This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the...This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the three-pulse photon echo's amplitude and efficiency is analyzed with the Maxwell-Bloch equations solved by finite-difference timedomain method.We demonstrate that the amplitude of three-pulse echo will increase with the increasing of thickness and the optimum thickness to generate three-pulse photon echo is 0.3 cm for Tm^(3+):YAG when the attenuation of the input pulse is taken into account.Meanwhile,we find the expression 0.09 exp(α'L),which is previously employed to describe the relationship between echo's efficiency and thickness,should be modified as 1.3 · 0.09 exp(2.4 ·α'L) with the propagation of echo considered.展开更多
Large calculation error can be formed by directly employing the conventional Yee’s grid to curve surfaces.In order to alleviate such condition,unconditionally stable CrankNicolson Douglas-Gunn(CNDG)algorithm with is ...Large calculation error can be formed by directly employing the conventional Yee’s grid to curve surfaces.In order to alleviate such condition,unconditionally stable CrankNicolson Douglas-Gunn(CNDG)algorithm with is proposed for rotationally symmetric multi-scale problems in anisotropic magnetized plasma.Within the CNDG algorithm,an alternative scheme for the simulation of anisotropic plasma is proposed in body-of-revolution domains.Convolutional perfectly matched layer(CPML)formulation is proposed to efficiently solve the open region problems.Numerical example is carried out for the illustration of effectiveness including the efficiency,resources,and absorption.Through the results,it can be concluded that the proposed scheme shows considerable performance during the simulation.展开更多
A highly efficient absorbing boundary condition suitable for use in the finitedtherence time-domain (FDTD) modelling of acoustic fields is presented in this paper. The new method seeks a least square esthoate of a tra...A highly efficient absorbing boundary condition suitable for use in the finitedtherence time-domain (FDTD) modelling of acoustic fields is presented in this paper. The new method seeks a least square esthoate of a transfer matrix for field components near truncating boundaries by matrir pseud-inversion. The proposed absorbing boundary is considerably more effective than most ekisting ones. The method is also computationally econondcal and robust.The performance of the new method is shown by numerical experiments on a point-source radiation problem, a wedge dimaction problem, and a scattering problem in which a plane wave is scattered by a circular cylinder.展开更多
In this paper, modifications to the finite-difference time-domain(FD-TD) method for modeling microwave pulse coupling into a slot, which is much narrower than one conventional FD-TD cell, are discussed. The coupling p...In this paper, modifications to the finite-difference time-domain(FD-TD) method for modeling microwave pulse coupling into a slot, which is much narrower than one conventional FD-TD cell, are discussed. The coupling process of microwave pulse into a slot is studied by using the modified FD-TD method, and the dependence of microwave coupling on slot sizes, the carrier frequencies and the polarization directions of the incident waves is analysed. Resonant and enhancement effects which occur in this process are observed. The condition at which the resonant effect takes place is also presented.展开更多
The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matchin...The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matching condition.The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab.Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions,which makes it a potential candidate to overcome the ionization blackout problem.展开更多
Metal-semiconductor Janus nanostructures with asymmetry and directionality have recently aroused significant interest,both in fundamental light-matter interactions mechanism and in technological applications.Here we r...Metal-semiconductor Janus nanostructures with asymmetry and directionality have recently aroused significant interest,both in fundamental light-matter interactions mechanism and in technological applications.Here we report the synthesis of different Au-ZnO Janus nanostructures via a facile one-pot colloid method.The growth mechanism is revealed by a series of designed synthesis experiments.The light absorption properties are determined by both the decrease of dipole oscillations of the free electrons and the plasmon-induced hot-electron transfer.Moreover,the finite-difference time-domain(FDTD)simulation method is used to elucidate the electric field distributions of these Janus nanostructures.展开更多
To efficiently simulate and calculate the radar cross section(RCS) related electromagnetic problems by employing the finite-difference time-domain(FDTD) algorithm, an efficient stretched coordinate perfectly matched l...To efficiently simulate and calculate the radar cross section(RCS) related electromagnetic problems by employing the finite-difference time-domain(FDTD) algorithm, an efficient stretched coordinate perfectly matched layer(ESC-PML) based upon the exponential time differencing(ETD) method is proposed.The proposed implementation can not only reduce the number of auxiliary variables in the SC-PML regions but also maintain the ability of the original SC-PML in terms of the absorbing performance. Compared with the other existed algorithms, the ETDFDTD method shows the least memory consumption resulting in the computational efficiency. The effectiveness and efficiency of the proposed ESC-PML scheme is verified through the RCS relevant problems including the perfect E conductor(PEC) sphere model and the patch antenna model. The results indicate that the proposed scheme has the advantages of the ETD-FDTD method and ESC-PML scheme in terms of high computational efficiency and considerable computational accuracy.展开更多
Objective In order to find early latent faults and prevent catastrophic failures, diagnosis of insulation condition by measuring technique of partial discharge(PD) in gas insulated switchgear (GIS) is applied in this ...Objective In order to find early latent faults and prevent catastrophic failures, diagnosis of insulation condition by measuring technique of partial discharge(PD) in gas insulated switchgear (GIS) is applied in this paper, which is one of the most basic ways for diagnosis of insulation condition. Methods Ultra high frequency(UHF) PD detection method by using internal sensors has been proved efficient, because it may avoid the disturbance of corona, but the sensor installation of this method will be limited by the structure and operation condition of GIS. There are some of electromagnetic (E-M) waves leak from the place of insulation spacer, therefore, the external sensors UHF measuring PD technique is applied, which isn’t limited by the operation condition of GIS. Results This paper analyzes propagated electromagnetic (E-M) waves of partial discharge pulse excited by using the finite-difference time-domain (FDTD) method. The signal collected at the outer point is more complex than that of the inner point, and the signals’ amplitude of outer is about half of the inner, because it propagates through spacer and insulation slot. Set up UHF PD measuring system. The typical PD in 252kV GIS bus bar was measured using PD detection UHF technique with external sensors. Finally, compare the results of UHF measuring technique using external sensors with the results of FDTD method simulation and the traditional IEC60270 method detection. Conclusion The results of experiment shows that the UHF technique can realize the diagnosis of insulation condition, the results of FDTD method simulation and the result UHF method detection can demonstrate each other, which gives references to further researches and application for UHF PD measuring technique.展开更多
In order to simulate metamaterial rotational symmetric open region problems,unconditionally stable perfectly match layer(PML)implementation is proposed in the body of revolution(BOR)finite-difference time-domain(FDTD)...In order to simulate metamaterial rotational symmetric open region problems,unconditionally stable perfectly match layer(PML)implementation is proposed in the body of revolution(BOR)finite-difference time-domain(FDTD)lattice.More precisely,the proposed algorithm is implemented by the Crank-Nicolson(CN)Douglas-Gunn(DG)procedure for BOR metamaterial simulation.The constitutive relationship of metamaterial can be expressed by the Drude model and calculated by the piecewise linear recursive convolution(PLRC)approach.The effectiveness including absorption,efficiency,and accuracy is demonstrated through the numerical example.It can be concluded that the proposed implementation is to take the advantages of the CNDG-PML procedure,PLRC approach,and BORFDTD algorithm in terms of considerable accuracy,enhanced absorption and remarkable efficiency.Meanwhile,it can be demonstrated that the proposed scheme can maintain its unconditional stability when the time step exceeds the CourantFriedrichs-Levy(CFL)condition.展开更多
An unsplit-field higher order nearly perfectly matched layer(NPML)based on the auxiliary differential equation approach is introduced in three-dimensional finite-difference timedomain lattices.The proposed scheme has ...An unsplit-field higher order nearly perfectly matched layer(NPML)based on the auxiliary differential equation approach is introduced in three-dimensional finite-difference timedomain lattices.The proposed scheme has the advantage of both the NPML scheme and the higher order concept in terms of the improved absorbing performance and considerable computational efficiency.By incorporating with the generalized material independent concept,the proposed implementation is indepen dent of the material’s type.Thus,it has the advantages of terminating arbitrary media without changing the updated equations in the PML regions.Its effectiveness and efficiency is further demonstrated through numerical examples.展开更多
In order to eliminate Courant-Friedrich-Levy(CFL) condition restraint and improvecomputational efficiency,a new finite-difference time-domain(FDTD)method based on the alternating-direction implicit(ADI) technique is i...In order to eliminate Courant-Friedrich-Levy(CFL) condition restraint and improvecomputational efficiency,a new finite-difference time-domain(FDTD)method based on the alternating-direction implicit(ADI) technique is introduced recently.In this paper,a theoretical proof of the stabilityof the three-dimensional(3-D)ADI-FDTD method is presented.It is shown that the 3-D ADI-FDTDmethod is unconditionally stable and free from the CFL condition restraint.展开更多
The influence of oxidation aperture on the output characteristics of the circularly symmetric vertical-cavity-surface-emitting laser(VCSEL)structure is investigated.To do so,VCSELs with different oxide aperture sizes ...The influence of oxidation aperture on the output characteristics of the circularly symmetric vertical-cavity-surface-emitting laser(VCSEL)structure is investigated.To do so,VCSELs with different oxide aperture sizes are simulated by the finite-difference time-domain(FDTD)method.The relationships among the field distribution of mode superposition,mode wavelength,output spectra,and far-field divergence with different oxide apertures are obtained.Further,VCSELs respectively with oxide aperture sizes of 2.7μm,4.4μm,5.9μm,7μm,8μm,9μm,and 18.7μm are fabricated and characterized.The maximum output power increases from 2.4 mW to 5.7 mW with oxide aperture increasing from 5.9μm to 9μm.Meanwhile,the wavelength tuning rate decreases from 0.93 nm/mA to 0.375 nm/mA when the oxide aperture increases from 2.7μm to 9μm.The thermal resistance decreases from 2.815℃/mW to 1.015℃/mW when the oxide aperture increases from 4.4μm to 18.7μm.It is demonstrated theoretically and experimentally that the wavelength spacing between adjacent modes increases with the augment of the injection current and the spacing becomes smaller with the oxide aperture increasing.Thus it can be reported that the aperture size can effectively reduce the mode overlaying but at the cost of the power decreasing and the wavelength tuning rate and thermal resistance increasing.展开更多
The key problem of finite-difference time-domain (FD-TD) method is the skillful application of special conditions on the boundaries of the computational domain. A new technique named Perfectly Matched Layer(PML) yield...The key problem of finite-difference time-domain (FD-TD) method is the skillful application of special conditions on the boundaries of the computational domain. A new technique named Perfectly Matched Layer(PML) yields a robust Absorbing Boundary Condition(ABC) independent of the angle of incidence and the frequency of outgoing waves. In this paper, the principle of the PML technique is briefly presented. Then some problems in the application and their settlements are discussed emphatically. Finally three numerical tests and a measured result are devoted to examine the accuracy and effectiveness of this approach.展开更多
The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of...The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end( E-E) and side-by-side( S-S) assembled Au nanorods dimers are studied through finite-difference time-domain( FDTD) simulation. With decreasing the gap spacing,the longitudinal SPR( SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR( SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover,a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region,blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field,the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.展开更多
The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the l...The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the layer average SARs for the inhomogeneousblock model of human body with different incident direction and different polarization of theincident waves are calculated.The results show that the appearance of maximum EM energyabsorption is not always at the situation of the front incidence and the local SARs are moreimportant for the interaction of the EM fields with human body.All results provide more infor-mation about the electromagnetic dosimetry for human body.展开更多
The optical response of metal nanoparticles can be modified through near-field or far-field interaction,yet the lattice plasmon modes(LPMs)considered can only be excited from the latter.Here instead,we present a theor...The optical response of metal nanoparticles can be modified through near-field or far-field interaction,yet the lattice plasmon modes(LPMs)considered can only be excited from the latter.Here instead,we present a theoretical evaluation for LPM excitation via the near-field coupling process.The sample is an arrayed structure with specific units composed of upper metal disks,a lower metal hole and a sandwiched dielectric post.The excitation process and underlying mechanism of the LPM and the influence of the structure parameters on the optical properties have been investigated in detail by using a finite-difference time-domain(FDTD)numerical method.Our investigation presented here should advance the understanding of near-field interaction of plasmon modes for LPM excitation,and LPMs could find some potential applications,such as in near-field optical microscopes,biosensors,optical filters and plasmonic lasers.展开更多
The micro-genetic algorithm (MGA) optimization combined with the finite-difference time-domain (FDTD) method is applied to design a band-notched ultra wide-band (UWB) antenna. A U-type slot on a stepped U-type UWB mon...The micro-genetic algorithm (MGA) optimization combined with the finite-difference time-domain (FDTD) method is applied to design a band-notched ultra wide-band (UWB) antenna. A U-type slot on a stepped U-type UWB monopole is used to obtain the band-notched characteristic for 5 GHz wireless local area network (WLAN) band. The measured results show that voltage standing wave ration (VSWR) less than 2 covers 3.1-10.6 GHz operating band and VSWR more than 2 is within 5.150-5.825 GHz notched one with the highest value of 5.6. Agreement among the calculated, HFSS simulated and measured results validates the effiectiveness of this MGA-FDTD method, which is efficient for UWB antennas design.展开更多
The electromagnetic properties of wire medium are studied by analyzing its transmission coefficient,and a homogeneous uniaxial effective permittivity tensor with one spatially dispersive component is obtained.In order...The electromagnetic properties of wire medium are studied by analyzing its transmission coefficient,and a homogeneous uniaxial effective permittivity tensor with one spatially dispersive component is obtained.In order to evaluate the validity of the equivalent model for scattering problems,the bistatic and monostatic radar cross sections(RCS)of a block of wire medium are investigated with the finitedifference time-domain(FDTD)method.The difference of RCS from the physical wire medium and the corresponding equivalent model has been compared and analyzed under various parameters of wire medium,which clearly demonstrates the accuracy of the equivalent model of wire medium.展开更多
This paper proposes a hybrid full-wave analysis using Finite-Difference Time-Domain (FDTD) and Wave Concept Iterative Process (WCIP) methods, developed to analyze locally arbitrarily shaped microwave structures and Mu...This paper proposes a hybrid full-wave analysis using Finite-Difference Time-Domain (FDTD) and Wave Concept Iterative Process (WCIP) methods, developed to analyze locally arbitrarily shaped microwave structures and Multilayer Planar structure. Using the equivalence principle, the original problem can be decomposed into two sub regions and solve each sub region separately. An interpolation scheme is proposed for communicating between the FDTD fields and WCIP wave, which will not require the effort of fitting the WCIP mesh to the FDTD cells in the interface region. This method is applied to calculate the scattering parameters of arbitrary (3-D) microwave structures. Applying FDTD to 3D discontinuity and WCIP to the remaining region preserves the advantages of both WCIP flexibility and FDTD efficiency. A comparison of the results with the FDTD staircasing data verifies the accuracy of the proposed method.展开更多
Because of its very low light extraction efficiency(LEE),LED is limited to be widely used under the condition of the internal quantum efficiency which up to 90%.In order to fullfill the design of a more efficient GaN-...Because of its very low light extraction efficiency(LEE),LED is limited to be widely used under the condition of the internal quantum efficiency which up to 90%.In order to fullfill the design of a more efficient GaN-based blue light LED,the model including deeply etched surface photonic crystals(PhCs)LED is discussed using mode analysis method from light waveguide theory.The distributions of all order modes in GaN layer are obtained by the effective index approximation.The light extraction efficiencies are also calculated by finite-difference time-domain method(FDTD).The emulated results fully coincide with the former analysis.Because the manufacture of the surface photonic crystal is feasible,the work can be very meaningful to design and manufacture the high efficiency GaN-based blue light LED in factory for a large amount.展开更多
基金Project supported by Tianjin Research Program Application Foundation and Advanced Technology,China(Grant No.15JCQNJC01100)
文摘This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the three-pulse photon echo's amplitude and efficiency is analyzed with the Maxwell-Bloch equations solved by finite-difference timedomain method.We demonstrate that the amplitude of three-pulse echo will increase with the increasing of thickness and the optimum thickness to generate three-pulse photon echo is 0.3 cm for Tm^(3+):YAG when the attenuation of the input pulse is taken into account.Meanwhile,we find the expression 0.09 exp(α'L),which is previously employed to describe the relationship between echo's efficiency and thickness,should be modified as 1.3 · 0.09 exp(2.4 ·α'L) with the propagation of echo considered.
文摘Large calculation error can be formed by directly employing the conventional Yee’s grid to curve surfaces.In order to alleviate such condition,unconditionally stable CrankNicolson Douglas-Gunn(CNDG)algorithm with is proposed for rotationally symmetric multi-scale problems in anisotropic magnetized plasma.Within the CNDG algorithm,an alternative scheme for the simulation of anisotropic plasma is proposed in body-of-revolution domains.Convolutional perfectly matched layer(CPML)formulation is proposed to efficiently solve the open region problems.Numerical example is carried out for the illustration of effectiveness including the efficiency,resources,and absorption.Through the results,it can be concluded that the proposed scheme shows considerable performance during the simulation.
文摘A highly efficient absorbing boundary condition suitable for use in the finitedtherence time-domain (FDTD) modelling of acoustic fields is presented in this paper. The new method seeks a least square esthoate of a transfer matrix for field components near truncating boundaries by matrir pseud-inversion. The proposed absorbing boundary is considerably more effective than most ekisting ones. The method is also computationally econondcal and robust.The performance of the new method is shown by numerical experiments on a point-source radiation problem, a wedge dimaction problem, and a scattering problem in which a plane wave is scattered by a circular cylinder.
文摘In this paper, modifications to the finite-difference time-domain(FD-TD) method for modeling microwave pulse coupling into a slot, which is much narrower than one conventional FD-TD cell, are discussed. The coupling process of microwave pulse into a slot is studied by using the modified FD-TD method, and the dependence of microwave coupling on slot sizes, the carrier frequencies and the polarization directions of the incident waves is analysed. Resonant and enhancement effects which occur in this process are observed. The condition at which the resonant effect takes place is also presented.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB340203)the National Natural Science Foundation of China(Grant Nos.61431010 and 61501350)the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2018JM6016 and 2016JM1001)
文摘The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matching condition.The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab.Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions,which makes it a potential candidate to overcome the ionization blackout problem.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274370 and 51471185)the National Key Research and Development Program of China(Grant Nos.2016YFJC020013 and 2018FYA0305800)
文摘Metal-semiconductor Janus nanostructures with asymmetry and directionality have recently aroused significant interest,both in fundamental light-matter interactions mechanism and in technological applications.Here we report the synthesis of different Au-ZnO Janus nanostructures via a facile one-pot colloid method.The growth mechanism is revealed by a series of designed synthesis experiments.The light absorption properties are determined by both the decrease of dipole oscillations of the free electrons and the plasmon-induced hot-electron transfer.Moreover,the finite-difference time-domain(FDTD)simulation method is used to elucidate the electric field distributions of these Janus nanostructures.
基金supported by the National Natural Science Foundation of China(61571022611971022)。
文摘To efficiently simulate and calculate the radar cross section(RCS) related electromagnetic problems by employing the finite-difference time-domain(FDTD) algorithm, an efficient stretched coordinate perfectly matched layer(ESC-PML) based upon the exponential time differencing(ETD) method is proposed.The proposed implementation can not only reduce the number of auxiliary variables in the SC-PML regions but also maintain the ability of the original SC-PML in terms of the absorbing performance. Compared with the other existed algorithms, the ETDFDTD method shows the least memory consumption resulting in the computational efficiency. The effectiveness and efficiency of the proposed ESC-PML scheme is verified through the RCS relevant problems including the perfect E conductor(PEC) sphere model and the patch antenna model. The results indicate that the proposed scheme has the advantages of the ETD-FDTD method and ESC-PML scheme in terms of high computational efficiency and considerable computational accuracy.
文摘Objective In order to find early latent faults and prevent catastrophic failures, diagnosis of insulation condition by measuring technique of partial discharge(PD) in gas insulated switchgear (GIS) is applied in this paper, which is one of the most basic ways for diagnosis of insulation condition. Methods Ultra high frequency(UHF) PD detection method by using internal sensors has been proved efficient, because it may avoid the disturbance of corona, but the sensor installation of this method will be limited by the structure and operation condition of GIS. There are some of electromagnetic (E-M) waves leak from the place of insulation spacer, therefore, the external sensors UHF measuring PD technique is applied, which isn’t limited by the operation condition of GIS. Results This paper analyzes propagated electromagnetic (E-M) waves of partial discharge pulse excited by using the finite-difference time-domain (FDTD) method. The signal collected at the outer point is more complex than that of the inner point, and the signals’ amplitude of outer is about half of the inner, because it propagates through spacer and insulation slot. Set up UHF PD measuring system. The typical PD in 252kV GIS bus bar was measured using PD detection UHF technique with external sensors. Finally, compare the results of UHF measuring technique using external sensors with the results of FDTD method simulation and the traditional IEC60270 method detection. Conclusion The results of experiment shows that the UHF technique can realize the diagnosis of insulation condition, the results of FDTD method simulation and the result UHF method detection can demonstrate each other, which gives references to further researches and application for UHF PD measuring technique.
基金supported by the National Key Laboratory of Science and Technology on Space Microwave(6142411032201)the National Key Research and Development Program of China(2020YFB1807400)+2 种基金the National Natural Science Foundation of China(6157102261971022)the National Key Laboratory Foundation of China(61424020305)。
文摘In order to simulate metamaterial rotational symmetric open region problems,unconditionally stable perfectly match layer(PML)implementation is proposed in the body of revolution(BOR)finite-difference time-domain(FDTD)lattice.More precisely,the proposed algorithm is implemented by the Crank-Nicolson(CN)Douglas-Gunn(DG)procedure for BOR metamaterial simulation.The constitutive relationship of metamaterial can be expressed by the Drude model and calculated by the piecewise linear recursive convolution(PLRC)approach.The effectiveness including absorption,efficiency,and accuracy is demonstrated through the numerical example.It can be concluded that the proposed implementation is to take the advantages of the CNDG-PML procedure,PLRC approach,and BORFDTD algorithm in terms of considerable accuracy,enhanced absorption and remarkable efficiency.Meanwhile,it can be demonstrated that the proposed scheme can maintain its unconditional stability when the time step exceeds the CourantFriedrichs-Levy(CFL)condition.
基金This work was supported by the National Natural Science Foundation of China(6157102261971022).
文摘An unsplit-field higher order nearly perfectly matched layer(NPML)based on the auxiliary differential equation approach is introduced in three-dimensional finite-difference timedomain lattices.The proposed scheme has the advantage of both the NPML scheme and the higher order concept in terms of the improved absorbing performance and considerable computational efficiency.By incorporating with the generalized material independent concept,the proposed implementation is indepen dent of the material’s type.Thus,it has the advantages of terminating arbitrary media without changing the updated equations in the PML regions.Its effectiveness and efficiency is further demonstrated through numerical examples.
基金Supported by the Specialized Research Fund for the Doctoral Program of Higher Education(No.20010614003)
文摘In order to eliminate Courant-Friedrich-Levy(CFL) condition restraint and improvecomputational efficiency,a new finite-difference time-domain(FDTD)method based on the alternating-direction implicit(ADI) technique is introduced recently.In this paper,a theoretical proof of the stabilityof the three-dimensional(3-D)ADI-FDTD method is presented.It is shown that the 3-D ADI-FDTDmethod is unconditionally stable and free from the CFL condition restraint.
文摘The influence of oxidation aperture on the output characteristics of the circularly symmetric vertical-cavity-surface-emitting laser(VCSEL)structure is investigated.To do so,VCSELs with different oxide aperture sizes are simulated by the finite-difference time-domain(FDTD)method.The relationships among the field distribution of mode superposition,mode wavelength,output spectra,and far-field divergence with different oxide apertures are obtained.Further,VCSELs respectively with oxide aperture sizes of 2.7μm,4.4μm,5.9μm,7μm,8μm,9μm,and 18.7μm are fabricated and characterized.The maximum output power increases from 2.4 mW to 5.7 mW with oxide aperture increasing from 5.9μm to 9μm.Meanwhile,the wavelength tuning rate decreases from 0.93 nm/mA to 0.375 nm/mA when the oxide aperture increases from 2.7μm to 9μm.The thermal resistance decreases from 2.815℃/mW to 1.015℃/mW when the oxide aperture increases from 4.4μm to 18.7μm.It is demonstrated theoretically and experimentally that the wavelength spacing between adjacent modes increases with the augment of the injection current and the spacing becomes smaller with the oxide aperture increasing.Thus it can be reported that the aperture size can effectively reduce the mode overlaying but at the cost of the power decreasing and the wavelength tuning rate and thermal resistance increasing.
基金Supported by the National Natural Science Foundation of China
文摘The key problem of finite-difference time-domain (FD-TD) method is the skillful application of special conditions on the boundaries of the computational domain. A new technique named Perfectly Matched Layer(PML) yields a robust Absorbing Boundary Condition(ABC) independent of the angle of incidence and the frequency of outgoing waves. In this paper, the principle of the PML technique is briefly presented. Then some problems in the application and their settlements are discussed emphatically. Finally three numerical tests and a measured result are devoted to examine the accuracy and effectiveness of this approach.
基金Supported by the National Natural Science Foundation of China(11274173,11374159)the Fundamental Research Funds for the Central Universities(NZ2013304,NJ20140005)Qing Lan Project of Jiangsu Province
文摘The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end( E-E) and side-by-side( S-S) assembled Au nanorods dimers are studied through finite-difference time-domain( FDTD) simulation. With decreasing the gap spacing,the longitudinal SPR( SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR( SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover,a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region,blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field,the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.
文摘The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the layer average SARs for the inhomogeneousblock model of human body with different incident direction and different polarization of theincident waves are calculated.The results show that the appearance of maximum EM energyabsorption is not always at the situation of the front incidence and the local SARs are moreimportant for the interaction of the EM fields with human body.All results provide more infor-mation about the electromagnetic dosimetry for human body.
基金Key Laboratory of Energy Conversion and Storage Technologies(Southern University of Science and Technology),Ministry of Education,Shenzhen,China,the National Key Research and Development Program of China(Grant No.2018YFB0406702)Professorship Startup Funding(Grant No.217056)+1 种基金Innovation-Driven Project of Central South University(Grant No.2018CX001)Project of State Key Laboratory of High Performance Complex Manufacturing,Central South University(Grant No.ZZYJKT2018-01).
文摘The optical response of metal nanoparticles can be modified through near-field or far-field interaction,yet the lattice plasmon modes(LPMs)considered can only be excited from the latter.Here instead,we present a theoretical evaluation for LPM excitation via the near-field coupling process.The sample is an arrayed structure with specific units composed of upper metal disks,a lower metal hole and a sandwiched dielectric post.The excitation process and underlying mechanism of the LPM and the influence of the structure parameters on the optical properties have been investigated in detail by using a finite-difference time-domain(FDTD)numerical method.Our investigation presented here should advance the understanding of near-field interaction of plasmon modes for LPM excitation,and LPMs could find some potential applications,such as in near-field optical microscopes,biosensors,optical filters and plasmonic lasers.
基金supported by the Shanghai Leading Academic Discipline Project (Grant No.S30108)
文摘The micro-genetic algorithm (MGA) optimization combined with the finite-difference time-domain (FDTD) method is applied to design a band-notched ultra wide-band (UWB) antenna. A U-type slot on a stepped U-type UWB monopole is used to obtain the band-notched characteristic for 5 GHz wireless local area network (WLAN) band. The measured results show that voltage standing wave ration (VSWR) less than 2 covers 3.1-10.6 GHz operating band and VSWR more than 2 is within 5.150-5.825 GHz notched one with the highest value of 5.6. Agreement among the calculated, HFSS simulated and measured results validates the effiectiveness of this MGA-FDTD method, which is efficient for UWB antennas design.
基金Supported by the National Natural Science Foundation of China(61102022)the Fundamental Research Foundation of Beijing Institute of Technology of China(20120542014)
文摘The electromagnetic properties of wire medium are studied by analyzing its transmission coefficient,and a homogeneous uniaxial effective permittivity tensor with one spatially dispersive component is obtained.In order to evaluate the validity of the equivalent model for scattering problems,the bistatic and monostatic radar cross sections(RCS)of a block of wire medium are investigated with the finitedifference time-domain(FDTD)method.The difference of RCS from the physical wire medium and the corresponding equivalent model has been compared and analyzed under various parameters of wire medium,which clearly demonstrates the accuracy of the equivalent model of wire medium.
文摘This paper proposes a hybrid full-wave analysis using Finite-Difference Time-Domain (FDTD) and Wave Concept Iterative Process (WCIP) methods, developed to analyze locally arbitrarily shaped microwave structures and Multilayer Planar structure. Using the equivalence principle, the original problem can be decomposed into two sub regions and solve each sub region separately. An interpolation scheme is proposed for communicating between the FDTD fields and WCIP wave, which will not require the effort of fitting the WCIP mesh to the FDTD cells in the interface region. This method is applied to calculate the scattering parameters of arbitrary (3-D) microwave structures. Applying FDTD to 3D discontinuity and WCIP to the remaining region preserves the advantages of both WCIP flexibility and FDTD efficiency. A comparison of the results with the FDTD staircasing data verifies the accuracy of the proposed method.
基金National Natural Science Foundation of China(No.61071087)Reward Fund of Outstanding Youth and Middle Age Scientist of Shandong Province(No.BS2009N5002)
文摘Because of its very low light extraction efficiency(LEE),LED is limited to be widely used under the condition of the internal quantum efficiency which up to 90%.In order to fullfill the design of a more efficient GaN-based blue light LED,the model including deeply etched surface photonic crystals(PhCs)LED is discussed using mode analysis method from light waveguide theory.The distributions of all order modes in GaN layer are obtained by the effective index approximation.The light extraction efficiencies are also calculated by finite-difference time-domain method(FDTD).The emulated results fully coincide with the former analysis.Because the manufacture of the surface photonic crystal is feasible,the work can be very meaningful to design and manufacture the high efficiency GaN-based blue light LED in factory for a large amount.
