Dielectric constant and dissipation factor

Dielectric constant (e) and dissipation factor (DF) are related to capacitance (C) and can be calculated from capacitance measurements. Capacitance, between a parallel-plate capacitor, is directly proportional to the dielectric constant of the insulator separating the conductors and the conductor area, A, andinverselyproportionaltothedistance,c/, between the conductors as shown in  

If the gap between the plates is filled with a dielectric material, the capacitance increases by a constant factor characteristic of that material. The dielectric constant, e, is defined as  

Because dielectric material affects the force with which two oppositely charged plates attract each other, the dielectric constant may also be defined as the relative effect of the medium on this force of attraction, according to Coulomb s equation  

The dissipation factor, DF, is the ratio of the resistive (loss) component of current 1 to the capacitive component of current, and equals the tangent of the dielectric loss angle, 5, as follows  

As for dielectric constant, test methods for dissipation factor may also be found in ASTM D150.[ l 

Aside from the advantage of the DOP and Ti02 described above, both the DOP and Ti02 have the same drawback of increasing the dissipation factor at low frequencies, as is shown in Fig. 6.17. An increase in this factor will reduce the efficiency of the actuation. Moreover, this increase will make the synthetic elastomer become hot during its actuation and therefore, will affect the overall performance of the actuator. 

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Electrical Properties. CeUular polymers have two important electrical appHcations (22). One takes advantage of the combination of inherent toughness and moisture resistance of polymers along with the decreased dielectric constant and dissipation factor of the foamed state to use ceUular polymers as electrical-wire insulation (97). The other combines the low dissipation factor and the rigidity of plastic foams in the constmction of radar domes. Polyurethane foams have been used as high voltage electrical insulation (213). 

Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

Figure 8.19 Schematic relationship between loss factor, dielectric constant, and dissipation factor...

Dielectric constant and dissipation factor measurements were conducted according to the procedures of ASTM D-150-87. Tensile strength and modulus and percent elongation were measured on an Instron model 1125 according to the procedures of ASTM-D-882-83. 

The result of the dielectric testing on these polymers was quite encouraging. All of the polymers that were tested demonstrated low dielectric constant and dissipation factor values. 

A new method for the syntheses of fluorocarbon polyarylate polymers has been demonstrated. The chemistry utilizes the [2jt+2rr] cyclodimerization of fluorinated olefins and generates polymers of novel composition. The first generation of polymers prepared by this method are polyarylate homopolymers. Theremoplastic polymers of high molecular weight can be achieved via neat or solution polymerization. One example of a thermoset polymer prepared by this method has a high Tg, low dielectric constant and dissipation factor, low moisture... 

Both the dielectric constant and dissipation factor are measured by comparison of results obtained with those obtained from a sample with known dissipation factor or dielectric constant values or substitution in an electrical bridge. 

In general, fluoropolymers possess the unique combination of high thermal stability, chemical inertness, unusual surface properties, low dielectric constants and dissipation factors, low water absorptivities, excellent weatherability and low flammabilities. Therefore there appears to be an ever-increasing market for fluoropolymers in spite of their relatively high cost [211,212],... 

Certain grades of ETFE are used for extruded foams with void contents from 20 to 50%. The closed foam cells are 0.001 to 0.003 in. (0.02 to 0.08 mm) in diameter. Special grades of ETFE processed in gas-injection foaming process may have void contents up to 70%. Foamed ETFE is used in electrical applications, mainly in cables, because it exhibits lower apparent dielectric constant and dissipation factor and reduces cable weight. 

Electrical Properties. The electrical properties of silicone gels are essentially the same as those of most clean, unfilled silicone elastomers and fluids. Typical values for dielectric constant and dissipation factor when tested at 25°C and 100 Hz are 2.7 to 2.9 and 0.001 to 0.002 respectively. Volume resistivity values, usually, fall in the 10 ohm- centimeter range. 

Water absorption of the resultant cured materials was measured after immersion for 24 hrs at room temperature and reported as % weight gain. The modulus was measured according to ASTM D 2240, and the dielectric constant and dissipation factor were measured using a method similar to ASTM D 150. Glass and melting transitions were measured by differential scanning calorimetry (DSC). The thermal stability was determined in a forced air oven... 

Figures 1 and 2 show the bulk electrical properties of the two cured molding compounds. The dielectric constant and dissipation factor were determined before and after moisture exposure. For moisture exposure, the samples were placed in an autoclave at 100% relative humidity, 15 psig, and 250°F for 500 hours. Measurements...

Polysulfone is UL listed for continuous service at 320F, although it will withstand higher temperatures intermittently. It offers a good combination of electrical properties dielectric strength and volume resistivities are high, while dielectric constant and dissipation factor are low. 

Articles on special types of polymers in various editions and volumes of the Encyclopedia of Polymer Science and Engineering, tabulations in the Polymer Handbook, and product brochures and catalogs on commercial polymers, were among the sources of data used for the dielectric constant and dissipation factor. 

Electrical properties. Fillers and additives significantly increase the porosity of polytetrafluoroethylene compounds. Electrical properties are affected by the void content as well as the filler characteristics. Dielectric strength drops while dielectric constant and dissipation factor rise. Metals, carbon, and graphite increase the thermal conductivity of PTFE compounds. Tables 3.19 and 3.20 present electrical properties of a few common compounds. 

PTFE dielectric constant and dissipation factors remain constant over a broad temperature range (-40 to 240°C) as seen in Fig. 3.28.1 They are not... 

The stability of PTFE is evidenced by a lack of change in its dielectric constant after aging at 300°C for a period of nine months (Table 3.31). There are no other plastics known to exhibit these properties. Exposure to weather has no effect on the dielectric constant and dissipation factor. Figure 3.30 summarizes the results of a ten-year study in south Florida where representative samples were exposed to the climatic elements. No change in dielectric constant or dissipation is detected as a result of weathering. 

Figure 3.103 Dielectric constant and dissipation factor vs outdoor exposure time.> >...

Tables 3.70 through 3.72 summarize the effect of one-year South Florida outdoor exposure on the electrical and mechanical properties of FEP. Little change has occurred in the dielectric breakdown strength, dielectric constant, and dissipation factor of FEP due to exposure. Tensile strength and break elongation measurements are essentially unchanged. The only decline is in the MIT flex life (ASTM D2176) of the one-year sample, which could be due to measurement error. The reason for a decrease in flex life could be the MIT method that has a high degree of uncertainty. Certainly, the other mechanical properties do not support the measured decline in the flex life.

It was discovered that a number of PVDF film properties, including electrical, could be altered by the extrusion and orientation conditions.The relationship between the extrusion and orientation process and the electrical properties of the film are important because of the application of PVDF films in miniaturized capacitors which are used in apparatus such as defibrillators. To compare the properties, extruded film, while in molten state, was brought in contact with chilled rollers at 80°C and cooled rapidly. The oriented film was stretched at 150°C in the longitudinal direction by a stretch ratio of 3.5, that is, its original length was increased by 3.5 times [Eq. (6.6)]. The dielectric constant and dissipation factor were measured as seen in Table 6.8. Orientation increased the dielectric constant and reduced the dielectric loss... 

Class 1 dielectrics include ceramics with relatively low and medium dielectric constants and dissipation factors of less than 0.003. The low range covers / static = 5 to 15, and the medium /Tstatic range is 15 to 500. 

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