Physics
Electromagnetic Waves in Matter
Electromagnetic waves in matter refer to the interaction of electromagnetic radiation with different types of materials. When electromagnetic waves pass through matter, they can be absorbed, transmitted, or reflected, depending on the properties of the material. This interaction is governed by the electrical and magnetic properties of the matter, and it plays a crucial role in various phenomena such as refraction, dispersion, and absorption.
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11 Key excerpts on "Electromagnetic Waves in Matter"
eBook - PDF- Y K Lim(Author)
- 1986(Publication Date)
- WSPC(Publisher)
Chapter VI PROPAGATION OF PLANE Electromagnetic Waves in Matter In traversing matter electromagnetic waves suffer scattering and absorption. These, as well as the phenomenon of dispersion, are related to the molecular structure of matter, so that a proper treatment of these phenomena must be carried out employing the principles of quantum mechanics. A reasonably satisfactory qualitative account can however be given on the basis of classical electrodynamics employing a simple mechanical model first proposed by Maxwell and Sellmeier independently, and later extended by Lorentz. 6.1 Basic Ideas Underlying the Classical Theory Microscopically, dielectric matter consists of neutral molecules or atoms which are made up of oppositely charged particles: ions and ions or electrons and ions bound together with certain definite binding energies. According to the classical theory, the opposite charges in a system are displaced parallel and antiparallel to the external electric field, when one is applied, forming dipoles. In the oscillating field of a traversing electromagnetic wave these molecular or electronic dipoles are forced to oscillate with the frequency of the wave. As a charge in a molecular or atomic system has a definite binding energy, the dipoles formed are endowed with definite natural or characteristic frequencies if they are approximated by harmonic oscillators. Thus, a 215 dielectric medium may be represented in the first approximation by an ensemble of harmonic oscillators which undergo forced oscillations as an electromagnetic wave passes by. In a conducting medium, it is the free electrons that participate in the forced oscillations. This case will be considered later. The oscillating dipoles emit radiation, while they absorb energy required for sustaining the vibration from the traversing wave. In the classical theory, the secondary radiation has the same frequency as the primary wave but is emitted in various directions.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa . Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave. ____________________ WORLD TECHNOLOGIES ____________________ A quantum theory of the interaction between electromagnetic radiation and matter such as electrons is described by the theory of quantum electrodynamics. Properties Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized wave propagating from right to left. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The physics of electromagnetic radiation is electrodynamics. Electromagnetism is the physical phenomenon associated with the theory of electrodynamics. Electric and magnetic fields obey the properties of superposition so that a field due to any particular particle or time-varying electric or magnetic field will contribute to the fields present in the same space due to other causes: as they are vector fields, all magnetic and electric field vectors add together according to vector addition. For instance, a travelling EM wave incident on an atomic structure induces oscillation in the atoms of that structure, thereby causing them to emit their own EM waves, emissions which alter the impinging wave through interference. These properties cause various phenomena including refraction and diffraction.
eBook - ePubHigh-Intensity X-rays - Interaction with Matter
Processes in Plasmas, Clusters, Molecules and Solids
- Stefan P. Hau-Riege(Author)
- 2012(Publication Date)
- Wiley-VCH(Publisher)
Chapter 4 Electromagnetic Wave PropagationWhen an x-ray beam irradiates a material, the electric-field distribution and with that photon absorption are determined by wave propagation effects. The energy deposition profile, in turn, determines the nature of the x-ray–matter interaction process. In this chapter we review wave-propagation phenomena in continuous and structured materials, and specifically discuss applications to reflective multilayers and dispersive grazing incidence optics, which are of particular relevance for x-ray optics.4.1 Electromagnetic Waves in MatterThe behavior of electromagnetic fields in matter can be described using Maxwell equations (1.23) –(1.26) . For now, we will limit our discussion to infinitely extended (unbounded), homogeneous, isotropic media. We consider monochromatic plane harmonic waves, which are the simplest and most fundamental one-dimensional electromagnetic waves. They can be written as(4.1)(4.2)The actual physical electric and magnetic field are the real parts of E and H . At each instant in time, E and H are constant on planes defined by r · k = const . We can build arbitrary solutions to the Maxwell equation by linear superpositions of the plane waves (4.1) and (4.2) .We further assume that the medium is isotropic and linear so that it can be described by the permittivity ε (ω), the permeability μ(ω), and the conductivity σ(ω), so that(4.3)(4.4)(4.5)In the general dynamic case, ε0 (ω) is a complex quantity due to absorption losses in the material.The plane wave equations (4.1) and (4.2) have to fulfill Maxwell equations (1.23) to (1.26) . We assume ρ = 0, that is the medium is charge-neutral. Inserting (4.1) and (4.2) into (1.23) to (1.26)
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 5 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
- Tamer Bécherrawy(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
Chapter 6Electromagnetic WavesA remarkable property of Maxwell’s equations (that was not possible to foresee before the formulation of the electromagnetic theory) is that they have solutions representing electromagnetic waves propagating at the speed of light in matter and in vacuum. The existence of these waves was experimentally confirmed, in 1890 by Hertz, who succeeded in producing them and verifying that they have the same propagation, interference, diffraction and polarization properties as light waves. Thus, Maxwell theory has enabled us to understand the nature of light as electromagnetic waves with very short wavelengths. Actually, we can produce and detect electromagnetic waves of frequencies varying between 10−2 Hz and 1032 Hz, that is, of wavelengths varying between 1010 m and 10−24 m. They play a very important part in nearly all branches of physics and have a considerable impact on economic, social, political and intellectual life. In this chapter, we recall the principal results of the electromagnetic theory, namely Maxwell’s equations. We discuss their wave solution and some applications of electromagnetic waves.6.1. Principal results of the electromagnetic theory
The basic concepts of the electromagnetic theory are the electric field E and the magnetic induction field B (also called magnetic field for short) defined by their action on a charge q of velocity v[6.1]In the presence of dielectrics, we also have to introduce the electric displacement (also called electric induction ) D = εo E + P where εo = 8.8541878 x10−12 A2 s4 /kg.m3is the electric permittivity of vacuum and P is the density of polarization (or simply polarization ), i.e. the electric dipole moment of the dielectric per unit volume. In the presence of magnetic materials, we also have to introduce the magnetic field strength (also called magnetic intensity ) H = B/µo - M where µo = µo = 4π x 10−7 kg.m/A2 s2 is the magnetic permeability of vacuum and M is the intensity of magnetization (or simply magnetization
eBook - PDFTransparent Ceramics
Materials, Engineering, and Applications
- Adrian Goldstein, Andreas Krell, Zeev Burshtein, Andreas Krell(Authors)
- 2020(Publication Date)
- Wiley-American Ceramic Society(Publisher)
11 2 Electromagnetic Radiation: Interaction with Matter To facilitate understanding of the issues debated in Chapters 3–5, this chapter discusses certain aspects of electromagnetic radiation interaction with matter in gen-eral, and with solid matter in particular, with emphasis on the relevant spectral range. The focus is on processes that lead to disruption of the light beams impacting solid objects: intensity loss, polarization change, and others. A quite large fraction of space is devoted to theoretical background necessary for interpretation of optical and magnetic electronic spectra. The intention is to provide, for that topic, a relatively easy-to-read text for the interested ceramicists. Original sources for acquiring this knowledge, while excellent, require exten-sive and in-depth knowledge of some aspects of physics and mathematics, often not part of the background ceramicists have acquired during their studies and from experience. Emphasis is put on theoretical spectroscopy because it is well presented in some books devoted to glass technology [B18, P14] while otherwise in books on ceramics engineering. 2.1 Electromagnetic Radiation: Phenomenology and Characterizing Parameters An accelerated charged particle generates electromag-netic radiation, roughly classified as “near field” and “far field.” Near field occurs in the light source vicinity and diminishes at distances of only several wavelengths away. The field radiation intensity decreases proportionately to the third power of distance. For example, loops of elec-trical currents (electron hordes in movement) produce a static magnetic field (magnetic dipole type), rapidly diminishing away from the source current. Moving charges, particularly antennas, which generate an alter-nating electric field (namely, an alternating electrical dipole), produce an alternating electromagnetic field propagating in space.
- Christopher John Coleman(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
2 The Fundamentals of Electromagnetic Waves The equations that describe electromagnetic fields are due to James Clerk Maxwell and were the culmination of the discoveries of many different scientists, particularly during the eighteenth and nineteenth centuries. The final form of the equations required the modification of previously existing laws, but led to a total description of electro- magnetism that has stood the test of time. Indeed, Maxwell’s equations were some of the few that came through the revolution of relativity unscathed. Further attesting to their correctness, they predicted radio waves and showed light to be an electromagnetic phenomenon. The following chapter develops some of the fundamental ideas of elec- tromagnetic waves, starting with Maxwell’s equations. In addition, it introduces some ideas concerning antennas that are of importance to the development of the propagation aspect of radio waves. 2.1 Maxwell’s Equations The more popular form of Maxwell’s equations is ∇ · B = 0 (2.1) ∇ · D = ρ (2.2) ∇ × E = − ∂ B ∂ t (2.3) ∇ × H = ∂ D ∂ t + J (2.4) where E , D, B, H are the electric intensity (V/m), electric flux density (C/m 2 ), mag- netic flux density (W/m 2 ) and magnetic intensity (A/m), respectively. The field sources are the electric charge distribution ρ (C/m 3 ) and the current distribution J (J = ρ v where v is the velocity field of the charge) given in A/m 2 . For an isotropic dielectric material, B = μH (2.5) D = E (2.6) where μ and are permeability and permittivity (sometimes known as the dielectric constant) of the material. These quantities can be tensor in nature if the propagation 15 16 The Fundamentals of Electromagnetic Waves medium is anisotropic, but we shall initially assume the medium to be isotropic and hence these quantities are scalars.
eBook - PDF- Stephen McKnight, Christos Zahopoulos(Authors)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
15 Electromagnetic waves What makes some materials transparent to electromagnetic waves and other materials opaque to the same waves? A screen room is an enclosure completely surrounded by conducting (usually copper) screen where low-noise experiments can be isolated from external electromagnetic interference. If a radio is playing inside a screen room when the copper screen door is shut, the radio immediately goes silent. How thick should the screen be to have the desired effect? Does this effect mean that there is no way to electromagnetically detect an explosive charge concealed inside an aluminum soda can? This is one of the problems that we will address in this chapter and the next where we look at solutions to Maxwell’s equations in the form of traveling waves and examine the propagation properties of these waves in various materials. It is a remarkable success of electromagnetic theory that the same four Maxwell’s equations can describe phenomena from near DC through radio-frequency up to optical properties. While we will not attempt to describe the mathematics around the extremely non-linear quantum regime described by the “photonics” field, we will at least point out in Chapter 16 where classical Maxwellian theory has limitations and where we would have to expand our assumptions to explain photonic phenomena. 15.1 Maxwell’s equations and electromagnetic waves in free space We will begin our treatment with Maxwell’s equations in differential form, as intro- duced in the last chapter. In fact, the derivation of electromagnetic waves is one of the strongest motivations for studying the differential form of Maxwell’s equation.
eBook - ePub- John R. Howell, M. Pinar Mengüc, Kyle Daun, Robert Siegel(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
Even though later studies have shown that quantum mechanics is a more general theory for energy transfer at all scales, EM wave theory is sufficient for understanding light and radiative energy propagation and its interaction with matter at most size ranges. The Maxwell equations can explain almost all fundamental physics, from nanoscales to stellar systems (Jackson 1998, Mishchenko et al. 2006). In the context of radiative transfer, the concepts of reflection, refraction, transmission, and scattering can be explained using these equations. In addition, values for these parameters, as well as absorptivity of materials can, in certain cases, be calculated from their optical and electrical properties, as shown for the applications in Chapter 3. However, the Maxwell equations do not account for blackbody emission, which needs to be considered separately and is discussed in Chapter 16. Here, relations between radiative, optical, and electrical properties are developed by considering wave propagation in a medium and the interaction between the EM wave and matter. An ideal interaction is considered for optically smooth, clean surfaces that reflect, refract, and transmit the incoming wave in a specular, i.e. mirror-like, behavior. Most real surfaces are not mirrorlike since almost all have surface roughness, contamination, impurities, and crystal-structure imperfections, requiring the development of different approximations to account for diffuse or diffuse-specular reflection, refraction, and transmission characteristics. The departures of real materials from the ideal conditions assumed in the theory can produce large variations of measured property values from theoretical predictions. Although the Maxwell equations cannot completely predict the radiative properties of real surfaces, they serve a number of useful purposes
eBook - PDF- W. G. Rees(Author)
- 2012(Publication Date)
- Cambridge University Press(Publisher)
This situation is important in understanding techniques for atmospheric temperature sounding. In situations where both absorption and scattering are important, the behaviour of electromagnetic radiation in the medium depends on the ratio of the scattering coefficient of the absorbing coefficient as well as on the optical thickness of the medium. If the ratio is much greater than 1 it indicates that a photon has a much greater chance of being scattered than of being absorbed, and an optically thick medium will be highly reflective. This multiple-scattering phenomenon is the reason why weakly absorbing materials, when finely subdivided, scatter radiation strongly. It is observed at visible wavelengths for clouds, snow and many powdered materials, in the near-infrared for healthy green-leafed vegetation, and at microwave frequencies for dry snow packs and vegetation canopies. 3.6 Interaction of electromagnetic radiation with real materials ................................................................................ We have now considered the factors that govern the reflection of electromagnetic radiation from solid and liquid surfaces, and its behaviour in inhomogeneous media, in some detail, and we ought now to try to use these ideas to understand the way electro-magnetic radiation interacts with some real materials. By extension, we can also consider the emission properties in those parts of the electromagnetic spectrum – namely, the thermal infrared and microwave regions – in which they are important. The treatment in this section is rather brief. A fuller discussion can be found in, for example, Elachi and van Zyl ( 2006 ). 94 Interaction of electromagnetic radiation with matter 3.6.1 Visible and near-infrared region The visible and near-infrared (VNIR) region of the electromagnetic spectrum, from 0.4 m m to about 2 m m, is still the most important for remote sensing of the Earth’s surface.
eBook - PDF- David J. Griffiths(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
9.3 Electromagnetic Waves in Matter 409 and (iv) says 1 μ 1 v 1 ˜ E 0 I − ˜ E 0 R = 1 μ 2 v 2 ˜ E 0 T . (9.104) Given the laws of reflection and refraction, Eqs. 9.102 and 9.104 both reduce to ˜ E 0 I − ˜ E 0 R = β ˜ E 0 T , (9.105) where (as before) β ≡ μ 1 v 1 μ 2 v 2 = μ 1 n 2 μ 2 n 1 , (9.106) and Eq. 9.103 says ˜ E 0 I + ˜ E 0 R = α ˜ E 0 T , (9.107) where α ≡ cos θ T cos θ I . (9.108) Solving Eqs. 9.105 and 9.107 for the reflected and transmitted amplitudes, we obtain ˜ E 0 R = α − β α + β ˜ E 0 I , ˜ E 0 T = 2 α + β ˜ E 0 I . (9.109) These are known as Fresnel’s equations, for the case of polarization in the plane of incidence. (There are two other Fresnel equations, giving the reflected and transmitted amplitudes when the polarization is perpendicular to the plane of incidence—see Prob. 9.17.) Notice that the transmitted wave is always in phase with the incident one; the reflected wave is either in phase (“right side up”), if α > β , or 180 ◦ out of phase (“upside down”), if α < β . 15 The amplitudes of the transmitted and reflected waves depend on the angle of incidence, because α is a function of θ I : α = 1 − sin 2 θ T cos θ I = 1 − [(n 1 / n 2 ) sin θ I ] 2 cos θ I . (9.110) In the case of normal incidence (θ I = 0), α = 1, and we recover Eq. 9.82. At grazing incidence (θ I = 90 ◦ ), α diverges, and the wave is totally reflected (a fact 15 There is an unavoidable ambiguity in the phase of the reflected wave, since (as I mentioned in the footnote to Eq. 9.36) changing the sign of the polarization vector is equivalent to a 180 ◦ phase shift. The convention I adopted in Fig. 9.15, with E R positive “upward,” is consistent with some, but not all, of the standard optics texts. 410 Chapter 9 Electromagnetic Waves that is painfully familiar to anyone who has driven at night on a wet road). Inter- estingly, there is an intermediate angle, θ B (called Brewster’s angle), at which the reflected wave is completely extinguished.
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