什麼是微波..........

什麼是微波..........

2 Answers

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  • Carson
    Lv 6
    1 decade ago
    Best Answer

    The microwave range includes ultra-high frequency (UHF) (0.3–3 GHz), super high frequency (SHF) (3–30 GHz), and extremely high frequency (EHF) (30–300 GHz) signals.

    Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is effectively opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

    Microwaves are electromagnetic waves with wavelengths shorter than one meter and longer than one millimeter, or frequencies between 300 megahertz and 300 gigahertz. (UHF, SHF, EHF) It is noteworthy that U.S. Military and IEEE definitions differ on mmW (millimeter wave) definition, which is a subdivision of Pozar's microwave definition of 300MHz to 300GHz (some define it as 300MHz to 30GHz). The IEEE defines mmW as 110GHz to 300GHz while military radar definitions use 30-300GHz for the mmW band.

    The name suggests a micrometer wavelength. However, the boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The term microwave generally refers to "alternating current signals with frequencies between 300 MHz (3×10^8 Hz) and 300 GHz (3×10^11 Hz)." (UHF, SHF, EHF) However, both IEC standard 60050 and IEEE standard 100 define "microwave" frequencies starting at 1 GHz (30 cm wavelength).

    Electromagnetic waves longer (lower frequency) than microwaves are called "radio waves". Electromagnetic radiation with shorter wavelengths may be called "millimeter waves", terahertz radiation or even T-rays.

    2007-11-27 07:24:28 補充:

    微波是頻率在300兆赫到300千兆赫的電磁波(波長1米 - 1毫米),通常是作為資訊傳遞而用於雷達、通訊技術中。而近代應用中又將它擴展為一種新能源,在工農業上用作加熱、乾燥;在化學工業中催使化學反應;在科研中激發等離子體等。家用微波爐就是微波能應用的一個典型例子。

    2007-11-27 07:30:32 補充:

    通常,一些介質材料由極性分子和非極性分子組成,在微波電磁場作用下,極性分子從原來的熱運動狀態轉向依照電磁場的方向交變而排列取向。產生類似摩擦熱,在這一微觀過程中交變電磁場的能量轉化為介質內的熱能,使介質溫度出現宏觀上的升高,這就是對微波加熱最通俗的解釋。 由此可見微波加熱是介質材料自身損耗電磁場能量而發熱。對於金屬材料,電磁場不能透入內部而是被反射出來,所以金屬材料不能吸收微波。水是吸收微波最好的介質,所以凡含水的物質必定吸收微波。

    2007-11-27 07:39:28 補充:

    微波加熱的特點1、加熱速度快2、均勻加熱3、節能高效4、易於控制5、低溫殺菌、無污染6、選擇性加熱7、比較傳統加熱方式更安全無害微波可以是用微波爐煮食的簡稱。

  • Anonymous
    1 decade ago

    微波是一種電磁波輻射,如X光、gamma光、紫外線、光、無線電波和雷達,電磁波輻射是電和磁波的震動,靠波將能量從一個源頭輸送到接收點,不經直接物質的輸送。如果眼睛看得到波的波動,看起來就像海浪,因為振動力量的不同,有不同速度、波長、頻率。微波的波長是15公分(6英吋)微波的頻率很高,每秒十億次以上,而且被人體和有水份的食物吸收。

    微波在商業用途上之一是「微波爐」,食物放在一個有電磁波絕緣的容器裏,吸收很強電子機產生的微波。微波能被濕的食物吸收,因為微波爐的頻率是水分子轉動的頻率(每秒24億次)相近。微波的激發使食物中的水立刻超熱,再將熱傳導到食物。這微波的激發不限於水,包括其他分子。微波爐的絕緣體不一定都理想,因此也發射到環境中,所產生的微波不能全被食物吸收,所剩餘的會經電線傳送到屋內。人體,包括腦和其他重要器官水平均佔70%。身體因此能有效的吸收微波輻射,微波被人體吸收後,對健康的影響是複雜的,需要進一步的研究,特別是不同年齡、健康狀況和胎兒的健康長期接觸後的問題。

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