V. S. Asadchy

Total Absorption of Electromagnetic Waves in Ultimately Thin Layers

We consider single-layer arrays of electrically small lossy particles that completely absorb electromagnetic waves at normal incidence. Required conditions for electromagnetic properties of bi-anisotropic particles have been identified in the most general case of uniaxial reciprocal and nonreciprocal particles. We consider the design possibilities offered by the particles of all four fundamental classes of bi-anisotropic inclusions: reciprocal chiral and omega particles and nonreciprocal Tellegen and moving particles. We also study the reflection/transmission properties of asymmetric structures with different properties when illuminated from the opposite sides of the sheet. It has been found that it is possible to realize single-layer grids which exhibit the total absorption property when illuminated from one side but are totally transparent when illuminated from the other side (an ultimately thin isolator). Other possible properties are co-polarized or twist polarized reflection from the side opposite to the absorbing one. Finally, we discuss possible approaches to practical realization of particles with the properties required for single-layer perfect absorbers and other proposed devices.

Flat Engineered Multichannel Reflectors

Recent advances in engineered gradient metasurfaces have enabled unprecedented opportunities for light manipulation using optically thin sheets, such as anomalous refraction, reflection, or focusing of an incident beam. Here we introduce a concept of multi-channel functional metasurfaces, which are able to control incoming and outgoing waves in a number of propagation directions simultaneously. In particular, we reveal a possibility to engineer multi-channel reflectors. Under the assumption of reciprocity and energy conservation, we find that there exist three basic functionalities of such reflectors: Specular, anomalous, and retro reflections. Multi-channel response of a general flat reflector can be described by a combination of these functionalities. To demonstrate the potential of the introduced concept, we design and experimentally test three different multi-channel reflectors: Three- and five-channel retro-reflectors and a three-channel power splitter. Furthermore, by extending the concept to reflectors supporting higher-order Floquet harmonics, we forecast the emergence of other multiple-channel flat devices, such as isolating mirrors, complex splitters, and multi-functional gratings.

Multi-channel reflectors: Versatile performance experimentally tested

We investigate multi-channel reflectors, such as a three-channel power splitter and a five-channel isolating mirror. These metasurface reflectors are able to control reflections from and into several directions while possessing a flat surface. We design, fabricate, and experimentally study these new devices, confirming that the performance is nearly perfect.

Magnetoelectric coupling without electric and magnetic response

We theoretically consider electrically small reciprocal particles, which show bianisotropic magneto-electric coupling. We study how strong the magneto-electric effect can be in comparison with the electric and magnetic polarizations induced directly by the corresponding electric and magnetic incident fields. In particular, we prove that it is not possible to realize a passive reciprocal particle, which would have exactly zero electric or magnetic polarizability but still exhibit magneto-electric coupling effects. On the other hand, we prove that magnetoelectric coupling coefficient can be very large as compared to both electric and magnetic polarizabilities of the same particle, in contrast to some claims found in the literature.

General approach to the synthesis of perfectly refractive metasurfaces

In this presentation we will introduce and discuss a general approach to the synthesis of metasurfaces for full control of reflected and transmitted fields. The method, which is applicable for any linear metasurface, is based on the use of an equivalent Z-matrix, connecting the tangential field components at the two sides on the metasurface. Finding the impedance matrix components, we are able to understand what physical properties of metasurface are needed in order to realize the desired response. Furthermore, we can find the required polarizabilities and/or susceptibilities of the metasurface unit cells and design the cell structures. In particular, we will discuss metasurfaces for perfect refraction into an arbitrary direction, explain possible alternative physical realizations and reveal the crucial role of bianisotropic coupling for design of perfectly matched metasurfaces for transmission control.

Large-area ground-free terahertz absorbers

In this work we introduce a planar ground-free terahertz absorber suitable for large-area manufacturing. The lack of a ground plane in the absorber design may pave the way for frequency-selective response that is an essential requirement for invisible sensors and wave filters. The absorber is to be manufactured using state-of-the-art techniques of large-area printing, within the frame of a joint project between Aalto University and the State Research Center of Finland (VTT). This new technology offers high resolution (up to 1 micrometer) and allows large-area deposition (up to several meters). At this stage of the work, we have designed a novel absorber and tested the performance of the proposed absorber numerically.