BRPI0621082A2 - field guide sets - Google Patents

Abstract

FIELD GUIDE SETS. The present invention relates to a field guide assembly that includes electrically conductive propeller plates configured to prevent bending in an empty microwave oven and in which the electrically conductive propeller plates are positioned with respect to them and to a support member plan to prevent overheating of the susceptor in an empty microwave oven.

Description

"FIELD GUIDE SETS" CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application claims the benefit of Provisional Patent Applications US 60 / 841,088 and US 60 / 841,108, each of which were filed on August 29, 2006 and the Provisional Patent Application US 60 / 751,544, which was filed in December 19, 2005 and is incorporated as a part of it for all purposes.

Field of the Invention

The present invention is directed to a field guide assembly which avoids bending when used in an empty microwave oven.

The object described herein is described in the following provisional applications filed contemporaneously with the present and assigned to the assignee of the present invention:

Arc Resistant Microwave Susceptor Set that Has Overheat Protection (CL-3534).

Background of the Invention

Microwave ovens use electromagnetic energy at frequencies that vibrate molecules within a food product to produce heat. The heat thus generated warms or cooks the food. However, the food is not heated to a temperature high enough to brown its surface in a crunchy texture (and still keeps the food grade).

To achieve this visual and tactile aesthetics, a susceptor formed from a substrate having a dissipative susceptor material thereon may be placed adjacent the surface of the food. When exposed to microwave energy, the susceptor material is heated to a temperature sufficient for the food surface to brown and crisp. The walls of a microwave oven impose limiting conditions that cause the energy distribution of the electromagnetic field to vary within the oven volume. These variations in the intensity and direction of the electromagnetic field, in particular the constituent of the electric field of that field, create relatively hot and cold regions in the furnace. These hot and cold regions cause uneven heating or cooking of the food. If a microwave susceptible material is present, the browning and crunchiness effect is correspondingly uneven.

To counter this uneven heating effect, a turntable may be used to rotate the food product in a circular path within the oven. Each portion of the food is exposed to a more uniform level of electromagnetic energy. However, the leveling effect occurs along circumferential paths and not along radial paths. Thus, using the turntable creates uneven heating bands within the food.

This effect can be more fully understood from the diagrammatic illustrations of Figures 1A and 1B.

Figure 1A is a top view of the interior of a microwave oven showing five regions (Hi to H5) of relatively high electric field intensity ("hot regions") and two relatively low electric field intensity regions ("C" and "C2"). cold regions "). A food product F having any arbitrary shape is disposed on a susceptor S which in turn is placed on a turntable Τ. The susceptor S is suggested by the dotted circle while the turntable is represented by the bold continuous line circle. Three representative locations on the surface of the food product F are illustrated by points J, K and L. Points J, K and L are located respectively at the radial positions P1, P2 and Ρ3 of the turntable Τ. As the turntable rotates, each point follows a circular path through the oven as indicated by the circular dashed lines.

As can be seen from Figure 1A, during a complete revolution the point J passes through a simple region Hi of relatively high electric field strength. During the same revolution, point K passes through a simple minor region H5 of relatively high electric field strength, while point L experiences three regions H2, H3, and H4 of relatively high electric field strength. Rotation of the turntable in a complete revolution thus exposes each of points J, K and L to a different total amount of electromagnetic energy. The differences in energy exposure at each of the three points during a complete rotation is illustrated by the diagram in Figure 1B.

Due to the number of hot regions encountered and cold regions avoided, the JeL points experience considerably more energy exposure than the K point. If the food product region near the point J path is considered fully cooked, then the region at The food product near the point L path will probably be overcooked or overly golden (if a susceptor is present). On the other hand, the region of the food product near the point K path will probably be undercooked.

Since non-uniform cooking due to the presence of hot and cold regions is undesirable, it has been found to be advantageous to employ a susceptor assembly formed by combining a field guide structure with a susceptor. The field guide structure includes one or more propeller plates, each having a conductive portion in a cardboard support. The field guide structure diminishes the effects of relatively high and low electric field strength regions within a microwave oven by redirecting and transferring these regions so that food warms, cooks, and browns more evenly. Using the field guide structure alone (i.e. without a susceptor) has also been found to be advantageous.

When a susceptor assembly is placed in an "empty" microwave oven (ie, an oven without a food product or other article being present) and the oven is energized, detrimental problems of susceptor overheating and / or guide structure overheating field and / or arching were observed.

By "susceptor overheating" (or similar terms) is meant the heating of the dissipative susceptor material to a degree where the susceptor substrate burns.

"Field guide frame overheating" (or similar terms) means heating the cardboard holder of the propeller plates to a degree that it burns. Such overheating may be caused by heat generated by the dissipative susceptor material or bending.

"Bowing" (or silimares) is an electrical discharge that occurs when a high intensity electric field exceeds the air burst limit. Typically, bowing occurs in the vicinity of the electrically conductive portions of the propeller plates, particularly along the ends and in particular at any closed corners. Bowing can cause discoloration, carbonization or, in extreme situations, fire and burning of the cardboard holder of the propeller plates.

The most common features to avoid bending are impractical in microwave oven applications. These features are also not suitable for disposable semi-ready food packaging. In view of the foregoing, it is believed advantageous to provide a field guide structure and a susceptor assembly that incorporates the same and avoids bowing, field guide overheating, and susceptor overheating.

Brief Description of the Invention

The present invention is directed to an arcuate field guide assembly which does not overheat when placed in an "empty" microwave oven, that is, an oven without a food product or other article being present. The microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength.

The field guide assembly includes a generally flat support member that has one or more mechanically connected propeller plates thereon. Each propeller plate has an electrically conductive portion in it. The electrically conductive portion is generally rectangular in shape with a predetermined length and width dimension and has a first end and a second end thereon. The electrically conductive portion of the propeller plate may be formed from a metal foil less than 0.1 mm thick.

In accordance with the present invention, the electrically conductive portion of each propeller plate is arranged at least a predetermined near distance from the flat support member. In the preferred example, the predetermined near distance is defined by the margin of a low conductivity material disposed between the conductive portion of the propeller plate and the support member. The predetermined near distance remains in the range 0.025 times the wavelength to 0.1 times the wavelength. Preferably, the margin surrounds the conductive portion. In addition to the arrangement of the electrically conductive portion of each propeller plate at the predetermined proximate distance of the support member, in accordance with an embodiment of the present invention, the corners of the electrically conductive portion are encircled by up to and including half. the width dimension of the conductive portion. According to an alternative embodiment of the present invention, instead of being surrounded, the electrically conductive portion of the propeller plate may be covered with an electrically non-conductive material selected from the group consisting of a polyimide tape, a spray coating. polyacrylic and a polytetrafluoroethylene spray coating. Still according to another alternative embodiment of the present invention, instead of being surrounded or covered, the electrically conductive portion of the propeller plate may be formed from a metal foil less than 0.1 mm thick with the foil folded over. at least one double thickness along its perimeter.

The first end of the conductive portion on each of the propeller plates is arranged at a distance at least a predetermined separation distance from the geometric center of the flat support member. The predetermined separation distance is at least 0.16 times the wavelength.

Brief Description of the Figures

The present invention will be more fully understood from the following detailed description taken in conjunction with the accompanying figures which form a part of this patent application and which:

Figure 1A is a top view showing the different electric field intensity regions within a microwave oven and showing the paths followed by three distinct J1KeL points located at respective radial positions P1, P2 and P3 on a turntable;

Figure 1B is a diagram showing the total energy exposure for a complete turntable rotation at each of the distinct points identified in Figure 1A;

Figure 2 is an illustrated view of a susceptor assembly with separate flat susceptor portions for clarity and showing various shape of the field guide frame plate ends with the conductive portions of the propeller plates directly adjacent to the susceptor. plan;

Figure 3 is an illustrated view similar to Figure 2 showing the propeller plates of the field guide structure with the conductive portions of the spaced flat susceptor propeller plates;

Figures 4A to 4C are top views illustrating respectively the linear ends, arcuate ends and curved ends of the propeller plates extending generally transversely across the plane susceptor in the compensated directions of a generally radial line. of the susceptor assembly;

Figures 4D to 4F are top views illustrating respectively the linear ends, arcuate ends and curved ends of the propeller plates extending generally transversely across the plane susceptor in a direction generally crossing a line. radius of the susceptor assembly;

Figures 5A and 5B are profile views taken along lines 5-5 in Figure 2 respectively illustrating a field guide propeller plate having a connection attached to a flat susceptor and a flexible hinged connection to the plate. in the latter case shown in idle and triggered positions;

Figure 6 is an illustrated view illustrating the attenuating effect of a single transverse electrically conductive propeller plate on the field vectors constituting the electric field component in the plane of the plane susceptor;

Figure 7A is a top view generally similar to Figure 1A showing the effect of the field guide structure of a susceptor assembly of the present invention on the high electric field intensity regions and again showing the paths followed by three distinct points J1KeL located at their respective radial positions Pi, P2 and P3 on a turntable;

Figure 7B is a diagram, similar to Figure 1B showing the total energy exposure for a complete turntable rotation at each distinct point, with the waveform of Figure 1B overlapping for ease of comparison;

Figures 8A, 9A and 10A are illustrated views of several preferred embodiments of a susceptor assembly according to the present invention, with flat susceptor portions separated for the sake of clarity;

Figures 8B, 9B and 10B are top views of the susceptor assembly shown in Figures 8A, 9A and 10A, respectively;

Figure 11 is an illustrated view of a field guide structure according to the present invention implemented using a single curved plate;

Figure 12 is an illustrated view of a field guide structure according to the present invention implemented using a flat helix plate with a single arc line thereon;

Figures 13A and 13B are respective profile and illustrated views of a field guide structure according to the present invention implemented using a flat propeller plate with two arc lines thereon;

Figures 14 and 15 are illustrated views of two additional implementations of a field guide structure according to the present invention, each having a plurality of flexibly connected propeller plates to form a collapsible structure;

Figure 16 is an illustrated view of a field guide assembly according to the present invention, wherein at least one plate is supported on a non-conductive substrate; and

Figures 17 and 18 are diagrams of the results of Examples 6 and 7, respectively;

Figure 19 is an illustrated view showing various helix plate configurations of the field guide structure with conductive portions having different shapes and positions;

Figure 20 is a top view of a susceptor assembly incorporating a six-plate field guide structure used in Examples 9 to 23;

Figure 21 is an enlarged enlarged view showing a plate configuration having a rectangular electrically conductive portion occupying the entire plate area;

Figure 22 is an enlarged enlarged view showing a plate configuration generally having a rectangular electrically conductive portion having rounded corners and a surrounding portion of the nonconductive margin;

Figure 23 is an enlarged enlarged view showing a plate configuration generally having a rectangular electrically conductive portion having rounded corners;

Figures 24, 25 and 26 are enlarged sectional views showing white helix plates having two generally spaced, electrically conductive portions, the conductive portions having rounded corners and having nonconductive corners surrounding each conductive portion; Figure 27 illustrates typical susceptor overheating in Examples 24 to 34;

Figure 28 is an enlarged view showing typical susceptor overheating and melting of the protective polymer coating on the susceptor;

Figure 29 shows the results of Examples 35 to 40; and

Figure 30 shows the results of Examples 61 to 64.

Detailed Description of the Invention

During the following detailed description, the characters of similar references refer to similar elements in all figures and drawings.

Referring to Figures 2 and 3 shown, these are a stylized illustrated view of a susceptor assembly generally indicated by reference numeral 10 in accordance with the present invention. The susceptor assembly 10 has a reference axis 10A extending through its geometric center 10C. The susceptor assembly 10 is in use disposed within the resonant cavity within a microwave oven Μ. Oven M is suggested only as a sketch in the Figures. In activity, a source in the furnace produces an electromagnetic wave having a predetermined wavelength. A typical microwave oven operates at a frequency of 2,450 MHz, producing a wave that has a wavelength in the order of 12 centimeters (12 cm) (about 4.7 inches). The walls W of microwave M impose boundary conditions that cause the distribution of electromagnetic field energy distribution within the furnace volume to vary. This generates a standing wave energy pattern within the furnace volume.

The susceptor assembly 10 comprises a conventional generally flat susceptor 12 having a field guide structure generally indicated in the numerical reference 14 attached thereto. As will be developed herein, the field guide structure 14 is useful for redirecting and transferring the high and low electric field intensity regions of the standing wave pattern within the furnace volume. When used in conjunction with a turntable, the positions of the redirected and transferred regions change continuously, thereby improving the heating uniformity, cooking, and browning of a food product placed in a susceptor assembly 10 including the guide frame. from field 16.

In one embodiment shown in Figures 2 and 3, the field guide structure 14 is disposed under the plane susceptor 12, although it should be noted that these relative positions may be reversed. Whatever the respective relative positions of the field guide structure 14 and the flat susceptor 12, a food product (not shown) being heated, baked or golden or other article is typically brought into contact with the flat susceptor 12.

The flat susceptor 12 shown in the figures is generally circular in outline although it may exhibit any desired predetermined shape consistent with the food product to be heated, baked or golden inside oven M. As shown in the detailed circled portion of the Figure 2, the flat susceptor 12 comprises a substrate 12S having an electrically dissipative layer 12C therein. Layer 12C is typically a thin coating of vacuum deposited aluminum.

Substrate 12S may be made from any of a variety of materials conventionally used for this purpose, such as cardstock, cardboard, fiberglass or a polymeric material such as polyethylene terephthalate, heat stabilized polyethylene terephthalate, polyethylene Ketone ester, polyethylene naphthalate, cellophane, polyimides, polyetherimides, polyesterimides, polyarylates, polyamides, polyolefins, polyamides or polycyclohexylenedimethylene terephthalate. The substrate 12S may be omitted if the electrically dissipative layer 12C is self supporting.

Field guide structure 14 includes one or more plates 16.

In the embodiment illustrated in Figures 2 and 3, 5 plates 16-1 to 16-5 are shown. Figures 4A to 4F illustrate the susceptor assemblies 10, wherein the field guide structure 14 has an N number for plates 16 ranging from 2 to 6. In general, any convenient number of plates 1, 2, 3 .. N may be used depending on the size of the flat susceptor and the end length, configuration, orientation and arrangement of the plates.

For illustration purposes, the plates shown in Figures 2 and 3 show a variety of end contours, as will be discussed.

The front and rear portions of each board define a 16S area surface. In Figures 2 and 3, the surface area 16S of each plate 16 is illustrated generally as rectangular, although it should be noted that a surface area of the plate can be conveniently configured as any flat figure, such as a triangle, parallelogram or a keystone. If desired, the 16 S surface area of a plate may be curved in one or more directions.

At least a portion of the front and / or rear surface of each of the plates 16 is electrically conductive. Any region of drawn Figures 2 and 3 having dashed shading indicates an electrically conductive portion 16C and a plate 16. An electrically conductive portion 16N of a plate 16 is indicated by dotted shading.

Each card has an end 16F extending between a first end 16D and a second end 16E. The 16E end of a board can display any of a variety of contours. For example, the 16F end of a plate may be linear, as illustrated by plates 16-1 to 16-3. Alternatively, the end 16F of a plate may be arcuate or bent along one or more arcuate or bent lines 16L as suggested by plate 16-4. In addition, the contour of the 16F end of a plate may be curved as suggested by plates 16-5 (Figures 2 and 3) and plate 16-1 '(Figure 3).

A plate may have its first end 16D and its second end 16E disposed at any predetermined respective points of origin and termination in the plane susceptor 12. The distance along the end 16F of a plate between its first end 16D and its second end 16E sets the limit length of the board. The plates in the field guide frame 14 may have any desired end length, subject to condition with respect to the length of the conductive portion 16C mentioned below.

The plates 16 may be constructed entirely from an electrically conductive sheet metal or other material. In such a case, the entire 16S surface of the plate is electrically conductive (for example, as shown in Figure 2 for plate 16-1). The length and width of the conductive portion 16C thus correspond to the length and width of the plate end.

Alternatively, a plate may be constructed as a layered structure formed from a dielectric substrate with an electrically conductive material laminated or coated on part or all of its front and rear surface area. One form of construction could use a cardboard substrate to which a subsequently adhesive electrically conductive sheet metal is applied.

If supplied less than the total surface area of a plate, the electrically conductive portion 16C may itself exhibit any convenient, e.g. trapezoidal (as shown for plates 16-2 and 16-3) or rectangular ( as shown for plates 16-4 and 16-5 and plate 16-1 'in Figure 3). The width dimension of the electrically conductive portion 16C of the plate should be about 0.1 to about 0.5 times the wavelength generated in the furnace. The conductive portion 16C of the plate has a length which should be at least about a distance of about 0.25 times the wavelength of the electromagnetic energy generated in the furnace. An end length of about 2 times the wavelength of the electromagnetic energy generated in the furnace defines a practical upper limit.

Whatever the shape of the conductive portion, it may be desirable to radiate or round the corners to prevent bending, as will be developed in conjunction with Figure 19.

Selecting the shape and length of the electrically conductive portion of the plate and spacing the conductive portion from the flat susceptor and other plates allows the attenuating effect of the plate field to be more precisely adapted.

Wherever its origin and termination points, a plate may also be arranged to pass through the geometric center 10C. Figure 2 shows the path of a linear end plate 16-1 extending through geometric center 10C of a first termination 16d originating adjacent the periphery of the susceptor. Figure 3 shows the path of a curved end plate 16-1 'extending through the geometric center 10C of a first termination 16D originating in the vicinity of the geometric center 10C. All other plates in Figures 2 and 3 have paths that originate at a point of origin in the vicinity of geometric center 10C and extend externally thereto. The plates 16 extend in a generally radial direction with respect to the geometric center 10C of the susceptor assembly 10. The plates 16 may be angularly spaced from about the center 10C at equal or unequal angles of separation. For example, angle 18 between plates 16-1 and 16-2 may be smaller than angle 20 between plates 16-2 and 16-3.

It should be noted that the term "generally radial" (or similar terms) does not require that each plate must remain exactly within a radius emanating from the center 10C. For example, the plates may be offset or inclined with respect to the radius. Figures 4A to 4C respectively illustrate linear end plates 16T, arcuate end plates 16B and curved end plates 16V which are offset with respect to radial lines R emanating from geometric center 10C. Similarly, Figures 4D to 4F respectively illustrate linear end plates 16T, arcuate end plates 16B and curved end plates 16R which are inclined with respect to radial lines R emanating from geometric center 10C. Other arrangements of the plates may be used to obtain the transverse orientation of the plates 16 with respect to the plane susceptor 12.

Each plate 16 is physically (i.e. mechanically) connected to the flat susceptor 12 at one or more connection points. A connection between a plate 16 and the flat susceptor 12 may be a fixed connection or a flexible hinged connection.

A fixed connection is shown in Figure 5A. In a fixed connection, a plate 16 is bonded to an appropriate adhesive 24 in a predetermined fixed orientation with respect to the plane susceptor 12. The orientation of the plate 16 is preferably at an angle of inclination in the range of about forty and five degrees (45 °) and about ninety degrees (90 °) with respect to the flat susceptor, although smaller angular orientations may provide a useful effect. In the most preferred example, plate 16 is substantially orthogonal to plane susceptor 12.

A flexible hinged connection is shown in Figure 5B. In this arrangement, a plate 16 is connected to the flat susceptor 12 by a hinge 26. The hinge may be produced from a flexible tape. In a hinged connection, plate 16 is moved from an idle position (shown in the dashed lines in Figure 5B) where the plate plane is substantially parallel to the plane susceptor to a driven position (shown in continuous lines in Figure 5B) . The hinge may be provided with an appropriate stop such that, in the actuated position, the plate is maintained at a desirable angle of inclination, preferably in the range of about forty five degrees (45 °) to about ninety degrees (90 °). °) with respect to the flat susceptor, and more preferably substantially orthogonal to the flat susceptor 12.

Whatever the shape of the construction, the configuration of the plate surface area, conductive portion shape, plate end contour, plate end length, plate conductive portion length, plate path with respect to the center of the susceptor and orientation of the plate with respect to the flat susceptor, the electrically conductive portion 16C of the plate 16 must be disposed no more than a predetermined proximate distance from an electrical loss layer 12C of the flat susceptor 12. In general, the predetermined proximate distance it should not be greater than about 0.25 times the wavelength of electromagnetic energy generated in the furnace. It should be understood that as long as a food product or other article is present, the predetermined near distance may be zero, meaning that the conductive portion 16C of the plate rests electrically against the loss layer 12C of the flat susceptor. In a typical implementation, shown in Figure 2, the loss layer 12C is supported on a dielectric substrate 12S, such that the end of the conductive portion 16C of the plate is spaced from the loss layer 12C by only the thickness of the substrate 12S. The vertical dimension of the non-conductive portions 16N may be used to control the height at which the flat susceptor 12 is held within the oven M.

Alternatively, as seen from Figure 3, the nonconductive portions 12N of the plates may be disposed adjacent to the plane susceptor 12. This arrangement has the effect of spacing the conductive portions 16C of the plates away from the loss layer 12C at greater distances. that the substrate thickness 12S. If desired, additional non-conductive portions 16N may be arranged along the opposite end of the plates to obtain the height control benefits discussed above.

The plane susceptor 12 and a surface area 16S of a plate 16 intersects along an intersecting line 12L extending in a generally transverse direction with respect to the plane susceptor 12. When crossed with the plane susceptor 12, an end plate linear 16 will produce a straight line of intersection 12L. A plate 16 having an arcuate or curved end when crossed with the flat susceptor 12 will produce an arcuate or curved intersecting line 12L, respectively. The magnitude of the arc angle or the shape of the intersection line curvature, as the case may be, will depend on the angle of inclination of the plate to the plane susceptor. If the intersection line is a straight line, an arcuate line, or a curved line, the extent of the conductive surface of the plate will be along the intersection line.

Having described the various structural details of a susceptor assembly 10 according to the present invention, this effect on a stationary electromagnetic wave can now be discussed. Figure 6 is a representation of the schematic diagram in which an embodiment of a susceptor assembly 10 having a single linear end plate 16 is connected in a substantially orthogonal orientation with respect to the underside of a planar susceptor 12. Cartesian axes are positioned to originate at geometric center 10C of set 10. Set 10 is arranged such that the plane susceptor 12 is in the Cartesian plane X-Ye that the conductive portion 16C of the surface 16S of plate 16 is in the Cartesian plane. X - Ζ. The intersection line 12L defined along the connection between plate 16 and the flat susceptor 12 extends transversely through the loss layer 12C of the flat susceptor 12 and is oriented along axis X1 as shown. The conductive portion 16C of the surface 16S of the plate 16 lies at a predetermined distance D in the Z direction of the plane susceptor loss layer 12. The conductive portion 16C of the surface 16S has a greater thickness (i.e. its Y dimension) than the depth of the effect on the skin of a conductor on the frequency of microwave operation.

An electromagnetic wave is made up of mutually orthogonal oscillating electric and magnetic fields. At any given moment, a stationary electromagnetic wave includes a constituent of the electric field E. At any given moment, the constituent of the electric field E is oriented in a given direction in Cartesian space and can have any given value.

The electric field E is itself resolvable in three components of the vectors, namely, Ex, Ey, Ez. Each vector component is oriented along its corresponding coordinate axis. Depending on the value of the electric field E, each vector component has a predetermined value of "x", "y", or "z" units, as appropriate.

A corollary of the Faraday Law of Electromagnetism is the boundary condition that the tangential electric field on the interface surface between two means must be continuous across that surface. A specific example of such an interface is between a perfect conductor and air. By definition, a perfect conductor must have a zero electric field within it.

Therefore, in particular, the tangential component of the electric field exactly within the conductor surface must be zero. Thus, from the above statement of the limit continuity condition, the tangential electric field in the air just outside the conductor must also be zero. Therefore, the general rule is that the tangential component of the electric field on the surface of a perfect conductor is always zero. If the conductor is good but not perfect, then the tangential component of the surface electric field may not be zero, but it remains very small. Thus, any electric field that exists just outside the surface of a good conductor must be substantially normal to that surface.

The application of this physical law dictates that within that surface area of plate 16 having the conductive portion 16C, only the component vector of the electric field, which is oriented perpendicular to that surface, namely, the Ey vector, is allowed to exist.

The electric field component vectors that lie on any plane tangent to the plate surface, (namely, the Ex vector and the Ez vector) are not allowed. In Figure 6, the tangent plane is the plane of the conductive portion of the plate surface.

If the conductive portion 16C of plate 16 were in electrical contact with the electrical loss layer 12C, the value of component vector Ex that lies along intersection line 12L and the value of component vector Ez would be zero, for reasons already discussed. However, the conductive portion 16C is not in electrical contact with the loss layer 12C, but is instead spaced from it by a distance D. However, the conductive portion of the plate surface exerts an attenuating effect which has its most pronounced action in extending the conductive portion of the plate surface.

Thus, the components of the Ex and Ez vectors of the wave electric field have only attenuated intensities "xa" and "za". The intensity values "xa" and "za" are each, some intensity value less than "x" and "z", respectively. The attenuation of the electric field component of the electromagnetic wave in the plane tangent to the plate surface results in the improvement of the oriented electric field component perpendicular to the conductive portion of the plate surface. Thus, the component vector Ey has an enhanced intensity value "y" greater than the intensity value of "y".

The degree of attenuation of the Ex vector component is dependent on the magnitude of the distance D and the orientation of the conductive portion 16C relative to the loss layer 12C. The attenuation effect is most pronounced when the distance D is less than one quarter (0.25) of the wavelength, for a typical microwave oven a distance of about three centimeters (3 cm). At an angle of inclination of less than ninety degrees, the permissible field (i.e. the field normal to the conductive surface of the plate) will itself have components acting in the susceptor plane.

This effect is used by the susceptor assembly 10 of the present invention to redirect and transfer relatively high electric field intensity regions within a microwave oven.

Figure 7A is a stylized top view generally similar to Figure 1A, illustrating the effect of plate 16 as it is driven by a turntable T in the direction of rotation shown by the arrow. The plate is shown in outline form and its thickness is exaggerated for the sake of clarity of explanation.

Consider the situation at Position 1, near where the plate first meets hot region H2. For the reasons explained above, only an electric field vector that has an attenuated intensity is allowed to exist in the hot region segment H2 covered by plate 16. However, although only an attenuated field is allowed to exist, the energy content of the electric field is not. It can simply disappear. Instead, the attenuation action in the region extending from the conductive portion of the plate manifests itself causing the electric field to transfer from its original location A at the plane susceptor 12 to a displaced location A '. This energy transfer is illustrated by the displacement arrow D.

As the rotational drag drives plates 16 to Position 2, a similar result is obtained. The attenuating action of the plate again allows only an attenuated field to exist in the region extending from the conductive portion of the plate. The energy in the electric field energy originally located at position B of the plane susceptor 12 is shifted to position B ', as suggested by the displacement arrow D'.

Similar displacements and energy transfers occur as plate 16 drags through all regions of H1 to H5 (Figure 1A) of relatively high electric field strength.

Use of the present invention in a microwave oven having mixer mode equipment will result in the same effect.

Figure 7B is a sketch showing the total energy exposure for a complete turntable rotation at each distinct point J, K and L. The corresponding waveform of the sketch of Figure 1B is superimposed on it.

It is clear from Figure 7B that the presence of a susceptor assembly 10 having the field guide 14 according to the present invention results in a total energy exposure that is substantially uniform. As a result, heating, baking and browning of the food product placed in the susceptor assembly 10 will be improved over the prior art situation.

Figures 8A and 8B, 9A and 9B and 10A and 10B illustrate preferred constructions of a susceptor assembly according to the present invention.

Figures 8A and 8B show a susceptor assembly 102 including a field guide structure 142 having five linear end plates 162-1 to 162-5. The five plates 162-1 through 162-5 are connected to the underside of the plane susceptor 12. The plates are substantially orthogonal to the plane susceptor 12 and are arranged equangularly about center 10C. Plate 162-1 extends through center 10C while plates 162-2 to 162-5 originate in the vicinity of center 10C. The conductive portion 162C covers the entire surface of each plate. If desired, the bottom ends of the field guide 142 may further be supported on a non-conductive flat support member 32.

The support member can be attached to all or some cards.

Figures 9A and 9B show a susceptor assembly 103 including a field guide structure 143 having two curved end plates 163-1 and 163-2. The two plates 163-1 and 163-2 are connected to the underside of a planar susceptor 12. The plates are substantially orthogonal to the planar susceptor 12 and are equally arranged about about center 10C. Signs intersect in the vicinity of downtown 10C. The conductive portion 163C covers the entire surface of each plate. Again, a non-conductive flat support member 32 may further support the lower ends of the field guide plates 143, if desired.

Figures 10A and 10B show a susceptor assembly 104 including a field guide structure 144 having six linear end plates 164-1 to 164-6. The six plates 164-1 through 164-6 are attached to the flat susceptor 12 at the bottom. The plates are substantially orthogonal to the plane susceptor 12 and are equally arranged about the center 10C. All plates originate near the center 10C. The conductive portion 164C covers the entire surface of each plate. A non-conductive flat support member 32 may be used.

If desired, the plates 164-1 and 164-4 may themselves be connected by a length of a non-conductive member 164N. Member 164N is shown in Figure 10A in the dashed outline with dashed shadow.

In a second aspect, the present invention is directed to various implementations of a detachable self-supporting field guide structure incorporating the teachings of the present invention.

Figures 11, 12, 13A and 13B illustrate a field guide structure formed from a single plate. In each implementation, the plate has an inflection zone in which a plate can be formed into a self-supporting structure oriented in a predetermined orientation with respect to the predetermined reference plane RP disposed within oven M. The plane RP may be conveniently defined as a plane in which the surface of a turntable or the surface of a food product or other article is disposed within the oven.

In Figure 11, the field guide structure 145 is implemented using a single curved plate 165. The plate 165 may be curved or may have at least one flexure or curvature region 165R defined between first and second end 165D and 165E. The conductive portion 165C covers the entire surface of the plate. In use, plate 165 may be produced in a self-supporting structure disposed in a predetermined orientation with respect to a predetermined reference cloth RP. Field guide structure 146 shows in Figure 12 that plate 166 has a single bend line or arc 166L-1 therein. In use, plate 166 may be bent or arched along curve line 166L-1 to define a self-supporting structure that lies in a predetermined orientation with respect to a predetermined RP reference cloth within the oven. Μ The same effect can be achieved by flexibly connecting two linear end plates along a flexible connecting line in place of the bent or arcuate line.

Figures 13A and 13B are respective top and illustrative views of a field guide structure 147 implemented using a conductive flat plate 167 with two arc lines 167L-1 and 167L-2. By bending plate 167 along arcuate lines 167L-1 and 167L-2 they form ears 167E-1 and 167E-2 which serve to support the linear plate in a predetermined desired orientation with respect to the predetermined reference plane RP inside oven M.

Figures 14 and 15 are illustrated views of two additional implementations of a detachable self-supporting field guide structure in accordance with the present invention. Each field guide structure has a plate arrangement that includes a plurality of flexibly connected plates to form a self-supporting structure.

In the field guide structure 148 shown in Figures 14 and 15, the plate arrangement comprising plates 168-1 to 168-5, each having an electrically conductive surface thereon. Each card is flexibly connected to the 168F connection point to at least one other card. The flexibly connected boards are capable of being turned towards and against them as suggested by the arrows 168J. In use, with the plates in the arrangement distant from each other, the field guide is capable of being self-sustaining with each plate in the arrangement being arranged in a predetermined orientation with respect to a predetermined reference plane RP within the oven. . In a modified embodiment, a reinforcement 168S may be attached to the free end of each of at least three plates. The stiffeners are made of any transparent material for microwave energy.

Field guide frame 149 in Figure 15 comprises a pair of plates 169-1 and 169-2, each plate having an electrically conductive surface thereon. Each card is flexibly connected at one 169F connection point to the other card. The flexibly connected boards are capable of being turned towards and against them as suggested by the 169J arrows. In use, with the plates in the arrangement distant from each other, the field guide is capable of being self-sustaining with each plate in the arrangement being arranged in a predetermined orientation with respect to a predetermined reference plane within the oven.

Although the plates in each of the embodiments illustrated in Figure 11 through 15 are shown with conductive portions extending over the entire surface of the plate, it should be understood that the conductive portion of either plate may exhibit any alternative shape.

It should also be noted that a field guide structure of the present invention need not be detachable, but instead may be self-sustaining through the use of an appropriate non-conductive support member. Figure 16 is an illustrated view of a field guide assembly generally indicated by reference character 31. The field guide assembly 31 shown in Figure 16 comprises at least one plate 16 connected to a flat non-conductive support member 32 in FIG. that the conductive surface of the plate is oriented in a predetermined orientation (shown generally as orthogonal to the support member). If additional plates are provided, these additional plates are supported on the same support member. The cards may or may not be connected to each other as desired. The support member can be attached below or above the board (s).

It should further be noted that any embodiment of a field guiding structure falling within the scope of the present invention may be used with a separate planar susceptor (described above). It should also be noted that for some of the food products, it may be desirable to place a second flat susceptor above the food product or to pack the food product with a flexible susceptor.

Examples

Examples 1-8 The operation of the field guide structure and a susceptor assembly according to the present invention can be more clearly understood from the following examples.

Introduction

For all of the following examples, commercially available microwave pizzas (DiGiorno® Microwa ve Four Cheese Pizza, 280 grams) were used in the baking experiments.

A flat susceptor comprised of a thin layer of steamed aluminum in the middle of a polyester and cardboard film was provided with the pizza in the package. This flat susceptor has been used with various implementations of the field guide structure of the present invention, as will be discussed. The end of the cardboard provided was molded to form an inverted U-shaped baking tray to spac the flat susceptor about 2.5 cm above a turntable in the microwave oven. A toast ring (intended for gilding the pizza ends) provided with the pizza in the package has not been used.

In all examples, the flat susceptor was placed directly on the turntable of a microwave oven. In all examples, frozen pizzas were placed directly on the flat susceptor and cooked at full power for 5 minutes, except for Example 5, which was cooked at low power for 7.5 minutes.

For comparison purposes, a group of three pizzas was cooked using only the flat susceptor without a field guide structure and another group of three pizzas was cooked using the flat susceptor with a field guide structure of the present invention.

The plates of each field guide structure were constructed using 0.002 inch (0.05 millimeter) thick aluminum foil, cardboard and tape.

For Examples 1 to 7, the field guide structure was placed in space under the plane susceptor. For Example 8, the field guide structure was positioned above the pie.

Gilding ε Gilding Profile Measurements

The percentage of gilding and the gilding profile of the pizza crust were measured following a procedure described in Papadakis, SE et al., 54 (12) 51 (2000). A lighting system was established and a digital camera (Nikon, model D1) was used to acquire the images of the bottom crust after cooking. A commercially available image and software program graphics were used to convert color parameters to the L-a-b model, the preferred color model for food searching. Following the suggestion from the reference procedure, the golden area percentage was defined as the percentage of pixels with an L brightness value of less than 153 (on a brightness scale from 0 to 255, with 255 being the brightest). Following the methodology described in the reference procedure, the gilding profile (ie, the percentage of gilded area as a function of radial position) was calculated.

The bottom crust image was divided into multiple concentric annular rings and the mean L value was calculated for each annular ring.

The following examples are believed to illustrate the improvements in gilding and gilding uniformity that resulted from the use of different field guide structures of the present invention.

Example 1

A DiGiorno® four-cheese microwave oven pizza was baked in a General Electric (GE) 1,100 watt microwave oven, model number JES1036WF001, as described in the introduction. When a field guide was employed, the field guide structure according to Figure 14 (without the supports 168S) was used. Plate 168-1 had a length dimension of 17.5 cm and a width dimension of 2 cm. The plates 168-2 to 168-5 each had a length dimension of 8 cm and a width dimension of 2 cm.

After cooking, an image of the bottom crust was acquired with the digital camera as described. From the image data, the percentage of the golden area was calculated using the procedures described. The average percentage of golden area for pizzas cooked without a field guide was determined to be 40.3%. The average golden area percentage for pizza cooked with a field guide was determined to be 60.5%.

Examples 2 to 5

The experiment described in Example 1 was repeated in four microwave ovens from different manufacturers. The furnace manufacturer, model number, maximum power output and cooking time for each example are summarized in Table 1. The table shows the percentage of gilding area with and without a field guide. It should be noted that the percentage of gilding area was improved in all cases.

Table 1

Comparison of Golden Area Percentage with ε without Field Guide

<table> table see original document page 30 </column> </row> <table>

Example 6

A 280-gram DiGiorno® four-oven microwave cheese pizza was baked in a Sharp 1,100-watt R-630DW oven. When a field guide structure was employed, the field guide structure according to Figure 15 was used. The plates 169-1 and 169-2 had a length dimension of 22.9 cm and a width dimension of 2 cm. The radius of curvature for each portion of a curved plate extending from connection point 169F was about 5.3 cm and had a curve angle of about 124 degrees.

After cooking, an image of the bottom crust was acquired with the digital camera and the percentage of golden area was calculated, all as described.

The average golden area percentage for pizzas cooked without a field guide was 55.2%. The average percentage of golden area for pizza cooked with a field guide was determined to be 73.8%. The gilding profile has been sketched and is shown in Figure 17.

Example 7

The experiment described in Example 6 was repeated using a Panasonic 1300 watt model NN5760WA oven. The average percentage of golden area for pizzas cooked without a field guide was 50.3%. The average percentage of golden area for pizzas cooked with a field guide structure was determined to be 51.7%. The substantially uniform gilding profile that follows from the use of the present invention could be seen from the sketch in Figure 18. From the observation of Figure 18, it can be seen that the gilding profile along the radius has been considerably improved with the use of a field guide structure.

Example 8

The experiment described in Example 1 was repeated in a Goldstar 700 watt microwave oven model MAL783W. When a field guide structure was employed, the field guide structure according to Figure 14 with the supports 168S was used. The supports were 5 cm high and were placed on the turntable to support the field guide just above the pizza. The course guide structure barely touched the top of the pizza after the pizza crust had risen.

After cooking (for 7.5 minutes at full power of the oven used), an image of the bottom crust was acquired with the digital camera and the percentage of the golden area was calculated, all as described.

The percentage of golden area for pizzas cooked without a field guide was 31.5%. The percentage of golden area for pizza cooked with a field guide was 65.1%. When a microwave susceptible assembly as described above is placed in an "empty" microwave oven (ie, an oven without a food product or other article being present), several detrimental problems have been observed. The problems are particularly acute in high voltage furnaces (that is, furnaces having a degree of strength typically greater than 9,000 W). In some cases, the microwave susceptor assembly may overheat even when an article is present.

As the dissipative layer 12 C of the flat susceptor 12 overheat, melt or carbonize the substrate 12S may occur. The susceptor may overheat to a degree that the susceptor substrate burns. The conductive portions of the field guide frame plates may bend in particular along the edges and in particular at the corners. Bowing causes the nonconductive support (typically cardboard) of the boards to discolor, char, or overheat to a degree that it ignites in flames. Overheating of the field guide structure may also be caused by overheating of the susceptor material.

Accordingly, it is believed to be advantageous to provide a field guide structure and a susceptor assembly incorporating the same as being "abuse tolerant", that is, a structure that avoids bending and / or guide overheating. and / or the occurrence of susceptor overheating.

Figure 19 is a composite view of a 10-10 susceptor assembly having a field guide structure 1410. The plates shown in Figure 19 illustrate the propeller plates that are used in the following Examples 9 to 64 herein.

The susceptor assembly 1010 includes a generally flat susceptor 12 having a substrate 12B with an electrically dissipative layer 12 C as described above in conjunction with Figure 2.

Field guide frame 1410 has at least one, but preferably a plurality of plates 1610 each mechanically connected to the plane susceptor 12. Each plate 16 ^ 10-1 through 16 ^ 10-8 shown in Figure 19 is formed of a 1610N substrate of a non-conductive material. Each plate is generally rectangular in shape. The 16 ^ 10N substrate is visible on some of the plates. The 16 ^ 10N substrate may have a flame retardant composition applied thereto.

It should be understood that the field guide structure 14 ^ 10 may alternatively be used in combination with a non-conductive flat support member 32 to define a field guide assembly generally indicated by reference character 31.

Each plate 16 ^ 10 has a surface 16 ^ 10S which is identified for illustration clarity only for plates 16 ^ 10-6. At least a portion 16 ^ 10C of the surface 1610S of each plate is electrically conductive. As will be described, the electrically conductive portion 16 ^ 10C of each plate 16 ^ 10 is positioned relative to the plane susceptor 12 and configured in various ways to avoid overheating and bending problems.

The conductive portion 16 ^ 10C of each plate 16 ^ 10 has a first end 15 ^ 10D and a second end 15 ^ 10E. Again, for clarity, the ends are indicated only on plates 16 ^ 10-6. The distance between the first and second ends 15 ^ 10D and 15 ^ 10E defines a predetermined length dimension for the conductive portion 16 ^ 10C. The conductive portion 1610C of each plate also exhibits a predetermined width dimension. As previously described (for example, in conjunction with Figures 2 and 3), the length dimension should be in the range of about 0.25 to about two (2) times the length of the stationary electromagnetic wave generated in the furnace. . The width dimension should be in the range of about 0.1 to about 0.5 times that wavelength.

Plate 1610-1 has a conductive portion 1610C-1 that occupies the entire rectangular surface. The conductive portion 1610C-1 adjoins the flat susceptor 12. Plate 1610-1 is typical of a plate structure that would overheat when used in an empty oven. A susceptor 12, when used with a field guide structure having plate 1610-1, may also overheat resulting in melting or charring of the susceptor substrate 12S. The conductive portion of plate 1610-1 may bend along its ends or corners.

The conductive portion 1610C-2 of plate 1610-2 is also rectangular in shape. The conductive portion 1610C-2 occupies only a portion of the plate surface, leaving part of the exposed substrate 1610N to define a margin 19L along the bottom edge. The conductive portion 1610C-2 adjoins the flat susceptor 12. The structure of plate 1610-2 has been shown to limit but not eliminate overheating of plate and susceptor when used in an empty furnace (Examples 36, 39). When used with a field guide structure having a plate 1610-2, the susceptor 12 may also overheat, resulting in melting or carbonization of the substrate 12S.

As will be developed, plates 1610-3 through 1610-5, 1610-7 and 1610-8 exemplify various positions and / or configurations of the 1610C conductive portions in accordance with the present invention wherein the susceptor overheating problems, and / or Field guide overheating and / or bending are prevented.

Plate 1610-3 is an example of a plate in which substrate 1610N is adjacent to planar susceptor 12. In this example, conductive portion 1610C-3 is positioned on the plate such that the upper edge 19T of non-conductive substrate material is exposed along the end of the plate adjacent to the susceptor 12. The margin 19T serves to spacer the conductive portion 1610C-3 from the plate 1610-3 at a predetermined near distance 21D away from the susceptor 12. The dimension 21D1 measured in the orthogonal direction at the plane of susceptor 12, the range of the 0.025 to 0.1 times the wavelength of the stationary electromagnetic wave produced in the microwave oven in which the susceptor assembly 1010 is being used remains. That is, the 21D dimension must be at least 0.025 times the wavelength. In addition, the 21D dimension must be no more than 0.1 times that wavelength (ie, the 21D dimension <0.1 times that wavelength). It should be mentioned that the maximum distance 17D referred to above and the maximum distance shown as the reference character D in Figure 6 (i.e. 0.25 wavelength) are dimensioned with the clear understanding that the microwave oven in that that plate is used would be full.

The conductive portion 1610C-4 of plate 1610-4 is sized such that part of its substrate 1610N is exposed to define radially inner and outer margins 19D and 19E, respectively. In addition, the upper margin 19T and the lower margin 19L of a 16N substrate material are exposed.

Plate 1610-5 is an example of a plate in which the conductive portion 1610C-5 is generally rectangular (similar to the conductive portion 1610C-4) but with rounded corners. The corners may be rounded to a radial dimension 15R up to and including half the width dimension of the conductive portion 1610C-5 (i.e. 15R <0.5 width). When the corners are rounded, the length of the conductive portion is defined by the radial extension of the conductive portion. The 1610-5 board also has margins 19T, 19L, 19D, 19E (similar to those shown on the 1610C-4 board). The size of the lower margin 19L is indicated by the reference character 21L.

Plate 1610-6 also exhibits a conductive portion 1610C-6 with rounded corners. However, the conductive portion 1610C-6 extends the maximum width of the plate and is contiguous with the plane susceptor 12. A predetermined near distance away from the plane susceptor 12 is not spaced.

Plate 1610-7 is an example of a plate having an electrically conductive portion 1610C-7 made of a metal foil that is folded as indicated in 1610C-7F to define at least one double thickness along its perimeter. Margins 19T, 19L, 19D, 19E (similar to those shown on plate 1610C-4) are present along their perimeter of conductive portion 1610C-7.

Plate 1610-8 has a conductive portion 1610C-8 that occupies the entire rectangular surface. For this plate, the required spacing 21D of the conductive portion 1610C-8 of the susceptor 12 is obtained by using a mounting arrangement in which the plate is physically separated from the susceptor.

Of course, it should be mentioned that the required spacing 21D can also be obtained by summing the separate distance of the susceptor and the margin width of an appropriately sized delimited plate (i.e. plate 1610-3, 1610-4, 1610-5 or 1610 -7).

As indicated in Figures 19 and 20, when a plurality of plates are used, the first end 1510D of the conductive portion of each plate is arranged at a predetermined separation distance 21S from the geometric center 12C from the plane susceptor 12 or from the center. geometry 32C of the flat support member 32, as appropriate. The distance of the separation 21S, measured in a direction parallel to the plane of the susceptor 21S, or the support member 31, must be at least 0.16 times the wavelength of the stationary electromagnetic wave produced in the microwave oven where the susceptor assembly 1010. is being used. It has been found that by arranging the first end 1510D of the conductive portion 1610C of each of the plates at the predetermined separation distance 21S from the geometric center 12C of the flat susceptor 12 decreases the occurrence of susceptor overheating in the vicinity of the susceptor center (Examples 18, 19, 20 - 22). By disposing of the electrically conductive portion of the plate, the predetermined near distance 21D of the electrically dissipative plane susceptor layer (however, that spacing is obtained) was also found to decrease the occurrence of susceptor overheating (Examples 35, 37). Further, the decrease in the occurrence of susceptor overheating can be achieved by providing the lower margin 19L (Examples 36, 39).

According to the present invention, the arrangement of the conductive portions of the plates at the predetermined separation distance 21S together with the arrangement of the conductive portions of the plates at the predetermined distance 21D from the plane susceptor prevents overheating from occurring. susceptor when used in an empty microwave oven.

Likewise, according to the present invention, the arrangement of the electrically conductive portion of the plate at the predetermined proximate distance 21D from the electrically dissipative layer of the flat susceptor and the rounding of the margins of the conductive portion with radius 15R prevents bending from occurring. when used in an empty microwave oven.

Further, according to the present invention, bowing in an empty microwave oven is prevented by arranging the electrically conductive portion of the plate at the predetermined proximate distance 21D of the electrically dissipative layer of the flat susceptor and by covering the conductive portion of the plate. either plate 1610-3 through 1610-7, 1610-7, 1610-7 with an electrically nonconductive material, such as a polyacrylic or polytetrafluoroethylene spray coating or a polyimide tape.

Further, according to the present invention, arranging the electrically conductive portion of the plate at the predetermined proximate distance 21 D of the electrically dissipative layer of the flat susceptor and increasing the perimeter thickness of a thin sheet conductive portion (as shown 1610-7) prevents bending when used in an empty oven.

Examples 9 to 23

The following examples describe the experiments that were performed to determine parameters that decrease or eliminate overheating and / or bending problems. A 1,100-watt General Electric microwave oven model JES1456BJ01 was used in Examples 9 through 23. Tests were performed with the oven empty, that is, no food products or other items were present in the oven. These Examples are summarized in Table 2 herein.

Example 9 was a borderless and rounded corner control example of the conductive portion of a single plate.

Examples 10 to 13 and 14 to 17 tested the effect of a nonconductive cover of the conductive portion of a single plate. In Examples 10 to 13, the conductive portion was 3A "(0.75"; 19mm) long with rounded corners; in Examples 14 to 17, the conductive portion was 1 "(25.4 mm) long with rounded corners.

Examples 18 to 20 tested the effect of center slot variation between radially opposed conductive portions on arching and overheating.

Examples 21 and 22 tested alternate materials for the conductive portions. Example 23 tested the effect of cardboard flame retardant treatment on bending and burning. Example 9

In this example a single plate has been configured and positioned with respect to the susceptor according to plate 1610-1 of Figure 19. An enlarged dimensioned view of such plate is shown in Figure 21. A 0.002 "aluminum foil conductive portion (0 .05 mm) bottom thickness 3 Vz (3.5 ") long by 1" adhesive (88.9 mm by 25.4 mm) from Merco Co., Hackensack, NJ with rounded corners was applied to a cardboard of the same size.The cardboard was International Paper (Grade Code 1355, 0.017 / 180 # Fortress Uncoated Cup Stock.) The plate was then taped to the underside of a commercial susceptor set supplied with the Four Cheese Pizza. DiGiorno® Microwave Oven (280 g) using the 0.001 "(0.025 mm) thick polyimide tape (El DuPont de Nemours and Company Kapton® polyimide tape). This configuration resulted in bending within 28 seconds when exposed empty in a microwave oven.

Examples 10 through 13

In these examples, the single plate has been configured and positioned relative to the susceptor according to plate 1610-5 of Figure 19. An enlarged dimensioned view of such plate is shown in Figure 22.

Examples 10 to 12 provided a protective covering of an electrically nonconductive material over the aluminum conductive portion in an effort to prevent bending. An uncovered version, Example 13, was also tested as a control.

Each plate had a 3 14 "(3.5"; 88.9 mm) long conductive portion and a 3A "(0.75"; 19.2 mm) length cut from the same 0.002 "aluminum foil ( 0.05 mm) adhesive background thickness used in Example 9, applied to a 4 "χ 1" rectangle (101.6 by 25.4 mm) of the same cellulose cardboard as in Example 9. The conductive portion was 3A " (0.75 "; 19.2 mm) long to ensure that the nonconductive cover covered all ends of the aluminum conductive portion. An upper margin of 1/8" (0.125 "; 3.2 mm) of the cardboard was exposed above the conductive portion. A 1/8 "(0.125"; 3.2 mm) margin dimension was about 0.025 times the wavelength. The conductive portion had all rounded corners within a radius of 3 / 8 "(0.375"; 9.6 mm).

A lower margin of 1/8 "(0.125"; 3.2 mm) of cardboard was also exposed below the conductive portion and% "(0.25"; 6.4 mm) of cardboard edge was exposed at each end.

Non-different conductive materials were used as the covers as follows:

Example 10 - 0.001 "(0.025 mm) thick by 1" (25.4 mm) length of polyimide tape (marketed under the trademark of Kapton® by E.I. DuPont of Nemours and Company);

Example 11 - Minwax polyacrylic spray;

Example 12 - polytetrafluoroethylene spray (marketed under the trademark of Teflon® by E.I. DuPont of Nemours and Company); Example 13 - Uncoated.

None of the plates showed any bending when exposed empty in a microwave oven for two minutes.

Examples 14 to 17 In these examples, a single plate has been configured and positioned relative to the susceptor according to plate 1610-6 of Figure 19. An enlarged dimensioned view of such plate is shown in Figure 23.

Examples 14 to 16 evaluated the same non-conductive protective covers disposed on the aluminum conductive portion as in Examples 10-12, respectively, but with the aluminum conductive portion being the same as 1 "(25.4 mm) long Again, an uncovered version, Example 17, was tested as a control. In each of these Examples, the conductive portion was a 0.002 "(0.05 mm) aluminum foil of 3 Vz adhesive backing thickness. (3.5 ") long by 1" (25.4 mm) long applied to a 4 "by 1" (101.6 mm by 25.4 mm) of cellulose cardboard as used in Examples 10 to 13 The conductive portion had all rounded corners within a radius of Vz (0.5 "; 12.7 mm) and had a margin of (0.25"; 6.4 mm) of exposed cardboard at both ends.

The different nonconductive materials were used as coverings as follows:

Example 14 - 0.001 "(0.025 mm) thick by 1" (25.4 mm) polyimide tape (marketed under the Kapton® trademark by E.I. DuPont of Nemours and Company);

Example 15 - Minwax polyacrylic spray;

Example 16 - polytetrafluoroethylene spray (marketed under the trademark of Teflon® by E.I. DuPont of Nemours and Company);

Example 17 - Uncoated.

In Example 14, the surface of the conductive portion was covered by the polyimide tape. The upper and lower extremities were not covered by the polyimide tape.

In Examples 15 and 16, the surface of the conductive portion was covered by the polyacrylic or polytetrafluoroethylene spray coating, respectively. The upper and lower ends of the aluminum conductive portion were covered only by the accidental spray of the polyacrylic or polytetrafluoroethylene coatings.

In Examples 14, 16 and 17, the lower end of the conductive portion arched in the center. Arching occurred very briefly after being exposed to empty in the microwave oven. In Examples 15, no arching occurred.

In particular, the results of the experiments were as follows:

Example 14 - Conductive portion of the 0.001 "(0.025 mm) coated Kapton® tape plate, arcuate after 16 seconds of exposure;

Example 15 - Conductive portion of plate coated with polyacrylic spray, not arched within 2 minutes;

Example 16 - Conductive portion of the polytetrafluoroethylene (Teflon®) spray-coated plate, arcuate after 12 seconds of exposure;

Example 17 - Conductive portion of uncovered plate arched after 17 seconds of exposure.

Figure 20 is a plate view of a susceptor assembly incorporating six field guide plates used in Examples 18 to 23. It can be assessed from Figure 20 wherein the end-to-end slot ("Slot") between the conductive portions of the diametrically opposed plates is twice the distance of the 21S separation.

Example 18

In this example, each of the six field guide plates of Figure 20 has been configured with the conductive portions according to plate 1610-5 of Figure 19.

As shown in Figure 24, three white plates each having 3 Vz (3.5 ") long by 0.75" long (88.9 mm by 19.2 mm) conductive portions with all rounded corners within a radius of 3/8 "(0.375"; 9.6 mm). The conductive portions were cut from the same 0.002 "(0.05 mm) adhesive backing aluminum foil used for the Examples. 9 to 17 above. Two of these conductive portions were placed on an 8 "by 1" (203.2 by 25.4 mm) of the cellulose cardboard rectangle used in Examples 9 to 17 such that there was no margin of 1/8 "(0.125"; 3.2 mm) of the exposed cardboard above and below the conductive portion and at the outer edges. An end-to-end slot (0.75 "; 19.2 mm) was left between the inner ends of each conductive portion.

Each of the three white plates was then curved in the middle to form a V shape and positioned under a susceptor with the vertex of each V in the center of the susceptor, thereby defining a separation distance of 21S (Figure 19) from 3/8 ". (0.375 "; 9.6 mm). V-shaped white plates were glued to the underside of the susceptor using a water-soluble adhesive such as Basic Adhesives, Inc. type BR-3885. The blanks were positioned such that the plates were evenly spaced in a radial axis pattern. The fully assembled susceptor assembly was arranged such that the pairs of the conductive portions were directly opposed in an end-to-end slot of (0.75 "; 19.2 mm).

There was no noticeable bending when this susceptor set was exposed to empty in the microwave oven, but the set burned when the cardboard substrate in the center overheated by 47 seconds.

Example 19

In this example, each of the six field guide plates of Figure 20 has been configured with the conductive portions according to plate 1610-5 of Figure 19.

The plates in this Example were constructed in the same manner as in Example 18 from the white plates as shown in Figure 25. The white plates were 8 "by 1%" (203.2 mm by 31.7 mm) rectangles of the same cardboard. of cellulose. The conductive portions were 3 3/8 "(3.375", 85.7 mm) in length and 1 "(25.4 mm) in length with all rounded corners within a radius of VS (0.5"; 12, 7 mm). The conductive portions were attached to the white cardboard to leave a 1/8 "(0.125"; 3.2 mm) margin of exposed cardboard above and below the conductive portion and at the outer edges. A 1 "(25.4 mm) end-to-end slot was left between the inner ends of each conductive portion.

As in Example 18, three of these V-folded white plates were glued to the underside of a susceptor defining a 21S separation distance (Figure 19) of 1/2 "(0.5"; 12.7 mm).

Again, there were no noticeable arcs when this susceptor set was exposed in the empty microwave oven, but the set did not burn into flames when the cardboard plates in the center heated up in one minute, eighteen seconds.

Example 20

In this example, each of the six field guide plates of Figure 20 has been configured with the conductive portions according to plate 1610-5 of Figure 19.

The plates in this Example were constructed in the same manner as in Examples 18 and 19 from the white plates as shown in Figure 26. The white plates were 8 "by 1 rectangles (203.2 mm by 31.7 mm) of the same cardboard. The conductive portions were 3 1/8 "(79.4 mm) in length and 1" (25.4 mm) in length with all corners rounded within 1/2 "(0.5" ; 12.7 mm). The conductive portions were attached to the white cardboard to leave a 1/8 "(0.125"; 3.2 mm) margin of exposed cardboard above and below the conductive portion and at the outer edges. The 1 V2 "(1.5"; 38.1 mm) end was left between the inner ends of each conductive portion.

As in Example 18 and 19, three of these white V-folded plates were glued to the underside of a susceptor defining a 21S separation distance (Figure 19) of 3Å "(0.75"; 19.2 mm).

There was no bending and burning when this susceptor assembly was exposed in the microwave oven for 5 minutes.

Example 21

The test of Example 20 was repeated using the conductive portions as shown in Figure 26. The conductive portions for this example were produced with a 0.002 "(0.05 mm) adhesive background thickness aluminum foil aluminum foil. Dennison Fasson® 0817 available from Avery-Dennison Specialty Tape Division1 Painesville, OH.

There was no bending and burning when this susceptor assembly was exposed to empty in the microwave oven for 5 minutes.

Example 22

The test of Example 20 was repeated using the conductive portions as shown in Figure 26. The conductive portions for this example were produced with the Shurtape AF973 adhesive backing thickness 0.002 "(0.05 mm) aluminum foil, Hickory, NC.

There was no bending and burning when this susceptor assembly was exposed to empty in the microwave oven for 5 minutes. The aluminum daughter of this tape performed acceptably, but the adhesive came off.

Example 23

Application of a flame retardant composition to prevent spontaneous burning of the plates was tested as in Example 23. The flame retardant using was an aqueous based resin known as Paper Seal ™ from Flame Seal® Products of Houston, TX. The susceptor assembly was constructed as in Example 18 with a Va (0.75 "; 19.2 mm) slot in the center between each pair of conductive portions as shown in Figure 24, thereby defining a separation distance of 21S (Figure 19 ) 3/8 "(0.375"; 9.6 mm).

The white cardboard was immersed in a flame retardant liquid bath and allowed to dry for a day after adhering to the conductive portions and assembling the susceptor assembly.

There were no arcs when an empty susceptor set was exposed in a microwave oven for five minutes. Unlike Example 18, the assembly did not burn into flames, suggesting that a flame retardant treatment of the cardboard was sufficient to prevent burning.

The tests of Examples 9 to 23 are summarized in Table 2.

Table 2

Ε Overheat Rating (N / A indicates "Not Applicable")

<table> table see original document page 46 </column> </row> <table> <table> table see original document page 47 </column> </row> <table> <table> table see original document page 48 < / column> </row> <table>

The observations from Examples 9 to 23 were:

(1) The combination of rounded corners in the conductive portion of a cardboard edge (i.e., a lower conductivity material) of at least 1/8 "(0.125"; 3.2 mm) (about 0.025 wavelengths of the standing wave in a microwave oven) that completely surrounds a conductive potion not covered by a plate prevented bending. It should be mentioned that the margin served to spacer the conductive portion of the plate from the susceptor by a predetermined near distance (Examples 18 to 23);

(2) The combination of a margin (predicted near distance) of at least 1/8 "(0.125"; 3.2 mm) and a separation distance from the inner ends of the conductive portions of the susceptor geometry center of 3A " (0.75 "; 19.2 mm) (about 0.16 the wavelength of the standing wave present in a microwave oven), ie a 1 1/4" (1.5 "center slot; 38.1 mm) between the opposing conductive portions prevented overheating and spontaneous combustion of the cardboard of a susceptor assembly when it was exposed in an empty microwave oven (Examples 20 to 22);

(3) Combination of a margin (predetermined near distance) of at least 1/8 "(0.125"; 3.2 mm) and a nonconductive cover of the conductive portion prevented bending (Examples 10 to 12). However, as can be seen from Examples 14 to 16, when the conductive portion was covered with a nonconductive cover and no margin was present, the bending occurred; and

(4) Application of the flame retardant to the cardboard prevented spontaneous combustion due to overheating with a susceptor geometric center separation distance of 3/8 "(0.375"; 9.6 mm) (about 0.08 inch length). wave), that is, a central slit (0.75 "; 19.2 mm) between the opposing conductive portions.

EXAMPLES 24 TO 64 GENERAL COMMENTS

In the following Examples 24 to 64, a susceptor assembly similar to that shown in Figure 20 was used inside a microwave oven to cook DiGiorno® Four Cheese Microwave Pizza (280 g). The results of these experiments are presented in Tables 3, 4A, 4B and 5 below.

Examples 24 to 50 and Examples 61 to 64 were performed to evaluate the effect of various plate designs on eliminating susceptor overheating during pizza baking in various microwave ovens. The remaining examples (namely Examples 51 to 60) were performed to evaluate the effect of various plate designs on the browning of pizza baked in various microwave ovens. As shown in Figure 20, each susceptor assembly included six identical equally spaced sixty (60) degrees plates mounted on a susceptor with a separation distance of 3/8 "(0.375"; 9.6 mm) 21S from each electrically conductive portion. from a plate to the geometric center of the susceptor.

The susceptor assemblies tested had substrates formed from various materials. Four different susceptor substrate materials were tested in combination with two different metallization thicknesses that formed the dissipative conductive layer.

The conductive portion of each plate was made using an adhesive bottom 0.002 "(0.05 mm) aluminum foil applied to an International Paper cellulose cardboard plate as previously described in conjunction with Examples 9 to 20. Each conductive portion was 3 ½ (3.5 "; 88.9 mm) long, but of different widths. Tables 3, 4A, 4B, and 5 each contain a column of alphabetic designators indicating the "Plate Type" tested. Each designator indicates a plate type as shown in Figure 19, with the "Width" dimension of the conductive portion and the "Margin" as follows:

Table 3

<table> table see original document page 50 </column> </row> <table> <table> table see original document page 51 </column> </row> <table>

Tables 3, 4A, 4B, and 5 also contain a column of alphabetic designators indicating the "Oven" used for the test. Each designator corresponds to a particular microwave oven manufacturer and model as follows:

Table 4

<table> table see original document page 51 </column> </row> <table>

Tables 3, 4A, 4B and 5 contain a column indicating the "Susceptor" used (i.e. substrate 12S and layer 12C).

The Susceptor in some of the Examples contained in Tables 3, 4a and 4B below is identified as "Control". The "Control" susceptor was the one supplied with the previously mentioned DiGiorno® Four Cheese Microwave Pizza (280 g). The "Control" susceptor included a cardboard substrate.

The "Susceptor" in some of the examples contained in Tables 3 and 5 below is identified by a reference designation comprising first and second hyphenated numeric values. The first numerical value represents the polymer substrate material of the susceptor, while the second numerical value denotes the thickness of the dissipative dissipative layer (vacuum deposited aluminum) metallization based on its measured optical density.

The first numeric value denotes the polymeric substrate material as follows:

<table> table see original document page 52 </column> </row> <table>

The second numerical value represents the measurement of the optical density thickness of the vacuum deposited aluminum foil as follows:

<table> table see original document page 52 </column> </row> <table> Therefore, for Example 29 in Table 3, a susceptor designated "12-3" indicates that it had a 300 gauge polyethylene terephthalate substrate. heat stabilizing film (Melinex® ST-507 film) (as denoted by the first numeral "12") and that the vacuum deposited metallization of aluminum had an optical density of 0.3 (as indicated by the second numeral "3" ).

Examples 24 to 34

A Type A plate susceptor assembly (as described above) was used to cook DiGiorno® Microwave Four Cheese Pizza (280 g) in the S-1,000 "or F-950 oven. As can be seen from Table 3, four types of susceptor substrate materials were used.The cooking time ranged from 5 to 6 minutes.All plate susceptor sets consistently overheated in the center.The severity of overheating increased with the cooking time for each material of the substrate. The susceptor substrate used Examples of overheating included burnt and melted spots on the surface of the susceptor which, in some cases, resulted in the transport of the molten susceptor material to the bottom of the pizza, as shown in Figures 27 and 28.

Examples 35 to 40

In Examples 35 to 40, the addition of a% "(0.25"; 6.4 mm) margin of cardboard to the top or bottom of the conductive portion of the plate was tested to assess its potential to eliminate overheating in the center of the susceptor. . As summarized in Table 3 below, in this series of tests the DiGiorno® Microwave Four Cheese Pizza was baked in the S-1,000 microwave oven for 6 minutes using susceptors having substrates 12-3. Field guide assemblies that display different board types A, B, C, D, E, and F have been tested. Example 35 uses a plate type Β; Example 36 uses a plate type C; Example 37 uses a plate type D; Example 38 uses a plate type Ε; Example 39 uses a plate type F; and Example 40 uses a board type A.

The results are summarized in Table 3.

Table 3

Susceptor Overheat Evaluation

<table> table see original document page 54 </column> </row> <table> <table> table see original document page 55 </column> </row> <table>

Table 3 illustrates that for plate susceptors having a defined separation distance between the interior of the conductive portion and the geometric center of the susceptor, the addition of an upper margin between the susceptor and the upper end of the conductive portion of the plate structure ( BeE plate types) have consistently avoided overheating of the susceptor. Non-margin plate susceptors (Type A and D plates) consistently lead to overheating in the center of the susceptor.

Plate susceptors having a lower (but not upper) margin of non-conductive material together with the conductive portion of the plate (CeF Type plates) somewhat reduce the severity of susceptor overheating, but do not completely eliminate the problem. These results from Examples 35 to 40 are illustrated in Figure 29.

Examples 41 to 60

A series of baking tests was performed with 5 microwave ovens identified above. The tests used susceptors with AeB plate types to evaluate the effect of adding a Va (0.25 "; 6.4 mm) cardboard margin along with the conductive portion of the plate. Examples 41 - 50 (summarized in Table 4A) and Examples 51 - 60 (summarized in Table 4B) respectively used the same test conditions. Examples 41 to 50 evaluated overheating. Examples 51 to 60 evaluated total microwave cooking performance, specifically the capacity of this configuration of the set capable of uniformly gilding the bottom of the pizza.The percentage gilding ("% gilding") of a pizza was measured in the same manner as described in conjunction with Examples 1 to 8. The measured gilding percentage was the average of three pizza samples.

Table 4a Overheating Rating

<table> table see original document page 56 </column> </row> <table>

Table 4B <table> table see original document page 56 </column> </row> <table> <table> table see original document page 57 </column> </row> <table>

The results shown in Tables 4A and 4B indicated that for plate susceptors having a defined separation distance between the interior of the conductive portion and the geometric center of the susceptor, the addition of a higher cardboard margin of V '(0.25 "). ; 6.4 mm) along with the conductive portion of the plate (Type B) consistently prevented overheating in the center of the susceptor.However, as noted in Table 4B, the overall cooking performance of a susceptor with a Type B plate decreased (as evidenced by the lowest average percentage of gilding).

Examples 61 to 64

Examples 61 to 64 evaluated the effect of the upper cardboard margin width between the susceptor and the upper end of the conductive portion of the plate on the overheating of the susceptor. This test series was also performed with DiGiorno® Four-Cheese Microwave Pizza baked for 6 minutes in an S-1,000 microwave oven. The susceptor assemblies had substrate materials 12-3 and Type A1 plates B, G, and H. These results from Examples 61 to 64 are illustrated in Figure 30 and summarized in Table 5.

Table 5

Evaluation of the Effect of Upper Margins on Overheating

<table> table see original document page 58 </column> </row> <table>

These tests indicated that for susceptors having a separation distance between the interior of the conductive portion and the geometric center of the susceptor, an upper cardboard margin of at least 1/8 "(0.125"; 3.2 mm) (i.e. , type plates BeG) between the susceptor and the upper end of the conductive portion of the plate structure was required to prevent overheating of the susceptor.

In general, the conclusions drawn for Examples 24 to 64 for susceptors having a defined separation distance between the interior of the conductive portion and the geometric center of the susceptor were:

(1) A margin of at least 1/8 "(0.125"; 3.2 mm) width between the susceptor and the upper end of the conductive portion of a plate prevented overheating of the susceptor. It should be mentioned that the margin served to spacer the conductive portion of the susceptor plate by a predetermined near distance;

(2) Irrespective of the substrate used, overheating at the center of the susceptor occurred for the susceptor assemblies using plates with an upper margin of less than 1/8 "(0.125"; 3.2 mm). This result was observed for all microwave ovens used.

(3) The severity of overheating (burning and melting) has increased with increased cooking time, higher susceptor substrate metallization or higher microwave oven strength.

Arching Prevention

When a field guide structure having one or more conductive portions is present in an energized microwave oven (with or without the presence of a susceptor), the conductive portion (s) cause an electric field disturbance. stationary in the oven. The conductive portion (s) concentrate the electric field near their ends, producing local electric field intensities that are much higher than the base electric field inside the furnace, ie the field strength before of the introduction of the conductive portion (s). As long as the oven is full, these higher field strengths are usually insufficient to cause air disruption.

However, when the oven is empty (that is, no food or other article is present) the base electric field increases by a level above that degree when the food or other article is present. In the event of a vacuum, the local intensity of the field along the end of a conductive portion may be sufficiently high to exceed the air burst threshold causing an arc flash to occur.

It is believed that when a field guide structure is used without a susceptor present, a conductive portion should be spaced by a margin of a lower conductivity material (e.g. a dielectric) at least a predetermined near distance from the flat support member. Preferably, the margin surrounds the conductive portion. The presence of the margin reduces the intensity of the local electric field at the extremities. The magnitude of this reduction is approximated by the following formula:

<formula> formula see original document page 60 </formula>

where E1 is the local electric field before the addition of margins; EI 'is the local electric field with the margin; εr 'is the relative dielectric constant of the margin material; and εr "is the relative dielectric loss of the margin material.

In essence, due to the presence of the surrounding margin, local fields are attenuated such that the air rupture limit is not exceeded, thereby avoiding bending.

When the field guide is used with a susceptor, the susceptor loss layer also plays a role in bending prevention. The dissipative layer absorbs some of the microwave energy in the oven and converts it to heat. This absorption reduces the intensity of the electric field in the oven. Heat flows into a food product or other present article.

However, when the oven is empty, there is no food product or other article present in the oven to dissipate the heat generated by the dissipative layer. This results in rapid overheating that damages the dissipative layer and causes its electrical conductivity to drop significantly. This reduces the loss layer's ability to absorb microwave energy.

Without this absorption by the loss layer, the intensity of the electric field in the furnace increases and the high intensity condition of the field along the end of a conductive portion may then exceed the air boundary rupture, causing an electrical discharge to occur in the furnace. shape of a bow. When the conductive portion (s) of the field guide structure (s) are believed to be spaced from the dissipative layer by a margin of a dielectric material, the margin reduces the intensity of the electric field. place at the ends.

Overheating Prevention

When a field guide structure having two conductive portions is present in an energized microwave oven, a concentrated field is created in the space between these conductive portions. When a material having a moderate dielectric loss factor, such as a flat cardboard support member or a susceptor, is placed in or near the region between the conducting portions, the concentrated field causes the material to rapidly heat up. Field concentration is a function of the separate spacing of the conductive portions. If the conductive portions are close enough, this concentrated field may cause the material to overheat sufficiently to burn into flames, as in the case of cardboard. Increasing the spacing between the conductive portions reduces this field concentration and thus prevents overheating.

Those skilled in the art, having the benefit of the teachings of the present invention may provide modifications thereof. Such modifications are to be construed as falling within the scope of the present invention as defined by the appended claims.

Claims (50)

1. FIELD GUIDE ASSEMBLY, for use in heating an article in a microwave oven, the field guide comprises: - a generally flat non-conductive support member; a field guide structure comprising at least one or more propeller plates mechanically connected to the support member, at least a portion of the plate being electrically conductive, the electrically conductive portion of the plate having a predetermined width dimension and a corner therein, the corner of the electrically conductive portion being surrounded by a radius of up to and including half the width dimension, the electrically conductive portion of the plate generally being arranged at least a predetermined near distance from the support member. , the predetermined near distance being defined by a margin of a low conductivity material, such that bending in the vicinity of the conductive portion is prevented when the field guide assembly is used in an empty microwave oven. FIELD GUIDE ASSEMBLY according to claim 1, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance is at least minus -0.025 times the wavelength. FIELD GUIDE ASSEMBLY according to claim 1, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance is not greater. at 0.1 times the wavelength. The field guide assembly of claim 1, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance remains within the range. 0.025 times the wavelength to 0.1 times the wavelength. FIELD GUIDE ASSEMBLY according to claim 1, wherein the electrically conductive portion of the plate is surrounded by a margin of a lower conductivity material. FIELD GUIDE ASSEMBLY according to claim 5, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the margin has a predetermined width dimension. where the margin width of the lowest conductivity material remains within the range of 0.025 times the wavelength to 0.1 times the wavelength. FIELD GUIDE ASSEMBLY according to claim 1, wherein the electrically conductive portion of the plate is covered with an electrically non-conductive material. The field guide assembly of claim 7 wherein the electrically nonconductive cover is selected from the group consisting of a polyimide tape, a polyacrylic spray coating and a polytetrafluoroethylene spray coating. A FIELD GUIDE ASSEMBLY according to claim 1, wherein the electrically conductive portion of the plate comprises a metal foil less than 0.1 mm thick and wherein the foil is folded over at least a double thickness at about 2 mm. your perimeter. Field guide assembly according to claim 1, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of the plate has a dimension of width which is about 0.1 times to about 0.5 times the wavelength. Field guide assembly according to claim 1, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of each plate is of a dimension. length, and wherein the length dimension is in the range of about 0.25 to about 2 times the wavelength. 12. FIELD GUIDE ASSEMBLY, for use in heating an article in a microwave oven, the field guide comprises: a generally flat support member; a field guide structure comprising at least one propeller plate mechanically connected to the support member, at least a portion of the plate being electrically conductive, the electrically conductive portion of the plate being covered with an electrically non-conductive material; - the electrically conductive portion of the plate being generally disposed at least at a predetermined near distance from the support member, - such that bending in the vicinity of the conductive portion is prevented when the field guide assembly is used in an empty microwave oven. Field guide assembly according to claim 12, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance is at least minus -0.025 times the wavelength. Field guide assembly according to claim 12, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance is not greater. at 0.1 times the wavelength. FIELD GUIDE SET according to claim 12, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance remains within the range. 0.025 times the wavelength to 0.1 times the wavelength. FIELD GUIDE ASSEMBLY according to claim 12, wherein the electrically conductive portion of the plate is surrounded by a margin of a lower conductivity material. Field guide assembly according to claim 16, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, wherein the margin has a predetermined length dimension. and wherein the margin width of the lowest conductivity material remains within the range of 0.025 times the wavelength to 0.1 times the wavelength. Field guide assembly according to claim 12, wherein the electrically nonconductive cover is selected from the group consisting of a polyimide tape, a polyacrylic spray coating and a polytetrafluoroethylene spray coating. Field guide assembly according to claim 12, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of the plate has a dimension of width which is about 0.1 times to about 0.5 times the wavelength. Field guide assembly according to claim 12, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of each plate is of a dimension. length, and wherein the length dimension is in the range of about 0.25 to about 2 times the wavelength. 21. FIELD GUIDE ASSEMBLY, for use in heating an article in a microwave oven, the susceptor assembly comprises: a generally flat support member; - at least one plate mechanically connected to the support member, at least a portion of the plate being electrically conductive, wherein the electrically conductive portion of the plate comprises a metal foil of less than 0.1 mm in thickness and wherein the daughter is bent over or at least a double thickness along its perimeter, - the electrically conductive portion of the plate being generally disposed at least at a predetermined distance from the electrically dissipative layer of the flat support member, - such that the occurrence of Bending in the vicinity of the conductive portion is prevented when the field guide assembly is used in an empty microwave oven. Field guide assembly according to claim 21, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance is at least minus -0.025 times the wavelength. Field guide assembly according to claim 21, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance is not greater. at 0.1 times the wavelength. The field guide assembly of claim 21, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance remains within the range. 0.025 times the wavelength to 0.1 times the wavelength. Field guide assembly according to claim 21, wherein the electrically conductive portion of the plate is surrounded by a margin of a lower conductivity material. Field guide assembly according to claim 25, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, wherein the margin has a predetermined width dimension. and wherein the margin width of the lowest conductivity material remains within the range of 0.025 times the wavelength to 0.1 times the wavelength. The field guide assembly of claim 21, wherein the conductive portion is covered with an electrically nonconductive cover. The field guide assembly of claim 21, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of the plate has a dimension of width which is about 0.1 times to about 0.5 times the wavelength. Field guide assembly according to claim 21, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of each plate is of a size. length, and wherein the length dimension is in the range of about 0.25 to about 2 times the wavelength. 30. FIELD GUIDE ASSEMBLY, for use in the microwave oven, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and field guide assembly comprises: - a member generally flat support having a geometric center; a field guide structure comprising at least six plates each mechanically connected to the support member, each plate being substantially orthogonal to the flat support member, at least a portion of each plate being electrically conductive, - the electrically conductive portion of the plate having a predetermined width dimension and a corner therein, the corner of the electrically conductive portion being surrounded by a radius of up to and including half the width dimension, - the electrically conductive portion of the plate being arranged at least a predetermined proximate distance from the flat support member, where the predetermined proximate distance is at least 0.025 times the wavelength, - such that bowing in the vicinity of the conductive portion is prevented when the guide assembly field switch is used in an empty microwave oven. 31. FIELD GUIDE ASSEMBLY, for use in heating an article in a microwave oven, the field guide assembly comprises: a generally flat support member having a geometric center; a field guide structure comprising a plurality of plates each mechanically connected to the support member, at least a portion of each plate being electrically conductive, the electrically conductive portion of the plate being arranged at least a predetermined proximate distance from the plate. support member, - the electrically conductive portion of each plate having a first end and a second end, the first end of the conductive portion on each of the plates being arranged at a distance of at least a predetermined separation distance from the center. flat support member, such that overheating of the field guide assembly is prevented when it is used in an empty microwave oven. The field guide assembly of claim 31, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined separation distance is at least 0.16 times the wavelength. The field guide assembly of claim 31, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined separation distance is at least 0.025 times the wavelength. The field guide assembly of claim 33, wherein the predetermined separation distance is at least 0.16 times the wavelength. The field guide assembly of claim 31, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined separation distance is not. greater than 0,1 times the wavelength. Field guide assembly according to claim 35, wherein the predetermined separation distance is at least 0.16 times the wavelength. The field guide assembly of claim 31, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the predetermined near distance remains within the range. 0.025 times the wavelength to 0.1 times the wavelength. FIELD GUIDE ASSEMBLY according to claim 37, wherein the predetermined separation distance is at least 0.16 times the wavelength. The field guide assembly of claim 31, wherein the electrically conductive portion of each plate is surrounded by a margin of a lower conductivity material. A field guide assembly according to claim 39, wherein the electrically conductive portion of each plate has a predetermined width dimension and a corner thereon, the corner of the electrically conductive portion being rounded to a radius of. up to and including half the width dimension. The field guide assembly of claim 39, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, wherein the margin has a predetermined width dimension. , and wherein the margin width is at least 0.025 times the wavelength. The field guide assembly of claim 39, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, wherein the margin has a predetermined width dimension. and wherein the margin has a predetermined width dimension, wherein the margin width of the low conductivity material is not greater than 0.1 times the wavelength. The field guide assembly of claim 39, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, wherein the margin has a predetermined width dimension. and wherein the margin has a predetermined width dimension, wherein the margin width of the low conductivity material remains within the range of 0.025 times the wavelength to 0.1 times the wavelength. Field guide assembly according to claim 31, wherein the electrically conductive portion of each plate is covered with an electrically non-conductive material. The field guide assembly of claim 44, wherein the electrically nonconductive cover is selected from the group consisting of a polyimide tape, a polyacrylic spray coating and a polytetrafluoroethylene spray coating. A field guide assembly according to claim 31, wherein the electrically conductive portion of the plate comprises a metal foil less than 0.1 mm thick and wherein the foil is folded over at least a double thickness to about 2 mm. your perimeter. The field guide assembly of claim 31, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of the plate has a dimension of width which is about 0.1 times to about 0.5 times the wavelength. The field guide assembly of claim 31, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and wherein the conductive portion of each plate is of a dimension. about 0.25 to about 2 times the wavelength. The field guide assembly of claim 31, wherein the electrically conductive portion of each plate has a predetermined width dimension and a corner thereon, the corner of the electrically conductive portion being rounded to a radius of. up to and including half the width dimension. 50. FIELD GUIDE ASSEMBLY, for use in the microwave oven, wherein the microwave oven is effective for generating a stationary electromagnetic wave having a predetermined wavelength, and the field guide assembly comprises: generally flat support member having a geometric center; - a field guide structure comprising at least six plates each mechanically connected to the support member, each plate being substantially orthogonal to the flat support member, - at least the portion of each plate being electrically conductive, the electrically conductive portion of each plate having a first end and a second end; - the first end of the conductive portion on each plate being arranged at a distance of at least a predetermined separation distance from the geometric center of the flat support member, the separation distance being at least 0.16 times the length. of wave; - the electrically conductive portion of the plate being arranged at least a predetermined near distance from the flat support member, wherein the predetermined near distance is at least 0.025 times the wavelength, - such that overheating occurs. The field guide assembly is prevented when it is used in an empty microwave oven.