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The theory of characteristic modes (TCM) is presented for arbitrarily shaped 3-D structures including perfect electric conductors (PECs) and homogeneous penetrable objects. It is shown that by properly expressing the weighting operator of the generalized eigenvalue equation in terms of the integral operators related to the radiated fields, TCM can be formulated directly for the surface integral equation formulation of the problem. This avoids symmetrization or other modifications of the equations. The eigenvalues are shown to be related to radiated, reactive, and dissipated power, and the corresponding far-field patterns are orthogonal. The previously introduced TCM formulations for PEC are special cases of this generalized TCM.

Metasurfaces are used to design mantle cloaks based on scattering cancellation which involves surface impedance analysis. Theory of characteristic modes is a good tool for analyzing the scattering of a metallic object because it is based on surface impedance and it brings physical insight into the radiation properties of a structure without an excitation source. The theory of characteristic modes is applied in the analysis of a cylindrical cloaking metasurface used to cloak an LTE antenna to prevent it from interfering with a UMTS antenna when both antennas are co-located on the same site. The result provides a physical insight into the principle and design of mantle cloaks. It shows that degenerate resonant modes of the cloak are used to compensate for the degenerate non-resonant modes of the antenna. There is a symmetry in the modal surface current distribution of the cloak and the direction of the fundamental modal current distribution of the cloak is at 90° to that of the UMTS antenna. Also, the UMTS antenna has a better impedance matching after cloaking.

Resonances, i.e., extrema of the eigenvalues of characteristic modes for closed perfectly conducting objects are investigated. The characteristic modal solutions based on the electric, magnetic, and combined field integral operators (EFIO, MFIO, and CFIO) are studied and compared with analytical solutions for a sphere. All these formulations are found to capture both external (radiating) and internal (cavity) resonances predicted by the analytical expressions. At the internal resonances, the eigenvalues obtained with the EFIO- and MFIO-based approaches are not correct, and the corresponding modes are nonunique. These solutions also exhibit a strong duality between the electric (TM) and magnetic (TE) type modes. A connection is found between the external and internal resonances and the condition numbers of the matrices. The modal expansion of the CFIO-based solution is correct, even though it also experiences the nonuniqueness of the EFIO- and MFIO-based solutions.

AP-S/URSI 2019, IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, Atlanta, ETATS-UNIS, 07-/07/2019 - 12/07/2019; High sensitivity in sensors, large group delays forfilters and slow light can be achieved by engineering electromag-netically induced transparency within a narrow electromagneticspectrum. The induced transparency is due to the eliminationof the effect of a medium caused by interaction betweentwo resonant states often referred to as the bright and darkmodes. Induced transparency are often attained by breaking thestructural symmetry of metamaterials as this allows interactionbetween the two modes. In a case of a given excitation, thereis a need to understand the behaviour of the various modesthus making the application of theory of characteristic modesrelevant to this work. This paper presents an approach toobtain electromagnetically induced transparency for a givenexcitation using the theory of characteristic modes. It presentshow electromagnetically induced transparency in a structurecan be systematically engineered by determining which modesare responsible for its occurrence and how to excite thesemodes. In our example, EIT occurred at 36 GHz wherethere was an interaction between the bright and dark modes.This provides an insightful way for designing structures forelectromagnetically induced transparency applications

The symmetric PMCHWT method of moments (MoM) impedance matrix allows for the characteristic modes (CMs) of a structure containing dielectric to be found. Recently, this impedance matrix was proven to provide non-real solutions which can be attributed to the MoM internal resonance problem. These internal resonances can be removed through different CM post-processing techniques. However, these studies focus on dielectric structures, whereas the majority of antennas utilize electric conductors as the radiators. As such, dielectrics are often neglected to simplify the CM analysis and hence the problem of internal resonance is overlooked. This work explores the extent of the internal resonance problem in mixed conductor-dielectric structures. The results reveal that the problem is severe even when the structures only contain small amounts of dielectric materials. Moreover, the significant impact of dielectrics on CMs reveals that dielectrics should be included in CM analysis to ensure high accuracy.

In this letter, new metrics are proposed to provide physical insight into the behavior of metamaterial based structures by means of the theory of characteristic modes. A relationship between the first eigenmode and an expression of the polarizability is proposed for a split ring resonator. It thus allows us to describe a link between the artificial magnetic response of a split ring resonator and modal characteristics. Using the new metrics proposed, a reactive impedance substrate based on metal-dielectric metamaterial excited by a parallel magnetic field is shown to exhibit artificial magnetism. These metrics are shown to propose good agreement with other analytical and numerical methods. This analysis should be useful when such metal-dielectric metamaterial structures are associated to radiating elements like antennas, since it could be performed in the near field region, unlike common approaches based on plane wave and far field assumptions.

Characteristic mode analysis has traditionally been constrained to problems which utilize only perfect electric conductors (PEC). Through forced symmetry of a method of moments surface integral equation and newly proposed post-processing, characteristic modes can be solved for any material in a computationally efficient manner. As an example, the characteristic modes are solved for a mobile terminal consisting of both PEC and dielectric materials.