Metamaterial Slab Research Articles

Nanoscale Tunable Optical Binding Mediated by Hyperbolic Metamaterials

Carefully designed nanostructures can inspire a new type of optomechanical interactions and allow surpassing limitations set by classical diffractive optical elements. Apart from strong near-field localization, a nanostructured environment allows controlling scattering channels and might tailor many-body interactions. Here we investigate an effect of optical binding, where several particles demonstrate a collective mechanical behavior of bunching together in a light field. In contrast to classical binding, where separation distances between particles are diffraction limited, an auxiliary hyperbolic metasurface is shown here to break this barrier by introducing several controllable near-field interaction channels. Strong material dispersion of the hyperbolic metamaterial along with high spatial confinement of optical modes, which it supports, allows achieving superior tuning capabilities and efficient control over binding distances on the nanoscale. In addition, a careful choice of the metamaterial slab’s thickness enables decreasing optical binding distances by orders of magnitude compared to free space scenarios due to the multiple reflections of volumetric modes from the substrate. Auxiliary tunable metamaterials, which allow controlling collective optomechanical interactions on the nanoscale, open a venue for new investigations including collective nanofluidic interactions, triggered biochemical reactions, and many others.

Comb-Like Modal Dispersion Diagram in a Double-Wire Medium Slab

We investigate the guided modes supported by a wire metamaterial slab formed by two mutually orthogonal and nonconnected sets of parallel metallic wires. It is demonstrated that the wire medium slab has a peculiar comb-like dispersion diagram. In the continuum approximation, the metamaterial supports a diverging number of guided mode branches that accumulate near the light line due to a strong hyperbolic response in the static limit. In a realistic system, the number of guided mode branches is finite and is determined by the density of wires. Remarkably, the guided modes may be characterized by a fast field variation along the transverse direction, which can be exploited to detect subwavelength particles or defects.

A Thin Double-Mesh Metamaterial Radome for Wide-Angle and Broadband Applications at Millimeter-Wave Frequencies

Antireflection has been a critical part in the design of optical and opto-electronic instruments. In the emerging millimeter (mm)-wave technology for the next-generation communication and autonomous driving, antireflection treatment is increasingly important due to the quasi-optical nature of electromagnetic waves at high frequencies. Enclosures that protect radar or communication phased arrays will introduce reflections if they are not designed properly. In this article, a novel metamaterial radome (meta-radome) is developed based on closely spaced metallic square meshes patterned on a thin dielectric substrate. We show that by deliberately employing the coupling between the meshes, the entire structure can be treated as a homogenized metamaterial slab with its wave impedance matched to that of free space. The resulting meta-radome can be optimized to have good transmission (> 90%) over an extremely wide range of angles of incidence (0° – 80°) for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. Since the meta-radome is not resonant, it has a very small Ohmic loss and broad bandwidth. In addition, the proposed meta-radome is very easy to fabricate with standard fabrication techniques. Thus, it can be very attractive for many practical microwave and mm-wave applications.

Investigation of Negative and Near-Zero Permeability Metamaterials for Increased Efficiency and Reduced Electromagnetic Field Leakage in a Wireless Power Transfer System

In order to meet both safety and efficiency requirements of wireless power transfer (WPT) systems, reducing electromagnetic field (EMF) leakage and improving efficiency are critical factors in the implementation of systems. Recently, metamaterials have exhibited the ability to control the electromagnetic wave propagation. In this paper, the WPT system integrating with near-field mu-near-zero (NF-MNZ) and mu-negative permeability (MNG) metamaterials is proposed to control EMF leakage below a certain level and improve transfer efficiency. The NF-MNZ and the MNG metamaterials are placed on both sides and in the middle of the WPT system, respectively. In addition, the property of the NF-MNZ metamaterial slab and its working principle on the WPT system are analyzed. The shielding performance of the NF-MNZ metamaterial are evaluated via numerical simulation and experimental investigation. Finally, the efficiency and the magnetic field strength of the WPT system with two different types of metamaterials have been investigated by the experimental measurements. At the transfer distance of 40 cm, the experimental results show that the efficiency of the WPT system is increased by 12.06% and the magnetic field strength is reduced by 62.09%.

Square‐ring metamaterial for radiation characteristics enhancement of an SIW cavity‐backed slot antenna

Design and analysis of a low-impedance metamaterial (MTM) along with its application to antenna design are presented in this manuscript. This low-impedance MTM is a square-ring (SR) resonator, which exhibits low-impedance property irrespective of the polarization and incident angle of the imposed EM wave. This SR MTM slab is placed directly atop an SIW cavity-backed slot antenna for gain enhancement, eliminating the air gap between them. The peak realized gain improvement in the broadside direction is 8.3 dB, whereas the overall thickness of the antenna is 0.103 λ0 at the operating frequency of 9.78 GHz. Moreover, the front-to-back ratio is 26.5 dB and the cross-polarization is negligibly altered by this gain enhancement method. This concept is experimentally verified with fabrication and measurements.

Analysis of Near-Field Effects for Electromagnetic Properties of Pasteur Chiral Metamaterial Slabs

This letter proposes a correct and robust retrieval method for extraction of electromagnetic properties of Pasteur chiral metamaterial (MM) slabs having asymmetrical transmission properties when near-field effects are present. The ray-tracing method has been applied to derive underlying equations for semi-infinite reflection coefficients of these slabs. A U-shaped Pasteur chiral MM slab was considered as a test slab to examine the near field effects on extracted semi-infinite reflection coefficients. It is noted that near-field effects should be taken into account for correct electromagnetic properties of Pasteur chiral MMs especially around resonance regions.

High‐gain antipodal Vivaldi antenna with metamaterial covers

A metamaterial slab covered antipodal Vivaldi antenna (MSAVA) is proposed to improve the radiation properties of the antipodal Vivaldi antenna (AVA). The metamaterial covers (MCs) consist of two types of metal rectangular ring arrays that have a higher effective permittivity than the substrate. The MCs can achieve a guiding effect and direct electromagnetic waves radiated from the side of AVA to the end-fire direction. The original AVA and the proposed MSAVA are simulated, fabricated and measured. The results show that of the two antennas is less than −10 dB in the frequency band of 0.95–11 GHz. Due to the introduction of MCs, MSAVA obtains a much narrower H-plane's half-power beamwidth, and the E-plane's is narrowed as well. The radiation gain is also improved in the frequency band. Moreover, the maximum gain of the proposed MSAVA is 17.67 dBi. Compared with the original AVA, the maximum gain is enhanced by 6.86 dB for the proposed MSAVA. The presented MSAVA featuring broad bandwidth, high gain and narrow beam has a high potential in ground penetrating radar, microwave imaging application and other broadband wireless systems.

Wireless Power Transfer System Based on Magnetic Dipole Coupling With High Permittivity Metamaterials

In this letter, we present a new approach for the performance improvement of a wireless power transfer (WPT) system by utilizing the high permittivity property of metamaterials (MTMs). Here, fully planar structures are considered to design the transmitting (Tx) and receiving (Rx) sections of the WPT system. The performance of the proposed system is enhanced by placing the MTM slabs at both sides of the Tx and Rx elements. The high permittivity property of MTM generates a strong magnetic dipole behavior, which increases the magnetic coupling between the Tx and Rx sections. As a result, the efficiency of the proposed system is improved significantly along with the transmission distance. The lateral and angular misalignments are also studied for the presented system. Finally, the prototypes of the proposed configuration are fabricated, and measurements are performed. The measured result confirms that a considerable amount of efficiency improvement is obtained from the proposed WPT system by the virtue of MTM usage.

Extraction of metamaterial constitutive parameters based on data-driven discontinuity detection

This paper presents an efficient data-driven method to extract the effective metamaterial parameters unambiguously. This method is based on detecting the discontinuity points in the real part of the refractive index and discerning the correct branch values at these discontinuities. The proposed method is numerically simple and does not require an infinite frequency integration. The performance of the proposed method is demonstrated by investigating thin and thick homogenous and periodically structured metamaterial slabs. This method attains correct values of the branch index and, hence, correct values of the refractive index at the entire frequency range for thin and thick slabs independently from its imaginary part. It, notably, succeeds in overcoming the frequency and dimension limits and saturation observed in the Kramers–Kronig (K–K) method in thick homogeneous and multi-cell periodically structured slabs. The proposed method also gives accurate values for the metamaterial parameters at resonance and at the negative parameter region.

Directivity enhancement of wire monopole antenna using magnetic metamaterials

This article proposes the use of a magnetic metamaterial (MTM) slab over the ground plane of a wire monopole antenna to improve its directivity. In this regard, mu very large (MVL) behavior of the metamaterial is utilized for enhancing the directivity of the monopole. Despite the directivity enhancement of about 5 dB, an improved bandwidth of 35% is obtained for the proposed configuration. Initially, a 2 × 3 array of a single MTM slab has been placed over the ground plane of the monopole. It is shown that, over the whole working band, a significant directivity improvement is maintained compared to the unloaded monopole. Further, the directivity performance has been investigated with different combination of MTM slab.

A new type of coherent electromagnetic radiation source based on interference effect between forward and backward waves in an active metamaterial slab

In this paper, we shall show first that both reflection and transmission can be significantly amplified when a beam of electromagnetic wave is normally incident into an active (even lossy) metamaterial slab with near-zero-real-part-of-impedance, which is attributed to effect of interference between forward and backward waves in the slab. Then we demonstrate that extended steady electromagnetic waves can be achieved using a double-slab structure, which may be applied to generate coherent electromagnetic wave with very narrow frequency band and very low divergence angle. This work provides feasible scheme to construct a new type of source of coherent electromagnetic radiation based on new physical mechanism.

Analysis of Wireless Power Transfer Using Superconducting Metamaterials

A spiral superconducting metamaterial with an effective negative permeability is presented for efficient wireless power transfer (WPT) using magnetic resonant coupling. The S-parameters of superconducting metamaterials unit cell with respect to different resonance frequencies are obtained by the finite element simulation. The effective permeability of the unit cell of superconducting metamaterials is derived by the S-parameter method, and an analysis of the resonant modes is performed by full-wave simulation. The 3 × 3 planar superconducting metamaterials slab is designed by the proposed unit cell to verify their effects in a WPT system. The effects of superconducting on efficiency enhancement are analyzed by both S-parameter and magnetic field distribution simulation. The optimal position of the superconducting metamaterials is acquired by analyzing the transfer efficiency. We show with simulation results that the transfer efficiency of the system can be improved significantly by the superconducting metamaterials through enhanced evanescent wave coupling and with the lower loss properties of the superconductor.

Retrieving effective material parameters of metamaterials characterized by nonlocal constitutive relations

The parameter retrieval is a procedure in which effective material properties are assigned to a given metamaterial. A widely used technique bases on the inversion of reflection and transmission from a metamaterial slab. Thus far, local constitutive relations have been frequently considered in this retrieval procedure to describe the metamaterial at the effective level. This, however, is insufficient. The retrieved local material properties frequently fail to predict reliably the optical response from the slab in situations that deviate from those that have been considered in the retrieval, e.g. when illuminating the slab at a different incidence angle. To significantly improve the situation, we describe here a parameter retrieval, also based on the inversion of reflection and transmission from a slab, that describes the metamaterial at the effective level with nonlocal constitutive relations. We retrieve the effective material parameters at the example of a fishnet metamaterial. We demonstrate that the nonlocal constitutive relation can describe the optical response much better than local constitutive relation would do. Our approach is widely applicable to a large class of metamaterials.

Study of cavity-enhanced dipole emission on a hyperbolic metamaterial slab

We theoretically study strong coupling of a dipole emitter positioned close to a hyperbolic metamaterial (HMM) slab. Enhanced dipole emission with a large Purcell factor originated from the superposition of p-wave resonant coupling and critical coupling to the high-k waveguide modes in a HMM slab is addressed, and the dependence of the slab thickness and the fill ratio of metallic nanorods in HMM on the emission strength is explicitly summarized. Via optimizing the mode coupling condition, we point out a general design rule for the HMM structure to yield a large Purcell factor. Furthermore, by incorporating a Si bullseye grating on the HMM slab, 18-fold far-field radiation enhancement owing to extraction of the mainly coupled resonant mode in HMM is presented.

Repulsive Casimir force between hyperbolic metamaterials.

The Casimir force between electric and magnetic hyperbolic metamaterial slabs is investigated. Due to hyperbolic dispersion, the electromagnetic features of these metamaterials along the optical axis are different from those perpendicular to the optical axis; consequently, these features contribute differently to the Casimir effect. The repulsive Casimir force is formed between electric and magnetic hyperbolic metamaterial slabs; moreover, hyperbolic dispersion can enhance the repulsive effect. However, by utilizing the extremely anisotropic behavior of hyperbolic metamaterials and changing the separation distance between the two slabs, the restoring Casimir force emerges. Additionally, by considering the dispersion of both the permittivity and the permeability of hyperbolic metamaterials, the Casimir force reaches several equilibrium points at different separation distances. Furthermore, the Casimir force at room temperature is discussed. Although the temperature can weaken the effect of the restoring Casimir force, stable equilibria may remain upon choosing suitable filling factors. This work shows that hyperbolic metamaterials have potential applications in micro- and nanoelectromechanical systems, especially for maintaining stability and overcoming adhesion problems.

Tunable deflection and asymmetric transmission of THz waves using a thin slab of graphene-dielectric metamaterial, with and without ENZ components

Tunable deflection of obliquely incident, linearly polarized terahertz waves is theoretically studied in a wide frequency range around 20 THz, by combining a thin slab of graphene-dielectric metamaterial (with ten layers of graphene), a dielectric grating, and a uniform polar-dielectric slab operating in the epsilon-near-zero (ENZ) regime. The modulation of the deflection intensity and deflection angle is done by varying the chemical potential of graphene, and is realized with or without connection to the asymmetric transmission. It is shown to depend on the location of the graphene-dielectric metamaterial slab, as well as on the incidence angle. Four scenarios of tunable deflection are found, including the ones realizable in two-component structures without an ENZ slab.

Perfect absorption in cascaded asymmetric hyperbolic metamaterial slabs

The absorption of single asymmetric hyperbolic metamaterial (AHM) slab and cascaded AHM slabs has been theoretically studied in this paper. The proposed AHM consists of Polymethyl methacrylate (PMMA) and silver sheet. The numerical results show that the absorption of the single AHM slab is very sensitive to the azimuth angle, and the average absorption over the azimuth angle is only 0.2. However, the absorption of the cascaded AHM slabs can reach 0.7 in all the azimuth angles, and the average absorption over the azimuth angle can reach 0.88. Compared with the average absorption of the single AHM slab, the average absorption of the cascaded AHM slabs increases threefold.

Reference-plane-invariant waveguide method for electromagnetic characterization of bi-axial bianisotropic metamaterials

In this paper, we investigate a reference-plane invariant (RPI) method for electromagnetic property extraction of bi-axial bianisotropic metamaterial (MM) slabs. In order to obtain unique properties, we applied the frequency varying technique in order to determine the location of the slab within its cell. For validation of the proposed method, we first simulated and then measured scattering parameters of a MM slab constructed by split-ring-resonators, next extracted its electromagnetic properties, and finally compared extracted properties by those retrieved by another method which requires reference-plane information. From the comparison, we noted that whereas our proposed method correctly retrieved electromagnetic properties without knowing the value of reference plane transformation factors, the accuracy of the tested method was seriously influenced by any inaccurate reference plane information.

Radiative heat transfer between two magnetodielectric metamaterial slabs with finite thickness in non-equilibrium situation

In this paper, we consider a system including two maghnetodielectric slabs with different temperature that are placed in vacuum at zero temperature and very short separation distances from each other. Based on the canonical quantization of the electromagnetic field in the presence of dissipative media, we investigate the radiative heat transfer arising from thermal and quantum fluctuations in out of thermal equilibrium but stationary situation. For this purpose, we calculate the ensemble average of Poynting vector by driving quantum correlation relations between noise polarization and magnetization operators and extracting the electromagnetic Green tensor of the system. Finally, we analyze the transferred radiation of aforementioned system by employing the numerical result of the Poynting vector.

Lateral radiative forces exerted by evanescent fields along a hyperbolic metamaterial slab

We show and investigate the optical forces acting on a particle in the vicinity of a planar waveguide which is filled with hyperbolic material and supports propagation across its plane (two-dimensional). The anisotropy axis of its medium lies in plane of the waveguide. In contrast to commonly considered pushing or pulling forces, acting in one-dimensional guiding structures, in the case of two-dimensional wave propagation, the angles between the momentum and the total energy flow may take any value around the circle. Accordingly, evanescent fields out of the slab exert lateral radiative forces on a nanoparticle oriented parallel to momentum being controllably different from the total energy flow direction. This provides a flexibility in manipulation by nanoparticles by employing suitably engineered hyperbolic structures.