Electric heating – Microwave heating – Waveguide applicator
Reexamination Certificate
1999-04-28
2001-07-24
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Waveguide applicator
C219S699000, C219S745000, C219S756000
Reexamination Certificate
active
06265702
ABSTRACT:
BACKGROUND
The invention relates to electromagnetic energy, and more particularly, to an electromagnetic exposure chamber with a focal region.
The recent popularity of microwaves has led to the discovery of new uses for microwave energy, uses that require an electromagnetic exposure chamber with a relatively uniform power distribution. In some cases, it is advantageous if the material can be passed through—rather than simply placed in—the exposure chamber.
Researchers have experimented with placing a test specimen in a free-space environment between two axially-facing paraboloidal reflectors. See U.S. Pat. No. 3,281,727 to Niebuhr et al entitled “Traveling Wave High Power Simulation.” At least one researcher has experimented with using a microwave source in an ellipsoidal shell. See U.S. Pat. No. 2,543,053 to Parker entitled “Radiant Energy High-Temperature Heating Apparatus” and U.S. Pat. No. 2,943,174 to Parker entitled “Radiant Energy Heating Apparatus.” These early experiments used bowl-like structures that focus the microwave in multiple directions towards a single point. The problem with these bowl-like structures is that they form a focal point that acts like a single concentrated hot spot. There is poor coupling at the focal point and the energy tends to reflect and scatter. A major concern with the Niebuhr et al patent is that as the waves reflect and scatter, the free space environment cannot contain the electromagnetic energy. A major concern with the Parker patents is that as the waves reflect and scatter, they will propagate towards the source.
There is a need for an electromagnetic exposure chamber that can uniformly focus the electromagnetic energy to a region, rather than a single point, so as to provide more uniform heating. One possible approach is described in our co-assigned and co-pending U.S. patent application Ser. No. 08/813,061 now U.S. Pat. Nos. 5,998,774 and 6,087,642 . In this earlier application, which is herein incorporated by reference, we describe an elliptical structure that focuses the energy in a single plane (or direction). The structure focuses the energy to a focal region that extends from a first substantially planar surface to a second substantially planar surface. The elliptical structure can contain the microwave energy and still allow the material to pass in and out of the chamber.
The disclosed structure can be used with dielectric slabs or without dielectric slabs. In certain instances, the dielectric slabs increase the uniformity across the focal region. However, as the diameter (or width) of the material decreases, the ability to couple the energy into the material also decreases. As a result, it is more difficult to heat the material. As discussed below, it is possible to increase the coupling and, in some instances, decrease the need for the dielectric slabs.
SUMMARY
According to one aspect of the invention, an electromagnetic exposure chamber has an exterior conducting surface that forms an interior cavity. The exterior conducting surface has a first substantially planar surface, a second substantially planar surface, a first end, and a second end. The first end has an opening for an electromagnetic wave. The electromagnetic wave forms an electric field. The second end has an elliptical shape that directs the electromagnetic wave to a focal region that extends from the first substantially planar surface to the second substantially planar surface.
According to another aspect of the invention, an opening through the first surface is a continuously open opening.
According to another aspect of the invention, an opening through the first surface is aligned with the electric field.
According to another aspect of the invention, the opening is aligned with the focal region.
According to another aspect of the invention, the electric field has a peak and the opening is aligned with the peak.
According to another aspect of the invention, the first end has a rectangular opening that has two short sides that connect the first surface and the second surface. The rectangular opening is configured to keep the electromagnetic wave in TE
10
mode.
According to another aspect of the invention, a continuously open opening has a choke that prevents the escape of electromagnetic energy. The choke surrounds the opening and extends outwardly from chamber's surface.
According to another aspect of the invention, an opening through the second surface is aligned with the opening through the first surface to form a path for the continuous flow of the material.
According to another aspect of the invention, the shape of the exterior cavity is designed to increase the length of the path and decrease the heating density.
According to another aspect of the invention, the shape of the exterior cavity is designed to decrease the length of the path and increase the heating density.
An advantage of the invention is that the electromagnetic wave is uniformly focused to a region, rather than a single point, so as to provide more uniform heating. Another advantage is that more energy is absorbed and the amount of heating is increased. Another advantage is that the need for dielectric slabs is decreased. Another advantage is that it is possible to contain the microwave energy and still allow the material to pass in and out of the chamber. Another advantage is that it is possible to control the power density of the focal region.
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Drozd J. Michael
Joines William T.
Burns Doane Swecker & Mathis L.L.P.
Industrial Microwave Systems, Inc.
Leung Philip H.
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