Electric heating – Microwave heating – Field modification
Reexamination Certificate
2001-03-08
2002-10-22
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Field modification
C219S750000, C219S747000, C219S751000, C333S231000
Reexamination Certificate
active
06469286
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an impedance varying unit which is built in a microwave cavity entrapping microwave or built in a waveguide which propagates microwave. The unit works on the microwave distributed throughout the structure of the cavity or the waveguide to change the propagation details of the wave. The present invention also relates to a microwave device as well as a high frequency heating appliance both using this impedance varying unit.
BACKGROUND ART
One of the methods to change the propagation details of the microwave traveling through a conventional waveguide is to place a metal member in a traveling path of the microwave in the waveguide, so that capacitive component or inductive component as impedance is added in the waveguide. For instance, the metal member is inserted from H plane (wide wall) in roughly parallel to E plane (narrow wall) to produce capacitive component within the waveguide, so that transmission characteristics of the microwave travelling the waveguide are changed.
In this waveguide, the metal member is movable with respect to metal walls constituting the waveguide. Some creative ideas and a given clearance are provided between the movable metal member and the walls of the waveguide in order to eliminate spark-occurrence therebetween. Regarding the clearance, an electric-wave-shielding-mechanism is provided in order to prevent the leakage of an electric wave from the clearance. Accordingly, the conventional waveguide requires a complicated and a large size construction due to this movable metal member.
There is another method for changing the transmission details of the microwave in the microwave cavity. For instance, the location of supplying section of the microwave to the microwave cavity is changed, or a method of coupling (magnetic field coupling or electric field coupling) with the microwave cavity is changed, so that standing-wave-distribution produced in the microwave cavity is changed.
In the microwave cavity explained above, when a distribution of the standing wave is changed, it is necessary to change physically the location of the supplying section or the coupling method. As a result, it is difficult to change the distribution of standing wave in time sequence.
Further, in a high frequency heating appliance, so called “mode stirrer” is available, which spins metal blades to reflect diffusely microwave in the microwave cavity where an object to be heated is placed. The mode stirrer reflects the microwave incident upon the blades in every direction, and it is difficult to reflect the wave into a specific area. Therefore, it is difficult to selectively provide inducible heat to a specific area of the object.
Still further, in a high frequency heating appliance, “mode turntable” is available, which rotates the object to be heated on a table in the microwave cavity. The mode turntable is to promote uniform heating by moving the object per se to the standing wave distribution produced in the microwave cavity, and a degree of the heating uniformity depends on the distribution of standing wave. This “mode turntable” does not positively change the distribution of the standing wave.
Japanese Patent Laid-Open Publication No. H08-330066 discloses a high frequency heating appliance, in which the direction of high frequency current running on the wall of the microwave cavity is varied, so that an exciting mode produced in the microwave cavity can be changed. This technique uses a plate on which a plurality of openings are arranged, and the plate is disposed on roughly the same plane as the microwave cavity wall, and the plate is driven to spin. Spinning the plate changes the direction of a longitudinal axis, thereby changing the direction of the high-frequency-current running on the microwave-cavity-wall, which also changes an exciting mode in the cavity. This intends to select an exciting mode adequate to the object to be heated, and to result in a heating distribution fit for the object.
However, this technique is formed by rotating an opening, and it is necessary to prevent the production of spark entailed by the spin of the metal member in the microwave cavity. This requires a spark preventive mechanism and makes the construction complicated. A longitudinal length of the opening must be more than a half of the wavelength of the microwave radiated in the cavity, so that a space necessary for rotating the opening occupies a large area on the wall where the opening is disposed. In the construction discussed above, exciting modes available in the cavity are limited due to the influence of the opening or the clearance for preventing the spark. This makes it difficult to obtain a heating distribution fit for the object.
DISCLOSURE OF THE INVENTION
The present invention addresses the problems discussed above, and aims to deal with the problem of spark occurrence and provide a compact size and controllable impedance-varying-unit. The impedance varying unit is mounted on a wall defining a microwave cavity, and the unit controls as well as varies the impedance of the wall, so that standing wave distribution produced in the microwave cavity can be varied in time-sequence. This is done by a microwave device of the present invention. The present invention also provides a high frequency heating appliance using this microwave device, and the appliance can selectively heat an object or realize uniform heating.
The impedance varying unit of the present invention comprises the following elements:
a waveguide section of which first end is terminated and a second end is opened; and
a movable body disposed within the waveguide section.
The movable body is driven and controlled, so that impedance at an open end of the waveguide section can be varied. For that purpose, the operating face of the unit is coupled to an arbitrary boundary of the cavity, so that leakage of electric wave from the operating face is eliminated.
A transmission mode TEn0 is used in the waveguide section (“n” is a positive integer), so that the impedance varying unit of the present invention can uniform the effect of incident microwave to the movable body and make the effect independent of “n”. As a result, design change such as enlarging the operating face can be done with ease.
Further, the movable body rotates on a rotary shaft defining the space to the terminal end of the waveguide section, so that the movable space of the movable body can be limited to a smaller space. As a result, the unit in a compact size can vary and control the impedance at the open end.
Still further, the movable body can be moved by changing the space to the terminal end of the waveguide section, so that a variable range of the impedance at the open end can be widened.
Yet further, the movable body is made of non-metallic material, so that a breakdown voltage between the body and the waveguide section can be raised. As a result, reliability of the unit against an input of high powered microwave can be guaranteed.
Further, when the impedance at the open end is zero (0), the open end works in the same manner as a metal wall, so that characteristic comparison with a case where the impedance varying unit is not used can be checked with ease.
At the open end, a phase difference between an incident wave to the waveguide section and a reflective wave therefrom becomes zero (0) so that effect of the microwave at the open end can be maximized.
Further, the impedance at the open end forms impedance of inductive component and capacitive component with zero centering in between. Thus the unit can be utilized for matching adjustment.
Still further, in the impedance varying unit of the present invention, a position detector detects a position of the movable body, so that the effect of the microwave at the open end can be positively controlled based on a signal of the position detector. Based on a signal from a microwave detector, the position of the movable body is determined, so that the microwave detector also works as a position detector for the movable body. As a result, other position detectors can
Ahagon Akira
Fukumoto Akemi
Nobue Tomotaka
Tani Tomoko
Yoshino Koji
Leung Philip H.
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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