The overall goals of the present PhD research are to explore the giant magnetoimpedance (GMI) and giant magnetocaloric (GMC) effects in functional magnetic materials and provide guidance on the optimization of the material properties for use in advanced magnetic sensor and refrigeration applications. GMI has attracted growing interest due to its promising applications in high-performance magnetic sensors. Research in this field is focused on the development of new materials with properties appropriate for practical GMI sensor applications. In this project, we have successfully set up a new magneto-impedance measurement system in the Functional Materials Laboratory at USF. We have established, for the first time, the correlation between sample surface, magnetic softness, critical length, and GMI in Co-based amorphous ribbon materials, which provide a good handle on selecting the suitable operating frequency range of magnetic materials for GMI-based field sensor applications. The impact of field-induced magnetic anisotropy on the GMI effect in Co-based nanocrystalline ribbon materials has also been investigated, providing an important understanding of the correlation between the microstructure, magnetic anisotropy, and GMI in these materials. We have shown that coating a thin layer of magnetic metal on the surface of a magnetic ribbon can reduce stray fields due to surface irregularities and enhance the magnetic flux paths closure of the bilayer structure, both of which, in effect, increase the GMI and its field sensitivity. This finding provides a new way for tailoring GMI in surface-modified soft ferromagnetic ribbons for use in highly sensitive magnetic sensors. We have also introduced the new concepts of incorporating GMI technology with superparamagnetic nanopthesiss for biosensing applications and with carbon nanotubes for gas and chemical sensing applications. GMC forms the basis for developing advanced magnetic refrigeration technology and research in this field is of topical interest. In this project, we have systematically studied the ferromagnetism and magnetocaloric effect in Eu8Ga16Ge30 clathrate materials, which are better known for their thermoelectric applications. We have discovered the GMC effect in the type-VIII clathrate and enhanced refrigerant capacity in the type-I clathrate. We have successfully used the clathrates as excellent host matrices to produce novel Eu8Ga16Ge30-EuO composite materials with desirable properties for active magnetic refrigeration technologies. A large refrigerant capacity of 794 J/kg for a field change of 5 T over a temperature interval of 70 K has been achieved in the Eu8Ga16Ge30-EuO composite with a 40%-60% weight ratio. This is the largest value ever achieved among existing magnetocaloric materials for magnetic refrigeration in the temperature range 10 K - 100 K. The excellent magnetocaloric properties of the Eu8Ga16Ge30-EuO composites make them attractive for active magnetic refrigeration in the liquid nitrogen temperature range.

This dissertation presents the first reported systematic investigation on the implementation of multilayer patch antennas over Fe3O4-based polymer nanocomposite (PNC) magneto-dielectric substrates. The PNC substrate is created by the monodispersion of Fe3O4 nanopthesiss, with mean size of 7.5nm, in a polymeric matrix of Polydimethylsiloxane (PDMS). Recently, magneto-dielectric substrates have been proposed by several researchers as a means for decreasing the size and increasing the bandwidth of planar antennas. Nevertheless, factors such as high loss and diminished control over magnetic and dielectric properties have hindered the optimal performance of antennas. In addition, the incompatibility and elevated complexity prevents integration of conventional magnetic materials with antennas and standard fabrication processes at printed circuit boards (PCBs) and wafer levels. Additionally, the low hysteresis losses exhibited by uniformly embedded superparamagnetic nanopthesiss complemented by the ease of integration of polymer nanocomposites in standard fabrication processes, offer promising solutions to resolve any of the complications and concerns foresaid. Towards this dissertation work, one multilayer antenna was constructed over a molded PDMS substrate along with three similar antennas built on PDMS-Fe3O4 PNC substrates with different Fe3O4 nanopthesis loading concentrations in the PDMS matrix of 80%, 50% and 30% by weight. This pioneering work in the experimental implementation and characterization of magneto-dielectric PNC antennas has not only resulted in antennas with different operational frequencies in the 3-5GHz band, but also expanded our knowledge base by correlating the concentration of magnetic nanopthesiss to key antenna performance metrics such as antenna bandwidth, antenna efficiency and miniaturization factors. Among the most significant results a magneto-dielectric antenna with maximum miniaturization factor of 57%, and a 58% increase in bandwidth, whilst retaining an acceptable antenna gain of 2.12dBi, was successfully demonstrated through the deployment of molded PDMS-Fe3O4 PNC substrate under external DC bias magnetic fields. This dissertation also presents a versatile process for constructing flexible and multilayer antennas by the seamless incorporation of a variety of materials such as PDMS, Liquid Crystal Polymer (LCP) laminates, metal clads and molded magneto-dielectric polymer nanocomposites with evenly embedded magnetic nanopthesiss.

Phase-change heat transfer is an important process used in many engineering thermal designs. Boiling is an important phase change phenomena as it is a common heat transfer process in many thermal systems. Phase change processes are critical to thermodynamic cycles as most closed loop systems have an evaporator, in which the phase change process occurs. There are many applications/processes in which engineers employ the advantages of boiling heat transfer, as they seek to improve heat transfer performance. Recent research efforts have experimentally shown that nanofluids can have significantly better heat transfer properties than those of the pure base fluids, such as water. The objective of this study is to improve the boiling curve of de-ionized water by adding aluminum oxide nanopthesiss in 0.1%, 0.2%, 0.3% and 0.4% wt concentrations in a sub-cooled pool boiling apparatus. Enhancement to the boiling curve can be quantified in two ways: (i) the similar heat fluxes of de-ionized water at smaller excess temperature, indicating similar quantity of heat removal at lower temperatures and (ii) greater heat fluxes than de-ionized water at similar excess temperatures indicating better heat transfer at similar excess temperatures. In the same fashion, the secondary objective is to increase the convective heat transfer coefficient due to boiling by adding different concentrations of aluminum oxide nanopthesiss.