EP1946623B1 - Device for igniting and generating an expanding diffuse microwave plasma and device for plasma treating surfaces and substances by using this plasma - Google Patents

Description

State of the art

The present invention relates to a device for igniting and generating a propagating, diffuse microwave plasma. The device is suitable for generating microwave plasmas for the purpose of plasma treatment of surfaces and substances, in particular of three-dimensional objects, as well as of particles under atmospheric pressure.

Microwave plasmas are eminently suitable for performing various plasma treatments, such as e.g. the activation, purification, coating, sterilization, modification and functionalization of surfaces. For this purpose, the use of a diffuse, largely homogeneous, expanded plasma is desired.

In known methods ( DE 4235914 A1 . EP0209469 . DE19726663 The ignition and production of such plasmas preferably takes place in the low-pressure region or near-atmospheric region. While booting up and application to the normal pressure range is possible, it makes the plasma treatment process very vulnerable and unstable. In the case of minor changes (eg due to gas flow, admixture of process gases as well as of aerosols and particles), the plasma is extinguished and has to be re-ignited with great difficulty.

Other known processes for plasma treatment under atmospheric pressure, such as the barrier discharge, are not suitable for the treatment of three-dimensional objects and highly structured surfaces.

Plasmajets of various designs ( DE19605518 . EP0968524 . US5798146 ) generally require a high gas flow to drive out the plasma, usually a special working gas and are problematic in the ignition behavior. In addition, they only generate a small plasma volume with a small diameter. As a result, they are not suitable for mass applications and too expensive to manufacture and operate.

Thus, a method would be advantageous for the ignition and generation of a spatially extended plasma in normal pressure or high pressure with high ignition safety and stable operation and the lowest possible gas throughput.

US-A-6 0430608 describes a plasma treatment apparatus in which the plasma is RF-powered by using a multi-element antenna symmetrically disposed on an antenna holder, two antennas forming a resonant circuit with each other. The antenna assembly is electrically connected to the RF source via a coaxial line. The antenna structure is separated from the process chamber and the substrate by a dielectric barrier. The substrate is in a vacuum chamber at a lower pressure. The entire power is transmitted to the plasma via the antenna arrangement. A plasma treatment under atmospheric pressure is not possible.

U.S.-A-5,401,351 describes a device for generating an RF-ECR plasma by means of a coaxially electrically coupled antenna and an arrangement of a plurality of permanent magnets for generating a magnetic field. The ECR technique is not transferable to atmospheric pressure.

EP-A-0 420 101 describes a device for generating a microwave plasma by a plurality of fins are arranged perpendicular to the electric field in the waveguide. Nothing is said about the type of ignition. Resonant circuits for generating a required for the plasma ignition resonance field strength can not be seen.

In US-B1-6,645,343 For example, a plasma reactor for plasma coating, plasma treatment and plasma etching is described, in which the plasma reactor itself is designed as a resonator. The plasma formation takes place within the plasma reactor in a vacuum, since a microwave window of dielectric material in the microwave coupling separates the different pressure ranges. Although there is a coaxial coupling of the microwaves in the plasma reactor, a resonant ignition structure is not visible on the inner conductor or on the outer conductor.

Disadvantage of this device is that the plasma can be ignited only in vacuum and there is no separation between the ignition phase and maintenance phase of the plasma, since a resonant ignition structure is not present.

In US-B2-6 841 201 An arrangement for producing a microwave-excited plasma at near-atmospheric conditions will be described. A coaxial microwave line structure and a resonant ignition structure can not be seen.

DE-A1-101 44 466 discloses a method and apparatus for generating a plasma in electromagnetic fields by electrodeless ignition in free space within an electromagnetic wave limiting structure. It shows Fig.1 a possible application with a specific ignition structure as a field strength exaggerating element with at least three arranged in resonance sub-elements.

DE-A1-103 27 853 shows a method and a device for plasma treatment on surfaces and substances within a wave-limiting waveguide structure by means of a moving plasma. The plasma is ignited in a closed chamber, whereby the plasma moves within the object to be treated, but does not emerge from this.

The elimination of elaborate vacuum technology and the low consumption of working and process gases as well as simple and safe handling make a broader and more cost-effective application of plasma treatment possible in many areas.

Presentation of the invention

The present invention is therefore based on the object of specifying a device for igniting and generating a diffuse, spatially extended microwave plasma, which can be realized in normal and high pressure in a simple and reliable manner and, in principle, without gas flow.

The diffused microwave plasma should make effective plasma treatment possible under atmospheric pressure due to its high stability with regard to plasma generation and entertainment, low gas consumption and large plasma volume.

The solutions according to the invention are represented in the patent claims.

1. a. dass die wellenbegrenzende Hohlstruktur (1) rohrförmig und an einem Ende (9) offen ausgeführt ist, wobei der Rohrdurchmessers < λ/2 (Lambda/2) der verwendeten Frequenz des Mikrowellengenerators beträgt,
2. b. dass das offene Ende (9) über das Ende des als resonante Zündstruktur (3) ausgebildeten Innenleiters (14) hinaus verlängert ist, und
3. c. die resonante Zündstruktur (3) selbst als koaxiale Struktur mit einem offenen Ende (7a) und einer resonanten Oberflächen-Länge von λ/2 gebildet wird, wobei Innenleiter (3b) der resonanten Zündstruktur (3) und Außenleiter (3a) der resonanten Zündstruktur (3) der koaxialen Struktur mit je λ/4 annähernd gleich lang sind..

Device for igniting and generating a propagating, diffuse microwave plasma consisting of a coaxial line, which is formed by a resonant ignition structure (3) in extension of the inner conductor (14) and a wave-limiting hollow structure (1) as an outer conductor. Furthermore, with the aid of a microwave generator (4) and a microwave feed (5), coupling takes place into the coaxial line which is formed from the inner conductor (14) with the resonant ignition structure (3) and the wave-limiting hollow structure (1). The device is characterized

1. a. in that the wave-limiting hollow structure (1) is tubular and open at one end (9), wherein the pipe diameter <λ / 2 (lambda / 2) is the frequency of the microwave generator used,
2. b. the open end (9) is extended beyond the end of the inner conductor (14) designed as a resonant ignition structure (3), and
3. c. the resonant ignition structure (3) itself is formed as a coaxial structure with an open end (7a) and a resonant surface length of λ / 2, inner conductor (3b) of the resonant ignition structure (3) and outer conductor (3a) of the resonant ignition structure (FIG. 3) of the coaxial structure with each λ / 4 are approximately equal in length.

1. a. dass die resonante Zündstruktur (3) in der wellenbegrenzenden Hohlstruktur (1) angeordnet ist und aus einem Innenleiter (3b) und einem Außenleiter (3a) der resonanten Zündstruktur (3) besteht, wobei der Innenleiter (14) und der Innenleiter (3b) der resonanten Zündstruktur (3) eine koaxialen Leitung bilden,
2. b. dass die wellenbegrenzende Hohlstruktur (1) rohrförmig und an einem Ende (9) offen ausgeführt ist, wobei der Rohrdurchmessers < λ/2 (Lambda/2) der verwendeten Frequenz des Mikrowellengenerators beträgt,
3. c. dass das offene Ende (9) über das Ende des Innenleiters (14) und über das Ende des Innenleiters (3b) der resonanten Zündstruktur (3) hinaus verlängert ist, und
4. d. dass der Innenleiter (3b) und der Außenleiter (3a), dessen elektrisch wirksame Länge durch die Länge des Innenleiters (3b) bestimmt ist, der resonanten Zündstruktur (3) die koaxiale Struktur mit einem offenen Ende (7a) und einer resonanten Oberflächen-Länge von λ/2 bilden.

A further embodiment of the device according to the invention consists of an inner conductor (14) and a wave-limiting hollow structure (1) as outer conductor, a microwave generator (4) and a microwave feed (5), which in the of the inner conductor (14) and the wave-limiting hollow structure (1). formed coaxial line, and is characterized

1. a. in that the resonant ignition structure (3) is arranged in the wave-limiting hollow structure (1) and consists of an inner conductor (3b) and an outer conductor (3a) of the resonant ignition structure (3), wherein the inner conductor (14) and the inner conductor (3b) are the resonant ignition structure (3) form a coaxial line,
2. b. in that the wave-limiting hollow structure (1) is tubular and open at one end (9), wherein the pipe diameter <λ / 2 (lambda / 2) is the frequency of the microwave generator used,
3. c. that the open end (9) is extended beyond the end of the inner conductor (14) and beyond the end of the inner conductor (3b) of the resonant ignition structure (3), and
4. d. in that the inner conductor (3b) and the outer conductor (3a), the electrically effective length of which is determined by the length of the inner conductor (3b), of the resonant ignition structure (3) have the coaxial structure with an open end (7a) and a resonant surface length of λ / 2 form.

The device is preferably applied in atmospheric pressure.

By applying a gas flow, a driving of the plasma is possible, which can cause an increase in the plasma volume according to the coupled power.

The device can be realized with any gases and their mixtures with and without gas flow.

A particularly interesting embodiment of the device is the generation of an expanding, diffuse plasma within a coaxial hollow structure. Here, the inner conductor is designed at the end as a resonant ignition structure so that a microwave coupling leads to the ignition of the plasma, but the plasma via the coaxial line self-powered. The diameter of the coaxial outer conductor is to be chosen so that according to the frequency used in the continuation of the outer conductor beyond the end of the inner conductor beyond a wave propagation through the open end of the outer conductor is not possible, however, a protrusion of the plasma from the opening is given.

If the resonant ignition structure in the vicinity of a field maximum of a microwave field is arranged so that the forming plasma grows into the field maximum, detachment of the plasma from the ignition structure can be achieved.

In an arrangement of the resonant ignition structure at one end of a waveguide and a feeding of the microwaves from the other end of the resonant ignition structure is largely decoupled from the microwave supply after formation of the plasma. This protects the ignition structure from the effects of the plasma.

Microwave frequencies of 400 to 10,000 MHz are suitable for the generation of the plasma.

The plasma can be influenced in its properties (eg temperature, expansion) by pulsation and modulation of the energy supply.

By a targeted arrangement of the resonant ignition structure within the wave-limiting hollow structure and a corresponding opening, the plasma can be reached from the wave-limiting hollow structure.

The device may be used in such a way that a diffuse microwave plasma emerging from the structure is ignited within a coaxial hollow structure, substances suitable for plasma treatment are supplied to the plasma and surfaces and substances to be treated are guided into the effective area of the plasma ,

The substances intended for the plasma treatment can be supplied in solid (powdery), liquid and gaseous form to the plasma.

To achieve a specific plasma effect, e.g. the generation of a specific UV radiation, a modulation and pulsation of the energy supply is suitable.

By selective feeding of the substances inside or outside the wave-limiting hollow structure, a selective and controllable modification of these substances takes place. Any undesirable reaction of the added substance on the ignition behavior and the ignition structure is prevented by the addition outside of the wave-limiting hollow structure.

A plasma treatment can be carried out only with atmospheric air under normal pressure. By feeding mixtures such as e.g. Aerosols can be achieved a specific effect.

By a defined supply of various gases, such as the process gas in the plasma core region and an inert gas as Hüllund inert gas to the plasma, a certain shielding of the plasma is to be achieved by atmospheric influences.

The device can be influenced in its scope and performance in that a plurality of plasma sources are arranged in series, annular to each other and one above the other or as an array.

• einen Mikrowellengenerator zum Erzeugen von Mikrowellen
• eine Mikrowellenleitung
• eine Mikrowelleneinspeisung
• eine wellenbegrenzenden Hohlstruktur
• eine resonante Zündstruktur
• eine Zuführvorrichtung für Stoffe

A preferred device contains the following elements:

• a microwave generator for generating microwaves
• a microwave line
• a microwave feed
• a wave-limiting hollow structure
• a resonant ignition structure
• a feeding device for substances

A device with these features can be configured appropriately by virtue of the fact that the microwave line is made flexible and substances are supplied to the plasma via a plurality of feed devices.

Brief description of the drawings

The invention will be explained below with reference to exemplary embodiments.

• Fig.1 eine schematische Darstellung einer Grundvorrichtung zur Erzeugung eines sich ausdehnenden, diffusen Mikrowellenplasmas,
• Fig.2 eine schematische Darstellung der erfindungsgemäßen Lösung in einer speziellen Ausführungsform zur Erzeugung eines sich ausdehnenden, diffusen Mikrowellenplasmas aus einer koaxialen wellenbegrenzenden Hohlstruktur heraus,
• Fig. 3 eine schematische Darstellung der erfindungsgemäßen Lösung in einer speziellen Ausführungsform der resonanten Zündstruktur als Koaxialstruktur,
• Fig. 4 Grundaufbau einer Plasmabehandlungsvorrichtung,
• Fig. 5 Plasmabehandlungsvorrichtung mit einer flexiblen Stoffzuführung.

Show it:

• Fig.1 a schematic representation of a basic device for generating an expanding, diffuse microwave plasma,
• Fig.2 a schematic representation of the solution according to the invention in a special embodiment for generating an expanding, diffuse microwave plasma from a coaxial wave-limiting hollow structure,
• Fig. 3 a schematic representation of the solution according to the invention in a special embodiment of the resonant ignition structure as a coaxial structure,
• Fig. 4 Basic structure of a plasma treatment apparatus,
• Fig. 5 Plasma treatment device with a flexible material feed.

Way (s) for carrying out the invention

In Fig. 1 FIG. 3 shows the schematic structure of a basic device for implementing the method for igniting and generating an expanding, diffuse microwave plasma within a wave-limiting hollow structure.

The device consists of a wave-limiting hollow structure 1, a resonant ignition structure 3, a microwave generator 4 and a microwave feed 5.

In Fig. 2 the schematic structure of the solution according to the invention in a specific embodiment for generating a propagating diffuse Mikrowellenplasmas 2 from a coaxial wave-limiting hollow structure 1 out.

For many plasma applications, especially for three-dimensional applications, a free emerging plasma under atmospheric conditions is of particular importance. Insofar the in Fig. 2 illustrated embodiment of the method a great market need.

The device consists of a wave-limiting hollow structure 1, a resonant ignition structure 3, a microwave generator 4, a flexible microwave line 8 and a microwave feed 5 into the wave-limiting hollow structure 1.

The wave-limiting hollow structure 1 is designed in this case as a tube with an open end 9. The diameter of the tube is selected according to the frequency used (2.45 GHz) so that wave propagation is not possible (<λ / 2 - small lambda / 2).

The microwave feed 5 via a flexible microwave line 8 in the wave-limiting hollow structure 1. The resonant ignition structure 3 is in extension of the inner conductor 14 of the coaxial line whose outer conductor is formed by the Wellenbegrenzende hollow structure 1, carried out so that on the one hand a direct energy input into the resonant Ignition structure 3 for plasma ignition 7 takes place and on the other hand with the wave-limiting hollow structure 1 as outer conductor a coaxial line is formed, is guided over the energy to the end of this coaxial line and thus outside the resonant ignition structure 3 builds up an electromagnetic field. Since the wave-limiting hollow structure 1 is extended beyond the end of the inner conductor 14, a wave propagation through the opening 9 to the outside is not possible. The microwave energy generated by the microwave generator 4 is partly coupled via the flexible microwave line 8 into the resonant ignition structure 3, so that a plasma ignition 7 takes place at the tip of the resonant ignition structure 3, and via the coaxial formed by the resonant ignition structure 3 and the wave-limiting hollow structure 1 Conducted to the end of this coaxial line, so that the ignited by the resonant ignition structure 3 plasma 2 is supplied via this coaxial line with energy so that a propagation of the plasma 2 takes place in such a way that a propagation to the outside is achieved.

The plasma 2 is ignited in air under atmospheric conditions and emerges from the opening 9 automatically.

According to the used frequency of 2.45 MHz and the power supplied, a plasma diameter and an exit length of several cm can be achieved.

Fig. 3 shows a schematic representation of the solution according to the invention in a particularly advantageous embodiment of the resonant ignition structure 3 as a coaxial structure with an open end 7a and with the outer conductor 3a and the inner conductor 3b of the resonant ignition structure 3. This is given by the fact that they act as a coaxial structure with a resonant Surface length of λ / 2 (lambda / 2) (half wavelength) or an odd multiple of λ / 2 (lambda / 2) is performed according to the frequency used. The depth of the resonant ignition structure 3 is approximately lambda / 4 in this example.

This resonant ignition structure 3 can be arranged both in the inner conductor 14 and in the outer conductor of the coaxial line.

In Fig. 4 the schematic basic structure of a surface plasma treatment apparatus is shown.

The microwave energy generated by a microwave supply 4 is fed coaxially into the wave-limiting hollow structure 1 via a preferably flexible microwave line 8. The wave-limiting hollow structure 1 is preferably dimensioned as a tube corresponding to the frequency of 2.45 GHz used here so that wave propagation is possible only in the region of the coaxial structure. Wave propagation beyond the open end of the wave-limiting structure 1, however, is not possible by sufficient extension of the wave-limiting structure 1.

The resonant ignition structure 3 is coupled as an extension of the coaxial feed 5 to the power supply, that at a Energieeinkopplung a high ignition field strength at the top of the resonant ignition structure 3 is formed, which is sufficient for plasma ignition 7, a supply of the ignited plasma 2 but more resonant from the Ignition structure 3 as an inner conductor 14 and the wave-limiting hollow structure 1 formed as an outer conductor coaxial line takes place.

Thus, depending on the amount of energy fed in, an expanding plasma 2 which propagates out of the opening of the wave-limiting structure 1 is produced.

A surface 13 to be treated is now placed in the effective area of the plasma 2 such that a desired treatment effect, e.g. an activation of the surface 13 is achieved.

The plasma treatment can be carried out without any active gas flow with air at atmospheric pressure. To actively design the plasma treatment, suitable substances can be supplied to the plasma 2 both inside and outside the wave-limiting structure 1 via a special delivery device 12 for achieving a defined treatment effect. By supplying a gas, further spreading of the plasma 2 is achieved. The substances are located in a container 10 and are supplied to the plasma 2 via the supply device 12. By replacing the container 10, various substances can be used depending on the desired application. By arranging the container 10 directly on the shaft-limiting hollow structure 1, a high flexibility and mobility of the device is given.

Fig. 5 shows one opposite Fig. 4 extended device with which provided for a plasma treatment substances are supplied via a flexible line 11 of the fabric containers 10 via the feed device for substances 12 to the plasma 2. By this design, various substances can be stored in separate containers 10 in larger quantities and supplied to the plasma 2 as needed. This embodiment is particularly advantageous in stationary systems with high processing capacities and throughputs.

LIST OF REFERENCE NUMBERS

1

wave-limiting hollow structure

2

plasma

3

resonant ignition structure

3a

Outer conductor of the resonant ignition structure 3

3b

Inner conductor of the resonant ignition structure 3

4

microwave generator

5

microwave feed

6

resonant circuit

7

plasma ignition

7a

open end of the coaxial ignition structure

8th

flexible microwave line

9

Opening in the wave-limiting hollow structure

10

Container for substances

11

flexible supply of substances

12

Feed device for substances

13

surface to be treated

14

Inner conductor of the coaxial line whose outer conductor is formed by the wave-limiting hollow structure 1

Claims (6)

1. Device for igniting and generating an expanding, diffuse microwave plasma, consisting of a coaxial line, which is formed by a resonant ignition structure (3) as an extension of an inner conductor (14) and a wave-limiting hollow structure (1) as an outer conductor, a microwave generator (4) and a microwave feed (5), which goes into the coaxial line formed by the inner conductor (14) with the resonant ignition structure (3) and the wave-limiting hollow structure (1), characterized

   a) in that the wave-limiting hollow structure (1) is of a tubular configuration that is open at one end (9) in order to achieve the effect that the plasma exits from the wave-limiting hollow structure, the tube diameter being < λ/2 (lambda/2) of the frequency used for the microwave generator,

   b) in that the open end (9) is extended beyond the end of the inner conductor (14) formed as the resonant ignition structure (3) and

   c) the resonant ignition structure (3) itself is formed as a coaxial structure with an open end (7a) and a resonant surface length of λ/2, the inner conductor (3b) of the resonant ignition structure (3) and the outer conductor (3a) of the resonant ignition structure (3) of the coaxial structure being of approximately the same length, each of λ/4.
2. Device for igniting and generating an expanding, diffuse microwave plasma, consisting of an inner conductor (14) and a wave-limiting hollow structure (1) as an outer conductor, a microwave generator (4) and a microwave feed (5), which goes into the coaxial line formed by the inner conductor (14) and the wave-limiting hollow structure (1), characterized

   a) in that a resonant ignition structure (3) is arranged in the wave-limiting hollow structure (1) and consists of an inner conductor (3b) and an outer conductor (3a) of the resonant ignition structure (3), the inner conductor (14) and the inner conductor (3b) of the resonant ignition structure (3) forming the coaxial line,

   b) in that the wave-limiting hollow structure (1) is of a tubular configuration that is open at one end (9) in order to achieve the effect that the plasma exits from the wave-limiting hollow structure, the tube diameter being < λ/2 (lambda/2) of the frequency used for the microwave generator,

   c) in that the open end (9) is extended beyond the end of the inner conductor (14) and beyond the end of the inner conductor (3b) of the resonant ignition structure (3), and

   d) in that the inner conductor (3b) of the resonant ignition structure and the outer conductor (3a), the electrically effective length of which is determined by the length of the inner conductor (3b) of the resonant ignition structure, of the resonant ignition structure (3) form the coaxial structure with an open end (7a) and a resonant surface length of λ/2.
3. Device according to Claim 1 or 2, characterized in that the microwave feed (5) takes place by way of a flexible microwave line (8).
4. Device according to Claim 1 or 2, characterized in that containers for substances (10) with a supply device (12) are arranged directly at the wave-limiting hollow structure (1).
5. Device according to Claim 1 or 2, characterized in that containers for substances (10) with supply devices (12) are connected to the wave-limiting hollow structure (1) by way of a flexible line (8, 11).
6. Device according to one of Claims 1 to 4, characterized in that the microwave feed (5) takes place in a modulated and pulsed manner.

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