Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Jing Wang, Ph.D.

Committee Member

Sylvia Thomas, Ph.D.

Committee Member

Arash Takshi, Ph.D.

Committee Member

John N. Kuhn, Ph.D.

Committee Member

Dario Arena, Ph.D.

Keywords

Soft Magnetic Ferrites, Complex Permeability, Complex Permittivity, Resonance Frequency, Patch Antenna, Reflection Coefficient

Abstract

Novel soft magnetic ferrite materials will play a crucial role in next-generation over one trillion sensors (also known as “trillion sensor economy) related to 5G communications and internet of things, as these materials can achieve improved wireless power and signal transfer efficiency with high operation frequency. In this work, Ni-Cu-Zn and Ni-Co-Zn ferrites with high permeability, high permittivity, and low magnetic and dielectric losses were prepared for RF and microwave device applications. Frequency dispersion of RF complex permeability of Ni-Cu-Zn ferrites prepared under different applied hydraulic pressures and durations have been thoroughly investigated. The Ni0.35Cu0.19Zn0.46Fe2O4 ferrites were prepared by conventional ceramic synthesis process. The obtained ferrite powders were pressed under different hydraulic pressures (4 MPa, 8 MPa, 12 MPa) over different durations (30 sec, 2min, 3min and 5 min). It was found that the complex permeability spectra change considerably with respect to the application of different hydraulic pressures and time duration. Porosity and grain size play an important role in affecting the permeability and magnetic loss tangent of the ferrite samples. A significant increase of the real part of the complex permeability from 96 to 139 is observed due to the application of hydraulic pressure of 12 MPa for 3 min as compared to a manually pressed sample. The magnetic loss tangent also increases from 0.01 to 0.02 as the imaginary part of the complex permeability increases, which is still acceptable for most of the wireless power transfer and wireless communication applications. It is postulated that the effect of elevated hydraulic pressure on ferrite powder-based composites increases the real part of permeability while influencing magnetic loss tangent less severely.

In this work, Ni-Cu-Zn and Ni-Co-Zn ferrites with high permeability and low magnetic loss were prepared and characterized for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO and Co2O3 dopants were employed during the synthesis of Ni-Cu-Zn and Ni-Co-Zn ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (µ’ of 4 -10) and relatively low magnetic loss tangent (tanδ_m of 0.01- 0.1) has been achieved at frequency range between in high frequency (HF) and ultra-high frequency (UHF) ranges. Addition of CuO, especially up to 3 wt%, and Co2O3 up to 0.25 mole percent can cause a significant increase in permeability, while noticeable reduction in magnetic losses has been observed for the doped ferrite sample. The resonance frequency of synthesized ferrites has also been shifted into the GHz range, when higher concentration of CuO dopants (> 5 wt%) and lower concentrations of Co2O3 were employed.

Electromagnetic properties of Ni-Co-Zn/Epoxy magnetic composite substrates filled with different volume fractions of ferrite particles have been studied and were analyzed using different mixture models. Based on the properties of the Ni-Co-Zn/Epoxy magnetic composite substrates, a prototype antenna for MICS band (401 MHz - 406 MHz) have been designed by using 3D EM simulations by ANSY/HFSS. Subsequently, the antenna design was implemented by compression molding method. The performance of the Ni-Co-Zn/Epoxy substrate based antenna was compared with the dielectric-only substrate antenna fabricated with a commercial microwave laminate (i.e., Rogers RO3010 with a permittivity εr=10.2). A miniaturization of 16 % in patch antenna area and a 104% enhancement in antenna bandwidth along with an acceptable gain of 1.85 dBi has been achieved by the patch antenna implemented by Ni-Co-Zn/Epoxy magnetic substrate as compared to the reference design fabricated using the dielectric core layer of a Rogers RO3010 laminate.

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