Device for absorbing electromagnetic waves, and faraday room comprising such a device

Abstract

A device (2) for absorbing electromagnetic waves is provided on the inside with: - a first compartment (4) and a second compartment (6) which are juxtaposed and electrically insulated from each other, - a plurality of solid bodies (14) housed in the first compartment (4), each solid body (14) being made of an electrically insulating material (16) coated with an electrically conductive material (18), and - at least one layer of electromagnetic compatibility fabric (20) housed in the second compartment (6).

Description

[0001] DESCRIPTION

[0002] TITLE: Electromagnetic wave absorption device and faradized room comprising such a device

[0003] Technical field

[0004] The technical field of the invention is the absorption of electromagnetic waves.

[0005] Previous techniques

[0006] The use of devices emitting electromagnetic waves in many fields of application, particularly in health, aviation or telecommunications, creates the need to isolate certain objects from certain unwanted electromagnetic radiation present in their environment.

[0007] For example, it might be desirable to isolate certain parts of a patient's body from electromagnetic radiation emitted by a medical device such as a scanner, or to isolate certain objects so that they do not interfere with other objects such as measuring devices.

[0008] It may also be useful to form an enclosure capable of isolating certain objects so that they are not disturbed by surrounding electromagnetic radiation, for example to measure electronic disturbances induced by equipment by reducing electromagnetic noise from other sources.

[0009] Typically, such an enclosure is not mobile. It is the objects to be isolated that must be mobile to be placed inside such an enclosure.

[0010] The present invention aims to provide a wave absorption solution suitable for many applications, suitable for many indoor and outdoor environments, effective over a wide frequency band, easy to transport and install.

[0011] Statement of the invention

[0012] The invention relates to a device for absorbing electromagnetic waves provided internally with: - a first compartment and a second compartment juxtaposed and electrically insulated from each other,

[0013] - a plurality of solid bodies housed in the first compartment, each solid body being formed from an electrically insulating material coated with an electrically conductive material, and at least one layer of electromagnetically compatible fabric housed in the second compartment.

[0014] Solid bodies are individualizable.

[0015] Electromagnetic compatibility fabric is a material used to create coatings or coverings that help mitigate electromagnetic interference, for example by blocking or reflecting certain electromagnetic waves.

[0016] The electromagnetically compatible fabric comprises, for example, yarns of an electrically conductive material in the weft of the fabric, or an absorbent material, such as a carbon material or such as ferrite, converting electromagnetic energy into heat.

[0017] The solid bodies housed in the first compartment and said layer of electromagnetically compatible fabric housed in the second compartment make it possible to effectively absorb electromagnetic waves over a broad spectral band, the incident electromagnetic waves being reflected by the solid bodies and absorbed by said layer of electromagnetically compatible fabric.

[0018] At least the first compartment can be fluid-tight.

[0019] The second compartment can also be fluid-tight.

[0020] The absorption device may further comprise at least one orifice in fluid communication with the first compartment, and at least one closing means for closing said orifice in a fluid-tight manner.

[0021] The orifice of the absorption device is capable of cooperating with a vacuum means for creating a vacuum in the first compartment of the absorption device.

[0022] When the first compartment of the absorption device is evacuated, the compactness of the solid bodies increases, improving the absorption efficiency of electromagnetic waves of the absorption device in a wide spectral band, for example from 3 to 18 GHz. In addition, the first compartment of the evacuated absorption device is more rigid.

[0023] The absorption device may further comprise an internal wall separating the first and second compartments.

[0024] Thus, the first and second compartments are isolated from each other by this wall, in particular a fluid cannot circulate between the first and second compartments.

[0025] Said inner wall may be formed from polyurethane.

[0026] Thus, the said internal wall is strong, flexible and light. The said wall also contributes to the insulating properties of the absorption device, the polyurethane having sound insulation properties.

[0027] The first and second compartments may each include at least one additional polyurethane wall.

[0028] Thus, the absorption device is suitable for outdoor environments. Polyurethane can be resistant to weather, UV rays and temperature variations.

[0029] Said electrically insulating material for solid bodies may comprise polystyrene.

[0030] Thus, the absorption device is of reduced mass and easy to transport.

[0031] Said electrically conductive material of solid bodies may comprise carbon black or graphite.

[0032] The absorption device may comprise at least two layers of electromagnetically compatible fabric housed in the second compartment.

[0033] In particular, the absorption device comprising two or three layers of electromagnetically compatible fabric housed in the second compartment is effective in absorbing electromagnetic waves while maintaining a reduced mass. The layers of electromagnetically compatible fabric may bear against each other. Said electrically conductive material of each solid body may represent between 1% and 3% of the mass of said solid body.

[0034] In particular, the percentage of the mass of the solid body of said electrically conductive material makes it possible to modify the electromagnetic wave absorption properties of the absorption device.

[0035] The largest dimension of solid bodies can be between 5 millimeters and 35 millimeters, in particular between 5 millimeters and 25 millimeters, in particular between 10 millimeters and 20 millimeters.

[0036] Solid bodies can be arranged in at least two superimposed layers.

[0037] Increasing the number of overlapping layers improves the absorption efficiency of the absorption device.

[0038] Solid bodies can be spherical in shape.

[0039] Thus, the compactness of solid bodies in the first compartment is high.

[0040] The diameter of spherical solid bodies can be identical or, on the contrary, vary from one solid body to another.

[0041] In this second case, the compactness of the solid bodies in the first compartment can be increased.

[0042] The present invention also relates to a faradized room comprising at least one absorption device as defined previously.

[0043] The faradized room can include an inflatable structure.

[0044] Said absorption device can be mounted on the inflatable structure.

[0045] Thus, the faradized room is light, easy to transport and install.

[0046] Brief description of the drawings

[0047] The present invention will be better understood upon studying the detailed description of embodiments, taken as non-limiting examples and illustrated by the appended drawings in which:

[0048] [Eig 1] is a schematic sectional view of an absorption device according to an exemplary embodiment of the invention; [Fig 2] is an example of measurement of a reflection coefficient in dB carried out at normal incidence on an absorption device according to an exemplary embodiment of the invention;

[0049] [Fig 3] is an example of an inflatable structure of a faradized room according to an exemplary embodiment of the invention; and

[0050] [Fig 4] is an example of a faradized room according to an exemplary embodiment of the invention.

[0051] Detailed description

[0052] Figure 1 schematically represents a device 2 for absorbing electromagnetic waves, here in the form of a panel, internally comprising a first compartment 4 and a second compartment 6 juxtaposed with the first compartment 4. In the figure, the first and second compartments 4, 6 are arranged one below the other.

[0053] The absorption device 2 comprises an internal wall 8, for example made of polyurethane, separating the first and second compartments 4, 6 in order to isolate them from each other.

[0054] The absorption device 2 comprises, for example, an upper wall 10 formed from a polyurethane material and jointly delimiting with the internal wall 8 of the absorption device 2 the first compartment 4. The upper 10 and internal 8 walls of the absorption device 2 can be assembled together by high-frequency welding in order to make the first compartment 4 fluid-tight.

[0055] The absorption device 2 comprises, for example, a lower wall 12 formed from a polyurethane material and jointly delimiting with the internal wall 8 of the absorption device 2 the second compartment 6. The lower 12 and internal 8 walls of the absorption device 2 can be assembled together by high-frequency welding in order to make the second compartment 6 fluid-tight.

[0056] The absorption device 2 comprises a plurality of solid bodies 14 housed in the first compartment 4. Each solid body 14 is here of spherical shape. Alternatively, the solid bodies 14 may be of the shape of a cube, a parallelepiped, or a cylinder.

[0057] All the solid bodies 14 are here of constant diameter, for example solid bodies 14 in the form of spheres of sixteen millimeters in diameter, with a tolerance of plus or minus one millimeter. Alternatively, the solid bodies 14 may be of different dimensions. For example, the largest dimension of the solid bodies 14 may be between 5 millimeters and 35 millimeters, more precisely between 5 millimeters and 25 millimeters, even more precisely between 10 millimeters and 20 millimeters.

[0058] Each solid body 14 is formed from an electrically insulating material 16, for example polystyrene, coated with an electrically conductive material 18, for example carbon black or graphite.

[0059] The absorption device 2 further comprises two layers of electromagnetically compatible fabric 20 housed in the second compartment 6. Alternatively, the absorption device 2 may comprise a single layer of electromagnetically compatible fabric 20 housed in the second compartment 6. Alternatively, the absorption device 2 may comprise more than two layers of electromagnetically compatible fabric 20 housed in the second compartment 6, for example three layers of electromagnetically compatible fabric 20 housed in the second compartment 6.

[0060] The absorption device 2 further comprises a vacuum valve 22 mounted in a fluid-tight manner through a hole 23 formed here in the upper wall 10. The vacuum valve 22 is fixed to the periphery of this hole 23 by any suitable means, for example welding, brazing, glue or by means of a seal.

[0061] The vacuum valve 22 internally delimits an orifice 24 which communicates with the first compartment 4. The vacuum valve 22 is provided with a closing means 25 for sealingly closing the orifice 24. In the illustrated embodiment, the closing means 25 comprises a non-return valve mounted in the orifice 24.

[0062] The vacuum valve 22 is intended to be connected to a vacuum means external to the absorption device 2, for example a pump, to place the first compartment 4 at a pressure lower than atmospheric pressure, for example a pressure 0.2 to 0.3 bar lower than atmospheric pressure. The relative vacuum thus obtained in the first compartment 4 is maintained under the effect of the closing means 25. Thus, the absorption device 2 is in a so-called “vacuum” state, giving it greater absorption efficiency over a wide spectral band.

[0063] In the illustrated embodiment, the vacuum valve 22 delimits the orifice 24 in fluid communication with the first compartment 4 and comprises the closing means 25. Alternatively, it is possible to provide other means, for example an orifice could be formed in the upper wall 10 to communicate fluidly with the first compartment 4, and be closed by a plug.

[0064] The solid bodies 14 of the absorption device 2 are here arranged in the first compartment 4 in two superimposed layers.

[0065] When the first compartment 4 is evacuated, the compactness of the solid bodies 14 of the absorption device 2 in the first compartment 4 increases. For example, when the first compartment 4 is evacuated, the spherical solid bodies 14 are arranged so that each spherical solid body 14 of the first superimposed layer is in contact with four spherical solid bodies 14 of the second superimposed layer.

[0066] Alternatively, the solid bodies 14 may be arranged in a single layer in the first compartment 4. Alternatively, the solid bodies 14 may be arranged in more than two superimposed layers in the first compartment 4.

[0067] Figure 2 represents reflection coefficient measurements in decibels carried out on an electromagnetic wave absorption device 2 at normal incidence and in double linear, vertical and horizontal polarization. The measurements were carried out for frequencies ranging from 4 gigahertz to 18 gigahertz, corresponding in particular to the microwave domain. Alternatively, the absorption device 2 can be used to absorb electromagnetic waves in other frequency domains, for example in the infrared domain, in particular up to 400 terahertz.

[0068] The measurements were carried out for four different types of solid bodies.

[0069] Curve 26 in thick and continuous line corresponds to spherical solid bodies 14 each composed of an electrically insulating material 16 in polystyrene coated with an electrically conductive material 18 in graphite representing 1% of the mass of the solid body 14, the spherical solid bodies 14 each having a diameter of 11 millimeters with a tolerance of plus or minus one millimeter.

[0070] Curve 28 in thick and broken line corresponds to spherical solid bodies 14 each composed of an electrically insulating material 16 in polystyrene coated with an electrically conductive material 18 in graphite representing 3% of the mass of the solid body 14, the spherical solid bodies 14 each having a diameter of 11 millimeters with a tolerance of plus or minus one millimeter.

[0071] Curve 30 in a thin, continuous line corresponds to spherical solid bodies 14, each composed of an electrically insulating material 16 made of polystyrene coated with an electrically conductive material 18 made of carbon black representing 1% of the mass of the solid body 14, the spherical solid bodies 14 each having a diameter of 8 millimeters with a tolerance of plus or minus one millimeter.

[0072] Curve 32 in thin, broken lines corresponds to spherical solid bodies 14, each composed of an electrically insulating material 16 made of polystyrene coated with an electrically conductive material 18 made of carbon black representing 3% of the mass of the solid body 14, the spherical solid bodies 14 each having a diameter of 16 millimeters with a tolerance of plus or minus one millimeter.

[0073] As shown in Figure 2, each of these four absorption devices 2 can absorb electromagnetic waves of frequencies between 4 gigahertz and 18 gigahertz. In particular, the absorption devices 2 comprising spherical solid bodies 14 composed of an electrically insulating material 16 made of polystyrene coated with an electrically conductive material 18 made of graphite absorb mainly electromagnetic waves of frequencies between 4 gigahertz and 7 gigahertz and between 15 gigahertz and 18 gigahertz. The absorption devices 2 comprising spherical solid bodies 14 composed of an electrically insulating material 16 made of polystyrene coated with an electrically conductive material 18 made of carbon black absorb over a wider frequency band.The absorption device 2 comprising spherical solid bodies 14 composed of an electrically insulating material 16 made of polystyrene coated with an electrically conductive material 18 made of carbon black representing 1% of the mass of the solid bodies 14 makes it possible to obtain even better electromagnetic reflection performance, with a reflection coefficient in decibels close to -6dB over a wide frequency band.

[0074] Figure 3 shows an inflatable structure 34 comprising a plurality of masts 36 or feet, a roof 38, and a plurality of stringers 40, each formed from an elongated inflatable element of revolution with captive air or inflatable tube.

[0075] The inflatable structure 34 here comprises six masts 36, each mast 36 being formed of an elongated element arranged vertically, and two stringers 40 each extending horizontally through a row of masts 36 of the inflatable structure 34 in order to reinforce the inflatable structure 34.

[0076] The roof 38 of the inflatable structure 34 here comprises a frame 42 supported by the masts 36 of the inflatable structure 34 and formed of a plurality of elongated elements arranged horizontally, here four in number, and a plurality of crosspieces 44 arranged horizontally, here three in number, extending inside the frame 42 of the roof 38 in order to reinforce the inflatable structure 34.

[0077] Each captive air inflatable elongated element of revolution is here in the form of an elongated cylindrical element of circular section. Each captive air inflatable elongated element of revolution is composed of a plurality of internal air chambers and an external envelope inside which the internal air chambers are housed.

[0078] The outer casing of the captive air inflatable elongated elements of revolution is formed of a fabric, for example DACRON®. Each internal air chamber of the captive air inflatable elongated elements of revolution is formed of a stretchable material, for example polyurethane. The internal air chambers form the framework of the captive air inflatable elongated elements of revolution. Alternatively, each captive air inflatable elongated element of revolution comprises an airtight casing, for example formed of a coated fabric. In this case, each captive air inflatable elongated element of revolution may be assembled by heat welding and each captive air inflatable elongated element of revolution may be without an internal air chamber.

[0079] Each captive air inflatable elongated element of revolution comprises one or more inflation points (not shown), in particular an inflation valve for simultaneously inflating the internal air chambers of the elongated element or several inflation valves for independently inflating the internal air chambers of the elongated element, so that each captive air inflatable elongated element of revolution can be inflated independently of the other captive air inflatable elongated elements of revolution.

[0080] Figure 4 shows a faradized room 46 comprising the inflatable structure 34 and a plurality of electromagnetic wave absorption devices 2 mounted on the roof 38 and on several side walls of the inflatable structure 34. Preferably, the absorption devices 2 are arranged continuously on the inflatable structure 34, in particular so that the solid bodies 14 are arranged on the inner side of the faradized room 46 and so that the electromagnetically compatible fabric layers 20 are arranged on the outer side of the faradized room 46.

Claims

CLAIMS 1. Device (2) for absorbing electromagnetic waves, characterized in that it is internally provided with: a first compartment (4) and a second compartment (6) juxtaposed and electrically insulated from each other, - a plurality of solid bodies (14) housed in the first compartment (4), each solid body (14) being formed from an electrically insulating material (16) coated with an electrically conductive material (18), and at least one layer of electromagnetically compatible fabric (20) housed in the second compartment (6).

2. Absorption device (2) according to claim 1, wherein at least the first compartment (4) is fluid-tight, the absorption device (2) further comprising at least one orifice (24) in fluid communication with the first compartment (4) and at least one closing means (25) for closing said orifice (24) in a fluid-tight manner.

3. Absorption device (2) according to one of claims 1 and 2, further comprising an internal wall (8) separating the first and second compartments (4, 6).

4. Wave absorption device (2) according to claim 3, wherein said inner wall (8) is formed from polyurethane.

5. Absorption device (2) according to any one of the preceding claims, wherein the first and second compartments (4, 6) each comprise at least one polyurethane wall.

6. Absorption device (2) according to any one of the preceding claims, wherein said electrically insulating material (16) of the solid bodies (14) comprises polystyrene.

7. Absorption device (2) according to any one of the preceding claims, wherein said electrically conductive material (18) of the solid bodies (14) comprises carbon black or graphite.

8. Absorption device (2) according to any one of the preceding claims, comprising at least two layers of electromagnetically compatible fabric (20) housed in the second compartment (6).

9. Absorption device (2) according to any one of the preceding claims, wherein said electrically conductive material (18) of each solid body (14) represents between 1% and 3% of the mass of said solid body (14).

10. Absorption device (2) according to any one of the preceding claims, wherein the largest dimension of the solid bodies (14) is between 5 millimeters and 35 millimeters, in particular between 5 millimeters and 25 millimeters, in particular between 10 millimeters and 20 millimeters. 1 1 . Absorption device (2) according to any one of the preceding claims, wherein the solid bodies (14) are arranged in at least two superimposed layers.

12. Absorption device (2) according to any one of the preceding claims, wherein the solid bodies (14) are spherical in shape.

13. Faradized room (46) comprising an inflatable structure (34) and at least one absorption device (2) according to any one of the preceding claims mounted on the inflatable structure (34).

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