L. Landesa

Method-of-moments formulation for the analysis of plasmonic nano-optical antennas

We present a surface integral equation (SIE) to model the electromagnetic behavior of metallic objects at optical frequencies. The electric and magnetic current combined field integral equation considering both tangential and normal equations is applied. The SIE is solved by using a method-of-moments (MoM) formulation. The SIE-MoM approach is applied only on the material boundary surfaces and interfaces, avoiding the cumbersome volumetric discretization of the objects and the surrounding space required in differential-equation formulations. Some canonical examples have been analyzed, and the results have been compared with analytical reference solutions in order to prove the accuracy of the proposed method. Finally, two plasmonic Yagi-Uda nanoantennas have been analyzed, illustrating the applicability of the method to the solution of real plasmonic problems.

Comparison of surface integral equation formulations for electromagnetic analysis of plasmonic nanoscatterers

The performance of most widespread surface integral equation (SIE) formulations with the method of moments (MoM) are studied in the context of plasmonic materials. Although not yet widespread in optics, SIE-MoM approaches bring important advantages for the rigorous analysis of penetrable plasmonic bodies. Criteria such as accuracy in near and far field calculations, iterative convergence and reliability are addressed to assess the suitability of these formulations in the field of plasmonics.

Surface integral equation formulation for the analysis of left-handed metamaterials

A surface integral equation (SIE) formulation is applied to the analysis of electromagnetic problems involving three-dimensional (3D) piecewise homogenized left-handed metamaterials (LHM). The resulting integral equations are discretized by the well-known method of moments (MoM) and solved via an iterative process. The unknowns are defined only on the interfaces between different media, avoiding the discretization of volumes and surrounding space, which entails a drastic reduction in the number of unknowns arising in the numerical discretization of the equations. Besides, the SIE-MoM formulation inherently includes the radiation condition at infinity, so it is not necessary to artificially include termination absorbing boundary conditions. Some 3D numerical examples are presented to confirm the validity and versatility of this approach on dealing with LHM, also providing some intuitive verifications of the singular properties of these amazing materials.

Optimization of an optical wireless nanolink using directive nanoantennas

Optical connects will become a key point in the next generation of integrated circuits, namely the upcoming nanoscale optical chips. In this context, nano-optical wireless links using nanoantennas have been presented as a promising alternative to regular plasmonic waveguide links, whose main limitation is the range propagation due to the metal absorption losses. In this paper we present the complete design of a high-capability wireless nanolink using matched directive nanoantennas. It will be shown how the use of directive nanoantennas clearly enhances the capability of the link, improving its behavior with respect to non-directive nanoantennas and largely outperforming regular plasmonic waveguide connects.

Bias of the Maximum Likelihood Doa Estimation from Inaccurate Knowledge of the Antenna Array Response

The estimators of directions of arrival of narrow-band signals using array antennas could be erroneous if we do not model adequately the behaviour of the global antenna system (for example, incorrect modeling of the mutual coupling or coupling of the antennas with the platform). In this paper we obtain an expression for evaluating the bias of the Maximum Likelihood estimators if we model incorrectly the behaviour of the antenna. The results indicate that if we consider an onboard array antenna as an ideal system (without electromagnetic effects) the performance of a direction of arrivals (DOA) estimation system may be degradated.

MLFMA-MoM for Solving the Scattering of Densely Packed Plasmonic Nanoparticle Assemblies

In this paper, we present a judicious combination of two renowned surface integral equation (SIE)-based techniques, namely, the multilevel fast multipole algorithm (MLFMA) and the method of moments (MoM), which synergize into a hybrid method that allows to address the analysis of large densely packed particle assemblies in an efficient and accurate way. This hybridization takes advantage of the repetition pattern inherent to these kinds of structures. Basically, the repeated self-coupling problems are squarely solved throughout the factorization of their MoM impedance matrix, whereas the cross-couplings through the surrounding medium are expedited via the MLFMA in the framework of a global iterative scheme. Some results are presented here to demonstrate the suitability of the proposed hybrid method to address large-scale nanoparticle arrays in the framework of nanoplasmonic biosensing applications.

Improving condition number and convergence of the surface integral-equation method of moments for penetrable bodies

Most of the surface integral equation (SIE) formulations for composite conductor and/or penetrable objects suffer from balancing problems mainly because of the very different scales of the equivalent electric and magnetic currents. Consequently, the impedance matrix usually has high- or ill-condition number due to the imbalance between the different blocks. Using an efficient left and right preconditioner the elements of the impedance matrix are balanced. The proposed approach improves the matrix balance without modifying the underlying SIE formulation, which can be selected solely in terms of accuracy. The numerical complexity of this preconditioner is O(N) with N the number of unknowns, and it can be easily included on any existing SIE code implementation.

APPLICATION OF THE FAST MULTIPOLE METHOD TO THE GENERALIZED FORWARD-BACKWARD ITERATIVE ALGORITHM

In a preious work, the generalized forward)backward () GFB method was proposed to compute the scattering from targets on rough ocean-like surfaces. In this paper, we deelop an acceleration of () the GFB method based on the fast multipole method FMM . The FMM is adapted to reduce the operational cost associated with the iteratie computations in the target regions. The proposed method is shown to conerge in a low number of iterations, and allows a significant reduction in the computational and storage costs with respect to the conentional GFB formulation. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 78)83, 2000. method. In both GFB methods GFB 6 and SA)GFB 7 , the solution is obtained through an iterative process based on the same general concepts as the FB method, combined with the direct MoM solution of the region containing the obsta- cle. So, the computational costs of the GFB methods can be 2 . . considered as the above-mentioned O N or O N costs, respectively, for the sea-surface integrations plus the addi- tional cost associated with the conventional MoM solution of the obstacle region. The latter cost may be predominant when the targets become electrically large. The MoM solution of a single obstacle region results in a dense n = n linear system, where n is the number of MoM basis functions in the obstacle region. The memory required 2 .

THE SYNTHESIS OF COMPLEX-ANGLE ZEROS FOR ON-BOARD ANTENNA ARRAYS

Shelkunoff circle synthesis techniques are only effective for equispaced antenna arrays. These techniques are based on reorganizing the zeros on the Shelkunoff circle. We propose a technique based on locating complex-direction zeros to synthesize arbitrary on-board antenna arrays. It is based on the analytical continuation of Green’s functions and on a new representation of the complex plane (analogous to the Shelkunoff circle).

Estimating correlation functions for dipoles in correlated Rician-fading scenarios

While the spatial correlation function between two dipoles is well known for Rayleigh fading, that for Rician fading is not available in the literature. Here, a Rician-fading correlation function is proposed for two dipoles separated by a given distance. The existing models for Rayleigh fading are based on the distance between elements. The new idea is to penalize the distance between elements in different ways as the degradation of the environment increases (with increasing Rician -factor). The resulting functions are validated against previously reported results.