Dielectric Metamaterials Research Articles

Design of annulus-based dielectric metamaterial cloak with properties of illusion optics

We propose a feasible design for an annulus-based dielectric metamaterial cloak to not only reduce Ohmic losses from metallic metamaterials but also avoid manual misalignment when utilizing discrete dielectric metamaterials. The designed cloak is authenticated by the finite-integration method, and the corresponding field distributions without and with hidden objects are found to reveal the invisibility of the cloak. In addition, illusion optics are comprehended by comparing the field distributions of the dielectric-metamaterial-cloak-based illusion-device and an illusion object. With the abovementioned characteristics of the proposed cloak using an annulus-based dielectric metamaterial, in simulation, we successfully approach the features of the reciprocal cloak, which conceals multiple objects with vision and movement.

Substrate‐Modulated Electromagnetic Resonances in Colloidal Cu2O Nanospheres

AbstractDielectric nanoparticles are expected to complement or even replace plasmonic nanoparticles in many optical and optoelectronic applications, because they exhibit small absorption losses and support strong electric and magnetic resonances simultaneously. Dielectric nanoparticles need to be deposited on various substrates in many applications. Understanding the substrate effect on the electromagnetic resonances of dielectric nanoparticles is of great importance for engineering their resonance properties and designing optical devices. In this study, moderate‐refractive‐index cuprous oxide nanospheres with uniform sizes and shapes are synthesized. The scattering spectra and images of the nanospheres deposited on three types of substrates are analyzed experimentally and theoretically. When supported on indium tin oxide–coated glass slides and Si wafers, the color of the nanospheres varies from blue, cyan, green, yellow, orange and red, covering almost the entire visible region. When deposited on gold films, the electromagnetic resonances of the nanospheres redshift intensively and a new effective magnetic resonance mode appears. The enhanced Raman scattering reveals that large electromagnetic field enhancements are produced in the gap region between the nanosphere and the substrate. The results shed light on the manipulation of the electromagnetic responses of dielectric nanoparticles and the design of dielectric metamaterials in the presence of various substrates.

Tunable dielectric metamaterial based on strontium titanate artificial atoms

Metamaterials are designed and manufactured artificially to manifest intriguing physical concepts and achieve unusual potential applications. However, the exotic properties of metamaterials normally originate from the resonance mechanism of artificial atoms, thus inevitably limited in narrow band and hindering their practical applications. Here, we numerically design and experimentally verify a novel tunable dielectric metamaterial based on strontium titanate artificial atoms to alleviate the bandwidth restriction of resonance metamaterial. By control of the magnetic resonance with the electric resonance, the tunable dielectric metamaterial can broaden the practical applications of metamtaterials and play an important role in all-optical communication devices.

Infrared dielectric metamaterials from high refractive index chalcogenides

High-index dielectric materials are in great demand for nanophotonic devices and applications, from ultrathin optical elements to metal-free sub-diffraction light confinement and waveguiding. Here we show that chalcogenide topological insulators are particularly apt candidates for dielectric nanophotonics architectures in the infrared spectral range, by reporting metamaterial resonances in chalcogenide crystals sustained well inside the mid-infrared, choosing Bi2Te3 as case study within this family of materials. Strong resonant modulation of the incident electromagnetic field is achieved thanks to the exceptionally high refractive index ranging between 7 and 8 throughout the 2–10 μm region. Analysis of the complex mode structure in the metamaterial allude to the excitation of circular surface currents which could open pathways for enhanced light-matter interaction and low-loss plasmonic configurations by coupling to the spin-polarized topological surface carriers, thereby providing new opportunities to combine dielectric, plasmonic and magnetic metamaterials in a single platform.

Effects of deterministic disorder at deeply subwavelength scales in multilayered dielectric metamaterials.

It is common understanding that multilayered dielectric metamaterials, in the regime of deeply subwavelength layers, are accurately described by simple effective-medium models based on mixing formulas that do not depend on the spatial arrangement. In the wake of recent studies that have shown counterintuitive examples of periodic and aperiodic (orderly or random) scenarios in which this premise breaks down, we study here the effects of deterministic disorder. With specific reference to a model based on Golay-Rudin-Shapiro sequences, we illustrate certain peculiar boundary effects that can occur in finite-size dielectric multilayers, leading to anomalous light-transport properties that are in stark contrast with the predictions from conventional effective-medium theory. Via parametric and comparative studies, we elucidate the underlying physical mechanisms, also highlighting similarities and differences with respect to previously studied geometries. Our outcomes may inspire potential applications to optical sensing, switching and lasing.

Coupling effects in dielectric metamaterials

Dielectric metamaterials have been proved to have broad applications in the microwave and optical frequency bands. However, as the components of the communication system shrink, the coupling effects caused by tight arrangements between the dielectric structures have not been carefully studied enough yet. In this paper, the deep coupling effects in limited space between the adjacent dielectric metamaterials cubes are investigated. According to the correlation between the coupling effect and the incident wave, the influence of coupling effect on the scattering characteristics of the structure is studied from three aspects: coupling effect parallel to the wave vector/electric field/magnetic field, respectively. Field distributions and constitutive parameters are also demonstrated to illustrate the relationship between the coupling effects and scattering coefficients.

Dielectric metamaterials with hexagonal lattice

We consider all-dielectric photonic structures with electric response consist of dielectric rods arranged in a hexagonal lattice. We construct gap map as a function of rod permittivity for a constant filling factor by analyzing photonic band diagrams. A near-boundary phase with a strong spatial dispersion is found, whereas in the case of a square lattice this phase does not exist. We observe ε-near zero modes in a metamaterial phase, which do not depend on a lattice orientation and a structure boundary.

Applications of dielectric pads, novel materials and resonators in 1.5T and 3T MRI

In order to boost the performance of magnetic resonance imaging without increasing the static magnetic field, it is necessary to increase its intrinsic sensitivity. This allows a reduction in the scanning time, increased spatial resolution, and can enable low-field strength systems (which are much cheaper and can be used to scan patients with metallic implants) to have a higher signal-to-noise ratio (SNR) so that they are comparable to more expensive higher field strength systems. In this contribution, we demonstrate radiofrequency field enhancing and shaping devices based on novel materials, such as high permittivity dielectric structures and metamaterials. These materials can substantially enhance SNR, thus potentially increasing image resolution or allowing faster examinations.

Ultra-narrowband dielectric metamaterial absorber with ultra-sparse nanowire grids for sensing applications

Due to their low losses, dielectric metamaterials provide an ideal resolution to construct ultra-narrowband absorbers. To improve the sensing performance, we present numerically a near-infrared ultra-narrowband absorber by putting ultra-sparse dielectric nanowire grids on metal substrate in this paper. The simulation results show that the absorber has an absorption rate larger than 0.99 with full width at half-maximum (FWHM) of 0.38 nm. The simulation field distribution also indicates that the ultra-narrowband absorption is originated from the low loss in the guided-mode resonance. Thanks to the ultra-narrow absorption bandwidths and the electric field mainly distributed out of the ultra-sparse dielectric nanowire grids, our absorber has a high sensitivity S of 1052 nm/RIU and a large figure of merit (FOM) of 2768 which mean that this ultra-narrowband absorber can be applied as a high-performance refractive index sensor.

Disordered Elastic Metasurfaces

The discovery of the disorder effect in traditional metamaterials has opened the possibilities in the search for the disordered metasurfaces. Photonic, dielectric and elastic metamaterials exhibiting the added value of the disorder effect on wave propagation physics, have been reported. Despite this extensive attention and progress in disordered metamaterials, the elastic metasurfaces however, involving disorder have not yet been reported. Here, we introduce the concept of disordered elastic metasurface composed of identical pillared resonators with a random arrangement in the subwavelength range. Based on theoretical formalism and direct acoustic measurement, we observe anomalous deflection and focusing effects of flexural waves in a plate, and elucidate in details the related physics. This research extends the disorder effect to metasurfaces and may lead to innovative acoustoelastic devices.

A Water-Based Huygens Dielectric Resonator Antenna

With its high-permittivity in the microwave frequency range, water has the potential as an alternative, inexpensive, bio-friendly and abundant material for many microwave applications such as dielectric resonator antennas and tunable metamaterials. Huygens antennas, composed of single-element structures supporting a special combination of electric and magnetic modes, provide an alternative route for compact and directive antennas. In this work, we investigate a subwavelength water-based Huygens dielectric resonator antenna with strongly excited electric and magnetic dipoles at around 350 MHz. Our antenna leads to the directivity of 6 and a radiation front-to-back ratio of 40.3 dB. Additionally, good matching to the feed-line and the surrounding free space were achieved with a reflection coefficient of −38.3 dB and a total efficiency of 57.8 %. The antenna was fabricated and characterized with excellent agreement between the measurements and the numerical results. Furthermore, several means of tuning the antenna were tested numerically and experimentally. We believe that the proposed water-based Huygens dielectric resonator antenna may serve as an easy–to–fabricate and cheap alternative for the VHF and low end of the UHF bands.

Voltage-controlled quantum valley Hall effect in dielectric membrane-type acoustic metamaterials

The research interest on phononic crystals now takes a new turn towards the acoustic/elastic analogies of the quantum concepts, e.g., the quantum Hall, quantum spin Hall and quantum valley Hall effects. One hallmark of these fundamental physical phenomena is the existence of topological edge/interface modes that propagate through the system along a designed path, with high robustness against week disorders. However, the working frequency ranges of the proposed topological phononic systems are usually very narrow, which therefore pose a clear limitation in practical applications. Motivated by this difficulty, we design and study a membrane-type metamaterial with tunable topological properties. The plane wave expansion method is employed to analyze its dispersion relation. A theoretical method is further proposed to conveniently calculate the valley Chern number. The theoretical and numerical results show the existence of topologically protected interface mode in the system. Its frequency range can be changed over a wide range by applying an electrical voltage, while the localization behavior of the interface mode is independent of the controlling operation. Consequently, we have successfully shown that the working frequency range of the topological phononic systems so derived can be significantly `broadened' and hence the practical application may be dramatically widened.

Effect of nonlocal metal–dielectric environments on concentration quenching of HITC dye

Understanding and harnessing energy transfer in organic and inorganic systems is of high fundamental and practical importance. In this work, we have experimentally studied the effect of lamellar hyperbolic metamaterials and metal/dielectric interfaces on the concentration-dependent luminescence quenching in thin polymeric poly (methyl methacrylate) films doped with 2-[7-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3,5-heptatrienyl]-1,3,3-trimethyl-3H-indoliumiodide dye molecules. The rate of the concentration quenching (energy transfer to quenching centers) was found to be approximately proportional to the square of the dye concentration. The concentration quenching was strongly inhibited in the vicinity of metallic films and lamellar metal–dielectric metamaterials with hyperbolic dispersion. The characteristic length-scale of the inhibition (the distance between the dye molecules and the metallic surface, at which the inhibition becomes significant) was found to be $\sim{47}\,\,{\rm nm}$∼47nm. It was much longer than the Forster radius (the characteristic distance of the donor–acceptor energy transfer, 5 nm to 7 nm), and smaller than the penetration of the surface plasmon polariton field to the dielectric ($ \ge {250}\,\,{\rm nm}$≥250nm). The explanation of the observed phenomenon is likely to be sought in terms of a model taking into account spectral overlap of the emission of donors and absorption of acceptors and/or collective behavior of emitters coupled with surface plasmons.

Dielectric metamaterials with quasicrystal structure

Three types of quasicrystal lattices based on the Penrose tiling are considered. We analyze the maximum filling fraction of these structures and find a design with the filling fraction corresponding to the case of periodic lattices. By using simulations of a Gaussian beam propagation through the quasicrystal structure we obtain a homogeneous field distribution that is a hallmark of near-zero regimes in metamaterials.

Simulation of Multilayer Graphene–Dielectric Metamaterial by Implementing SBC Model of Graphene in the HIE-FDTD Method

An improved FDTD method is introduced to propose a new numerical simulation approach for a multilayer graphene–dielectric metamaterial (MGDM) structure, which is a promising effective medium with tunable constitutive parameters in terahertz photonic devices. We applied the hybrid implicit–explicit FDTD (HIE-FDTD) method, which is a popular method for analyzing dimensionally non-uniform structures with fine features in one or two directions to model the MGDM structure. Considering the ignorable atomic thickness of graphene layers in the structure, we increased the fine dimension of the mesh to the scale of the dielectric layer using the surface boundary condition (SBC) method for modeling the graphene sheets; this means that we integrated the SBC model of graphene in the HIE-FDTD method. Therefore, the thickness limitations of both graphene and dielectric layers can be eliminated in the computational resources. Accordingly, we implemented the introduced method in a proposed tunable graded index (GRIN) lens structure based on the MGDM and achieved valid results.

Ultra-narrowband mid-infrared absorber based on Mie resonance in dielectric metamaterials

Ultra-narrowband absorbers can be applied in many applications. We propose a mid-infrared ultra-narrowband absorber with TM polarization (magnetic field is parallel to grating grooves) based on dielectric metamaterials in this paper. The simulation results show that the absorption rate larger than 0.99 can be achieved at the resonance wavelength, and the absorption bandwidth is less than 10 nm. The simulated field distribution shows that the ultra-narrowband absorption in this absorber originates from Mie resonance. In addition, the absorber preserves high absorption rates up to 4° which means that our absorber has high directivity. Our results show that the ultra-narrowband absorbers can be applied as a thermal emitter.

Silicon-based light absorbers with unique polarization-adjusting effects

We propose and demonstrate a silicon-based absorber platform, which can show three different kinds of polarization-adjusting behaviors under certain structural features. First, perfectly polarization-dependant absorption is observed when the rings are packed with a relatively large gap distance. The classical Malus law is reproduced by the absorption spectra via this asymmetrical system. Then, the polarization-adjusting response can be strongly weakened when the dimer rings are physically contacted with each other, suggesting a polarization-independent absorption. Third, partially matched polarization-manipulation absorption can be further achieved when the absorber is formed by closely packed rings dimer. These findings show remarkable different behaviors to that of the conventional metallic plasmons, introducing impressive insight on the polarization manipulation behaviors of the high-index dielectric resonators, metamaterials and metasurface.

Study of the opto – electronic coupling in some complementary metallic – dielectric metamaterials used as biosensors

Using of the metamaterials improves the sensitivity and resolution of sensor devices, having multiple applications in biomedicine (imaging, biomarkers, telemedicine, etc.). We have studied the effect of different types of ordering in the lattices of nanostructures inside the metamaterial samples. Structures consisting of metallic atoms (tens of nanometers diameter) arranged relative periodically in a dense dielectric matrix have been analyzed by simulation methods. We have focused on the opto-electronic coupling phenomena and the interactions between plasmons and the applied field. A study of the electron scattering processes was performed, the simulational data being used to calculate the reflectance and permittivity in function of the wavelength, in the range of 500…2300 nm. The electromagnetic properties of the metamaterial samples depending on particles shape, dimensions and on the reports between metallic inclusions dimensions and the dimensions of the dielectric matrix where are included have been studied and new configurations were proposed in order to improve the metamaterial sensors performance. We expect an increment in the response to the exciting field of about 7%, in a more dense state of spins characterising the new material samples.

Tunable superconducting Josephson dielectric metamaterial

We demonstrate a low-dissipation dielectric metamaterial with tunable properties based on the Josephson effect. Superconducting wires loaded with regularly spaced Josephson junctions (critical current Ic ≈ 0.25 μA) spanning a K-band waveguide and aligned with the microwave electric fields create a superconducting dielectric metamaterial. Applied dc current tunes the cutoff frequency and effective permittivity of this unique electric metamaterial. The results are in agreement with an analytical model for microwave transmission through the artificial dielectric medium.

Phase-Modulated Scattering Manipulation for Exterior Cloaking in Metal-Dielectric Hybrid Metamaterials.

Artificially structured metamaterials with metallic or dielectric inclusions are extensively studied for exotic light manipulations via controlling the local-resonant modes in the microstructures. The coupling between these resonant modes has drawn growing interest in recent years due to the advanced functional metamaterial making the microstructures more and more complex. Here, the suppression of magnetic resonance of a dielectric cuboid, an analogue to the scattering cancellation effect or radiation control system, realized with an exterior cloaking in a hybrid metamaterial system, is demonstrated. Furthermore, the significant modulation of the absorption of the dielectric resonator in the hybrid metamaterial is also demonstrated. The physical insight of the experimental results is well illuminated with a classical double-harmonic-oscillator model, from which it is revealed that the complex coupling, i.e., the phase of coupling coefficient, plays a crucial role in the overall response of the metal-dielectric hybrid system. The proposed design strategy is anticipated to form a more straightforward and efficient paradigm for practical applications based on radiation control via versatile mode couplings.