High-frequency electromagnetic applicator

Abstract

The invention relates to an electromagnetic field applicator comprising, along a longitudinal axis (XX'): a first flared portion having a pointed end for insertion into one end of a waveguide; and a second portion having a rounded end extending from the first portion, and enabling the transmission of the electromagnetic field. Figure for the 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 specifically that of high-frequency near-field applicators. Prior art

[0002] The electromagnetic compatibility industry offers two types of applicators known as "near-field" devices: 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 inherent limitations hinder their use in certain applications.

[0003] First, the maximum proposed frequency is limited to 6 GHz. Furthermore, 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 adequate protection. In electronics, loops are used to create inductors. The characteristic of inductors is that they oppose high frequencies; an impulsive or sinusoidal signal is distorted, with some of its energy reflected back and some stored in the inductor. The inductive nature of the induction loops will reflect a large part (almost all) of the incident wave back onto 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 allow respectively a high electromagnetic field but whose orientation is not controlled (monopole), and an electromagnetic field whose orientation is controlled but whose amplitude and frequency rise are limited (magnetic loop).

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

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

[0007] - to apply a high electromagnetic field whose orientation is controlled and preferably close to, 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 to guarantee the protection of microwave emission systems supplying the applicator, thanks to the non-inductive nature of the device. Description of the invention

[0010] The invention aims to remedy, at least in part, the drawbacks of the prior art, and more particularly to provide an electromagnetic field applicator that allows, among other things, the application of a strong electromagnetic field with a controlled orientation, preferably close to, or even very close to, plane wave conditions, and provides better spectral coverage than other devices. Preferably, this device is non-inductive.

[0011] To this end, an object of the invention relates to an electromagnetic field applicator which comprises, along a longitudinal axis: • A first flared part having a pointed end that can be inserted at one end of a waveguide; • A second rounded end section, combined with the flared shape, allows the electromagnetic field to be transmitted.

[0012] An electromagnetic field applicator according to the invention is adapted to transmit an electromagnetic field with good plane wave conditions, 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 of less than 10% of the incident level and guarantees the protection of the microwave transmission systems powering the applicator. Indeed, this applicator has a non-inductive character, unlike magnetic loops, allowing for frequency increases with little or no loss. Monopoles and magnetic loops do not provide such good matching with respect to the electromagnetic frequencies used and result in strong reflection of the incident microwave signal.

[0013] According to one embodiment, the flared shape may include a cone along the longitudinal axis, and may then be extended by a frustoconical part cut by four intersecting planes parallel to the axis of the cone and facing each other in pairs: • the first two intersecting planes being distant from each other and 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 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 can be in contact with the base of the frustoconical portion, or the second part can be connected to the first part in a plane perpendicular to the axis. Preferably, the first part has a uniform dielectric permittivity.

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

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

[0017] The waveguide can be capable of transmitting waves in at least one frequency band X, and / or Ku, and / or Ka: an applicator according to the invention can thus adapt, by scaling effect, to different waveguides and consequently, it can 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 for 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 an additive manufacturing or machining step in the mass. Brief description of the drawings

[0020] Other aspects, objectives, advantages and features of the invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0021] [Fig.1A] is a schematic front view of the electromagnetic field applicator;

[0022] [Fig.1B] is a schematic top view of the electromagnetic field applicator;

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

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

[0025] [Fig.3] is an example of the E field 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 throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are inclusive, unless otherwise stated.

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

[0030] For the purposes of this application, a wave is said to be plane if the wave vector defining its direction of propagation is constant in both sense and direction. This direction is called the wave propagation direction, 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 flat 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 impedance of free space (377 Q).

[0031] Figures IA, IB and IC are respectively schematic front, top and side views of an applicator 1 according to an embodiment of the invention.

[0032] A three-dimensional XYZ direct coordinate system is defined herein and for the remainder of the description, where the X and Z axes form a plane parallel to the principal plane of the applicator 1, and where the Y axis is oriented along the thickness of the applicator 1, from the first face Fl towards the second face Fl'. As can be seen from these figures, an electromagnetic field applicator according to the invention has symmetry with respect to the XY plane and 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 flared from a first end 6, in the shape 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 enabling the transmission of the electromagnetic field.

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

[0035] The applicator 1 can be made from a dielectric, preferably biodegradable polylactic acid, and can be used in 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 flared, conical portion 2, in this example. The conical shape, whose apex has an angle α, for example less than 20 degrees, thus includes a pointed end 6 which allows for the gradual adaptation of the dielectric permittivity of air to that of the dielectric material. Indeed, when an electromagnetic wave propagates in a medium or waveguide, 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 portion (or even all of it if the difference is very large) of the microwave signal is reflected. In the case of a waveguide, the incident signal is reflected back to the generator. The pointed shape allows for the gradual integration of the different relative permittivity in order to avoid this reflection.Furthermore, reflection generates a standing wave phenomenon (SWR, or standing wave rate) which can create and impose high voltages on the generator. Some generators can tolerate any standing wave rate. However, ensuring the non-reflectivity of these waves allows for the use of less expensive generators and improved user safety. Moreover, the non-reflectivity of the applicator allows for a greater increase in intensity. Thus, an applicator according to the invention can radiate almost all of the incident power, and the waveguide, due to its characteristic impedance, is capable of tolerating strong electromagnetic fields.

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

[0038] The conical portion 2 is extended by a frustoconical portion 3 along the longitudinal axis X. This shape also allows for slight focusing of the EM field. As illustrated in Figures IA and IB, the frustoconical portion 3 is the part between the two dashed lines.

[0039] This frustoconical portion 3 has a thickness extending along the Y-axis between a first face Fl and a second Fl'. The faces Fl and Fl' are parallel to each other and opposite each other. In this example, the faces Fl and Fl' are substantially flat.

[0040] The thickness of the frustoconical portion 3, defined along the Y-axis between the first and second faces F1 and F2', is chosen to ensure good contact or adhesion of the applicator 1 against the inner walls of the rectangular waveguide 5 when it is inserted into it (examples of waveguide dimensions are given below), in order to force the electric field to pass through the dielectric. The base of the frustoconical portion 3 extends along the Z-axis between a first face F2 and a second face F2' (see [Fig. 1A]). The faces F2 and F2' are parallel to each other and opposite each other. In this example, the faces F2 and F2' are substantially flat.The base of the frustoconical section 3 has a transverse dimension in the XZ plane between the first and second faces F2, F2', which, again, is chosen to ensure good application or adhesion of the applicator 1 against the inner walls of the rectangular waveguide 5 (see examples below) when it is inserted into it, 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 provide flat surfaces that allow for better application or adhesion of the applicator against the walls of the rectangular waveguide 5.

[0041] The frustoconical 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 combination of the conical part 2 and the frustoconical part 3, has a height h which depends on the angle a

[0043] [Forml]

[0044] h = (F2F3 / 2 tan (oc / 2)

[0045] The frustoconical 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 portion 4 has at least a radius of curvature equal to (F2F'2) / 2, for example, between approximately 3.5 mm and 11.4 mm for the waveguide examples given below. The rounded portion allows for slight focusing of the output electromagnetic field and promotes plane wave conditions at short distances. As shown in [Fig. 1A], this second part 4 connects to the first part 3 along a plane perpendicular to the axis (X) of the device. Preferably, the connection provides 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 that can vary depending on the frequencies it is to carry. For example, the waveguide 5 can be a WR90 or GT16 type waveguide (a waveguide suitable for the X frequency band, the reference in "GT" being the British reference) with internal dimensions of approximately 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 about 23 mm x 0 mm (example mentioned above) and about 7.1 mm x 3.6 mm (Ka band, WR28 or GT22 guide), for example 15.8 mm x 7.9 mm (Ku band, WR62 or GT18 guide) or about 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 within the frequency range from approximately 8 GHz to 40 GHz originating 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 thanks to 3D printing 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 and 10 GHz. The numerical study was performed using the commercial software CST Microwave Studio to achieve a gradual matching of the wave impedance (the target value of 377 ohms). Figure 3 shows the radiation of the applicator 1 thus manufactured 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, the periodic peaks III of medium intensity (400 V / m) of this same electric field propagating in air are visible.

[0050] The simulation and the experiment were compared; Table 1 below shows this comparison at a frequency of 9 GHz. A discrepancy between the numerical simulation and the measurement is often observed due to non-ideal conditions. Experimentation at high frequencies revealed a discrepancy between simulation and experimentation. The simulation was performed using an imaginary perfect metal (PEC), in which there are no losses. In contrast, the experiment was conducted using a WR90 brass waveguide, which does exhibit losses. Furthermore, the transition from the coaxial feed to propagation within the waveguide behaves like an antenna whose position depends on the frequency. The WR90 waveguide is designed for frequencies between 8 and 12 GHz; the transition position is a compromise aimed at minimizing losses across the entire frequency band. These differences become more pronounced as the frequency increases. The higher the frequency, the greater the emphasis placed on achieving a high level of mechanical engineering, a good surface finish, and high purity of the conductive material.

[0051] [Tables 1] @ 9GHz for 1 W E-field at contact E-field at 35 mm Simulation 800 Vm 1250 V.m1 Measurement 680 Vm 1212 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 viewed from the front. The horizontal arrows IV in [Fig. 4A] represent the low-intensity magnetic field 0 A / m. Arrows V, VI, and VII (see [Fig. 4B]) represent the low-intensity electric field 0 V / m, the medium-intensity electric field between 500 and 600 V / m, and the high-intensity electric field between 900 and 1000 V / m, respectively.

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

[0054] At the tip of a device according to the invention, the plane wave conditions are not entirely met; however, strong, highly localized electric field levels are obtained, while ensuring orthogonality of the magnetic and electric field components. At 4 cm from the applicator outlet, the illumination is slightly less localized and the electric field levels slightly lower, but all the plane wave illumination conditions are met.

[0055] The problems related to the orientation of the electric field are resolved by the orthogonality of the E and H components. The reasons for this phenomenon are presented below. When the electromagnetic wave propagates through 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 field behavior in this zone, whereas in the other zones these characteristics are not guaranteed. In particular, in the field region In the far field, meaning that as the distance from the source increases, the wavefronts become increasingly planar, the electric and magnetic fields are both sinusoidal, their amplitude decreases inversely with the distance, and they are orthogonal to each other and to the z-direction of propagation (Poynting vector). The E / H ratio between the electric and magnetic fields is equal to the characteristic impedance of free space, which is 377 ohms. Thus, it is observed that the invention, according to experiments, makes it possible to obtain the characteristics of a far-field region only 4 cm from the device's output. More precisely, far-field characteristics are found at a close distance, in particular the orthogonality of the fields to each other and to their propagation vector, and the E / H ratio is constant.

[0056] One application of a device according to the present invention is the study of the susceptibility of electronic components to electromagnetic interference. In order to evaluate the reaction of an electronic component subjected to electromagnetic interference, a device according to the invention makes it possible to apply the microwave interference to the component under test. More specifically, the device makes it possible to apply to an electronic component an electromagnetic field that is 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 strong electromagnetic fields to biological tissues, representative of those that can be generated by an electromagnetic weapon, in order to assess their potential danger to humans. It can also be used for treatment applications on pathogenic tissues by applying electromagnetic radiation.

Claims

Demands

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 shape 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 allowing to transmit an electromagnetic field, Characterized in that the first part (2, 3) comprises, along the longitudinal axis, a cone (2), then is 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 in pairs: the first two planes (Fl, Fl') being distant from each other and forming first flat surfaces of support on the edges of the waveguide;the two second planes (F2, F2') being distant from each other and forming second flat support surfaces on the edges of the waveguide, the first flat support surfaces being perpendicular to the second flat support surfaces.;

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

3. 3. Applicator according to one of claims 1 or 2, the second part connecting to the first part in a plane perpendicular to the axis (X).

4. Applicator according to any one of claims 1 to 3, the applicator is made of dielectric material, for example polylactic acid.

5. Electromagnetic field emission device comprising an applicator according to any one of claims 1 to 4 and a rectangular waveguide (5).

6. Device according to claim 5, the waveguide being capable of transmitting waves in at least one frequency band X, and / or Ku, and / or Ka.

7. Method of generating an electric field comprising the steps of: - Insertion of an applicator according to one of claims 1 to 4 at the output of a waveguide (5);

8.

9. - then sending an intense electromagnetic field into this waveguide; Method according to claim 7, the electric field being directed towards an electronic component or towards a biological tissue. Method of manufacturing an applicator according to any one of claims 1 to 4, comprising an additive manufacturing or machining step in solid.

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