Maoyan Wang

FDTD Study on Scattering of Metallic Column Covered by Double-Negative Metamaterial

Electromagnetic scattering of metallic column covered by double-negative (DNG) metamaterials is simulated with auxiliary differential equation method in Finite-Difference Time-Domain method. Lossy Drude polarization and magnetization models are used to simulate DNG media. Numerical result shows that though the backward scattering of metallic column covered by DNG media decrease, the forward scattering increase. The effects to the backward scattering caused by the variation of DNG medias depth, plasma frequency, damping frequency and incident wave frequency are discussed.

FDTD STUDY ON WAVE PROPAGATION IN LAYERED STRUCTURES WITH BIAXIAL ANISOTROPIC METAMATERIALS

The Gaussian beam propagation in multi-layered structures that include indefinite anisotropic metamaterial (AMM) are simulated with shift operator method in Finite-Difference Time-Domain method (FDTD). The excitations of backward and forward surface affected by the types of biaxial AMM are investigated. Numerical results show that the directions of the guided wave excited are influenced by the sign of z component of relative permeability tensor of AMM that determines the energy flow is positively refracted or negatively refracted. Positive or negative Goos-Hanchen shift associated with Total Cutoff media are also shown.

Radiation pressure of active dispersive chiral slabs

We report a mechanism to obtain optical pulling or pushing forces exerted on the active dispersive chiral media. Electromagnetic wave equations for the pure chiral media using constitutive relations containing dispersive Drude models are numerically solved by means of Auxiliary Differential Equation Finite Difference Time Domain (ADE-FDTD) method. This method allows us to access the time averaged Lorentz force densities exerted on the magnetoelectric coupling chiral slabs via the derivation of bound electric and magnetic charge densities, as well as bound electric and magnetic current densities. Due to the continuously coupled cross-polarized electromagnetic waves, we find that the pressure gradient force is engendered on the active chiral slabs under a plane wave incidence. By changing the material parameters of the slabs, the total radiation pressure exerted on a single slab can be directed either along the propagation direction or in the opposite direction. This finding provides a promising avenue for detecting the chirality of materials by optical forces.

Improved Extraction of Coupling Matrix and Unloaded Q from S-Parameters of Lossy Resonator Filters

Abstract—This paper presents a two-stage optimization method for accurately extracting the coupling matrix (CM) and the unloaded quality factor (unloaded Q) of each resonator from the measured (or simulated) S-parameters of lossy cross-coupled resonator bandpass filters. The method can be used in computer-aided tuning (CAT) of microwave filters to accelerate filter design and physical realization. In our method, the Cauchy method is employed for determining characteristic polynomials of the S-parameters in the normalized lowpass frequency domain, and the CM and unloaded Q are extracted by two-stage optimization method using genetic algorithm. With respect to the previous methods available in the literatures, the proposed method allows the CM extraction of the filter with sourceload coupling. Moreover, the accuracy and robustness of the method can be improved due to the usage of the second stage optimization. The proposed method is applied to the diagnosis of a general coupled resonator filter with/without source-load coupling.

Propagation Matrix Method Study on THz Waves Propagation in a Dusty Plasma Sheath

Terahertz (THz) waves propagation in a stratified media slab containing dusty plasmas are investigated using the propagation matrix method. The dispersive permittivity of conductors and dusty plasmas at THz frequencies are given. After the validation of the method is performed, the propagation properties of aluminum coated by dusty plasmas with and without vacuum interlayer are compared. The THz reflection and transmission coefficients for a dusty plasma slab with different medium parameters are discussed.

Study on Reflectivity and Wavenumber Occurring Polar Mesosphere Summer Echoes

Polar Mesosphere Summer Echoes (PMSE) are very strong radar echoes near the polar mesopause at local summer. PMSE have been approved to be associated with charged dust or aerosols in the dusty ionosphere. In the paper, the differential scattering cross section based on Born approximation in dusty plasma is derived, and the backscattering cross section per unit volume in published papers are summarized. Comparing the two results between the differential scattering cross section and the backscattering cross section per unit volume, one finds that the statistically experimental conclusion can be verified by the theoretical result. The results show that the reflectivity is inverse proportional to the fourth power of the wavenumber and charged dust grains play an important role in the occurrence of PMSE. The scattering of electromagnetic waves on charged dust particles may be a tool to explore the generation mechanism of PMSE.

Wave propagation and Lorentz force density in gain chiral structures

The electromagnetic coupling and mechanical interaction between a plane wave and dispersive gain chiral structures are investigated using the Auxiliary Differential Equation Finite Difference Time Domain (ADE-FDTD) method. Utilizing the constitutive relations containing frequency-dependent Lorentzian models and a Condon model, the wave equations and time-averaged Lorentz force density for the magneto-electric coupling chiral media are presented. Numerical results show that the cross-polarized transmission coefficient is larger than the co-polarized transmission coefficient for a gain chiral slab with certain thickness. The gradient force engendered by bound currents of the cross-polarized waves in chiral media is larger than the scattering force to pull the slab towards the incident source. The complicated optical pulling or pushing force density among slabs, which is illuminated by a normally incident plane wave, containing chiral materials with different medium parameters is achieved.

Mie series for electromagnetic scattering of a conducting sphere coated with chiral metamaterials

Abstract The electromagnetic scattering of a conducting sphere coated with chiral metamaterials is formulated in terms of Mie series method. Field decomposition scheme is implemented to split electromagnetic wave in chiral metamaterials into a right-handed circularly polarized wave and a left-handed circularly polarized wave. By applying the continuous boundary condition on the interfaces of the two-layer sphere, the expanded coefficients for the scattered fields are obtained by solving the electromagnetic wave in the spherical harmonics vector function. The validity of theoretical formulations and program is verified by reference results. The co-polarized and cross-polarized radar cross scattering of a conducting sphere coated with double-negative, single-negative chiral metamaterials compared to normal media and chiral media are investigated.

Pulling cylindrical particles using a soft-nonparaxial tractor beam

In order to pull objects towards the light source a single tractor beam inevitably needs to be strongly nonparaxial. This stringent requirement makes such a tractor beam somewhat hypothetical. Here we reveal that the cylindrical shape of dielectric particles can effectively mitigate the nonparaxiality requirements, reducing the incidence angle of the partial plane waves of the light beam down to 45° and even to 30° for respectively dipole and dipole-quadrupole objects. The optical pulling force attributed to the interaction of magnetic dipole and magnetic quadrupole moments of dielectric cylinders occurs due to the TE rather than TM polarization. Therefore, the polarization state of the incident beam can be utilized as an external control for switching between the pushing and pulling forces. The results have application values towards optical micromanipulation, transportation and sorting of targeted particles.

The interaction of terahertz waves and a dusty plasma slab with Epstein distribution

Abstract The Auxiliary Differential Equation Finite Difference Time Domain (ADE-FDTD) method is applied to study the electromagnetic scattering of a dusty plasma sheath with Epstein distribution. The charging response factor of dust particles and angular plasma frequency of the dusty plasma are functions of space-varying electron density with an Epstein profile. The verification of the numerical ADE-FDTD algorithm for the dusty plasma is given. The propagation properties of Terahertz (THz) waves through a dusty plasma slab affected by the characteristic parameter and modulation factor of the Epstein distribution are discussed. The absorption coefficients of the slab influenced by the electron density, density of dust particles, and effective collision frequency are studied. It is shown that Terahertz waves may be an efficient tool for high density dusty plasmas detection and diagnostics.