Electromagnetic damping

Cage effect. Electromagnetic radiation will be caged in small compartments of m-size according to interference. Quantumelectrodynamic calculations propose an increase of the radiation density up to a factor of 106, and correspondingly the release of radiation will be damped. 

Additional complications arise when the EM wave in a dissipative medium approaches a vacuum interface at an oblique angle [26]. The incident and reflected wave fields then become inhomogeneous (damped) in the direction of propagation. As a consequence the matching at the interface to a conventional undamped electromagnetic wave in vacuo becomes impossible. 

Exercise. Apply the result (2.10) to a plane electromagnetic wave in a medium whose dielectric constant varies randomly with x. How is it possible for the wave to be damped although the medium gains no energy ... 

In Maxwell s theory, this dispersion of energy is considered to be negligible, and no damping occurs during the propagation of an electromagnetic wave. Let us consider the plane waves propagating in the z direction ... 

The galactic redshift could obviously be attributed to the damping of the electromagnetic waves emitted from various galaxies in random motion within a stationary universe. Now, comparison between Hubble relativistic linear law and the logarithmic law that comes out from Maxwell electromagnetic wave equation shows that, in any case, the logarithmic law fits experimental data very well and thus better than linear law. 

At the other limit, when r > 1, the time of travel of the signal across the gap Z and back is longer than the lifetime of the electromagnetic fluctuation. The damping term goes to zero almost exponentially ... 

The electromagnetic fields of the right- and left-propagating polaritons, respectively, follow the wave equations with the speeds and damping rates of the different frequency components dispersed according to the frequency- and wavevector-dependent complex refractive index n = v/e(k, oj). A typical example of the dispersion of these modes is shown in Fig. 1 for the case of a real permittivity e. The term Ao(r,t) represents the envelope of the wavepacket on the phonon-polariton coordinate A. Note that this phonon-polariton coordinate is a linear combination of ionic and electromagnetic displacements, which both contribute to the polarization... 

Fic. 35.—Apparatus for measuring the effect of humidity on the damping of electromagnetic waves. 1, screw press 2, measurement cell 3, electrode 4, bow dynanometer 5, starch sample. (Reprinted with permission from M. Boruch, S. Brzezinski, and A. Palka, Acta Aliment. Pol., 11 (1985) 115-124.)... 

Fig. 7. Electromagnetic waves and sound waves. When the frequency of the waves (light or sound) equals the natural frequency of the chemical group or polymer, an absorption peak is found. The energy is converted into molecular motion, i.e., heat. Illustrated for the damping curve are the / -transition, the glass transition, and the liquid-liquid transition.

Figure 1 shows the entire test system in schematic form. The test sample is comprised of two specimens of a viscoelastic damping polymer loaded in shear by force from an electromagnetic shaker. Each specimen is cemented between a centrally located, driven steel sample block and one of two clamped reaction blocks. The dimensions of each block in this apparatus are 25.4mm height,... 

In general, dielectric materials can absorb and dissipate energy bom an electromagnetic field by several processes, such as ionic hopping, dipole releixation, damping of molecular vibrations Qnfra-red) and of dectronic vibrations (optical). 

The motion actually observed by i.r. absorption is a small part of the whole pattern, since for effective absorption one must match both frequency and wavelength in the electromagnetic and crystal osdllations. Absorption occurs essentially at the frequency of the longest waves present in the crystal These waves are damped by anharmonic interaction with the numerous short-wave modes, except at very low temperatures where interaction with ctystal ddects and surfaces takes over. In spite of the complexity of the process one has to expect a simple lineshape and a fairly simple temperature dependence for a wave propagating in one crystal direction. 

In contrast to dielectrics, the electromagnetic waves that penetrate metals are damped the extinction coefficient k in the complex refractive index n = n — ik is not equal to zero, but generally greater than n. For the spectral emissivity s Xn normal to the surface, the electromagnetic theory delivers the relationship... 

The purpose of these storage systems is to damp power fluctuations in the power grid to prevent computer crashes and equipment failure. Energy is stored in powerful electromagnets and can be retrieved whenever there is a need to stabilize line voltage during unanticipated disturbance in the power grid. 

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