Metamaterial Slab Research Articles

Subwavelength acoustic focusing by surface-wave-resonance enhanced transmission in doubly negative acoustic metamaterials

We present analytical and numerical analyses of a yet unseen lensing paradigm that is based on a solid metamaterial slab in which the wave excitation source is attached. We propose and demonstrate sub-diffraction-limited acoustic focusing induced by surface resonant states in doubly negative metamaterials. The enhancement of evanescent waves across the metamaterial slab produced by their resonant coupling to surface waves is evidenced and quantitatively determined. The effect of metamaterial parameters on surface states, transmission, and wavenumber bandwidth is clearly identified. Based on this concept consisting of a wave source attached on the metamaterial, a high resolution of λ/28.4 is obtained with the optimum effective physical parameters, opening then an exciting way to design acoustic metamaterials for ultrasonic focused imaging.

Asymmetric transmission of chiral metamaterial slab with double L resonators

In this paper, a three-layered chiral structure with double L resonators on both sides of dielectric substrate is proposed, which can realize asymmetric transmission of linearly polarized wave in near-infrared band. The asymmetric transmission parameter of linearly polarized wave can reach a maximum of 0.9. Due to non-C4 symmetry of the structure, we introduce Stokes parameters to describe the polarization state of the wave. The physical mechanism of asymmetric transmission and hybridized plasmon mode is also analyzed in detail.

Determination of constitutive parameters of homogeneous metamaterial slabs by a novel calibration-independent method

A calibration-independent line-line method for broadband and simultaneous constitutive parameters determination of homogeneous metamaterial (MM) slabs is proposed. It is shown that the sufficient condition for parameters retrieval by the proposed method is to measure uncalibrated (raw) complex scattering parameters of measurement cells (different air regions in free-space) which are completely and partially loaded by the two identical metamaterial slabs. The stability of derived equations for different measurement uncertainty cases is analyzed. We have validated the proposed method by using simulated scattering parameters of a MM slab with split-ring-resonators and then by comparing the extracted electromagnetic parameters with those of a general method used in the literature in the cases with and without a small offset in reference-plane positions (as well as other measurement errors). From this comparison, we note that while the general method does not eliminate those errors, the proposed method not only does not introduce the non-physical anti-resonance behavior but also removes the measurement errors arising from different mechanisms such as inaccurate reference-plane positions and mismatched connections.

Metamaterial magnetoinductive lens performance as a function of field strength

Metamaterials are artificial composites that exhibit exotic electromagnetic properties, as the ability of metamaterial slabs to behave like lenses with sub-wavelength resolution for the electric or the magnetic field. In previous works, the authors investigated magnetic resonance imaging (MRI) applications of metamaterial slabs that behave like lenses for the radiofrequency magnetic field. In particular, the authors investigated the ability of MRI metamaterial lenses to increase the signal-to-noise ratio (SNR) of surface coils, and to localize the field of view (FOV) of the coils, which is of interest for parallel MRI (pMRI) applications. A metamaterial lens placed between a surface coil and the tissue enhances the sensitivity of the coil. Although the metamaterial lens introduces losses which add to the losses of the tissue, the enhancement of the sensitivity can compensate these additional losses and the SNR of the coil is increased. In a previous work, an optimization procedure was followed to find a metamaterial structure with minimum losses that will maximize the SNR. This structure was termed magnetoinductive (MI) lens by the authors. The properties of surface coils in the presence of MI lenses were investigated in previous works at the proton frequency of 1.5T systems. The different frequency dependence of the losses in both the MI lenses and the tissue encouraged us to investigate the performance of MI lenses at different frequencies. Thus, in the present work, the SNR and the pMRI ability of MI lenses are investigated as a function of field strength. A numerical analysis is carried out with an algorithm developed by the authors to predict the SNR behavior of a surface coil loaded with a MI lens at the proton frequencies of 0.5T, 1.5T and 3T systems. The results show that, at 0.5T, there is a gain in the SNR for short distances, but the SNR is highly degraded at deeper distances. However, at 1.5T and 3T, the MI lenses provide a gain in the SNR up to a certain penetration depth, which is deeper at 3T, and do not degrade the SNR at deeper distances. These numerical results are checked by means of an experiment. Moreover, a second experiment developed with two-channel arrays of surface coils loaded with MI lenses shows that the pMRI ability of the lenses also improves from 1.5T to 3T. This improvement was quantified by means of the calculation of the GRAPPA g-factor.

A single metamaterial plate as bandpass filter, transparent wall, and polarization converter controlled by polarizations

We propose an anisotropic homogeneous metamaterial flat plate having multiple functionalities under different polarizations of incident waves. From the theoretical analysis based on Maxwell's equations, we demonstrate that a single one-dimensional anisotropic metamaterial slab with the tailored constitutive parameters serves as a bandpass filter, a transparent wall, and a polarization converter under illuminations of differently polarized waves. We present a special structural unit to realize the tailored constitutive parameter tensors of the anisotropic metamaterial from which a three-dimensional metamaterial flat plate is designed and fabricated. The measured results agree very well to theoretical calculations and full-wave simulations, demonstrating the excellent performance of the polarization-controlled multiple functionalities of the single metamaterial plate.

Experimental investigation of compact metamaterial for high efficiency mid-range wireless power transfer applications

We investigate a compact metamaterial for enhanced magnetic coupling in a resonator coupled wireless power transfer system operating at around 6.5 MHz. The metamaterial is constructed by realizing an array of three-turn spiral resonators on a thin slab. Although the metamaterial has its own loss, the experimental results show that the proposed metamaterial slab enhances the power transmission capability. The number of unit cells in the array is an important parameter, because exceeding a certain number of unit cells does not enhance the efficiency due to the loss of the slab. Furthermore, strong surface mode resonance is observed when two slabs are assembled with proper gap spacing between them. By using the optimization approach, we achieve a significant efficiency improvement at a mid-range distance. The measured efficiencies are 71.1% and 54.3% at a 0.6 and 1.0 m distance, respectively. At a 1.0 m distance, this efficiency performance corresponds to a 270% improvement compared to a case with no metamaterial slab. In addition, we experimentally confirm the threshold distances above which the metamaterial shows enhanced performance.

Coherent control of birefringence and optical activity

We show that polarization effects due to anisotropy and chirality affecting a wave propagating through a thin slab of material can be controlled by another electromagnetic wave. No nonlinearity of the metamaterial slab is required and the control can be exercised at arbitrarily low intensities. In proof-of-principle experiments with anisotropic and chiral microwave metamaterials, we show that manifestations of linear and circular birefringence and dichroism can be modulated by the control wave from their maximum value to zero.

Highly efficient wireless power transfer using metamaterial slab with zero refractive property

A highly efficient wireless power transfer using a metamaterial slab with a zero refractive property is proposed. The proposed metamaterial slab consists of a spiral structure, a lumped element and a via through the ground. A prototype of a wireless power transfer system and a metamaterial slab was designed and fabricated. Experiment results prove the transfer efficiency improvement with the proposed metamaterial slab. The power transfer efficiency is improved by reducing the radiation loss through focusing the magnetic field. The power transfer efficiency is above 45% at a distance of 100-150 mm, and the resonant frequency is 6.78 MHz. The sizes of the transmitting coil and the metamaterial slab are 140 × 210 mm and 50 × 70 mm, respectively.

Tunable spin-dependent splitting of light beam in a chiral metamaterial slab

Spin-dependent splitting of the reflected beam for the chiral metamaterial slab is investigated by analyzing the spatial transverse shifts (TSs) of the two spin-dependent components of the reflected beam. Two components refer to the right-circularly polarized and left-circularly polarized reflected wave components. The influences of the physical parameters and the polarization of the incident beam on the spin-dependent splitting are discussed. The results show that two components are asymmetric due to the cross-polarization of the electromagnetic fields in chiral slab. By adjusting the angle of incidence and the polarization state of the incident beam, the spatial splitting can be enhanced. Moreover, the effect of the thickness on the spatial TSs of the two components becomes weak with increasing the angle of incidence. To oneʼs interest, the spin-dependent splitting also can be realized for two special linear (TE and TM) polarization. Our study may provide an opportunity to realize and control the transverse splitting of the light, and open up the possibility for developing new nanophotonic devices.

Planar Magnetic Metamaterial Slabs for Magnetic Resonance Imaging Applications

A type of planar magnetic metamaterial is proposed with a square winding microstructure as a superlens for magnetic resonance imaging (MRI) applications. A direct magnetic field mapping measurement demonstrates that the radio-frequency magnetic field passing through the superlens is increased by as high as 46.9% at the position of about 3 cm behind the superlens. The resonance frequency of the fabricated slabs is found to be in good agreement with the target frequency (63.6 MHz) for a 1.5T MRI system. MRI experiments with the magnetic superlens show that the intensity of the image and the SNR (signal-to-noise ratio) are both enhanced, implying promising MRI applications of our planar magnetic superlens.

Simulation of An Asymmetric TM Metamaterial Waveguide Absorber

This paper tackles the simulation of an asymmetric  TM mode absorption  in a lossy metamaterial (left-handed) slab (LHM) sandwiched between a lossy substrate and coverd by a losseless dielectric cladding. The asymmetry solutions of the eigen value equation describe lossy –guided modes with complex –valued propagation constants . The dispersion relations , normalized field and the longitudinal attenuation were numerically solved for a given set of parameters: frequency range; film’s thicknesses; and TM mode order. I found out that high order modes which are guided in thinner films are generally have more loss of power than low-order modes since the mode attenuation along z-axis increases to negative values by the mode's order increase and the film thickness decrease . Moreover,  LHM , at incident wavelength =1.9, refractive index=and at thickness ,   guides the power better than RHM or metal one. This LHM  is appropriate for solar cell applications. For arbitrary LHM, at frequency band of wavelengt(600, 700 to 1200 )nm,  the best absorption is attained at longer wavelengths and for lower order modes at wider films.

Optical Propagation Through Graded-Index Metamaterials in the Presence of Gain

We present a comparative theoretical study of electromagnetic wave propagation through randomly structured isotropic and stratified anisotropic active metamaterial slabs, whose refractive indices vary smoothly from positive values on one end of the slabs to negative values on the other. The chief advantage of our two configurations over recent hypothetical structures is that they can be made from real materials using common fabrication techniques. We find that even a small excess of gain (loss) in the randomly structured slab can result in a strong resonant amplification (absorption) of incident field on the length scale of an optical wavelength. This collective effect—somewhat similar to Landau amplification (damping) in a collisionless plasma—may prove useful in making compact optical amplifiers and perfect light absorbers.

Improving Ultra Wide Band Imaging using a Metamaterial Slab

quality of tomographic images formed from diffracting waves deteriorates due to the limitations in capturing evanescent waves. The waves carry detailed information about the body being imaged. Metamaterials are being recently used to amplify and focus evanescent waves. Here, the physical characteristics of a superlens made out of a silver metamaterial slab are studied. A description of the equations for wave propagation inside the metamaterial is shown. The dependence of the cutoff frequency of a superlens on the thickness of the slab is discussed. Suitable physical dimensions of a superlens are proposed for cross sectional imaging of objects with geometrical shapes. Simulations are done to test the validity of the proposed solution.

Refractive index switching based on loss controlling in a doped metamaterial slab

An all-optical refractive index switch is proposed based on coherent control of a doped double-negative metamaterial slab. By embedding the three-level atoms through the left-handed slab, the effective permittivity of the slab becomes a function of the doped atom’s susceptibility. Absorption properties manipulation of the doped atoms leads to active control over the total loss of the metamaterial slab. This way the refractive index of the slab can be switched between negative and positive by the change of the relative phase of the applied fields. This may offer active control over the transmission in a wide range from 0 to 0.58.

Improving Ultra Wide Band Imaging using a Metamaterial Slab

quality of tomographic images formed from diffracting waves deteriorates due to the limitations in capturing evanescent waves. The waves carry detailed information about the body being imaged. Metamaterials are being recently used to amplify and focus evanescent waves. Here, the physical characteristics of a superlens made out of a silver metamaterial slab are studied. A description of the equations for wave propagation inside the metamaterial is shown. The dependence of the cutoff frequency of a superlens on the thickness of the slab is discussed. Suitable physical dimensions of a superlens are proposed for cross sectional imaging of objects with geometrical shapes. Simulations are done to test the validity of the proposed solution.

Ultrafast all-optical modulation with hyperbolic metamaterial integrated in Si photonic circuitry.

The integration of optical metamaterials within silicon integrated photonic circuitry bears significantly potential in the design of low-power, nanoscale footprint, all-optical functionalities. We propose a novel concept and provide detailed analysis of an on-chip ultrafast all-optical modulator based on an hyperbolic metamaterial integrated in a silicon waveguide. The anisotropic metamaterial based on gold nanorods is placed on top of the silicon waveguide to form a modulator with a 300x440x600 nm(3) footprint. For the operating wavelength of 1.5 μm, the optimized geometry of the device has insertion loss of about 5 dB and a modulation depth of 35% with a sub-ps switching rate. The switching energy estimated from nonlinear transient dynamic numerical simulations is 3.7 pJ/bit when the transmission is controlled optically at a wavelength of 532 nm, resonant with the transverse plasmonic mode of the metamaterial. The switching mechanism is based on the control of the hybridization of eigenmodes in the metamaterial slab and the Si waveguide.

Omnidirectional non-radiative wireless power transfer with rotating magnetic field and efficiency improvement by metamaterial

In this paper, omnidirectional wireless power transfer (OWPT) via magnetic resonant coupling is proposed based on rotating magnetic field. In contrast to conventional WPT, the proposed wireless power transmitter consists of two orthogonal loops with 90° feeding phase difference. Both theoretical analyses and numerical simulations show that such transmitter generates rotating magnetic field and can provide wireless power to multiple receivers moving around it. In addition, a cylindrical metamaterial slab with negative permeability is used to improve the efficiency of the OWPT system, for the unique property of enhancing evanescent wave of metamaterials. It is shown that the efficiency of the OWPT can be improved to more than five times of that of the original one by the metamaterial slab.

Power analysis of multilayer structures composed of conventional materials and bi-anisotropic metamaterial slabs

In this paper, we analyze wave propagation properties (transmitted, reflected, and absorbed powers) of composite multilayer structures consisting of bi-anisotropic metamaterial (MM) slabs and conventional isotropic materials. We also separately investigate the propagation properties of bi-anisotropic MM slabs and conventional materials to better interpret the results. We consider two different bi-anisotropic MM slab structures composed of only split-ring-resonators (SRRs) and composing SRRs and a rod. In the analysis, we apply the well-known transfer matrix method to obtain transmitted, reflected, and absorbed powers of the composite structures. From the analysis, we note the following three important results. First, while the transmitted powers from forward and backward directions of the multilayer structure are identical (reciprocal feature), reflected (and absorbed) powers from forward and backward directions of the multilayer structure are different. This difference arises from reflection asymmetric nature of the bi-anisotropic MM slabs. Second, whereas the conventional material loss influences propagation characteristics aside resonance frequencies of bi-anisotropic MM slabs, bi-anisotropic MM loss worsens propagation properties of the multilayer structure at resonance frequencies of these slabs. Third, variations in (or determination of) electromagnetic properties of low-loss thin conventional materials in between two bi-anisotropic MM slabs can be realized at frequencies in which conventional materials demonstrate thickness-resonance effect.

Improving Power Transfer Efficiency of a Short-Range Telemetry System Using Compact Metamaterials

Wireless power transfer using resonant inductive coupling has been employed in a number of applications, including wireless charging of electronic devices and powering of implanted biomedical devices. In these applications, power is transferred over short distances, which are much smaller (~ λ/100) than the wavelength of operation. In such systems, the power transfer efficiency of the link is inversely related to the range of operation. The power transfer efficiency is principally a function of the Q's of the individual coils and the coupling between them. In this paper, we demonstrate improvements in power transfer efficiencies using negative permeability metamaterials by increasing the mutual coupling between coils. A metamaterial slab is designed for operation at 27 MHz and is compact in size. The power transfer efficiency of the telemetry system in free space is compared to that in the presence of the metamaterial placed near one of the coils. The efficiency of the system increased in the presence of the metamaterial even as the free-space separation was held constant. This shows that compact negative permeability metamaterials can be used to increase power transfer efficiency of short-range telemetry systems used in various applications.

Phase dependent coherent control of group delay in a doped metamaterial slab

A scheme is proposed for the coherent control of the group delay for a light beam traveling through a double-negative metamaterial (DNM) slab. By doping three-level atoms into the DNM slab, phase control over the transmission and reflection behaviors of the active layer is achieved. This way, tunable and simultaneous subluminal and superluminal transmission and reflection are achievable. We discuss the effect of the relative phase of the applied fields and the rate of incoherent pumping on the group delay of a probe pulse propagating through the DNM slab. It is shown that group delays of the transmitted and reflected beams are completely phase dependent. We also find that transmission of a probe field propagating through the DNM slab is actively controllable in a wide range by controlling the relative phase of the incident fields with no need to alter physical parameters of the metamaterial.