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Acoustic metamaterials and phononic crystals represent a promising platform for the development of noise-insulating systems characterized by a low weight and small thickness. Nevertheless, the operational spectral range of these structures is usually quite narrow, limiting their application as substitutions of conventional noise-insulating systems. In this work, the problem is tackled by demonstration of several ways for the improvement of noise-insulating properties of the periodic structures based on coupled Helmholtz resonators. It is shown that tuning of local coupling between the resonators leads to the formation of a broad stopband covering ∼3.5 octaves (200–2100 Hz) in the transmission spectra. This property is linked to band structures of the equivalent infinitely periodic systems and is discussed in terms of bandgap engineering. The local coupling strength is varied via several means, including introduction of chirped structures and lossy resonators with porous inserts. The stopband engineering procedure is supported by genetic algorithm optimization, and the numerical calculations are verified by experimental measurements. [ABSTRACT FROM AUTHOR]

Noise pollution remains a challenging problem requiring the development of novel systems for noise insulation. Extensive work in the field of acoustic metamaterials has led to various ventilated structures which, however, are usually demonstrated for rather narrow regions of the audible spectrum. In this work, the idea of metamaterial‐based systems is further extended, developing the concept of a metahouse chamber representing a ventilated structure for multiple band noise insulation. Broad stop‐bands originate from strong coupling between pairs of Helmholtz resonators constituting the structure. The averaged transmission −18.6 dB are demonstrated numerically and experimentally within the spectral range from 1500 to 16 500 Hz. The sparseness of the structure together with the possibility to use optically transparent materials suggest that the chamber may be also characterized by partial optical transparency depending on the mutual position of structural elements. The obtained results are promising for development of novel noise‐insulating structures advancing urban science. [ABSTRACT FROM AUTHOR]

In this study, the application of thermite reactions in Nb2O5–Al system in the fabrication of novel NbAl3/Al2O3 composites was investigated. Combining the thermite reactions with self-propagating high-temperature synthesis (SHS) technique in compressed powder mixtures of Nb2O5 + Al resulted in layer-by-layer progress of the exothermic reaction, controlled formation of the desired products and their coexistence in each reacted layer. Characterization of the products using X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) techniques showed that all samples were composed of a metallic matrix including NbAl3 as the main compound, along with Al2O3 as ceramic reinforcing phase. Differential thermal analysis (DTA) analysis was used to study the mechanism of reaction using both stoichiometric and over-stoichiometric amounts of aluminum. The effect of such parameters as stoichiometry and green density of the samples on the combustion temperature, formed phases, microstructure, and hardness of the obtained composites was investigated using samples with stoichiometric as well 20 wt% and 40 wt% excess aluminum, and samples with green densities of 75%, 85%, and 95% of theoretical maximum density (TMD). The presence of excess aluminum resulted in prolonged reaction times, lower combustion temperatures, and lower mean values of hardness. While the variations in green density had no remarkable effect on the microstructural features of products within the density range under study, the most intensive reactions, highest combustion temperature, and highest mean value of hardness were encountered in samples with green density of 85%TMD. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a widely used wireless technology for contactless data exchange. Owing to international standardization and one-way security nature of the communication protocol, RFID tags, holding sensitive information, may be a subject to theft. One of the major security loopholes is the so-called far-field attack, where unauthorized interrogation is performed from a distance, bypassing the user's verification. This loophole is a penalty of using a dipole-like RFID tag antenna, leaking wireless information to the far-field. Here we introduce a new concept of anapole-enabled security, prohibiting far-field attacks by utilizing fundamental laws of physics. Our design is based on radiationless electromagnetic states (anapoles), which have high near-field concentration and theoretically nulling far-field scattering. The first property enables performing data readout from several centimeters (near-field), while the second prevents attacks from a distance, regardless an eavesdropper's radiated power and antenna gain. Our realization is based on a compact 3 cm high-index ceramic core–shell structure, functionalized with a thin metal wire and an integrated circuit to control the tag. Switching scheme was designed to provide a modulation between two radiation-less anapole states, blocking both up and down links for a far-field access. The anapole tag demonstrates more than 20 dB suppression of far-field interrogation distance in respect with a standard commercial tag, while keeping the near-field performance at the same level. The proposed concept might significantly enhance the RFID communication channel in cases, where information security prevails over cost constrains. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a widely used technology for contactless data readout. Numerous passive RFID tags are available on the market, and in a vast majority of cases, their designs are based on flat meandered dipole architectures. However, besides technological advantages, those realizations suffer from polarization mismatch issues and limited spatial sectors, from which flat tags can be interrogated. Here, we demonstrate and analyze a miniature omnidirectional tag accessible from all 4π stereo angles with a commercial RFID reader. Our design is based on exploring all three dimensions, which allows achieving close to perfect angular coverage by overlapping several multipole resonances of a structure. An optimized metal strip with a nontrivial geometry is wrapped on a high permittivity ceramic sphere for miniaturization purposes. As a result, a 3 cm device (tenths of an operational wavelength) is demonstrated to be readable from a 1.5 m distance without any dependence on the interrogation direction. Compact omnidirectional tags can remove hard restrictions on a mutual orientation between information holders and interrogating systems. Those capabilities are essential in many applications, including logistics, animal activity monitoring, and security, to name just a few. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a mature technology that allows contactless reading of data via a wireless communication link. While communication protocols in this field are subject to international regulations, there are plenty of opportunities to improve hardware realization of antenna devices that support this technology. In particular, readout range extension and miniaturization of passive RFID tags is an important challenge with far-reaching goals. Here, we introduce and analyze a new concept of high-permittivity ceramic tag that relies on different physical principles. Instead of using conduction currents in metallic wires to drive electronic chips and generate electromagnetic radiation, high-permittivity components rely on excitation of displacement currents. Those are efficiently converted to actual electric current which drives the memory chip. Practical aspects of this approach are improved robustness to environmental fluctuations, footprint reduction, and readout range extension. In particular, our high-permittivity ceramic (ε ~ 100) elements have demonstrated a 25% reading range improvement in comparison to commercial tags. In case when state-of-the-art readers and RFID chips are used, the readout distances of the developed ceramic tags can reach 22 m. This number can be further extended with improved matching circuits. Miniature RFID tags, capable to establish long-range communication channels, can find use in many applications, including retail, security, Internet of Things, and many others. [ABSTRACT FROM AUTHOR]

In this work, we develop a self-consistent approach for calculation of the Purcell factor and Lamb shift in highly dispersive hyperbolic metamaterial accounting for the effective dipole frequency shift. Also we theoretically predict the possi- bility of spontaneous topological transition, which occurs not due to the external change of the system parameters but only due to the Lamb shift. [ABSTRACT FROM AUTHOR]

Following the suggestion of Rodriguez-Fortuno et al. [Phys. Rev. Lett. 112, 033902 (2014)], we study the repulsive force acting on a electric dipole placed over a surface of epsilon-near-zero (ENZ) metamaterial. The dependence of the repulsive force value on the dipole size has been studied. We show that the effect of finite size drastically affects the values of the repulsive force as compared to the point-dipole case. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The influence of iron, copper and nitrate ions on free-radical processes in rats and the dependence between dose and effect of pro-oxidants were studied. Rats were divided into 14 groups and administered differing concentrations and combinations of chemicals with drinking water. Concentrations of iron, copper and nitrate in the water were 1, 0.5 and 0.33 of maximum permissible concentrations (MPCs) for every chemical. The action of the investigated pollutants on the intensity of free-radical processes was estimated by the determination of conjugated dienes in liver homogenate and the intensity of Fe2+-induced chemiluminescence of the blood serum. It is estimated that chemicals entering the organism in doses that do not exceed their MPC lead to an increase in free-radical oxidation in comparison to the controls. A maximal effect of iron on the concentration of conjugated dienes was observed in a dose equal to 0.33 MPC, while copper and nitrate possess maximal activity in concentrations of 0.5 MPCs. Fast flash amplitude of chemiluminescence in serum was not dose-dependent in rats obtaining iron and copper, while nitrate had a reverse dose-dependent effect. Total luminosity was maximal in doses of chemicals equal to 0.33 MPCs. The combined action of pollutants was more evident in comparison to isolated chemicals in doses equal to 1 MPC. [ABSTRACT FROM AUTHOR]