Title:
MICROWAVE SEAL FOR ELECTRONIC RANGE
United States Patent 3668357


Abstract:
The disclosed microwave seal for electronic range comprises a choke coupling type microwave cavity communicating with a clearance between a range main body and a door in addition to a microwave seal of any desired type. The microwave cavity serves to choke the second harmonic frequency component of the microwave energy to prevent the same from leaking from the range, while the microwave seal serves to prevent the basic frequency component of the microwave energy from leaking.



Inventors:
KOBAYASHI KYOZO
Application Number:
05/083162
Publication Date:
06/06/1972
Filing Date:
10/22/1970
Assignee:
MITSUBISHI DENKI KK.
Primary Class:
International Classes:
H05B6/76; (IPC1-7): H05B9/06
Field of Search:
219/10.55
View Patent Images:
US Patent References:
3249731Oven1966-05-03Johnson
3242303Microwave heating apparatus1966-03-22Crapuchettes
3197600Door for microwave ovens1965-07-27Muller
3182164Electromagnetic energy seal1965-05-04Ironfield



Primary Examiner:
Truhe V, J.
Assistant Examiner:
Jaeger, Hugh D.
Claims:
1. In a microwave oven: a heating compartment having means therein defining an access opening; an end wall encircling said access opening; a movably mounted door movable to effect opening and closing of said access opening; a microwave energy oscillator for radiating microwave energy having a given fundamental frequency into said heating compartment; means defining a first clearance between a portion of said heating compartment and the opposed adjacent portion of said door; means defining a second clearance between said end wall and the opposed adjacent portion of said door; and a microwave energy seal comprising means defining a first microwave cavity in communication with said first clearance and having a length equal to one-fourth of the wavelength of said fundamental frequency of the microwave energy thereby presenting a sufficiently high impedance to choke the fundamental frequency component of said microwave energy, and means defining a second microwave cavity in communication with said second clearance and having a length equal to one-eighth of the wavelength of said fundamental frequency of the microwave energy thereby presenting a sufficiently high impedance to choke the second harmonic frequency component of said microwave energy; whereby said microwave oven is sealed

2. A microwave oven according to claim 1; wherein said means defining a second microwave cavity comprises an ornamental frame member connected to said end wall and having a configuration defining said second microwave

3. A microwave oven according to claim 1; wherein said means defining a second microwave cavity comprises an ornamental frame member attached to said door in opposed spaced-apart relationship therewith and defining

4. A microwave oven according to claim 1; wherein said first clearance, second clearance, first microwave cavity and second microwave cavity are all disposed adjacent one side of said door; and means defining a similar arrangement of clearances and microwave cavities adjacent the other side of said door.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to microwave seals for electronic ranges.

2. Description of the Prior Art

The so-called electronic range for heating and cooking foods or the like through the use of high frequency electromagnetic energy is generally provided with a clearance between the range main body and the door and various kinds of sealing means are provided in the clearance for sealing the microwave energy generated from a magnetron disposed in the range. One of the most widely used sealing means is the choke coupling type sealing device. This is because a relatively high sealing effect can be obtained, and, since no mechanical contact is employed, free from the fear of deterioration due to the secular change of the sealing means. The conventional microwave seal of the choke coupling type for electronic ranges has comprised a range main body for accommodating the food to be heated and a door for obtaining easy access to the food, the clearance between the main body and the door being provided with a microwave cavity, thereby to decrease the microwave energy which is to leak from that clearance.

This arrangement, however, has been disadvantageous in that the microwave seal employed therein is effective only for a basic frequency component of the microwave energy generated from the magnetron incorporated in the range and quite useless for the high frequency component of the generated microwave energy. More specifically, the conventional seal of the choke coupling type has comprised a microwave cavity having a depth equal to one fourth of the wavelength of the basic frequency wave alone. Therefore, with the conventional sealing device, the microwave sealing effect can be expected only in terms of the basic frequency wave energy, while the second harmonic frequency component can not at all be expected to be sealed. This is because, since the second harmonic frequency component of the microwave energy has a wavelength one-half the basic wavelength, the impedance thereof is at its minimum at the clearance between the range main body and the door.

The magnetrons generally used in the electronic range, however, radiate the required electromagnetic wave energy having a frequency of, for example, 2,450 MHz together with its harmonic frequency components, in particular, relatively large amount of second harmonic frequency component. Although the amount of the second harmonic frequency energy escaping from the clearance is not so high as to cause undesirable effect to the human body, the wireless communication network utilizing the frequency band corresponding to the second harmonic frequency has been often caused to have a serious radio wave trouble.

Accordingly, an object of the invention is to provide a new and improved microwave seal for use in electronic ranges eliminating the above mentioned disadvantages of the conventional device.

Another object of the invention is to provide a microwave seal for use in electronic ranges and which is simple in construction and still effective for sealing not only the basic frequency component of the microwave energy but also the harmonic frequency component.

Further object of the invention is to provide a microwave seal for electronic ranges capable of being easily constructed by utilizing an ornamental frame provided around the front face of the range.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a microwave seal for an electronic range comprising a microwave seal means and a microwave cavity having a depth equal to one-eighth of the wavelength of a basic frequency component of the employed microwave energy to prevent a second harmonic frequency component of the microwave energy from leaking from the electronic range main body.

The invention also provides a microwave seal for sealing the microwave energy radiated from the electromagnetic wave oscillator disposed in the electronic range, comprising a first microwave cavity having a depth equal to one-fourth of a wavelength of a basic frequency component of said microwave energy to prevent the basic frequency component of said microwave energy from leaking from said electronic range, and a second microwave cavity having a depth equal to one-eighth of the wavelength of said basic frequency component of said microwave energy to prevent a second harmonic frequency component of said microwave energy from leaking from the electronic range, said first and second microwave cavities being formed to communicate with a clearance formed between said electronic range main body and said door when the door is closed.

BRIEF DESCRIPTION OF THE DRAWING

The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a front view of an electronic range to which the microwave seal constructed in accordance with the present invention can be applied;

FIG. 2 is a fragmental sectional view useful for explaining the invention;

FIG. 3 is an enlarged fragmental sectional view showing one portion of FIG. 2;

FIGS. 4 and 5 are fragmental sectional views similar to FIG. 3 but showing modifications of the invention.

Throughout the several FIGS. the like reference characters designate the identical or corresponding components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing and in particular to FIG. 1 thereof, it is seen that an electronic range to which the present invention can be applied comprises an electronic range main body generally designated by the reference numeral 10 and a door generally designated by the reference numeral 30. The illustrated electronic range is of the conventional design except for having the microwave seal of the present invention which will hereinafter be described in detail.

FIGS. 2 and 3 show a fragmental section of the front portion of the electronic range main body 10 and the door 30 at their closed position as viewed from the top thereof. In these Figures, it is seen that the range main body 10 comprises a housing 12 enclosing a heating compartment 14 for accomodating and heating the food to be heated or cooked. It is to be understood that a microwave oscillator such as a magnetron for radiating microwave energy having a given fundamental frequency is disposed in the heating compartment 14, although it is not illustrated. The door 30 capable of opening and closing the heating compartment 14 is provided on the front portion of the range main body 10 for the purpose of providing an easy access of the interior of the electronic range.

At that front portion of the main body 10 close to and encircling the door 30 is formed a rectangular ornamental frame 16 made of any suitable metallic material and having substantially U-shaped rectangular channel configuration which serves as a microwave cavity 18. One of the legs of the U of the ornamental frame 16 is elongated to be fixedly attached to the outer surface of the housing 12 to form the microwave cavity 18 open at that side close to the periphery of the door 30. The microwave cavity 18 thus formed has a depth or length equal to one-eighth of the wavelength of the basic frequency component of the microwave energy as shown in FIG. 3. Since the end wall A of the microwave cavity 18 is positioned at the distance equal to one-eighth of the basic wavelength of the microwave energy as measured from the center (illustrated by a dash line in FIG. 3) of a gap B formed between the shorter leg of the U of the frame 16 and a wall 20 of the electronic range main body 10 defining the other end of the microwave cavity 18, the point at which the basic frequency electromagnetic wave energy exhibits its maximum impedance comes at the gap B formed between an end of the shorter leg of the U and the opposing portion of the wall 20.

Similarly, the door 30 which is adapted to fit to the front portion of the range main body 10 with a predetermined clearance therebetween has another microwave cavity 32 defined by an extension 34 and a side wall of the door 30 and having a depth or length equal to one-fourth of the basic wavelength of the microwave energy as measured from the center of a gap D formed between the extension 34 and a wall 36 of the door 30 defining the other end thereof as illustrated in FIG. 3. It is easily understood that the maximum impedance point of the microwave energy reflected at an end wall C of the cavity 32 is located at the gap D forming an entrance of the cavity 32 for the microwave energy.

With the arrangement as above described, one part of the microwave energy generated from the magnetron mounted inside the heating compartment 14 travels through the clearance formed between the main body 10 and the door 30 to enter into the first microwave cavity 32 formed in the door 30. The basic frequency component of the microwave energy is choked at the gap D because of the gap D is the maximum impedance point with respect to the basic frequency component. However, at the gap D, the second harmonic frequency component of the microwave is at its minimum in impedance because the distance between the end wall C and the center of the gap D equals one-half of the wavelength of the second harmonic frequency component. This allows the second harmonic frequency component of the microwave energy to leak from that gap D.

According to the invention, however, since the electronic range further comprises the second microwave cavity 18 having the depth equal to one-eighth of the basic wavelength of the microwave energy, the second harmonic frequency component leaked from the gap D is captured by the second microwave cavity 18 and choked at the gap B. This is because the center of the gap B is located at the distance equal to one-eighth of the basic wavelength from the end wall A of the second microwave cavity 18 so that the maximum impedance point of the second harmonic frequency component falls on this gap B.

From the foregoing description, it is easily understood that, according to the present invention, not only the microwave energy of the basic frequency, but also the electromagnetic wave energy of the second harmonic frequency generated from the magnetron are prevented from leaking from the clearance between the range main body and the door.

Also, since the ornamental frame encircling the front face of the electronic range is utilized as a member for forming a microwave cavity, the microwave sealing effect can be obtained with a simple construction without any additional component.

FIG. 4 shows another embodiment of the invention wherein the second microwave cavity 18 of FIG. 3 is formed on the edge portion of the door 30 instead of on the range main body 10. As seen from FIG. 4, the second microwave cavity 18 is defined by an extension 38 of a substantially L-shaped cross section member projecting from the front face of the door 30. In other respects, the microwave seal illustrated in FIG. 4 is of the identical construction to that shown in FIG. 3.

FIG. 5 shows still another embodiment of the invention wherein the first microwave cavity 32 which corresponds to that illustrated in FIG. 4 is modified. FIG. 5 shows that the first microwave cavity 32 is formed on the edge portion of the opening of the range main body 10 instead of on the door 30. The first microwave cavity 32 is defined by a reduced portion formed on that portion of the main body 10 facing to the side wall of the door 30 and an elongated member 22 projecting from the inner wall of the heating compartment 14. In other respects, the seal is of the identical design to that illustrated in FIG. 4.

From the foregoing description, it is easily understood that the operations of the microwave seals illustrated in FIGS. 4 and 5 are quite identical to that of the device previously described in conjunction with FIGS. 1 to 3.

As has been heretofore described, the invention provides a microwave seal for electronic ranges effective not only for the basic frequency component of the microwave energy, but also for the second harmonic frequency component of the microwave energy with a simple and compact construction.

Although the invention has been described only in terms of a few modifications, it is to be understood that the various modifications can also be performed without departing from the spirits of the invention.