信息科學(xué)與電子工程專業(yè)英語--unit3

1、Technical English,For Information Science and Electronic Engineering,Unit 3,EM Fields, Antenna and Microwaves,Part I,Electromagnetic Field,3,New Words,4,1,The electromagnetic field is a physical field produced by electri

2、cally charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. It is one of

3、the four fundamental forces in the nature (the others are gravitation, the weak interaction, and the strong interaction),電磁場在空間無限延伸，并描述電磁相互作用。,5,2,The field can be viewed as the combination of an electric field and a mag

4、netic field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field. The way in which charges and currents int

5、eract with the electromagnetic field is described by Maxwell’s equations and the Lorentz force law.,電荷和電流與電磁場相互作用的方式由麥克斯韋方程組和洛倫茲力定律所描述。,6,3,From a classical point of view, the electromagnetic field can be regarded as a s

6、mooth, continuous field, propagated in a wavelike manner, whereas from a quantum mechanical point of view, the field can be viewed as being composed of photons.,從經(jīng)典的角度，電磁場可認(rèn)為是光滑、連續(xù)的場，以波動方式傳播；而從量子力學(xué)的角度，場可看作是由光子組成的。,7,4 St

7、ructure of the electromagnetic field,The electromagnetic field may be viewed in two distinct ways.Continuous structure: Classically, electric and magnetic fields are thought of as being produced by smooth motions of cha

8、rged objects. For example, oscillating charges produce electric and magnetic fields that may be viewed in a “smooth”, continuous, wavelike manner.,例如，振蕩電荷產(chǎn)生電場和磁場，可看成平滑的、連續(xù)的波動方式。,8,5,In this case, energy is viewed as bein

9、g transferred continuously through the electromagnetic field between any two locations. For instance, the metal atoms in a radio transmitter appear to transfer energy continuously. This view is useful to a certain extent

10、 (radiation of low frequency), but problems are found at high frequencies (see ultraviolet catastrophe). This problem leads to another view.,The ultraviolet catastrophe, also called the Rayleigh-Jeans catastrophe, was a

11、prediction of early 20th century classical physics that an ideal black body at thermal equilibrium will emit radiation with infinite power.,9,6,Discrete structure: The electromagnetic field may be thought of in a more “c

12、oarse” way. Experiments reveal that electromagnetic energy transfer is better described as being carried away in photons with a fixed frequency. Planck’s relation links the energy E of a photon to its frequency n through

13、 the equation: E = h n,普朗克的關(guān)系式將光子的能量E及其頻率n 通過下式聯(lián)系起來,10,6,where h is Planck’s constant, named in honor of Max Planck, and n is the frequency of the photon. For example, in the photoelectric effect – the emission of elect

14、rons from metallic surfaces by electromagnetic radiation – it is found that increasing the intensity of the incident radiation has no effect, and that only the frequency of the radiation is relevant in ejecting electrons

15、.1,例如在光電效應(yīng)中，即因電磁輻射而從金屬表面發(fā)射電子的現(xiàn)象，我們發(fā)現(xiàn)增加入射輻射的強度并無影響，只有輻射頻率與發(fā)射的電子有關(guān)。,11,7,This quantum picture of the electromagnetic field has proved very successful, giving rise to quantum electrodynamics, a quantum field theory describi

16、ng the interaction of electromagnetic radiation with charged matter.,已經(jīng)證明電磁場的量子描述是非常成功的，引出了量子電動力學(xué)，一種描述電磁輻射與帶電物體之間的相互作用的量子場理論。,12,8 Dynamics of the electromagnetic field,In the past, electrically charged objects were thou

17、ght to produce two types of field associated with their charge property. An electric field is produced when the charge is stationary with respect to an observer measuring the properties of the charge and a magnetic field

18、 (as well as an electric field) is produced when the charge moves (creating an electric current) with respect to this observer.,相對于測量電荷性質(zhì)的觀察者，電荷靜止時產(chǎn)生電場，電荷運動（產(chǎn)生電流）時產(chǎn)生磁場（和電場）。,13,8,Over time, it was realized that the elect

19、ric and magnetic fields are better thought of as two parts of a greater whole – the electromagnetic field.2,隨著時間的推移，人們認(rèn)識到電場和磁場是電磁場這一整體的兩個部分。,14,9,Once this electromagnetic field has been produced from a given charge dist

20、ribution, other charged objects in this field will experience a force (in a similar way that planets experience a force in the gravitational field of the Sun). If these other charges and currents are comparable in size t

21、o the sources producing the above electromagnetic field, then a new net electromagnetic field will be produced.3,電磁場中其它帶電體就會受到一個力的作用,如果另外這些電荷和電流的大小與產(chǎn)生上述電磁場的源是可比的，那么將產(chǎn)生一個新的凈電磁場。,15,9,Thus, the electromagnetic field may be

22、 viewed as a dynamic entity that causes other charges and currents to move, and which is also affected by them. These interactions are described by Maxwell’s equations and the Lorentz force law.,電磁場可以認(rèn)為是一個動力學(xué)實體，它促使其它電荷和電

23、流運動，同時又受它們影響。,Part II,Microstrip Antenna,17,New Words,18,New Words,19,1,In telecommunication, there are several types of microstrip antennas (also known as printed antennas) the most common of which is the microstrip pat

24、ch antenna or patch antenna. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate with a continuous metal layer

25、bonded to the opposite side of the substrate which forms a ground plane.1,片狀天線是一種窄帶寬波束的天線，通過將天線單元圖樣蝕刻到粘貼在絕緣基底上的金屬軌跡而制成，基底的另一面則粘貼連續(xù)的金屬層形成接地平面。,20,1,Common microstrip antenna radiator shapes are square, rectangular, circul

26、ar and elliptical, but any continuous shape is possible. Some patch antennas eschew a dielectric substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the resulting structure is less r

27、obust but provides better bandwidth.,一些片狀天線為了避免絕緣基底，在接地平面的上空用絕緣逆電流器懸掛一個金屬貼片；這種結(jié)構(gòu)的魯棒性不是很好，但能提供更好的帶寬。,21,1,Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mount

28、ed on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices.2,因為這種天線外形低矮，機械強度大，并且形狀上適應(yīng)性強，通常裝在飛機或太空飛行器外表，或組合在移動無線電通信設(shè)備上。,22,2,Microstrip antennas are also relatively inexpen

29、sive to manufacture and design because of the simple 2-dimensional physical geometry. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the reso

30、nant frequency. A single patch antenna provides a maximum directive gain of around 6-9 dBi.,因為其簡單的二維形狀,dBi: decibel isotropic, the forward gain of an antenna compared with the isotropic antenna, which uniformly distribut

31、es energy in all directions.,23,2,It is relatively easy to print an array of patches on a single (large) substrate using lithographic techniques. Patch arrays can provide much higher gains than a single patch at little a

32、dditional cost; matching and phase adjustment can be performed with printed microstrip feed structures, again in the same operations that form the radiating patches.,通過平板印刷技術(shù)我們很容易在單個大絕緣體上印刷貼片陣列。,用形成輻射電波的片狀微帶天線的同樣機理，可對印刷微

33、帶天線的饋電結(jié)構(gòu)進(jìn)行匹配和相位調(diào)節(jié)。,24,2,The ability to create high gain arrays in a low-profile antenna is one reason that patch arrays are common on airplanes and in other military applications.,以低矮的天線構(gòu)成高增益陣列的能力是片狀天線廣泛用于飛機和其他軍事應(yīng)用的原因之一。

34、,25,3,The most commonly employed microstrip antenna is a rectangular patch. The rectangular patch antenna is approximately a one-half wavelength long section of rectangular microstrip transmission line. When air is the a

35、ntenna substrate, the length of the rectangular microstrip antenna is approximately one-half of a free-space wavelength.,矩形貼片天線長近似為矩形微帶傳輸線的一段，其長度等于半波長。,矩形微帶天線的長度大約為自由空間波長的一半,26,3,Since the antenna is loaded with a dielec

36、tric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases. The resonant length of the antenna is slightly shorter because of the extended electric “fringing

37、 fields” which increase the electrical length of the antenna slightly.,天線的諧振長度略短一些，這是因為邊緣場稍微增加了天線的電氣長度。,Fringing fields: the electric fields produced by scattered electrons in an electron microscope.,27,3,An early model

38、of the microstrip antenna is a section of microstrip transmission line with equivalent loads on either end to represent the radiation loss.,微帶天線的一個早期模型是一段微帶傳輸線，在一端具有等效負(fù)載，代表輻射損耗。,28,4,The dielectric loading of a microstri

39、p antenna affects both its radiation pattern and impedance bandwidth. As the dielectric constant of the substrate increases, the antenna bandwidth decreases which increases the Q factor of the antenna and therefore decre

40、ases the impedance bandwidth.3,隨著基底介電常數(shù)的增大，天線的帶寬減小，其Q值提高，因而阻抗帶寬減小。,29,4,This relationship did not immediately follow when using the transmission line model of the antenna, but is apparent when using the cavity model whic

41、h was introduced in the late 1970s. The radiation from a rectangular microstrip antenna may be understood as a pair of equivalent slots.,當(dāng)使用天線的傳輸線模型時這種情況并沒有發(fā)生，到了七十年代后期出現(xiàn)空腔模型時這種情況就顯現(xiàn)出來了。,30,4,These slots act as an array a

42、nd have the highest directivity when the antenna has an air dielectric and decreases as the antenna is loaded by material with increasing relative dielectric constant.,這些狹縫就像一個陣列，當(dāng)天線使用空氣電介質(zhì)時方向性最好，但是當(dāng)天線的負(fù)載材料的相對介電常數(shù)增加時方向性會

43、減弱。,31,5,An advantage inherent to patch antennas is the ability to have polarization diversity. Patch antennas can easily be designed to have various polarizations, using multiple feed points, or a single feed point with

44、 asymmetric patch structures.4 This unique property allows patch antennas to be used in many types of communications links that may have varied requirements.,片狀天線能很容易地通過多個饋點或具有非對稱片結(jié)構(gòu)的單一饋點設(shè)計成具有各種極化特性。,32,6,The half-wave r

45、ectangular microstrip antenna has a virtual shorting plane along its center. This may be replaced with a physical shoring plane to create a quarter-wavelength microstrip antenna. This is sometimes called a half-patch.,沿中

46、心的虛擬短路平面,用物理短路平面替代上述虛擬短路平面就可以做成四分之一波長微帶天線,33,6,The antenna only has a single radiation edge (equivalent slot) which lowers the directivity/gain of the antenna. The impedance bandwidth is slightly lower than a half-wavele

47、ngth full patch as the coupling between radiating edges has been eliminated.,由于沒有輻射邊緣之間的耦合，所以阻抗帶寬比半波長全貼片窄。,Part III,Microwaves,35,New Words,36,New Words,37,1,Microwaves are electromagnetic waves with wavelengths longer t

48、han those of terahertz (THz) frequencies, but relatively short for radio waves. Microwaves have wavelengths approximately in the range of 30 cm (frequency = 1 GHz) to 1 mm (300 GHz). This range of wav

49、elengths has led many to question the naming convention used for microwaves as the name suggests a micrometer wavelength.1,這個波長范圍已經(jīng)使人對命名習(xí)慣提出了問題，因為微波使人聯(lián)想到微米波長。,38,1,However, the boundaries between far infrared light, tera

50、hertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The same equations of electromagnetic theory apply at all frequencies.,…是相當(dāng)

51、隨意的，在不同的學(xué)科領(lǐng)域有不同的用法,39,1,Apparatus and techniques may be described as “microwave” when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is no longer

52、 accurate.,信號的波長與設(shè)備的尺度大致相同,集總元件電路理論不再準(zhǔn)確,40,1,The term microwave generally refers to “alternating current signals with frequencies between 300 MHz (3?108 Hz) and 300 GHz (3?1011 Hz).” However, both IEC

53、 standard 60050 and IEEE standard 100 define “microwave” frequencies starting at 1 GHz (30 cm wavelength).,41,2,The existence of electromagnetic waves, of which microwaves are part of the frequency spectrum, was predicte

54、d by James Clerk Maxwell in 1864 from his equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF r

55、egion.,構(gòu)建了在UHF頻段產(chǎn)生和檢測微波的裝置，證明電磁波的存在,42,2, 3,In 1894 J. C. Bose publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves. The microwave range i

56、ncludes ultra-high frequency (UHF) (0.3–3 GHz), super high frequency (SHF) (3–30 GHz), and extremely high frequency (EHF) (30–300 GHz) signals.,微波傳播的研究,43,4,Above 300 GHz, the absorption of electromag

57、netic 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.,地球大氣對高于300 GHz的電磁輻射的吸收是如此之大，以

58、至于變得實際上是不透明，直到所謂的紅外線和可見光窗口的頻率范圍，大氣又變得透明。,44,5 Devices,Vacuum tube based devices operate on the ballistic motion of electrons in a vacuum under the influence of controlling electric or magnetic fields, and include the mag

59、netron, klystron, traveling wave tube (TWT), and gyrotron.2,基于電子管的器件是在受控制電場和磁場影響的真空內(nèi)由電子的沖擊運動而工作的，包括磁控管，速調(diào)管，行波管和振動陀螺儀。,45,5,These devices work in the density modulated mode, rather than the current modulated mode. This me

60、ans that they work on the basis of clumps of electrons flying ballistically through them, rather than using a continuous stream.3,這意味著它們是基于真空管發(fā)出的電子簇工作的，而不是用連續(xù)的電子流。,46,6 Uses,A microwave oven works by passing microwave ra

61、diation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm), through the food. Water, fat, and sugar molecules in the food absorb energy from the microwave beam in a process called dielectric heating

62、.,47,6,Many molecules (such as those of water) are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and therefore rotate as they try to align themselves with the a

63、lternating electric field induced by the microwave beam.,它們一端帶正電，另一端帶負(fù)電,它們力圖與微波波束所引起的交變電場保持一致,48,6,This molecular movement creates heat as the rotating molecules hit other molecules and put them into motion. Microwave he

64、ating is most efficient on liquid water, and much less so on fats and sugars (which have less molecular dipole moment), and frozen water (where the molecules are not free to rotate).,旋轉(zhuǎn)分子撞擊其它分子，使他們運動，這種分子運動產(chǎn)生熱量。,微波加熱對液態(tài)水

65、是最有效的，其次為脂肪和糖類（分子偶極矩較少）以及冷凍水（分子不能自由轉(zhuǎn)動）。,49,6,Microwave heating is sometimes incorrectly explained as a rotational resonance of water molecules: such resonance only occurs at much higher frequencies, in the tens of gigahe

66、rtz. Moreover, large industrial/commercial microwave ovens operating in the 900 MHz range also heat water and food perfectly well.,微波加熱有時被錯誤地解釋為水分子的旋轉(zhuǎn)共振，而這種共振只能發(fā)生在數(shù)十千兆赫的高頻。,此外，大型工業(yè)/商業(yè)微波爐在900兆赫范圍內(nèi)工作，也能很好地加熱水和食物。,50,7

67、,A common misconception is that microwave ovens cook food from the “inside out”. In reality, microwaves are absorbed in the outer layers of food in a manner somewhat similar to heat from other methods. The rays from a mi

68、crowave electrically manipulate water particles to cook food.,實際上與其它加熱方法類似，微波被食物外層吸收。,51,7,It is actually the friction caused by the movement that creates heat and warms the food. The misconception arises because microwa