Characterization and Applications of Micro- and Nano- Ferrites at Microwave and Millimeter Waves
materials are one of the most widely used magnetic materials in microwave and millimeter
wave applications such as radar, wireless communication. They provide unique properties
for microwave and millimeter wave devices especially non-reciprocal devices. Some
ferrite materials with strong magnetocrystalline anisotropy fields can extend these
applications to tens of GHz range ... read morewhile reducing the size, weight and cost. This thesis
focuses on characterization of such ferrite materials as micro- and nano-powder and the
fabrication of the devices. The ferrite materials with strong magnetocrystalline
anisotropy field are metal/non-metal substituted iron oxides oriented in low crystal
symmetry. The ferrite materials characterized in this thesis include M-type hexagonal
ferrites such as barium ferrite (BaFe12O19), strontium ferrite (SrFe12O19), epsilon
phase iron oxide (ε-Fe2O3), substituted epsilon phase iron oxide
(ε-GaxFe2-xO3, ε-AlxFe2-xO3). These ferrites exhibit great anisotropic
magnetic fields. A transmission-reﬂection based in-waveguide technique that
employs a vector network analyzer was used to determine the scattering parameters for
each sample in the microwave bands (8.2-40 GHz). From the S-parameters, complex
dielectric permittivity and complex magnetic permeability are evaluated by an improved
algorithm. The millimeter wave measurement is based on a free space quasi-optical
spectrometer. Initially precise transmittance spectra over a broad millimeter wave
frequency range from 40 GHz to 120 GHz are acquired. Later the transmittance spectra are
converted into complex permittivity and permeability spectra. These ferrite powder
materials are further characterized by x-ray diffraction (XRD) to understand the
crystalline structure relating to the strength and the shift of the ferromagnetic
resonance affected by the particle size. A Y-junction circulator working in the 60 GHz
frequency band is designed based on characterized M-type barium micro- and nano-ferrite.
A new fabrication process using ferrite composite is proposed to integrate the
Y-junction circulator into the semiconductor substrate. Theoretical design of a high
gain Traveling Wave Tube (TWT) amplifier using a metamaterial (MTM) structure and
cold-test of the MTM structure are also included in this dissertation. An SWS working
around 6 GHz below the X-band waveguide TE10 cutoff frequency is
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Electrical Engineering.
Advisor: Mohammed Afsar.
Committee: Douglas Preis, Austin Napier, and Nian Sun.
Keywords: Electrical engineering, Electromagnetics, and Materials Science.read less
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