GB2318039A

GB2318039A - Microwave oven with circularly polarised radiation

Info

Publication number: GB2318039A
Application number: GB9720971A
Authority: GB
Inventors: Ho Kyeong Lee
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 1996-10-04
Filing date: 1997-10-02
Publication date: 1998-04-08
Also published as: KR19980025604A; JPH10134955A; GB9720971D0; KR100237641B1

Abstract

A microwave oven comprises a waveguide 2 that converts a linearly polarized wave into a circularly polarized wave which is applied to the object 5 to be heated. This ensures more uniform heating of the object. The waveguide comprises an axial section plate 6 which divides the waveguide into two parts. The section plate is formed of a resistance film, ferrite or a conductor plate, which is a quarter of a wavelength long.

Description

WAVEGUIDE OF MICROWAVE OVEN The present invention relates to a microwave oven, and in particular to an improved waveguide of the microwave oven capable of generating a circular polarized wave by inserting a section plate such as a dielectric therein and thus uniformly heating an object.

Figure 1 is a cross-sectional view illustrating the construction of a conventional microwave oven. As shown therein, a magnetron 1 generates a microwave which is guided by a waveguide 2 and heats an object placed on a turntable 4 of an oven cavity, here the specific character of the microwave is determined by a shape of the waveguide 2.

Figure 2 is a perspective view of a waveguide of which each side of a section is a x b. As shown therein, if the section of the waveguide 2 is a rectangle, the microwave thereof becomes a linear polarized -wave of which a direction of a magnetic and electric field does not change with respect to a time change. Here, the direction of the magnetic and electric field of the linear polarized wave does not change.

Figure 3 shows each direction of electric fields El, E2, E3 of the linear polarized wave, and electric dipoles EP1, EP2, EP3 of a heated object. As shown therein, a direction of the electric dipoles EP1, EP2, EP3 of the heated object is not uniform as X1, X2, or X3 shows in the diagram, while a direction of the electric field of the linear polarized wave is uniform to a certain direction among El, E2, E3. Namely, the electric dipoles EPI1 EP2, EP3 of the heated object are randomly arranged.

According to the theory of dielectric heating, how much the heated object is heated depends upon a force which an electric dipole of the heated object receives, and the force is determined by a direction of the electric field applied to the heated object. And, when a direction of the electric field makes a right angle with that of the heated object, the heated object receives the greatest force.

If a direction of the electric field of the microwave radiated through the waveguide 2 is El, illustrated in Fig.3, the electric dipole EP3 receives the greatest force of which the direction X3 makes a right angle with the direction El, and the electric dipole EP2 does not receive any force since the direction X2 thereof is in accordance with the direction E2 of the electric field.

That is, when a direction of the electric field of the linear polarized wave is El, the electric dipole EP3 of which a direction is X3 is heated in the whole heated object, however the electric dipole EP2 with a direction of X2 is not, and the electric dipole EP1 with a direction of X1 is less heated than the electric dipole EP3.

Accordingly, in a microwave wherein the linear polarized wave is radiated through the rectangular-shaped waveguide, electric dipoles among the whole electric dipoles of the heated object, of which a direction is in accordance with a direction of the electric field of the linear polarized wave are effectively heated, and the rest are less heated or not heated at all. That is, the heated object is not uniformly heated, accordingly efficiency of the microwave is dropped.

Accordingly, it is an aim of embsciments of the present invention to Uniformly heat an object regardless of a direction of an electric dipole of the heated object by changing a direction of a electric field of an electromagnetic wave radiated from a waveguide.

According to one aspect of the invention there is provided a waveguide of a microwave oven wherein the object is heated by the electromagnetic wave which is generated by a magnetron and guided by the waveguide, comprising a section plate inserted in the waveguide which divides an inner part of the waveguide into two parts at a traveling direction of the electromagnetic wave, thus enabling a circular polarized wave to be radiated through the waveguide.

Additional advantages, obviects and features of embodiments of the invention will became rrore apparent from the description which follows.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: Figure 1 is a cross-sectional view illustrating the construction of a conventional microwave oven; Figure 2 is a perspective view of a waveguide of which each side of a section is a x b; Figure 3 is a diagram illustrating each direction of electric fields of a microwave and electric dipoles; and Figure 4 is a perspective view of a waveguide of a microwave oven eiioodying to the present invention.

Figure 4 is a perspective view of an embodiment of a waveguide of a microwave oven according to the present invention. As shown therein, a waveguide 2 of which each side of a rectangular section is a x b, and a section plate 6 is installed in the waveguide 2 and divides an inner part of the waveguide into two parts at a traveling direction of the electromagnetic wave, thus enabling a circular polarized wave to be radiated through the waveguide.

The operation of the section plate errbodying the present invention will now be described.

As referred to sec 6. 18 - 6. 19 of MICROWAVE TRANSMISSION CIRCUIT of George L. Ragan, if a dielectric plate which divides an inner section of a waveguide into two parts at a traveling direction R of an electromagnetic wave is installed when the electromagnetic wave generated by a magnetron is guided by the waveguide, the electromagnetic wave radiated out of the waveguide becomes a circular polarized wave of which a direction of an electric field continually changes according to a time change.

As shown in Figure 4, supposing that a circular polarized wave is radiated through the waveguide 2, a time tl changes to t2 and to t3, and as shown in Figure 3, a direction of an electric field of the circular polarized wave changes to El when the point of time is to, the direction changes to E2 when t2, and the direction changes to E3 when t3, since the point of time is to, the direction of the electric field of the circular polarized wave is El, the electric dipole EP3 receives the greatest force, when t2, the direction becomes E2 whereby the electric dipole EP1 receives the greatest force, and when t3, the direction becomes E3, thus the electric dipole EP2 receives the greatest force.

As an electric dipole which receives the greatest force continually changes according to the time change, whereby the whole electric dipoles of the object are uniformly heated. An average of the force which each electric dipole receives with respect to the time becomes even, which means that the object is uniformly heated.

Accordingly, the section plate is inserted in the waveguide of the microwave oven in eTbodimBnts of the present invention, thereby enabling the circular polarized wave to be radiated, so that the object can uniformly be heated.

In addition, a resistance film, ferrite, or a conductor plate of a length of A/4 can be used for the section plate 6, and here A is a wavelength of the circular polarized wave. Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention as recited in the accompanying claims.

Claims

What is claimed is:

1. A waveguide for a microwave oven, comprising: a section plate which divides an inner part of the waveguide into two parts at a travelling direction of the electromagnetic wave, thus enabling a circular polarized wave to be radiated through the waveguide.

2. A waveguide of claim 1, wherein the section plate is formed of a resistance film, ferrite, or a conductor plate.

3. A waveguide as claimed in claim 1, wherein the section plate has a length of /4.

4. A waveguide as claimed in claim 1, wherein the section plate has a length of the section plate is formed of a resistance film, ferrite, or a conductor plate of a length of /4.

5. A microwave oven in which, in use, an object is heated by an electromagnetic wave which is guided by a waveguide as claimed in any one of claims 1 to 4.

6. A microwave oven substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.