JP2004184031A

JP2004184031A - Microwave oven

Info

Publication number: JP2004184031A
Application number: JP2002354096A
Authority: JP
Inventors: Haruo Matsushima; 治男松島
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2002-12-05
Filing date: 2002-12-05
Publication date: 2004-07-02
Anticipated expiration: 2022-12-05
Also published as: JP4069736B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave oven with a built-in heater on the bottom face, having improved uniform heating performance. <P>SOLUTION: A center axis 5 and a waveguide 1 are provided at the center of the top face of an oven casing 4. A cylindrical waveguide excited in an H-11 mode by the waveguide is rotated around the axis, whereby a rotating antenna is actualized for primarily radiating electric power in the state of being rotated, which is difficult to actualize in the past, resulting in uniform heating operation. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、均一加熱性能を向上させたオーブン機能付き電子レンジに関するものである。
【０００２】
【従来の技術】
従来、電子レンジの均一加熱方式には、負荷である被加熱物を回転させるいわゆるターンテーブル方式と、マイクロ波の放射源たるアンテナを回転させる方式との二種類があった。ターンテーブル方式は文字どうり負荷を載せたテーブルを回転させる方式であり、視覚的効果と比較的良好な加熱性能により、広く採用されてきた。一方、放射源を回転させる方式は、本来の放射源たるマグネトロンを回転させる事は困難であり、その代わりに、導波管に結合したアンテナを回転させる方式が実用化されていたが、均一加熱の点では若干劣ると言わざるを得ない性能であった（例えば、特許文献１参照。）。
【０００３】
図９はその主要部断面図であるが、導波管１内部は矩形Ｈ０１モードが励振され、図に矢印で描いた如き電界があり、導波管内部に挿入された回転アンテナ２の垂直部分２ａにはこの電界により電流Ｉｖが流れる。この電流が垂直部分２ａの下端に到達する間にマイクロ波が放射され、水平部に流れる電流Ｉｈはほとんどなくなると想像される。アンテナ自体が回転しても放射源である垂直部分は位置変化がなく、放射源が回転しているとは言い難い方式であった。
【０００４】
ターンテーブル方式も必ずしも万能ではなく、欧米の本格的オーブンの四角い天板や金網を棚から容易に出し入れする方式と比較すると、操作性で劣るだけでなく、食品の積載範囲が円形テーブル内部に限定される点や、回転の振動等による液体のこぼれ、多段調理が困難である点などがあり、最近はターンテーブルを取り去り、加熱室の底部にマイクロ波を通過するセラミック板をに設け、その下でアンテナを回転させるノンターン方式が普及しだしている。
【０００５】
また、類似の形状を持つ円筒形状の回転アンテナと、管内波長が等しい断面長方形の突出し導波管とを有するものもある（特許文献２参照。）。
【０００６】
【特許文献１】
特開昭５８―１８１２８９号公報
【特許文献２】
特開昭５２−００６１４７号公報
【０００７】
【発明が解決しようとする課題】
しかしこの方式も底面にヒーターを設ける事ができない為、本格的オーブンと比較すると、まだ物足りない。オーブンにとって下火は最も重要であるが、上記ノンターンは本来の意味の下火が設けられない為に、熱源を後方に設け、その熱を風として移動させ、下火の役割を与える熱風循環方式を採用している。しかしながら底面には熱容量が大きく、熱の不良導体でもあるセラミック板があるので、結果的に熱効率が低くなり、下火の調節も困難である。欧米のオーブンは熱風循環方式であっても加熱室底面にヒーターを設ける例が多い。加熱室内部の底面付近にヒーターを設けた例と、加熱室外部、底面の下に密着してヒーターを取付ける例とがあり、各々長所短所があるが、何れにしろ下火がそれだけ重要である証である。
【０００８】
加熱室底面にヒーターを設けた本格的オーブンを実現するには、底面に一切の回転機構を設けずに、しかも均一性能が優れた方式が必要である。その為には、マイクロ波放射源自体が回転する機構を底面以外、例えば上面に設ける方式が望まれる。放射アンテナそのものが回転する本来の意味の回転アンテナが必要なのである。
【０００９】
前述した如く、マグネトロン自体を回転させる事は困難であるが、マグネトロンが取付けられた導波管を回転させる事はマグネトロンそのものよりは多少簡単であると想像できる。本発明は、この考えを実現せんとするもので、底面にヒーターを設けた本格的オーブンに採用可能な、回転する放射源を上面に設け、均一加熱性能に優れた電子レンジを提供することを目的とする。
【００１０】
【課題を解決するための手段】
前記従来の課題を解決するために、本発明の電子レンジは、オーブン箱と、導波管と、マグネトロンと、円筒導波管とを有し、オーブン箱の天面略中央を中心軸として前記円筒導波管を回転させ、前記マグネトロンと導波管は前記円筒導波管をＨ１１モードに励振させてなる構成である。
【００１１】
これによって、Ｈ１１モードに励振された円筒導波管がオーブン箱天面中央を中心軸として回転しているのでマグネトロンから伝送された電力が回転しながらオーブン箱に放射されるので良く攪拌され、均一加熱性能が向上する。
【００１２】
【発明の実施の形態】
請求項１に記載の発明は、オーブン箱と、導波管と、マグネトロンと、円筒導波管とを有し、オーブン箱の天面略中央を中心軸として前記円筒導波管を回転させ、前記マグネトロンと導波管は前記円筒導波管をＨ１１モードに励振させてなる構成である。これによって、Ｈ１１モードに励振された円筒導波管がオーブン箱天面中央を中心軸として回転しているのでマグネトロンから伝送された電力が回転しながらオーブン箱に放射されるので良く攪拌され、均一加熱性能が向上する。
【００１３】
請求項２に記載の発明は、導波管は矩形断面を有し、Ｈ０１モードに励振され、その管内波長を前記Ｈ１１モードに励振された円筒導波管の管内波長と等しくした構成であり、これによって円筒導波管は、回転途中の任意の角度において常にＨ０１モードの矩形導波管に円形の端面を対向させるので矩形Ｈ０１モードと同一方向の電界を持つ円形Ｈ１１モードが円筒内部に励振され、安定した電力伝達が行なわれる。
【００１４】
請求項３に記載の発明は、オーブン箱天面略中央に円筒形状の攪拌室を設け、前記Ｈ１１モードに励振された円筒導波管をこの攪拌室内部に収納した構成であり、これによって矩形導波管から円筒導波管へ伝達されなかった電力も、円筒導波管の外側と攪拌室の内側との間で一種の回転を受けるので、本来の円筒導波管を通過した電力とが共に同期して回転する為に攪拌効果が増加する。
【００１５】
請求項４に記載の発明は、オーブン箱天面に、連続する複数の線分で構成されたシーズヒーターを設け、少なくとも攪拌室下方及びその周囲１／４波長の範囲内部のシーズヒーターは、前記円筒導波管Ｈ１１モードの主電界と直交する線分のみとした構成であり、これにより電界とシーズヒーターとが直交するので円筒導波管と被加熱物との間にシーズヒーターが存在するにも関わらず、電界は乱され無い。従って攪拌効果、均一加熱性能は良好に維持される。
【００１６】
請求項５に記載の発明は、攪拌室周囲１／４波長の範囲外で、シーズヒーターとオーブン箱天面とを金属で接続してなる構成であり、これにより電界が乱されずにヒーターが保持、固定され、信頼性の高い電子レンジが実現できる。
【００１７】
【実施例】
以下本発明の実施例について、図面を参照しながら説明する。
【００１８】
（実施例１）
図１は、本発明の第１の実施例における電子レンジの主要部分の断面を示す図である。導波管１は幅８６ｍｍ、高さ４０ｍｍの矩形断面を持ち、高さ方向で曲げられ、Ｃの字を伏せた様な形状をしている。Ｃの字の一端、短い垂直部分１ａは、円筒形状の攪拌室３の天面中央に固定される。攪拌室３はオーブン箱４の天面中央に固定される。攪拌室３の内部には直径約１００ｍｍ長さ６０ｍｍの円筒導波管である回転アンテナ２がセラミック丸棒５に固定された状態で収納される。
【００１９】
セラミック丸棒５は前記導波管１の４５度傾斜部分の壁面及び壁面に固定された金属製軸受６を貫通して外部に伸び、受動歯車７が取り付けられる。受動歯車７は駆動歯車８と勘合し、駆動歯車８はモーター９の出力軸に取り付けられる。丸棒５は導波管１の終端１ａの中心、攪拌室３である円筒の中心軸、及びオーブン箱４のほぼ中央全てと一致する。導波管１の終端垂直部１ａの攪拌室３との結合部には薄いマイカ板製の蓋１０が取り付けられ、この中央に開けられた丸孔と、前記金属製軸受６とで丸棒５を、導波管１の終端１ａの中央を通って、垂直に支持する。攪拌室３の底面にはガラス板１１が金属製固定板１２により取り付けられる。
【００２０】
その下方、オーブン箱４の天面近くにシーズヒーター１３が取り付けられる。オーブン箱４の左右壁面は凹凸の溝形状４ａが形成され、その凹溝に金属製すのこ網１４が着脱自在に挿入される。すのこ網１４は周囲の四角い額縁状の比較的太い線材１４ａと、この対向する辺を結ぶ細い線材１４ｂから成り、細い線材１４ｂは、図には３２個の小さな円として描かれており、図の表面に垂直で互いに平行、中央付近は狭く、左右の周辺付近は広い間隔で固定される。図示の如く凹溝は３対あり、すのこ網１４は全ての凹溝に挿入可能である。このすのこ網１４の上に描いたのは陶磁器製スープカップ１５であり、左右に丸い取っ手が有る。導波管１の前記１ａとは反対側にはマグネトロン１６が取り付けられる。なおオーブン箱４の底面下方には下火の役割を担うヒーターが取り付けられるが、本実施例を説明する上で必要無いので省略し、描かない。
【００２１】
図２は図１のＡ−Ａ’ 面から見た平面図である。ヒーター１３は上下に走る６本の線分１３ａと、これらを結ぶ曲線部分１３ｂ及び左右一対の支持金具１３ｃ、１３ｄと、この支持金具とオーブン箱の天面とを結ぶ吊下げ金具１３ｅ、１３ｆとから成る。このシーズヒーター１３の下方にはすのこ網１４上に載せられたスープカップ１５が４個描かれている。図の上部に描かれた台形は熱風吹き出し部分１７であり、下部に描かれた横長の長方形は扉１８である。中央部には二点鎖線で導波管１、回転アンテナ２及び攪拌室３を描いた。攪拌室の外側約３０ｍｍの破線は、攪拌室から１／４波長の領域３ａである。前述の支持金具１３ｃ、１３ｄと、吊下げ金具１３ｅ、１３ｆはこの領域３ａの外に位置している。
【００２２】
図３は回転アンテナ２とセラミック丸棒５とが組み立てられた状態を示す斜視図である。セラミック丸棒５の上端付近には小さな丸穴５ａが開けられ、前述の受動歯車７との固定に用いられる。下部には二ヵ所、所謂Ｄカット部分５ｂ（本図２では良く見えない。図５参照）が設けられる。薄い金属板製、回転アンテナ２の円筒部分２ａは、固定部分２ｂで二重に重ねられて溶接され、直径約１００ｍｍ、高さ約６０ｍｍの円筒形状を持つ。固定部２ｂ周囲には細長い角孔２ｅ（図４参照）が合計４個開けられ、下端が左側に４５度曲がったｆ字形状、アルミナ磁器製のアンテナ固定具１９の４５度曲がった部分１９ａ（図６参照）が挿入される。ｆ字上端１９ｂの四半円部分とその下の突起部分とは前記セラミック丸棒５のＤカット部５ｂの半分に勘合する形状とする。一対のアンテナ固定具１９によりセラミック丸棒５のＤカット部分５ｂを両側から鋏み、この時、下端の４５度曲がった部分は互いに外側を向く。固定金具２０は両端を４５度折り曲げた形状（図６参照）であり、この両端４５度部分と前記アンテナ固定具１９下端の４５度曲がった部分とを接する様にして回転アンテナ２にビス止めする。その結果アンテナ固定具１９は回転アンテナ２の角孔２ｅの外側を支点として回動し、左右のｆ字上端部１９ｂが近づき、Ｄカット５ｂに勘合して回転アンテナ２とセラミック丸棒５とを固定する。本実施例ではセラミック丸棒５の中心と回転アンテナ２の円筒の中心とは約２０ｍｍ離した。
【００２３】
図４は回転アンテナ２の斜視図、図５はセラミック丸棒の斜視図、図６はアンテナ固定具１９の斜視図であり、図７は固定金具２０の斜視図である。
【００２４】
以上のように構成された電子レンジについて、以下にその動作、作用を説明する。
【００２５】
まず、導波管１の寸法及びマグネトロン１６の発振周波数２４５０ＭＨｚと導波管１への取り付け方法により、内部には矩形Ｈ０１モードが励振され、その電界は高さ４０ｍｍの方向を向く。その結果、終端１ａ付近で電界は図２の中央部に描いた如く、左右方向を向く。図８はその電界付近を取り出して描いた平面図であり、導波管１の終端１ａ、攪拌室３及び回転アンテナ２を示す。図８の左右は同一の状態を示す平面図であるが、左には導波管１内部の電界を、右には回転アンテナ内部の電界を、各々左右に分けて描き、両者の差を強調した。上中下の差はアンテナ２の回転角度の差であり、時計廻りに上から４５度づつ回転した状態を示す。
【００２６】
左側半分の導波管１内部では、矢印で描いた電界は上述の如く左右方向を向き、導波管１の中央が強く、密集し、両端は弱く、疎らになる。最も強い位置は攪拌室３の中央でもある。いわゆるＨ０１モード、長方形導波管における最も遮断周波数の低いモードである。この電界により、右半分に描いたアンテナ２内部電界では、円筒の中心付近に密集した円弧状の電界が発生する。円筒導波管における最も低い遮断周波数を持つＨ１１モードである。幅８６ｍｍの長方形導波管におけるＨ０１モードの管内波長と、直径１００ｍｍの円筒導波管におけるＨ１１モードの管内波長は共に多くの教科書に記載されているのでここでは省略するが、両者はほぼ等しい値を有する。
【００２７】
Ｈ１１モード電界の最も強い位置はアンテナ２の中央であり、攪拌室３の中央からは少しずれた位置、本実施例では前述の如く約２０ｍｍ離れた位置である。導波管１の終端１ａを垂直に取付け、円筒導波管である回転アンテナ２の中心軸も垂直にし両者を接近させたので図の左右方向に電界を持つ導波管１のＨ０１モードから、同じく左右方向の電界である円筒導波管のＨ１１モードにスムーズに変換されるのである。時計廻りに角度が変化し、円筒の中心位置が変化しても、円筒は左右方向の電界を受け、常に左右方向のＨ１１モードを維持する。つまり円筒導波管２を円筒の中心と平行な軸を中心として回転させているので常に両導波管の電界が一致する訳である。もしも回転アンテナ２が長方形であれば、電力がスムーズに流れる角度と、ほとんど流れない角度とが存在し、攪拌効果は激減する。
【００２８】
回転アンテナたる円筒導波管２の長さを６０ｍｍ、約半波長とした理由は、アンテナ上部、導波管１に面した部分においてまだ主力である左図に類似の電界が、円筒導波管としてのアンテナ内部を半波長進むことにより本来の円筒導波管の電界分布、つまり右に描いた状態に変化すると考えられるからである。実際、長さを５０ｍｍ、４０ｍｍと短縮すると攪拌効果が減少し、食品の均一加熱性能が低下する。例えば図２に描かれたスープカップ１５に約１７５ｃｃの１％程度の塩分濃度を持つ食塩水をいれ、図の如く４カップを同時に加熱し、冷蔵温度から約６０℃温度上昇させた時、各々のカップを攪拌して温度測定後、４カップの平均温度上昇に対する４カップの最高温度と最低温度との差をパーセント表示すると、円筒の長さが６０ｍｍの場合は４％から８％程度に収まるが、高さ５０ｍｍで１５％から２０％程度、４０ｍｍでは１５％から２５％程度に増大してしまう。
【００２９】
この結果から見て、円筒導波管２の長さを６０ｍｍ約半波長にすることにより円筒導波管２底部にはＨ１１モードが励振され、その中心部にある強い電界が、半径約２０ｍｍの円軌道で回転し、オーブン箱４内部の電界分布を攪拌、均一化すると考えられる。
【００３０】
図２に描かれた如く、オーブン箱内部は左右はほぼ対称形状と言えるが、前後はヒーター１３の形状も対称では無く、熱風吹き出し部分１７と扉１８も対称形状では無い。従来のスタラー攪拌による均一加熱方式では、前後左右対称形状にする事が前提であり、対称形状から離脱するほど均一加熱から遠のいた性能となるのが常であったが、本実施例では前後対称が幾分崩れているにも関わらずスープカップの４点分布が均一を維持されている。放射源自体を回転する事がそれほど有効であると考えられる。
【００３１】
以上のように、本実施例においては、オーブン箱と、導波管と、マグネトロンと、円筒導波管とを有し、オーブン箱の天面略中央を中心軸として前記円筒導波管を回転させ、前記マグネトロンと導波管は前記円筒導波管をＨ１１モードに励振させたものであり、これによって、Ｈ１１モードに励振された円筒導波管がオーブン箱天面中央を中心軸として回転し、マグネトロンから伝送された電力が回転しながらオーブン箱に放射されるので良く攪拌され、均一加熱性能が向上する。マグネトロン自体は回転しないが、その代行としてＨ１１モードに励振された円筒導波管が回転することにより、従来不可能であった本来の意味の回転アンテナが実現できたのである。
【００３２】
前述の従来例、特開昭５２−６１４７は円筒形状の回転アンテナ（５）と、管内波長が等しい断面長方形の突出し導波管（２）とを有する点で本発明と類似であるが、根本的に異なるものである。形状の差異としては従来例はオーブン箱の底面に設け、本実施例は上面に設けている点が異なる。従来例は明細に記載されている如く、一般に加熱され難いと言われる食品中央底部を強く加熱する目的の為、回転アンテナを底面、食品載置台の直下に設けたものである。その結果、回転アンテナたる円筒導波管のＨ１１モード電界と食品載置台とが平行になり、それに伴いその上に載せられた食品底面も電界と平行になり、その結果強く加熱され、それ以外の部分はあまり加熱されないのである。特に円筒導波管の真上に位置する食品部分は強く加熱されるが、少し外れるとほとんど加熱されない。この点、本発明は今まで述べてきた様に、被加熱物との結合を避ける為にオーブン箱の上面へ移動し、そこで回転しながらオーブン箱内部にマイクロ波を放射することにより内部電界を攪拌し、均一加熱を実現するものであり、食塩水４カップも均一に加熱する性能を持っている。
【００３３】
上述の従来例と本実施例との根本的な差を生じせしめた『電界と被加熱物とが平行になる場合には強く加熱される』現象を従来例が積極的に利用し、その結果『電界と被加熱物とが直交する場合は全く加熱されない』欠点をもたらした事は明細にも記載されていない点もあいまって、あまり認識されていない。しかし本発明との本質的な差を理解する為に必要であるので少しく説明する。
【００３４】
マックスウエルの電磁方程式から導かれるポインテイングベクトルの式はその微分形が種々の教科書に記載されている。ただし加熱に用いる場合は次に示す積分形の方が理解し易い。
【００３５】
【数１】

【００３６】
この式は、表面ｓで囲まれた、体積ｖの物体に流入するエネルギー、つまりポインテイングベクトルＰ＝Ｅ×Ｈが、物体内部でどの様に振る舞うかを表している。左辺のｎは物体表面ｓの法線ベクトルであり、これとＰとの内積を全表面に亙って積分したものが左辺である。物体内部に流入する全エネルギーを表す。負号が付いているのは、外向きの法線ベクトルと逆方向、つまり物体の内側に進むポインテイングエネルギーを正方向にする為である。蛇足であるが、ベクトルＰは電界Ｅに垂直かつ磁界Ｈにも垂直である。
【００３７】
右辺の第一項は物体内部の単位体積当りの抵抗損による発熱を全体積に亙って積分したものであり、物体全体の発熱を表す。第二項は蓄積されている電界および磁界エネルギーの同じく物体全体に亙る積分であり、蓄積される電磁界エネルギーの増加を表す。
【００３８】
導波管からオーブン箱内部に放射された電磁界は複雑であるから、微分方程式を解いてその性質を解明することは出来ないが、導波管内部であれば解ける場合があるので、それを求め、オーブン箱内部の現象を類推する方法を取る。Ｈ０１モードに励振された矩形導波管の内部中央に、図１０、図１１に示す如く電界と平行及び垂直に厚さｔの負荷を挿入した時の電磁界は微分方程式から求める事ができる。ｘ方向の空気中の伝播定数をη、負荷中の伝播定数をζとし、導波管の進行方向の伝播定数γとした時、γ２＝ω２μ０ε０―η２―π２／ｂ２であり、電磁界は次式で与えられる。空気中を意味する０と、負荷中を意味する１とをサフィックスとして式に記載する。なお空気中の式と、負荷内部の式は異なるが、両者の境界上では電磁界の接線成分が等しいから、負荷中の電磁界のみを記載する。
【００３９】
図１０の電界と負荷が平行の場合、Ｃを定数として
Ｅｘ０＝Ｅｘ１＝Ｅｚ０＝Ｅｚ１＝０
Ｅｙ１＝Ｃ１γＣｏｓｈ｛ζ（ａ／２−ｘ）｝ｅｘｐ（−γｚ）
Ｈｘ１＝（ζ２＋ω２μ０ε１）Ｓｉｎｈ｛ζ（ａ／２−ｘ）｝ｅｘｐ（−γｚ）／（ｊωμ０）
Ｈｙ１＝Ｈｙ０＝０
Ｈｚ１＝Ｃ１ζγ Ｓｉｎｈ｛ζ（ａ／２−ｘ）｝ｅｘｐ（−γｚ）／（ｊωμ）
ここでη及びζは複素数であり、次の連立方程式の解（主値）である。
【００４０】
−ηＣｏｔｈ（ηｄ）＝ζＴａｎｈ（ζｔ／２）
−η２＋ζ２＝ω２μ０ε０εｒ（１−ｊｔａｎδ）−ω２μ０ε０
導波管の中央に置かれた厚さｔの負荷を上述のポインテイングベクトルの式に当てはめると物体の表面ｓは左右の空気と接した面および導波管の上下に接した面とに分けて考えると、空気と接する面の電界はＥｙ１であり、磁界はＨｚ１である。これらの積であるポインテイングベクトルＰは右手系であって、図に実線の矢印で描いた電界Ｅの方向から破線の矢印で描いた磁界Ｈの方向へ、旋回した時に右ネジの進む方向を向く。これを当てはめるとＥｙ１を正とすると、Ｈｚ１はｘ＝ａ／２＋ｔ／２において負方向を向き、ｘ＝ａ／２−ｔ／２では逆に正方向を向く。従ってポインテイングベクトルＰは図に白抜きの矢印で描いた如く、左右共に物体の内部を向く。これは物体内部に電力が流入し、その電磁界により発熱が生じる事を意味する。
【００４１】
図１１の電界と負荷とが直交する場合、便宜上ＸＹを入れ替えて表現する。Ｄは定数である。
【００４２】
Ｅｘ１＝Ｄ１（ζ２＋ω２μ０ε０）Ｃｏｓｈ｛ζ（ａ／２−ｘ）｝Ｓｉｎ（ｙπ／ｂ）ｅｘｐ（−γｚ）／（ｊωε１）
Ｅｙ１＝−Ｄ１ζ（π／ｂ）Ｓｉｎｈ｛ζ（ａ／２−ｘ）｝Ｃｏｓ（ｙπ／ｂ）ｅｘｐ（−γｚ）
Ｅｚ１＝Ｄ１ζγＳｉｎｈ｛ζ（ａ／２−ｘ）｝Ｓｉｎ（ｙπ／ｂ）ｅｘｐ（−γｚ）
Ｈｘ１＝Ｈｘ０＝０
Ｈｙ１＝Ｄ１γＣｏｓｈ｛ζ（ａ／２−ｘ）｝Ｓｉｎ（ｙπ／ｂ）ｅｘｐ（−γｚ）／（ｊωε１）
Ｈｚ１＝Ｄ１（π／ｂ）Ｃｏｓｈ｛ζ（ａ／２−ｘ）｝Ｃｏｓ（ｙπ／ｂ）ｅｘｐ（−γｚ）
ここでη及びζは複素数であり、次の連立方程式の解（主値）である。
【００４３】
（η／ε０）Ｔａｎｈ（ηｄ）＝−（ζ／ε１）Ｔａｎｈ（ζｔ／２）
−η２＋ζ２＝ω２μ０ε０εｒ（１−ｊｔａｎδ）−ω２μ０ε０
主電界Ｅｘ１を上向きとすると、これとＨｙ１とで形成されるポインテイングベクトルはｚ方向を向き、Ｈｚ１とで形成されるポインテイングベクトルはｙ方向を向き、共に負荷と空気との境界面に平行を成すから、負荷物体内部には電力が流入しない事を意味する。つまり主電界と直交して負荷を置いても全く加熱されないのである。なお派生した電界Ｅｙ１はのＣｏｓ（ｙπ／ｂ）成分を持つからｙ＝０およびｙ＝ｂにおいて最大値を取る。この電界成分とＨｚ１とで形成されるポインテイングベクトルはｘ方向、つまり物体の内部方向を向いている。実際、負荷の端部で非常に弱い加熱が確認できる。
【００４４】
これを図１２に描いた従来例の円筒導波管と負荷との関係に当てはめると、円筒による主電界と平行になる負荷の中央部、図でハッチングを施した部分は強く加熱され、その周囲、電界がたてに通過する部分はほとんど加熱されないのである。図１２の従来例は一般に最も加熱され難い食品中央底部を強く加熱する事には成功したものの、均一加熱には失敗した例である。それは前述の如く、導波管の電界と負荷とを直接結合させたからである。その点、本発明は円筒導波管を負荷から十分離れた天面に位置させ、負荷との直接結合が無い状態で電磁界エネルギーをオーブン箱内部空間に回転放射するものである。これが従来例との差である。
【００４５】
また本実施例では、図２に描いた如く、シーズヒーター１３は主要部分１３ａが前後に走る構成である。導波管１及び回転アンテナ２内部の電界が図２の中央部に矢印で描いた様に常に左右方向であるから両者は垂直に交り、電界に与える影響が小さく、食塩水４カップの均一加熱性能も変化しない。当業者に良く知られる如く、金属の表面で、電界は垂直成分だけを持ち、平行成分は０となる。従ってヒーター１３が、電界と平行な左右に走る部分を持っていると、その左右方向の電界を弱めてしまうのである。支持金具１３ｃ、１３ｄは左右一対であるが、左右を連続させれば単純になる。しかし今述べた様に、連続させると中央部分は電界主要部分と平行となる。しかも攪拌室から１／４波長の範囲内部、電界の主要部分からごく近くに位置する事になる。その結果として、前述の食塩水４カップの加熱ムラは１６％程度に悪化する。従って左右を分離したのである。
【００４６】
支持金具とオーブン箱の天面とを結ぶ吊下げ金具１３ｅ、１３ｆとはこれも位置によりムラに影響を与える。しかし支持金具ほどには顕著では無く、また支持金具の位置に規制されるから、必然的に支持金具と同様に１／４波長の範囲外に制限される。
【００４７】
【発明の効果】
以上のように、本発明によれば、従来困難であったマイクロ波放射体を回転させる事が可能となり、底面付近にヒーターを取付けた本格的オーブンに組み込み可能で、かつ均一加熱性能の優れた電子レンジを提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例１における電子レンジの断面図
【図２】本発明の実施例１における平面図
【図３】本発明の実施例１における回転アンテナの斜視図
【図４】本発明の実施例１における回転アンテナ、円筒の斜視図
【図５】本発明の実施例１における丸棒の斜視図
【図６】本発明の実施例１におけるアンテナ固定具の斜視図
【図７】本発明の実施例１における固定金具の斜視図
【図８】本発明の実施例１における回転アンテナ付近の平面図
【図９】従来の電子レンジの要部断面図
【図１０】従来例の作用説明図
【図１１】従来例の作用説明図
【図１２】従来の電子レンジの要部断面図
【符号の説明】
１導波管
２回転アンテナ（円筒導波管）
３攪拌室
４オーブン箱
５丸棒（中心軸）
９モーター（回転機構）
１６マグネトロン[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a microwave oven with an oven function that has improved uniform heating performance.
[0002]
[Prior art]
Conventionally, there have been two types of uniform heating methods for microwave ovens: a so-called turntable method for rotating an object to be heated as a load, and a method for rotating an antenna that is a radiation source of microwaves. The turntable method is a method of rotating a table on which a character load is placed, and has been widely adopted because of its visual effect and relatively good heating performance. On the other hand, in the method of rotating the radiation source, it is difficult to rotate the magnetron, which is the original radiation source, and instead, the method of rotating the antenna coupled to the waveguide has been put to practical use. In this respect, the performance has to be said to be slightly inferior (for example, see Patent Document 1).
[0003]
FIG. 9 is a cross-sectional view of the main part, in which the rectangular H01 mode is excited inside the waveguide 1 and there is an electric field as shown by the arrow in the figure. A current Iv flows through 2a due to this electric field. It is assumed that the microwave is radiated while the current reaches the lower end of the vertical portion 2a, and the current Ih flowing in the horizontal portion is almost eliminated. Even when the antenna itself is rotated, the vertical portion, which is the radiation source, does not change its position, and it is hard to say that the radiation source is rotating.
[0004]
The turntable method is not always versatile, and it is not only inferior in operability compared to the method in which a square top plate or wire mesh of a full-scale oven in Europe and the United States is easily taken in and out of the shelf, but also the food loading range is limited to the inside of the circular table There is a point that is spilled, liquid spills due to vibration of rotation, etc., multi-stage cooking is difficult, etc.Recently, the turntable is removed, and a ceramic plate that passes microwaves is provided on the bottom of the heating chamber, and below it The non-turn method of rotating the antenna by using is becoming popular.
[0005]
In addition, there is one having a cylindrical rotating antenna having a similar shape, and a protruding waveguide having a rectangular section and having the same guide wavelength (see Patent Document 2).
[0006]
[Patent Document 1]
JP-A-58-181289 [Patent Document 2]
JP-A-52-006147
[Problems to be solved by the invention]
However, this method cannot provide a heater on the bottom, so it is still unsatisfactory compared to a full-scale oven. The lower fire is the most important for the oven, but in the non-turn, because the lower fire is not provided in the original sense, a heat source is provided at the rear, the heat is transferred as wind, and the hot air circulation method that gives the role of the lower fire Is adopted. However, since the bottom has a large heat capacity and a ceramic plate which is also a poor conductor of heat, the resulting thermal efficiency is low and it is difficult to control the lower fire. Even in European and American ovens, there are many examples in which a heater is provided on the bottom of the heating chamber even if the hot air circulation system is used. There is an example in which a heater is provided near the bottom of the heating chamber, and an example in which the heater is attached closely to the outside of the heating chamber and under the bottom. Each has advantages and disadvantages, but in any case, lower fire is more important. It is proof.
[0008]
In order to realize a full-scale oven having a heater on the bottom of the heating chamber, a system having excellent uniform performance without providing any rotating mechanism on the bottom is required. For that purpose, it is desired to provide a mechanism in which the microwave radiation source itself rotates, for example, on the upper surface other than the bottom surface. It is necessary to have a rotating antenna in the original meaning in which the radiation antenna itself rotates.
[0009]
As described above, it is difficult to rotate the magnetron itself, but it can be imagined that rotating the waveguide on which the magnetron is mounted is somewhat easier than the magnetron itself. The present invention is intended to realize this idea and provides a rotating microwave radiation source on the upper surface, which can be used in a full-scale oven having a heater on the bottom surface, and provides a microwave oven excellent in uniform heating performance. Aim.
[0010]
[Means for Solving the Problems]
In order to solve the conventional problem, a microwave oven according to the present invention includes an oven box, a waveguide, a magnetron, and a cylindrical waveguide, and the center axis is substantially centered on a top surface of the oven box. The cylindrical waveguide is rotated, and the magnetron and the waveguide are configured to excite the cylindrical waveguide in the H11 mode.
[0011]
As a result, since the cylindrical waveguide excited in the H11 mode rotates around the center of the top surface of the oven box as a central axis, the electric power transmitted from the magnetron is radiated to the oven box while rotating, so that it is well stirred and uniform. Heating performance is improved.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 has an oven box, a waveguide, a magnetron, and a cylindrical waveguide, and rotates the cylindrical waveguide around a substantially center of a top surface of the oven box as a central axis, The magnetron and the waveguide are configured by exciting the cylindrical waveguide in the H11 mode. As a result, since the cylindrical waveguide excited in the H11 mode rotates around the center of the top surface of the oven box as a central axis, the electric power transmitted from the magnetron is radiated to the oven box while rotating, so that it is well stirred and uniform. Heating performance is improved.
[0013]
The invention according to claim 2 has a configuration in which the waveguide has a rectangular cross section, is excited in the H01 mode, and has a guide wavelength equal to the guide wavelength of the cylindrical waveguide excited in the H11 mode. As a result, the circular waveguide always faces the H01 mode rectangular waveguide at an arbitrary angle during rotation, so that the circular H11 mode having an electric field in the same direction as the rectangular H01 mode is excited inside the cylinder. , And stable power transmission is performed.
[0014]
The invention according to claim 3 is a configuration in which a cylindrical stirring chamber is provided substantially at the center of the top surface of the oven box, and the cylindrical waveguide excited in the H11 mode is housed in the stirring chamber. The power that is not transmitted from the waveguide to the cylindrical waveguide also undergoes a kind of rotation between the outside of the cylindrical waveguide and the inside of the stirring chamber. Since they rotate synchronously, the stirring effect increases.
[0015]
The invention according to claim 4 is characterized in that a sheathed heater constituted by a plurality of continuous line segments is provided on the top surface of the oven box, and the sheathed heater at least below the stirring chamber and within a quarter wavelength region around the stirring chamber, This is a configuration in which only the line segment orthogonal to the main electric field of the cylindrical waveguide H11 mode is provided. Since the electric field is orthogonal to the sheath heater, the sheath heater exists between the cylindrical waveguide and the object to be heated. Nevertheless, the electric field is not disturbed. Therefore, the stirring effect and the uniform heating performance are favorably maintained.
[0016]
The invention according to claim 5 is a configuration in which the sheathed heater and the top surface of the oven box are connected by a metal outside the range of 1/4 wavelength around the stirring chamber, whereby the electric field is not disturbed and the heater is A microwave oven that is held and fixed and has high reliability can be realized.
[0017]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
(Example 1)
FIG. 1 is a diagram showing a cross section of a main part of a microwave oven according to a first embodiment of the present invention. The waveguide 1 has a rectangular section with a width of 86 mm and a height of 40 mm, is bent in the height direction, and has a shape in which a letter C is turned down. One end of the letter C and a short vertical portion 1a are fixed to the center of the top surface of the cylindrical stirring chamber 3. The stirring chamber 3 is fixed to the center of the top of the oven box 4. A rotating antenna 2 which is a cylindrical waveguide having a diameter of about 100 mm and a length of 60 mm is accommodated in the stirring chamber 3 while being fixed to a ceramic round bar 5.
[0019]
The ceramic round bar 5 extends to the outside through the wall surface of the 45-degree inclined portion of the waveguide 1 and the metal bearing 6 fixed to the wall surface, and the passive gear 7 is attached. The passive gear 7 is engaged with the drive gear 8, and the drive gear 8 is attached to the output shaft of the motor 9. The round bar 5 coincides with the center of the end 1 a of the waveguide 1, the central axis of the cylinder serving as the stirring chamber 3, and almost the center of the oven box 4. A lid 10 made of a thin mica plate is attached to a portion of the waveguide 1 where the vertical end portion 1a of the waveguide 1 is connected to the stirring chamber 3, and a round hole 5 Are vertically supported through the center of the end 1a of the waveguide 1. A glass plate 11 is attached to a bottom surface of the stirring chamber 3 by a metal fixing plate 12.
[0020]
Below this, a sheath heater 13 is attached near the top surface of the oven box 4. The left and right wall surfaces of the oven box 4 are formed with an uneven groove shape 4a, and a metal saw net 14 is detachably inserted into the groove. The gauze net 14 is composed of a relatively square wire 14a having a square frame shape around the wire and a thin wire 14b connecting the opposite sides, and the thin wire 14b is drawn as 32 small circles in FIG. It is perpendicular to the surface and parallel to each other, narrow near the center, and fixed at wide intervals around the left and right sides. As shown in the figure, there are three pairs of grooves, and the gauze net 14 can be inserted into all the grooves. The soup cup 15 made of ceramic is drawn on the screen 14 and has round handles on the left and right. A magnetron 16 is mounted on the side of the waveguide 1 opposite to the side 1a. In addition, a heater that plays a role of lowering the heat is attached below the bottom surface of the oven box 4, but it is not necessary for the description of the present embodiment, so that it is omitted and not drawn.
[0021]
FIG. 2 is a plan view seen from the AA 'plane of FIG. The heater 13 includes six line segments 13a that run up and down, a curved portion 13b connecting these lines, a pair of left and right support brackets 13c and 13d, and hanging brackets 13e and 13f connecting the support bracket and the top surface of the oven box. Consists of Below the sheath heater 13, four soup cups 15 placed on a grid 14 are drawn. The trapezoid drawn in the upper part of the figure is a hot air blowing part 17, and the horizontally long rectangle drawn in the lower part is a door 18. The waveguide 1, the rotating antenna 2, and the stirring chamber 3 are drawn in the center by a two-dot chain line. A broken line of about 30 mm outside the stirring chamber is a region 3a of a quarter wavelength from the stirring chamber. The above-mentioned support fittings 13c and 13d and hanging fittings 13e and 13f are located outside this area 3a.
[0022]
FIG. 3 is a perspective view showing a state where the rotating antenna 2 and the ceramic round bar 5 are assembled. A small round hole 5a is formed near the upper end of the ceramic round bar 5 and is used for fixing to the passive gear 7 described above. Two so-called D-cut portions 5b (not clearly seen in FIG. 2; see FIG. 5) are provided at the lower portion. The cylindrical portion 2a of the rotating antenna 2, which is made of a thin metal plate, is overlapped and welded at the fixed portion 2b, and has a cylindrical shape with a diameter of about 100 mm and a height of about 60 mm. A total of four elongated rectangular holes 2e (see FIG. 4) are formed around the fixing portion 2b, and the lower end is bent to the left by 45 degrees in an f-shape. The antenna fixing member 19 made of alumina porcelain is bent by 45 degrees 19a ( 6) is inserted. The quarter-circle portion of the f-shaped upper end 19b and the protruding portion thereunder are shaped so as to fit into half of the D-cut portion 5b of the ceramic round bar 5. The D-cut portion 5b of the ceramic round bar 5 is scissored from both sides by a pair of antenna fixtures 19, and at this time, the 45-degree bent portions at the lower ends face each other. The fixing bracket 20 has a shape in which both ends are bent at 45 degrees (see FIG. 6), and is screwed to the rotary antenna 2 so that the 45-degree portions at both ends and the 45-degree bent portion at the lower end of the antenna fixing device 19 are in contact with each other. . As a result, the antenna fixture 19 rotates around the outside of the rectangular hole 2e of the rotary antenna 2 as a fulcrum, the upper ends 19b of the right and left f-shapes approach, and the rotary antenna 2 and the ceramic round bar 5 are fitted together with the D cut 5b. Fix it. In this embodiment, the center of the ceramic round bar 5 and the center of the cylinder of the rotary antenna 2 are separated by about 20 mm.
[0023]
4 is a perspective view of the rotary antenna 2, FIG. 5 is a perspective view of a ceramic round bar, FIG. 6 is a perspective view of an antenna fixture 19, and FIG. 7 is a perspective view of a fixture 20.
[0024]
The operation and operation of the microwave oven configured as described above will be described below.
[0025]
First, a rectangular H01 mode is excited inside according to the dimensions of the waveguide 1, the oscillation frequency of the magnetron 16 at 2450 MHz, and the method of attaching the waveguide to the waveguide 1, and the electric field is directed to a direction of a height of 40 mm. As a result, the electric field in the vicinity of the terminal end 1a is directed in the left-right direction as depicted in the center of FIG. FIG. 8 is a plan view in which the vicinity of the electric field is taken out, and shows the end 1 a of the waveguide 1, the stirring chamber 3, and the rotating antenna 2. The left and right of FIG. 8 are plan views showing the same state, but the electric field inside the waveguide 1 is drawn on the left and the electric field inside the rotating antenna is drawn on the right and left separately, and the difference between the two is emphasized. did. The difference between the upper, middle, and lower positions is a difference in the rotation angle of the antenna 2 and indicates a state in which the antenna 2 is rotated clockwise by 45 degrees from above.
[0026]
Inside the waveguide 1 in the left half, the electric field drawn by the arrow points in the left-right direction as described above, and the center of the waveguide 1 is strong and dense, and both ends are weak and sparse. The strongest position is also the center of the stirring chamber 3. The so-called H01 mode is a mode having the lowest cutoff frequency in a rectangular waveguide. Due to this electric field, in the electric field inside the antenna 2 drawn in the right half, a dense arc-shaped electric field is generated near the center of the cylinder. The H11 mode having the lowest cutoff frequency in a cylindrical waveguide. The guide wavelength of the H01 mode in a rectangular waveguide having a width of 86 mm and the guide wavelength of the H11 mode in a cylindrical waveguide having a diameter of 100 mm are both described in many textbooks, and are omitted here. Having.
[0027]
The position where the H11 mode electric field is strongest is the center of the antenna 2 and a position slightly deviated from the center of the stirring chamber 3, and in this embodiment, a position separated by about 20 mm as described above. The end 1a of the waveguide 1 is attached vertically, the center axis of the rotating antenna 2 which is a cylindrical waveguide is also made vertical, and both are brought close to each other. Similarly, the electric field is smoothly converted to the H11 mode of the cylindrical waveguide, which is an electric field in the left-right direction. Even if the angle changes clockwise and the center position of the cylinder changes, the cylinder receives the electric field in the left-right direction and always maintains the H11 mode in the left-right direction. That is, since the cylindrical waveguide 2 is rotated about an axis parallel to the center of the cylinder, the electric fields of both waveguides always coincide. If the rotating antenna 2 is rectangular, there are angles at which power flows smoothly and angles at which power hardly flows, and the stirring effect is drastically reduced.
[0028]
The reason for setting the length of the cylindrical waveguide 2 as a rotating antenna to 60 mm and about a half wavelength is that an electric field similar to the left figure, which is still the main force in the upper part of the antenna facing the waveguide 1, is generated by the cylindrical waveguide. It is considered that the electric field distribution of the original cylindrical waveguide, that is, the state depicted on the right, changes by traveling a half wavelength inside the antenna. Actually, when the length is reduced to 50 mm or 40 mm, the stirring effect is reduced, and the uniform heating performance of the food is reduced. For example, a salt solution having a salt concentration of about 1% of about 175 cc is added to the soup cup 15 shown in FIG. 2, and four cups are simultaneously heated as shown in FIG. After stirring the cups and measuring the temperature, when the difference between the maximum temperature and the minimum temperature of the four cups with respect to the average temperature rise of the four cups is expressed as a percentage, when the cylinder length is 60 mm, the difference falls within about 4% to 8%. However, the height increases from about 15% to about 20% at a height of 50 mm, and from about 15% to about 25% at a height of 40 mm.
[0029]
From these results, the H11 mode is excited at the bottom of the cylindrical waveguide 2 by setting the length of the cylindrical waveguide 2 to about half the wavelength of 60 mm, and a strong electric field at the center of the H11 mode has a radius of about 20 mm. It is thought that it rotates in a circular orbit and stirs and homogenizes the electric field distribution inside the oven box 4.
[0030]
As shown in FIG. 2, the inside of the oven box can be said to have a substantially symmetrical shape on the left and right, but the shape of the heater 13 is not symmetrical between the front and the back, and the hot air blowout portion 17 and the door 18 are not symmetrical. In the conventional uniform heating method by stirrer stirring, it is premised that the shape is symmetrical in the front-rear and left-right directions, and the performance is farther from the uniform heating as the shape departs from the symmetrical shape. Despite a slight collapse, the four-point distribution of the soup cup is maintained uniform. It is considered that rotating the radiation source itself is very effective.
[0031]
As described above, in this embodiment, the oven box, the waveguide, the magnetron, and the cylindrical waveguide are provided, and the cylindrical waveguide is rotated around the center of the top surface of the oven box as a central axis. The magnetron and the waveguide excite the cylindrical waveguide in the H11 mode, whereby the cylindrical waveguide excited in the H11 mode rotates around the center of the top of the oven box as a central axis. Since the power transmitted from the magnetron is radiated to the oven box while rotating, the power is well stirred and the uniform heating performance is improved. Although the magnetron itself does not rotate, instead of this, the rotation of the cylindrical waveguide excited in the H11 mode makes it possible to realize a rotating antenna having the original meaning that was impossible in the past.
[0032]
The above-mentioned conventional example, Japanese Patent Application Laid-Open No. 52-6147, is similar to the present invention in that it has a cylindrical rotating antenna (5) and a protruding waveguide (2) having a rectangular cross section having the same guide wavelength. Are different. The difference in shape is that the conventional example is provided on the bottom surface of the oven box, and the present embodiment is provided on the upper surface. In the prior art, as described in the specification, a rotating antenna is provided on the bottom surface, directly below the food table for the purpose of strongly heating the central bottom of the food, which is generally difficult to heat. As a result, the H11 mode electric field of the cylindrical waveguide serving as a rotating antenna and the food placing table become parallel, and the food bottom placed thereon also becomes parallel to the electric field, and as a result, it is strongly heated, and The part is not heated very much. In particular, the food portion located directly above the cylindrical waveguide is strongly heated, but is slightly heated when slightly removed. In this regard, as described above, the present invention moves to the upper surface of the oven box in order to avoid coupling with the object to be heated, and radiates microwaves inside the oven box while rotating, thereby generating an internal electric field. Stirring and uniform heating are realized, and 4 cups of salt water have the ability to heat evenly.
[0033]
The conventional example positively utilizes the phenomenon that "the electric field and the object to be heated are strongly heated when they are parallel", which caused a fundamental difference between the above-described conventional example and the present embodiment. It is not widely recognized that the disadvantage that "the electric field is not heated at all when the electric field and the object to be heated are perpendicular to each other" has not been described in the specification. However, it is necessary to understand the essential difference from the present invention, so that it will be described a little.
[0034]
The expression of the pointing vector derived from Maxwell's electromagnetic equation is described in various textbooks in terms of its differential form. However, when used for heating, the integral type shown below is easier to understand.
[0035]
(Equation 1)

[0036]
This equation shows how the energy flowing into the object having the volume v surrounded by the surface s, that is, the pointing vector P = E × H behaves inside the object. N on the left side is a normal vector of the object surface s, and the left side is obtained by integrating the inner product of this and P over the entire surface. Represents the total energy flowing into the body. The reason why the minus sign is added is to make the pointing energy traveling in the opposite direction to the outward normal vector, that is, inward of the object, in the positive direction. The vector P is perpendicular to the electric field E and perpendicular to the magnetic field H.
[0037]
The first term on the right side is obtained by integrating the heat generated due to the resistance loss per unit volume inside the object over the entire volume, and represents the heat generated by the entire object. The second term is the integral of the stored electric and magnetic field energies, also over the object, and represents an increase in the stored electromagnetic field energy.
[0038]
Since the electromagnetic field radiated from the waveguide into the oven box is complicated, its properties cannot be clarified by solving differential equations, but it may be solved inside the waveguide. Find and analogize the phenomenon inside the oven box. The electromagnetic field when a load having a thickness t is inserted parallel and perpendicular to the electric field as shown in FIGS. 10 and 11 in the center of the inside of the rectangular waveguide excited in the H01 mode can be obtained from the differential equation. When the propagation constant in the air in the x direction is η, the propagation constant in the load is ζ, and the propagation constant in the traveling direction of the waveguide is γ, γ2 = ω2μ0ε0−η2-π2 / b2. Given by the formula. 0 which means in the air and 1 which means in the load are described in the formula as suffixes. Although the equation in the air and the equation inside the load are different, only the electromagnetic field in the load is described since the tangential components of the electromagnetic fields are equal on the boundary between the two.
[0039]
When the electric field and the load in FIG. 10 are parallel, Ex0 = Ex1 = Ez0 = Ez1 = 0, where C is a constant.
Ey1 = C1γCosh ｛ζ (a / 2−x)｝ exp (−γz)
Hx1 = (ζ2 + ω2μ0ε1) Sinh ｛ζ (a / 2−x)｝ exp (−γz) / (jωμ0)
Hy1 = Hy0 = 0
Hz1 = C1 {γ Sinh} (a / 2−x) Δexp (−γz) / (jωμ)
Here, η and ζ are complex numbers, and are solutions (principal values) of the following simultaneous equations.
[0040]
−ηCoth (ηd) = ζTanh (ζt / 2)
−η2 + ζ2 = ω2μ0ε0εr (1-jtanδ) −ω2μ0ε0
When the load of thickness t placed at the center of the waveguide is applied to the above-described pointing vector equation, the surface s of the object is divided into a surface in contact with air on the left and right and a surface in contact with the top and bottom of the waveguide. When considered, the electric field on the surface in contact with air is Ey1, and the magnetic field is Hz1. The pointing vector P, which is the product of these, is a right-handed system, and indicates the direction in which the right-hand screw advances when turning, from the direction of the electric field E drawn by the solid arrow to the direction of the magnetic field H drawn by the broken arrow. Turn around. When this is applied, assuming that Ey1 is positive, Hz1 points in a negative direction at x = a / 2 + t / 2 and conversely turns in a positive direction at x = a / 2-t / 2. Therefore, the pointing vector P points to the inside of the object on both the left and right sides, as depicted by the white arrows in the figure. This means that power flows into the object and heat is generated by the electromagnetic field.
[0041]
When the electric field and the load in FIG. 11 are orthogonal to each other, they are expressed by exchanging XY for convenience. D is a constant.
[0042]
Ex1 = D1 (ζ2 + ω2μ0ε0) Cosh ｛ζ (a / 2−x)｝ Sin (yπ / b) exp (−γz) / (jωε1)
Ey1 = −D1ζ (π / b) Sinh ｛ζ (a / 2−x)｝ Cos (yπ / b) exp (−γz)
Ez1 = D1 {γSinh} (a / 2-x)｝ Sin (yπ / b) exp (−γz)
Hx1 = Hx0 = 0
Hy1 = D1γCosh ｛ζ (a / 2−x)｝ Sin (yπ / b) exp (−γz) / (jωε1)
Hz1 = D1 (π / b) Cosh ｛ζ (a / 2−x)｝ Cos (yπ / b) exp (−γz)
Here, η and ζ are complex numbers, and are solutions (principal values) of the following simultaneous equations.
[0043]
(Η / ε0) Tanh (ηd) = − (ζ / ε1) Tanh (ζt / 2)
−η2 + ζ2 = ω2μ0ε0εr (1-jtanδ) −ω2μ0ε0
When the main electric field Ex1 is directed upward, the pointing vector formed by this and Hy1 points in the z direction, and the pointing vector formed by Hz1 points in the y direction, and both are parallel to the boundary between the load and the air. This means that no electric power flows into the load object. In other words, even if a load is placed perpendicular to the main electric field, it is not heated at all. Since the derived electric field Ey1 has the Cos (yπ / b) component, it takes the maximum value at y = 0 and y = b. The pointing vector formed by this electric field component and Hz1 points in the x direction, that is, in the direction inside the object. In fact, very weak heating can be seen at the end of the load.
[0044]
Applying this to the relationship between the conventional cylindrical waveguide and the load illustrated in FIG. 12, the central portion of the load parallel to the main electric field by the cylinder, the hatched portion in the figure, is strongly heated, and The portion where the electric field passes through is hardly heated. The conventional example shown in FIG. 12 is an example in which the heating of the center bottom of the food, which is generally hardest to be heated, succeeded, but the uniform heating failed. This is because the electric field of the waveguide and the load are directly coupled as described above. In this regard, the present invention locates the cylindrical waveguide on the top surface sufficiently distant from the load and rotationally radiates the electromagnetic field energy into the oven box interior space without direct coupling with the load. This is a difference from the conventional example.
[0045]
In this embodiment, as shown in FIG. 2, the sheath heater 13 has a configuration in which a main portion 13a runs back and forth. Since the electric field inside the waveguide 1 and the rotating antenna 2 is always in the left-right direction as indicated by the arrow in the center of FIG. 2, they intersect perpendicularly, and the influence on the electric field is small. The heating performance does not change. As is well known to those skilled in the art, at the surface of a metal, the electric field has only a vertical component and a zero parallel component. Therefore, if the heater 13 has a portion running in the left and right direction parallel to the electric field, the electric field in the left and right direction is weakened. The support brackets 13c and 13d are paired on the left and right. However, as has just been described, the central portion is parallel to the main portion of the electric field when it is made continuous. In addition, it is located within a quarter wavelength range from the stirring chamber and very close to the main part of the electric field. As a result, the heating unevenness of the above-described 4 cups of salt solution is reduced to about 16%. Therefore, the left and right were separated.
[0046]
The hanging metal fittings 13e and 13f connecting the supporting metal and the top surface of the oven box also affect the unevenness depending on the position. However, it is not as remarkable as the support fitting and is restricted by the position of the support fitting, so that it is inevitably limited to outside the range of 1/4 wavelength like the support fitting.
[0047]
【The invention's effect】
As described above, according to the present invention, it has become possible to rotate a microwave radiator, which has been difficult in the past, and can be incorporated into a full-scale oven having a heater near the bottom surface, and has excellent uniform heating performance. A microwave oven can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a microwave oven according to Embodiment 1 of the present invention. FIG. 2 is a plan view of Embodiment 1 of the present invention. FIG. 3 is a perspective view of a rotary antenna according to Embodiment 1 of the present invention. FIG. 5 is a perspective view of a rotary antenna and a cylinder according to the first embodiment of the present invention. FIG. 5 is a perspective view of a round bar according to the first embodiment of the present invention. FIG. 6 is a perspective view of an antenna fixture according to the first embodiment of the present invention. FIG. 8 is a perspective view of a fixture in the first embodiment of the present invention. FIG. 8 is a plan view of the vicinity of a rotary antenna in the first embodiment of the present invention. FIG. 9 is a sectional view of a main part of a conventional microwave oven. FIG. 11 is an operation explanatory view of a conventional example. FIG. 12 is a sectional view of a main part of a conventional microwave oven.
1 waveguide 2 rotating antenna (cylindrical waveguide)
3 Stirring chamber 4 Oven box 5 Round bar (center axis)
9 Motor (rotation mechanism)
16 magnetron

Claims

An oven box, a waveguide, a magnetron, and a cylindrical waveguide, wherein the cylindrical waveguide is rotated about a center of the top surface of the oven box as a center axis, and the magnetron and the waveguide are A microwave oven wherein the cylindrical waveguide is excited in an H11 mode.

2. The microwave oven according to claim 1, wherein the waveguide has a rectangular cross section, is excited in the H01 mode, and has a guide wavelength equal to the guide wavelength of the cylindrical waveguide excited in the H11 mode.

2. The microwave oven according to claim 1, wherein a cylindrical stirring chamber is provided substantially at the center of the top surface of the oven box, and the cylindrical waveguide excited in the H11 mode is accommodated in the stirring chamber.

A sheath heater composed of a plurality of continuous line segments is provided on the top surface of the oven box. 4. The microwave oven according to claim 3, wherein the microwave oven comprises only a line segment orthogonal to.

The microwave oven according to claim 4, wherein the sheathed heater and the top surface of the oven box are connected by metal outside the range of 1/4 wavelength around the stirring chamber.