Electric heating – Microwave heating – Field modification
Patent
1997-04-18
1999-11-16
Leung, Philip H.
Electric heating
Microwave heating
Field modification
219749, 219754, 219695, H05B 672, H05B 678
Patent
active
059862491
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a high frequency heating apparatus for heating objects to be heated such as food or the like.
BACKGROUND ART
A microwave oven as a representative high frequency heating apparatus has conventionally been constructed as shown in FIGS. 1-7.
A microwave oven of FIG. 1 is of a general structure employing a turntable 1. In this microwave oven, electromagnetic waves emitted from a magnetron 2 as an electromagnetic wave emission means are transmitted via a waveguide 3 to a heating chamber 4, where the waves are distributed as standing waves that are determined by the shape of the heating chamber 4 and the position of an opening 5 through which the electromagnetic waves are radiated into the heating chamber 4. A food 6 generates heat correspondingly to an electric field component of the standing waves and a dielectric loss of the food 6. The electric power P [W/m.sup.3 ] absorbed per unit volume of the food 6 is expressed by the intensity of an applied electric field E [V/m], the frequency f [Hz], the dielectric constant .epsilon.r and the dielectric tangent tan.delta. of the food 6 in an expression (1) below. The heating distribution of the food 6 is generally determined by the distribution of the standing waves of the electromagnetic waves and, hence, the heating distribution on concentric circles is uniform due to a rotating of the turntable 1.
In FIG. 1, reference numeral 19 denotes a control means, 22 denotes a motor, 23 denotes a weight sensor, and 27 denotes a fan.
As other examples of the uniforming means, a stirrer system has been employed in which electromagnetic waves are stirred by a constant rotation of a metallic plate inside the heating chamber. Electromagnetic waves are also taken out from the waveguide 3 by a rotary waveguide (emission part) 8 having a coupling part 7 and are emitted through an emission port 9, as shown in FIG. 2, in other words, the opening part itself has been rotated constantly. In this case, the rotary waveguide 8 has been built on a bottom face of the heating chamber 4 and rotated constantly at all times by a motor 10, and the whole of a bottom part of the heating chamber 4 has been covered with a cover 11 of a material allowing the electromagnetic waves to pass therethrough.
Actually, however, most of the apparatuses in the market are of the turntable type.
Some apparatuses are provided with a plurality of opening parts, wherein an exit for the electromagnetic waves is switched to provide a uniform a heating distribution. FIG. 3 shows an apparatus of the kind having two openings 5 defined in a side wall of the heating chamber 4 (Japanese Patent Laid-Open Publication No. 4-319287).
A plurality of magnetrons and a plurality of waveguides are installed in some cases to constitute a plurality of opening parts (Japanese Patent Laid-Open Publication Nos. 61-181093 and 4-345788).
Alternatively, one waveguide is branched in many directions to form a plurality of waveguides while there is arranged a single magnetron, thereby constituting a plurality of opening parts (Japanese Patent Laid-Open Publication No. 61-240029 and Japanese Utility Model Laid-Open Publication No. 1-129793).
In a different constitution, end faces 14 of two sub waveguides 13 are moved at positions facing a plurality of openings 5, as indicated in FIG. 4, so that the electromagnetic waves may be directed to one opening 5 which apparently is easy for the electromagnetic waves to pass through, to thereby uniform the heating distribution (Japanese Patent Laid-Open Publication No. 5-74566).
In a system of FIG. 5, a metallic part 12 is moved within the single waveguide 3 having a plurality of openings 5, so that the opening 5, which apparently is easy for the electromagnetic waves to pass through, is selected to thereby uniform the heating distribution (Japanese Patent Laid-Open Publication Nos. 3-11588 and 5-121160).
In FIGS. 6 and 7, a plurality of openings are formed at upper and lower parts of the heating chamber, and the openings 5 at the lower part are switched
REFERENCES:
patent: 4616119 (1986-10-01), Shin
patent: 4804812 (1989-02-01), Tanaka et al.
patent: 4896005 (1990-01-01), Skubich
patent: 4937418 (1990-06-01), Boulard
patent: 5352873 (1994-10-01), Carlsson et al.
Ahagon Akira
Kashimoto Takashi
Shibuya Makoto
Yoshino Koji
Leung Philip H.
Matsushita Electric - Industrial Co., Ltd.
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