Magnetic Metamaterials Research Articles

Peculiarities of propagation of electroinductive waves in magnetic metamaterials

The coupling of doubly split ring resonators in the GHz range has been experimentally, analytically, and numerically studied in order to design a metamaterial with dominant electrical coupling as a model of nanoscale metamaterials. An example of propagation of GHz electroinductive waves in a metamaterial is demonstrated.

Bi-gyrotropic single-negative magnetic materials in the presence of longitudinal magnetization: A transfer matrix approach

In a single-negative medium, electric permittivity (ϵ) or magnetic permeability (μ) coefficients are negative. In order to use the potential of magnetic metamaterials, in the present study, we have investigated bi-gyrotropic single-negative magnetic materials (BSNMMs) having their ϵ and μ in the form of non-diagonal tensors. At first, we have introduced a transfer matrix method (TMM)-based approach for studying optical and magneto-optical (MO) properties of BSNMMs and multilayer structures containing them in the case of longitudinal configuration of magnetization. Then, we have studied numerical computation on the reflection geometry for both ϵ-negative and μ-negative typical BSNMMs for different permittivity and permeability values.

High efficiency second and third harmonic generation from magnetic metamaterials by using a grating

Metamaterials can be used to generate harmonic signals in small thicknesses, but they suffer from low efficiency. Here, we introduce a new method for amplifying second and third harmonic generation from magnetic metamaterials. We show numerically that by using a grating structure under the metamaterial, the grating and the metamaterial form a resonator which leads to a higher absorption in the metamaterial. By this method we could increase the absorption of the structure in the magnetic resonance up to 25% of the initial value. This leads to the generation of second and third harmonic signals with a higher efficiency from this metamaterial-based nonlinear media. We confirmed this idea in the nanostrip metamaterials and saw the amplitude of the second harmonic generation was doubled and the amplitude of the third harmonic generation increased by a factor of 4 in comparison to the same structure without grating.

Decoupling technique of patch antenna arrays with shared substrate by suppressing near-field magnetic coupling using magnetic metamaterials**Project supported in part by the National Natural Science Foundation of China (Grant Nos. 61331005, 61471388, 61501503, 61501502, 61501497, 51575524, 61302023, and 11304393) and the Natural Science Foundation of Shaanxi Province, China (Grant Nos. 2015JM6300 and 2015JM6277).

In this paper, we propose the decoupling technique of patch antenna array by suppressing near-field magnetic coupling (NFMC) using magnetic metamaterials. To this end, a highly-integrated magnetic metamaterials, the substrate-integrated split-ring resonator (SI-SRR), is firstly proposed to achieve negative permeability at the antenna operating frequency. By integrating SI-SRR in between two closely spaced antennas, magnetic fields are blocked in the shared substrate due to negative permeability of SI-SRR, reducing NFMC between the two antennas. To verify the technique, a prototype was fabricated and measured. The measured results demonstrated that the isolation can be enhanced by more than 17 dB even when the gap between the two patch antennas is only about 0.067λ. Due to high integration, this technique provides an effective alternative to high-isolation antenna array.

Enhancing isolation of antenna arrays by simultaneously blocking and guiding magnetic field lines using magnetic metamaterials

In this article, we propose to enhance the isolation of antenna arrays by manipulating the near-field magnetic coupling between adjacent antennas using magnetic metamaterials (MMs). Due to the artificially designed negative or large permeability, MMs can concentrate or block the magnetic field lines where they are located, which allows us to tune the near-field magnetic coupling strengths between antennas. MMs can play a two-fold role in enhancing antenna isolation. On one hand, the magnetic fields can be blocked in gaps between adjacent antennas using MMs with negative permeability; on the other hand, the magnetic fields can be pulled towards the borders of the antenna array using MMs with large permeability. As an example, we demonstrated a four-element patch antenna array with split-ring resonators (SRR) integrated in the substrate. The measured results show that the isolation can be enhanced by more than 10 dB with the integration of SRRs, even if the gap between antennas is only about 0.082λ. This work provides an effective alternative to the design of high-isolation antenna arrays.

Magnetic Metamaterials: A comparative study of resonator geometry and metal conductivity

In this work, split ring resonators based metamaterials are studied for microwave, terahertz and infrared frequency regimes. Two different geometries, circular and rectangular split ring resonators based metamaterials are investigated numerically for different frequency regimes. Our study indicates that the effect of metal conductivity and resonator geometry shows very little impact on the fundamental resonance mode. However the higher order modes go through significant frequency tuning because of the change in resonator geometry. We have further shown that the metal conductivity is an important parameter for the metamaterials employed in infrared domains.

Magnetic hyperbolic metamaterial of high-index nanowires

We show that the axial component of the magnetic permeability tensor is resonant for a wire medium consisting of high-index epsilon-positive nanowires, and its real part changes the sign at a certain frequency. At this frequency the medium experiences the topological transition from the hyperbolic to the elliptic type of dispersion. We show that the transition regime is characterized by extremely strong dependence of the permeability on the wave vector. This implies very high density of electromagnetic states that results in the filamentary pattern and noticeable Purcell factor for a transversely oriented magnetic dipole.

Bulk magnetic terahertz metamaterials based on dielectric microspheres.

Rigid metamaterials were prepared by embedding TiO2 microspheres into polyethylene. These structures exhibit a series of Mie resonances where the lowest-frequency one is associated with a strong dispersion in the effective magnetic permeability. Using time-domain terahertz spectroscopy, we experimentally demonstrated the magnetic nature of the observed resonance. The presented approach shows a way for low-cost massive fabrication of mechanically stable terahertz metamaterials based on dielectric microresonators.

Isolation enhancement of patch antenna array via metamaterial integration

ABSTRACTA high‐isolation coaxial‐fed antenna array is proposed through the integration of metamaterial. To this end, a magnetic metamaterial, the substrate‐integrated split‐ring resonator (SI‐SRR), is designed and integrated in the shared substrate between two closely spaced antennas. Due to negative permeability of SI‐SRR, magnetic fields are blocked in the shared substrate. By suppressing the near‐field magnetic coupling, enhanced isolation between the two antennas is obtained. The antenna array was fabricated and measured. Both the simulated and measured results show that the proposed antennas can provide an isolation of 34.5 dB in the operation band, even when the gap between the two antennas is only nearly about 0.033λ. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2321–2325, 2016

Multiple omnidirectional defect modes and nonlinear magnetic-field effects in metamaterial photonic superlattices with a polaritonic defect

We report the existence of multiple omnidirectional defect modes in the zero-n¯ gap of photonic stacks, made of alternate layers of conventional dielectric and double-negative metamaterial, with a polaritonic defect layer. In the case of nonlinear magnetic metamaterials, the optical bistability phenomenon leads to switching from negligible to perfect transmission around these defect modes. We hope these findings have potential applications in the design and development of multichannel optical filters, power limiters, optical-diodes and optical-transistors.

Large-Scale and Defect-Free Silicon Metamaterials with Magnetic Response.

All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. Here, we experimentally demonstrate a silicon based large-scale magnetic metamaterial, which is fabricated with standard photolithography and conventional reactive ion etching process. The periodically arrayed silicon sub-wavelength structures possess electric and magnetic responses with low loss in mid-infrared wavelength range. We investigate the electric and magnetic resonances dependencies on the structural parameters and demonstrate the possibility of obtaining strong dielectric-based magnetic resonance through a broad band range. The optical responses are quite uniform over a large area about 2 × 2 cm2. The scalability of this design and compatibility fabrication method with highly developed semiconductor devices process could lead to new avenues of manipulating light for low-loss, large-area and real integrated photonic applications.

Quasistatic Metamaterials: Magnetic Coupling Enhancement by Effective Space Cancellation.

A novel and broadly applicable way to increase magnetic coupling between distant circuits in the quasistatic regime is introduced. It is shown how the use of magnetic metamaterials enhances the magnetic coupling between emitting and receiving coils. Results are experimentally demonstrated by measuring a boost on the efficiency of the wireless transmission of power between distant circuits.

Electric and magnetic resonances in optical metamaterial for efficient absorption enhancement in ultrathin CdTe-based photovoltaic cells

Light absorption plays a key role in photovoltaic devices, especially in thin-film CdTe-based solar cells. Here we study the enhancement of optical absorption in a ultrathin CdTe layer by embedding it into optical magnetic metamaterials. In a periodic metal-CdS-CdTe-metal sandwiched structure, the absorption of transverse magnetic polarized light has been significantly enhanced. The maximum enhancement is around 3 times, which is attributed to the strong local field enhancement in the CdTe thin film. Importantly, due to the coexistence of large electric resonance and magnetic resonance in magnetic metamaterials, the enhancement of light absorption has been obtained in a broadband from 400 nm to 800 nm, which is almost 1.5 times of that of the conventional CdTe-based photovoltaic device and covers the strongest part of the solar spectrum. Moreover, such absorption enhancement is also valid for a wide range of incident angles. We believe that our finding can lead to a variety of important applications in ultrathin CdTe-based solar cell technology.

Enhancement of magnetic dipole emission at yellow light with polarization-independent hexagonally arrayed nanorods optical metamaterials

Here we demonstrate the control of magnetic dipole spontaneous emission at yellow light by polarization-independent hexagonally arrayed nanorods magnetic metamaterials. By embedding a magnetic dipole into a polarization-independent magnetic metamaterial consisting of hexagonal arrays of paired silver nanorods, the radiative emission enhancement and the Purcell factor around 590 nm have been dramatically increased 44 times for a significant general far-field emission enhancement and 57 times for a maximum general magnetic dipole near-field emission enhancement, respectively. Moreover, the polarization-independent enhancements are found to be a robust variation of the dipole’s positions and structure geometries, showing nice fabrication tolerance for practical applications.

Artificial metamaterials for reprogrammable magnetic and microwave properties

We demonstrate a reliable method for realizing various antiferromagnetic states in lithographically defined, dipolar coupled rhomboid nanomagnets. We directly probe the remanent state using magnetic force microscopy and measured the microwave absorptions using broadband ferromagnetic resonance spectroscopy technique. Reprogrammable microwave absorption properties are shown by switching between ferromagnetic and antiferromagnetic remanent states using a simple field initialization. There is a direct correlation between the magnetic remanent states and the microwave responses. Experimental results were supported by micromagnetic simulations which show a good agreement. The results may find applications in low power magnonic devices based on reprogrammable magnetic metamaterials.

Hierarchical self-assembly of a bulk metamaterial enables isotropic magnetic permeability at optical frequencies

Raspberry-like magnetic nanoclusters are synthesized and self-assembled to form a bulk magnetic metamaterial.

Magnonic band structure of domain wall magnonic crystals

Magnonic crystals are prototype magnetic metamaterials designed for the control of spin wave propagation. Conventional magnonic crystals are composed of single domain elements. If magnetization textures, such as domain walls, vortices and skyrmions, are included in the building blocks of magnonic crystals, additional degrees of freedom over the control of the magnonic band structure can be achieved. We theoretically investigate the influence of domain walls on the spin wave propagation and the corresponding magnonic band structure. It is found that the rotation of magnetization inside a domain wall introduces a geometric vector potential for the spin wave excitation. The corresponding Berry phase has quantized value $4 n_w \pi$, where $n_w$ is the winding number of the domain wall. Due to the topological vector potential, the magnonic band structure of magnonic crystals with domain walls as comprising elements differs significantly from an identical magnonic crystal composed of only magnetic domains. This difference can be utilized to realize dynamic reconfiguration of magnonic band structure by a sole nucleation or annihilation of domain walls in magnonic crystals.

Design and Full Characterization of Planar Active Magnetic RF Metamaterials

Applications of metamaterials have been limited by parasitic resistive losses. We present the design and measurement of split ring resonators with embedded active field effect transistor circuits comprising a magnetic metamaterial. We show that the imaginary part of the effective permeability changes sign within the bandwidth of the negative differential resistance region, creating a stable gain medium. We present experimental reflection and transmission measurements showing a sign change in the permeability loss term and two applications of such a metamaterial. use as a mu-negative near field parasitic element for small magnetic antennas and as an amplifying material in free space. We show the active metamaterial can provide property enhancement compared with related passive structures in both applications, providing a path to overcoming parasitic loss in previously demonstrated metamaterial structures.

Experimental Demonstration of Anomalous Field Enhancement in All-Dielectric Transition Magnetic Metamaterials.

Anomalous field enhancement accompanied by resonant absorption phenomenon was originally discussed in the context of plasma physics and in applications related to radio-communications between the ground and spacecraft returning to Earth. Indeed, there is a critical period of time when all communications are lost due to the reflection/absorption of electromagnetic waves by the sheath of plasma created by a high speed vehicle re-entering the atmosphere. While detailed experimental studies of these phenomena in space are challenging, the emergence of electromagnetic metamaterials enables researchers exceptional flexibility to study them in the laboratory environment. Here, we experimentally demonstrated the strong localized field enhancement of magnetic field for an electromagnetic wave propagating in Mie-resonance-based inhomogeneous metamaterials with magnetic permeability gradually changing from positive to negative values. Although these experiments were performed in the microwave frequency range, the proposed all-dielectric approach to transition metamaterials can be extended to terahertz, infrared, and visible frequencies. We anticipate that these results, besides most basic science aspects, hold the potential for numerous applications, including low-intensity nonlinear transformation optics, topological photonics, and the broader area of surface and interface science.

Nanostructured magnetic metamaterials based on metal-filled carbon nanotubes

Hybrid systems formed by carbon nanotubes filled with metal represent a class of nanomaterials with manifold functionality that can find applications in different fields as, for example, magnetic storage and spintronics. Here a detailed and comprehensive study is reported on the magnetic properties of template grown cobalt cluster-filled multiwall carbon nanotube arrays. The temperature and magnetic field dependence of the samples magnetization are investigated in the range 5–760 K and from −50 kOe to +50 kOe, respectively. Hysteresis cycles are slightly open and transmission electron microscopy reveals that the cobalt clusters inside the nanotubes exhibit a crystalline nature. The zero-field cooling/field-cooling magnetization temperature dependence, analyzed in the framework of a “two-state” progressive crossover model, reveals spin disorder and suggests a spin glass-like scenario. These findings show that cobalt-filled nanotube arrays represent a unique system of magnetically coupled nanostructures, allowing to envision a new class of nanoscale carbon-based magnetic metamaterials, ideal platforms for novel magneto-electronic devices.