ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 28 Jan 2023 12:55:26 GMT2023-01-28T12:55:26Z50111- Analysis of scattering by large inhomogeneous bi-anisotropic objects using AIMhttps://scholarbank.nus.edu.sg/handle/10635/55092Title: Analysis of scattering by large inhomogeneous bi-anisotropic objects using AIM
Authors: Hu, L.; Li, L.-W.; Yeo, T.-S.
Abstract: In this paper, electromagnetic scattering of a plane wave by large inhomogeneous arbitrarily shaped bi-anisotropic objects is solved by Adaptive Integral Method (AIM). Based on Maxwell equations and constitutive relationship for general bi-anisotropic media and using Volume Integral Equations (VIE), the electromagnetic fields are derived as functions of equivalent volume sources. Then the integral equations are discretized using Method of Moments (MoM). Because of the dense matrix property, MoM cannot be used to solve electromagnetic scattering by large objects. Therefore, AIM is adopted to reduce the memory requirement and speed up the solution process. Comparison between AIM and MoM with respect to CPU time and memory requirement is done to show the efficiency of AIM in solving electromagnetic scattering by large objects. Numerical results are obtained for some canonical cases and compared with Mie theory, in which excellent agreement is observed. some new numerical results are also presented for the more general bi-anisotropic material media.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/550922009-01-01T00:00:00Z
- ASED-AIM analysis of scattering by large-scale finite periodic arrayshttps://scholarbank.nus.edu.sg/handle/10635/81985Title: ASED-AIM analysis of scattering by large-scale finite periodic arrays
Authors: Hu, L.; Li, L.-W.; Yeo, T.-S.
Abstract: In this paper, the Adaptive Integral Method (AIM) has been extended to characterizing electromagnetic scattering by large scale finite periodic arrays with each cell comprising of either dielectric or metallic objects, by utilizing accurate sub-entire-domain (ASED) basis function. The solution process can be carried out in two steps. In the first step, a small problem is solved in order to construct ASED basis functions to be implemented for the second step. When dielectric materials are involved in the cell which results in a large number of unknowns for the small problem, the AIM can be used to accelerate the solution process and reduce the memory requirement. In the second step, the entire problem is solved using the ASED basis function constructed in the first step. The AIM can be enhanced with the ASED basis function implemented to solve the entire problem more efficiently. When calculating the near interaction impedance matrix, computation time can be significantly reduced by using the near impedance matrix in the first step. The complexity analysis shows that the computational time is O(N0 log N0)+O(M log M) and memory requirement is O(N0)+O(M), where N0 denotes the number of cells and M stands for the number of elements in one cell. The results calculated respectively by the ASED-AIM and the existing AIM are then compared and an excellent agreement has been observed, which demonstrates the accuracy of the proposed method. In the meantime, memory and computational time requirements have been considerably reduced using the ASED-AIM as compared to the existing AIM. Finally, an example with over 10 million unknowns is given to demonstrate the efficiency of the proposed method.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/819852009-01-01T00:00:00Z
- Isotropic non-ideal cloaks providing improved invisibility by adaptive segmentation and optimal refractive index profile from ordering isotropic materialshttps://scholarbank.nus.edu.sg/handle/10635/56419Title: Isotropic non-ideal cloaks providing improved invisibility by adaptive segmentation and optimal refractive index profile from ordering isotropic materials
Authors: Qiu, C.W.; Hu, L.; Zouhdi, S.
Abstract: Mimicking the ideal cloak, which is anisotropic and inhomogeneous, can be achieved by alternating homogeneous isotropic materials, whose permittivity and permeability of each isotropic coating can be determined from effective medium theory. An improved two-fold method is proposed by optimally discretizing the cloak and re-ordering the combination of the effective parameters of each layer to form a smooth step-index profile. The roles of impedance matching and index matching are investigated for cloaking effects. Smoothing the index profile leads to better invisibility than that obtained by smoothing the impedance profile, since the forward scattering can be further diminished. Nonlinear-transformationbased spherical ideal cloaks are studied, and improved design method is explored together with different segmentation schemes. Significant improvement in invisibility is always observed for the optimal segmentation in virtual space with the proposed two-fold design method no matter how nonlinear the coordinate transformation is. © 2010 Optical Society of America.
Mon, 05 Jul 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/564192010-07-05T00:00:00Z
- Polarization-invariant directional cloaking by transformation opticshttps://scholarbank.nus.edu.sg/handle/10635/57085Title: Polarization-invariant directional cloaking by transformation optics
Authors: Agarwal, K.; Chen, X.; Hu, L.; Liu, H.; Uhlmann, G.
Abstract: We propose a three-dimensional directional cloak for arbitrarily polarized incoming electromagnetic waves, motivated by the fact that there will be negligible scattering when the direction of impinging wave coincides with the axial direction of a very thin and elongated perfectly electric conducting (PEC) scatterer. The performance of the cloak under different polarizations of incoming waves are numerically investigated. The case in which the direction of incoming wave is perturbed of the ideal direction is also quantitatively studied. Numerical simulations show that the directional cloaking device is able to tolerate a large range of tilted angles of incoming waves.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/570852011-01-01T00:00:00Z
- An accurate and robust approach for evaluating VIE impedance matrix elements using SWG basis functionshttps://scholarbank.nus.edu.sg/handle/10635/69266Title: An accurate and robust approach for evaluating VIE impedance matrix elements using SWG basis functions
Authors: Hu, L.; Li, L.-W.; Yeo, T.-S.; Vahldieck, R.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/692662008-01-01T00:00:00Z
- CBFM-based p-FFT method: A new algorithm for solving large-scale finite periodic arrays scattering problemshttps://scholarbank.nus.edu.sg/handle/10635/69566Title: CBFM-based p-FFT method: A new algorithm for solving large-scale finite periodic arrays scattering problems
Authors: Hu, L.; Li, L.-W.
Abstract: In this paper, a novel p-FFT method based on characteristic basis function method (CBFM) has been proposed and implemented to solve electromagnetic scattering by large scaled finite periodic arrays. The CBFs can be constructed by solving the integral equations associated with one unit cell at plane wave incidence from different incident angles and with different polarizations. Then, the unit cell can be considered as an element in solving the whole array problem. When characterizing an array of a very large number of unit cells with a large number of CBFs per unit cell, the resultant linear equation system is too large to be directly solved. The p-FFT method can be integrated by utilizing the CBFs to accelerate the solution to large scale array problems and to reduce memory requirements. The proposed method can be used to solve both 2D and 3D array problems. Numerical examples are shown to demonstrate the high accuracy and efficiency of the proposed new method. Large scale array problems are considered at the end of the paper. ©2009 IEEE.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/695662009-01-01T00:00:00Z
- Spherical cloaking using nonlinear transformations for improved segmentation into concentric isotropic coatingshttps://scholarbank.nus.edu.sg/handle/10635/57469Title: Spherical cloaking using nonlinear transformations for improved segmentation into concentric isotropic coatings
Authors: Qiu, C.-W.; Hu, L.; Zhang, B.; Wu, B.-I.; Johnson, S.G.; Joannopoulos, J.D.
Abstract: Two novel classes of spherical invisibility cloaks based on nonlinear transformation have been studied. The cloaking characteristics are presented by segmenting the nonlinear transformation based spherical cloak into concentric isotropic homogeneous coatings. Detailed investigations of the optimal discretization (e.g., thickness control of each layer, nonlinear factor, etc.) are presented for both linear and nonlinear spherical cloaks and their effects on invisibility performance are also discussed. The cloaking properties and our choice of optimal segmentation are verified by the numerical simulation of not only near-field electric-field distribution but also the far-field radar cross section (RCS). © 2009 Optical Society of America.
Mon, 03 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/574692009-08-03T00:00:00Z
- Efficient current-based hybrid analysis of wire antennas mounted on a large realistic aircrafthttps://scholarbank.nus.edu.sg/handle/10635/55791Title: Efficient current-based hybrid analysis of wire antennas mounted on a large realistic aircraft
Authors: Zhao, W.-J.; Li, J.L.-W.; Hu, L.
Abstract: An efficient hybrid analysis which hybridizes surface-wire integral equations (SWIE) with physical optics (PO) approximation is presented for wire antennas attached to an electrically large aircraft platform. In the analysis, the whole surface of the platform and antennas is divided into three regions, namely, the method of moments (MoM) region, the PO region and a region referred to as the joint PO-MoM (POM) region in this paper. The MoM region, generally, the smallest one among the three regions, includes wires, wire-surface junctions and a small part of the platform surface surrounding the junctions. A large part of the remaining platform surface forms the PO region with the rest being the POM region which is situated between the MoM and PO regions. The POM region is treated as a MoM region on the one hand so that the total MoM region is sufficiently large to well characterize the platform-attached antennas, whereas it is also regarded as a PO region on the other hand so that its interaction with the PO region needs not to be precisely considered so as to drastically reduce computational requirements. © 2006 IEEE.
Sun, 01 Aug 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/557912010-08-01T00:00:00Z
- Electromagnetic scattering by finite periodic arrays using the characteristic basis function and adaptive integral methodshttps://scholarbank.nus.edu.sg/handle/10635/55839Title: Electromagnetic scattering by finite periodic arrays using the characteristic basis function and adaptive integral methods
Authors: Hu, L.; Li, L.-W.; Mittra, R.
Abstract: We introduce a novel technique that combines the AIM algorithm with the characteristic basis function method (CBFM) to solve the problem of electromagnetic scattering by large but finite periodic arrays. An important advantage of using the CBFM for this problem is that we only need to analyze a single unit cell to construct the characteristic basis functions (CBFs) for the entire array. The CBFs are generated by illuminating a single unit cell with a plane wave incident from different angles, for both the θ- and φ-polarizations. The initial set of CBFs, generated in the manner described above, are then downselected by applying a singular value decomposition (SVD) procedure and retaining only the left singular vectors whose corresponding singular values fall above a threshold. Next, in the conventional CBFM, we derive a reduced matrix by applying the Galerkin procedure and solve it directly if its size is manageable. However, when solving an array problem, which precludes the direct-solve option, we can utilize the adaptive integral method (AIM) algorithm, detailed below, not only to accelerate the solution but to reduce memory requirements as well. Numerical examples are included in this communication to demonstrate the accuracy and the numerical efficiency of the proposed technique. © 2006 IEEE.
Wed, 01 Sep 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/558392010-09-01T00:00:00Z
- Spherical cloaking with homogeneous isotropic multilayered structureshttps://scholarbank.nus.edu.sg/handle/10635/57470Title: Spherical cloaking with homogeneous isotropic multilayered structures
Authors: Qiu, C.-W.; Hu, L.; Xu, X.; Feng, Y.
Abstract: We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers. © 2009 The American Physical Society.
Wed, 01 Apr 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/574702009-04-01T00:00:00Z
- Dyadic Green's function for aplanatic solid immersion lens based sub-surface microscopyhttps://scholarbank.nus.edu.sg/handle/10635/55711Title: Dyadic Green's function for aplanatic solid immersion lens based sub-surface microscopy
Authors: Hu, L.; Chen, R.; Agarwal, K.; Sheppard, C.J.R.; Phang, J.C.H.; Chen, X.
Abstract: We present the derivation of the dyadic Green's function for the aplanatic solid immersion lens based microscopy system. The presented dyadic Green's function is general and is applicable at non-aplanatic points as well in the object plane. Thus, the electromagnetic wave formulation is used to describe the optical system without paraxial assumptions. Various important and useful properties of SIL based microscopy system are also presented. The effect of the numerical aperture of the objective on the peak intensities, resolutions and the depth of field are also reported. Some interesting longitudinal effects are also reported. © 2011 Optical Society of America.
Mon, 26 Sep 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/557112011-09-26T00:00:00Z