Dielectric, constant loss factor

The values of e and e" of a food material play a critical role in determining the interaction of the microwave electric field with the material. A discussion of these interactions follows. A "map" of foods plotted against their dielectric parameters was introduced by Bengtsson and Risman (1971). Table 1 gives values for the dielectric constant, loss factor and penetration depth, and Figure 1 shows a "map" of these values for common foods. 

Electrical properties Resistivity Conductivity Dielectric constant Loss factor Breakdown strength Electromechanical coupling constant... 

The electrical properties of interest for ceramics include conductivity, resistivity, dielectric breakdown strength, dielectric constant, loss factor, and electromechanical coupling. Most ceramics do not have high electrical conductivity, and thus ceramics have found application as electrical insulators for many years. The electrical insulating capability of some ceramics is also retained under high electric field this is referred to as high dielectric breakdown strength... 

Table 4.1 Dielectric constants, loss factors and dissipation factors for some common solvents (3 GHz microwave radiation, 25° C)...

Glass code Strain point Annealing Softening Working point point point Density, g/cm Poisson s ratio volume resistivity Power factor, % Dielectric constant Loss factor, %... 

Keywords— Permittivity, benign, malignant, breast tumour, urine, dielectric constant, loss factor, loss tangent. 

The purpose of this research is to analyze the permittivity of urine in order to differentiate between malignant tumuor from benign tumuor. Three parameters of permittivity are investigated dielectric constant, loss factor and loss tangent. 

Sihcone fluids have good dielectric properties, loss factor, specific resistance, and dielectric strength at normal operating conditions, and the properties vary only slightly with temperature (59,328,350). The properties in combination with relatively low flammabiUty have led to the use of siUcones in transformers and other large electrical appHcations (351). The dielectric constant of a 1000-cSt oil is 2.8 at 30°C and 2.6 at 100°C. The loss factor is low,... 

The field strength and the frequency are dependent on the equipment, while the dielectric constant, dissipation factor, and loss factor are material-dependent. The electric field strength is also dependent on the location of the material within the microwave/radio-frequency cavity (Turner and Ferguson, 1995), which is one reason why domestic microwave ovens have rotating turntables (so that the food is exposed to a range of microwave intensities). This mechanism is the major one for the generation of heat within materials by these electromagnetic fields. 

Polymers containing hydrolysable groups or which have hydrolysable groups introduced by oxidation are susceptible to water attack. Hydrolyzable groups such as esters, amides, nitriles, acetals, and certain ketones can react with water and cause deterioration of the polymer. The dielectric constant, power factor, insulation resistance, and water absorption are most affected by hydrolysis. For polyesters, polyamides, cellulose, and cellulose either and esters, the hydrolysable groups are weak links in the chain, and hydrolysis of such polymers can cause serious loss of strength. A summary of water absorption characteristics of common plastic and rubbers is presented in Table 1.15. 

D0150(2) Dielectric constant, dissipation factor, loss tangent, tan 8... 

As with the dynamic mechanical relaxations, it is also possible to check the dielectric behavior of the sample. In this case the thermal analysis is carried out measuring the dielectric constant, dissipation factor, loss index, and phase angle as a function of temperature and frequency. In order to see a dielectric effect, a dipole must be connected with the molecular motion. In this way dielectric relaxation may be more specific than DMA. A combination of DMA, dielectric measurements, and DSC is often needed for a detailed interpretation of the properties of the materials. ... 

The dielectric constant is an expression of the ratio of capacitance of a capacitor with plastic as the dielectric to the capacitance of the same capacitor with air as the dielectric. The loss factor, by contrast, is a measure of the energy that an insulating substance in an alternating field transforms into heat and is therefore lost as electrical energy. The dielectric characteristic values are material constants. They are dependent on temperature and frequency range and also on ambient conditions such as humidity, for example [8]. 

Tetralluoroethylene polymer has the lowest coefficient of friction of any solid. It has remarkable chemical resistance and a very low brittleness temperature ( — 100°C). Its dielectric constant and loss factor are low and stable across a broad temperature and frequency range. Its impact strength is high. 

Power factor, like the dielectric constant, is a property that represents a power loss that takes place when a wire insulation becomes the dielectric of a condenser because of a surrounding sheath or other conducting medium. 

Sheet Miea. Good quahty sheet mica is widely used for many iadustrial appHcations, particularly ia the electrical and electronic iadustries, because of its high dielectric strength, uniform dielectric constant, low power loss (high power factor), high electrical resistivity, and low temperature coefficient (Table 6). Mica also resists temperatures of 600—900°C, and can be easily machined iato strong parts of different si2es and shapes (1). 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

The observed dielectric constant M and the dielectric loss factor k = k tan S are defined by the charge displacement characteristics of the ceramic ie, the movement of charged species within the material in response to the appHed electric field. Discussion of polarization mechanisms is available (1). 

Figure 6.3. The variation of dielectric constant e and the loss factor e" with frequency. (After Frith and Tucketl, reproduced by permission of Longmans, Green and Co. Ltd.)...

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