Abstract:
A device for heating relatively wide planar materials is formed by at least two parallel waveguides. Each waveguide has an opening that forms a single opening for a planar material. The planar material is propelled in a direction parallel to the propagation of an electronic wave. If each waveguide is kept in TE mode, heating is uniform across the planar material. Power splitters, septums, tuning stubs, and impedance matching can be used to control the heating in each waveguide.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to electromagnetic energy, and more particularly, to rapid and continuous drying of a planar material.  
         BACKGROUND  
         [0002]    In U.S. Pat. No. 5,958,275, a planar material is passed through a serpentine wave guide that has more than one straight segment The planar material is passed in a direction that is perpendicular to the propagation of an electromagnetic wave in each straight segment. The planar material is passed through a series of diagonal openings to account for attenuation of the electromagnetic wave.  
           [0003]    In Metaxas et al, “Industrial Microwave Heating,” Peregrinus on behalf of the Institution of Electrical Engineers, London, United Kingdom and co-pending and co-assigned application Ser. No. 09/372,749, a planar material is passed in a direction parallel to the propagation of the electromagnetic wave. In Metaxas and the &#39;749 application, it is preferable to keep the electromagnetic wave in TE 10  mode so that there is a peak half way between the top conducting surface and the bottom conducting surface. In Metaxas and the &#39;749 application, the width of the exposure region is limited by the size of the waveguide. In order to dry carpets, rugs, or other relatively wide materials, the waveguide would have to be prohibitively tall. There is a need for an exposure chamber that can be used to rapidly and continuously heat relatively wide materials.  
         SUMMARY  
         [0004]    A device for heating relatively wide planar materials is formed by at least two parallel waveguides. Each waveguide has an opening that forms a single opening for a planar material. The planar material is propelled in a direction parallel to the propagation of an electromagnetic wave in each waveguide. If each waveguide is kept in TE 10  mode, heating is uniform across the planar material. Power splitters, septums, tuning stubs, and impedance matching can be used to control the heating in each waveguide.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The foregoing, and other objects, features, and advantages of the invention will be more readily understood upon reading the following detailed description in conjunction with the drawings in which:  
         [0006]    [0006]FIG. 1 is an example of a cascaded planar exposure chamber;  
         [0007]    [0007]FIG. 2 is an illustration of a planar material being passed through a cascaded planar exposure chamber;  
         [0008]    [0008]FIG. 3 is another example of a cascaded planar exposure chamber;  
         [0009]    [0009]FIG. 4 is an example of an extended planar exposure chamber; and  
         [0010]    [0010]FIG. 5 is an example of a staggered waveguide structure. 
     
    
     DETAILED DESCRIPTION  
       [0011]    In the following description, specific details are discussed in order to provide a better understanding of the invention-However, it will be apparent to those skilled in the art that the invention can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and circuits are omitted so as to not obscure the description of the invention with unnecessary detail.  
         [0012]    Utilizing the techniques described below, it is possible to create an exposure region for planar materials of virtually any width. The material can be exposed to a uniform energy distribution or virtually any pre-specified energy distribution across the width of the material. In an exemplary embodiment, individual chambers are juxtaposed (or cascaded). Or alternatively, the chamber is extended to create a wider exposure region. In either case, the material  20  is passed through the chamber  10  in a z direction parallel to the propagation of the electromagnetic wave.  
         [0013]    In the cascaded planar exposure chamber design  40 , a series of individual chambers  10  are in direct contact or in close proximity. Power into the series  40  of individual chambers  10  can be provided by a single chamber  12  (or more specifically a single waveguide). Using a power splitter  60 , energy can be split into multiple chambers  14  (e.g. such as waveguide power splitter) and then into each individual exposure chamber  10 . The power splitter  60  could be as simple as placing septums  62  into the single waveguide  12  parallel to the broad wall  13  of the waveguide  12 . Using these power splitters  60  may require impedance matching to insure maximum transfer of power to each individual chamber  14 .  
         [0014]    In the cascaded planar exposure chamber  40 , it is possible to design each individual chamber  10  so that only the TE 10  mode is supported in each individual chamber  10  (i.e. waveguide in this case). This is not a necessity, but does give the advantage that the distribution of energy is well known and controllable. The material is fed through this structure  40  along the length of the chamber. If materials  20  passes through the entire structure  40 , the structure  40  will have openings  30  between individual chambers  10  for the material Thus, between each individual chamber  10  there will be a gap  30  due to either metal thickness or an intentional gap. This gap  30  is herein referred to as a septum  62 . The distance between the top septum  67  and the bottom septum  65  will typically be small enough to allow the material  20  to pass through. In the septum gap  30 , microwave field lines will tend to extend to connect the field lines from one chamber  10  to the adjoining chamber  10 . The narrower the septum gap  30 , the more this will occur, and thus the more uniformity across the material  20 . However, there will be a large field intensity built up at the edge  63  and  64  of the septum  65  and  67  particularly when the septum gap  30  is narrow. This will cause high energy zones in the materials  20  in the gaps  30  between the chambers  10 . This effect can be reduced or eliminated by placing a low loss dielectric material  20  such as Teflon on the edge  63  or  64  of the septum  65  or  67 .  
         [0015]    Material  20  can be fed through the structure  40  either through the middle of the structure  40  or at an angle (making an angle along the length of the structure). If each individual chamber  10  is in TE 10  mode, then the maximum energy will be in the center of the chamber  10 . If the material  20  is placed in the middle of the structure  40 , the material  20  near the generator will experience the maximum energy intensity. Because the material  20  causes the wave to attenuate, the energy intensity will decrease in the material  20  further from the generator. This approach is acceptable for materials  20  that can absorb the maximum amount of energy available. At the same time, there are cases where the material  20  cannot accept a high field intensity and the energy should be introduced gradually into the material  20 . A simple example of this is a curing process. Likewise, there are examples where the material  20  needs to be initially hit with a large field intensity and then be exposed to a small amount of energy. This would be true in the case where a material  20  needed to brought up to temperature quickly and then maintained at some temperature. Creating an angle to which the material passes through the chamber can accommodate both of these cases. Or more generally, one can place the material  20  at an off peak zone of energy distribution in one or more locations in the chamber. See, for example, U.S. Pat. No. 5,958,275 or U.S. patent application Ser. No. 09/372,749.  
         [0016]    In the preferred embodiment, the distribution of energy in each individual chamber  10  would be a rectangular waveguide  10  operating in the TE 10  mode. The material  20  would either pass through the center of this chamber  40  along the direction of the waveguide  10  or pass through the chamber at an angle but still in the direction of the waveguide  10 . Each individual chamber  10  would be tuned so that the maximum amount of energy would be allowed to transmit. The system would be fed by a single waveguide  10  which operates in the TE 10  mode. The power would be split into each chamber  10  equally. It is also preferable, but not necessary, that each component  10  after the power split is in phase. The result of this would be that the material  20  is uniformly exposed across the width of the material  20 . In this embodiment, septum gaps  30  would need to be made as narrow as possible and dielectric barriers would be used to minimize or eliminate hot spot zones directly under the septum edges  63  and  64 . The material  20  can be placed either in the center of the chamber  40  or some off peak zone at some point in the chamber  40 . The placement will be depend on what is required for the process in terms of a temporal heating profile for the material  20 .  
         [0017]    [0017]FIG. 1 shows a simple embodiment of the invention. In FIG. 1, one waveguide  10  is split into four waveguide sections  10  that are side by side. FIG. 2 shows that the same embodiment with material  20  placed in the center of the chamber  40 . In FIG. 2, each individual chamber is maintained in TE 10 . Notice that uniformity is created across the width of the material  20 .  
         [0018]    [0018]FIG. 3 shows a more involved embodiment that highlights many of the aspects of the invention. In FIG. 3, energy is launched into the chamber  140  through a generator into a rectangular waveguide  155  operating in the TE 10  mode. This initial waveguide  155  is split into three equal and in phase components  165  all in TE 10  mode using a power splitter  160  with septums  162  inside of a waveguide  160 . Each of the three waveguides  165  is then split into three additional individual waveguides  100  (a three-to-nine power splitter  170 ) all in TE 10  mode. These individual waveguides  100  are cascaded to form a chamber  40  of individual chambers  100  separated by a narrow septum  101 . The transition between the nine waveguides  100  and the body of the chamber  120  is curved to minimize reflections. Material  20  is passed through the resulting cascaded planar exposure chamber  120 . In this case, the material  20  is passed through the center of the chamber  120 . Chokes  180  are used at the material entrance  130  and exit  135  of the system  140  to reduce leakage to acceptable levels. At the exit end  135  of the chamber  140 , the individual chambers  100  are recombined into three waveguides  195  using a nine-to-three power combiner  190 . These three waveguide sections  195  are then terminated in a water/absorbing load  200 . This creates a traveling wave in the chamber  140 .  
         [0019]    As a final concept, with the cascaded planar exposure chamber  140 , it is possible to vary the amount of energy in each individual chamber  100 . Thus, it is possible to create virtually any heating pattern across the width of the material  20 . This would be practical if one wanted to heat the center of the material  20  different from the edges of the material  20 . For example, if there was a strip on the edge of a fabric that was thicker than the center of the fabric, one may want to put more energy into the outer chambers  100   vii  and  100   viii  and less in the center chambers  100   iii  and  100   iv . There are two primary ways to create an unequal split of energy. First, the stub tuners  150  could be used to create imperfect matches in the chambers that did not need as much energy. Second, the power splitter  160  could be designed to create an unequal split.  
         [0020]    [0020]FIG. 4 is an illustration of an extended planar exposure chamber. In FIG. 4, the height x of a TE 10  waveguide is kept constant, but the exposure width y is extended. The effect of simply widening the exposure region is that modes beyond TE 10  are generated. If the height x is not changed from the standard curing chamber  10 , then the only modes that are created are across the exposure width y. As a result, energy is still highest in the center of the chamber  10  but hot and cold spots appear along the exposure region. However, by staggering these hot and cold spots, it may be possible to create uniformity as the material  20  passes through the chamber  10 . Also, using a dielectric wheel placed in the chamber  10  could help increase uniformity across the width y of the chamber  10 . This embodiment is not as robust as the cascaded planar exposure chamber  40 , but it is easier to build.  
         [0021]    The primary advantage of a cascaded planar exposure chamber  40  or an extended planar exposure chamber  140  is that it is possible to create a uniform energy distribution across the width y of a planar material  20 . The cascaded planar exposure chamber  40  or  140  in particular will create a uniform energy distribution across the width y of virtually any material  20 . Thus, the system  40  or  140  can handle virtually any material. Moreover, it is possible to create any heating pattern across the width y of the material  20  by varying the power in each individual chamber  10 .  
         [0022]    [0022]FIG. 5 illustrates a staggered waveguide structure  300 . Staggered waveguide structure  3   00  can be positioned in between, for example, the three-to-nine splitter  170  and the exposure chamber  120 . Staggered waveguide structure  300  allows access to and/or adjustment of stub tuner  150  and directional coupler  152 . Stub tuner  150  allows one to maximize (or optimize) the power in each individual chamber  100 . Directional coupler  152  allows one to measure the energy delivered to each individual chamber  100 , and thus, determine whether there is an even split of the power after the three-to-nine power splitter  170 . Staggered structure  300  provides additional space for stub tuners  150  and directional couplers  152  that might otherwise not be available. Staggered structure  300  comprises a first waveguide  250  and a second waveguide  260 , both having a first end  255  and a second end  265 . First waveguide  250  bends away from second waveguide  260  at first end  255  such that more space is available for stub tuners  150  and directional couplers  152 . First waveguide  250  bends towards second waveguide  260  at second end  265  such that chambers  100  are in direct contact or in close proximity.  
         [0023]    In other words, the first waveguide  250  is directed with respect to the second waveguide  260  such that the waveguides  250  and  260  flow away from each other, creating more space for at least one waveguide than if the waveguides were not directed. In other words, the waveguides  250  and  260  begin adjacent to each other and can end up adjacent to each other. In other words, the waveguides  250  and  260  have enough space such that at least one waveguide can have a certain device attached to it where the space was created.  
         [0024]    While the foregoing description makes reference to particular illustrative embodiments, these examples should not be construed as limitations. Thus, the present invention is not limited to the disclosed embodiments, but is to be accorded the widest scope consistent with the claims below.