MICROWAVE RADIATION HEAT TREATMENT DEVICE

Abstract

DEVICE FOR HEAT TREATMENT BY MICROWAVE RADIATION The present invention relates to a device for treating a product comprising: An enclosure (1) intended to contain the product to be treated, A waveguide (3) arranged between the enclosure (1) and a generator (4) configured to produce electromagnetic waves, An impedance matching unit (5) configured to vary an impedance in the waveguide (3) in order to make it correspond to the input impedance of the enclosure (1), A stirring unit (7) for stirring the product contained in the enclosure (1), Characterized in that the device further comprises a wave trapping unit (6). Abstract figure: Figure 2

Description

Title of the invention: DEVICE FOR HEAT TREATMENT BY MICROWAVE RADIATION FIELD OF THE INVENTION

[0001] The present invention relates to the general technical field of devices for treating plant biomass of any plant species known to those skilled in the art, for example parts of vines.

[0002] The biomass to be treated may be dry or wet, and its treatment may be carried out in the presence (or not) of an aqueous solvent.

[0003] Such a treatment device allows the extraction of metabolites from plant biomass, said metabolites being able to be polyphenols or any other type of secondary metabolites known to those skilled in the art.

[0004] The metabolites thus extracted can be used in different fields of application, such as biocontrol applications or cosmetic applications.

[0005] In the following, the device according to the invention will be described with reference to the treatment of a dry plant biomass rich in polyphenols (such as parts of vines) in the presence of an aqueous solvent, it being understood by those skilled in the art that the device according to the invention can be used for the treatment of any type of plant biomass - dry or wet - in the presence or absence of one (or more) aqueous solvent(s). STATE OF THE ART 1. Presentation

[0006] Plant biomass extracts rich in polyphenols are known to those skilled in the art.

[0007] Many studies have focused on the extraction of biomass to obtain an extract rich in polyphenols, all presenting several drawbacks with regard to the economic viability of the processes, such as low yields or very long extraction times, or limiting their use post-extraction, and in particular the use of toxic organic solvents.

[0008] Document WO 2018 / 115296 describes a process for preparing a dry plant biomass extract, rich in polyphenols, comprising: - A step of extracting the dry biomass by bringing it into contact with an aqueous solvent, and - A step of recovery of the aqueous phase enriched in polyphenols.

[0009] During the extraction step, the plant biomass / aqueous solvent mixture is treated, at a pressure of between 50 and 950 mbar (5,000 and 95,000 Pa), by applying to the mixture:

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017] - electromagnetic waves with a frequency between 10 MHz and 100 GHz, preferably between 433 MHz and 30 GHz, and even more preferably between 915 MHz and 28 GHz, and - mixing the mixture. The present invention aims to propose a heat treatment device allowing the implementation of the method according to WO 2018 / 115296. In particular, the present invention relates to a device for treating a product for the extraction of a substance of interest, the treatment device being configured to: - Stir the product, and - Apply to the product electromagnetic waves of frequency between 10MHz and 100GHz, preferably between 433MHz and 30GHz, and even more preferably between 915MHz and 28GHz. 2. Problems associated with the use of electromagnetic waves: minimizing electromagnetic leakage levels The use of electromagnetic waves for industrial, scientific and medical applications is subject to compliance with several standards for the protection of people and the protection of communications networks: - Standard EN 50413 for the exposure of people, - The EN 50499 standard for worker exposure, - The EN 55011 standard for the protection of telecommunications networks. The use, on an industrial scale, of electromagnetic waves with a frequency equal to 915 MHz requires in particular compliance with standard NE 55011. This stipulates that the electromagnetic radiation emitted towards the outside, by a device generating electromagnetic waves with a frequency equal to 915 MHz, must be lower than a threshold value of - 40 dB microvolt per meter, at 30 m from said device. This helps to avoid disruptions to telecommunications networks. Any exceeding of this threshold value may be sanctioned, without notice, by the immediate shutdown of the device deemed to be faulty. An aim of the present invention is to propose a device for heat treatment using electromagnetic waves which makes it possible not to exceed the levels of electromagnetic leakage imposed by standard EN 55011. SUMMARY To this end, the invention proposes a device for treating plant biomass, the treatment device comprising: - An enclosure intended to contain the plant biomass to be treated, the enclosure comprising a lower partition, an upper partition and at least one side partition extending between the upper and lower partitions, at least one of the partitions including a through inlet and a hole, - A waveguide connected to the through inlet for the circulation, towards the interior of the enclosure, of incident electromagnetic waves produced by a generator, - An impedance matching unit configured to vary an impedance in the waveguide to match said impedance in the waveguide to an input impedance of the enclosure, - A stirring unit for stirring the plant biomass contained in the enclosure, said stirring unit comprising a shaft extending through the hole and blades mounted on the shaft and extending inside the enclosure, characterized in that the device further comprises a wave trapping unit, said wave trapping unit including at least one wave trap associated with the hole for the passage of the shaft of the stirring unit, said wave trap being configured to form phase-shifted electromagnetic waves from electromagnetic waves reflected by the plant biomass, by modifying the phase of said reflected electromagnetic waves, the phase-shifted electromagnetic waves being in phase opposition with the reflected electromagnetic waves in a plane containing the hole.

[0018] In the context of the present invention, the term "connected to" means a first element directly connected to a second element, or indirectly connected to the second element, in particular by means of a third element arranged between the first and second elements.

[0019] Preferred, but not limiting, aspects of the present invention are as follows: - The wave trap comprises a metal frame curved into a loop, said frame being positioned around the hole for the passage of the shaft of the mixing unit; - The metal frame may extend inside the enclosure so as to surround a portion of the shaft of the brewing unit; - The metal frame comprises an electromagnetic wave entry / exit slot, the dimensions of said frame being determined so that the electromagnetic waves entering the metal frame at the entry / exit slot, exit said metal frame in phase opposition; - The frame is fixed to the enclosure and can include: • An upper section in contact with the partition including the hole for the shaft to pass through, the upper section extending parallel to the partition including the hole, • A lower section parallel to the upper section, • An outer panel between the upper and lower panels, the edges of the upper panel being connected to the edges of the upper and lower panels further from the hole, and • A free section parallel to the external section, the free section including: • A connecting edge connected to the lower panel closest to the hole, • A free edge opposite the connecting edge,

[0020] So that the lower section extends opposite the shaft, at a non-zero distance from said shaft and is in contact neither with the shaft nor with the upper section; - The sum of the widths: • From the upper pan, • From the external side, • From the lower pan and • Free pan

[0021] is equal to a multiple of the wavelength of the reflected waves plus a quarter of the wavelength of the reflected waves; - The thickness of the panels is approximately equal to the thickness of the walls of the waveguide; - The wave trap is made of a non-magnetic conductive material, such as aluminum or stainless steel. DETAILED DESCRIPTION OF THE INVENTION

[0022] An example of a device for processing a product will now be described with reference to the figures. In these different figures, equivalent elements are designated by the same numerical reference. 1. General information

[0023] The treatment device described below allows the preparation of an extract rich in metabolites (polyphenols and / or other secondary metabolite(s)) by extraction of a dry (or wet) biomass with an (or without) aqueous solvent.

[0024] According to the invention, the term “aqueous solvent” means water or an aliphatic alcohol / water mixture, in particular ethanol / water.

[0025] The plant biomass may, for example, be a biomass containing polyphenols, in particular trans-resveratrol, trans-e-viniferin, trans-piceatannol and trans-vitisin. A person skilled in the art is familiar with this biomass originating from plants known to contain these polyphenols, used alone or in mixtures, generally dicotyledonous plants such as vines, tea or even Japanese knotweed, more particularly vines.

[0026] When the biomass is dry, that is to say obtained by drying the aforementioned plants, it can consist of dry parts of plants of the genus Vitis, in particular Vitis vinifera Vitis labrusca, Vitis riparia, Vitis rupestris, Vitis berlandieri, Vitis amurensis, Vitis coignetiae, Vitis vulpina, Vitis acerifolia, Vitis aestivalis, Vitis ro-tundifolia and more particularly Vitis vinifera. According to an advantageous embodiment of the invention, the dry biomass comprises or is made up of vine shoots.

[0027] Alternatively, the biomass may be wet. In this case, the water molecules contained in the biomass may make it possible to avoid the use of aqueous solvent.

[0028] This device allows the implementation of a process for extracting metabolites such as polyphenols.

[0029] This method is characterized by the combination of at least two constraints applied to the plant biomass (dry or wet) in the presence (or not) of an aqueous solvent: i. electromagnetic waves of frequency between 10 MHz and 100 GHz, preferably between 433 MHz and 30 GHz, and even more preferably between 915 MHz and 28 GHz, and ii. mixing, and / or iii. a depression or a pressure of 50 to 950 mbar.

[0030] In the following, the device according to the invention will be described with reference to the treatment of a mixture composed of a dry biomass and an aqueous solvent, it being understood by those skilled in the art that this device can be used with other types of products. 2. Processing device

[0031] With reference to [Fig.l], an example of a treatment device according to the invention is illustrated. The device comprises: - An enclosure 1, - A 3 waveguide, - A 5 impedance matching unit, - A wave trapping unit 6, and - A mixing unit 7.

[0032] As will become apparent below, the presence of a wave trapping unit 6 makes it possible to limit the risks of electromagnetic waves leaking towards the outside of the treatment device while limiting the risk of creating an electric arc.

[0033] The enclosure 1 is intended to be connected to a generator 4 via the waveguide 3, this generator 4 being able to be integrated or dissociated from the processing device.

[0034] The generator 4 is configured for the emission of electromagnetic waves of frequency between 10 MHz and 100 GHz, preferably between 433 MHz and 30 GHz, and even more preferably between 915 MHz and 28 GHz, corresponding to waves in the microwave domain.

[0035] A person skilled in the art will know how to choose the frequency most suited to the implementation of the process, in particular depending on the biomass, to optimize the extraction process. Advantageously, the frequency of the electromagnetic waves ranges from 915 MHz to 2.45 GHz. Advantageously, the frequency of the electromagnetic waves will be chosen according to known industrial devices for generating electromagnetic waves on an industrial scale, in particular electromagnetic wave generators with frequencies below 1500 MHz, more advantageously around 915 MHz.

[0036] A person skilled in the art will also be able to choose the power of the electromagnetic waves best suited to the biomass and the extracts obtained. The power of the electromagnetic waves advantageously ranges from 300 W to 200 kW, more advantageously from 1 to 100 kW. This power will be chosen in particular according to the volume to be treated and the time that will be necessary for the extraction. For example, the power of the electromagnetic waves can be chosen according to the following ratio: for 1 kg of material to be extracted the power of the electromagnetic waves is from 1 to 10 kW, ideally 2 to 6 kW. 2.1 Speaker

[0037] The enclosure 1 makes it possible to define an enclosed space in which it is possible to generate a depression (or an overpressure), that is to say a space in which it is possible to reduce (or increase) the pressure to a value lower (or higher) than atmospheric pressure, in particular to a pressure between 50 and 950 mbar.

[0038] The enclosure 1 is configured to withstand pressures greater than or less than atmospheric pressure. Furthermore, the enclosure 1 is configured to resist corrosion. Finally, the enclosure 1 is configured to withstand temperatures greater than or equal to 200°C.

[0039] Such an enclosure 1 may have different shapes and be made from different non-magnetic conductive materials to ensure this function. In the embodiment illustrated in [Fig.l], the enclosure 1 has a cylindrical shape, and is essentially made of stainless steel plates.

[0040] This waterproof enclosure 1 comprises: - A lower partition 11 forming a bottom of the enclosure 1, - A curved upper partition 12 forming a ceiling of the enclosure 1, and - One (or more) vertical lateral partition(s) 13 extending between the upper and lower partitions 11, 12.

[0041] The lower partition 11 may be flat or concave towards the inside of the enclosure 1. It comprises an orifice 111 to allow an operator to access the inside of the enclosure 1. In operation, this orifice 111 is closed by a hatch (or door) 112 normally locked in a sealed manner by any technique known to those skilled in the art, for example by bolting the hatch 112 onto the lower partition 11, a sealing gasket (for example rubber) being mounted between the orifice 111 and the facing hatch 112 (i.e. between the edges of the orifice and the edges of the hatch facing each other). Of course, the lower partition 11 may comprise more than one orifice 111 closable by a hatch 112. Furthermore, the reader will appreciate that this (or these) orifice(s) 111 closable by one (or more) hatch(es) 112 may be arranged in a partition 12, 13 other than the lower partition 11.

[0042] The upper partition 12 comprises a through inlet 121 at which the waveguide 3 is connected. Thus, the incident waves (electromagnetic waves produced by the generator 4) circulating in the waveguide 3 emerge in the enclosure 1 through the inlet 121. Of course, this inlet 121 can be arranged in the lateral partition 13 (or in the lower partition 11) rather than the upper partition 12. The upper partition 12 also comprises a hole 122 for the passage of a shaft 71 of the mixing unit 7.

[0043] The enclosure 1 may comprise a through-hole to which a pump (not shown) is connected for generating a vacuum in the enclosure 1.

[0044] Such an enclosure 1 being known to those skilled in the art, it will not be described in more detail below. 2.2 Waveguide

[0045] The waveguide 3 allows the propagation of the electromagnetic waves produced by the generator 4 towards the interior of the enclosure 1.

[0046] The waveguide 3 may consist of a parallelepiped tube of rectangular cross-section capable of advantageously propagating the electromagnetic wave in the TE01 mode including: - A first end capable of being connected to the generator 4, this first end defining an opening for receiving the electromagnetic waves produced by the generator 4; - A second end capable of being connected to the enclosure 1, this second end defining an opening for diffusing electromagnetic waves inside the enclosure 1.

[0047] Such a waveguide 3 is made of a material impervious to electromagnetic waves, for example of a conductive material (non-magnetic metal) of the stainless steel or aluminum type. 2.3 Impedance Matching Unit

[0048] The impedance matching unit 5 makes it possible to locally adjust the impedance in the waveguide 3 to match it to the input impedance in the enclosure 1. The power transfer between the generator 4 and the enclosure 1 is thus optimized.

[0049] More precisely, the impedance matching unit 5 allows the correction impedance to bring the power level of the residual reflected waves (electromagnetic waves reverberated by the enclosure 1) to the lowest level. In particular, the impedance matching unit 5 makes it possible to correct the power level of the reflected waves according to the evolution (during treatment) of the dielectric characteristics of the mixture (dry biomass + aqueous solvent) placed in the enclosure 1.

[0050] Thus, in accordance with the rules of the art in the field of power transfers, an impedance adaptation is carried out in order to avoid the return of reflected power at the input of the enclosure 1 to the generator 4.

[0051] This impedance adaptation can be carried out by acting on the adjustment elements of the impedance adapter 5 as a function of data transmitted by measuring probes (not shown) of the energy reflected by the enclosure 1.

[0052] These measuring probes can be integrated into the generator 4.

[0053] The impedance matching unit 5 may be of any type known to those skilled in the art.

[0054] Moreover, just as in the prior art, the processing device can also comprise a circulator 9 between the waveguide 3 and the generator 4 to absorb the reflected waves which would otherwise be reinjected into the generator 4. This makes it possible to ensure protection of the magnetron (not shown) installed in the generator 4.

[0055] Such an impedance matching unit 5 being known in the prior art, it will not be described in more detail below. 2.4 Brewing unit

[0056] The stirring unit 7 makes it possible to stir the biomass / solvent mixture to be treated in order to homogenize the microwave treatment of this mixture.

[0057] The stirring unit 7 comprises a shaft and two (or four) blades at one end of the shaft, the other end of the shaft being connected to a motor M to induce rotation of the shaft and the blades.

[0058] Preferably, the mixing is carried out by rotating the blades at a rotation speed ranging from 3 to 20 revolutions per minute. 2.5 Wave trapping unit

[0059] The wave trapping unit 6 allows: - On the one hand, to limit the risks of electromagnetic waves leaking to the outside of the device, and - On the other hand, reduce the risk of electric arcing in the event of poor contact between two metal parts.

[0060] The wave trapping unit 6 comprises a wave trap 6a - called a "wave trap ¥4 wave trap" - positioned at the hole 122 made in the upper partition 12 for the passage of the shaft. This wave trap limits the risks of arc formation electric at hole 122.

[0061] Indeed, the electromagnetic waves present in the enclosure 1 generate surface currents on the internal faces of the partitions constituting the enclosure 1. These surface currents must be able to circulate without encountering a break in conduction in the metal / metal contact zones. In the event of a local break in conduction, an arc may be generated in this zone.

[0062] However, at the hole 122 provided in the upper partition of the enclosure, the shaft cannot be in perfect contact with the edges of the hole to allow it to rotate.

[0063] As described in more detail below, the wave trap 6a makes it possible to obtain the equivalent of a metal / metal contact without having a “physical” contact between the hole and the shaft 71 of the stirring unit 7.

[0064] With reference to [Fig.2], the wave trap 6a extends inside the enclosure 1. More precisely, the wave trap 6a is arranged in the enclosure 1 around the hole 122 so that the shaft 71 of the mixing unit 7 extends along an axis of symmetry of the wave trap 6a.

[0065] The wave trap 6a has the shape of a metal frame intended to be positioned around the hole 122 for the passage of the shaft 71. This metal frame curved into a loop of rectangular section comprises an entry / exit slot 65 for the electromagnetic waves. The dimensions of the frame are determined so that the electromagnetic waves entering the metal frame at the entry / exit slot 65, exit said metal frame in phase opposition and thus lead to creating the equivalent of a metal / metal short circuit.

[0066] Thus, the wave trap 6a makes it possible to block rising waves at the axis passage, ensuring effective shielding while limiting the risks of creating arcs.

[0067] The wave trap 6a comprises fixing means to enable it to be mounted on the internal face of the upper partition 12 of the enclosure 1. These fixing means comprise, for example, a peripheral annular collar 66 capable of being bolted, brazed, or welded onto the enclosure 1.

[0068] With reference to [Fig. 3], the wave trap 6a comprises an interior chamber C delimited by a plate curved in a loop, here of rectangular shape, with a free face 61 which extends opposite the shaft 71 of the mixing unit 7.

[0069] More specifically, the wave trap 6a comprises: - An upper panel 62 extending parallel to the partition 12, the upper panel 62 having an inner edge 62a and an outer edge 62b, the inner edge 62a being closer to the shaft 71 than the outer edge 62b, - An external panel 63 extending perpendicular to the partition 12, the panel external 63 having an upper edge 63a connected to the external edge 62b of the upper panel 62, and a lower edge 63b, the lower edge 63b being closer to the lower partition 11 than the upper edge 63a, - A lower panel 64 extending parallel to the upper panel 62, the lower panel 64 having an outer edge 64a connected to the lower edge 63b of the outer panel 63, and an opposite inner edge 64b, the inner edge 64b being closer to the shaft 71 than the outer edge 64a, - The free panel 61 extending perpendicularly to the partition 12, the free panel 61 having a connecting edge 61a connected to the internal edge 64b of the lower panel 64, and an opposite free edge 61b, the free edge being closer to the upper partition 12 than the connecting edge 61a.

[0070] The free lower face 61 extends opposite the shaft 71, at a non-zero (and the smallest possible) distance “d” from the latter so that the free face is never in physical contact with the shaft 71 to allow the latter to rotate around its axis of rotation. Thus, the free face 61 defines, with the shaft 71, a passage forming the inlet / outlet slot 65 of the wave trap.

[0071] Advantageously, the dimensions of the different sections 61-64 (and in particular the widths L61, L62, L63 and L64 of the different sections) are determined (experimentally or by modeling) to be equal to a multiple of the wavelength of the electromagnetic waves plus a quarter of the latter so that the waves leaving the wave trap (hereinafter referred to as "outgoing waves") are out of phase by half a wavelength with the waves entering the wave trap (hereinafter referred to as "incoming waves"). The incoming and outgoing waves are thus in phase opposition and thus lead to the creation of the equivalent of a metal / metal short circuit.

[0072] Indeed, the operating principle of the wave trap is based on the combination of two waves (incoming wave and outgoing wave) which cross in phase opposition at the level of the entry / exit slot 65.

[0073] In the case of the device according to the invention, a portion of the waves present in the enclosure 1 propagate to the hole 122 associated with the wave trap 6a and penetrate into it at the level of the inlet / outlet slot 65. These waves propagate in the wave trap 6a following the different sections 61-64 constituting it, to exit the wave trap through the inlet / outlet slot 65 (i.e. the inlet / outlet slot of the metal frame). The waves exiting the wave trap interfere in phase opposition with the waves entering the wave trap 6a.

[0074] The phase of the outgoing waves depends on the distance traveled (Dp) in the wave trap 6a, and in particular on the widths of the different sections 61-64 constituting the wave trap 6a (DP=L62 + L63 + LM + 2xL6i). Those skilled in the art will appreciate that these dimensions are dependent on the frequency used for electromagnetic waves.

[0075] The determination of the dimensions of the wave trap 6a (making it possible to ensure that the outgoing waves Os are in phase opposition with the incoming waves OE) can be carried out experimentally, or be carried out on the basis of modeling results.

[0076] Such a wave trap 6a makes it possible to limit the risks of reflected waves leaking outwards as well as the risks of generating an electric arc at the hole 122.

[0077] Of course, the wave trapping unit 6 may comprise several wave traps. For example, in the embodiment illustrated in [Fig.l], the device comprises a second wave trap 6b associated with the access orifice 111 of the enclosure 1. Each wave trap 6a, 6b may have a different shape (circular, square, rectangular, etc.), in particular a shape adapted to the shape (circular, square, rectangular) of the orifice 111 or the hole 122 with which the wave trap is associated. 2.6 Conclusions

[0078] The processing device described above has the advantage of satisfying the various standards for the protection of people and communications networks, and in particular the EN 55011 standard for the protection of telecommunications networks, the criteria of which are very strict.

[0079] The wave trapping unit 6 has the advantage of cancelling, at the hole 122 managed in the enclosure for the passage of the shaft of the mixing unit, the electromagnetic waves present in the enclosure 1. The risks of electromagnetic waves leaking towards the outside of the device are thus reduced while lowering the risks of arcs.

[0080] The reader will have understood that numerous modifications can be made to the invention described above without materially departing from the new teachings and advantages presented here. Brief description of the drawings

[0081] Other advantages and characteristics of the invention will emerge more clearly from the following description of several variant embodiments, given as non-limiting examples, from the appended drawings in which: - [Fig.l] is a schematic representation of a treatment device according to the invention, - Figures 2 and 3 are first and second schematic representations of a wave trap - called a "wave trap" - of the treatment device illustrated in [Fig.l].

Claims

Claims

1. Device for treating plant biomass, the treatment device comprising: - An enclosure (1) intended to contain the plant biomass to be treated, the enclosure (1) comprising a lower partition (11), an upper partition (12) and at least one lateral partition (13) extending between the upper and lower partitions (11, 12), at least one of the partitions (11, 12, 13) including a through inlet mouth (121) and a hole (122), - A waveguide (3) connected to the through inlet mouth (121) for the circulation, towards the interior of the enclosure (1), of incident electromagnetic waves produced by a generator (4), - An impedance matching unit (5) configured to vary an impedance in the waveguide (3) in order to match said impedance in the waveguide (3) to an input impedance of the enclosure (1), - A stirring unit (7) for stirring the plant biomass contained in the enclosure (1), said stirring unit comprising a shaft (71) extending through the hole (122) and blades mounted on the shaft and extending inside the enclosure (1), characterized in that the device further comprises a wave trapping unit (6), said wave trapping unit (6) including at least one wave trap (6a) associated with the hole (122) for the passage of the shaft of the stirring unit (7), said wave trap (6a) being configured to form phase-shifted electromagnetic waves from electromagnetic waves reflected by the plant biomass, by modifying the phase of said reflected electromagnetic waves, the phase-shifted electromagnetic waves being in phase opposition with the reflected electromagnetic waves in a plane containing the hole (122).

2. Device according to claim 1, wherein the wave trap (6a) comprises a metal frame curved into a loop, said frame being positioned around the hole (122) for the passage of the shaft of the stirring unit.

3. Device according to claim 2, in which the metal frame extends inside the enclosure (1) so as to surround a portion of the shaft (71) of the stirring unit (7).

4. Device according to any one of claims 2 or 3, in which the metal frame comprises an electromagnetic wave entry / exit slot, the dimensions of said frame being determined so that the electromagnetic waves entering the metal frame at the entry / exit slot, exit said metal frame in phase opposition.

5. Device according to any one of claims 2 to 4, in which the frame is fixed to the enclosure (1) and comprises: - An upper panel (62) in contact with the partition (12) including the hole (122) for the passage of the shaft (71), the upper panel (62) extending parallel to the partition (12) including the hole (122), - A lower panel (64) parallel to the upper panel (62), - An external panel (63) between the upper and lower panels (62, 64), the edges (63a, 63b) of the upper panel (63) being connected to the edges (62b, 64a) of the upper and lower panels (62, 64) furthest from the hole (122), and - A free panel (61) parallel to the external panel (63), the free panel including: • A connecting edge (61a) connected to the nearest lower panel (64) of the hole (122), • A free edge opposite the connecting edge, so that the lower face (61) extends opposite the shaft (71),at a non-zero distance from said shaft (71) and is not in contact with the shaft (71) or with the upper face (62).,

6. Device according to claim 5, in which the sum of the widths: - Of the upper panel (62), - Of the external panel (63), - Of the lower panel (64) and - Of the free panel (61) is equal to a multiple of the wavelength of the reflected waves ad-

7. conditioned by a quarter of the wavelength of the reflected waves. Device according to any one of claims 5 or 6, in

8. wherein the thickness of the panels is substantially equal to the thickness of the walls of the waveguide (3). Device according to any one of claims 1 to 7, in which the wave trap (6a) is made of a non-magnetic conductive material, such as aluminum or stainless steel.

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