arXiv subjects

Weng Cho Chew

Publications and source records attributed to Weng Cho Chew.

27 records · Page 2Linked to original sources

arXiv2015

Unidirectional and Wavelength Selective Photonic Sphere-Array Nanoantennas

We design a photonic sphere-array nanoantenna (NA) exhibiting both strong directionality and wavelength selectivity. Although the geometric configuration of the photonic NA resembles a plasmonic Yagi-Uda NA, it has different working principles, and most importantly, reduces the inherent metallic loss from plasmonic elements. For any selected optical wavelength, a sharp Fano-resonance by the reflector is tunable to overlap spectrally with a wider dipole resonance by the sphere-chain director leading to the high directionality. The work provides design principles for directional and selective photonic NAs, which is particularly useful for photon detection and spontaneous emission manipulation.

physics.optics↗

arXiv2015

Observing Abnormally Large Group Velocity at the Plasmonic Band Edge via a Universal Eigenvalue Analysis

We developed a novel universal eigenvalue analysis for 2D arbitrary nanostructures comprising dispersive and lossy materials. The complex dispersion relation (or complex Bloch band structure) of a metallic grating is rigorously calculated by the proposed algorithm with the finite-difference implementation. The abnormally large group velocity is observed at a plasmonic band edge with a large attenuation constant. Interestingly, we found the abnormal group velocity is caused by the leaky (radiation) loss not by metallic absorption (Ohmic) loss. The periodically modulated surface of the grating significantly modifies the original dispersion relation of the semi-infinite dielectric-metal structure and induces the extraordinarily large group velocity, which is different from the near-zero group velocity at photonic band edge. The work is fundamentally important to the design of plasmonic nanostructures.

physics.optics↗

arXiv2015

Combined Field Integral Equation Based Theory of Characteristic Mode

Conventional electric field integral equation based theory is susceptible to the spurious internal resonance problem when the characteristic modes of closed perfectly conducting objects are computed iteratively. In this paper, we present a combined field integral equation based theory to remove the difficulty of internal resonances in characteristic mode analysis. The electric and magnetic field integral operators are shown to share a common set of non-trivial characteristic pairs (values and modes), leading to a generalized eigenvalue problem which is immune to the internal resonance corruption. Numerical results are presented to validate the proposed formulation. This work may offer efficient solutions to characteristic mode analysis which involves electrically large closed surfaces.

math-ph↗

arXiv2014

Multilevel Fast Multipole Algorithm for Characteristic Mode Analysis

Characteristic mode (CM) analysis poses challenges in computational electromagnetics (CEM) as it calls for efficient solutions of dense generalized eigenvalue problems (GEP). Multilevel fast multipole algorithm (MLFMA) can greatly reduce the computational complexity and memory cost for matrix-vector product operations, which is powerful in iteratively solving large scattering problems. In this article, we demonstrate that MLFMA can be easily incorporated into the implicit restarted Arnoldi (IRA) method for the calculation of CMs, where MLFMA with the sparse approximate inverse (SAI) preconditioning technique is employed to accelerate the construction of Arnoldi vectors. This work paves the way of CM analysis for large-scale and complicated three-dimensional ($3$-D) objects with limited computational resources.

math.NA↗

arXiv2014

Vector Potential Electromagnetic Theory with Generalized Gauge for Inhomogeneous Anisotropic Media

Vector and scalar potential formulation is valid from quantum theory to classical electromagnetics. The rapid development in quantum optics calls for electromagnetic solutions that straddle quantum physics as well as classical physics. The vector potential formulation is a good candidate to bridge these two regimes. Hence, there is a need to generalize this formulation to inhomogeneous media. A generalized gauge is suggested for solving electromagnetic problems in inhomogenous media which can be extended to the anistropic case. The advantages of the resulting equations are their absence of low-frequency catastrophe. Hence, usual differential equation solvers can be used to solve them over multi-scale and broad bandwidth. It is shown that the interface boundary conditions from the resulting equations reduce to those of classical Maxwell's equations. Also, classical Green's theorem can be extended to such a formulation, resulting in similar extinction theorem, and surface integral equation formulation for surface scatterers. The integral equations also do not exhibit low-frequency catastrophe as well as frequency imbalance as observed in the classical formulation using E-H fields. The matrix representation of the integral equation for a PEC scatterer is given.

physics.class-ph↗

arXiv2013

A novel efficient numerical solution of Poisson equation for arbitrary shapes in two dimensions

We propose a novel efficient algorithm to solve Poisson equation in irregular two dimensional domains for electrostatics. It can handle Dirichlet, Neumann or mixed boundary problems in which the filling media can be homogeneous or inhomogeneous. The basic idea of the new method is solve the problem in three steps: (i) First solve the equation $\nabla\cdot\mathbf D=ρ$. The inverse of the divergence operator in a restricted subspace is found to yield the electric flux density $\mathbf D$ by a fast direct solver in O(N) operations. The $\mathbf D$ so obtained is nonunique with indeterminate divergence-free component. Then the electric field is found by $\mathbf E=\mathbf D/ε$. But $\nabla\times\mathbf E=0$ for electrostatic field; hence, $\mathbf E$ is curl free and orthogonal to the divergence free space. (ii) An orthogonalization process is used to purify the electric field making it curl free and unique. (iii) Then the potential $ϕ$ is obtained by solving $\nabla ϕ=-\mathbf E$ or finding the inverse of the gradient operator in a restricted subspace by a similar fast direct solver in O(N) operations. Treatments for both Dirichlet and Neumann boundary conditions are addressed. Finally, the validation and efficiency are illustrated by several numerical examples. Through these simulations, it is observed that the computational complexity of our proposed method almost scales as O(N) where N is the triangle patch number of meshes. Consequently, this new algorithm is a feasible fast Poisson solver.

math-ph↗

arXiv2013

Casimir Force for Arbitrary Objects Using the Argument Principle and Boundary Element Methods

Recent progress in the simulation of Casimir forces between various objects has allowed traditional computational electromagnetic solvers to be used to find Casimir forces in arbitrary three-dimensional objects. The underlying theory to these approaches requires knowledge and manipulation of quantum field theory and statistical physics. We present a calculation of the Casimir force using the method of moments via the argument principle. This simplified derivation allows greater freedom in the moment matrix where the argument principle can be used to calculate Casimir forces for arbitrary geometries and materials with the use of various computational electromagnetic techniques.

quant-ph↗

arXiv2012

A novel fast solver for Poisson equation with the Neumann boundary condition

In this paper we present a novel fast method to solve Poisson equation in an arbitrary two dimensional region with Neumann boundary condition. The basic idea is to solve the original Poisson problem by a two-step procedure: the first one finds the electric displacement field $\mathbf{D}$ and the second one involves the solution of potential $ϕ$. The first step exploits loop-tree decomposition technique that has been applied widely in integral equations within the computational electromagnetics (CEM) community. We expand the electric displacement field in terms of a tree basis. Then, coefficients of the tree basis can be found by the fast tree solver in O(N) operations. Such obtained solution, however, fails to expand the exact field because the tree basis is not completely curl free. Despite of this, the accurate field could be retrieved by carrying out a procedure of divergence free field removal. Subsequently, potential distribution $ϕ$ can be found rapidly at the second stage with another fast approach of O(N) complexity. As a result, the method dramatically reduces solution time comparing with traditional FEM with iterative method. Numerical examples including electrostatic simulations are presented to demonstrate the efficiency of the proposed method.

math-ph↗

arXiv2010

Efficient Evaluation of Casimir Force in Arbitrary Three-dimensional Geometries by Integral Equation Methods

In this paper, we generalized the surface integral equation method for the evaluation of Casimir force in arbitrary three-dimensional geometries. Similar to the two-dimensional case, the evaluation of the mean Maxwell stress tensor is cast into solving a series of three-dimensional scattering problems. The formulation and solution of the three-dimensional scattering problem is well-studied in classical computational electromagnetics. This paper demonstrates that this quantum electrodynamic phenomena can be studied using the knowledge and techniques of classical electrodynamics.

quant-ph↗