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Register a new userBalanced and optimal bianisotropic particles: Maximizing power extracted from electromagnetic fields
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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 the resonance canonical chiral and omega particles are found analytically. Such optimal particles have extreme properties in scattering (for example, zero backscattering or invisibility). Planar arrays of optimal particles possess extreme properties in reflection and transmission (e.g., total absorption or magnetic-wall resonance), and volumetric composites of optimal particles realize, for example, such extreme materials as the chiral nihility medium.
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We consider a novel method of cloaking objects from the surrounding electromagnetic fields in the microwave region. The method is based on transmission-line networks that simulate the wave propagation in the medium surrounding the cloaked object. The electromagnetic fields from the surrounding medium are coupled into the transmission-line network that guides the waves through the cloak thus leaving the cloaked object undetected. The cloaked object can be an array or interconnected mesh of small inclusions that fit inside the transmission-line network.
Three objections to the canonical analytical treatment of covariant electromagnetic theory are presented: (i) only half of Maxwells equations are present upon variation of the fundamental Lagrangian; (ii) the trace of the canonical energy-momentum tensor is not equivalent to the trace of the observed energy-momentum tensor; (iii) the Belinfante symmetrization procedure exists separate from the analytical approach in order to obtain the known observed result. It is shown that the analytical construction from Noethers theorem is based on manipulations that were developed to obtain the compact forms of the theory presented by Minkowski and Einstein; presentations which were developed before the existence of Noethers theorem. By reformulating the fundamental Lagrangian, all of the objections are simultaneously relieved. Variation of the proposed Lagrangian yields the complete set of Maxwells equations in the Euler-Lagrange equation of motion, and the observed energy-momentum tensor directly follows from Noethers theorem. Previously unavailable symmetries and identities that follow naturally from this procedure are also discussed.
For two electrically small nonreciprocal scatterers an analytical electromagnetic model of polarizabilities is developed. Both particles are bianisotropic: the so-called Tellegen-omega particle and moving-chiral particle. Analytical results are compared to the full-wave numerical simulations. Both models satisfy to main physical restrictions and leave no doubts in the possibility to realize these particles experimentally. This paper is a necessary step towards applications of nonreciprocal bianisotropic particles such as perfect electromagnetic isolators, twist polarizers, thin-sheet phase shifters, and other devices.
Starting from Stratton-Panofsky-Phillips-Jefimenko equations for the electric and magnetic fields generated by completely arbitrary charge and current density distributions at rest, we derive far-zone approximations for the fields, containing all components, dominant as well as sub-dominant. Using these approximate formulas, we derive general formulas for the total electromagnetic linear momentum and angular momentum, valid at large distances from arbitrary, non-moving charge and current sources.
We discuss the behaviour of the Larmor frequency shift and the longitudinal relaxation rate due to non-uniform electromagnetic fields on an assembly of spin 1/2 particles, in adiabatic and nonadiabatic regimes. We also show some general relations between the various frequency shifts and between the frequency shifts and relaxation rates. The remarkable feature of all our results is that they were obtained without any specific assumptions on the explicit form of the correlation functions of the fields. Hence, we expect that our results are valid both for diffusive and ballistic regime of motion and arbitrary cell shapes and surface scattering. These results can then be applied to a wide variety of realistic systems.
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