Permittivity and Permeability Measurements of CISR sheets for Microwave Absorber Applications

Complex permittivity (epsilon(r)) and complex permeability (mu(r)) of Carbonyl Iron filled Silicon Rubber (CISR) sheets are calculated from measured S-11 and S-21 by reflection and transmission method for microwave absorber applications. Rectangular Dielectric Waveguide (RDWG) system operating in frequency range of 4 to 8 GHz is used for measurement of S-11 and S-21. RDWG system is non-destructive in nature. For S-11 and S-21 measurements, TRL (Through, Reflect, Line) calibration method and time domain gating in VNA are used to calibrate and remove all measurement errors associated with the RDWG system due to multiple reflections. Five CISR sheets are fabricated with 0%, 19%, 24%, 33% and 43% of Carbonyl Iron (CI) powder by volume. For design multilayered microwave absorbers, epsilon(r) and mu(r) values are required for arbitrary volume fraction of CI in CISR sheets. In this paper, epsilon(r) and mu(r) are obtained by using exponential dielectric mixture theory or by using linear interpolation techniques.