Abstract:
The aim of the invention is to provide an alternative to the intensive treatment of a product, especially plasma treatment, in specific areas only. Towards this end, the invention provides a device for producing microwaves for treating workpieces, comprising at least one microwave antenna with an extended conductor for producing alternating electromagnetic fields, a housing that substantially extends over the length of the conductor, and an extended microwave decoupling area which follows the conductor and which is located in the housing. The housing is formed by at least one resonant cavity, which has a long shape and follows the course of the microwave antenna. The resonant cavity has at least one tapering, closed, first crown area and the decoupling area essentially extends in the focussing area of the resonant cavity. An at least non-divergent housing area adjoins the resonant cavity.

Description:
BACKGROUND OF THE INVENTION 
   The invention concerns a microwave generating device for the treatment of workpieces with at least one microwave antenna connected to a microwave source, the antenna having an elongated conductor for the production of alternating electromagnetic fields, with a housing forming a cavity resonator and with an output region for the microwaves located in a widening portion of the housing substantially in a focus region of the housing resulting from that widening, wherein an at least non-diverging housing region adjoins the widening portion of the housing. 
   WO 96/23318 (corresponds to DE 195 07 077 C1) discloses a plasma reactor categorizing the invention which comprises a rotationally symmetrical cavity in the form of an ellipsoidal resonator. The free end of a coupling pin is disposed at a first focusing point while a second focusing point of the ellipsoidal resonator is surrounded by a quartz cap thereby forming a plasma treatment region about that focusing point. Disadvantageously, the treatment region is small and concentrated only radially about the focusing point. 
   DE 195 03 205 C1 discloses a device for producing plasma in an underpressure container by means of alternating electromagnetic fields, wherein a rod-shaped conductor is guided, within a pipe of insulating material, through the underpressure container. The inner diameter of the pipe is larger than the diameter of the conductor and the pipe is filled with gas to prevent plasma from being generated therein. Plasma is produced in the direct surroundings of the pipe, since the rays are most intense at that location. The influence of the high energy input on the pipe, the change of the radiation due to impurities and the danger of forming a coating about the pipe are all disadvantages of this procedure. 
   DE 39 23 390 A1 discloses a device for generating a large area evaporated film using at least two separated activated gases. Towards this end, two microwave conducting cavities, each having its associated microwave generator, are disposed parallel to two opposite sides of a substantially rectangular housing. Rod antennas extend from the microwave generator in an alternating manner and at right angles to the extension of the conducting cavities, which are likewise parallel to each other, which penetrate into the housing, and which end and are terminated within the housing at the corresponding sides facing away from the respective conducting cavity. Standing microwaves of differing intensities are formed along the antennas. A certain degree of homogeneity is attained through the parallel configuration of the antennas and the staggered feeding thereof on opposite sides. This configuration is structurally demanding and therefore expensive. 
   It is the underlying purpose of the invention to further improve a device of this kind for the production of microwaves, in particular, for the continuous treatment of large workpieces. 
   SUMMARY OF THE INVENTION 
   This object is achieved in accordance with the invention with a device of this kind in that the cavity resonator has a longitudinal shape and follows the extension of a microwave antenna generating a homogeneous treatment zone throughout its length, wherein the extended output of the microwaves follows the conductor and substantially extends along the extended focal region of the cavity resonator. 
   It is also an underlying purpose of the invention to create a large microwave treatment region for the treatment of workpieces which is as homogeneous as possible and which also permits continuous treatment. 
   This latter purpose is achieved with a device of the above mentioned kind in that the housing is made from at least one elongated resonator which follows the extension of the microwave antenna, wherein the cavity resonator has at least one closed, tapered first tip region with the output region substantially extending along a the focal region of the cavity resonator, wherein at least a non-diverging housing region adjoins the widening tip region. 
   The invention produces a treatment zone which is homogeneous in its longitudinal direction and linearly extended for concentrating the microwaves at least for parallel orientation thereof, wherein the width of the treatment zone transverse to the longitudinal direction can be varied through suitable housing shapes. 
   The coupling of microwaves can be effected in different ways. In accordance with a first preferred embodiment, the microwave antenna is an electrically conducting elongated conductor which is surrounded by a dielectric and located at the focusing region of the cavity resonator, wherein either the dielectric is a solid body closely surrounding the conductor or the dielectric is formed by gas which can be radially limited by a dielectric pipe surrounding the conductor. 
   In an alternative embodiment, the microwave antenna is a coaxial, conducting structure with inner and outer conductors. The outer conductor can be a partial cylinder, which only partially surrounds the inner conductor and which is disposed at a region of the inner conductor facing away from the tip region of the cavity resonator. Alternatively, the outer conductor is a coating on a dielectric surrounding the inner conductor. The outer conductor may have at least one opening facing the tip region of the cavity resonator which is located in the focusing region of the cavity resonator and which is formed from slits or holes. 
   In a further embodiment, the microwave antenna is a waveguide with outlet openings disposed in the focusing region of the cavity resonator to function as the output region. 
   The microwaves can be introduced into the microwave conductor antennas either from one end or from both ends. 
   For thermal treatment of workpieces, the non-divergent region which adjoins the first tip region is formed by parallel walls. However, in a preferred embodiment, the non-divergent region is a second tip region continuously tapering from the first tip region, and the workpiece can be located substantially in the focusing region of the second tip region. The tapering region can have a parabolic or partially elliptical cross-section. In addition to microwave thermal treatment, this embodiment is particularly suited for plasma treatment of material, wherein the plasma treatment region must be separated from the microwave production region for controlling the gases used, in particular with respect to pressure, gas type and gas flow. 
   This latter requirement can be realized if the separating body is substantially a flat wall, or if the separating body is a semi-cylindrical coating disposed above the treatment focus and rigidly and closely connected to the housing wall. Alternatively, the separating body is a dielectric pipe which surrounds the treatment focus. 
   In a further preferred embodiment, the first tip region and the non-divergent region are disposed at a finite angle with respect to one another and a reflecting surface is provided between the two regions, in particular, for preventing emitted vapor or drops of liquid from impinging on the microwave antenna during the treatment of workpieces. 
   To increase the microwave intensity in the treatment region, at least two first tip regions, each comprising a microwave antenna, can be disposed parallel to one another to merge into a common non-divergent region. In accordance with a first alternative embodiment, the at least two first tip regions are disposed next to one another. 
   In a further embodiment, two microwave antennas are disposed diagonally opposite to one another relative to a second treatment focus. To further increase the energy input, in particular during plasma treatment, several microwave antennas in associated cavity resonators can also be provided which are symmetrically disposed about a treatment focus. 
   In a further embodiment, several microwave antennas are disposed in parallel, next to one another and in their associated cavity resonators at least on one side of a workpiece. This increases the treatment region. 
   The inventive device can be used in different ways. 
   In a first application variant, winding mandrels can be provided for the treatment inside the housing and at least one deflecting or guiding means is disposed in the vicinity of the working focus. In accordance with the invention, a mixer is disposed in the treatment region for microwave treatment of bulk material. Treatment is thereby discontinuous and the bulk material in the plasma treatment room must be exchanged after treatment. For quasi-continuous treatment, a screw conveyor is disposed in the region of the working focus to supply the material to be treated. For exhausting waste gas, a gas guiding pipe is disposed to extend along the treatment focus and is provided with a pump. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and features of the invention can be extracted from the claims and the following description which describes in detail embodiments of the invention with reference to the drawings. 
       FIG. 1   a  shows a longitudinal section of an inventive embodiment of a device for producing microwaves and plasma treatment with a linear conductor disposed in a dielectric; 
       FIG. 1   b  shows a cross-section of the embodiment of  FIG. 1   a;    
       FIG. 1   c  shows a perspective view of the additional embodiment of  FIGS. 1   a ,  1   b;    
       FIG. 2  shows an inventive device for producing microwaves with two microwave antennas; 
       FIG. 3  shows another embodiment of the inventive device comprising a linear conductor shielded by a partially open conductive coating; 
       FIG. 4  shows an embodiment comprising a coaxial conductor with slitted outer conductor; 
       FIG. 5  shows an embodiment in accordance with  FIG. 4 , wherein the outer conductor is punched; 
       FIG. 6  shows a further embodiment of the inventive device comprising a slatted waveguide; 
       FIG. 7  shows a further schematic representation of a first embodiment for the microwave radiation of sheets; 
       FIG. 8  shows a further schematic representation of a second embodiment for the microwave radiation of sheets; 
       FIG. 9  shows a further schematic representation of a third embodiment for the microwave radiation of sheets; 
       FIG. 10  shows a first embodiment for microwave radiation of a sheet with increased heat input into the sheet; 
       FIG. 11  shows a second embodiment for microwave radiation of a sheet with increased heat input into the sheet; 
       FIG. 12  shows an embodiment for microwave radiation of a sheet comprising two parallel microwave sources; 
       FIG. 13  shows a further embodiment of an inventive device for microwave radiation of a sheet with several, adjacent microwave antennas; 
       FIG. 14  shows a first embodiment of the inventive device for producing plasma, in particular for coating objects; 
       FIG. 15  shows a second embodiment of the inventive device for producing plasma, in particular for coating objects; 
       FIG. 16  shows a third embodiment of the inventive device for producing plasma, in particular for coating objects; 
       FIG. 17  shows a fourth embodiment of the inventive device for producing plasma, in particular for coating objects; 
       FIG. 18  shows a first embodiment for producing plasma using two or more microwave antennas which extend parallel to one another; 
       FIG. 19  shows a second embodiment for producing plasma using two or more microwave antennas which extend parallel to one another; 
       FIG. 20  shows a third embodiment for producing plasma using two or more microwave antennas which extend parallel to one another. 
       FIG. 21  shows an embodiment for continuous plasma treatment of a sheet; 
       FIG. 22  shows an embodiment for plasma treatment of bulk material comprising a mixer; 
       FIG. 23  shows a device for continuous microwave treatment of the medium in a screw conveyor as well as a device for waste gas purification through microwaves; and 
       FIG. 24  shows a device for treating waste gas. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the embodiment of  FIGS. 1   a  and  1   b , the inventive device  1  for producing microwaves has an elliptic cross-section and comprises a microwave antenna  2  with an elongated linear conductor  3  in the form of a rod, wire or copper pipe which is surrounded by a dielectric  4 , e.g. in the form of a quartz pipe or ceramic rod disposed at a separation and containing air. 
   The microwaves are input via one or both ends of the conductor  3 , usually through microwave adapters (not shown in detail). 
   The described microwave antenna  2  is in an adjoining elongated cavity resonator  6  of at least partially parabolic or elliptic contour (in the present example of elliptic cross-section) which has a first tip region  8  extending parallel to the antenna  2  or conductor  3  and having a first focusing region defined by the line of focus of parallel, symmetrically incident rays. In the embodiment of  FIGS. 1   a ,  1   b , and  1   c , the linear conductor  3  is located exactly in the focusing region of the cavity resonator  6  or its (first) tip region  8 . In this embodiment, the cavity resonator  6  comprises a second tip region with a second elongated treatment focusing region F′ designated with a cross (X), which is surrounded by a pipe  10  in which plasma is produced for plasma treatment of a workpiece, e.g. sealing in a plasma phase of a gas. 
   The inventive device can also be used for heating a workpiece  7  (indicated in FIG.  2 ), such as a sheet, e.g. for drying the sheet or for curing a layer disposed thereon.  FIG. 2  shows such an application. A cavity resonator  6  comprising two first tip regions  8 , 8 ′ has an elliptic cross-section in this embodiment. Two microwave antennas  2 , 2 ′ and their wire-shaped (inner) conductors  3 , 3 ′ are located in the focusing regions of the cavity resonator  6  for heating at a separation from the microwave antennas  2 , 2 ′ by the microwave antenna radiation thereof. 
   Heating only from one side is also fundamentally possible in a cavity resonator  6  of parabolic or semi-elliptical shape. Further embodiments of the invention are described below. 
   In the embodiment of  FIG. 3 , a partially open coaxial conductor structure is disposed within the cavity resonator  6  for microwave input. The conductor structure is formed by an inner conductor  3  disposed in a dielectric  4 . The dielectric has a partially open conducting coating  9  disposed coaxially to the conductor in the region facing away from the tip  8   a  of the cavity resonator  6 . Microwave radiation is thereby directed towards the tip  8   a  (end face region) of the cavity resonator and reflected into the remaining region of the cavity resonator and onto the workpieces to be treated (further details below). 
     FIGS. 4 and 5  also show a coaxial conductor structure forming a microwave antenna  2 . In this embodiment, a conductor  3  is surrounded at a separation by a conducting pipe (outer conductor  12 ) which has outlet slits or circular holes  13  on its side facing the tip  8   a  of the cavity resonator  6 . In the embodiment of  FIG. 4 , the microwave radiation is therefore guided as in FIG.  3 . The ratio between slit length and width is advantageously constant over the entire length of the coaxial conductor  11 . This is, however, not absolutely necessary. 
   While in the embodiments of  FIGS. 1 and 3 , the conductor or inner conductor  3  is in the focusing region of the cavity resonator  6 , this is not the case in  FIGS. 4 and 5 . In these embodiments, the plane of the outlet slits  13  is disposed in the focusing region F of the cavity resonator  6 . 
   The embodiment of  FIG. 6  of an inventive device shows a waveguide  14  as microwave conductor which is disposed in the upper region of the cavity resonator  6  such that the outlet slits  13  of the waveguide  14  facing the inside of the cavity resonator  6  are also in the focusing region F of the cavity resonator, indicated by a cross. The absent tip of the cavity resonator is indicated therein. 
     FIG. 7  shows a cavity resonator  6  with only one first tip region  8  for microwave treatment of a workpiece  16  in the form of a material sheet extending below the tip region. 
   For certain reasons, it may be required to chose a larger separation between the microwave antenna  2  and the workpiece  16  to be treated. For this reason, a spacer  17  with parallel walls adjoins the parabolic or partially elliptic tip region  8  of the cavity resonator  6  in the embodiment of  FIG. 8  of the inventive device. The workpiece  16  extending below the microwave antenna  2  adjoins the spacers  17 . This embodiment having spacers  17  can also be symmetrical with two microwave antennas in correspondence with FIG.  2 . 
   The sheet, in general a workpiece, can also be located in a treatment focusing region F′ of a cavity resonator  6  or of a second tip region having different structural parameters than the first tip region  8  focusing the microwaves produced by the microwave antenna  2  located therein, e.g. can have a cross-sectional shape of a flatter parabola. 
   For certain reasons, it might be reasonable or necessary not to direct the microwave radiation directly onto the workpiece, e.g. if vapor or liquid exits therefrom during treatment which can soil and possibly damage the microwave antenna. This is prevented in the embodiment of FIG.  9 . In this embodiment, a housing section  19  with parallel walls adjoins the first tip region  8  at an angle, preferably right angles, wherein the workpiece  16  is drawn through below its end. An angularly disposed reflector surface  20  is provided between the first tip region  8  and the housing part  19  to direct the microwaves produced in the microwave antenna  2  onto the workpiece  16 . 
   To increase the intensity of the microwave treatment in a treatment region oriented transverse to the transport direction of the workpiece  16  and parallel to the microwave antenna  2 , a cavity resonator  6  with two focusing regions can be provided in which the microwave conductor or the outlet region of the microwaves is disposed in the manner described in  FIGS. 1 through 4 , wherein the workpiece is drawn through the other treatment focus region F′ (FIG.  10 ). In this embodiment, the microwaves produced by the microwave antenna  2  are focused into the second focusing region F′ and thereby onto the workpiece. For a two-sided treatment, a corresponding cavity resonator  6 ′ having a second microwave antenna  2 ′ can be provided, as shown in  FIG. 11 , at the side of the workpiece  16  facing away from the microwave antenna  2  and the first tip region  8 . 
   To increase the one-sided intensity of the microwave treatment of a workpiece  16 , two microwave antennas  2 , 2 ′ can be disposed on one side in first tip regions  8 , 8 ′ associated therewith, wherein the tip regions  8 , 8 ′ of the cavity resonator, in particular their symmetrical surfaces which extend at an angle with respect to another, are disposed and oriented such that the treatment regions  22  of both microwave antennas  2 , 2 ′ substantially coincide (FIG.  12 ). 
   Moreover, it may be required to treat a workpiece  16 , e.g. a sheet, over a longer period of time or a longer sheet with microwaves which is not possible with a microwave antenna or two microwave antennas directed onto the same region. In this case, several microwave antennas  2 , 2 . 1 , 2 . 2 ., 2 . 3  . . . . can be oriented next to and parallel to one another and disposed in first tip regions  8 , 8 . 1 , 8 . 2 , 8 . 3  . . . . of the cavity resonator whose symmetrical central surfaces are disposed parallel to one another (see FIG.  13 ). 
   The workpiece must not be a sheet but can also be bulk material or the like transported on a conveyor belt through the treatment region. In addition to thermal treatment of such workpieces in the above-described fashion, the inventive device can also be used for plasma coating of a workpiece or of workpieces using microwaves. 
   In this case, the plasma treatment zone in which the workpiece or workpieces are located must be physically separated from the microwave producing region in which the microwave antenna  2  is located, since the conditions of the gases in the microwave producing region and in the plasma treatment zone must be different to prevent production of plasma in the microwave producing regions and to produce plasma in the plasma treatment zone. 
   Advantageously, the microwave concentration in the plasma treatment zone is increased for producing plasma by providing a second focusing region F′ in the plasma treatment zone in addition to the first focusing region in which the microwave antenna  2  is located. As above, these zones are indicated by crosses (X) in the figures described below. 
   In the embodiment of  FIG. 14 , the microwave producing zone  23  and the plasma treatment zone  24  are only separated by a separating wall  26  of dielectric material. 
   In the embodiment of  FIG. 15 , the plasma treatment zone is surrounded by a pipe  27  introduced into the cavity resonator  6 . 
   In the embodiment of  FIG. 16 , the plasma treatment zone  24  about the focusing region F′ in the first end region  8  is separated from the microwave producing region  23  by a partial cylinder  28 , which is connected to first end region walls in a gas-tight manner. 
   In the embodiment of  FIG. 17 , the first tip region  8  surrounding the microwave antenna  2  and the second tip region  8 ′ surrounding the focusing region F′ in the plasma treatment zone are disposed at an angle with respect to one another, i.e. their central planes are not aligned but oriented at an angle. The microwave radiation acts in a similar fashion as in the embodiment of  FIG. 9  via a reflector surface  20  disposed at an angle with respect to the microwave antenna  2  for reflection into the plasma treatment zone at the second focusing region F′. A second separating wall  26 ′ can be provided in addition to the separating wall  26 . 
   Several microwave antennas  2 , 2 . 1 , 2 . 2  . . . can be provided to increase the microwave input into the plasma treatment zone  24  (see FIGS.  18  through  20 ). When producing microwaves for plasma treatment, the (several) microwave antennas  2 , 2 . 1  . . . . are thereby disposed symmetrically about the plasma treatment zone  24  ard the second focusing region F′ of the device, which is the same for all microwave antennas. For the case of two microwave antennas  2 , 2 . 1 , the antennas are disposed diagonally with respect to a treatment focus F′ extending through the two microwave antennas and the intermediate treatment focus F, (FIG.  18 ). For three microwave antennas  2 , 2 . 1 , 2 . 2 , the antennas are located at an angle of 120° about the treatment focus F′ (FIG.  19 ). For four microwave antennas, the antennas are correspondingly disposed at angles of 90° about the treatment focus F′ ( FIG. 20 ) etc. 
   For thermal treatment, a single workpiece, e.g. a sheet workpiece  16 , can be drawn through the treatment region below the microwave source thereby entering and exiting same. However, this is not possible for plasma treatment of a workpiece, such as plasma coating of a sheet. The entire workpiece must remain in the plasma treatment region during treatment. Correspondingly, in the embodiment of  FIG. 21 , two winding mandrels  31 , 32  are provided in the plasma treatment region  24 , wherein the sheet is unwound from one (e.g.  31 ) and wound onto the other ( 32 ). 
   Since the winding mandrels  31 , 32  should be located directly in the treatment i.e. application zone or in the second focus, however, the goods to be treated must be guided therethrough, and on the other hand, the design of the housing or the wall of the plasma treatment region determines the spatial relationship for producing the second focusing region, the embodiment of  FIG. 21  includes a deflecting roller  33  in the focusing region to guide the sheet  16 . It is also possible to dispose several guiding rollers parallel to one another in the focusing region. 
   The embodiment of  FIG. 22  concerns the microwave plasma treatment of bulk material. To ensure uniform and good coating of all parts of the bulk material, the plasma treatment zone  24  of the embodiment of  FIG. 20  includes a mixer  34  whose axis preferably extends parallel to the microwave antenna  2 . 
   While the embodiment of  FIG. 22  provides discontinuous treatment of the material to be treated, the embodiment of  FIG. 23  shows an alternative to the continuous microwave treatment. Towards this end, a worm conveyor is provided in the region of the treatment focus F′ for continuous supply of the goods to be treated from a supply container into a receptacle. During plasma treatment, the space defined by the container and the jacket of the worm conveyor  35  must be sealed and contain a treatment gas in a suitable manner. This is not required for continuous heat treatment of bulk material supplied by a worm conveyor  35 , e.g. for drying the bulk material. 
   In accordance with the invention as illustrated in  FIG. 24 , treatment of waste gas is also possible waste gas is supplied along the focusing line F′ in a pipe by means of a supply pump  42 , e.g. a water jet pump.