Contents 6 Dielectric Properties

Another example is the influence of the electrical resistance of PVC cable insulation. This is caused not by the organic pigment itself but by ethoxylated surfactants, which are added as auxiliaries in the manufacture of these pigments, especially azo pigments. Contrary to a repeatedly expressed view, a possible electrolyte content, which laked azo pigments for example can have, has no effect on the dielectric properties of PVC [34]. Some pigment manufacturers offer special product ranges with verified dielectric properties for this purpose. 

P.R.57 1 is employed in cable insulations because of its good dielectrical properties. It is much more lightfast in rigid PVC transparent colorations (0.1% pigment) equal step 6 on the Blue Scale, while white reductions with TiOz match between step 4 and step 2, depending on the standard depth of shade and on the TiOz content. 

The dielectric properties of water have been extensively used to determine moisture content in food systems. However, only veiy recently have we used the complex dielectric properties of emulsions in the microwave frequency region to characterize both emulsion type and water content [50-52], We have developed both a cavity resonance dielectrometer capable of operating at 8-11 GHz and an interference dielectrometer operating at 23.45 GHz. 

Mudgett, R., Goldblith, S., Wang, D., and Westphal, W. 1977. Prediction of dielectric properties in solid food of high moisture content at ultrahigh and microwave frequencies. Journal of Food Processing and Preservation 1 119-151. 

Distributed circuit methods use coaxial lines, waveguides and resonant cavities at microwave frequencies. The circuits are designed for measuring an attenuation factor and a phase factor, from which sample dielectric properties can be calculated. The sample may form the dielectric medium between the two conductors of a coaxial line (Scaife et al, 1971), or an open coaxial line is brought into contact with the sample surface (Roussy and Pearce, 1995). Fagan et al, (2004) used an open coaxial line method to demonstrate that the moisture and salt contents of processed cheese could be predicted by measuring dielectric properties over a range of frequencies. 

This depends on the relaxation times of the molecules in the material, which, in turn, depends on the nature of the functional groups and the volume of the molecule. Generally, the dielectric properties of a material are related to temperature, moisture content, density and material geometry. 

The industrial ceramics produced by conventional sintering of 8-phase Si3N4 powders synthesized by SHS (Petrovskii et al, 1981) can be used as high-temperature articles with attractive dielectric properties (tan6=4.4 10 at/= 10 Hz, and dielectric strength, Ea=9.2 kV/mm). Also, silicon nitride powders with a relatively high a-phase content ( 80%) have been used for the production of advanced structural ceramics with good mechanical properties ([Pg.109]

At 0=0.270 and 0=0.353 the dielectric properties of the system were found to change upon ageing of the samples. Because of the "ageing effect",the SPS dielectric curves of 0=0.270 as well as the DPS ones of 0=0.353, flatten and a trend like that observed on the samples with wery low water content results (Figure 1-a,curve Fage(j)-... 

Heat content and heat flow Heat content and heat flow Dielectric properties Mechanical relaxation Volume expansion Electrical properties Molecular relaxations Molecular mobility... 

A. Thermal or RF contact current bums should be treated in a similar manner as conventional bums. Although similar, RF bums, whether thermal of contact current burns, are different from conventional burns in that contiguous tissue are not necessarily affected. Which tissues are affected depends on the frequency of the incident radiation and the dielectric properties and/or water content of the affected tissues. All other reported symptoms such as headaches, nausea, fatigue, anxiety, etc. should be treated in conventional manners, as appropriate. 

Food is a complex mixture of different components and its dielectric properties are highly dependent on its compositions. Moisture content and salt concentration usually play a major role in determining the dielectric properties of foods. Figure 3.1 shows the relationship between the dielectric loss factor components and temperature. 

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