extends below the solid dielectric layer 9, substantially perpendicular to it. Furthermore, it then has an inner face 21 covered with an electrically conductive material for guiding the wave.

Alternatively, the entire mechanical support 2 is made of an electrically conductive material, for example metal. Under these conditions, the inner face of the mechanical support 2 is also made with the same electrically conductive material.

In these two cases, the inner face 21 of the mechanical support 2 thus forms the second electrical conductor.

It is then possible to define a distance H equivalent to those used previously, between the first electrical conductor 4 and the inner face 21 of the mechanical support 2 having a function similar to that of the second electrical conductor described in the preceding examples.

The distance H between the inner face 21 (second electrical conductor) and the first electrical conductor 4 is shown in FIG. 12. It can be more precisely defined as being the distance separating the first electrical conductor 4 from the plane perpendicular to the upper face 22 of the support 2, this upper face 22 being the face closest to the first electrical conductor 4.

Again, the means 6 for deforming the membrane 3 is capable of modifying this distance H to at least 100%. The means 6 for deforming the membrane 3 can moreover modify the distance H between the two electrical conductors 4, 5 up to at least 150%, 300%, 500%, 600%, 700%, 800%, 900% or even up to at least 1000%.

In all the examples presented above, the dielectric fluid 9 'which is generally air could also be a liquid or a colloidal solution. On the other hand, the dielectric element 9 may, when it is used, be a multiphasic material, such as a foam. More generally, the solid dielectric element 9 may be chosen from alumina, glasses, teflon glasses, quartz, teflon, polyimides, a liquid crystal polymer, a foam or a microwave substrate.

It should also be noted that a means for controlling the state of deformation of the membrane 3 may be disposed thereon. It may for example be a piezo-resistive gauge.

The reconfigurable hyperfrequency device experimentally tested (FIG. 1) comprises a fluidic means for deforming the membrane, in this case a syringe pump, an orifice being provided in the device for injecting a dielectric fluid such as air under the membrane 3.

It is quite possible to use other fluidic means such as a peristaltic micropump, or a pump or micropump diaphragm, paddle or piston.

A microwave device whose fluidic means 6 is a peristaltic pump is shown in FIG. 13. This peristaltic micropump 6 can inject or take up air in the cavity situated between the membrane 3 and the second electrical conductor 5, via of an orifice 12.

The fluidic means 6 is, in this case, formed by three cavities 61, 62, 63 in series. These cavities are connected to one another by communication orifices (not referenced) for a dielectric fluid, namely air in these experiments. The air enters the fluidic medium 6 through an inlet port E.

In addition, the upper part of each of these cavities 61, 62, 63 comprises an ultrasonic diaphragm 64, 65, 66 similar to the membrane 3 on which the first electrical conductor 4 is disposed. These membranes are in this case made of PDMS.

A permanent magnet 67, 68, 69 is inserted into each of the membranes 64, 65, 66 respectively. An electromagnetic coil 670, 680, 690 is housed in a support 22, vis-à-vis, respectively, of a permanent magnet 67, 68, 69.

Permanent magnets 67, 68, 69 may for example be made of NdFeB (Neodynium-Iron-Boron) or SmCo (Samarium-Cobalt). Typically, they are characterized by remanence of the order of Tesla.

The operation of such a peristaltic pump 6 is as follows.

When an electromagnetic coil 670 is activated, the permanent magnet located opposite is attracted, which deforms the corresponding ultrouple membrane 64 so as to plug the corresponding cavity 61. In FIG. 13, the cavity is shown. 61 closed, the other two 62, 63 being open.

This peristaltic pump can provide flow rates up to a few tens of μΙ / min, generally less than 100pl / min. The power of such a pump is of the order of a few hundred milliWatts.

Thus, after introducing air into the first cavity 61, it is closed, which sends air into the second cavity 62. The operation is performed again with the other two cavities 62, 63 so that the air is brought gradually into the cavity located between the membrane 3 and the second electrical conductor 5.

It is understood that other opening / closing means of the cavities 61, 62, 63 could be envisaged, in particular other magnetic means having an identical function.

FIG. 14 represents various structures obtained in the manufacturing method of the reconfigurable microwave device of FIG. 13.

Steps (a) to (d) shown in Fig. 14 are the same as steps (a) to (d) shown in Fig. 2.

Then, PDMS is spin coated on the Ti / SiO ₂ bilayer, with several magnets. The bilayer serves as a means of hanging between PDMS and gold. Then, a PDMS frame, having several cavities (in this case four) interconnected by orifices, is glued after activation with ultraviolet or oxygen plasma on the PDMS previously coated. The resulting structure is shown in Fig. 14 (e).

Finally, the sacrificial layer of molybdenum is removed, for example by etching with hydrogen peroxide, and the silicon substrate removed. The structure thus released is transferred to a copper layer intended to form the second electrical conductor 5. An additional support comprising several magnetic means (in this case coils) is secured to the structure. Finally, the structure shown in FIG. 14 (f) is obtained.

Moreover, it is quite possible to implement a means 6 for deforming the electromagnetic membrane 3 and having the same function as the fluidic means mentioned above.

For example, the first electrical conductor 4 may also have a magnetic function, the means 6 for deforming the membrane 3 is a means for applying a controllable magnetic field 11 intended to interact with the first electrical conductor 4.

The first electrical conductor 4 may be a permanent magnet or a ferromagnetic material. On the other hand, the means 11 for applying a magnetic field may be a coil, a conductor traversed by an electric current, a moving magnet or a magnetoelectric compound.

In this case, the first electrical conductor 4 can be made from one of the following elements: SmCo (Samarium-Cobalt), AINiCo (Aluminum-Nicket-Cobalt), FePt (Iron-Platinum), NdFeB (Neodynium-Iron -Bore), Fe-Ni alloys, Fe-Ni-Mo, Ni, Co, Iron alloys, Cobalt alloys, Nickel alloys.

FIGS. 15 (a) and 15 (b) show two variants, provided by way of example, of implantation within the microwave device reconfigurable, the first electrical conductor 4 having a permanent magnet function, and the coil 11.

In the case in point, the reconfigurable microwave device is shown with two dielectrics between the two conductors 4, 5, namely a dielectric fluid such as air ("dielectric No. 1") in contact with the membrane 3, the below which is disposed a solid dielectric 9 ("dielectric No. 2"), for example alumina or made of a multiphase material such as a foam.

In FIG. 15 (a), the deformable membrane 3 is located from the upper part of the mechanical support 2 and extends towards the outside of the reconfigurable microwave device, the electromagnetic coil 11 being in turn housed in a formed cavity under the second electrical conductor 5.

In Fig. 15 (b), the position of the diaphragm and the first electrical conductor disposed thereon on the one hand and the position of the second dielectric member disposed on the solid dielectric member 9 are reversed. The deformable membrane 3 thus extends inside the reconfigurable microwave device, the electromagnetic coil 11 being housed in a cavity formed under the membrane 3.

A method of manufacturing the reconfigurable microwave device 1 shown in Fig. 15 (a) is provided in Fig. 16, the first electrical conductor 4 being made of a SmCo alloy.

A sacrificial layer of molybdenum is first deposited on a silicon substrate. Then, a positive resin is patterned by photolithography. A Cr / SmCo / Cr trilayer is then deposited by sputtering and then patterned by a lift-off process. The structure thus obtained is shown in Figure 16 (a). Typically, the layers of chromium have a thickness of about 100 nm, and the SmCo layer has a thickness of about 2 m. This structure is then annealed at a temperature of 550 ° C under vacuum. The resulting structure is shown in Figure 16 (b).

Another positive resin is then deposited by photolithography and a Ti / SiO ₂ bilayer is deposited. The deposition of the Ti layer is carried out by spraying to a thickness of about 50 nm. It is followed by the deposition of the Si0 ₂ layer, over a thickness of 50nm also, by PECVD. A "lift-off" pattern is then performed. The structure then obtained is shown in FIG. 16 (c).

Then, PDMS is spin-coated on the Ti / SiO ₂ bilayer, this bilayer serving as a hanging medium for the PDMS. Then, a PDMS frame, having a cavity, is stuck after activation with ultraviolet or oxygen plasma on the previously coated PDMS. The resulting structure is shown in Figure 16 (d).

The sacrificial layer of molybdenum is removed, for example by etching with hydrogen peroxide, and the silicon substrate removed. The structure thus released is transferred to a copper layer provided with a solid dielectric 9, for example alumina, this copper layer being intended to form the second electrical conductor 5, Figure 16 (e).

Finally, an electromagnetic coil 11 and an additional support element are added to the structure of FIG. 16 (e) in order to produce the electromagnetic means for deforming the membrane 3.

The structure shown in Fig. 16 (f) corresponds to that which is thus shown in Fig. 15 (a).

Alternatively, the first electrical conductor 4 may comprise an electrical conduct itself and a magnetic element separate from said conductor.

In this case, the magnetic element can be chosen from NdFeB (Neodymium-Iron-Boron), ferrites, rare earths or alloys and iron compounds. The structures shown in Figures 15 (a) and 15 (b) may also apply here. The process illustrated in FIG. Correspondence with the device of Figure 1 (a) can be used, step (a) then consisting in providing the deposition of a magnetic element and the actual electrical conductor.

The magnetic element may be a permanent magnet or a ferromagnetic material. Furthermore, the means 1 1 for applying a magnetic field may be a coil, a conductor traversed by an electric current, a movable magnet or a magnetoelectric compound.

As a variant, the deformable membrane 3 may have a magnetic function, the means 6 for deforming the membrane 3 being a means 11 for applying a controllable magnetic field intended to interact with the membrane 3.

The magnetic function provided by the membrane 3 can be that of a permanent magnet or a ferromagnetic material. Again, the means 1 for applying a magnetic field may be a coil, a conductor traversed by an electric current, a movable magnet or a magnetoelectric compound.

The deformable membrane 3 may comprise a magnetic powder. For example, the membrane 3 may be a composite material comprising 50% PDMS and 50% magnetic powder. The magnetic powder may be ferrite powder. If for example it is the ferrite powder referenced HM 410, one can obtain a membrane 3 having a permanent magnet function remanence of 0.03 Tesla.

Alternatively, the magnetic powder may be selected from a powder of NdFeB, FePt, SmCo, Fe, Fe-Ni, Fe-Ni-Mo, Ni, Co, Fe alloys, Ni alloys, Co. alloys.

Again, the structures shown in Figs. 15 (a) and 15 (b) can be found here, however, with the modifications mentioned above. Moreover, the method illustrated in FIG. 2 can be used with a membrane comprising a magnetic powder, and the addition of a final step corresponding to the step shown in FIG. 16 (f). A fluidic or electromagnetic means 6 for deforming the membrane 3 as described above can be used indifferently with any of the structures described in support of FIGS. 4 and 6 to 12.

Alternatively, a means 6 for deforming the membrane

3 providing the same function may be selected from a magnetoelastic, piezoelectric, electrostrictive, thermal, electrorheological, magnetorheological means, based on a thermal shape memory alloy or magnetic shape memory alloy. As mentioned above, it is therefore understood that these alternative means are adapted to exert a deformation force on the membrane 3 whose value is compatible with the deformation properties of this membrane 3, so as to make the best use of the deformation capabilities of the membrane 3.

Finally, it should be noted that the structures described in support of Figures 1, 4 and 6 to 12 represent only a basic structure. Indeed, if a device according to the invention can be made from this basic structure, combined with a fluidic or electromagnetic means for deforming the membrane 3, it is possible to envisage a microwave device according to the invention provided with several structures associated bases.

Claims

1. Device (1) reconfigurable microwave characterized in that it comprises:

a mechanical support (2) of at least one elastically deformable membrane (3), said membrane (3) having an elastic modulus of less than or equal to 500 MPa;

at least one first electrical conductor (4) disposed on the membrane;

at least one dielectric element (9, 9 ', 31, 32);

at least one second conductor (5, 21) electrically isolated from the first electrical conductor (4); and

means (6) for deforming the membrane (3), said means (6) being adapted to exert a deformation force capable of modifying the distance H between the first electrical conductor (4) and the second electrical conductor (5, 21 ) up to at least 100%.

2. reconfigurable microwave device according to claim 1, wherein the means (6) for deforming the membrane is selected from electromagnetic, fluidic, magnetoelastic, piezoelectric, electrostrictive, thermal, electrorheological, magnetorheological means, based on an alloy with thermal shape memory or magnetic shape memory alloy.

3. Reconfigurable microwave device according to one of the preceding claims, wherein the membrane (3) is a silicone polymer, for example polydimethylsiloxane (PDMS), or an elastomer.

4. Reconfigurable microwave device according to one of the preceding claims, wherein the membrane (3) is textured or micro-structured.

Reconfigurable microwave device according to one of the preceding claims, wherein the operating frequency is greater than or equal to 30GHz.

Reconfigurable microwave device according to one of the preceding claims, wherein the mechanical support (2) is made of the same material as the membrane.

Reconfigurable microwave device according to one of the preceding claims, wherein the first conductor (4) electric also has a magnetic function and the means (6) for deforming the membrane (3) is a means (11) for applying a field controllable magnetic device for interacting with the first (4) electrical conductor.

8. Reconfigurable microwave device according to the preceding claim, wherein the first conductor (4) is a permanent magnet or a ferromagnetic material.

9. Reconfigurable microwave device according to the preceding claim, wherein the first electrical conductor (4) is made from one of the following: SmCo, AINiCo, FePt, NdFeB, a Fe-Ni alloy, a Fe-Ni alloy -Mo or other Iron alloys.

Reconfigurable microwave device according to claim 7, wherein the first electrical conductor (4) comprises an electrical conduct itself and a magnetic element separate from said conductor and the means (6) for deforming the membrane (3) is a means (11). ) for applying a controllable magnetic field for interacting with the magnetic element associated with the electrical conductor (4).

11. Reconfigurable microwave device according to the preceding claim, wherein the magnetic element is selected from NdFeB, ferrites, compounds and alloys of iron or rare earth compounds.

12. reconfigurable microwave device according to one of claims 1 to 6, wherein the deformable membrane (3) also has a magnetic function and the means (6) for deforming the membrane is a means (1) for applying a controllable magnetic field likely to interact with the membrane.

Reconfigurable microwave device according to the preceding claim, wherein the deformable membrane (3) comprises a magnetic powder, for example a ferrite powder, NdFeB, FePt, SmCo, Fe, Fe-Ni, Fe-Ni-Mo, Ni, Co, or a powder of iron alloys, nickel alloys or cobalt alloys.

Reconfigurable microwave device according to one of claims 7 to 13, wherein the means (11) for applying a controllable magnetic field is a coil, a conductor traversed by an electric current, a movable magnet or a magnetoelectric element.

15. reconfigurable microwave device according to one of claims 1 to 6, wherein the means (6) for deforming the membrane is a micropump, for example peristaltic, capable of injecting a dielectric fluid, for example air, liquids or colloidal solutions, between the membrane and its mechanical support.

16. Reconfigurable microwave device according to one of the preceding claims, wherein there is provided at least two dielectric elements.

(9, 9 '), the first dielectric element (9) being a fluid and the second dielectric element (9) being a solid or a multiphasic material such as foam.

Reconfigurable microwave device according to the preceding claim, wherein the second dielectric element (9) is chosen from: alumina, glasses, teflon glasses, quartz, teflon, polyimides, a liquid crystal polymer, a foam or a microwave substrate.

18. Reconfigurable microwave device according to one of the preceding claims, wherein there is provided a means for controlling the state of deformation of the membrane (3) disposed thereon, for example a piezoresistive gauge.

19. Reconfigurable microwave device according to one of the preceding claims having one of the following functions: antenna, phase shifter, cavity based frequency selective surfaces, phased array, reflector array, filter.