Dielectric systems

Mcllhagger, A., Brown, D., and Hill, B. (2000). The development of a dielectric system for the on-line cure monitoring of the resin transfer moulding process. Composites Part A Appl. Sci. Manuf. 31(12), 1373-1381. 

The operating frequencies are determined by the capacitance of the electrode dielectric system in general multiple electrodes require a lower frequency. If possible it is preferable to use more than one electrode—as this gives a more uniform discharge, more even treatment and a lower gap current—enabling the dissipation of more power and so lengthening the lives of electrodes and dielectric. 

It is well known that in isotropic and purdy dielectric systems (i.e. in the absence of condudivity and didectric loss) ellipsoidal particles always tend to be aligned with their longest axis parallel to the applied field. This is in prindple not true, however, if the conductivity of the material involved must also be taken into account Nevertheless, it can be shown that still one of the prindpal axes of the ellipsoid is oriented parallel to the field in the state of minimum energy (setting aside very abnormal cases where the complex dielectric constant of the particle is described by a tensor whose principal axes do not coindde with those of the ellipsoid). 

The three phase dielectric system backbone-waterlayer-air of a real RF aerogel is reduced to a two layer system. The third phase (air) is neglected because of its relative low influence (compared to the other two phases) on the compound dielectric permittivity according to its own material parameters e and k. In order to explain the measured spectra by Maxwell-Wagner polarization processes due to the absorbed water we propose the following model. ... 

Impedance data are presented in different formats to emphasize specific classes of behavior. The impedance format emphasizes the values at low frequency, which t5rpically are of greatest importance for electrochemical systems that are influenced by mass transfer and reaction kinetics. The admittance format, which emphasizes the capacitive behavior at high frequencies, is often employed for solid-state systems. The complex capacity format is used for dielectric systems in which the capacity is often the feature of greatest interest. 

As shown in Example 16.1, the admittance format is ideally suited for analysis of dielectric systems for which the leading resistance can be neglected entirely. 

The characteristic frequency evident as a peak for the imaginary part of the complex-capacitance in Figures 16.12(b) and 16.13(b) has a value corresponding exactly to fc = 27tReC) only for the blocking system. As found for data presentation in admittance format, the presence of a Faradaic process confounds use of graphical techniques to assess this characteristic frequency. Like the admittance format, the complex capacitance is not particularly well suited for analysis of electrochemical and other systems for which identification of Faradaic processes parallel to the capacitance represents the aim of the impedance experiments. It is particularly well suited for analysis of dielectric systems for which the electrolyte resistance can be neglected. 

R. L. Hurt and J. R. Macdonald, "Distributed Circuit Elements in Impedance Spectroscopy A Unified Treatment of Conductive and Dielectric Systems," Solid State Ionics, 20 (1986) 111-124. 

Application in Monte Carlo simulations of inhomogeneous dielectric systems... 

Problem 16.8. Let us use the superscript (0) for the state of the dielectric system where the charge distribution is zero. This implies that P ° r) = 0 so that the reorganization energy of any other state relative to this one is... 

Pressed lead azide is a two-phase dielectric system consisting of azide crystals of various dimensions and air in the pores at ambient pressure. Its dielectric strength varies with the density, crystal dimensions, thickness, etc. 

Suppose that the dielectric system relaxes due to the application of a constant field E at time t = 0. Then equation (4.5.10) simplifies to... 

The dielectric measurements were performed on an automated difference dielectric system (10, 11, 12). Thin films of the purified polymer (less than 1 mm) were cast at room temperature directly onto the cell from three successive 5-mL applications of a 1.0% (w/v) acetone solution. Each application was allowed to dry in a closed environment. After a suitable film was obtained, it was vacuum dried for 12 h. The original films were run, irradiated, and rerun, allowing us to observe the effects of irradiation on the same sample. The temperature range investigated was from —200° to 100°C, over a frequency range of 0.234-20.0 kHz. The thin films were used to... 

Difference dielectric measurements were obtained by placing the unirradiated PNF spectra in the memory of the dielectric system, and subtracting the unirradiated spectra from the irradiated. 

Another self assembled monolayer which has been applied to OFETs is based on phosphonic acids. Phosphonic acids attach to many metals and metal oxides, including alumina, and provide essentially the same passivation and surface energy engineering on that dielectric system [40]. 

Beginning with the work by Ohno and Yonezawa on PFN-PFW systems in the late 1970s [8], many multicomponent dielectric systems have been evaluated and put into manufacture. Some of the patented compositions developed for multilayer capacitor (MLC) application were recently summarized by Shrout and Dougherty [9]. Other compositions were developed for piezoelectric sensors and electrostrictive actuator applications [10]. Most of the compositions used for capacitor dielectrics are based on PFN [8], PMN [11-14], or PZN [15]. 

If the power reqnirement is high, over 50 kW, economics favor the dielectric system. 

Heterogenous dielectric systems exhibit some special properties, among which most notable is interfacial polarization caused by hindered charge movement at the interfaces. This effect makes dielectric spectroscopy (AC and DC methods), in combination with other methods of structure determination, a usefol tool in studying the following phenomena in composite materials ... 

Conductive System (k = Z) General System Normalized Dielectric System (k = )... 

The circuit shown in Eigure 2.2.2a is just that originally proposed by Cole and Cole [1941] for dielectric systems. It yields capacitances Co in the ft) 0 limit and C in the ft) —> °o limit. When one uses the Eq. (18) definition of the CPE admittance, it leads to the following expression for e. 

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