Permittivity alternating currents

Electrochemical and Electrical Methods. Electrochemical and electrical methods for studying film properties and corrosion phenomena have been extensively reviewed (29-31). Comparisons of corrosion test results with direct current measurements of conductivity suggest that visible corrosion is associated with film resistance less than about 1 Mohm/cm, but this condition may well correspond with the occurrence of virtual pores in the film allowing development of local conductive pathways. In studies of the equivalent alternating current resistance as a function of frequency, Kendig and Leidheiser (44) found that the development of a region of slope -1 on a log permittivity versus log frequency plot... 

For all real electrical insulating materials, the alternating current through a capacitor using the material as dielectric is different in phase from the voltage across the capacitor by an angle less than 90, and therefore mathematically the impedance of the capacitor is treated as a complex quantity. The angle for a capacitor with vacuum dielectric is 90, and therefore the permittivity (see below) is itself a complex number. 

Chemists often reason in terms of dielectric permittivity (e) or infrared spectra (a) while electrical engineers and physicists consider tangent loss (tg = e"/s ) and alternative current conductivity (free charges (where the complex impedance formalism is well-suited) and bound charges (where the description of the permittivity s = e (co) — ie"(co) is more suitable) can be distinguished. Such a distinction is not straightforward in superionic conductors, however, in which some conducting species are in a quasi-liquid state and in particular, for proton conductors. In the latter, the proton (attached... 

Dielectric dispersion. It is the change with the frequency of an applied alternating current (AC) field of the dielectric permittivity of a suspension of colloidal particles. The phenomenon... 

In the presence of an alternating current, the polarization of the material can follow the changes of the electric field only in the lower-frequency region. As the frequency increases, polarization is no longer able to follow the changes of the field, and consequently a dispersion of the dielectric permittivity occurs with increasing frequency (Figure 8.9). 

Displacement of mobile charges is often spatially limited due to heterogeneous stmcture of the polymer matericds or blocking electrodes therefore, the dc conductance may be not observable, but alternative current (ac) conductivity (cfac) can be found at sufficiently high frequencies. If the limitation of carrier mobility occurs at the phase boundary, the interfacial polarization occurs. The polarization may also be induced by the reorientation of the dipoles present in the stmcture of maciomolecules in the direction of electrical field. The polarization effects are related to dielectric properties characterized by complex dielectric permittivity which is frequency... 

AKernating current conductivity The alternating current conductivity (trjc) measurements are usrraUy carried out in a frequency range between 10" and 10 Hz for the sandwich-type samples. The equivalent parallel capacitance C co) and conductance G co) are obtained from the experiments and then they are transformed into different representations, like complex resistivity p, complex conductivity a, complex modulus M, and complex permittivity ... 

When applying an alternating electric field to a polymer placed between two electrodes, the response is generally attenuated and the output current is out of phase compared with the input voltage. This response stems from the polymer s capacitive component and its conductive or loss component, as represented by a complex dielectric permittivity measured frequencies f, and temperatures T ... 

When a field E is applied across a dielectric (a simple parallel plate condenser, for example), the resulting displacement current, D is related to E as D = eE. In glasses, which are dielectrically isotropic, the permittivity, 8 behaves as a scalar quantity and is equal to D E. While E is an experimentally controlled alternating field of arbitrary frequency, D and s are the material dependent responses and Z), which represents the polarization current is not always in phase with E. s is, therefore, a complex frequency dependent quantity. The complex permittivity, e, is defined as... 

Practically, DMTA is limited to low frequencies (up to tens of hertz) and, consequently, provides information about relatively slow processes. Dielectric spectroscopy is a related approach in which an alternating electric field is applied to a sample and the complex permittivity is then obtained from phase and amplitude measurements of current and voltage again, it is possible to consider data in the frequency domain, the temperature domain, or even as frequency/temperature contour maps.2 ° 2 See Refs. 230 and 232 for a theoretical account of the underlying physics. The approach can provide information in the frequency range W -io" coupling the applied electric field... 

Some LB films exhibit a temperature-dependent pyroelectric coefficient that makes them candidates for thermal imaging applications (1). Both X- and Z-type films and alternating Y-type films (Fig. 6) can be built with permanent polarization, whose magnitude is often temperature-dependent. Their pyroelectric coefficient p is small relative to standard semiconducting and ceramic materials, but so is their permittivity e this makes their ratio p/s, the figure of merit, comparable to that as for currently employed inorganic materials. The advantage of LB methods is that they can be used to prepare very thin, very uniform films. 

The admittance composed of conductivity o and permittivity ZoZ regulates the steady-state current flowing through a dielectric sample subjected to an alternating voltage. The quantity is given in complex notation by... 

Many materials systems are currently under consideration as potential replacements for Si02 as the gate dielectric material for sub-0.l-ftm CMOS technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band... 

The electrical testing of polyethylene materials seeks to determine the response of a sample to various types of electric fields. Variables include voltage, current (alternating and direct), contact or noncontact conditions, and various types of surface contamination. Methods of characterizing the electrical properties of polyethylene fall into two general categories those that determine electrical characteristics predictive of end use performance and those that seek to rank materials with respect to one another. The first type is exemplified by the measurement of relative permittivity, the second by the determination of arc resistance. 

Alternating eurrent loss and permittivity Electrieal insulation Direet eurrent electrical resistance High voltage, low current arc resistance Dieleetric constant and dissipation factor Corona discharge... 

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