Abstract
Here we introduce the concept of ‘optimal particles’ for strong interactions with electromagnetic fields. We assume that a particle occupies a given electrically small volume in space and study the required optimal relations between the particle polarizabilities. In these optimal particles, the inclusion shape and material are chosen so that the particles extract the maximum possible power from given incident fields. It appears that for different excitation scenarios the optimal particles are bianisotropic chiral, omega, moving and Tellegen particles. The optimal dimensions of resonant canonical chiral and omega particles are found analytically. Such optimal particles have extreme properties in scattering (e.g., zero backscattering or invisibility). Planar arrays of optimal particles possess extreme properties in reflection and transmission (e.g. total absorption or magnetic-wall response), and volumetric composites of optimal particles realize, for example, such extreme materials as the chiral nihility medium.
Highlights
Let us consider an electrically small particle excited by a given external electromagnetic field, for example, a plane wave
What would be the optimal relation between the polarizabilities of the particle to ensure the most effective interaction with the incident fields, provided that the overall size of the particle is fixed and we cannot increase the absolute values of the polarizabilities? In this study we consider particles which respond only as electric and magnetic dipoles
This is in agreement with the earlier studies of chiral particles as the optimal particles for interactions with propagating circularly polarized waves [7, 9, 10], where it was assumed that the particles were reciprocal
Summary
Let us consider an electrically small particle excited by a given external electromagnetic field, for example, a plane wave. If arbitrarily high-order multipole moments are resonantly excited and contribute to the process of receiving power, there is no limit on how much power can be absorbed by a finite-size particle This follows from the general relation between the maximal absorption cross section σabs max and gain G of an arbitrary reciprocal antenna operating in a reciprocal environment The goal of the present work is to find the optimal particles which would interact most effectively with waves of other polarizations (in particular, linear) and with both propagating and evanescent incident fields. We expect that such optimal inclusions will open a way to realizing particle arrays and volumetric composites with extreme properties, as we see from the known example of the optimal spiral. We define the optimal particle as one which extracts the maximum (or minimum) power from given incident fields
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