Investigations On Radiation, Transmission And Scattering At Interfaces Consisting Of Artificial Electromagnetic Materials

Artificial materials consist of carefully designed unit cells at the subwavelength scale.Due to the possibility of manipulating electromagnetic(EM)waves at such a small scale,artificial materials become one of the most important parts of modern electromagnetic theory and applications.Because they usually show unique properties,which could not be found in natural materials,artificial materials could also be named as metamaterials.Artificial materials not only pave the way of EM device designs,including antennas,filters and waveguides,but also act as a powerful platform to investigate condensed matter physics,accelerating the development of basic physics.Recently,surface plasmons(SPs)as well as spoof surface plasmon polaritons(SSPPs),impedance interface waveguides,topological photonics,analog of electromagnetic induced transparency(A-EIT),and all dielectric metasurfaces become hot topics in the field of artificial materials.In order to study these phenomena and related potential applications,this thesis focuses on electromagnetic phenomena happening at interfaces,including radiation,excitation,transmission,scattering,and resonance.This thesis investigates a series of key issues.Main contents can be divided into several parts as listed below:(1)Radiation phenomenon of SSPPs transmission lines(TLs)is investigated,and a miniaturized SSPPs TL is proposed.SSPPs are surface waves existing at the air-metal interfaces.Radiation from SSPPs is not obvious,thus,in the previous researches,radiation was ignored.This work investigated radiation from SSPPs,establishing corresponding travelling wave antenna model.Using gradient loaded resistors,we divided radiation into transition radiation and travelling wave radiation.Theoretical model,simulations and measurements all indicate that the radiation is the dominant part of loss at microwave band,bringing potential noise to systems.We further used post-wall techniques to design a miniaturized SSPPs TL.Quasi-TEM waves in the slotlines are transformed into surface waves smoothly.The design halves the size of traditional coplanar waveguide(CPW)transitions and strengthens the slow wave effect dramatically.(2)According to the adiabatic mode-matching technique,we propose broadband transitions between conventional transmission lines and 1D artificial impedance interface waveguides consisting of transverse electric and transverse magnetic impedance surfaces.In the past,it was difficult to excite impedance interface waveguides with high efficiency.In pioneering works,researchers had to fabricate electric probe directly at the interface to excite the line wave mode,but the coupling efficiency was very low.Two examples exciting line wave mode from slotline and CPW are proposed in our work.Both scattering parameters and near-field measurements indicate the transmission efficiency is high.And simulated and measured dispersion curves also prove the existence of interface modes.The proposed technique paves further applications based on interface waveguides.(3)Topological edge modes in long-range disorder are investigated,presenting a new method to design topological photonics with amorphous characteristics.As is well-known,honeycomb-lattice with C3 symmetry can support valley topological edge mode,which is immune to local disorder.But when long-range disorder exists within the whole lattice,whether topological edge modes are still robust or not is still unknown.We discover that when lattice undergoes foam-like long-range disorder deformation,the robust valley topological edge modes are still observable.With the increase of disorder,the foam-like geometric characteristic no longer exists and the band gap disappears.We further utilized 3D print technique to design and fabricate a corresponding sample and conducted the experiment in the microwave band.Robust topological valley transport was found in the spectrum.Simulated and measured results match well,meaning that the topological transport can happen even the whole lattice undergoes long-range foam-like deformation.(4)Magnetoinductive waves based on split ring resonators(SRRs)are investigated.We propose tunneling propagation of SSPPs and gradient magnetoinductive metasurfaces featured with ‘rainbow trapping' effects.Previous tunneling designs focus on evanescent waves in hole waveguides,below the cutoff frequency.In this paper,SRRs chains were loaded along the propagation direction of SSPPs,resonant tunneling transmission was realized above the cutoff frequency.Proposed design extends the catalog of tunneling phenomena and can be utilized to design multi-pass band filters.Most previous ‘rainbow trapping' designs are based on the dispersion engineering,waves of different wavelengths are stopped at different positions,but reflection always exist.We loaded gradient SRRs arrays orthogonal to a main transmission line.Waves of different wavelengths were trapped in corresponding magnetoinductive channels of metasurfaces.Long oscillation lifetime enhanced absorption in substrates and metal patches dramatically,thus energy was dissipated in the form of heat loss.Reflection and radiation can be ignored,and the topology realizes the ‘rainbow trapping' effect without reflection and acts as a new type of absorptive filters.A series of single-point,multi-point,and broadband absorptive band-rejection filters were designed as examples,whose band-rejection performance is ideal and terminal impedance is maintained well,eliminating unwanted influences of reflected signals to systems.(5)Near-field excitation of SPs based on dielectric nano-particle arrays is designed,and A-EIT metasurface based on spoof-MLSP and SRRs is proposed.Both systems act as strong coupling systems,and are analyzed based on Lorentz coupling model.Traditional near-field excitation methods of SPs are based on metallic nano-particles,whose ohmic loss is large,thus the excitation efficiency is not perfect.Here in our model,magnetic dipole mode of silicon nano-particles,whose ohmic loss is low,was utilized to excite SPs at the interface between air and gold film.Frequency splitting was found at Fourier spectra which matched well with theoretical results from Lorentz coupling model.Moreover,we arranged SRRs and spoof-MLSPs to establish bright-dark mode system to realize A-EIT.SRRs,as bright resonators,were excited by plane waves directly,and spoof-MLSPs,as dark resonators,were further excited by near-field couplings.Transparent window was realized due to strong coupling.Theoretical,simulated,and measured results match well with each other.The structure can enhance the interaction between matters and structures,and the sharp transmission peak could be applied to design novel sensor.(6)Lattice-tailored Mie scatterings of all-dielectric metasurfaces are investigated.Samples consisting of alumina spheres were fabricated and measured in the microwave band,paving the development of all dielectric artificial structures in the microwave band.In traditional designs,artificial materials rely on the performance of metallic unit cells with different geometric shapes and are fabricated based on printed circuit board(PCB)technique.Complex shapes,unstable physical and chemical properties are the main drawbacks of traditional metasurfaces based on PCB.We investigated all dielectric structures based on alumina particles whose scattering properties can be designed by simply tailoring the lattice constant instead of specific shapes of every unit cell.The structure has many advantages: low loss,high hardness,corrosion resisting,thermostability,making the work meaningful in all-dielectric artificial electromagnetic structure designs.This thesis focuses on radiation,transmission and scattering at interfaces consisting of artificial electromagnetic materials.Several key issues are investigated,paving the development of artificial electromagnetic materials.