Cryogenic complex anisotropic permittivity of magnesium fluoride

Abstract

The complex tensor permittivity of MgF 2 has been measured using whispering gallery mode and quasi TE 0np dielectric post resonator techniques as a function of frequency and temperature. MgF 2 exhibits uniaxial anisotropy. At room temperature permittivity component parallel to the anisotropy axis is 4.77 ± 0.2% and the component perpendicular to anisotropy axis is 5.49 ± 0.2%. Dielectric loss tangent component perpendicular to anisotropy axis is approximately 4 × 10 −5 and dielectric loss tangent component parallel to anisotropy axis is approximately 7 × 10 −5 at 39 GHz and room temperature. Losses at room temperature increase quasi-linearly with frequency. At the temperature of 15 K measured loss tangent values for both the components of the dielectric loss tangent were about 1 × 10 −6 at 39 GHz. The RF and microwave losses of magnesium fluoride (MgF 2) crystal are low as compared with other commonly used Fluorides. MgF 2 is hygroscopic and dielectric losses of this material vary with the contents of water.