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 $\mu \mathrm{W}/{\mathrm{cm}}^2$. 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.

Electromagnetic scattering on subwavelength structures is attracting much attention owing to the broad range of possible applications where this phenomenon can be used. Fundamental limits of the scattering cross section, which are 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 scattering potentials. We demonstrate pathways to spectrally overlap several eigenmodes of a resonator in a way such that they interfere constructively and increase the scattering cross section. As a particular example, we demonstrate spectral overlapping of several electric and magnetic modes in a subwavelength ceramic resonator. The optimized structures have a dipolar scattering cross-section limit exceeding that for a sphere by up to a factor of 4. The revealed rules, which link symmetry groups with fundamental scattering limits, allow assessment of the designs and performance of subwavelength superscatterers, which can be used in label-free imaging, compact antennas, long-range radio-frequency identification, and many other fields.

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 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 several different physical principles. Instead of using conduction currents in metallic wires to drive electronic chips and provide electromagnetic radiation, high-permittivity components rely on excitation of displacement currents. Those are efficiently converted to actual electric current with 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, and they could 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.

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.

Resonant states underpin a variety of metastructures that exhibit remarkable capabilities for the effective control of acoustic waves at subwavelength scales. The development of metamaterials relies on rigorous mode engineering, providing the implementation of the desired properties. At the same time, the application of metamaterials is still limited, as their building blocks are frequently characterized by complicated geometry and cannot be tuned easily. In this work, we consider a simple system of coupled Helmholtz resonators and study their properties associated with the tuning of coupling strength and symmetry breaking. We numerically and experimentally demonstrate the excitation of the quasibound state in the continuum in the resonators placed in free space and in a rectangular cavity. It is also shown that tuning the intrinsic losses via introducing porous inserts can lead to spectral splitting or merging of quasibound states in the continuum and the occurrence of exceptional points. The obtained results open opportunities for the development of simple and easily tunable metastructures based on Helmholtz resonances.

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.