第一篇：翻譯練習(xí)1 中英文

四級翻譯練習(xí)——分類詞匯及練習(xí)

（一）歷史文化類 烹調(diào)

魚肉滿架

象征意義

農(nóng)歷

陽歷

端午節(jié)

元宵節(jié)

清明節(jié)

重陽節(jié)

放逐

忠臣

糯米粽子

祭祀亡靈

龍舟比賽

中秋節(jié)

滿月

蜜餞

豆沙

蛋黃

海鮮

家禽

八寶飯

米羹

油條

麻花

叉燒包

粥

芋頭

蔥油餅

放鞭炮

耍龍燈

耍獅子

拜年

cooking cuisine well stocked with fish and meat symbolic significance lunar calendar solar calendar Dragon Boat Festival Lantern Festival Pure Brightness Day Double Ninth Day be exiled loyal minister glutinous rice dumplings wrapped in bamboo leaves in memory of sb.dragon boat races Mid Autumn Festival full moon preserved fruits bean paste egg yolk seafood poultry eight treasure rice rice balls fried sticks fried twisted stick steamed bun with roast pork porridge taro pan-fried cake with sesame seeds and green onion let off firecrackers play the dragon lantern play the lion dance pay a new-year call

Chinese Dragon 對龍圖騰的崇拜在中國大約已綿延了八千多年。中國龍是古人將魚、蛇、馬、牛等動物與云霧、雷電等自然天象集合而成的一種神物。中國龍的形成與中華民族的多元融合過程同步。和西方的龍不一樣，在中國人的心目中，龍具有振奮騰飛的寓意和團(tuán)結(jié)凝聚的精神，而不是魔怪。

Dragon worship in China has been around for the last 8, 000 years.The ancients in China considered the dragon(or long)that combines animals including the fish, snake, horse and ox with cloud, thunder, lightning and other natural phenomena.The Chinese dragon was formed in accordance with the multicultural process of the Chinese nation.Unlike dragon in the West, the Chinese believes that it signifies innovation and cohesion, rather than a monster.Dumplings 餃子是深受中國人民喜愛的傳統(tǒng)食品。相傳為古代醫(yī)圣張仲景發(fā)明。餃子的制作是包括： 1）搟皮、2）備餡、3）包餡水煮三個步驟。其特點是皮薄餡嫩，味道鮮美，形狀獨(dú)特，百食不厭。民間有“好吃不過餃子”的俗語。中國人接親待客、逢年過節(jié)都有包餃子吃的習(xí)俗，寓意吉利。對重視親情的中國人來說，吃餃子，更是歡度除夕、辭舊迎新必不可少的內(nèi)容。

Dumplings are one of the Chinese favorite traditional food.According to an ancient Chinese legend, dumplings were first made by the medical saint---Zhang Zhongjing.There are three steps in making dumplings: 1)make dumpling wrappers out of flour;2)prepare the stuffing;3)make dumplings and boil them.With thin and elastic dough skin, fresh and tender stuffing, delicious taste, and unique shapes, dumplings are worth eating hundreds of times.There’s an old saying that “Nothing could be more delicious than dumplings”

During the Spring Festival and other holidays, or when treating relatives and friends, Chinese like to follow the custom of eating dumplings.To those Chinese who stress family love, having dumplings at the moment the old year is replaced by the new is an essential part of bidding farewell to the old and ushering in the new year.Dragon boat festival 端午節(jié)，又叫龍舟節(jié)，是為了紀(jì)念愛國詩人屈原。屈原是一位忠誠和受人敬仰的大臣（minister）,他給國家?guī)砹撕推胶头睒s。但最后因為受到誹謗（vilify）而最終投河自盡。人們撐船到他自盡的地方，拋下粽子，希望魚兒吃粽子，不要吃屈原的身軀。幾千年來，端午節(jié)的特色在于吃粽子（glutinous dumplings）和賽龍舟，尤其是在一些河湖密布的南方省份。

The Duanwu Festival, also called the Dragon Boat Festival, is to commemorate the patriotic poet Qu Yuan.He was a loyal and highly esteemed minister, who brought peace and prosperity to the state but ended up drowning himself in a river as a result of being vilified.People got to the spot by boat and cast glutinous dumplings into the water, hoping that the fishes ate the dumplings instead of his body.For thousands of years, the festival has been marked by glutinous dumplings and dragon boat races, especially in the southern provinces where there are many rivers and lakes.Chinese Kung Fu 中國功夫，又叫武術(shù)，是一項傳統(tǒng)體育項目。它承載著豐富的中華民族傳統(tǒng)文化，其核心思想是儒家的中庸和養(yǎng)氣之說，同時兼容了道家、佛家的思想。中國武術(shù)源遠(yuǎn)流長、流派（sect）林立、拳種繁多，講究剛?cè)岵?jì)、內(nèi)外兼修，蘊(yùn)含著先哲們對生命和宇宙的參悟。如今，人們學(xué)習(xí)功夫大多出于自身興趣，或是為了強(qiáng)身健體。有很多中國武館甚至開到了國外。

Being a traditional sport, Chinese kung fu, or martial arts carries traditional Chinese culture in abundance.Its core idea is derived from the Confucian theory of both “the mean and harmony” and “cultivating qi” known as nourishing one’s spirit).Meanwhile, it also includes thoughts of Taoism and Buddhism.Chinese kung fu has a long history, with multi-various sects and many different boxing styles, and emphasizes coupling hardness with softness and internal and external training.It contains the ancient great thinkers’ pondering of life and the universe.Nowadays, people practice kung fu mostly for their own interests or for health.Some of martial arts centers could ever be found overseas.Chinese Characters 漢字是從古代用以記事的簡單圖畫，經(jīng)過不斷演變發(fā)展最終成為一種兼具形、意、韻（rthyme）的獨(dú)特文字。漢字有五種基本筆畫（stroke），即：橫、豎、撇、捺、折，但在外國人眼中看來，就像一個個小方塊，因此，也被稱為“方塊字”。對他們來說，學(xué)習(xí)漢語一個很大的難點在于漢字的大部分發(fā)音都無法從字形上推測出來。Chinese characters has been gradually involved from simple pictures used to help people remember things to a unique character system that embodies image, idea, and rhyme at the same time.Chinese characters, consisting of five basic strokes, i.e.“---“(the horizontal stroke)“│”(the vertical stroke), “／”(the left-falling stroke), “＼”(the right-falling stroke), and “乙”(the turning stroke), are a set of blocks in the eyes of foreigners though.To them, a great difficulty to learn it lies that one can not infer the pronunciation from the character.

第二篇：中英文句子翻譯練習(xí)

漢英句子翻譯練習(xí)

Title: 漢英翻譯技巧：合并(Combination)

(A)in terms of simple sentences(1)天氣寒冷，河水都結(jié)冰了。It was so cold that the river froze.(丁樹德，“英漢漢英翻譯教學(xué)綜合指導(dǎo)”，天津大學(xué)出版社，1996)(2)理論必須密切聯(lián)系實際，這是我們應(yīng)當(dāng)牢記的一條原則。That theory must go hand in hand with practice is a principle we should always keep in mind.（丁樹德，“英漢漢英翻譯教學(xué)綜合指導(dǎo)”，天津大學(xué)出版社，1996）

(3)他在戰(zhàn)斗中表現(xiàn)突出，受到連長的表揚(yáng)。He was commended by the company commander for his distinguished performance in the battle.(丁樹德，“英漢漢英翻譯教學(xué)綜合指導(dǎo)”，天津大學(xué)出版社，1996)(4)年滿十八歲的公民，都有選舉權(quán)和被選舉權(quán)。All citizens who have reached the age of eighteen have the right to vote and to stand for election.（丁樹德，“英漢漢英翻譯教學(xué)綜合指導(dǎo)”，天津大學(xué)出版社，1996）

(5)當(dāng)時，友誼商店只對外賓開放，不對中賓開放。At the time the friendship store was exclusively open to foreign visitors.（王大偉，“現(xiàn)代漢英翻譯技巧”，世界圖書出版公司，1999）（本科四年級以上）

(B)in terms of compound sentences(6)她對自己所取得的成就充滿了自豪，這也不是沒有道理的。She is justifiably proud of her achievements.(“現(xiàn)代漢英翻譯技巧” 王大偉 世界圖書出版公司 1999)(7)這家小工廠經(jīng)過技術(shù)改造，發(fā)展很快，使人感到驚訝不已。This small factory underwent a technological renovation, thus developing with surprising speed.（王大偉，“現(xiàn)代漢英翻譯技巧”，世界圖書出版公司，1999）（本科四年級以上）

(8)只要看一眼這封信，你就會明白你上當(dāng)了。A glance at this letter will convince you that you have been taken in.(朱巧蓮，“漢譯英之合譯法”，“上?？萍挤g”，2001, No.1)(9)看門人驚呆了，喘著粗氣，搖搖晃晃地走下樓梯。The janitor staggered down the stairway, stunned and gasping.(朱巧蓮，“漢譯英之合譯法”，“上?？萍挤g”，2001, No.1)(10)還是熱，心里可鎮(zhèn)定多了。涼風(fēng)，即使是一點點，給了人們許多希望。（老舍“駱駝祥子”）It was still hot but everyone felt much better, for the breeze, though slight, brought them hope.（馮慶華編著，“英漢互譯實用翻譯教程”，上海外語教育出版社，2000）（本科四年級以上）

Title: 漢英翻譯技巧：補(bǔ)償(Compensation)

C-E.1.九州 Jiuzhou--a poetic name for China-北京外國語大學(xué)英語系《漢英詞典》組編，《漢英詞典》，外語教學(xué)與研究出版社。

2.八股文 Eighth-part essay prescribed for the imperial civil service examinations--known for its rigidity of form and poverty of ideas-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。

3.狗咬呂洞賓,不識好人心 Like the dog that bit Lu Tungpin--you bite the hand that feeds you.-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。

4.貓哭老鼠--假慈悲 The cat weeping over the dead mouse--shed crocodile tears.-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。

5.蘇軾: Su Shi(formerly translated as Su Shih, 1037-1101),alias Su Dongpo, writer and calligrapher of the Song Dynasty.-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。

6.秀才 Xiucai, one who passed the imperial examination at the county level in the Ming and Qing Dynasties-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。7.牛郎織女 the Cowherd and the Girl Weaver-two figures in ancient Chinese fairy tale(Later it also refers to husband and wife who live far apart.)-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。

8.藍(lán)田人 Lantian Man, ape-man of about 600,000 years ago whose fossil remains were found in Lantian, Shanxi Province in 1964-吳景榮，程鎮(zhèn)球主編，《新時代漢英大詞典》，商務(wù)印書館。

9.開綠燈 turn on the green light(provide conveniences for certain affairs, so that they could proceed smoothly)-張震久，袁憲軍編，《漢英中國專有名稱和術(shù)語簡明詞典》，北京大學(xué)出版社。

10.梅雨季節(jié) plum rain season(about 1-month rainy season usu.beginning in early summer when plum fruit becomes ripe in the middle and lower reaches of the Yangtze River)or moldy season, a rainy season when everything goes moldy easily in the said area.(陳剛)Title: 漢英翻譯技巧：分譯(division)

(1)不久，她提著籃子回來了。Very soon she came back, holding a basket in her hand.（劉慎軍、李洪民、楊斌、劉寶編著，“按實例學(xué)英語翻譯”，北京工業(yè)大學(xué)出版社，2001）(2)他拉過一把椅子放在客人背后。He drew up a chair and placed it behind the visitor.（劉慎軍、李洪民、楊斌、劉寶編著，“按實例學(xué)英語翻譯”，北京工業(yè)大學(xué)出版社，2001）

(3)周萍一個人從飯廳走上來，望望花園，冷清清的，沒有一人。Zhou Ping appears from the dining room.He is alone.He peers out at the garden.It is silent and deserted.（宋天錫、袁江、袁冬娥編著，李鵬飛審校，“翻譯新概念英漢互譯實用教程”，國際工業(yè)出版社）

(4)他哼著曲子從山上走下來。He walked down the hill, singing softly to himself.（劉慎軍、李洪民、楊斌、劉寶編著，“按實例學(xué)英語翻?quot;，北京工業(yè)大學(xué)出版社，2001）

(5)人民的覺悟是不容易的，要去掉人民頭腦中的錯誤思想，需要我們做很多切切實實的工作。The political awakening of the people is not easy.It requires much earnest effort on our part to rid their minds of wrong ideas.（”英漢翻譯手冊“）

(6)我們的目的一定要達(dá)到，我們的目的一定能夠達(dá)到。Our goal must be attained.Our goal will be attained.（單其昌著，楊憲益校，”漢英翻譯技巧“，外語教學(xué)與研究出版社，1999）

(7)我們的革命已經(jīng)獲得全世界廣大人民的同情和歡呼，我們的朋友遍于全世界。Our revolution has won the sympathy and acclaim of the people of all countries.We have friends all over the world.（單其昌著，楊憲益校，”漢英翻譯技巧“，外語教學(xué)與研究出版社，1999）

(8)我們恢復(fù)和采取這些貿(mào)易方式的原因很簡單：我們出口商品就是為了滿足國外客戶消費(fèi)方面的需要。The reason why we have restored and adopted these trade practices is very simple.Our export commodities are for the use and consumption of our foreign customers.（單其昌著，楊憲益校，”漢英翻譯技巧“，外語教學(xué)與研究出版社，1999）

(9)這次大會充分發(fā)揚(yáng)了民主，大家心情舒暢，生動活潑；真正開成了一個團(tuán)結(jié)的大會，勝利的大會。The conference has given full expression to democracy;the atmosphere has been lively and the delegates have enjoyed ease of mind.Ours has indeed been a congress of unity, a congress of victory.（鐘述孔著 《英漢翻譯手冊》 商務(wù)印書館 1980?br>

(10)這些國家的共產(chǎn)黨和進(jìn)步黨派，正促使它們的政府和我們做生意，以致建立外交關(guān)系，這是善意的，這就是援助。The Communist Parties and progressive groups in these countries are urging their governments to established trade and even diplomatic relations with us.This is goodwill, this is help.（鐘述孔著 《英漢翻譯手冊》 商務(wù)印書館 1980）

Title: 漢英翻譯技巧：形合(Hypotaxis)

1.讓壁立的巖石，靜靜流著的小河，風(fēng)過處便竊竊私語的樹林，都作為自己的親密鄰居。

All the company she had were the steep cliffs, the gently flowing stream, and the trees that whispered in the wind.(楊莉藜<英漢互譯教程>河南大學(xué)出版社)2.漢朝人在宮殿和墓前的石室里，多喜歡繪畫或雕刻古來的帝王、孔子的弟子、列士、列女、孝子之類的圖。

People of the Han Dynasty liked to have paintings or caved relief of rulers of old, disciples of Confucius, eminent scholars and ladies and filial sons in the palaces or the stone chambers before their tombs.(楊莉藜<英漢互譯教程>河南大學(xué)出版社)3.不必說碧綠的菜畦，光滑的石井欄，高大的皂莢樹，紫紅的桑椹…… I need not speak of the green vegetable plots, the slippery stone coping round the well, the tall honey locust tree, or the purple mulberries.(楊莉藜<英漢互譯教程>河南大學(xué)出版社)4.盡著他的腿的力量走了一天，問了一天，沒有消息。

As long as his legs would move he walked on, asking, but by the end of the day he still had no news.(楊莉藜<英漢互譯教程>河南大學(xué)出版社)5.七股大水，從水庫的橋孔躍出，仿佛七幅閃光黃錦，直鋪下去，碰著嶙峋的亂石，激起一片雪白水珠，脫線一般，撒在洄漩的水面。

Seven torrents were rushing through the archways of the bridge like seven glittering rolls of cloth of gold cascading on to the jagged rocks below and scattering snow-white bubbles like a string of broken beads on the swirling water.(<中國現(xiàn)代散文卷>外語教學(xué)與研究出版社，中國文學(xué)出版社)6.月光如流水一般，靜靜地瀉在這一片葉子和花上。薄薄的青霧浮起在荷塘里，葉子和花仿佛在牛乳中洗過一樣；又像籠著輕紗的夢

Moonlight cascaded like water over the locus leaves and flowers, and a light blue mist floating up from the pool made them seem washed in milk or caught in a gauzy dream.。(<中國現(xiàn)代散文卷>外語教學(xué)與研究出版社，中國文學(xué)出版社)7.另一方面，必須用上述材料進(jìn)行廣泛宣傳，使人們認(rèn)識到，自然保護(hù)區(qū)是保護(hù)自然及文化遺產(chǎn)的基本單位，它們是在人類進(jìn)步里程中長期斗爭中形成的，對經(jīng)濟(jì)建設(shè)有著重要的作用。

On the other hand, it is necessary to carry on the extensive publicity, enabling the public to know that the protected areas are the basic unit of the management of the natural and cultural heritages which are formed in the struggle process against the nature by human beings and will play an important role in the economic construction.(馮志杰<漢英科技翻譯指要>中國對外翻譯出版公司)8.為保護(hù)海洋環(huán)境，促進(jìn)海洋經(jīng)濟(jì)發(fā)展，必須提高對海洋環(huán)境監(jiān)測的認(rèn)識，增加投入，加強(qiáng)”熱點“海域的監(jiān)測，減少海洋的損失，加強(qiáng)海洋生物監(jiān)測，避免潛伏的海洋災(zāi)害發(fā)生。

In order to promote the development of sustainable marine economy and conserve marine environment, we should pay great attention to reinforcing awareness of marine environmental monitoring, increasing investment and strengthening the monitoring in ”hot spots“ as well as biological monitoring to avoid marine calamity.(馮志杰<漢英科技翻譯指要>中國對外翻譯出版公司)9.飯菜雖然簡單，但別有一番風(fēng)味，屋外一團(tuán)漆黑，穿過松林的風(fēng)發(fā)出如火車的轟鳴聲，我們在搖曳不定的煤油燈下豪情與老人干杯。

When we enjoyed the simple but tasty food and drank cheerful toasts with the old man under the flickering oil-lamp, darkness reigned the outside world where the wind was thundering through the pinewood like a train.(<中國現(xiàn)代散文卷>外語教學(xué)與研究出版社，中國文學(xué)出版社)10.仍像往常一樣，把晴美的陽光抹上滿峽的樹林，叫帶露的樹葉都亮得耀人的眼睛。

Just as on any other day, the morning sun spread its fine light over the wooded valley, till the dewy leaves and grass glistened with a dazzling brightness.(<中國現(xiàn)代散文卷>外語教學(xué)與研究出版社，中國文學(xué)出版社)

Title: 漢英翻譯技巧：音譯(transliteration)

1.胡同：hutong(” Beijing Weekend “, No.520)2.餃子：jiaozi（《音義兼譯--外來語中譯之首選》，《中國翻譯》，2001/6）

3.武術(shù)：wushu（同上）4.普通話：putonghua（同上）

5.旗袍：qipao（同上）

6.上海： Shanghai（以上6例皆可作為”標(biāo)準(zhǔn)漢音“的例子。）

7.豆腐：tofu（《音義兼譯--外來語中譯之首選》，《中國翻譯》，2001/6 或p.25,《詞語翻譯叢談》，中國對外翻譯出版公司）/dou-fu(p.25,《詞語翻譯叢談》，中國對外翻譯出版公司)8.功夫： gongfu（《音義兼譯--外來語中譯之首選》，《中國翻譯》，2001/6）

9.乒乓：ping-pong（同上）

10.炒面：chow mien（同上）

(以上例8-10也可作為回譯EC部分的例子)

Title: 漢英翻譯技巧：習(xí)語(Translation of Idioms)直譯

(1)男男女女都七嘴八舌地說出他們的惦記和盼念。With seven mouths and eight tongues, all were talking together.They tried to tell how they had missed him.（張培基習(xí)語漢譯英研究）

(2)亡羊補(bǔ)牢 to mend the fold after a sheep is lost（同上）直譯加注

司馬昭之心，已是路人皆知。This Sima Zhao trick is obvious to every man in the street.(3)(Sima zhao was a prime minister of Wei(220-265)who nursed a secret ambition to usurp the throne.The emperor once remarked: ”Sima Zhao's intention is obvious to every man in the street.“（呂瑞昌等 漢英翻譯教程）

(4)你說這話，意思是要領(lǐng)導(dǎo)上三請諸葛？

What you say implies that the leadership should ask you three times, like Zhuge Liang, doesn't it?(Zhuge Liang, a statesman and strategist in the State of Shu during the period of wisdom and resourcefulness in Chinese folklore.)（張培基習(xí)語漢譯英研究）同義習(xí)語套用

(5)晴天霹靂

a bolt from the blue(同上)(6)只有破釜沉舟地跟他們拼，還許有翻身的一天。

All you can do is to burn your boats and fight them in the hope that one day you'll come out on top.（同上）意譯

(7)我要有個三長兩短，你給玉山捎個話！

If anything should happen to me , let Yushan know!(呂瑞昌等 漢英翻譯教程)(8)大智若愚 A truly wise person does not show off his(her)ability.（張培基習(xí)語漢譯英研究）

直譯加意譯

(9)瞎子點燈白費(fèi)蠟 as useless as a blind man lighting a candle(張培基習(xí)語漢譯英研究)(10)梅她一個單身人，無親無故。

Mei was all by herself and far from home, without a single relative or friend to help her.（呂瑞昌等 漢英翻譯教程）臨時變體

(11)換湯不換藥（張培基習(xí)語漢譯英研究）

old wine in new bottles(原有習(xí)語為 new wine in old bottles)(12)守株待兔（同上）

to wait for gains without pains(原有習(xí)語為 No pains, no gains)省略

(13)這女子真有沉魚落雁之容，閉月羞花之貌。（張培基習(xí)語漢譯英研究）The girl's beauty would put the flowers to shame.(14)冷淡的陽關(guān)照著他們的愁眉苦臉和長發(fā)白眼。（呂瑞昌等 漢譯英教程）The cold, pale sunlight fell on their gloomy faces, long hair and lusterless eyes.增添

(15)螳螂捕蟬，黃雀在后(張培基習(xí)語漢譯英研究)The mantis stalks the cicada, unaware of the oriole lurking behind itself.(16)樹倒猢猻散（同上）

Once the tree falls, the monkeys on it will flee helter-skelter.混喻的回避

(17)讓我們乘風(fēng)破浪，奮勇前進(jìn)。（同上）

Let us march forward valiantly, braving all difficulties and hardships!(如果直譯成Let us march forward valiantly, braving winds and waves 之類的句子，其中就出現(xiàn)了march和 waves 的混喻問題。解決的辦法是1，”乘風(fēng)破浪“和”奮勇前進(jìn)“在意義上本是相互重復(fù)，加以”乘風(fēng)破浪“這個習(xí)語由于使用過多實際上以不存在什么形象性，英譯時可略成Let us march forward valiantly!2, 意譯法處理習(xí)語”乘風(fēng)破浪“，成Let us march forward valiantly, braving all difficulties and hardships!)粗俗語的回避

借用同義習(xí)語或意譯等方法回避。

(18)她不滿意人家說她是三槍打不出一個悶屁的落后的人。（同上）It annoyed her that people should say that she was backward and that no amount of coaxing would open her mouth to speak.相對應(yīng)的英語粗俗語來代替原文中的漢語粗俗語。(19)混蛋！再打一個電話去！叫他馬上來見我?。ㄍ希?/p>

”You blasted idiots!Go and ring him up again and tell him to come round at once!"

第三篇：中英文翻譯

Fundamentals This chapter describes the fundamentals of today’s wireless communications.First a detailed description of the radio channel and its modeling are presented, followed by the introduction of the principle of OFDM multi-carrier transmission.In addition, a general overview of the spread spectrum technique, especially DS-CDMA, is given and examples of potential applications for OFDM and DS-CDMA are analyzed.This introduction is essential for a better understanding of the idea behind the combination of OFDM with the spread spectrum technique, which is briefly introduced in the last part of this chapter.1.1 Radio Channel Characteristics Understanding the characteristics of the communications medium is crucial for the appropriate selection of transmission system architecture, dimensioning of its components, and optimizing system parameters, especially since mobile radio channels are considered to be the most difficult channels, since they suffer from many imperfections like multipath fading, interference, Doppler shift, and shadowing.The choice of system components is totally different if, for instance, multipath propagation with long echoes dominates the radio propagation.Therefore, an accurate channel model describing the behavior of radio wave propagation in different environments such as mobile/fixed and indoor/outdoor is needed.This may allow one, through simulations, to estimate and validate the performance of a given transmission scheme in its several design phases.1.1.1 Understanding Radio Channels In mobile radio channels(see Figure 1-1), the transmitted signal suffers from different effects, which are characterized as follows: Multipath propagation occurs as a consequence of reflections, scattering, and diffraction of the transmitted electromagnetic wave at natural and man-made objects.Thus, at the receiver antenna, a multitude of waves arrives from many different directions with different delays, attenuations, and phases.The superposition of these waves results in amplitude and phase variations of the composite received signal.Doppler spread is caused by moving objects in the mobile radio channel.Changes in the phases and amplitudes of the arriving waves occur which lead to time-variant multipath propagation.Even small movements on the order of the wavelength may result in a totally different wave superposition.The varying signal strength due to time-variant multipath propagation is referred to as fast fading.Shadowing is caused by obstruction of the transmitted waves by, e.g., hills, buildings, walls, and trees, which results in more or less strong attenuation of the signal strength.Compared to fast fading, longer distances have to be covered to significantly change the shadowing constellation.The varying signal strength due to shadowing is called slow fading and can be described by a log-normal distribution [36].Path loss indicates how the mean signal power decays with distance between transmitter and receiver.In free space, the mean signal power decreases with the square of the distance between base station(BS)and terminal station(TS).In a mobile radio channel, where often no line of sight(LOS)path exists, signal power decreases with a power higher than two and is typically in the order of three to five.Variations of the received power due to shadowing and path loss can be efficiently counteracted by power control.In the following, the mobile radio channel is described with respect to its fast fading characteristic.1.1.2 Channel Modeling The mobile radio channel can be characterized by the time-variant channel impulse response h(τ , t)or by the time-variant channel transfer function H(f, t), which is the Fourier transform of h(τ , t).The channel impulse response represents the response of the channel at time t due to an impulse applied at time t ? τ.The mobile radio channel is assumed to be a wide-sense stationary random process, i.e., the channel has a fading statistic that remains constant over short periods of time or small spatial distances.In environments with multipath propagation, the channel impulse response is composed of a large number of scattered impulses received over Np different paths，Where

and ap, fD,p, ?p, and τp are the amplitude, the Doppler frequency, the phase, and the propagation delay, respectively, associated with path p, p = 0,..., Np ? 1.The assigned channel transfer function is

The delays are measured relative to the first detectable path at the receiver.The Doppler Frequency

depends on the velocity v of the terminal station, the speed of light c, the carrier frequency fc, and the angle of incidence αp of a wave assigned to path p.A channel impulse response with corresponding channel transfer function is illustrated in Figure 1-2.The delay power density spectrum ρ(τ)that characterizes the frequency selectivity of the mobile radio channel gives the average power of the channel output as a function of the delay τ.The mean delay τ , the root mean square(RMS)delay spread τRMS and the maximum delay τmax are characteristic parameters of the delay power density spectrum.The mean delay is

Where

Figure 1-2 Time-variant channel impulse response and channel transfer function with frequency-selective fading is the power of path p.The RMS delay spread is defined as Similarly, the Doppler power density spectrum S(fD)can be defined that characterizes the time variance of the mobile radio channel and gives the average power of the channel output as a function of the Doppler frequency fD.The frequency dispersive properties of multipath channels are most commonly quantified by the maximum occurring Doppler frequency fDmax and the Doppler spread fDspread.The Doppler spread is the bandwidth of the Doppler power density spectrum and can take on values up to two times |fDmax|, i.e.，1.1.3Channel Fade Statistics The statistics of the fading process characterize the channel and are of importance for channel model parameter specifications.A simple and often used approach is obtained from the assumption that there is a large number of scatterers in the channel that contribute to the signal at the receiver side.The application of the central limit theorem leads to a complex-valued Gaussian process for the channel impulse response.In the absence of line of sight(LOS)or a dominant component, the process is zero-mean.The magnitude of the corresponding channel transfer function

is a random variable, for brevity denoted by a, with a Rayleigh distribution given by

Where

is the average power.The phase is uniformly distributed in the interval [0, 2π].In the case that the multipath channel contains a LOS or dominant component in addition to the randomly moving scatterers, the channel impulse response can no longer be modeled as zero-mean.Under the assumption of a complex-valued Gaussian process for the channel impulse response, the magnitude a of the channel transfer function has a Rice distribution given by

The Rice factor KRice is determined by the ratio of the power of the dominant path to thepower of the scattered paths.I0 is the zero-order modified Bessel function of first kind.The phase is uniformly distributed in the interval [0, 2π].1.1.4Inter-Symbol(ISI)and Inter-Channel Interference(ICI)The delay spread can cause inter-symbol interference(ISI)when adjacent data symbols overlap and interfere with each other due to different delays on different propagation paths.The number of interfering symbols in a single-carrier modulated system is given by

For high data rate applications with very short symbol duration Td < τmax, the effect of ISI and, with that, the receiver complexity can increase significantly.The effect of ISI can be counteracted by different measures such as time or frequency domain equalization.In spread spectrum systems, rake receivers with several arms are used to reduce the effect of ISI by exploiting the multipath diversity such that individual arms are adapted to different propagation paths.If the duration of the transmitted symbol is significantly larger than the maximum delay Td τmax, the channel produces a negligible amount of ISI.This effect is exploited with multi-carrier transmission where the duration per transmitted symbol increases with the number of sub-carriers Nc and, hence, the amount of ISI decreases.The number of interfering symbols in a multi-carrier modulated system is given by

Residual ISI can be eliminated by the use of a guard interval(see Section 1.2).The maximum Doppler spread in mobile radio applications using single-carrier modulation is typically much less than the distance between adjacent channels, such that the effect of interference on adjacent channels due to Doppler spread is not a problem for single-carrier modulated systems.For multi-carrier modulated systems, the sub-channel spacing Fs can become quite small, such that Doppler effects can cause significant ICI.As long as all sub-carriers are affected by a common Doppler shift fD, this Doppler shift can be compensated for in the receiver and ICI can be avoided.However, if Doppler spread in the order of several percent of the sub-carrier spacing occurs, ICI may degrade the system performance significantly.To avoid performance degradations due to ICI or more complex receivers with ICI equalization, the sub-carrier spacing Fs should be chosen as

such that the effects due to Doppler spread can be neglected(see Chapter 4).This approach corresponds with the philosophy of OFDM described in Section 1.2 and is followed in current OFDM-based wireless standards.Nevertheless, if a multi-carrier system design is chosen such that the Doppler spread is in the order of the sub-carrier spacing or higher, a rake receiver in the frequency domain can be used [22].With the frequency domain rake receiver each branch of the rake resolves a different Doppler frequency.1.1.5Examples of Discrete Multipath Channel Models Various discrete multipath channel models for indoor and outdoor cellular systems with different cell sizes have been specified.These channel models define the statistics of the 5 discrete propagation paths.An overview of widely used discrete multipath channel models is given in the following.COST 207 [8]: The COST 207 channel models specify four outdoor macro cell propagation scenarios by continuous, exponentially decreasing delay power density spectra.Implementations of these power density spectra by discrete taps are given by using up to 12 taps.Examples for settings with 6 taps are listed in Table 1-1.In this table for several propagation environments the corresponding path delay and power profiles are given.Hilly terrain causes the longest echoes.The classical Doppler spectrum with uniformly distributed angles of arrival of the paths can be used for all taps for simplicity.Optionally, different Doppler spectra are defined for the individual taps in [8].The COST 207 channel models are based on channel measurements with a bandwidth of 8–10 MHz in the 900-MHz band used for 2G systems such as GSM.COST 231 [9] and COST 259 [10]: These COST actions which are the continuation of COST 207 extend the channel characterization to DCS 1800, DECT, HIPERLAN and UMTS channels, taking into account macro, micro, and pico cell scenarios.Channel models with spatial resolution have been defined in COST 259.The spatial component is introduced by the definition of several clusters with local scatterers, which are located in a circle around the base station.Three types of channel models are defined.The macro cell type has cell sizes from 500 m up to 5000 m and a carrier frequency of 900 MHz or 1.8 GHz.The micro cell type is defined for cell sizes of about 300 m and a carrier frequency of 1.2 GHz or 5 GHz.The pico cell type represents an indoor channel model with cell sizes smaller than 100 m in industrial buildings and in the order of 10 m in an office.The carrier frequency is 2.5 GHz or 24 GHz.COST 273: The COST 273 action additionally takes multi-antenna channel models into account, which are not covered by the previous COST actions.CODIT [7]: These channel models define typical outdoor and indoor propagation scenarios for macro, micro, and pico cells.The fading characteristics of the various propagation environments are specified by the parameters of the Nakagami-m distribution.Every environment is defined in terms of a number of scatterers which can take on values up to 20.Some channel models consider also the angular distribution of the scatterers.They have been developed for the investigation of 3G system proposals.Macro cell channel type models have been developed for carrier frequencies around 900 MHz with 7 MHz bandwidth.The micro and pico cell channel type models have been developed for carrier frequencies between 1.8 GHz and 2 GHz.The bandwidths of the measurements are in the range of 10–100 MHz for macro cells and around 100 MHz for pico cells.JTC [28]: The JTC channel models define indoor and outdoor scenarios by specifying 3 to 10 discrete taps per scenario.The channel models are designed to be applicable for wideband digital mobile radio systems anticipated as candidates for the PCS(Personal Communications Systems)common air interface at carrier frequencies of about 2 GHz.UMTS/UTRA [18][44]: Test propagation scenarios have been defined for UMTS and UTRA system proposals which are developed for frequencies around 2 GHz.The modeling of the multipath propagation corresponds to that used by the COST 207 channel models.HIPERLAN/2 [33]: Five typical indoor propagation scenarios for wireless LANs in the 5 GHz frequency band have been defined.Each scenario is described by 18discrete taps of the delay power density spectrum.The time variance of the channel(Doppler spread)is modeled by a classical Jake’s spectrum with a maximum terminal speed of 3 m/h.Further channel models exist which are, for instance, given in [16].1.1.6Multi-Carrier Channel Modeling Multi-carrier systems can either be simulated in the time domain or, more computationally efficient, in the frequency domain.Preconditions for the frequency domain implementation are the absence of ISI and ICI, the frequency nonselective fading per sub-carrier, and the time-invariance during one OFDM symbol.A proper system design approximately fulfills these preconditions.The discrete channel transfer function adapted to multi-carrier signals results in

where the continuous channel transfer function H(f, t)is sampled in time at OFDM symbol rate s and in frequency at sub-carrier spacing Fs.The duration

s is the total OFDM symbol duration including the guard interval.Finally, a symbol transmitted onsub-channel n of the OFDM symbol i is multiplied by the resulting fading amplitude an,i and rotated by a random phase ?n,i.The advantage of the frequency domain channel model is that the IFFT and FFT operation for OFDM and inverse OFDM can be avoided and the fading operation results in one complex-valued multiplication per sub-carrier.The discrete multipath channel models introduced in Section 1.1.5 can directly be applied to(1.16).A further simplification of the channel modeling for multi-carrier systems is given by using the so-called uncorrelated fading channel models.1.1.6.1Uncorrelated Fading Channel Models for Multi-Carrier Systems These channel models are based on the assumption that the fading on adjacent data symbols after inverse OFDM and de-interleaving can be considered as uncorrelated [29].This assumption holds when, e.g., a frequency and time interleaver with sufficient interleaving depth is applied.The fading amplitude an,i is chosen from a distribution p(a)according to the considered cell type and the random phase ?n,I is uniformly distributed in the interval [0,2π].The resulting complex-valued channel fading coefficient is thus generated independently for each sub-carrier and OFDM symbol.For a propagation scenario in a macro cell without LOS, the fading amplitude an,i is generated by a Rayleigh distribution and the channel model is referred to as an uncorrelated Rayleigh fading channel.For smaller cells where often a dominant propagation component occurs, the fading amplitude is chosen from a Rice distribution.The advantages of the uncorrelated fading channel models for multi-carrier systems are their simple implementation in the frequency domain and the simple reproducibility of the simulation results.1.1.7Diversity The coherence bandwidth of a mobile radio channel is the bandwidth over which the signal propagation characteristics are correlated and it can be approximated by

The channel is frequency-selective if the signal bandwidth B is larger than the coherence bandwidth.On the other hand, if B is smaller than , the channel is frequency nonselective or flat.The coherence bandwidth of the channel is of importance for evaluating the performance of spreading and frequency interleaving techniques that try to exploit the inherent frequency diversity Df of the mobile radio channel.In the case of multi-carrier transmission, frequency diversity is exploited if the separation of sub-carriers transmitting the same information exceeds the coherence bandwidth.The maximum achievable frequency diversity Df is given by the ratio between the signal bandwidth B and the coherence bandwidth，The coherence time of the channel is the duration over which the channel characteristics can be considered as time-invariant and can be approximated by

If the duration of the transmitted symbol is larger than the coherence time, the channel is time-selective.On the other hand, if the symbol duration is smaller than , the channel is time nonselective during one symbol duration.The coherence time of the channel is of importance for evaluating the performance of coding and interleaving techniques that try to exploit the inherent time diversity DO of the mobile radio channel.Time diversity can be exploited if the separation between time slots carrying the same information exceeds the coherence time.A number of Ns successive time slots create a time frame of duration Tfr.The maximum time diversity Dt achievable in one time frame is given by the ratio between the duration of a time frame and the coherence time, A system exploiting frequency and time diversity can achieve the overall diversity

The system design should allow one to optimally exploit the available diversity DO.For instance, in systems with multi-carrier transmission the same information should be transmitted on different sub-carriers and in different time slots, achieving uncorrelated faded replicas of the information in both dimensions.Uncoded multi-carrier systems with flat fading per sub-channel and time-invariance during one symbol cannot exploit diversity and have a poor performance in time and frequency selective fading channels.Additional methods have to be applied to exploit diversity.One approach is the use of data spreading where each data symbol is spread by a spreading code of length L.This, in combination with interleaving, can achieve performance results which are given for

by the closed-form solution for the BER for diversity reception in Rayleigh fading channels according to [40]

Whererepresents the combinatory function，and σ2 is the variance of the noise.As soon as the interleaving is not perfect or the diversity offered by the channel is smaller than the spreading code length L, or MCCDMA with multiple access interference is applied,(1.22)is a lower bound.For L = 1, the performance of an OFDM system without forward error correction(FEC)is obtained, 9

which cannot exploit any diversity.The BER according to(1.22)of an OFDM(OFDMA, MC-TDMA)system and a multi-carrier spread spectrum(MC-SS)system with different spreading code lengths L is shown in Figure 1-3.No other diversity techniques are applied.QPSK modulation is used for symbol mapping.The mobile radio channel is modeled as uncorrelated Rayleigh fading channel(see Section 1.1.6).As these curves show, for large values of L, the performance of MC-SS systems approaches that of an AWGN channel.Another form of achieving diversity in OFDM systems is channel coding by FEC, where the information of each data bit is spread over several code bits.Additional to the diversity gain in fading channels, a coding gain can be obtained due to the selection of appropriate coding and decoding algorithms.中文翻譯 1基本原理

這章描述今日的基本面的無線通信。第一一個的詳細(xì)說明無線電頻道，它的模型被介紹，跟隨附近的的介紹的原則的參考正交頻分復(fù)用多載波傳輸。此外，一個一般概觀的擴(kuò)頻技術(shù)，尤其ds-cdma，被給，潛力的例子申請參考正交頻分復(fù)用，DS對1。分配的通道傳輸功能是

有關(guān)的延誤測量相對于第一個在接收器檢測到的路徑。多普勒頻率

取決于終端站，光速c，載波頻率fc的速度和發(fā)病路徑分配給速度v波αp角度頁具有相應(yīng)通道傳輸信道沖激響應(yīng)函數(shù)圖1-2所示。

延遲功率密度譜ρ（τ）為特征的頻率選擇性移動無線電頻道給出了作為通道的輸出功能延遲τ平均功率。平均延遲τ，均方根（RMS）的時延擴(kuò)展τRMS和最大延遲τmax都是延遲功率密度譜特征參數(shù)。平均時延特性參數(shù)為

有

圖1-2時變信道沖激響應(yīng)和通道傳遞函數(shù)頻率選擇性衰落是權(quán)力頁的路徑均方根時延擴(kuò)展的定義為 同樣，多普勒頻譜的功率密度（FD）的特點可以定義

在移動時變無線信道，并給出了作為一種金融衍生工具功能的多普勒頻率通道輸出的平均功率。多徑信道頻率分散性能是最常見的量化發(fā)生的多普勒頻率和多普勒fDmax蔓延fDspread最大。多普勒擴(kuò)散是功率密度的多普勒頻譜帶寬，可價值觀需要兩年時間| fDmax|，即

1.1.3頻道淡出統(tǒng)計

在衰落過程中的統(tǒng)計特征和重要的渠道是信道模型參數(shù)規(guī)格。一個簡單而經(jīng)常使用的方法是從假設(shè)有一個通道中的散射，有助于在大量接收端的信號。該中心極限定理的應(yīng)用導(dǎo)致了復(fù)雜的值的高斯信道沖激響應(yīng)過程。在對視線（LOS）或線的主要組成部分的情況下，這個過程是零的意思。相應(yīng)的通道傳遞函數(shù)幅度

是一個隨機(jī)變量，通過給定一個簡短表示由瑞利分布，有

是的平均功率。相均勻分布在區(qū)間[0，2π]。

在案件的多通道包含洛杉磯的或主要組件除了隨機(jī)移動散射，通道脈沖響應(yīng)可以不再被建模為均值為零。根據(jù)信道脈沖響應(yīng)的假設(shè)一個復(fù)雜的值高斯過程，其大小通道的傳遞函數(shù)A的水稻分布給出

賴斯因素KRice是由占主導(dǎo)地位的路徑權(quán)力的威力比分散的路徑。I0是零階貝塞爾函數(shù)的第一階段是一致kind.The在區(qū)間[0，2π]分發(fā)。

1.1.4符號間（ISI）和通道間干擾（ICI）

延遲的蔓延引起的符號間干擾（ISI）當(dāng)相鄰的數(shù)據(jù)符號上的重疊與互相不同的傳播路徑，由于不同的延遲干涉。符號的干擾在單載波調(diào)制系統(tǒng)的號碼是給予

對于高數(shù)據(jù)符號持續(xù)時間很短運(yùn)輸署<蟿MAX時，ISI的影響，這樣一來，速率應(yīng)用，接收機(jī)的復(fù)雜性大大增加。對干擾影響，可以抵消，如時間或頻域均衡不同的措施。在擴(kuò)頻系統(tǒng)，與幾個臂Rake接收機(jī)用于減少通過利用多徑分集等，個別武器適應(yīng)不同的傳播路徑的干擾影響。

如果發(fā)送符號的持續(xù)時間明顯高于大的最大延遲運(yùn)輸署蟿最大，渠道產(chǎn)生ISI的微不足道。這種效果是利用多載波傳輸?shù)牡胤?，每發(fā)送符號的增加與子載波數(shù)控數(shù)目，因此，ISI的金額減少的持續(xù)時間。符號的干擾多載波調(diào)制系統(tǒng)的號碼是給予

可以消除符號間干擾由一個保護(hù)間隔（見1.2節(jié)）的使用。

最大多普勒在移動無線應(yīng)用傳播使用單載波調(diào)制通常比相鄰?fù)ǖ?，這樣，干擾對由于多普勒傳播相鄰?fù)ǖ赖淖饔貌皇且粋€單載波調(diào)制系統(tǒng)的問題距離。對于多載波調(diào)制系統(tǒng)，子通道間距FS可以變得非常小，這樣可以造成嚴(yán)重的多普勒效應(yīng)ICI的。只要所有子載波只要是一個共同的多普勒頻移金融衍生工具的影響，這可以補(bǔ)償多普勒頻移在接收器和ICI是可以避免的。但是，如果在對多普勒子載波間隔為幾個百分點的蔓延情況，卜內(nèi)門可能會降低系統(tǒng)的性能顯著。為了避免性能降級或因與ICI卜內(nèi)門更復(fù)雜的接收機(jī)均衡，子載波間隔財政司司長應(yīng)定為

這樣說，由于多普勒效應(yīng)可以忽略不擴(kuò)散（見第4章）。這種方法對應(yīng)于OFDM的1.2節(jié)中所述，是目前基于OFDM的無線標(biāo)準(zhǔn)遵循的理念。

不過，如果多載波系統(tǒng)的設(shè)計選擇了這樣的多普勒展寬在子載波間隔或更高，秩序是在頻率RAKE接收機(jī)域名可以使用[22]。隨著頻域RAKE接收機(jī)每個支部耙解決了不同的多普勒頻率。

1.1.5多徑信道模型的離散的例子

各類離散多與不同的細(xì)胞大小的室內(nèi)和室外蜂窩系統(tǒng)的信道模型已經(jīng)被指定。這些通道模型定義的離散傳播路徑的統(tǒng)計信息。一種廣泛使用的離散多徑信道模型概述于下。造價207[8]：成本207信道模型指定連續(xù)四個室外宏蜂窩傳播方案，指數(shù)下降延遲功率密度譜。這些頻道功率密度的離散譜的實現(xiàn)都是通過使用多達(dá)12個頻道。與6頻道設(shè)置的示例列于表1-1。在這種傳播環(huán)境的幾個表中的相應(yīng)路徑延遲和電源配置給出。丘陵地形導(dǎo)致最長相呼應(yīng)。

經(jīng)典的多普勒頻譜與均勻分布的到達(dá)角路徑可以用于簡化所有的頻道?；蛘撸煌亩嗥绽兆V定義在[8]個人頻道。207信道的成本模型是基于一個8-10兆赫的2G，如GSM系統(tǒng)中使用的900兆赫頻段信道帶寬的測量。造價231[9]和造價259[10]：這些費(fèi)用是行動的延續(xù)成本207擴(kuò)展通道特性到DCS1800的DECT，HIPERLAN和UMTS的渠道，同時考慮到宏觀，微觀和微微小區(qū)的情況為例?？臻g分辨率與已定義的通道模型在造價259?？臻g部分是介紹了與當(dāng)?shù)厣⑸?，這是在基站周圍設(shè)幾組圓的定義。三種類型的通道模型定義。宏細(xì)胞類型具有高達(dá)500?5000米，載波頻率為900兆赫或1.8 GHz的單元尺寸。微細(xì)胞類型被定義為細(xì)胞體積約300米，1.2 GHz或5 GHz載波頻率。細(xì)胞類型代表的Pico與細(xì)胞體積小于100工業(yè)建筑物和辦公室中的10 m階米室內(nèi)信道模型。載波頻率為2.5 GHz或24千兆赫。造價273：成本273行動另外考慮到多天線信道模型，這是不是由先前的費(fèi)用的行為包括在內(nèi)。

CODIT [7]：這些通道模型定義的宏，微，微微蜂窩和室外和室內(nèi)傳播的典型案例。各種傳播環(huán)境的衰落特性是指定的在NakagamiSS）的不同擴(kuò)頻碼L是長度，如圖1-3所示的系統(tǒng)。沒有其他的分集技術(shù)被應(yīng)用。QPSK調(diào)制用于符號映射。移動無線信道建模為不相關(guān)瑞利衰落信道（見1.1.6）。由于這些曲線顯示，辦法，AWGN信道的一對L時，對MC-SS系統(tǒng)性能有很大價值。

另一種實現(xiàn)形式的OFDM系統(tǒng)的多樣性是由前向糾錯信道編碼，在這里，每個數(shù)據(jù)位的信息分散在幾個代碼位。附加在衰落信道分集增益，編碼增益一個可因適當(dāng)?shù)木幋a和解碼算法的選擇。

第四篇：中英文翻譯

蓄電池 battery 充電 converter 轉(zhuǎn)換器 charger

開關(guān)電器 Switch electric 按鈕開關(guān) Button to switch 電源電器 Power electric 插頭插座 Plug sockets

第五篇：中英文翻譯

特種加工工藝

介紹

傳統(tǒng)加工如車削、銑削和磨削等，是利用機(jī)械能將金屬從工件上剪切掉，以加工成孔或去除余料。特種加工是指這樣一組加工工藝，它們通過各種涉及機(jī)械能、熱能、電能、化學(xué)能或及其組合形式的技術(shù)，而不使用傳統(tǒng)加工所必需的尖銳刀具來去除工件表面的多余材料。

傳統(tǒng)加工如車削、鉆削、刨削、銑削和磨削，都難以加工特別硬的或脆性材料。采用傳統(tǒng)方法加工這類材料就意味著對時間和能量要求有所增加，從而導(dǎo)致成本增加。在某些情況下，傳統(tǒng)加工可能行不通。由于在加工過程中會產(chǎn)生殘余應(yīng)力，傳統(tǒng)加工方法還會造成刀具磨損，損壞產(chǎn)品質(zhì)量。基于以下各種特殊理由，特種加工工藝或稱為先進(jìn)制造工藝，可以應(yīng)用于采用傳統(tǒng)加工方法不可行，不令人滿意或者不經(jīng)濟(jì)的場合：

1.對于傳統(tǒng)加工難以夾緊的非常硬的脆性材料； 2.當(dāng)工件柔性很大或很薄時； 3.當(dāng)零件的形狀過于復(fù)雜時；

4.要求加工出的零件沒有毛刺或殘余應(yīng)力。

傳統(tǒng)加工可以定義為利用機(jī)械（運(yùn)動）能的加工方法，而特種加工利用其他形式的能量，主要有如下三種形式： 1.熱能； 2.化學(xué)能； 3.電能。

為了滿足額外的加工條件的要求，已經(jīng)開發(fā)出了幾類特種加工工藝。恰當(dāng)?shù)厥褂眠@些加工工藝可以獲得很多優(yōu)于傳統(tǒng)加工工藝的好處。常見的特種加工工藝描述如下。

電火花加工

電火花加工是使用最為廣泛的特種加工工藝之一。相比于利用不同刀具進(jìn)行金屬切削和磨削的常規(guī)加工，電火花加工更為吸引人之處在于它利用工件和電極間的一系列重復(fù)產(chǎn)生的（脈沖）離散電火花所產(chǎn)生的熱電作用，從工件表面通過電腐蝕去除掉多余的材料。

傳統(tǒng)加工工藝依靠硬質(zhì)刀具或磨料去除較軟的材料，而特種加工工藝如電火花加工，則是利用電火花或熱能來電蝕除余料，以獲得所需的零件形狀。因此，材料的硬度不再是電火花加工中的關(guān)鍵因素。

電火花加工是利用存儲在電容器組中的電能（一般為50V/10A量級）在工具電極（陰極）和工件電極（陽極）之間的微小間隙間進(jìn)行放電來去除材料的。如圖6.1所示，在EDM操作初始，在工具電極和工件電極間施以高電壓。這個高電壓可以在工具電極和工件電極窄縫間的絕緣電介質(zhì)中產(chǎn)生電場。這就會使懸浮在電介質(zhì)中的導(dǎo)電粒子聚集在電場最強(qiáng)處。當(dāng)工具電極和工件電極之間的勢能差足夠大時，電介質(zhì)被擊穿，從而在電介質(zhì)流體中會產(chǎn)生瞬時電火花，將少量材料從工件表面蝕除掉。每次電火花所蝕除掉的材料量通常在10-5～10-6mm3范圍內(nèi)。電極之間的間隙只有千分之幾英寸，通過伺服機(jī)構(gòu)驅(qū)動和控制工具電極的進(jìn)給使該值保持常量。化學(xué)加工

化學(xué)加工是眾所周知的特種加工工藝之一，它將工件浸入化學(xué)溶液通過腐蝕溶解作用將多余材料從工件上去除掉。該工藝是最古老的特種加工工藝，主要用于凹腔和輪廓加工，以及從具有高的比剛度的零件表面去除余料?；瘜W(xué)加工廣泛用于為多種工業(yè)應(yīng)用（如微機(jī)電系統(tǒng)和半導(dǎo)體行業(yè)）制造微型零件。

化學(xué)加工將工件浸入到化學(xué)試劑或蝕刻劑中，位于工件選區(qū)的材料通過發(fā)生在金屬溶蝕或化學(xué)溶解過程中的電化學(xué)微電池作用被去除掉。而被稱為保護(hù)層的特殊涂層所保護(hù)下的區(qū)域中的材料則不會被去除。不過，這種受控的化學(xué)溶解過程同時也會蝕除掉所以暴露在表面的材料，盡管去除的滲透率只有0.0025～0.1 mm/min。該工藝采用如下幾種形式：凹坑加工、輪廓加工和整體金屬去除的化學(xué)銑，在薄板上進(jìn)行蝕刻的化學(xué)造型，在微電子領(lǐng)域中利用光敏抗蝕劑完成蝕刻的光化學(xué)加工(PCM)，采用弱化學(xué)試劑進(jìn)行拋光或去毛刺的電化學(xué)拋光，以及利用單一化學(xué)活性噴射的化學(xué)噴射加工等。如圖6.2a所示的化學(xué)加工示意圖，由于蝕刻劑沿垂直和水平方向開始蝕除材料，鉆蝕（又稱為淘蝕）量進(jìn)一步加大，如圖6.2b所示的保護(hù)體邊緣下面的區(qū)域。在化學(xué)造型中最典型的公差范圍可保持在材料厚度的±10%左右。為了提高生產(chǎn)率，在化學(xué)加工前，毛坯件材料應(yīng)采用其他工藝方法（如機(jī)械加工）進(jìn)行預(yù)成形加工。濕度和溫度也會導(dǎo)致工件尺寸發(fā)生改變。通過改變蝕刻劑和控制工件加工環(huán)境，這種尺寸改變可以減小到最小。

電化學(xué)加工

電化學(xué)金屬去除方法是一種最有用的特種加工方法。盡管利用電解作用作為金屬加工手段是近代的事，但其基本原理是法拉第定律。利用陽極溶解，電化學(xué)加工可以去除具有導(dǎo)電性質(zhì)工件的材料，而無須機(jī)械能和熱能。這個加工過程一般用于在高強(qiáng)度材料上加工復(fù)雜形腔和形狀，特別是在航空工業(yè)中如渦輪機(jī)葉片、噴氣發(fā)動機(jī)零件和噴嘴，以及在汽車業(yè)（發(fā)動機(jī)鑄件和齒輪）和醫(yī)療衛(wèi)生業(yè)中。最近，還將電化學(xué)加工應(yīng)用于電子工業(yè)的微加工中。

圖6.3所示的是一個去除金屬的電化學(xué)加工過程，其基本原理與電鍍原理正好相反。在電化學(xué)加工過程中，從陽極（工件）上蝕除下的粒子移向陰極（加工工具）。金屬的去除由一個合適形狀的工具電極來完成，最終加工出來的零件具有給定的形狀、尺寸和表面光潔度。在電化學(xué)加工過程中，工具電極的形狀逐漸被轉(zhuǎn)移或復(fù)制到工件上。型腔的形狀正好是與工具相匹配的陰模的形狀。為了獲得電化學(xué)過程形狀復(fù)制的高精度和高的材料去除率，需要采用高的電流密度（范圍為10～100 A/cm2)和低電壓（范圍為8～30V）。通過將工具電極向去除工件表面材料的方向進(jìn)給，加工間隙要維持在0.1 mm范圍內(nèi)，而進(jìn)給率一般為0.1～20 mm/min左右。泵壓后的電解液以高達(dá)5～50 m/s的速度通過間隙，將溶解后的材料、氣體和熱量帶走。因此，當(dāng)被蝕除的材料還沒來得及附著到工具電極上時，就被電解液帶走了。

作為一種非機(jī)械式金屬去除加工方法，ECM可以以高切削量加工任何導(dǎo)電材料，而無須考慮材料的機(jī)械性能。特別是在電化學(xué)加工中，材料去除率與被加工件的硬度、韌性及其他特性無關(guān)。對于利用機(jī)械方法難于加工的材料，電化學(xué)加工可以保證將該材料加工出復(fù)雜形狀的零件，這就不需要制造出硬度高于工件的刀具，而且也不會造成刀具磨損。由于工具和工件間沒有接觸，電化學(xué)加工是加工薄壁、易變形零件及表面容易破裂的脆性材料的首選。激光束加工

LASER是英文Light Amplification by Stimulated Emission of Radiation 各單詞頭一個字母所組成的縮寫詞。雖然激光在某些場合可用來作為放大器，但它的主要用途是光激射振蕩器，或者是作為將電能轉(zhuǎn)換為具有高度準(zhǔn)直性光束的換能器。由激光發(fā)射出的光能具有不同于其他光源的特點：光譜純度好、方向性好及具有高的聚焦功率密度。

激光加工就是利用激光和和靶材間的相互作用去除材料。簡而言之，這些加工工藝包括激光打孔、激光切割、激光焊接、激光刻槽和激光刻劃等。

激光加工（圖6.4）可以實現(xiàn)局部的非接觸加工，而且對加工件幾乎沒有作用力。這種加工工藝去除材料的量很小，可以說是“逐個原子”地去除材料。由于這個原因，激光切削所產(chǎn)生的切口非常窄。激光打孔深度可以控制到每個激光脈沖不超過一微米，且可以根據(jù)加工要求很靈活地留下非常淺的永久性標(biāo)記。采用這種方法可以節(jié)省材料，這對于貴重材料或微加工中的精密結(jié)構(gòu)而言非常重要?？梢跃_控制材料去除率使得激光加工成為微制造和微電子技術(shù)中非常重要的加工方法。厚度小于20 mm的板材的激光切割加工速度快、柔性好、質(zhì)量高。另外，通過套孔加工還可有效實現(xiàn)大孔及復(fù)雜輪廓的加工。

激光加工中的熱影響區(qū)相對較窄，其重鑄層只有幾微米?；诖?，激光加工的變形可以不予考慮。激光加工適用于任何可以很好地吸收激光輻射的材料，而傳統(tǒng)加工工藝必須針對不同硬度和耐磨性的材料選擇合適的刀具。采用傳統(tǒng)加工方法，非常難以加工硬脆材料如陶瓷等，而激光加工是解決此類問題的最好選擇。

激光切割的邊緣光滑且潔凈，無須進(jìn)一步處理。激光打孔可以加工用其他方法難以加工的高深徑比的孔。激光加工可以加工出高質(zhì)量的小盲孔、槽、表面微造型和表面印痕。激光技術(shù)正處于高速發(fā)展期，激光加工也如此。激光加工不會掛渣，沒有毛邊，可以精確控制幾何精度。隨著激光技術(shù)的快速發(fā)展，激光加工的質(zhì)量正在穩(wěn)步提高。

超聲加工

超聲加工為日益增長的對脆性材料如單晶體、玻璃、多晶陶瓷材料的加工需求及不斷提高的工件復(fù)雜形狀和輪廓加工提供了解決手段。這種加工過程不產(chǎn)生熱量、無化學(xué)反應(yīng)，加工出的零件在微結(jié)構(gòu)、化學(xué)和物理特性方面都不發(fā)生變化，可以獲得無應(yīng)力加工表面。因此，超聲加工被廣泛應(yīng)用于傳統(tǒng)加工難以切削的硬脆材料。在超聲加工中，實際切削由液體中的懸浮磨?；蛘咝D(zhuǎn)的電鍍金剛石工具來完成。超聲加工的變型有靜止（傳統(tǒng)）超聲加工和旋轉(zhuǎn)超聲加工。

傳統(tǒng)的超聲加工是利用作為小振幅振動的工具與工件之間不斷循環(huán)的含有磨粒的漿料的磨蝕作用去除材料的。成形工具本身并不磨蝕工件，是受激振動的工具通過激勵漿料液流中的磨料不斷緩和而均勻地磨損工件，從而在工件表面留下與工具相對應(yīng)的精確形狀。音極工具振動的均勻性使超聲加工只能完成小型零件的加工，特別是直徑小于100 mm 的零件。

超聲加工系統(tǒng)包括音極組件、超聲發(fā)生器、磨料供給系統(tǒng)及操作人員的控制。音極是暴露在超聲波振動中的一小塊金屬或工具，它將振動能傳給某個元件，從而激勵漿料中的磨粒。超聲加工系統(tǒng)的示意圖如圖6.5所示。音極/工具組件由換能器、變幅桿和音極組成。換能器將電脈沖轉(zhuǎn)換成垂直沖程，垂直沖程再傳給變幅桿進(jìn)行放大或壓抑。調(diào)節(jié)后的沖程再傳給音極/工具組件。此時，工具表面的振動幅值為20～50μm。工具的振幅通常與所使用的磨粒直徑大致相等。

磨料供給系統(tǒng)將由水和磨粒組成的漿料送至切削區(qū)，磨粒通常為碳化硅或碳化硼。另外，除了提供磨粒進(jìn)行切削外，漿料還可對音極進(jìn)行冷卻，并將切削區(qū)的磨粒和切屑帶走。

Nontraditional Machining Processes Introduction

Traditional or conventional machining, such as turning, milling, and grinding etc., uses mechanical energy to shear metal against another substance to create holes or remove material.Nontraditional machining processes are defined as a group of processes that remove excess material by various techniques involving mechanical, thermal, electrical or chemical energy or combinations of these energies but do not use a sharp cutting tool as it is used in traditional manufacturing processes.Extremely hard and brittle materials are difficult to be machined by traditional machining processes.Using traditional methods to machine such materials means increased demand for time and energy and therefore increases in costs;in some cases traditional machining may not be feasible.Traditional machining also results in tool wear and loss of quality in the product owing to induced residual stresses during machining.Nontraditional machining processes, also called unconventional machining process or advanced manufacturing processes, are employed where traditional machining processes are not feasible, satisfactory or economical due to special reasons as outlined below: 1.Very hard fragile materials difficult to clamp for traditional machining;2.When the workpiece is too flexible or slender;3.When the shape of the part is too complex;4.Parts without producing burrs or inducing residual stresses.Traditional machining can be defined as a process using mechanical(motion)energy.Non-traditional machining utilizes other forms of energy;the three main forms of energy used in non-traditional machining processes are as follows: 1.Thermal energy;2.Chemical energy;3.Electrical energy.Several types of nontraditional machining processes have been developed to meet extra required machining conditions.When these processes are employed properly, they offer many advantages over traditional machining processes.The common nontraditional machining processes are described in the following section.Electrical Discharge Machining(EDM)

Electrical discharge machining(EDM)sometimes is colloquially referred to as spark machining, spark eroding, burning, die sinking or wire erosion.It is one of the most widely used non-traditional machining processes.The main attraction of EDM over traditional machining processes such as metal cutting using different tools and grinding is that this technique utilizes thermoelectric process to erode undesired materials from the workpiece by a series of rapidly recurring discrete electrical sparks between workpiece and electrode.The traditional machining processes rely on harder tool or abrasive material to remove softer material whereas nontraditional machining processes such as EDM uses electrical spark or thermal energy to erode unwanted material in order to create desired shapes.So, the hardness of the material is no longer a dominating factor for EDM process.EDM removes material by discharging an electrical current, normally stored in a capacitor bank, across a small gap between the tool(cathode)and the workpiece(anode)typically in the order of 50 volts/10amps.As shown in Fig.6.1, at the beginning of EDM operation, a high voltage is applied across the narrow gap between the electrode and the workpiece.This high voltage induces an electric field in the insulating dielectric that is present in narrow gap between electrode and workpiece.This causes conducting particles suspended in the dielectric to concentrate at the points of strongest electrical field.When the potential difference between the electrode and the workpiece is sufficiently high, the dielectric breaks down and a transient spark discharges through the dielectric fluid, removing small amount of material from the workpiece surface.The volume of the material removed per spark discharge is typically in the range of 10-5 to 10-6 mm3.The gap is only a few thousandths of an inch, which is maintained at a constant value by the servomechanism that actuates and controls the tool feed.Chemical Machining(CM)

Chemical machining(CM)is a well known non-traditional machining process in which metal is removed from a workpiece by immersing it into a chemical solution.The process is the oldest of the nontraditional processes and has been used to produce pockets and contours and to remove materials from parts having a high strength-to-weight ratio.Moreover, the chemical machining method is widely used to produce micro-components for various industrial applications such as microelectromechanical systems(MEMS)and semiconductor industries.In CM material is removed from selected areas of workpiece by immersing it in a chemical reagents or etchants, such as acids and alkaline solutions.Material is removed by microscopic electrochemical cell action which occurs in corrosion or chemical dissolution of a metal.Special coatings called maskants protect areas from which the metal is not to be removed.This controlled chemical dissolution will simultaneously etch all exposed surfaces even though the penetration rates of the material removed may be only 0.0025-0.1mm/min.The basic process takes many forms: chemical milling of pockets, contours, overall metal removal, chemical blanking for etching through thin sheets;photochemical machining(pcm)for etching by using of photosensitive resists in microelectronics;chemical or electrochemical polishing where weak chemical reagents are used(sometimes with remote electric assist)for polishing or deburring and chemical jet machining where a single chemically active jet is used.A schematic of chemical machining process is shown in Fig.6.2a.Because the etchant attacks the material in both vertical and horizontal directions, undercuts may develop(as shown by the areas under the edges of the maskant in Fig.6.2b).Typically, tolerances of ±10% of the material thickness can be maintained in chemical blanking.In order to improve the production rate, the bulk of the workpiece should be shaped by other processes(such as by machining)prior to chemical machining.Dimensional variations can occur because of size changes in workpiece due to humidity and temperature.This variation can be minimized by properly selecting etchants and controlling the environment in the part generation and the production area in the plant.Electrochemical Machining(ECM)

Electrochemical metal removal is one of the more useful nontraditional machining processes.Although the application of electrolytic machining as a metal-working tool is relatively new, the basic principles are based on Faraday laws.Thus, electrochemical machining can be used to remove electrically conductive workpiece material through anodic dissolution.No mechanical or thermal energy is involved.This process is generally used to machine complex cavities and shapes in high-strength materials, particularly in the aerospace industry for the mass production of turbine blades, jet-engine parts, and nozzles, as well as in the automotive(engines castings and gears)and medical industries.More recent applications of ECM include micromachining for the electronics industry.Electrochemical machining(ECM), shown in Fig.6.3, is a metal-removal process based on the principle of reverse electroplating.In this process, particles travel from the anodic material(workpiece)toward the cathodic material(machining tool).Metal removal is effected by a suitably shaped tool electrode, and the parts thus produced have the specified shape, dimensions, and surface finish.ECM forming is carried out so that the shape of the tool electrode is transferred onto, or duplicated in, the workpiece.The cavity produced is the female mating image of the tool shape.For high accuracy in shape duplication and high rates of metal removal, the process is operated at very high current densities of the order 10-100 A/cm2,at relative low voltage usually from 8 to 30 V, while maintaining a very narrow machining gap(of the order of 0.1 mm)by feeding the tool electrode with a feed rate from 0.1 to 20 mm/min.Dissolved material, gas, and heat are removed from the narrow machining gap by the flow of electrolyte pumped through the gap at a high velocity(5-50 m/s), so the current of electrolyte fluid carries away the deplated material before it has a chance to reach the machining tool.Being a non-mechanical metal removal process, ECM is capable of machining any electrically conductive material with high stock removal rates regardless of their mechanical properties.In particular, removal rate in ECM is independent of the hardness, toughness and other properties of the material being machined.The use of ECM is most warranted in the manufacturing of complex-shaped parts from materials that lend themselves poorly to machining by other, above all mechanical methods.There is no need to use a tool made of a harder material than the workpiece, and there is practically no tool wear.Since there is no contact between the tool and the work, ECM is the machining method of choice in the case of thin-walled, easily deformable components and also brittle materials likely to develop cracks in the surface layer.Laser Beam Machining(LBM)

LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.Although the laser is used as a light amplifier in some applications, its principal use is as an optical oscillator or transducer for converting electrical energy into a highly collimated beam of optical radiation.The light energy emitted by the laser has several characteristics which distinguish it from other light sources: spectral purity, directivity and high focused power density.Laser machining is the material removal process accomplished through laser and target material interactions.Generally speaking, these processes include laser drilling, laser cutting, laser welding, and laser grooving, marking or scribing.Laser machining(Fig.6.4)is localized, non-contact machining and is almost reacting-force free.This process can remove material in very small amount and is said to remove material “atom by atom”.For this reason, the kerf in laser cutting is usually very narrow , the depth of laser drilling can be controlled to less than one micron per laser pulse and shallow permanent marks can be made with great flexibility.In this way material can be saved, which may be important for precious materials or for delicate structures in micro-fabrications.The ability of accurate control of material removal makes laser machining an important process in micro-fabrication and micro-electronics.Also laser cutting of sheet material with thickness less than 20mm can be fast, flexible and of high quality, and large holes or any complex contours can be efficiently made through trepanning.Heat Affected Zone(HAZ)in laser machining is relatively narrow and the re-solidified layer is of micron dimensions.For this reason, the distortion in laser machining is negligible.LBM can be applied to any material that can properly absorb the laser irradiation.It is difficult to machine hard materials or brittle materials such as ceramics using traditional methods, laser is a good choice for solving such difficulties.Laser cutting edges can be made smooth and clean, no further treatment is necessary.High aspect ratio holes with diameters impossible for other methods can be drilled using lasers.Small blind holes, grooves, surface texturing and marking can be achieved with high quality using LBM.Laser technology is in rapid progressing, so do laser machining processes.Dross adhesion and edge burr can be avoided, geometry precision can be accurately controlled.The machining quality is in constant progress with the rapid progress in laser technology.Ultrasonic Machining(USM)

Ultrasonic machining offers a solution to the expanding need for machining brittle materials such as single crystals, glasses and polycrystalline ceramics, and for increasing complex operations to provide intricate shapes and workpiece profiles.This machining process is non-thermal, non-chemical, creates no change in the microstructure, chemical or physical properties of the workpiece and offers virtually stress-free machined surfaces.It is therefore used extensively in machining hard and brittle materials that are difficult to cut by other traditional methods.The actual cutting is performed either by abrasive particles suspended in a fluid, or by a rotating diamond-plate tool.These variants are known respectively as stationary(conventional)ultrasonic machining and rotary ultrasonic machining(RUM).Conventional ultrasonic machining(USM)accomplishes the removal of material by the abrading action of a grit-loaded slurry, circulating between the workpiece and a tool that is vibrated with small amplitude.The form tool itself does not abrade the workpiece;the vibrating tool excites the abrasive grains in the flushing fluid, causing them to gently and uniformly wear away the material, leaving a precise reverse from of the tool shape.The uniformity of the sonotrode-tool vibration limits the process to forming small shapes typically under 100 mm in diameter.The USM system includes the Sonotrode-tool assembly, the generator, the grit system and the operator controls.The sonotrode is a piece of metal or tool that is exposed to ultrasonic vibration, and then gives this vibratory energy in an element to excite the abrasive grains in the slurry.A schematic representation of the USM set-up is shown in Fig.6.5.The sonotrode-tool assembly consists of a transducer, a booster and a sonotrode.The transducer converts the electrical pulses into vertical stroke.This vertical stroke is transferred to the booster, which may amplify or suppress the stroke amount.The modified stroke is then relayed to the sonotrode-tool assembly.The amplitude along the face of the tool typically falls in a 20 to 50 μm range.The vibration amplitude is usually equal to the diameter of the abrasive grit used.The grit system supplies a slurry of water and abrasive grit, usually silicon or boron carbide, to the cutting area.In addition to providing abrasive particles to the cut, the slurry also cools the sonotrode and removes particles and debris from the cutting area.