Designing nanostructured materials and metamaterials for energy applications

Xiao, John Q.The microwave wireless power transfer system can be divided into five elements, including energy emission component, energy harvesting module, energy storage component, power conditioning component and functioning module. This dissertation is dedicated to developing a new class of microwave wireless power transfer system by investigating the first three elements. To increase the energy harvesting efficiency, the metamaterial absorber based energy harvesting device was introduced. The investigation to this new device started with a transmission line model to characterize the metamaterial absorber and followed by demonstration in both simulation and experiment for the energy harvesting based on metamaterial absorber with varies of substrate materials. Both simulation and experimental results are qualitatively consistent with the transmission line model prediction that the signal transfer ratio reduces when the dielectric loss of the substrate increases. The highest experientially demonstrate signal transfer ratio reaches 96% when using Rogers 5880LZ as the substrate material. In order to increase the transmission efficiency between the emission component and energy harvesting module, it is desired to identify the incident wave direction from the energy harvesting perspective and enhance the antenna gain from both emission and energy harvesting perspectives. To identify the incident wave direction, we have adapted the basic design of metamaterial absorber to fabricate a microwave subwavelength imaging device. Similar to an optical camera, such device is able to track the incident wave direction when combining with a microwave lens. The performance test of the imaging device based on metamaterial absorber has shown that it can not only identify the position of the focused beam with an accuracy of 1% wavelength in the far field imaging test, but also is capable of carrying out near field imaging by capturing the electromagnetic power distribution with ignorable distortion to the original power distribution. The gain enhancement was proposed by placing a artificial magnetic conductor (AMC) underneath the radiation antenna. AMC is able to reflect the microwave with a phase shift of between -90 and 90 degree in a frequency band, call in-phase reflection band. We have built a transmission line model for AMC. Derivation based on this transmission line model reveals that the in-phase reflection bandwidth has a theoretical limit as a function of the thickness and permeability of AMC substrate. The method of making the in-phase reflection bandwidth of an AMC sample approaching its theoretical limit has been proposed. Experimentally, a ratio to the theoretical limit of 98.5% has been achieved, which is the highest compared to a number of reported values in AMC simulation and experiment results. By comparing out proposed method to two previously reported methods, we found that our proposed method gives more restricted value. Finally, work has been carried out to develop a new class of energy storage component for the microwave wireless transfer system. A Fe-Ni based electrochemical negative electrodes has been experimentally demonstrated by sintering chemically prepared Fe–Ni nanoparticles into a nanoporous pellet with thickness of 65 μm and mass loading density of 20 mg/cm-2. This electrode is consisted of nanoscale mixture of an Fe-rich body-centered cubic Fe(Ni) phase and a Ni-rich face-centered cubic Fe–Ni phase. The high conductive and structure stability is provided by the Ni-rich phase and the electrochemically active component of the electrodes is produced by the selective conversion of the Fe-rich phase to hydroxides. The experimental measurement shows the compositionally optimized electrodes exhibit a specific capacitance in excess of 350 F/g by normalizing to the whole electrode mass and retain more than 85% of their maximum specific capacitance after 2000 charging/discharging cycles. This desirable combination of physical and electrochemical properties indicates that such electrodes may be useful as the negative electrode in high performance asymmetric supercapacitors.University of Delaware, Department of Physics and AstronomyPh.D