The Study On Metamaterial Design And Applications For Absorber And Wireless Power Transfer

Electromagnetic(EM)metamaterials(MMs)exhibits exceptional physical properties,which are not available in natural materials.The design of novel MMs,the exploration of EM response of the unit-cell structure,and extension of its theoretical analytical methods have promoted its applications of military stealthy,photoelectric devices,wireless power transfer and so on.In this thesis,some designs of MM absorbers and negative permeability MMs for applications of wireless power transfer systems are investigated theoretically,experimentally and by simulation.The application analysis are fully researched.The main works and innovative points of this thesis are listed as follows.(1)Based on the I-shaped cross structure,the triple band MM absorber is designed.The I-shaped cross structure absorber is constructed and analyzed by the simulations.Based on the theory of perfect impedance matching,we further designed a triple band MM absorber by integrating three different sizes of split ring resonators into one unit cell.Finally,based on the interference theory,the designed I-shaped cross structure absorbers are quantitatively analyzed,which provides good insight into the physics behind the absorbing structure.The results indicate that the proposed triple-band MM absorber achieves above 99%absorption rates at 9.85 GHz,13.05 GHz and 14.93 GHz,respectively.(2)The broadband design of the MMs absorber based on double-circle rings(OCRs)and welded with lumped resistances.Based on above idea,a broadband MMs absorber using DCRs loaded lumped components is proposed.Surface current distributions and energy loss distribution are used to analyze the absorption characteristics and explain its absorption mechanism of the unit cell structure.At the same time,the corresponding equivalent circuit model is established to further understand its principle of EM wave absorbing.MM characteristics of polarization insensitive and wide angles of incidence of waves are also investigated by simulations.Simulation and experimental results indicate that this absorber is with the absorbance of more than 90%from 8.87-16.47GHz,the relative bandwidth reaches 60%.(3)The design of high-impedance surface-based broadband MM absorber is proposed.The presented MM absorber consists of octagonal ring-shaped resistive patches.Based on equivalent EM parameters retrieve,the results illustrate the characteristic of perfect impedance matching with free space,at the same time,surface current and energy loss distributions of the unit cell structure to qualitatively explain its wideband absorption mechanism.MM characteristics of polarization insensitive and wide angles of incidence of waves are also investigated by simulations,and the results demonstrate that the proposed absorber has polarization-insensitive feature and the good properties under oblique incidence.Based on the interference theory,the designed broadband absorber is quantitatively analyzed,which provides good insight into the physics behind the absorbing structure.Compared with previous reports,we first apply the extended interference theory model to the broadband MM abosrber.The experiments indicate that the proposed absorber achieves the absorbance of more than 90%from 3.65-13.93 GHz,the relative bandwidth reaches 117%.(4)The magnetic resonant wireless power transfer(WPT)systems are designed based on negative permeability MMs.Firstly,a negative permeability MM is designed based on capacitively loaded split ring resonators(CLSRRs).This MM slab has a negative relative permeability ?=-1 at the resonant frequencies around 16.30 MHz.In theory,the negative permeability MM can refocus EM field,propagating waves and amplify evanescent waves,which can improve power transfer efficiency(PTE)of WPT system.The distributions of magnetic in WPT system are characterized using EM simulations and it indicates that coupled magnetic field density of WPT in receiver side can be effectively enhanced.A 16.30 MHz WPT set-up which transmission performance can be tested by a vector network analyzer(VNA).By integrating MM in the WPT system,the experimental tests verify that the measured PTE with one and two MM slabs have respectively 10%and 17%improvement compared to the case without MM.Then,to further optimize negative permeability MM structures,a magnetic MM based on capacitive loaded spiral resonators(CLSRs)is designed.The effective permeability is negative value at 13.56MHz and investigated theoretically,experimentally and by simulation.The experimental set-up for a 13.56MHz WPT system is built,which transmission performance can be tested by a VNA.The experimental results demonstrated that a maximum efficiency improvement of 41.7%can be obtained with MM at transfer distance of 30 cm.The proposed MM is applied in a more practical WPT system(with a low power light bulb load)to reveal its effects.The bulb brightness intuitively verifies the efficiency improvement in the WPT system with the MM.The design of MMs absorber laid a theoretical foundation for broadband design of novel absorbing materials,and we first apply the extended interference theory model to the broadband MM abosrber which provides good insight into the physics behind the absorbing structure.The proposed series MM absorbers also opened up a new path for the design and realization of high performance absorbing materials.From the perspective of MMs for artificially manipulating EM field and waves,it provides a wider space for the application WPT compared the MM design and WPT technology.The negative permeability MMs and their applications to WPT verify that MMs play an important role in enhancing PTE of WPT systems.This research provides an important theoretical guiding significance for bottleneck problem of WPT technology such as power transmission efficiency,electromagnetic compatibility and so on.