A shielded, conductor-backed coplanar waveguide technique is used to determine the complex permittivity and loss tangent of nano magnetic composite materials over X-band. The test composite material is synthesized by reinforcing cobalt ferrite particles with average crystallite diameter 7.36 nm in low density polyethylene matrix with 2% and 4% volume fractions. The complex permittivity for low density polyethylene matrix and the composite samples, evaluated from the present technique at 9.887 GHz, are verified with cavity perturbation technique resonating at the same frequency. A new mathematical approach, using element-to-element correspondence of the ABCD matrix, is applied to calculate the complex propagation constant. The formulation facilitates evaluation of complex propagation constant over the test frequency range using scalar scattering parameters without altering the coplanar waveguide geometry. The mathematical formulation is verified by performing permittivity measurements for air over the X-band.
Abstract-A tunable microwave notch filter is developed on magnetodielectric material having low saturation magnetization to attain low external dc magnetic field for biasing. A simple microstrip line at 10 GHz is developed on nickel ferrite/low density polyethylene nanocomposite system as substrates and its microwave transmission response is studied in X-band. Composite system is developed by dispersing nano sized nickel ferrite (∼6.63 nm) in low density polyethylene to obtain a homogeneous flexible substrate. Saturation magnetization of 4% volume fraction of the composite is found to be 1.8745 emu/g. Tunability of Q value and insertion loss is studied with magnitude of external dc magnetic field and at different angles of its orientation with the axial plane. A very low field up to 250 G is sufficient to tune the selectivity. An insertion loss of ∼ −30 dB and Q ∼ 375 at 10.2 GHz is observed. The interaction of magneto static modes with orientation of the applied dc magnetic bias with respect to rf magnetic field is discussed with couple mode theory. Good cutoff behaviour of more than 28 dB is observed at magnetic field angles from 23.52 • to 34.21 • . The experimental and theoretical couplings show close proximity.
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