EP0122840B1 - Microwave treating apparatus, especially for coupling devices of an electromagnetic wave to an absorbent material - Google Patents

Abstract

1. Treating apparatus for the transfer of electromagnetic energy from a microwave source to a material to be heated, in particular a slow wave type device co-operating with a coupling device between the microwave source and the material ot be heated, possibly comprising a means for conveying said material to be heated, consisting of in particular gas fluid or liquid propulsing and sustaining means, wherein said coupling device comprises a principal multi dielectric structure presenting a dielectric permittivity gradient and radiating a damped wave in the presence of said material to be heated, the latter being positioned at a distance from this multi dielectric structure of less than one wavelength, the principal multi dielectric structure co-operating with one or several secondary multi dielectric structures, positioned at a distance from the principal structure of no greater than one wavelength and being excited by this structure in the presence of said material to be heated, said material to be heated having a dielectric permittivity greater than that of the immediately adjacent dielectric.

Description

The present invention relates to a microwave applicator for heating dielectric or multi-dielectric materials which may include a metallic element in any form.

• - une source de micro-ondes, généralement constituée par un magnétron,
• - un dispositif de couplage, notamment un guide d'ondes, et
• - un applicateur, qui assure le transfert d'énergie entre la source de micro-ondes et le corps à chauffer.

In microwave heating applications, in combination:

• - a microwave source, generally consisting of a magnetron,
• - a coupling device, in particular a waveguide, and
• - an applicator, which ensures the transfer of energy between the microwave source and the body to be heated.

• - applicateurs à cavité ou à résonateur, qui sont utilisés pour la cuisson d'aliments et d'autres applications industrielles;
• - applicateurs à onde progressive, dans lesquels le matériau à chauffer, sous forme de feuilles ou de fils, traverse un guide d'ondes fendu à section transversale rectangulaire;
• - applicateurs à onde lente, dans lesquels le matériau à chauffer se déplace à proximité d'une ligne de propagation ouverte interagissant avec le champ électrique extérieur inhomogène de la ligne, et
• - applicateurs à onde libre, qui est pratiquement constitué par une antenne qui transmet l'énergie électromagnétique à des pièces de grandes dimensions, que l'on ne peut pas placer dans une enceinte fermée.

Existing applicators are grouped into four main types:

• - cavity or resonator applicators, which are used for cooking food and other industrial applications;
• - traveling wave applicators, in which the material to be heated, in the form of sheets or wires, passes through a split waveguide of rectangular cross section;
• - slow wave applicators, in which the material to be heated moves close to an open propagation line interacting with the inhomogeneous external electric field of the line, and
• - free wave applicators, which is practically constituted by an antenna which transmits electromagnetic energy to large parts, which cannot be placed in a closed enclosure.

In applicators, in particular slow wave, it is known to produce the scrolling of the product to be heated by a conveyor system by carpet, by Archimedes screw, by vibrator, and by lift and aerodynamic propulsion (cf. US Patent n ° 3,549,848).

In microwave heating, it is also known to use the properties of the permittivity gradients of the dielectrics to form structures exhibiting a permittivity gradient, as described in "Journal of Microwawe Power" 10 (1) 1975.

The main drawbacks of these systems lie in the mode of interaction of the electromagnetic wave with the dielectric material to be heated: in fact, the dielectric material introduced into the electromagnetic field disturbs the latter and mutes the line to the generator. To respond to this problem, it is necessary either to complicate the applicators by introducing automatic adaptation members, or to sacrifice performance by using ferrite circulators.

On the other hand, the leakage of electromagnetic energy through the openings, in the case of continuous heat treatment, poses major problems.

In addition, it is difficult to efficiently heat a dielectric material having a metallic element.

In addition, since each application defines the criteria for choosing the most suitable applicator in the above combination, it is necessary to specifically adapt the applicator, which makes it very expensive to develop it to obtain a good yield. .

The present invention relates to an electromagnetic energy transfer applicator between a microwave source and a material to be heated, in particular of the slow wave type and cooperating with a coupling device between the microwave source and the material. to be heated, as well as with a possible scrolling device for said material to be heated, in particular constituted by a propulsive-lifting device with gaseous or liquid fluid, or any other scrolling device known per se, which applicator is characterized in that said device coupling consists of a main multi-dielectric structure having a dielectric permittivity gradient and radiating an evanescent wave in the presence of said material to be heated when the latter is placed at a distance less than a wavelength relative to this multi-structure dielectric which main multi-dielectric structure (A) cooperates with one or more multi-dielectric structures ues secondary (B), which are arranged at a distance not exceeding a wavelength relative to the main structure (A) and which are excited by the latter in the presence of said material to be heated (10), which material to be heated has a dielectric permittivity greater than that of the immediately adjacent dielectric.

According to an advantageous arrangement of this embodiment, the secondary structure or structures are arranged symmetrically with respect to the material to be heated.

According to another advantageous embodiment of the applicator according to the invention, the main multi-dielectric structure is rigid and with circular symmetry so as to heat a fluid material.

According to an advantageous embodiment of the applicator according to the invention, said multi-dielectric structures are staggered in the mass of the fluid material to be heated.

According to yet another advantageous embodiment of the applicator according to the invention, the main multi-dielectric structure is flexible so as to adapt to the shape of the material to be heated, even of very large volume, or to wrap around the latter.

According to an advantageous embodiment of the applicator according to the invention, the main multi-dielectric structure and the secondary multi-dielectric structure form a two-wire line which can be wound around the material to be heated.

According to another advantageous embodiment of the applicator according to the invention, in the case where it comprises a propulsion device. fluid lift, the dielectric permittivity of the fluid used is such that it does not disturb the coupling.

According to yet another embodiment of the applicator according to the invention, the frequency of the electromagnetic energy is between 0.3 GHz and 300 GHz.

When a dielectric material travels between the empty space between these main and secondary multi-dielectric structures, part of the incident wave flowing in the main structure penetrates into the material to be heated, due to its comparatively high dielectric permittivity, and , according to its characteristics, a fraction of the energy is absorbed, while the other fraction penetrates into the secondary structure (s) and performs the same path further, undergoing a weakening each time it passes through the material to be heated.

The advantage of such an arrangement on all known coupling devices is that the adaptation of the microwave generator is always very good, whatever the dielectric material to be heated and its position relative to the walls, provided that its dielectric permittivity is greater in the above direction.

The multi-dielectric structure being of the slow wave type, the wave which leaves this structure is said to be evanescent, that is to say that it is a wave whose fields do not connect, therefore the wave does not propagate according to Maxwell's equations. The propagation of such a wave does not exceed a wavelength in the air. The remaining energy is therefore very low at a short distance, which is advantageous for the construction of the ovens.

• - la configuration des champs électriques dans le volume formé entre les deux structures est hybride et homogène,
• - le couplage d'énergie est proportionnel à la quantité de matériau à chauffer, et
• - la combinaison des différents diélectriques dans le volume d'interaction permet de maîtriser le chauffage.

It should also be noted that:

• - the configuration of the electric fields in the volume formed between the two structures is hybrid and homogeneous,
• - the energy coupling is proportional to the quantity of material to be heated, and
• - the combination of the different dielectrics in the interaction volume makes it possible to control the heating.

In addition to the foregoing provisions, the invention also comprises other provisions, which will emerge from the description which follows.

• - la figure 1 représente un applicateur selon l'invention sans le matériau à chauffer, comportant deux structures multi-diélectriques à gradient de permittivité diélectrique, situées l'une en face de l'autre à une distance ne dépassant pas une longueur d'onde;
• - la figure 2 représente l'applicateur de la figure 1 en présence du matériau à chauffer;
• - la figure 3 et la figure 4, coupe transversale de la figure 3, représentent la coopération de l'applicateur selon l'invention avec un dispositif propulso-sustentateur gazeux connu en soi;
• - la figure 5 représente un applicateur coopérant avec un dispositif propulso-sustentateur liquide;
• - la figure 6 représente un applicateur coopérant avec un dispositif propulso-sustentateur composé d'un lit de particules solides fluidisées;
• - la figure 7 représente un applicateur comportant une structure multi-diélectrique à gradient de permittivité diélectrique destinée à chauffer un liquide contenu dans un récipient fermé;
• - la figure 8 représente un applicateur comportant une pluralité de structures multi-diélectriques secondaires disposées en quinconce dans un conduit traversé par le matériau à chauffer, et
• - la figure 9 représente un applicateur comportant une structure multi-diélectrique principale souple entourant un objet volumineux à chauffer, notamment pour la mise hors gel d'arbres fruitiers.

The invention will be better understood using the additional description which follows which refers to the drawings in which:

• - Figure 1 shows an applicator according to the invention without the material to be heated, comprising two multi-dielectric structures with dielectric permittivity gradient, located one opposite the other at a distance not exceeding a wavelength ;
• - Figure 2 shows the applicator of Figure 1 in the presence of the material to be heated;
• - Figure 3 and Figure 4, cross section of Figure 3, show the cooperation of the applicator according to the invention with a propellant gas lift device known per se;
• - Figure 5 shows an applicator cooperating with a liquid propellant-lift device;
• - Figure 6 shows an applicator cooperating with a propellant-lift device composed of a bed of fluidized solid particles;
• - Figure 7 shows an applicator comprising a multi-dielectric structure with a dielectric permittivity gradient intended to heat a liquid contained in a closed container;
• FIG. 8 represents an applicator comprising a plurality of secondary multi-dielectric structures staggered in a duct through which the material to be heated passes, and
• - Figure 9 shows an applicator comprising a main flexible multi-dielectric structure surrounding a bulky object to be heated, in particular for frosting fruit trees.

It should be understood, however, that these drawings and the corresponding descriptive parts, are given solely by way of illustration of the subject of the invention, of which they do not in any way constitute a limitation.

The device shown in FIG. 1 comprises a set of two multi-dielectric structures A and B spaced apart by a wavelength p. The electromagnetic energy source 1 excites the structure A composed of two dielectrics 2 and 3, the element 2 of which has a permittivity lower than that of the element 3. The main incident wave 4, in the absence of material to be heated, is reflected at 6 until the auxiliary charge 8. Part 5 of the wave 4 propagates in the space between the two structures A and B. The structure B is not excited.

FIG. 2 represents the assembly A and B with a material 10 to be heated, which is included in the volume delimited by the two internal faces 9 of the structures A and B and whose permittivity is greater than that of the element 3.

The presence of this body 10 therefore modifies the propagation in the structure A in such a way that the evanescent wave 5 crosses the material to be heated 10 and enters the structure B to undergo a reflection 11. On the other hand, during the first reflection in structure A, the incident wave continues to propagate by successive reflections by repeating the phenomenon of coupling on the material.

The combination of incident waves leaving structure A and reflected waves coming from structure B gives an intense electric field in the interaction space, even very close to the metal walls 12.

FIG. 3 shows an example of application with a propellant-air lift box 14. The air jets exiting at 15 lift and propel the profile 16 in the longitudinal axis of the structure without disturbing the coupling; the adjusting members 13 allow to adjust the coupling on structure B (cf. figure 4).

FIG. 5 represents a structure combined with a liquid drive system 17 which may for example be an oil, the material 18 being in suspension.

FIG. 6 represents a structure combined with a propulsion system in a fluidized bed of solid particles 18 transporting materials to be heated 16.

FIG. 7 represents a structure 19 immersed in a closed metal box 20 filled with a material to be heated 21.

FIG. 8 represents a grouping of structures 22 staggered in a duct 23 without specification and where the material to be heated 24 circulates.

FIG. 9 represents a flexible structure 25 surrounding a bulky object to be heated, for example the freezing of fruit trees.

By way of nonlimiting example, the structure represented by the arrangement of FIGS. 1 to 4 can be applied to the heating of the extruded rubber profiles with a view to their vulcanization or polymerization or crosslinking, or even to electric cables.

The arrangement of Figures 5 and 6 can be applied to the continuous heating of powdered or granular materials.

The arrangement of Figure 7 allows the heating of materials inside a closed metal enclosure of any size, such as preserved.

The arrangement of Figure 8 allows the heating of very large volumes without special shielding precautions, for example the drying of grains moving by gravity in any duct.

The arrangement of FIG. 9 represents the heating of a tree or a greenhouse by a flexible structure 25. The energy coupling is carried out only on the regions close to 26 of the object to be heated 24 less than a length d 'wave.

As is apparent from the above, the invention is in no way limited to those of its embodiments and of application which have just been described more explicitly; on the contrary, it embraces all the variants which may come to mind of the technician in the matter without departing from the scope or the scope of the present invention.

Claims (9)

1. Treating apparatus for the transfer of electromagnetic energy from a microwave source to a material to be heated, in particular a slow wave type device co-operating with a coupling device between the microwave source and the material to be heated, possibly comprising a means for conveying said material to be heated, consisting of in particular gas fluid or liquid propulsing and sustaining means, wherein said coupling device comprises a principal multi dielectric structure presenting a dielectric permittivity gradient and radiating a damped wave in the presence of said material to be heated, the latter being positioned at a distance from this multi dielectric structure of less than one wavelength, the principal multi dielectric structure co-operating with one or several secondary multi dielectric structures, positioned at a distance from the principal structure of no greater than one wavelength and being excited by this structure in the presence of said material to be heated, said material to be heated having a dielectric permittivity greater than that of the immediately adjacent dielectric.

2. Treating apparatus in accordance with claim 1, wherein the secondary structure or structures are arranged symmetrically with respact to the material to be heated.

3. Treating apparatus in accordance with claim 1, wherein the principal multi dielectric structure is rigid and circularly symmetric so as to heat a fluid material.

4. Treating apparatus in accordance with one of the claims 1 & 3, wherein the multi dielectric structures are arranged in a zig-zag manner in the mass of the fluid material to be heated.

5. Treating apparatus in accordance with claim 1, wherein the principal multi dielectric structure is flexible and capable of being adapted to the shape of the material, possibly being of large volume, to be heated, or else capable of being wound around the material to be heated.

6. Treating apparatus in accordance with claims 1 and 5, wherein the principal multi dielectric structure and the secondary multi dielectric structure form a bifilar cable capable of being wound around the material to be heated.

7. Treating apparatus in accordance with claim 1, wherein the principal dielectric structure and the secondary multi dielectric structure or structures comprise a terminal auxiliary load.

8. Treating apparatus in accordance with claim 1, wherein, in the case comprising a propulsing and sustaining fluid, the dielectric permittivity of the fluid used is such that it does not interfere with the coupling.

9. Treating apparatus in accordance with one of the claims 1 to 8, wherein the frequency of the electromagnetic energy is between 0.3 GHz and 300 GHz.

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