Measurement Of Dielectric Loss Factor Research Articles

Dielectric cure monitoring and optimization of film adhesives

Abstract Dielectric loss factor measurements were studied as a means for cure cycle monitoring and optimization of structural film adhesives. Three film adhesives were included in the study: a high-temperature-curing epoxy (175°C cure), a low-temperature-curing epoxy (120°C cure) and a 175°C curing polyimide. Generally, three regions can be distinguished in the dielectric loss factor with respect to heating time. First, the softening or flow region, where the loss factor exhibits a plateau and in which the resin viscosity attains low values. Second, the polymerization peak where the loss factor attains a maximum, and finally the region where the loss factor approaches an asymptote, indicating completion of curing. In the present study the three regions were first characterized as functions of heating time for each adhesive using a laboratory oven. Next, the heating conditions were optimized in an autoclave where lap shear specimens were prepared for mechanical properties evaluation, in addition to in situ monitoring of the dielectric loss factor. In the final stage of the study, dielectric cure monitoring was shown to be adequate for characterizing and establishing optimized time-temperature-pressure processing conditions for aged epoxy film adhesives.

Measurement of Dielectric Constant and Loss Factor of Powder Materials in the Microwave Region

A system has been developed to measure the dielectric properties of powder materials using X band microwave frequencies. The measurement is conducted in a microwave cavity oscillating in the TM012 mode and resonant at 9.4kMc. Relatively small amounts of material are needed, and samples are introduced into the cavity using a quartz tube. The limitation of the perturbation theory as a basis for computation is examined experimentally. The suitability of different equations correlating the apparent dielectric constant of the powder material with the intrinsic values of the solid (crystalline or fused solids) is demonstrated by the data.

The Measurement of Dielectric Constant and Loss Factor of Liquids and Solutions between 250 and 920 Mc./s. by Means of a Coaxial Transmission Line

The Measurement of Dielectric Constant and Loss Factor of Liquids and Solutions between 250 and 920 Mc./s. by Means of a Coaxial Transmission Line