Microstrip-Tunable Band-Pass Filter Using Ferrite (Nanoparticles) Coupled Lines

In this paper, we designed, fabricated, and characterized a novel band-pass filter using ferrite nanoparticles as the active element in microstrip geometry. Two 50-Omega Cu transmitting/receiving antennas (one side fed and the other side shorted) were fabricated by photolithography on top of a thick layer of ferrites (Fe₃O₄) nanoparticles. The filter is based on ferromagnetic resonance. It is very compact and has very wide frequency tunability. Linear dependence is obtained between the resonance frequency and the applied dc magnetic field. The bandwidth and Q-factor of the filter are observed to be almost constant over the field range studied. Theoretical calculations have been performed considering the ferrite nanoparticles as an effective medium with effective demagnetization. The frequency for different applied fields was calculated for different volume fractions, and it is shown theoretically that the control of band-pass frequency can also be achieved by varying the volume fraction of the nanoparticles in the effective medium.