High frequency electromagnetic applicator

Abstract

The invention relates to an electromagnetic field applicator, comprising, along a longitudinal axis (XX'): a first part of flared shape having a first end, in the form of a point, intended to be inserted at one end of a waveguide; and a second part having a second rounded end, extending the first part, and making it possible to transmit the electromagnetic field. Figure for abstract: Fig. 1A

Description

Title of the invention: High frequency electromagnetic applicator Technical field

[0001] The field of the invention is that of electromagnetic compatibility and more precisely that of high-frequency near-field applicators. State of the prior art

[0002] The industry in the field of electromagnetic compatibility offers two types of so-called "near-field" applicators: a monopole and a magnetic loop. Their function is to apply an electromagnetic field to an object under test. However, for both types of applicators, various intrinsic limitations to the devices hinder the use of these tools for certain applications.

[0003] First of all, the maximum frequency proposed is limited to 6 GHz. In addition, the electromagnetic coupling conditions offered by these devices are not representative of an incident wave propagating in air (plane wave condition). In addition, the level of the reflection coefficient of these devices is very high and can damage the microwave generators that power them without suitable protection. In electronics, loops are used to create inductors. The particularity of inductors is that they oppose high frequencies, a pulsed or sinusoidal signal being distorted and part of its energy returned and another stored in the inductor. The inductive nature of the induction loops will return a large part (almost all) of the incident wave to the microwave generator and the power of the signal induced on the object under test becomes low and the generator risks being damaged.

[0004] Finally, the monopole and the magnetic loop respectively allow a high electromagnetic field but whose orientation is not controlled (monopole), and an electromagnetic field whose orientation is controlled but whose amplitude and frequency increase are limited (magnetic loop).

[0005] The problem therefore arises of finding a new method and a new device to at least partially overcome these drawbacks.

[0006] In particular, the problem arises of finding a new process and a new device allowing:

[0007] - to apply a high electromagnetic field whose orientation is controlled and preferably close, or even very close, to plane wave conditions (electric field perpendicular to the magnetic field and ratio between these two normal components (electric and magnetic field) of 377 ohms (E(x) / H(y) = 377);

[0008] - and / or to provide better spectral coverage than the magnetic loop;

[0009] - and / or to have improved reflectivity compared to existing solutions, in order to guarantee the protection of the microwave emission systems supplying the applicator, thanks to the non-inductive nature of the device. Statement of the invention

[0010] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose an electromagnetic field applicator making it possible, among other things, to apply a high electromagnetic field whose orientation is controlled, preferably close, or even very close, to plane wave conditions and to provide better spectral coverage than other devices. Preferably, this device has a non-inductive character.

[0011] To this end, an object of the invention relates to an electromagnetic field applicator which comprises, along a longitudinal axis: • A first flared-shaped portion having a tip-shaped end that can be inserted into one end of a waveguide; • A second rounded end part, associated with the flared shape, allowing the electromagnetic field to be transmitted.

[0012] An electromagnetic field applicator according to the invention is suitable for transmitting an electromagnetic field with good plane wave conditions, a controlled orientation and provides better spectral coverage. The reflectivity parameters of an applicator according to the present invention are less than -10 dB, which ensures a reflection level less than 10% of the incident level and guarantees the protection of the microwave transmission systems supplying the applicator. Indeed, this applicator has a non-inductive character unlike magnetic loops, allowing a rise in frequencies without, or with little, losses. Monopoles and magnetic loops do not allow for such good adaptation with regard to the electromagnetic frequencies used and provide a strong reflection of the incident microwave signal.

[0013] According to an exemplary embodiment, the flared shape may comprise a cone along the longitudinal axis, then may be extended by a truncated cone-shaped part cut by four intersecting planes parallel to the axis of the cone and facing each other two by two: • the first two intersecting planes being distant from each other and being able to form first flat support surfaces, for example on the edges of a waveguide; • the two second intersecting planes being distant from each other and being able to form second flat support surfaces, for example on the edges of a waveguide; preferably, the first flat support surfaces are perpendicular to the second flat support surfaces.

[0014] The entire flat face of the rounded end may be in contact with the base of the frustoconical portion, or the second part connects to the first part along a plane perpendicular to the axis. Preferably, the first part is of uniform dielectric permittivity.

[0015] The applicator may be made of dielectric material, for example polylactic acid.

[0016] The invention also relates to a device for emitting electromagnetic fields comprising an applicator according to the invention and a rectangular waveguide.

[0017] The waveguide may be capable of transmitting waves in at least one frequency band X, and / or Ku, and / or Ka: an applicator according to the invention may thus adapt, by scale effect, to different waveguides and consequently, it may send intense electromagnetic fields in different frequency bands, in particular in a frequency range from approximately 8 GHz to 40 GHz.

[0018] The invention also relates to a method of generating an electromagnetic field which comprises the steps of: • Insertion of an applicator according to the invention at the outlet of a waveguide; • Then sending an intense electromagnetic field into the waveguide, for example towards an electronic component or biological tissue.

[0019] The invention also relates to the method of manufacturing an applicator according to one of the preceding claims comprising a step of additive manufacturing or machining in the mass. Brief description of the drawings

[0020] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0021] [Fig.lA] is a schematic front view of the electromagnetic field applicator;

[0022] [Fig.lB] is a schematic top view of the electromagnetic field applicator;

[0023] [Fig.IC] is a schematic right-hand view of the electromagnetic field applicator;

[0024] [Fig.2] schematically and partially illustrates the applicator inserted inside a rectangular waveguide;

[0025] [Fig.3] is an example of field E radiated by a waveguide equipped with an applicator according to the invention, for 1 W injected;

[0026] [Fig.4A] and [Fig.4B] illustrate an E field and an H field at the output of a waveguide equipped with an applicator according to the invention.

[0027] Detailed description of particular embodiments

[0028] In the figures and in the remainder of the description, the same references represent identical or similar elements. Furthermore, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise indicated.

[0029] The invention relates generally to an electromagnetic field applicator, to an electromagnetic field emitting device, to a method of generating an electromagnetic field and to a method of manufacturing an applicator.

[0030] In the context of this application, a wave is said to be plane if the wave vector that defines its direction of propagation is constant in sense and direction. This direction is called the direction of propagation of the wave and the plane perpendicular to the wave vector containing the vectors E and B is called the wave plane, with E and B orthogonal to each other. Consequently, the electric and magnetic fields are not only orthogonal to each other; they are also orthogonal to the propagation axis. The plane wave has successive wave planes that are sufficiently plane and parallel in the propagation medium considered. Furthermore, the amplitude of the electric field is 377 times greater than that of the magnetic field. This value is the constant of proportionality between the two fields and is called the vacuum impedance (377 Q).

[0031] Figures 1A, 1B and 1C are respectively schematic front, top and side views of an applicator 1 according to an exemplary embodiment of the invention.

[0032] Here and for the remainder of the description, a three-dimensional direct reference frame XYZ is defined, where the X and Z axes form a plane parallel to the main plane of the applicator 1, and where the Y axis is oriented along the thickness of the applicator 1, from the first face F1 in the direction of the second face F1'. As can be understood from these figures, an electromagnetic field applicator according to the invention has a symmetry with respect to the XY plane and a symmetry with respect to the XZ plane. A generatrix of the shape of the applicator is parallel to the Y axis.

[0033] The structure of an electromagnetic field applicator according to the invention comprises, along a longitudinal axis: • a first part 2, 3 of flared shape from a first end 6, in the form of a point, which can be inserted at one end of a waveguide; • a second part 4 having a second rounded end, extending the first part, and capable of or allowing the electromagnetic field to be transmitted.

[0034] Note that the flared shape of the first part of an applicator according to the invention allows for gradual insertion at the outlet of a rectangular guide so as not to damage the applicator. As regards the rounded end, it allows for slight focusing of the electromagnetic field at the outlet and promotes short-distance plane wave conditions.

[0035] The applicator 1 can be made from a dielectric, preferably biodegradable polylactic acid, and can be used during 3D printing. A dielectric material is an insulator that prevents the passage of any electric current and thus prevents possible electric arcs.

[0036] The applicator 1 comprises a part 2 of flared, conical shape, in this example. The conical shape whose apex has an angle α, for example less than 20 degrees, thus comprises a pointed end 6 which allows the progressive adaptation of the dielectric permittivity of the air towards that of the dielectric material. Indeed, when an electromagnetic wave propagates in a medium or a guide, its propagation speed depends on the relative dielectric permittivity of the medium. If it encounters another medium whose permittivity is very different from that in which it propagates, a part (or even the entirety if the difference is very large) of the microwave signal is reflected. In the case of a waveguide, the incident signal is returned to the generator. The pointed shape makes it possible to progressively integrate the different relative permittivity in order to avoid this reflection.In addition, the reflection generates a standing wave phenomenon ("SWR", or standing wave ratio) which can create and impose high voltages at the generator. Some generators can tolerate any standing wave ratio. However, guaranteeing the non-reflectivity of these waves allows the use of less expensive generators and better safety for the user. In addition, the non-reflectivity of the applicator allows a greater increase in intensity. Thus, an applicator according to the invention will be able to radiate almost all of the incident power and the waveguide, by its characteristic impedance, is capable of tolerating strong electromagnetic fields.

[0037] Figures 1A and 1B give representations of this conical part 2 delimited, along the X axis, by a dotted line.

[0038] The conical part 2 is extended by a truncated conical part 3 along the longitudinal axis X. This shape also allows a slight focusing of the EM field. As illustrated in Figures 1A and 1B, the truncated conical part 3 is the part between the two dotted lines.

[0039] This truncated part 3 has a thickness which extends along the Y axis between a first face F1 and a second F1'. The faces F1 and F1' are parallel to each other and opposite each other. In this example, the faces F1 and F1' are substantially flat.

[0040] The thickness of the frustoconical part 3, defined along the Y axis between the first and second faces F1, F1', is chosen so as to obtain good application or adhesion of the applicator 1 against the inner walls of the rectangular waveguide 5 when it is introduced therein (examples of dimensions of the waveguide are given below), in order to force the electric field to pass through the dielectric. The base of the frustoconical part 3 extends along the Z axis between a first face F2 and a second face F2' (see [Fig.lA]). The faces F2 and F2' are parallel to each other and opposite each other. In this example, the faces F2 and F2' are substantially planar.The base of the truncated part 3 has a transverse dimension in the XZ plane between the first and second faces F2, F2', which, again, is chosen so as to obtain good application or adhesion of the applicator 1 against the inner walls of the rectangular waveguide 5 (see examples below) when it is introduced therein, in order to force the electric field to pass through the dielectric. The flat support surfaces Fl, Fl' are perpendicular to the flat surfaces F2 and F'2. The faces Fl, Fl', F2 and F'2 make it possible to have flat surfaces allowing better application or adhesion of the applicator against the walls of the rectangular waveguide 5.

[0041] The truncated conical part 3 is preferably made of a dielectric material with the same dielectric permittivity as the conical part 2.

[0042] The cut cone, resulting from the association between the conical part 2 and the truncated conical part 3 has a height h which depends on the angle a

[0043] [Forml]

[0044] , (F2F'2) / 2 h= M

[0045] The truncated cone-shaped part 3 is extended by a rounded part 4 along the longitudinal axis X. The rounded part is seen from the side in [Fig.lC].

[0046] The rounded part 4 has at least one radius of curvature equal to (F2F'2) / 2 for example between approximately 3.5 mm and 11.4 mm for the examples of waveguides given below. The rounded part allows a slight focusing of the electromagnetic field at the output and favors short-distance plane wave conditions. As seen in [Fig.lA], this second part 4 is connected to the first part 3 along a plane perpendicular to the axis (X) of the device. Preferably, the connection ensures a continuous curvature. This second part 4 is preferably made of a dielectric material with the same dielectric permittivity as parts 2 and 3.

[0047] As illustrated in [Fig.2], an applicator 1 according to the invention can be inserted inside a rectangular waveguide 5 having dimensions which can vary depending on the frequencies which it must transport. For example, the waveguide 5 can be a WR90 or GT16 type guide (guide which is suitable for the X frequency band, the reference in "GT" being the British reference) with internal dimensions substantially 10mm x 23mm; other waveguides can be chosen, depending on the desired frequency: examples are given on the Fabman-ip website (https: / / fr.fabman-jp.com) or on https: / / www.atmmicrowave.com / flange-size-type / , for the X, Ku, K, Ka ranges, with internal dimensions varying between approximately 23 mm x 0 mm (example mentioned above) and approximately 7.1 mm x 3.6 mm (Ka band, WR28 or GT22 guide), for example still 15.8 mm x 7.9 mm (Ku band, WR62 or GT18 guide) or approximately 10.7 mm x 4.3 mm (K band, WR42 or GT20 guide).The waveguide is capable of transmitting an intense electromagnetic field, for example in at least one frequency band X, and / or Ku, and / or Ka, more generally an electromagnetic field in at least one frequency band included in the frequency range from approximately 8 GHz to 40 GHz coming from a microwave generator.

[0048] An applicator according to the invention can be produced by 3D printing. Depending on the size of the guide, it will be possible to adapt the size of the applicator during its manufacture using 3D printer technology.

[0049] A numerical study was conducted and a prototype was tested. For the experiment, an applicator manufactured for a WR90 waveguide was used with an electromagnetic field having a frequency between 8-10 GHz. The numerical study was carried out on commercial software CST Microwave studio in order to achieve a progressive adaptation of the wave impedance (the target value of 377 ohms). [Fig. 3] shows the radiation of the applicator 1 thus produced installed in a waveguide 5. This figure illustrates the periodic peaks I of high intensity (1238 V / m) and II of low intensity (0 V / m) of the electric field propagating in the waveguide 5. In addition, we can see the periodic peaks III of medium intensity (400 V / m) of this same electric field propagating in the air.

[0050] Simulation and experiment were compared, table [Table 1] below shows this comparison at the frequency of 9 GHz. A discrepancy between numerical simulation and measurement is often observed due to non-ideal conditions of the experiment in high frequencies. It is therefore possible to note a discrepancy between the simulation and the experiment. The simulation was carried out with an imaginary perfect metal (PEC), in which there are no losses. While the experiment was carried out using a WR90 brass waveguide with losses. In addition, the transition from the coaxial feed to the propagation in the guide behaves like an antenna whose position depends on the frequency. The WR90 waveguide is designed for frequencies between 8 and 12 GHz, the position of the transition is a compromise to minimize losses over the entire frequency band. These differences become more pronounced as the frequency increases. The higher the frequency, the more we will seek to have good mechanical performance, a good surface finish and good purity of the conductive material.

[0051] [Tables 1] @ 9GHz for 1 W Field E at contact Field E at 35 mm Simulation 800 Vm 1,250 V.m1 Measurement 680 Vm 1,212 V.m1

[0052] [Fig.4A] and [Fig.4B] show the orthogonality of the two components of the electromagnetic field as well as the coaxial power supply 7 and the applicator 8 seen from the front. The horizontal arrows IV of [Fig.4A] represent the low intensity magnetic field 0 A / m. The arrows V, VI and VII (see [Fig.4B]) represent respectively the low intensity electric field OV / m, medium intensity between 500 and 600 V / m and high intensity between 900 and 1000 V / m.

[0053] The air wave impedance (377 Ohms) is reached at 4 cm from the end 4 in the axis of the waveguide (value confirmed by experimentation).

[0054] At the end of a device according to the invention, the plane wave conditions are not entirely met; however, strong, very localized electric field levels are obtained, while ensuring orthogonality of the components of the magnetic and electric fields. At 4 cm from the output of the applicator, the illumination is a little less localized and the electric field levels a little weaker, but all the plane wave illumination conditions are ensured.

[0055] The problems related to the orientation of the electric field are solved thanks to the orthogonality of the E and H components. The reasons that explain this phenomenon are presented in the following. When the electromagnetic wave is propagated in the air, it passes through three propagation zones: the Rayleigh zone, the Fresnel zone and finally the Fraunhofer zone. The Fraunhofer zone is the far-field region for the propagation of electromagnetic waves: certain characteristics dominate the behavior of the field in this zone while in the other zones these characteristics are not ensured. In particular, in the field region far, that is to say as the distance from the source increases, the wavefronts are more and more planar, the electric and magnetic fields are both sinusoidal and their amplitude decreases as a function of the inverse of the distance and orthogonal to each other and to the z direction of propagation (Poynting vector), the E / H ratio between the electric field and the magnetic field is equal to the characteristic impedance of free space which is 377 ohms. Thus, it is noted that the invention, according to the experiments, makes it possible to offer characteristics of a far field zone at only 4 cm from the output of the device. More precisely, characteristics of the far field are found at a close distance, in particular the orthogonality of the fields between them and to their propagation vector and the E / H ratio is constant.

[0056] An application of a device according to the present invention is the study of the susceptibility of electronic components to electromagnetic aggression. In order to evaluate the reaction of an electronic component subjected to electromagnetic aggression, a device according to the invention makes it possible to apply the microwave aggression to the component under test. More precisely, the device makes it possible to apply to an electronic component an electromagnetic field as representative as possible of an incident wave (far field) without illuminating the neighboring component and thus to locate and understand the malfunction phenomena.

[0057] The invention can also be used in the field of electromagnetic compatibility as well as in that of directed energy weapons and the understanding of the phenomena induced by the latter.

[0058] Applications in the field of biology are also possible. For example, a device according to the present invention makes it possible to apply significant electromagnetic fields to biological tissues, representative of those that can be generated by an electromagnetic weapon, in order to assess any potential danger to humans. It can also be used for treatment applications on pathogenic tissues by applying electromagnetic radiation.

Claims

Claims

1. Electromagnetic field applicator (1), comprising, along a longitudinal axis (X): - a first part (2, 3) of flared shape having a first end, in the form of a point, intended to be inserted at one end of a waveguide; - a second part (4) having a second rounded end, extending the first part, and making it possible to transmit an electromagnetic field.

2. Applicator according to claim 1, the first part (2, 3) comprising along the longitudinal axis a cone (2), then being extended by a frustoconical part (3) cut by four intersecting planes (Fl, Fl', F2, F2') parallel to the axis (X) of the cone and facing each other two by two: the first two planes (Fl, Fl') being distant from each other and forming first flat bearing surfaces on the edges of a waveguide; the second two planes (F2, F2') being distant from each other and forming second flat bearing surfaces on the edges of a waveguide, the first flat bearing surfaces being perpendicular to the second flat bearing surfaces.

3. Applicator according to one of claims 1 or 2, the first part (2, 3) being of uniform dielectric permittivity.

4. 4. Applicator according to one of claims 1 to 3, the second part connecting to the first part along a plane perpendicular to the axis (X).

5. Applicator according to one of claims 1 to 4, the applicator is made of dielectric material, for example polylactic acid.

6. Device for emitting electromagnetic fields comprising an applicator according to one of claims 1 to 5 and a rectangular waveguide (5).

7. Device according to claim 6, the waveguide being capable of transmitting waves in at least one frequency band X, and / or Ku, and / or Ka.

8. A method of generating an electric field comprising the steps of: - Insertion of an applicator according to one of claims 1 to 5 at the output of a waveguide (5); - then sending an intense electromagnetic field into this waveguide;

9. A method according to claim 8, the electric field being directed towards an electronic component or towards biological tissue.

10. Method of manufacturing an applicator according to one of claims 1 to 5, comprising a step of additive manufacturing or machining in the mass.

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