【正文】 photochemical machining(pcm)for etching by using of photosensitive resists in microelectronics。 without producing burrs or inducing residual machining can be defined as a process using mechanical(motion) machining utilizes other forms of energy。Nontraditional Machining Processes IntroductionTraditional or conventional machining, such as turning, milling, and grinding etc., uses mechanical energy to shear metal against another substance to create holes or remove machining processes are defined as a group of processes that remove excess material by various techniques involving mechanical, thermal, electrical or chemical energy or binations of these energies but do not use a sharp cutting tool as it is used in traditional manufacturing hard and brittle materials are difficult to be machined by traditional machining traditional methods to machine such materials means increased demand for time and energy and therefore increases in costs。此時(shí)，工具表面的振動(dòng)幅值為20～50μm。音極是暴露在超聲波振動(dòng)中的一小塊金屬或工具，它將振動(dòng)能傳給某個(gè)元件，從而激勵(lì)漿料中的磨粒。傳統(tǒng)的超聲加工是利用作為小振幅振動(dòng)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。這種加工過(guò)程不產(chǎn)生熱量、無(wú)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(wú)應(yīng)力加工表面。激光技術(shù)正處于高速發(fā)展期，激光加工也如此。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(wèn)題的最好選擇。另外，通過(guò)套孔加工還可有效實(shí)現(xiàn)大孔及復(fù)雜輪廓的加工。激光打孔深度可以控制到每個(gè)激光脈沖不超過(guò)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。簡(jiǎn)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。激光束加工LASER是英文Light Amplification by Stimulated Emission of Radiation 各單詞頭一個(gè)字母所組成的縮寫詞。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(wú)須考慮材料的機(jī)械性能。為了獲得電化學(xué)過(guò)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）。在電化學(xué)加工過(guò)程中，從陽(yáng)極（工件）上蝕除下的粒子移向陰極（加工工具）。利用陽(yáng)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(wú)須機(jī)械能和熱能。濕度和溫度也會(huì)導(dǎo)致工件尺寸發(fā)生改變。由于蝕刻劑沿垂直和水平方向開(kāi)始蝕除材料，鉆蝕（又稱為淘蝕）量進(jìn)一步加大?；瘜W(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(guò)發(fā)生在金屬溶蝕或化學(xué)溶解過(guò)程中的電化學(xué)微電池作用被去除掉。電極之間的間隙只有千分之幾英寸，通過(guò)伺服機(jī)構(gòu)驅(qū)動(dòng)和控制工具電極的進(jìn)給使該值保持常量。這個(gè)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(chǎng)。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(lái)電蝕除余料，以獲得所需的零件形狀。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。由于在加工過(guò)程中會(huì)產(chǎn)生殘余應(yīng)力，傳統(tǒng)加工方法還會(huì)造成刀具磨損，損壞產(chǎn)品質(zhì)量。特種加工是指這樣一組加工工藝，它們通過(guò)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(lái)去除工件表面的多余材料。由于這些曲線顯示，辦法，AWGN信道的一對(duì)L時(shí)，對(duì)MCSS系統(tǒng)性能有很大價(jià)值。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(zhǎng)度，如圖13所示的系統(tǒng)。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?？臻g部分是介紹了與當(dāng)?shù)厣⑸洌@是在基站周圍設(shè)幾組圓的定義?；蛘?，不同的多普勒譜定義在[8]個(gè)人頻道。與6頻道設(shè)置的示例列于表11。這些通道模型定義的離散傳播路徑的統(tǒng)計(jì)信息。是目前基于OFDM的無(wú)線標(biāo)準(zhǔn)遵循的理念。對(duì)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。符號(hào)的干擾在單載波調(diào)制系統(tǒng)的號(hào)碼是給予對(duì)于高數(shù)據(jù)符號(hào)持續(xù)時(shí)間很短運(yùn)輸署如果發(fā)送符號(hào)的持續(xù)時(shí)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。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(dòng)散射，通道脈沖響應(yīng)可以不再被建模為均值為零。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(guò)程。平均時(shí)延特性參數(shù)為有圖12時(shí)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(yè)的路徑均方根時(shí)延擴(kuò)展的定義為 同樣，多普勒頻譜的功率密度（FD）的特點(diǎn)可以定義在移動(dòng)時(shí)變無(wú)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。分配的通道傳輸功能是有關(guān)的延誤測(cè)量相對(duì)于第一個(gè)在接收器檢測(cè)到的路徑。第一篇：中英文翻譯Fundamentals This chapter describes the fundamentals of today’s wireless a detailed description of the radio channel and its modeling are presented, followed by the introduction of the principle of OFDM multicarrier addition, a general overview of the spread spectrum technique, especially DSCDMA, is given and examples of potential applications for OFDM and DSCDMA are introduction is essential for a better understanding of the idea behind the bination of OFDM with the spread spectrum technique, which is briefly introduced in the last part of this Radio Channel Characteristics Understanding the characteristics of the munications medium is crucial for the appropriate selection of transmission system architecture, dimensioning of its ponents, 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 choice of system ponents is totally different if, for instance, multipath propagation with long echoes dominates the radio , an accurate channel model describing the behavior of radio wave propagation in different environments such as mobile/fixed and indoor/outdoor is may allow one, through simulations, to estimate and validate the performance of a given transmission scheme in its several design Understanding Radio Channels In mobile radio channels(see Figure 11), 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 manmade , at the receiver antenna, a multitude of waves arrives from many different directions with different delays, attenuations, and superposition of these waves results in amplitude and phase variations of the posite received spread is caused by moving objects in the mobile radio in the phases and amplitudes of the arriving waves occur which lead to timevariant multipath small movements on the order of the wavelength may result in a totally different wave varying signal strength due to timevariant multipath propagation is referred to as fast is caused by obstruction of the transmitted waves by, ., hills, buildings, walls, and trees, which results in more or less strong attenuation of the signal to fast fading, longer distances have to be covered to significantly change the shadowing varying signal strength due to shadowing is called slow fading and can be described by a lognormal distribution [36].Path loss indicates how the mean signal power decays with distance between transmitter and 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 of the received power due to shadowing and path loss can be efficiently counteracted by power the following, the mobile radio channel is described with respect to its fast fading Channel Modeling The mobile radio channel can be characterized by the timevariant channel impulse response h(τ , t)or by the timevariant channel transfer function H(f, t), which is the Fourier transform of h(τ , t).The