On-Site Wireless Power Generation

Conventional wireless power transfer systems consist of a microwave power generator and a microwave power receiver separated by some distance. To realize efficient power transfer, the system is typically brought to resonance, and the coupled-antenna mode is optimized to reduce radiation into the surrounding space. In this scheme, any modification of the receiver position or of its electromagnetic properties results in the necessity of dynamically tuning the whole system to restore the resonant matching condition. It implies poor robustness to the receiver location and load impedance, as well as additional energy consumption in the control network. In this study, we introduce a new paradigm for wireless power delivery based on which the whole system, including transmitter and receiver and the space in between, forms a unified microwave power generator. In our proposed scenario the load itself becomes part of the generator. Microwave oscillations are created directly at the receiver location, eliminating the need for dynamical tuning of the system within the range of the self-oscillation regime. The proposed concept has relevant connections with the recent interest in parity-time symmetric systems, in which balanced loss and gain distributions enable unusual electromagnetic responses.Comment: 10 pages, 13 figure

Broadband reflectionless metasheets: Frequency-selective transmission and perfect absorption

Energy of propagating electromagnetic waves can be fully absorbed in a thin lossy layer, but only in a narrow frequency band, as follows from the causality principle. On the other hand, it appears that there are no fundamental limitations on broadband matching of thin absorbing layers. However, known thin absorbers produce significant reflections outside of the resonant absorption band. In this paper we explore possibilities to realize a thin absorbing layer which produces no reflected waves in a very wide frequency range, while the transmission coefficient has a narrow peak of full absorption. Here we show, both theoretically and experimentally, that a wide-band-matched thin resonant absorber, invisible in reflection, can be realized if one and the same resonant mode of the absorbing array unit cells is utilized to create both electric and magnetic responses. We test this concept using chiral particles in each unit cells, arranged in a periodic planar racemic array, utilizing chirality coupling in each unit cell but compensating the field coupling at the macroscopic level. We prove that the concept and the proposed realization approach also can be used to create non-reflecting layers for full control of transmitted fields. Our results can have a broad range of potential applications over the entire electromagnetic spectrum including, for example, perfect ultra-compact wave filters and selective multi-frequency sensors.Comment: 9 pages, 10 figure

Full light absorption in single arrays of spherical nanoparticles

In this paper we show that arrays of core-shell nanoparticles function as effective thin absorbers of light. In contrast to known metamaterial absorbers, the introduced absorbers are formed by single planar arrays of spherical inclusions and enable full absorption of light incident on either or both sides of the array. We demonstrate possibilities for realizing different kinds of symmetric absorbers, including resonant, ultra-broadband, angularly selective, and all-angle absorbers. The physical principle behind these designs is explained considering balanced electric and magnetic responses of unit cells. Photovoltaic devices and thermal emitters are the two most important potential applications of the proposed designs.Comment: (e.g.: 18 pages, 5 figures

Metamaterials: optical activity without chirality

We report that the classical phenomenon of optical activity, which is traditionally associated with chirality (helicity) of organic molecules, proteins, and inorganic structures, can be observed in artificial planar media which exhibit neither 3D nor 2D chirality. We observe the effect in the microwave and optical parts of the spectrum at oblique incidence to regular arrays of nonchiral subwavelength metamolecules in the form of strong circular dichroism and birefringence indistinguishable from those of chiral three-dimensional media

Communication in networks with hierarchical branching

We present a simple model of communication in networks with hierarchical branching. We analyze the behavior of the model from the viewpoint of critical systems under different situations. For certain values of the parameters, a continuous phase transition between a sparse and a congested regime is observed and accurately described by an order parameter and the power spectra. At the critical point the behavior of the model is totally independent of the number of hierarchical levels. Also scaling properties are observed when the size of the system varies. The presence of noise in the communication is shown to break the transition. Despite the simplicity of the model, the analytical results are a useful guide to forecast the main features of real networks.Comment: 4 pages, 3 figures. Final version accepted in PR

Effect of SLM parameters on the structure and properties of CP-Ti

Selective laser melting (SLM) is an additive manufacturing technique, which allows varying the relative porosity at the micro and macro levels. In this study, the microstructure, including the porous structure, of cp-Ti Grade 1 ELI produced by SLM and the effect of the scanning parameters on mechanical properties are studied. The mechanical properties are analyzed in terms of ISO 5832-2 for metal implants for surgery. The cp-Ti samples processed by SLM are characterized by increased strength due to the low porosity condition and the acicular martensitic structure. The ductility data scattering is explained by the stratified distribution of porosity in the metal after SLM. © 2018 Author(s)

Transfer-matrix DMRG for stochastic models: The Domany-Kinzel cellular automaton

We apply the transfer-matrix DMRG (TMRG) to a stochastic model, the Domany-Kinzel cellular automaton, which exhibits a non-equilibrium phase transition in the directed percolation universality class. Estimates for the stochastic time evolution, phase boundaries and critical exponents can be obtained with high precision. This is possible using only modest numerical effort since the thermodynamic limit can be taken analytically in our approach. We also point out further advantages of the TMRG over other numerical approaches, such as classical DMRG or Monte-Carlo simulations.Comment: 9 pages, 9 figures, uses IOP styl

Macroscopic invisibility cloaking of visible light

Invisibility cloaks, which used to be confined to the realm of fiction, have now been turned into a scientific reality thanks to the enabling theoretical tools of transformation optics and conformal mapping. Inspired by those theoretical works, the experimental realization of electromagnetic invisibility cloaks has been reported at various electromagnetic frequencies. All the invisibility cloaks demonstrated thus far, however, have relied on nano- or micro-fabricated artificial composite materials with spatially varying electromagnetic properties, which limit the size of the cloaked region to a few wavelengths. Here, we report the first realization of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding, for a specific light polarization, three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices

Uncertainty of atmospheric microwave absorption model: impact on ground-based radiometer simulations and retrievals

This paper presents a general approach to quantify absorption model uncertainty due to uncertainty in the underlying spectroscopic parameters. The approach is applied to a widely used microwave absorption model (Rosenkranz, 2017) and radiative transfer calculations in the 20–60&thinsp;GHz range, which are commonly exploited for atmospheric sounding by microwave radiometer (MWR). The approach, however, is not limited to any frequency range, observing geometry, or particular instrument. In the considered frequency range, relevant uncertainties come from water vapor and oxygen spectroscopic parameters. The uncertainty of the following parameters is found to dominate: (for water vapor) self- and foreign-continuum absorption coefficients, line broadening by dry air, line intensity, the temperature-dependence exponent for foreign-continuum absorption, and the line shift-to-broadening ratio; (for oxygen) line intensity, line broadening by dry air, line mixing, the temperature-dependence exponent for broadening, zero-frequency line broadening in air, and the temperature-dependence coefficient for line mixing. The full uncertainty covariance matrix is then computed for the set of spectroscopic parameters with significant impact. The impact of the spectroscopic parameter uncertainty covariance matrix on simulated downwelling microwave brightness temperatures (TB) in the 20–60&thinsp;GHz range is calculated for six atmospheric climatology conditions. The uncertainty contribution to simulated TB ranges from 0.30&thinsp;K (subarctic winter) to 0.92&thinsp;K (tropical) at 22.2&thinsp;GHz and from 2.73&thinsp;K (tropical) to 3.31&thinsp;K (subarctic winter) at 52.28&thinsp;GHz. The uncertainty contribution is nearly zero at 55–60&thinsp;GHz frequencies. Finally, the impact of spectroscopic parameter uncertainty on ground-based MWR retrievals of temperature and humidity profiles is discussed.</p

Features of the formation of communities of microorganisms adapting to the existing conditions in different types of agrophytocenoses

The article is devoted to studying the features of the formation of communities of microorganisms, adapting to the conditions of existence in various types of agrophytocenose