Design of Tunable Multi-Band Metamaterial Perfect Absorbers Based on Magnetic Polaritons

A tunable multi-band metamaterial perfect absorber is designed in this paper. The absorber made of a composite array of gold elliptical and circular disks on a thick metallic substrate, separated by a thin dielectric spacer. The absorptivity and the field enhancement of proposed structures are numerically investigated by the finite difference time domain method. Three absorption peaks (1.15, 1.55, and 2.05 μm) with the maximal absorption of 99.2, 99.7, and 97.3% have been achieved, respectively. By altering the dimensions of associated geometric parameters in the structure, three resonance wavelengths can be tuned individually. Physical mechanism of the multi-band absorption is construed as the resonance of magnetic polaritons. And the absorber exhibits the characteristics that are insensitive to the polarization angle due to its symmetry. The research results can have access to selective control of thermal radiation and the design of multi-band photodetectors.

     

Dynamically Tunable Electromagnetically Induced Transparency in Graphene and Split-Ring Hybrid Metamaterial

In this letter, a novel hybrid metamaterial consisting of periodic array of graphene nano-patch and gold split-ring resonator has been theoretically proposed to realize an active control of the electromagnetically induced transparency analog in the mid-infrared regime. A narrow transparency window occurs over a wide absorption band due to the coupling of the high-quality factor mode provided by graphene dipolar resonance and the low-quality factor mode of split-ring resonator magnetic resonance, which is interpreted in terms of the phase change and surface charge distribution. In addition to the obvious dependence of the spectral feature on the geometric parameters of the elements and the surrounding environmental dielectric constant, our proposed metamaterial shows great tunabilities to the transparency window by tuning the Fermi energy of the graphene nano-patch through electric gating and its electronic mobility without changing the geometric parameters. Furthermore, our proposed metamaterial combines low losses with very large group index associated with the resonance response in the transparency window, showing it suitable for slow light applications and nanophotonic devices for light filter and biosensing.     

Microwave absorption by magnetite: A possible mechanism for coupling nonthermal levels of radiation to biological systems

The presence of trace amounts of biogenic magnetite (Fe₃O₄) in animal and human tissues and the observation that ferromagnetic particles are ubiquitous in laboratory materials (including tissue culture media) provide a physical mechanism through which microwave radiation might produce or appear to produce biological effects. Magnetite is an excellent absorber of microwave radiation at frequencies between 0.5 and 10.0 GHz through the process of ferromagnetic resonance, where the magnetic vector of the incident field causes precession of Bohr magnetons around the internal demagnetizing field of the crystal. Energy absorbed by this process is first transduced into acoustic vibrations at the microwave carrier frequency within the crystal lattice via the magnetoacoustic effect; then, the energy should be dissipated in cellular structures in close proximity to the magnetite crystals. Several possible methods for testing this hypothesis experimentally are discussed. Studies of microwave dosimetry at the cellular level should consider effects of biogenic magnetite. © 1996 Wiley-Liss, Inc.     

Noninvasive Cardiac Flow Assessment Using High Speed Magnetic Resonance Fluid Motion Tracking

Cardiovascular diseases can be diagnosed by assessing abnormal flow behavior in the heart. We introduce, for the first time, a magnetic resonance imaging-based diagnostic that produces sectional flow maps of cardiac chambers, and presents cardiac analysis based on the flow information. Using steady-state free precession magnetic resonance images of blood, we demonstrate intensity contrast between asynchronous and synchronous proton spins. Turbulent blood flow in cardiac chambers contains asynchronous blood proton spins whose concentration affects the signal intensities that are registered onto the magnetic resonance images. Application of intensity flow tracking based on their non-uniform signal concentrations provides a flow field map of the blood motion. We verify this theory in a patient with an atrial septal defect whose chamber blood flow vortices vary in speed of rotation before and after septal occlusion. Based on the measurement of cardiac flow vorticity in our implementation, we establish a relationship between atrial vorticity and septal defect. The developed system has the potential to be used as a prognostic and investigative tool for assessment of cardiac abnormalities, and can be exploited in parallel to examining myocardial defects using steady-state free precession magnetic resonance images of the heart.     

Manipulate the Transmissions Using Index-Near-Zero or Epsilon-Near-Zero Metamaterials with Coated Defects

We investigate the wave transmissions through an index-near-zero (INZ) or epsilon-near-zero (ENZ) metamaterial containing various kinds of coated cylindrical defects. We find that thin coatings of the defects can dramatically change the transmission behaviors. For example, perfect magnetic conductor (PMC) defects embedded in an INZ or ENZ metamaterial yield total reflections for transverse magnetic polarized waves (Hao et al., Appl Phys Lett 96:101109, 2010). However, if the PMC defects are coated with dielectric shells, total transmissions could be achieved by tuning their permittivity values or geometric sizes. The permittivity differences of dielectric shells for total reflections and transmissions in the INZ or ENZ metamaterial could be very small, implying potential applications, such as ultrasensitive sensors and switches.     

Broadband Mid-infrared Dual-Band Double-Negative Metamaterial: Realized Using a Simple Geometry

We design and numerically demonstrate a novel metamaterial structure consisting of a dielectric layer sandwiched between two silver films and is perforated with two kinds of square-shaped holes at different angles, which is a dual-band double-negative (each band possesses simultaneously negative permittivity and permeability) metamaterial with broad NRI bands in mid-infrared region(3–30 μm). The broadband of NRI contributed to the strong magnetic resonance caused by the excitation of surface plasmon polaritons. The influence of the number of square-shaped holes on the properties of the designed structures are also investigated by analyzing and comparing the transmission, permeability, permittivity, refractive index, and figure of merit. Then, by optimizing the structural parameters, the proposed structure exhibits a negative band with a figure of merit of 3.3, which is to our knowledge larger than previously reported plasmonic metamaterial in mid-infrared region(M-IR). The value of negative refractive index(NRI) reaches −6 and the bandwidth of NRI can reach up to 4.2 THz in the low-frequency band of M-IR region, which is the widest NRI band in M-IR spectrum at present as far as we know. Moreover, the metamaterial structure is simple and easy to be manufactured with standard fabrication techniques. This work will be very meaningful in designing dual-band negative-index material with broad NRI band and low loss. Finally, the proposed metamaterial has huge potential applications in multiband or broadband devices.

     

Simulation of the propagation effects in the HF-EPR spectra of non-diluted magnetic materials

The high field EPR spectra of non-diluted magnetic material are affected by propagation effects when the wavelength of the exciting radiation is of the same order of magnitude of the optical path within the sample. Beyond the optical path, the shape of the spectra is determined by the dielectric constant and by the magnetization of the material and through these quantities it depends on the temperature. A detailed knowledge of the physical properties of the material is therefore mandatory for a complete study of the phenomenon. In order to demonstrate the propagation effect, the 285 GHz EPR spectra of tetramethyl-ammonium manganese chloride (TMMC) were recorded as a function of temperature and a simulation of the spectra was performed on the basis of a simplified model of the propagation of far infrared radiation around the resonance field. The universality of the effect was illustrated by measuring other magnetic materials such as ferrite.     

Perfect Absorption of Light by Coherently Induced Plasmon Hybridization in Ultrathin Metamaterial Film

We demonstrated numerically that light can be totally absorbed by an ultrathin metamaterial film through coherently induced plasmon hybridization. Two fundamental modes, namely symmetrical and antisymmetrical modes, are observed in the metal–insulator–metal structure and attributed to the electric and magnetic resonance, respectively. Each kind of resonance is related to a distinct absorption peak for the corresponding coherent inputs. In particular, it is found that the antisymmetrical absorption is almost omnidirectional and suitable for divergent beams with arbitrary polarization and angle of incidence. To interpret the interaction of magnetic and electric fields with the structure, effective material parameters of the metamaterial are also retrieved, showing good agreement with the intuitive discussion. Furthermore, the general condition of coherent perfect absorption in a metamaterial thin film is given, which could be helpful for the design and understanding of such absorbers.     

<Emphasis Type="Bold">A Research of Magnetic Control Ferrite Photonic Crystal Filter</Emphasis>

In this article, an anisotropic magnetized ferrite photonic crystal model is analyzed by using the finite-difference time-domain method. The electromagnetic wave propagates in anisotropic ferrite material and forms two kinds of Eigen propagation mode: left-hand circular polarization (LCP) mode and right-hand circular polarization (RCP) mode. Therefore, the ferrite material is used to produce photonic crystal and wave polarized by these two kinds of polarization modes can be obtained. Because the electromagnetic properties of the ferrite material are greatly influenced by the bias magnetic field, the ferrite photonic crystal band gap can be controlled by adjusting the intensity of the bias magnetic field, and then a magnetron photonic crystal filter is formed. The results show that the magnetic photonic crystal with the bias magnetic field to the LCP/RCP wave forms different pass band and band gap, which can obtain different forms of polarized wave.     

Magnetic Coupling Effect on Nonlinear Properties in Negative Index Metamaterials with a Kerr Nonlinearity

We investigate magnetic coupling effect on nonlinear electromagnetic properties in a three-dimensional negative index metamaterial constituted by arrays of conducting wires and split-ring resonators embedded into a Kerr nonlinear dielectric. Numerical results show that the switches of nonlinear electromagnetic properties between right-handed and left-handed properties depend closely on magnetic coupling strength, which can be divided into several different coupling regions according to the angular frequency of incident light and the nonlinear types (focused or defocused) of the dielectric. These properties may be instructive for designing optimizely composite metamaterials with negative refraction and provide various routes to manipulating light.     

Tunable Fano Resonances in Mid-Infrared Waveguide-Coupled Otto Configuration

A planar silicon carbide/dielectric multilayer structure is investigated in Otto geometry, where surface phonon polaritons and planar waveguide mode can be coupled to realize Fano resonances under transverse magnetic polarization. The resonance coupling is analytically demonstrated using the coupled harmonic oscillator model and numerically presented through rigorous coupled-wave analysis calculations, which shows that the coupling strength between different resonances and the resonant wavelength matching condition plays an important role in the bandwidth and position of the Fano resonance (FR); the magnetic field distribution was also shown to explain the origin of FRs qualitatively.

     

Terahertz Dual-Band Polarization Insensitive Electromagnetically Induced Transparency-Like Metamaterials

In this paper, an electromagnetically induced transparency-like metamaterial for terahertz is designed. The structure is based on cross-shaped and SRRs composite elements. It can achieve dual-frequency transparent window in a wide frequency band and is insensitive to electromagnetic wave polarization. The resonance points of transmission peaks are 198.55 and 254.18 GHz, respectively. The electromagnetic transmittance can reach 95.6% and 97.7%, respectively, which has excellent electromagnetic transmission effect. The measured results are in good agreement with the trend of simulation curve. At the same time, flexible polyimide with stable performance is selected as the base material of metamaterial dielectric, which can be widely used in microwave fields such as filters, sensors, and slow light devices.

     

Light Amplification with Low-Gain Material: Harvesting Harmonic Resonance Modes of Surface Plasmon Polaritons on a Magnetic Meta-Surface

We theoretically show that it is feasible to utilize harmonic resonance modes of surface plasmon polaritons on a magnetic meta-surface for light amplification with low-gain material. The required threshold and optimal gain strength for active layer can be substantially reduced to about one-tenth as compared with those utilizing fundamental resonance modes. The findings provide a simple and practical metamaterial approach for light amplification with most of the existing active media.     

New Type Design of the Triple-Band and Five-Band Metamaterial Absorbers at Terahertz Frequency

A new scheme to achieve a simple design of triple-band metamaterial absorber at terahertz frequency is presented. In this scheme, we employ a traditional sandwich structure, which is consisted of a metallic resonator and an appropriate thickness of the dielectric layer backed with an opaque metallic board, as the research object. Three strong but discrete resonance peaks with the narrow bandwidths and high absorptivities are realized. The combination of the dipolar resonance, LC (inductor-capacitor circuit) resonance, and the surface resonance of the metallic resonator determines the triple-band absorption. Numerical results also show that the frequencies of the three absorption bands and the number of the resonance peaks can be effectively tuned by adjusting or changing the geometric parameters of the metallic resonator. Moreover, we present a simple design of five-band terahertz absorber by further optimizing the sizes of the metallic elements in the top layer of the metamaterial. The design of the unit structures will assist in designing innovative absorbing devices for spectroscopy imaging, detection, and sensing.     

Tailoring Active Far-Infrared Resonator with Graphene Metasurface and Its Complementary

Far-infrared part of electromagnetic spectrum and its technological details have been highly sought after due to its myriad applications including imaging, spectroscopy, industry control, and communication. However, lack of efficient components of electronic and photonic sources/detectors working in this particular spectrum has impeded its widespread application. One of the bottlenecks lies in the compact far-infrared polarization-sensitive resonator/modulator in compatible with pixel-detector for far-infrared spectroscopy. In this work, we demonstrate strong electric resonance response in perforated graphene sheet at this particular electromagnetic region. The results demonstrate inherently different natures for the strong electromagnetic response between graphene-based and metallic metamaterials. Unlike the metallic metamaterials relying on the geometrical inductance for magnetic response, the electric resonance caused by localized dipole/multipolar modes is found to be dominated in graphene and thus enabling sub-wavelength confinement of electromagnetic field. The Babinet’s principle is proposed to be applied for broadband far-infrared modulation and resonant filters design of graphene-based metamaterial. The active tunable electric resonance through electrostatic doping on the graphene-based patterns provides efficient route for compact biosensing, far-infrared imaging, and detection.     

A Design for Band Enhanced Dielectric Absorber Based on Fractal-Like Structure

A dielectric metamaterial absorber has been proposed, which consists of fractal-like structure and conductive sheet. The fractal-like structure is made by the high permittivity dielectric and also is covered by the conductive sheet. Absorptivity of such a dielectric metamaterial absorber is 99.1%, which can be found at 10.196 GHz; meanwhile, the absorber is polarization insensitive. To enhance the bandwidth of absorber, a novel absorber also is proposed, whose bandwidth is 0.566 GHz, which ranges from 9.752 to 10.318 GHz, and relative bandwidth is 5.64%. The maximum absorptivity can reach to 99.8%, and the proposed absorber also is polarization insensitive. In the meantime, the absorber shows excellent performance which is incident angle insensitive; when the incident angle is increased to 70°, the absorptivity is larger than 75%.

     

All-Optical Switching and Routing with a Nonlinear Metamaterial

We report the dynamic control characteristics of electromagnetic wave propagation in a nonlinear metamaterial by an applied electric field, which is constructed by an array of metallic nanowires embedded into a nonlinear dielectric. Numerical results show that the composite structure can appear three kinds of interesting interconversion characteristics among positive refraction, negative refraction, and cut-off states by adjusting the intensity of the applied electric field. Consequently, we can switch all-optically light states between the total reflection state (OFF state) and the total transmission state (ON state), as well as control light propagation route dynamically. Moreover, we also elaborate on the dependency of the refraction angles of energy flow and wave vector, and Brewster angle on the applied electric field and the orientation angle φ. These properties open up an avenue for potential applications of nonlinear metamaterials in nanophotonic devices such as all-optical switches, routers, and wave cut-off devices.     

Inverse Design of Dielectric Resonator Cloaking Based on Topology Optimization

In many applications, a cloaked resonator is highly desired, which can harvest and maximize the energy within the resonator without being detected. This paper presents the resonator cloaking achieved by topology optimization-based inverse design methodology. The resonator cloaking is inversely designed by solving the topology optimization problem with minimizing the ratio of the scattering field energy outside the cloak and the cloaked resonating field energy. By inversely designing the resonator cloaking with relative permittivity 2 for both the resonator and cloak, the topology optimization-based inverse design methodology is demonstrated, where the incident angle sensitivity is considered to derive incident angle insensitive design. Then, the proposed methodology is applied for the cases with resonator and cloak materials chosen from dielectrics with low, moderate and high permittivity, respectively. The derived results demonstrate that the resonator cloaking can be categorized into three types, which are the Fabry-Pérot resonance cloaking, Mie resonance cloaking and hybrid resonance cloaking.     

Development of Cellular Magnetic Dipoles in Magnetotactic Bacteria

Magnetotactic bacteria benefit from their ability to form cellular magnetic dipoles by assembling stable single-domain ferromagnetic particles in chains as a means to navigate along Earth's magnetic field lines on their way to favorable habitats. We studied the assembly of nanosized membrane-encapsulated magnetite particles (magnetosomes) by ferromagnetic resonance spectroscopy using Magnetospirillum gryphiswaldense cultured in a time-resolved experimental setting. The spectroscopic data show that 1), magnetic particle growth is not synchronized; 2), the increase in particle numbers is insufficient to build up cellular magnetic dipoles; and 3), dipoles of assembled magnetosome blocks occur when the first magnetite particles reach a stable single-domain state. These stable single-domain particles can act as magnetic docks to stabilize the remaining and/or newly nucleated superparamagnetic particles in their adjacencies. We postulate that docking is a key mechanism for building the functional cellular magnetic dipole, which in turn is required for magnetotaxis in bacteria.     

Separation of cells labeled with immunospecific iron dextran microspheres using high gradient magnetic chromatography

Immunospecific magnetic microspheres, consisting of ferromagnetic iron dextran conjugated to Protein A, were used to specifically label red blood cells (RBC) for cell separation studies using high gradient magnetic chromatography ( HGMC ). When 10(7)-10(8) RBC labeled with Protein A-iron dextran microspheres were applied to a column containing 30 mg stainless steel wire placed in a 7.5 kilogauss magnetic field, 96 +/- 2% of the cells were retained in the column. These cells could be eluted by removing the magnetic field and mechanically agitating the column. The retention of labeled cells by HGMC was shown to be dependent on the applied magnetic field and the amount of wire packed into the column. HGMC in conjunction with cell labeling with immunospecific iron dextran microspheres have useful applications for the separation of specific cell types.