Dissipation factors

The dissipation factor or (dielectric loss) is a measure of the loss rate of energy of a mode of oscillation in a dissipative system. A low dissipation factor implies efficient electrical insulation. 

The dissipation factor is defined as the ratio of in-phase power. It may also be defined as the tangent of the loss angle. It is frequency dependent. The lower the dissipation factor the more efficient the insulator system. 

Germer [1] has discussed the increasing use of PEEK for miniature electronics. Some examples of these are electrolytic capacitors, potentiomer components and micro-connectors. Ele discusses the thermal, electrical and mechanical properties of this polymer and gives data on permittivity and dissipation factor and heat resistance. 

Dissipation factors (5.2) range from very low, for example, polyolefins (i.e., exceUait rating) to relatively high, for example, nylons and polyvinyl fluoride. Methods for the measurement of the dissipation factor are listed in Table 5.1. 

The dielectric properties of materials are defined by two different parameters, namely the dielectric constant and the dielectric loss. The dielectric constant, e, describes the ability of a molecule to be polarized by the electric field. At low frequencies, e reaches a maximum as the maximum amount of energy can be stored in the material. The dielectric loss, s, measures the efficiency with which the energy of the electromagnetic radiation can be converted into heat. The dielectric loss goes through a maximum as the dielectric constant falls [16]. The dissipation factor (tan d) is the ratio of the dielectric loss of the sample, also called loss factor , to its dielectric constant tan 8 = e /s. 

Here kij is the thermal-conductivity tensor. Note that other notations are also used in the literature, e.g. k = k or K =k. 

In isotropic and cubic dielectric materials, the electric displacement field D, the electric field E, and the polarization P are connected by the relation 

The quality factor Q of the dielectric is the reciprocal of the dissipation factor  

In anisotropic crystals, these equations should be written in tensor form  

Hooke s law states that for sufficiently small deformations the strain is directly proportional to the stress. Thus the strain tensor S and the stress tensor T obey the relation 

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Dielectric constant (60 Hz) Dielectric constant (10 Hz) Dissipation (power) factor (60 Hz) Dissipation factor (10 Hz) 3-4... 

Dielectric strength, kV mm Electrical Volume (dc) resistivity, ohm-cm Dielectric constant (60 Hz) Dielectric constant (10 Hz) Dissipation (power) factor (60 Hz) Dissipation factor (10 Hz) Mechanical Compressive modulus, 10Mb in-2 9.8-12 24-31 16-24 1014-1016 4.5-6.0 19 335-600 14 ... 

Electrical Properties. The low polarizabiHty of perfluorinated Hquids makes them exceUent insulators. Theh dielectric strengths are about 40 kV (ASTM D877) dissipation factors are about 0.0001 at 1 MH2 dielectric constants are about 1.8 volume resistivities are about 1 x 10 ohm-cm (ASTM D257) (17). 

Polytetrafluoroethylene transitions occur at specific combinations of temperature and mechanical or electrical vibrations. Transitions, sometimes called dielectric relaxations, can cause wide fluctuations in the dissipation factor. 

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 dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

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 Insulation. The substitution of a gas for part of a soHd polymer usuaUy results in large changes in the electrical properties of the resulting material. The dielectric constant, dissipation factor, and dielectric strength are aU generaUy lowered in amounts roughly proportional to the amount of gas in the foam. 

Fig. 10. Power factor at 1 MHz vs temperature for some commercial glasses. Courtesy of Corning Inc. The power factor is the ratio of the power ia watts dissipated ia a material to the product of the effective siausoidal voltage and current ia volt-amperes. When the dissipation factor is less than 0.1, the power...

Grade 1—T1 Flex strength, MPa Water absorption, % Permittivity, 1 MHz Dissipation factor, 1 MHz Impact strength, J/m Dielectric breakdown parallel to laminations, kV... 

To minimize electrical losses, especially at high frequencies, a low dissipation factor is required. High volume resistance provides good insulation to prevent... 

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