通信工程 外文翻译---组织化学中的物理微波技术

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1、附 录 英文原文及中文翻译 （一）英文原文 Physics of microwave technology in histochemistry L P KOK and M E BOON. Institute for Theoretical Physics, University of Groningen, P.O. Box 800, 9700 A V Groningen, The Netherlands Leiden Cytology and Pathology Laboratory, Leiden, The Netherlands SummaryMicrowave technology ha

2、s become important in preparatory techniques for microscopy in many different ways. This paper discusses various aspects of the physics of microwaves, It gives some theoretical background to understand the practical procedures. Some peculiarities in the optics of microwaves are pointed out, and the

3、practical implications in particular of choosing the size and shape of samples and containers are discussed. Diffusion rates and chemical-reaction rates increase exponentially with temperature, so that precise temperature control is essential in most histochemical procedures. Such control is complic

4、ated by localized heating of the system, and of temperature sensors themselves, which may occur as a result of microwave irradiation. Introduction Sample preparation for histochemistry is an art, based on physical and chemical processes. Microwaves can influence both processes. In this light, a mult

5、idisciplinary team in The Netherlands and some other European countries made an effort to look for benefits of microwave technology in all fields of preparatory techniques. Fruits of this effort are described in detail elsewhere (Boon & Kok, 1988； Kok &Boon, 1990). Knowledge of both histochemistry a

6、nd physics is needed to exploit the potentials of the application of microwave irradiation in histochemistry. Key factors in all preparatory techniques are diffusion (a physical process) and chemical-reaction rates. They are influenced by temperature increase, and hence by microwave irradiation. The

7、 main effect of microwave irradiation in histochemistry is controllable temperature increase. If microwave irradiation is optimally applied, the resulting microscopical images are of superior quality because of good process control. In this paper some relevant physics is reviewed: reflection and ref

8、raction, absorption, standing-waveeffects, hot spots, temperature control and temperature measurement in the microwave oven. Some history and the link with optics About one century ago, in 1888, Hertz discovered that electromagnetic radiation in the microwave and radio regions of the spectrum displa

9、ys the same basic behaviour as visible light. In fact, he showed that 66cm microwaves travel in straight lines, and can be reflected, refracted, and polarized in the same way light waves can. Thus microwaves exhibit diffraction and interference in the same way as visible light albeit on a different

10、scale of length. The basic unit of length is the wavelength () of the radiation, and all objects in microwave applications have to be measured in terms of this length scale. Large and small refer to size expressed in. However, the wavelength of electromagnetic waves depends on the medium in which th

11、ey propagate. Connected to this is the fact that the velocity of electromagnetic waves within most media is smaller than the velocity in vacuum or air. A wave has different wavelengths in different media. What remains the same is the frequency of the wave(expressed in Hz, named after Hertz). The uni

12、fying feature of all electromagnetic waves is that at all frequencies they have the same velocity in vacuum, c. Insidea medium the velocity vair smaller. In air the difference is small: a factor 1.000294. In fact, the factor by which it differs depends on the frequency； the quoted figure is for visi

13、ble light in air. Theratio n = c/v is the refractive index of the medium. For light in water n 1.33. Fluid water is a very special substance. At microwave frequencies c/v = 9. This means that refraction is anomalously large, and that the wavelength inside water is much smaller than in air. For examp

14、le, for 2.45 GHz microwaves (used inkitchen and laboratory ovens), instead of 12.2cm, water is merely 12.2/9 1.36 cm. Hence, in microwave applications in an aqueous environment an object is qualified as small when it is smaller than a centimeter.Large means its linear dimension at least exceedswater

15、 At low frequencies (e.g., 50Hz mains, or 8MHz personal computer) electromagnetic-radiation aspects of the distribution of electromagnetic energy may be ignored. By contrast, at high frequency (e.g., visiblelight) these radiation aspects become dominant. Thinking in terms of lengths: if the characte

16、ristic electromagnetic wavelength is much larger than the typical sizes in our system (equipment), we may ignore radiation aspects. The fundamental property of microwave technique is that it considers applications in which the characteristic wavelength is roughly the same size as the system (equipme

17、nt, circuit . . . . ), or smaller, but yet not so small that we can merely use optical-ray techniques. Nevertheless, the lessons from optics can be a useful guide in predicting the behaviour of systems involving media and microwaves. This will be in particular the case when the characteristic wavele

18、ngth .is smaller than the typical size of the objects involved. The next two sections focus on this optical limit. We shall first discuss the optics of microwaves propagating without absorption effects, i.e., we shall first make the simplifying assumption that the penetration depth in media (other t

19、han the perfectly reflecting metals) is infinitely large. Optics of microwaves； reflection and refraction Perfectly conducting metal surfaces act like perfect mirrors to microwaves. This is the basic principle for the confinement of microwaves inside the oven chamber of the microwave oven, and for t

20、he transport of microwaves inside hollow metal wave guides. At th e interface of two different dielectric media both reflection and refraction take place. Part of the incident wave (incident angle i) is reflected with angle of reflection r (with r = i), and another part is transmitted inside the med

21、ium. Thereby the direction of propagation in general is altered. How much is expressed by the refraction law of Snell: nisin i = nt sin t. Here t is the angle of refraction, and niand nt are the refractive indices of the first and the second medium, respectively. In the special case of incidence fro

22、m vacuum, ni = 1 exactly, and the case of incidence from air, nair 1. in both cases we effectively have sin i / sin t = n, where n is the relative refractive index, n 1. There is a fundamental relationship between n and the relative permittivity: n = V 时 . For water, is anomalously large and in the

23、order of 81, so that n 9. Because sin i1, one finds easily that the angle of refraction, t in this case, is never larger than arcsin (1/9) 6.4 。 Also for other substances commonly used in the pathology laboratory, can be quite large, see Boon &Kok(1988). Upon entering these materials therefore, them

24、icrowaves will tend to propagate more or less perpendicular to the boundary of the medium. Because there is both reflection and refraction it is of interest to know which fraction Q of a propagating microwave actually enters the object, and which fraction (hence 1-Q) is reflected. The fraction depen

25、ds on the polarization of the wave. For waves with the electric-field vector parallel to the interface this fraction is Q1。 In the orthogonal polarization state this fraction is denoted by Q2。 What does Snells law teach us in the case of transition from a medium like water to vacuum (or air)? For th

26、is transition from medium i (water) to air, one has 9siniwater = sin t. Unlesswater is sufficiently close to zero this equation has no real solution. This means there is no refraction, and thus there is perfect (100%) reflection back into the water. In other words: once the wave is refracted into th

27、e convex water mass, there is a great chance it remains caught inside. Focusing effects and absorption of microwave energy So far we have discussed the optics of a plane microwave hitting a flat interface between two media. We now turn to curved boundary surfaces. Here again reflection and refractio

28、n occur. The curvature of the surface may be used to focus microwaves. For example, a parabolic metallic mirror will concentrate microwaves incident parallel to the axis upon reflection in the focal point. Radio telescopes are examples of such mirrors. Similarly, microwave beams refracted at curved

29、surfaces can show a focusing effect. As an illustrative example let us consider a spherical volume of a medium like water, in air. This is an excellent model for a potato, a tomato, or an egg. Again, as in the previous section, we disregard for the time being absorption of the microwaves inside the

30、medium. In Figure 1 we show the results of the ensuing computations for various values of n: n=l, 1.2, 1.4, 4,9, and, respectively. For n=l the material of the sphere is completely microwave transparent. The waves pass without being deflected. For larger values of n the deflection of rays becomes appreciable. For n =1.4 there is focusing on the axis outside the sphere. For n 2 the focal region has shifted inside the sphere. With increasing n this effect becomes more pronounced. For n=9 (appropriate for