Dielectric loss factors frequency effects

Detailed examination of the relaxations requires isothermal scans of relative permittivity and dielectric loss factor as a function of frequency/ so that effective dipole movements and activation energies of relaxation times may be obtained. A typical pair of plots of d and e" values against log/is shown in Fig. 3.7. Graphs of dielectric data of this kind are sometimes called, rather... 

Mirin is a condiment with almost 40%-50% sugar and is widely used in Japanese cuisine. Dielectric loss factor of mirin is affected by both the dipolar loss component and the ionic conductivity. Ionic conductivity is lower at higher microwave frequencies. The combined effect of temperature, microwave frequency, and sugar content is complex and hard to describe. Nevertheless, the e" increases with frequency and temperature. The penetration depth decreases as the processing temperature increases. The effect of temperature on the is significant at lower processing frequencies at higher frequencies, temperature has only moderate effect on the d. Tanaka et al. (2005) reported similar results for soy sauce. It was noted by Liao et al. (2003) that this trend is distinctive for thick or complex solutions. 

Hence, the dc contribution to the dielectric loss factor at 20°C can be neglected. First at lower frequencies and higher temperatures a still relative small dc conduction effect is calculated, for exatiple at 100 Hz ... 

While the dielectric properties of a polymer system clearly have engineering value, changes in dielectric behavior with composition yield fundamental information. The behavior of the dielectric loss factor, tan 5, for the polyurethane/polystyrene sequential IPN was investigated by Lipatov et al Employing a frequency of 300 Hz, they studied the effect of filler over the temperature range -130 to 20°C. In this temperature range, the polystyrene does not exhibit a maximum in tan S however, the polyurethane does, at a temperature just below 0°C. Figure 7.1 shows the effect of Aerosil content on the loss peak. For convenience, the maxima in tan 8 are collected in Table 7.1. 

As already stated, the addition of metallic fillers to a formulation serves to decrease the electrical insulation, but there may be other effects on the compound s electrical properties that may need to be taken into account. The frequency dependence of the dielectric loss factor increases as the metallic particles offset the low loss factors of the binder system. The loss factor is defined as the product of the power factor and the dielectric constant and is a measure of the signal absorption by the compound. Normally, low loss factors are desirable, particularly where a material is to be used in devices operating at high speed such as gallium arsenide based semiconductors, and this should be taken into account when formulating with conductive extenders. 

The frequency response of a DR coupled to a microwave circuit is shown in Fig. 5.34. The selectivity Q of the resonator is given by /r/A/ and, under conditions where the energy losses are confined to the dielectric and not to effects such as radiation loss or surface conduction Q (tan (5)-1 where tan 3 is the loss factor for the dielectric. 

The power-loss meter is the most common type of dielectric moisture meter. It senses the product of the dielectric constant and loss factor. Generally, the loss factor increases with wood moisture content but may exhibit variations from this behavior depending on the frequency of measurement (JO, 11, 14). An increase in temperature produces effects similar to increasing moisture content, with interaction between these two parameters. Therefore, temperature adjustments of meter readings are complex, sometimes increasing and sometimes decreasing the scale reading as temperature increases... 

Cheese is another popular dairy product, which is rich in protein, calcium, and phosphorus. The dielectric properties of cheese are important in developing new microwave processing methods. Everard et al. (2006) studied the effects of different microwave frequencies (300 MHz-3 GHz) on the dielectric properties of cheese. Their results showed that the dielectric constant (e ) and the loss factor (e") both decreased as the processing frequency increased. Eor e, the decrease with increasing frequency followed a linear path. In the case of s", the relationship was inversely proportional. Nelson and Bartley (2000) and Wang et al. (2003) both reported similar decrease in e and e" as the frequency increased from 27 to 1800MHz and 27 to 915 MHz, respectively. 

Beef is one of the important meats in many different cuisines and is consumed all over the world. It is a rich source of selenium, zinc, iron, vitamin B, and carnitine. The dielectric constant (s ) and the loss factor (s") of beef both increase at higher temperatures. For example, s values of lean beef at 27.12MHz were 36.0 and 68.8 at -5°C and -1°C, respectively. Temperatures in the range of -1°C and 10°C did not have a significant effect on s and s" at any microwave frequency. Higher temperature had more effect on s" for all meats at 27.12 MHz and s" increased with temperature (Ryynanen, 1995 Shukla and Anantheswaran, 2001). 

Two basic contributions are expected to the variation of dielectric properties of a hydrated material with respect to those of a dry one that of the polar water molecules themselves and the second one due to the modification of the various polarization and relaxation mechanisms of the matrix material itself by water [37]. In the low frequency region of measurements, there is a third contribution, often ignored in works dealing with high frequency measurements, which arises from the influence of moisture on conductivity and conductivity effects. The increase of electrical conductivity of the sample is the major effect present in wet samples dielectric response is often masked by conductivity, and it superposes the dielectric processes in the loss spectra and demands a conductivity correction of the dielectric loss spectra [9]. This dc conductivity strongly affects the modifled loss factor, e". In this case, it can be expressed as shown in the following equation ... 

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