ASTM D2149-13 (R2021) pdf free download.Standard Test Method for Permittivity (Dielectric Constant) and Dissipation Factor of Solid Dielectrics at Frequencies to 10 MHz and Temperatures to 500 °C.
3. Terminology
3.1 Definirions.
3.1.1 Permittivity and dissipation factor are fully defined in Terminology D171 1. Briefly, the permittivity of an insulating material is the ratio of the capacitance between two conductors when embedded in the material to the capacitance between the same configuration of conductors in a vacuum (or air). The dissipation factor is the ratio of the resistive to capacitive currents in the dielectric. The product of the permittivity and dissipation factor is the loss index.
4. Significance and Use
4. 1 Permittivity and dissipation factor arc sensitive to changes in chemical composition, impurities, and homogeneity. Measurement of these properties is. therefore, useful for quality control and for determining the effect of environments such as moisture, heat, or radiation.
5. Apparatus
5. 1 Measuring Circuits—Suitable measuring circuits are described in Test Methods D150. For measurements from
50 Hz to 100 kHz a substitution method using a low-voltage capacitance bridge is recommended. For measurements at
1 MHz and above, a resonant-circuit susceptance variation method is recommended. The Q of the circuit has to be at least 200 except for very low loss materials, for which a Q of 500 or higher is desirable.
5.2 Test Enclosure—Unless testing only at room temperature, it is necessary to adapt a Hartshorn-Ward type specimen holder to a temperature-controlled test enclosure. Where applicable, use the requirements for a grade A enclosure as in Specification El97. A suggested arrangement is shown in Fig. 1. This arrangement provides terminal connections away from the temperature zone.
5.3 Specimen Holder—The suggested arrangement shown in Fig. 1 incorporates the following requirements:
5.3.1 The selection of the metals is of utmost importance. The metal has to be of good thermal and electrical conductivity and yet be oxidation resistant and have sullicient strength to maintain its mechanical dimensions after repeated heating. AISI Stainless No. 316 fulfills these requirements except for the thermal conductivity. The time required for a specimen to reach equilibrium in a holder made from this material is quite long. Precious metal alloys such as type B silver-magnesium- nickel have better overall properties hut require special heat treating.
5.3.2 The preferable insulator materials are aluminum oxide, beryllium oxide, or polytetrafluoroethylene.
5.3.3 Use electrodes 50 mm in diameter and at least 5 mm thick, with sharp corners. Maintain electrode parallellism to within 0.01 mm.ASTM D2149 pdf download.