One-way transparent sheets

In this paper we introduce the concept of metasurfaces which are fully transparent when looking from one of the two sides of the sheet and have controllable functionalities for waves hitting the opposite side (one-way transparent sheets). We address the question on what functionalities are allowed, considering limitations due to reciprocity and passivity. In particular, we have found that it is possible to realize one-way transparent sheets which have the properties of a twist-polarizer in reflection or transmission when illuminated from the other side. Also one-way transparent sheets with controllable co-polarized reflection and transmission from the opposite side are feasible. We show that particular non-reciprocal magneto-electric coupling inside the sheet is necessary to realize lossless non-active transparent sheets. Furthermore, we derive the required polarizabilities of constituent dipole particles such that the layers composed of them form one-way transparent sheets. We conclude with design and simulations of an example of a nonreciprocal one-way transparent sheet functioning as an isolating twist-polarizer.Comment: 8 pages, 4 figure

Functional Metasurfaces

This thesis studies the use of functional metasurfaces composed of single arrays of polarizable unit cells in order to manipulate electromagnetic waves. The main topics that are studied are absorbing metasurfaces, metamirrors, Huygens' metasurfaces, and parity-time-symmetric metasurfaces.  In the first part of the thesis, we introduce the general theory of off-band-transparent absorbing metasurfaces. First, we consider metasurfaces which symmetrically absorb electromagnetic waves hitting any of their sides. As an example for symmetric absorbing metasurfaces, we introduce a novel off-band-transparent light absorber composed of a single array of core-shell particles. We continue this study by introducing the concept of asymmetric absorbing metasurfaces. We study single-layer sheets which work as total absorbers only from one side and investigate what functionalities can be engineered for illumination from the opposite side.  The second part of the thesis is devoted to the concept of off-band-transparent reflecting metasurfaces. We consider both symmetric and asymmetric metamirrors. We show how arrays of electrically small resonant bianisotropic particles can be employed to fully reflect electromagnetic plane waves hitting any of their sides while enabling independent and full control over the phase of waves reflected from their different sides.  The third part of the thesis focuses on the concept of Huygens' metasurfaces. We first present the concept of symmetric and asymmetric transparent metasurfaces. We introduce one-way transparent metasurfaces which offer controllable functionalities for waves hitting their non-transparent sides. We furthermore introduce the concept of all-angle Huygens' metasurfaces. These metasurfaces are reflectionless for any arbitrary input wavefront while enabling manipulation of transmitted waves in unprecedented ways.  In the last part of the thesis, we study the concept of parity-time-symmetric metasurfaces. Utilizing these metasurfaces, it is shown how electromagnetic plane waves can be fully recreated behind a highly reflecting metallic screen. The proposed structure works as a new form of one-dimensional cloak which is capable of cloaking an almost fully reflective metallic screen in both spectrally and angularly selective manner

Least Upper Bounds of the Powers Extracted and Scattered by Bi-anisotropic Particles

The least upper bounds of the powers extracted and scattered by bi-anisotropic particles are investigated analytically. A rigorous derivation for particles having invertible polarizability tensors is presented, and the particles with singular polarizability tensors that have been reported in the literature are treated explicitly. The analysis concludes that previous upper bounds presented for isotropic particles can be extrapolated to bi-anisotropic particles. In particular, it is shown that neither nonreciprocal nor magnetoelectric coupling phenomena can further increase those upper bounds on the extracted and scattered powers. The outcomes are illustrated further with approximate circuit model examples of two dipole antennas connected via a generic lossless network.Comment: 9 pages, 1 figure

Balanced and optimal bianisotropic particles: maximizing power extracted from electromagnetic fields

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