Automated dielectric measurements on low loss solid materials

Precise measurements of dielectric loss (tanδ) and permittivity (ε¹) are required on a routine basis in the quality control of dielectrics in applications where these properties vitally affect the performance of the completed system. Examples are afforded by the low-loss polyethylene (P.E.) used in submarine telephone cables, alumina substrates for microwave integrated circuits and glass-ceramics used as radomes. In each application the particular property of interest is different and thus the method of measurement needs to be specifically tailored to the controlling specification. Two basic principles, however, apply over the frequency range of interest 100kHz to 10 GHz: (a) the value of tanδ must be measured at the frequency of application of the material, preferably by comparison with a material of negligible loss (e.g. a dry gas); (b) the permittivity is best measured at low frequencies (<; 12 MHz), provided that the dielectric loss is low (<; 1000 μrad) and known over the frequency range concerned.