The Finite-difference Time-domain Method And Its Multi-physical Applications

The finite-difference time-domain(FDTD)method has been the research focus for many years because of its simplicity and high efficiency,and is one of the major methods in computational electromagnetics.Although the theoretical frame of the FDTD method is basically mature,there are still many problems needed to be further studied.Now,the FDTD method is often used to solve other physical problems or electromagnetic related multi-physical problems,i.e.,quantum,electromagnetic-thermal analysis,electromagnetic particle-in-cell(EM-PIC)simulation.Revolving around one national 973 project,we systematacially investigate several problems in the FDTD frame,that is,the waveport,mesh generation,and EM-PIC for predicting multipactor.We obtain series of achievements for those problems.The major work and contribution of the author are:·We propose the virtual domain scheme to implement the FDTD waveport.The virtual domain is built by simple assignment of the FDTD iteration coefficients.The virtual domain is used to absorb electromagnetic wave through communication with port plane of the waveguide.There are many merits of the proposed scheme.The scheme is very concise and behaves as zero-thickness plane.Through the specally designed communication,there is no reflection between the virtual domain and inner part of waveguide.The conformal method is automatically contained because of the above assignment.The outstanding feature is the perfect-electric-conductor(PEC)condition of the port plane with respect to the outer domain of the waveguide,which ensures that the waveguide simulation is not disturbed by the electromagnetic field outside of the waveguide.The thickness of the perfectly matched layer(PML)in virtual domain can be specified arbitrarily.The source can be set just at the port plane.·To stimulate the waveguide mode quantificationally,we propose the thorough power-to-amplitude transformation(PAT)theory.In terms of the quantitative complex amplitude,we unify the PAT theory for multicarrier and wideband impulse wave.We systematacially study all kinds of sources to stimulate the waveguide mode quantificationally,i.e.,hard source,electric current source,magnetic current source,total field and scatted field(TFSF)source,transparent field source,and PN source,and propose strategies to implement them in the frame of virtual domain.·We propose a new scheme for mesh generation based on ray tracing.In the new scheme,we propose additional mesh flags,rigorous staircase criteria and generalized consistency modification.The new scheme overcomes the error of identifying the inner/outer of the object,and the inaccurate intersecting area,according to conventionally adopted parity rationale for the tangential situations.Hence,we can improve the accuracy of the conformal method.Furthermore,we propose a running strategy to genetate the intersectiong information efficiently.·For the problem of multipactor,we propose a fast EM-PIC numerical method.According to the wideband PAT(WBPAT),we can first extract complex amplitudes at multiple frequencies,which are then used to drive the motion of particles.Hence,the FDTD iterations are avoided.We can also adopt bigger time step without the restriction of the Courant condition.We can just simulate the problem in a local region.As a result,the speed-up ratio can be improved by three orders of magnitude.For the collision triangle patches,we propose a new scheme.We just correlate triangle patches in these partly filled cells according to the law of separation axes.Hence,the original triangle patches of the geometrical model are used for collision,which are more accurate.For multiple objects,we propose the merging algorithm to handle these cells shared by multiple objects.The particle can find the accurate triangle to collide in cells shared by multiple objects.