Physical properties dielectric frequency dependence

If the structure of water depends on distance from a surface, so must its physical properties, including its dielectric function. We noted in Section 9.5 that at microwave frequencies the dielectric function of water changes markedly when the molecules are immobilized upon freezing as a consequence, the relaxation frequency of ice is much less than that of liquid water. Water irrotationally bound to surfaces is therefore expected to have a relaxation frequency between that of water and ice. 

Dipole-dipole interaction between molecules placed in an oscillating electric field results in energy being transferred from the oscillating field to the sample. This phenomenon manifests itself as a frequency dependent dielectric constant and is a property common to all materials. The physical basis of the measurement is expressed by Equation 3. 

In order to investigate the origin and the physical properties of SPPs, we consider a metal-dielectric interface described by the plane z = 0 (see Fig. 1.6). The local frequency-dependent dielectric function is supposed to change in a stepwise manner from the dielectric with e z) = (for z > 0) to the metal with c(z) =... 

A. Previous models of water (see 1-6 in Section V.A.l) and also the hat-curved model itself cannot describe properly the R-band arising in water and therefore cannot explain a small isotope shift of the center frequency vR. Indeed, in these models the R-band arises due to free rotors. Since the moment of inertia I of D20 molecule is about twice that of H20, the estimated center of the R-band for D20 would be placed at y/2 lower frequency than for H20. This result would contradict the recorded experimental data, since vR(D20) vR(H20) 200 cm-1. The first attempt to overcome this difficulty was made in GT, p. 549, where the cosine-squared (CS) potential model was formally (i.e., irrespective of a physical origin of such potential) applied for description of dielectric response of rotators moving above the CS well (in this work the librators were assumed to move in the rectangular well). The nonuniform CS potential yields a rather narrow absorption band this property agrees with the experimental data [17, 42, 54]. The absorption-peak position Vcs depends on the field parameter p of the model given by... 

From the value of the resonant frequency and its change with temperature or other external parameters the permittivity of a dielectric sample and its temperature or field dependence can be determined. In case of superconductors, the temperature dependence of the magnetic field penetration depth can be determined [8], Since the mode spectrum of a resonator is controlled both its physical dimensions and by the material properties, the physical dimensions of all resonator components have to be known with tight tolerances. Relative changes of permittivity or penetration depth can be determine with much higher accuracy than absolute values. 

The role of inherent polarization and ionic transport effects in actuation mechanism of EAPap actuators are investigated. To physically investigate the actuation mechanism, several tests are performed. X-ray diffraction (XRD) spectra are compared before and after electrical activation and the possibility of crystalline structure change is observed. Dielectric property measurement indicates a dependence of the dielectric constant on fiber direction, as well as on frequency, humidity, and temperature. Thus, we conclude that piezoelectric effect and ionic migration effect are in the EAPap at the same time associated with dipole moment of cellulose paper ingredients. The amount of these effects may depend on environmental condition. 

If a polymer mass containing only truly covalent bonds free from dipoles is placed in an electric field there is an instantaneous electron shift (electron polarization) but no actual movement of the molecules themselves. If this field is between two charged plates the polymer acts as a dielectric in a capacitor and the capacity of the charged plates is increased. The factor by which the capacity is increased is known as the dielectric constant or permittivity. Because it depends on virtually instantaneous electron movement the value of the dielectric constant is not dependent on temperature nor on the frequency (if the field is subject to alternation). The dielectric constant of such materials is frequently equal to the square of the refractive index and both properties may be calculated from a knowledge of the chemical bonds present. The method of making such a computation is given in most standard texts on physical chemistry. 

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