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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.

Capabilities to monitor the purity and mixture composition of liquids with the aid of low-cost portable devices can grant essential advantages in maintaining personal health safety. The overwhelming majority of consumer wireless devices operate at relatively small operational bandwidth, thus not allowing for retrieving material composition via dispersion characteristics. To mitigate the bandwidth limitations, resonant methods, granting precision in a small frequency window, might be of use. Here, we demonstrate a liquid sensor able to provide 90.5 kHz/RIU sensitivities owing to a resonator, supporting high-quality factor quasi-bound states in the continuum. The sensor's architecture encompasses a high-permittivity ceramic resonator and a capillary wrapped around it. The volumetric design increases the overlap between the electromagnetic mode and the liquid under test while maintaining resonant conditions within a relatively narrow frequency band. To demonstrate the capabilities of the proposed method, the UHF RFID band was considered, and temperature dependence of the distilled water permittivity was retrieved. Interfacing standalone low-cost electromagnetic sensors with widely available consumer-level wireless devices offers promising opportunities that contribute to the paradigm shift toward IoT. [ABSTRACT FROM AUTHOR]

This article reviews recent developments in designing and testing new types of materials which can be: (i) placed around the body for in vivo imaging, (ii) be integrated into a conventional RF coil, or (iii) form the resonator itself. These materials can improve the quality of MRI scans for both in vivo and magnetic resonance microscopy applications. The methodological section covers the basic operation and design of two different types of materials, namely high permittivity materials constructed from ceramics and artificial dielectrics/metasurfaces formed by coupled conductive subunits, either in air or surrounded by dielectric material. Applications of high permittivity materials and metasurfaces placed next to the body to neuroimaging and extremity imaging at 7 T, body and neuroimaging at 3 T, and extremity imaging at 1.5 T are shown. Results using ceramic resonators for both high field in vivo imaging and magnetic resonance microscopy are also shown. The development of new materials to improve MR image quality remains an active area of research, but has not yet found significant use in clinical applications. This is mainly due to practical issues such as specific absorption rate modelling, accurate and reproducible placement, and acceptable size/weight of such materials. The most successful area has been simple "dielectric pads" for neuroimaging at 7 T which were initially developed somewhat as a stop-gap while parallel transmit technology was being developed, but have continued to be used at many sites. Some of these issues can potentially be overcome using much lighter metasurfaces and artificial dielectrics, which are just beginning to be assessed. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a widely used wireless technology for contactless data exchange between a passive information carrier (tag) and an active interrogation device (reader). Being sensitive to a surrounding environment, RFID tags are usually designed per application. Here, we demonstrate an RFID tag with three essential functions available simultaneously, namely, small footprint, long reading range, and capability of on-metal labeling. Our design is based on a compact high-index ceramic resonator and an inductively coupled small metal ring functionalized with an RFID chip. The tag operates at magnetic dipolar resonance, which interacts with the metal object subject to labeling. Specifically, a 16.5 mm $\times16.5$ mm $\times12$ mm footprint device, placed on a 40 cm $\times40$ cm metal sheet, was successfully interrogated from 22 m with no violation of international effective isotropic radiated power (EIRP) standards. Currently, it is the smallest on-metal RFID tag with a reading range of over 20 m. Multifunctional miniature long-range ceramic tags are attractive for use in numerous practical applications, including the Internet of Small Things (IoST) and many others. [ABSTRACT FROM AUTHOR]

Topological photonics provides exceptional opportunities to control electromagnetic waves with a great potential for applications. Most of the proposed photonic systems support topological edge states with fixed parameters, thus hindering their practical applications. The study of nonlinear and tunable effects in topological systems enlarges applications of topological phenomena. Here, we propose an approach for the manipulation of photonic topological edge states based on temperature tuning. We design and demonstrate experimentally topological zigzag arrays composed of high-index resonators. The resonators are fabricated from ferroelectrics that brings an opportunity to dynamically change their permittivity by heating. We study the emergence of topological edge states in zigzag arrays of ferroelectric particles supporting the Mie resonances and demonstrate the topological transition induced by heating individual resonators in the array. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a widely used approach for a short-range contactless data exchange, i.e., employed in billing systems. During the last years, unauthorized access has become an issue, as it has been proven on numerous unpleasant occasions. A typical theft scheme is based on approaching a victim with a card reader. However, a straightforward adaptation of the reader’s antenna elements allows performing the attack from a distance, opening a severe security loophole. Here, we propose and demonstrate hardware-based protection capable of preventing a far-field attack of this kind. Our solution is based on an RFID chip shielding with an opaque metal. The Faraday type of the enclosure has a small aperture, which suppresses electromagnetic field leakage from the device. This property affects both up and down interrogation links, virtually making the far-field attack impossible. Activation of the card is done by holding it in hand–this way, it is made accessible to an authorized readout, which still remains wireless. The physical principle of the operation is placing a high-index dielectric structure next to a subwavelength aperture, making it electromagnetically larger and, as a result, supporting the field leakage. Our experimental prototype, validated by several different users, shows the capability to diminish far-field attacks on ultrahigh frequency (UHF) RFID tags. This hardware security solution can find usage in numerous applications, such as biometric passports, credit cards, and many others, where unauthorized access to sensitive data is highly undesirable. [ABSTRACT FROM AUTHOR]

Wireless sensors find use in many practical applications, where wired connections possess a limitation. New realms of global connectivity and data exchange among various devices suggest putting a sensor on a consumable level, where electronic circuits are not affordable from an economic standpoint. Chipless approaches, aiming to address the later issue, typically come with a penalty of performance degradation and, in many cases, is seen as a compromise solution. Here, we demonstrate a concept of the extremely sensitive temperature sensor based on the bound states in the continuum (BIC) approach. A ceramic half-cylinder above a ground plane is designed to support high quality factor supercavity modes with a strong resonant dependence on an ambient temperate. The operation of the sensor is experimentally demonstrated in a broad range of temperatures, spanning from 25 to 105 °C with an average sensitivity of 4 MHz/°C. The key element, leading to this performance, is high-quality ceramics, which allows supporting confined modes with moderately low Ohmic losses and extremely high-quality factors above 1000. High-performance chipless devices, which are capable to accommodate several functions with a single platform, open a venue to a new generation of wireless distributed sensors, where the main technological and outlay efforts are placed on an interrogation side. [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]

Dielectric resonators made of high permittivity materials with low losses have been extensively studied for application in magnetic resonance imaging (MRI) and magnetic resonance spectroscopy. They can focus, redistribute, and enhance the radio frequency magnetic field in a controlled way. In this Letter, we investigate coupled very-high permittivity dielectric resonators for clinical bilateral breast MRI. The resonators are tuned to support a TE mode within the frequency of 3 T MRI and implemented as a pair of coaxial hollow cylinders consisting of ceramic rings with extremely high permittivity (ε ∼ 870) and low loss. We study the electromagnetic coupling between two resonators placed in the near field and analyze the impact of symmetric and antisymmetric mode excitation on the sensitivity of the MRI machine. We experimentally verify that the coupling of the mode with symmetric field distribution to the radio frequency body birdcage coil allows us to enhance the receive sensitivity substantially and to decrease the excitation power needed to provide the optimal transmit efficiency, thus making the MRI procedure safer. Our work offers a practical method to realize a simple yet very effective system based on dielectric resonators for bilateral breast imaging. [ABSTRACT FROM AUTHOR]

The metasurfaces concept allows developing and advancing the methods to control the near electromagnetic field pattern in almost arbitrary ways. This property, among other things, is making them an essential platform for useful applications, for example, to improve magnetic resonance imaging (MRI) characteristics through local enhancement of the transmit efficiency as well as the increase in the sensitivity of the radio frequency coils. In this letter, we investigate a compact metasurface-based resonator formed as an array of parallel copper wires with capacitive loads printed on the low-loss dielectric substrate. We demonstrate how to tailor the spectral characteristics of the metasurface eigenmode as well as to control precisely the homogeneity of the near-field pattern by changing the effective capacitance of the structure. We experimentally verify that by tuning the metasurface characteristics, it is possible to decrease the excitation power needed to provide the optimal transmit efficiency of the body coil, thus making the MRI procedure safer. Our approach offers a practical method to control the electromagnetic near-field pattern and has potential in various applications, such as MRI and wireless power transfer. [ABSTRACT FROM AUTHOR]

A new class of phenomena stemming from topological states of quantum matter has recently found a variety of analogies in classical systems. Spin-locking and one-way propagation have been shown to drastically alter scattering of electromagnetic waves, thus offering an unprecedented robustness to defects and disorder. Despite these successes, bringing these new ideas to practical grounds meets a number of serious limitations. In photonics, when it is crucial to implement topological photonic devices on a chip, two major challenges are associated with electromagnetic dissipation into heat and out-of-plane radiation into free space. Both these mechanisms may destroy the topological state and seriously affect the device performance. Here, we demonstrate experimentally that the topological order for light can be implemented in all-dielectric on-chip prototype metasurfaces, which mitigate the effect of Ohmic losses by using exclusively structured dielectric materials, and we reveal that coupling of the system to the radiative continuum does not affect topological properties. We demonstrate the spin-Hall effect of light for spin-polarized topological edge states through near-field spectroscopy measurements. [ABSTRACT FROM AUTHOR]

Metasurfaces is a rapidly developing area with quite many prospective applications in light manipulation, aberration-free optical imaging, and security. One potential area where metasurface approaches may provide a valuable contribution is medical imaging. In this paper, a novel subwavelength metasurface-inspired resonator design is presented, which is employed to enhance the sensitivity of magnetic resonance imaging (MRI). To this end, the resonator is formed by an array of capacitively loaded telescopic wires is placed inside the scanner in a close proximity of the studied object. The telescopic design of the structure permits to mechanically adjust its eigenmode resonance frequency to the operational frequency of a 1.5T MRI machine, thus making it possible to enhance and redistribute the radiofrequency magnetic field of an available radiofrequency coil in the region of interest and therefore significantly increase the sensitivity of the receiver. [ABSTRACT FROM AUTHOR]

The sensitivity of magnetic resonance imaging (MRI) is dictated by the signal-to-noise ratio. It was recently noted that the signal-to-noise ratio could be substantially increased via excitation of certain metasurface eigenmodes. Here, we provide a detailed discussion of the wire metasurface eigenmode impact on the sensitivity of MRI. We experimentally show that due to the spatial redistribution of the electromagnetic near field, mediated by the metasurface eigenmode, the received signal from the studied object becomes essentially dependent on its position on the metasurface. Moreover, we analyzed how the metasurface performance significantly depends on the dimensions of an examined object. Our work provides metasurface design guidelines for substantial enhancement of MRI sensitivity. [ABSTRACT FROM AUTHOR]

In this paper, we have studied a practical design of a broadband linear-to-circular polarizer based on a self-complementary metasurface composed of zigzag-shaped metal strips printed on a dielectric substrate. The term self-complementary indicates that the structure is identical to its complement, except for some translation smaller than the periodicity. This property together with the nonresonant response of the unit cells ensures broadband conversion from linear polarization to circular polarization. Although we have experimentally achieved a relative 3-dB-axial-ratio (AR) bandwidth (BW) of 53%, in principle, it could reach up to 70.5%. Moreover, the studied metasurface has a very small periodicity, which avoids any higher order grating lobes and provides angular stability of the phenomenon. In fact, the relative 3-dB-AR BW obtained in experiments stays always above 40% for incidence angles within ±30°. An excellent agreement was achieved among theory, simulations, and experiments. [ABSTRACT FROM PUBLISHER]

The discovery of two-dimensional topological photonic systems has transformed our views on the propagation and scattering of electromagnetic waves, and the quest for similar states in three dimensions is open. Here, we theoretically demonstrate that it is possible to design symmetry-protected three-dimensional topological states in an all-dielectric platform, with the electromagnetic duality between electric and magnetic fields being ensured by the structure design. Magneto-electrical coupling plays the role of a synthetic gauge field that determines a topological transition to an 'insulating' regime with a complete three-dimensional photonic bandgap. We reveal the emergence of surface states with conical Dirac dispersion and spin-locking, and we numerically confirm robust propagation of the surface states along two-dimensional domain walls with first-principles studies. The proposed system represents a table-top platform capable of emulating the relativistic dynamics of massive Dirac fermions and the surface states can be interpreted as Jackiw-Rebbi states bound to the interface separating domains with particles of opposite masses. [ABSTRACT FROM AUTHOR]

Employing nonlocal homogenization approach, we investigate the properties of a metamaterial consisting of parallel metallic wires with dielectric coating. We demonstrate that manipulation of dielectric contrast between wire dielectric shell and host material at fixed frequency results in dynamic switching of metamaterial dispersion regime from elliptic to the hyperbolic one, i.e. the topological transition takes place. It is proved that such transition can be induced by the variation of the metamaterial temperature. Our findings thus pave a way to the implementation of a tunable 'elliptic-hyperbolic' metamaterial. [ABSTRACT FROM AUTHOR]

Photonic structures offer unique opportunities for controlling light-matter interaction, including the photonic spin Hall effect associated with the transverse spin-dependent displacement of a light beam that propagates in specially designed optical media. However, due to small spin-orbit coupling, the photonic spin Hall effect is usually weak at the nanoscale. Here we suggest theoretically and demonstrate experimentally, in both optics and microwave experiments, the photonic spin Hall effect enhanced by topologically protected edge states in subwavelength arrays of resonant dielectric particles. Based on direct near-field measurements, we observe the selective excitation of the topological edge states controlled by the handedness of the incident light. Additionally, we reveal the main requirements to the symmetry of photonic structures to achieve the topology-enhanced spin Hall effect, and also analyse the robustness of the photonic edge states against the long-range coupling. [ABSTRACT FROM AUTHOR]

The radiation dynamics of optical emitters can be manipulated by properly designed material structures modifying local density of photonic states, a phenomenon often referred to as the Purcell effect. Plasmonic nanorod metamaterials with hyperbolic dispersion of electromagnetic modes are believed to deliver a significant Purcell enhancement with both broadband and nonresonant nature. Here, we have investigated finite-size resonators formed by nanorod metamaterials and shown that the main mechanism of the Purcell effect in such resonators originates from the supported hyperbolic modes, which stem from the interacting cylindrical surface plasmon modes of the finite number of nanorods forming the resonator. The Purcell factors delivered by these resonator modes reach several hundreds, which is up to 5 times larger than those in the ε-near-zero regime. It is shown that while the Purcell factor delivered by the Fabry-Pérot modes depends on the resonator size, the decay rate in the ε-near-zero regime is almost insensitive to geometry. The presented analysis shows a possibility to engineer emission properties in structured metamaterials, taking into account their internal composition. [ABSTRACT FROM AUTHOR]

We suggest a novel type of photonic topological edge states in zigzag arrays of dielectric nanoparticles based on optically induced magnetic Mie resonances. We verify our general concept by the proof-ofprinciple microwave experiments with dielectric spherical particles, and demonstrate, experimentally, the ability to control the subwavelength topologically protected electromagnetic edge modes by changing the polarization of the incident wave. [ABSTRACT FROM AUTHOR]

We study waveguiding of the electromagnetic energy below the diffraction limit with arrays of dielectric nanoparticles through the excitation of both electric and magnetic Mie resonances. We analyze the dispersion characteristics of such coupled-resonator optical waveguides by means of the coupled-dipole approximation and then verify the validity of the coupled-dipole model by comparing the results with direct numerical simulations. We reveal that a chain of silicon nanoparticles with realistic material losses can guide light for the distances exceeding several tens of micrometers, which is significantly better than the guiding by any plasmonic waveguide with the propagation distances less than 1 μm. We verify the main concept and our theoretical findings experimentally at microwaves for an array of ceramic particles. [ABSTRACT FROM AUTHOR]

We demonstrate experimentally Fano resonances in all-dielectric oligomers clusters of dielectric particles. We study two structures consisting of a ring of six ceramic spheres with and without a central particle and demonstrate that both structures exhibit resonant suppression of the forward scattering associated with the Fano resonance originated from the excitation of magnetic dipole modes. By employing the near-field measurement techniques, we establish the relation between near- and far-field properties of the Fano resonances and identify directly their origin. We support our findings by an analytical approach based on the discrete-dipole approximation and find an excellent agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A theoretically revealed effect [Belov et al., Opt. Lett. 34, 527 (2009)] of the significant enhancement of evanescent harmonics inside a wire medium slab is experimentally verified in the microwave frequency range. The phenomenon originates from resonant pumping of standing waves into which evanescent waves are converted inside the slab. We find a good agreement between experimental data, numerical simulations and theory. [ABSTRACT FROM AUTHOR]

We demonstrate how to realize an indefinite media with hyperbolic isofrequency surfaces in wavevector space by employing two-dimensional metamaterial transmission lines. We classify different types of such media, and visualize the peculiar character of wave propagation by study of the cross-like emission pattern of a current source placed in the lattice center. Our results are supported by a solution of the Kirchhoff equations, an analytical theory, and experimental data. [ABSTRACT FROM AUTHOR]

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

The Purcell effect is defined as a modification of the spontaneous emission rate of a quantum emitter at the presence of a resonant cavity. However, a change of the emission rate of an emitter caused by an environment has a classical counterpart. Any small antenna tuned to a resonance can be described as an oscillator with radiative losses, and the effect of the environment on its radiation can be modeled and measured in terms of the antenna radiation resistance, similar to a quantum emitter. We exploit this analogue behavior to develop a general approach for calculating the Purcell factors of different systems and various frequency ranges including both electric and magnetic Purcell factors. Our approach is illustrated by a general equivalent scheme, and it allows resenting the Purcell factor through the continuous radiation of a small antenna at the presence of an electromagnetic environment. [ABSTRACT FROM AUTHOR]

Natural diamagnetism, while being a common phenomenon, is limited to permeability values close to unity. Artificial diamagnetics, to the contrary, can be engineered to provide much lower values and may even possess an effective permeability close to zero. In this letter, we provide an experimental confirmation of the possibility to obtain extremely low permeability values by manufacturing an isotropic metamaterial composed of conducting cubes. We show that the practical assembly is quite sensitive to fabrication tolerances and demonstrate that permeability of about μ=0.15 is realisable. [ABSTRACT FROM AUTHOR]

Being motivated by the recent theoretical proposal of nanoantennas based on high-permittivity dielectric spheres [A. E. Krasnok et al., JETP Lett. 94, 22113 (2011)], we suggest and verify experimentally the concept of all-dielectric antennas in the microwave frequency range. In addition to the electric resonance, each sphere exhibits a very strong magnetic resonance, resulting in a narrow radiation pattern and overall high directivity of such antennas. We find an excellent agreement between the experimental data and numerical results and verify directly high-performance characteristics of such all-dielectric antennas potentially scalable to the nanoscale and operation at the optical frequency range. [ABSTRACT FROM AUTHOR]

The article cites a research study that describes a new class of photonic systems result in bandgap opening at one of the spin-valley photonics, whereas the other valley exhibits Dirac-like conical dispersion. It shows a robust pseudospin- and valley-polarized one-way Klein tunneling, exhibiting marked implications on photon transport.