## 1. Introduction

[2] In electromagnetics, numerical techniques have been essential in the development of new technology in the last two decades. The rapidly growing computer capacity and calculation speeds make accurate solutions of very complex problems feasible. This has been especially true in the design of antennas. Whereas 30 years ago, the design of an antenna was based on simple analytical models, or trial and error strategies, nowadays, simulations seem to be as crucial to the design as real measurements. The first practical codes were based on integral equations, solved with the method of moments (MOM) [*Aronson et al.*, 1967]. They offered a very good approximation for the computational capacity available at that time. Later, differential equation techniques like the finite element method (FEM), and the finite difference time domain (FDTD), and other related techniques, also were heavily developed and adopted by the community. A good overview on the comparison of the different computational techniques can be found in the works of *Miller* [1988] and *Peterson et al.* [1998]. The core differences between integral and differential equation techniques are of course well-known: (1) the prenumerical analytical effort required to set up the calculation procedure, (2) the solution domain that has to be discretized, and (3) the implementation of the radiation condition, especially important for antennas. MOM requires a considerably greater analytical effort of the code developer. However, only components sustaining currents need to be discretized. This gives rise to a relatively small number of unknowns. The radiation condition is automatically included. These observations make the MOM an ideal candidate to analyze in a very efficient way a certain category of topologies. Nevertheless, nowadays the emphasis in the user community of computational tools has clearly shifted toward differential techniques. This is due to the combination of two factors: the enormous increase in available computer resources and the generality of these techniques. Since differential techniques in principle are able to analyze virtually anything, the investment in such a tool is very attractive from a budget point of view. As a consequence, many topologies which are inherently more suited for MOM tools, are analyzed and/or designed in literature with slower tools based on differential techniques. This does not mean that MOM tools have disappeared. They are indispensable in problems involving large scatterers, topologies in layer structures with very thick and/or thin layers, configurations with sharp edges, etc. Actually, it is a recent trend of some major differential software tool vendors to also offer MOM capabilities in their software pallet. Also, in newly emerging fields, the MOM still has its important role to play.

[3] This paper considers the application of MOM in plasmonics, i.e., at very high (IR and optical) frequencies. This research field is now high profile in many physics departments all over the world. It can easily be checked that, although there are some papers using the method of moments [*Gallinet and Martin*, 2009; *Kern and Martin*, 2010; *Gallinet et al.*, 2010; *Chremmos*, 2010; *Alegret et al.*, 2008; *Smajic et al.*, 2009], most researchers use differential equation tools to perform their research [see, e.g., *Kappeler et al.*, 2007; *Qiang et al.*, 2004; *Verellen et al.*, 2009]. In most cases the integral equation formulation used is a surface integral equation [*Gallinet and Martin*, 2009; *Kern and Martin*, 2010; *Gallinet et al.*, 2010]. *Chremmos* [2010] uses a magnetic type scalar integral equation to describe surface plasmon scattering by rectangular dielectric channel discontinuities. Even the use of the magnetic current formalism to describe holes, classical at microwave frequencies, already has been used in plasmonics [*Alegret et al.*, 2008]. In this paper, it will be shown that, in the current status of this research field, MOM should certainly be taken into account as a very competitive computational tool.