Dissipation factors values

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. 

Remove specimen adjust micrometer so that the instrument indication of capacitance is returned to its original value C. Record the dissipation factor value D. Record the micrometer reading mj. 

Electrical properties The dielectric strength of PTFE varies with the thickness and decreases with increasing frequency. It remains practically constant up to 300 °C and does not vary even after a prolonged treatment at high temperatures (6 months at 300 °C). PTFE has very low dielectric constant and dissipation factor values that remain unchanged up to 300 °C in a frequency field of up to 10 GHz, even after a prolonged thermal treatment... 

Quantitatively, lower dissipation factors result in higher-quality, higher-performance electrical or electronic systems, having lower electrical losses. Dissipation factor values have no units because they are mathematical ratios. Low dissipation factor values, desirable for electronic plastics, would be below 0.01 and 0.001. Two other terms for dissipation factor are loss tangent and tan delta. A related term is quality factor or Q factor, which is the reciprocal of the dissipation factor. See also dielectric properties electronic plastic. 

The main driver for fluoroplastic foams has been the insulation for data transmission cables. An example is coaxial cables that have relatively thick insulation. Its low dielectric constant and dissipation factor are desirable electrical properties. Air has the ideal dielectric constant (1.0). The ideal dissipation factor for data-cable insulation is zero. Perfluoropolymers have low dielectric constant and dissipation factor values (Table 11.2, see Ch. 6 for additional data). Foaming perfluorinated fluoropolymers further reduces the dielectric constants toward 1.0 and moves the dissipation factors closer to zero because the resin is replaced with air-filled cells in the insulation. The decrease in the dielectric constant is proportional for example, FEP insulation with 60% void content had a dielectric constant of More uniform foam cell size and smaller cells yield foams with the best electrical properties. 

The dielectric loss characteristics of polar polymers are much more complicated, as would be expected from the theoretical aspects described above. The range of values in the dissipation factor for a variety of plastic material is tremendous (see Figs. 35 and 36). The absorption peaks also vary greatly in width. In general, the dissipation factor at a given frequency and temperature cannot be predicted for other conditions. The common practice of providing one value at perhaps 1000 Hz is obviously completely inadequate in the functional sense. For a meaningful evaluation, it is necessary to obtain dissipation factor values over... 

In air, PTFE has a damage threshold of 200—700 Gy (2 x 10 — 7 x 10 rad) and retains 50% of initial tensile strength after a dose of 10" Gy (1 Mrad), 40% of initial tensile strength after a dose of 10 Gy (10 lad), and ultimate elongation of 100% or more for doses up to 2—5 kGy (2 X 10 — 5 X 10 rad). During irradiation, resistivity decreases, whereas the dielectric constant and the dissipation factor increase. After irradiation, these properties tend to return to their preexposure values. Dielectric properties at high frequency are less sensitive to radiation than are properties at low frequency. Radiation has veryHtde effect on dielectric strength (86). 

The electneal properties of PTFE are dominated by its extremely tow dielectric constant (2.1) This value is invanant over a broad range ot temperatures (- 40 to 250 °C) and frequencies (5 Hzto 10 GHz). Smularly, PTFE has an unusually low dissipation factor, which is also quite mdependent of temperature and frequency fhis behavior results from the high degree of dipolar symmetry of the perfluonnated and unbranched chains The dielectnc strength, resistivity, and arc resistance are very high... 

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. 

Relative to microelectronic applications, the out-of-plane dielectric constant for BPDA-PFMB films measmed after aging at 50% relative humidity for 48 h at 23°C was between 2.8 and 2.9 (0.1 kHz to 1 MHz) (ASTM D-150-81These values are considerably lower than that of commercial polyimides such as PMDA-ODA (pyromellitic dianhydride, PMDA) (s = 3.5 at 1 kHz and 3.3 at 10 MHz). The dielectric constant and tan 8 (dissipation factor) were temperature- and frequency-dependent. The dielectric constant, which was independent of temperature until near 210°C increased above this point until a frequency-dependent maximum was reached at about 290°C. The dissipation factor, which was also independent of temperatme below 200°C, underwent a rapid increase with no maximum between 200 and 400°C owing to ion conductivity. The temperatme at which this increase occurred increased as the frequency increased. The films also... 

With conventional heating, energy transfer occurs mainly through conduction and convection. With microwaves, the primary mechanism is dielectric loss4,52. The dielectric loss factor (loss factor, s") and the dielectric constant ( ) of a material are two determinants of the efficiency of heat transfer to the sample. Their quotient ( "/ ) is the dissipation factor (tan 8), high values of which indicate ready susceptibility to microwave energy. 

The standard method for making measurements of dielectric properties is to place a sample between closely spaced parallel conducting plates, and to monitor the AC equivalent capacitance and dissipation factor of the resulting capacitor. The capacitance is proportional to the dielectric permittivity (e ) at the measurement frequency, and the dissipation factor in combination with the value can be used to extract the dielectric loss factor (e"). ... 

Class II/III dielectrics consist of high-permittivity ceramics based on ferro-electrics. They have er values between 2000 and 20 000 and properties that vary more with temperature, field strength and frequency than Class I dielectrics. Their dissipation factors are generally below 0.03 but may exceed this level in some temperature ranges and in many cases become much higher when high a.c. fields are applied. Their main value lies in their high volumetric efficiency (see Table 5.1). 

The effects of temperature and frequency on the permittivity and dissipation factor of a high-purity alumina ceramic are shown in Fig. 5.24. The discrepancies between the permittivity levels in Fig. 5.24 and values given elsewhere are probably due to differences in microstructure and measurement technique. Reliable room temperature values for er for single-crystal sapphire at 3.4GHz are 9.39 perpendicular to the c axis and 11.584 parallel to it, which are close to the values measured optically. The average er to be expected for a fully dense ceramic form is therefore 10.12, and values close to this have been determined. Nothwithstanding the uncertainties there is no doubt that the general behavioural pattern indicated by Fig. 5.24 is correct and typical of ceramic dielectrics. 

The final quantity to be defined has been the source of much confusion. The loss tangent of the sample is the same as the dissipation factor defined above however, the loss tangent of the medium is a dielectric property. To distinguish between them, we shall refer to tan 8X as the sample loss tangent, having the value... 

One should not emphasize the values of the constants in Equation 1 since a change in measurement conditions (i.e., the dissipation factor at the appropriate temperature at another experimentally measurable frequency) leads to different values, although the form is retained. 

Figure 8 shows a set of load-displacement curves for HM5411EA tested at 1 mm/s. Following the EWF procedure, the plot of the specific work of fracture, uy vs. ligament length, / is produced (Fig.9). It can be seen that linear approximation fits the data very well. From the Intercept between the fitted line and the y-axes, the value of 25.18 kJ/m is obtained for the essential work of fracture. This value represents fracture toughness under plane stress conditions. The slope of the linear fit represents the plastic work dissipation factor, Pwp, where is a shape factor associated with the shape and size of the plastic zone, and Wp is the plastic work dissipation per unit volume of material. The values of fiwp for all cases are given in Table 1.

The viscosity of a sample reflects its ability to absorb microwave energy because it affects molecular rotation. The effect of viscosity is best illustrated by considering ice water. When water is frozen, the water molecules become locked in a crystal lattice. This greatly restricts molecular mobility and makes it difficult for the molecules to align with the microwave field. Thus, the dielectric dissipation factor of ice is low (2.7 X 10 at 2450 MHz). When the temperature of the water is increased to 27°C, the viscosity decreases and the dissipation factor rises to a much higher value (12.2). 

Major results. Figure 14.7 shows that the resistivity of aluminum-filled PMMA changes abruptly. Smaller volumes of filler contribute a little to resistivity but, after certain threshold value of filler concentration, further additions have little contribution. A similar relationship was obtained for nickel powder the only difference is in the final value of resistivity, which was lower for nickel due to its higher conductivity. The same conclusions can be obtained from conductivity deteiminations of epoxy resins filled with copper and nickel. Figure 14.8 shows the effect of temperature on the electric conductivity of butyl rubber filled with different grades of carbon black. In both cases, conductivity decreases with temperature, but lamp black is substantially more sensitive to temperature changes. Even more pronounced changes with temperature were detected for the dielectric loss factor and dissipation factor for mineral filled epoxy." ... 

---