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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.

A method of synthesizing dispersion-strengthened aluminum matrix composites using a powder metallurgical technique and an in situ method was considered. Methods combination was aimed at ensuring energy efficiency, avoiding vacuum treatment of the reaction medium, and using inert gasses to protect from oxidation. Reinforcement phase precursors are capable of ensuring good wettability of dispersed particles by the molten matrix metal. The options of the methods’ practical implementation are presented by the example of producing aluminum matrix composites filled with various functional particles.

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.

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 ( $\varepsilon ~ \sim ~100$ ) 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.

Bound states in the continuum (BICs) are non-radiating solutions of the wave equation with a spectrum embedded in the continuum of propagating waves of the surrounding space. The complete decoupling of BICs from the radiation continuum makes their excitation impossible from the far-field. Here, we develop a general theory of parametric excitation of BICs in nonlinear systems with Kerr-type nonlinearity via spontaneous symmetry breaking, which results in a coupling of a BIC and a bright mode of the system. Using the temporal coupled-mode theory and perturbation analysis, we found the threshold intensity for excitation of a BIC and study the possible stable and unstable solutions depending on the pump intensity and frequency detuning between the pump and BIC. We revealed that at some parameters of the pump beam, there are no stable solutions and the BIC can be used for frequency comb generation. Our findings can be very promising for use in nonlinear photonic devices and all-optical networks., 17 pages, 9 figures

Radio frequency identification (RFID) allows performing a remote readout of data from passive battery-free tags, interrogated with an active reader. Quite a few efforts, concentrating on antennas design, have been explored, pushing interrogating distances to tens of meters. Here we develop a new concept of miniature high-permittivity ceramic tags, capable to extend reading range quite substantially. Instead of using conduction currents in metallic wires to drive electronic chips and provide electromagnetic radiation, our approach relies on excitation of displacement currents in high-permittivity resonators. Practical aspects of this approach include improved robustness to environmental fluctuations, footprint reduction, and readout range extension. Our architecture is shown to perform reading range up to 19 meters, if state of the art electronic components is in use, having the smallest size among long-range RFID passive tags. Miniature RFID tags, capable to establish long-range communication channels, can find use in numerous applications.

Electromagnetic scattering on subwavelength structures keeps attracting attention owing to abroad range of possible applications, where this phenomenon is in use. Fundamental limits of scattering cross-section, being well understood in spherical geometries, are overlooked in cases of low-symmetry resonators. Here, we revise the notion of superscattering and link this property with symmetry groups of the scattering potential. We demonstrate pathways to spectrally overlap several eigenmodes of a resonator in a way they interfere constructively and enhance the scattering cross-section. As a particular example, we demonstrate spectral overlapping of several electric and magnetic modes in a subwavelength entirely homogeneous ceramic resonator. The optimized structures show the excess of a dipolar scattering cross-section limit for a sphere up to a factor of four. The revealed rules, which link symmetry groups with fundamental scattering limits, allow performing and assessing designs of subwavelength supperscatterers, which can find a use in label-free imaging, compact antennas, long-range radio frequency identification, and many other fields., 9 pages, 5 figures

An efficient modulation of backscattered energy is one of the key requirements for enabling efficient wireless communication channels. Typical architectures, being based on either electronically or mechanically modulated reflectors, cannot be downscaled to subwavelengths dimensions by design. Here we show that integrating high-index dielectric materials with tunable subwavelength resonators allows achieving an efficient backscattering modulation, keeping a footprint of an entire structure small. An interference between high-order Mie resonances leads to either enhancement or suppression of the backscattering, depending on a control parameter. In particular, a ceramic core-shell, driven by an electronically tunable split ring resonator was shown to provide a backscattering modulation depth as high as tens of the geometrical cross-section of the structure. The design was optimized towards maximizing reading range of radio frequency identification (RFID) tags and shown to outperform existing commercial solutions by orders of magnitude in terms of the modulation efficiency. The proposed concept of multipole engineering allows one to design a new generation of miniature beacons and modulators for wireless communication needs and other relevant applications.

In this work we generalize the notion of superscattering and associate it with a symmetry group of a scattering object. Using the group theory approach we describe a way to spectrally overlap several eigenmodes of a resonator in order to achieve scattering enhancement. Importantly, this can be done by simple variation of geometric parameters of the system, implying that the symmetry is preserved. We also demonstarte that a scattering cross-section limit of a spherical object is not valid for the case of non-spherical geometries. As an example, we use finite-size ceramic cylinder and demonstrate that a dipolar scattering cross-section limit of a spherical object can be exceeded by more then 3 times. The obtained results may be promising for design of antennas and radio frequency identification systems.

Radio frequency identification (RFID) is one of the commonly used approaches to a short-range wireless data exchange. 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.

High-permittivity ceramic components, being traditional building blocks of dielectric resonant antennas, are proposed and demonstrated to serve as efficient elements in radio frequency identification (RFID). While common RFID- tags utilize conduction currents in metal wires, our concept relies on excitation of high-quality factor resonant modes, activating a non-resonant metal ring, functionalized with an RFID chip. Our cascaded scheme demonstrates several advantages over conventional approaches, including footprint miniaturization and reading range enhancement of tags. In particular, high permittivity ceramic (e∼100) cylinder-based tags were shown to be detected from 25% larger distance in comparison to commercial tags.

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.

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 possibility of spontaneous topological transition, which occurs not due to the external change of the system parameters but only due to the Lamb shift.

The optical bound state in the continuum (BIC) is characterized by an extremely high-quality factor resulting in a drastic enhancement of light-matter interaction phenomena. We study the optical response of a one-dimensional photonic crystal slab with Kerr focusing nonlinearity in the vicinity of BICs analytically and numerically. We predict a strong nonlinear response including multistable behavior, self-tuning of BICs to the frequency of incident waves, and breaking of symmetry protected BICs. We show that all of these phenomena can be observed in silicon photonic structure at the pump power of several $\ensuremath{\mu}\mathrm{W}/{\mathrm{cm}}^{2}$. We also analyze the modulation instability of the obtained solutions and the effect of the finite size of the structure on the stability. Our findings have strong implications for nonlinear photonics and integrated optical circuits.

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)